Direct C−H arylation for the synthesis of conjugated polymers

PDF

Download

Open document

Transcript (if available)

Content
DIRECT C−H ARYLATION FOR THE SYNTHESIS OF CONJUGATED POLYMER S

by

Nemal S. Gobalasingham

A Dissertation Presented to the
FACULTY OF THE USC GRADUATE SCHOOL
UNIVERSITY OF SOUTHERN CALIFORNIA
In Partial Fulfillment of the
Requirements for the Degree
DOCTOR OF PHILOSOPHY
(CHEMISTRY)

December 2017

Copyright © 2017 Nemal S. Gobalasingham
ii

EPIGRAPH

What we’ve learned is but a mere handful of sand;
what we have yet to learn is like the world itself. – Avvaiyar

iii
DEDICATION

To my Parents, my Sister, and Jillian—for always supporting me.

iv
PREFACE
Before I acknowledge the incredible contributions and support I have received and
expound on my scientific contributions, I write this preface to share some of what I have
learned these past years for those readers who do not have the scientific background to
fully understand this dissertation. I have always strived to share my work and knowledge
with others, regardless of their level of experience in chemistry. At its core, my work
encompasses efforts to develop both materials for flexible polymer solar cells but also
methods toward achieving these materials with more sustainable strategies.
My motivation for this work ultimately stems from my desire to develop alternative
energy sources. Our sun is more than capable of supplying our energy demands until the
end of civilization, so it is particularly attractive as a source of energy, especially when
compared to finite fossil fuels. Diversifying our energy sources and improving energy
efficiency will ultimately be the most tenable approach toward energy that meets current
world demand without crippling our future energy supply.
Conjugated polymers are capable of absorbing light and generating electricity but
making them often requires very toxic chemicals and can be tough to mass produce. My
research efforts are in an emerging field of chemistry, called direct arylation
polymerization, that can make these polymers without “prepping” them with these toxic
chemicals. Like with many things, sometimes taking a shortcut does not pan out well, and
historically, this method can lead to less effective materials. My work has primarily been
focused on optimizing this method so that it can produce high quality polymers but also
ways to make the generation very scalable. Lastly, I explored ways to save two steps toward
these polymers, saving both time and energy toward these potentially useful materials.
v
ACKNOWLEDGEMENTS

As I reflect on this accomplishment, I cannot help but recognize the successes and
failures that have guided me in this long but rewarding journey. Rarely can you succeed
without the support of others and this is particularly true for me. My parents immigrated to
the U.S. from Sri Lanka with almost nothing—for their sacrifice, their courage, their
unending support, for the opportunities they have given me, and for their unconditional
love, I can only offer the thanks that comes from years of being fortunate, honored, and
proud to be your son. And to my sister, who has always had my back and has been my
friend for the longest time, you have made me a better person.
For this accomplishment, I owe a truly special thanks to my a dvisor, Prof. Barry C.
Thompson. In the more than five years we have known each other, Dr. Thompson has
always supported me and encouraged me to achieve my very best. He inspires through his
incredible passion for science, his kindness, and his incredible patience. From teaching me
to tackle problems from different angles, to being a model of hard work and perseverance,
I am thankful for your excellent mentorship and will miss our scientific discussions very
much. Thank you for giving me the opportunity to learn from you.
My development as a graduate student would not be possible without supportive
colleagues. For giving me a strong foundation in conjugated polymer synthesis, I would
like to thank Dr. Andrey Rudenko, Dr. Bing Xu, and Alia Latif for their mentorship. I
would like to especially thank Andrey for his advice and mentorship toward inheriting the
DArP mantle from him. He is a brilliant scientist and truly taught me a lot. With regards to
OPV fabrication and characterization, I thank Dr. Petr Khlyabich, Dr. Sangtaik Noh, and
vi
Alia for collectively teaching me the art that is solar cell preparation. I owe a special thanks
to Petr for his advice, guidance, and never-ending support. I would also like to thank
Sangtaik for his advice, humor, synthetic expertise, and dedication to our productive
collaborative efforts.
Sincere thanks must also go to soon-to-be Dr. Şeyma Ekiz. She was one of the first
people I met at USC and we joined Barry’s group together. For your help, guidance, advice,
and friendship, I owe you many Boba teas. I would also like to thank Robert Pankow, who
has become a good friend and collaborator. I will miss our coffee breaks, scientific (and
baseball) discussions, and our lunches, especially those with our dear friend Qingpei Wan,
the unrelenting hard worker. There are many other members of the BCT group, past and
present, that I owe sincere thanks too, many of whom have taught me, given me the honor
of teaching them, or simply have gotten to know in and around the lab. In addition to those
mentioned above, these include Dr. Alejandra Beier, Dr. Jenna Howard, Betsy Melenbrink,
and Sanket Samal, but also many undergraduates and visiting students, like Alejandro
Cuellar Delucio, Juliette Sabatier, John Munteanu, and John Luke McConn. Thanks for the
memories and best of luck in all your endeavors.
I also offer my deep appreciation to Dr. Francesco Livi and his advisor Prof. Eva
Bundgaard from the Technical University of Denmark (DTU), for a truly enjoyable and
rewarding collaboration. To Francesco, you are truly a great chemist, a great friend, and I
am grateful for all your help and advice these past years. Along with Prof. Bundgaard, I
would also like to thank Prof. Frederik Krebs, Dr. Martin Helgensen, Dr. Jon Carlé, Dr.
Ole Hagemann, and the supportive staff at DTU, including Birgit Oksbjerg and Bente
Schlichting, for having me visit Denmark and work on DArP in continuous flow.
vii
In addition to those in the BCT group and DTU, I would like to thank my fellow
graduate students and postdocs at USC, with whom I have had the privilege to interact with
and who have let me borrow numerous chemicals, given me assistance, or have been great
acquaintances. These include Dr. Richard Giles, Dr. Sankarganesh Krishnamoorthy, Dr.
Haipeng Lu, Blair Combs, Dr. Yao Lu, Prof. Denise Femia, Kavita Belligund, Archith
Nirmalchandar, Debanjan Mitra, Rasha Hamze, Dr. Sean Culver, Dr. Shiliang (Nemo)
Zhou, and Dr. Jeff Celaje as well as the groups they represent.
Additionally, I would like to thank Prof. G.K Surya Prakash, Prof. Mark E
Thompson, Prof. Richard L. Brutchey, and Prof. Aiichiro Nakano for agreeing to serve on
my screening and qualifying examination committee and for both Prof. Prakash and Prof.
Nakano for serving on my defense committee. For giving me the means to live in LA for
many years, for her unending support and advice, and for her friendship, I would especially
like to thank Dr. Jennifer Moore, who has made my experience as a teaching assistant for
organic chemistry truly rewarding and enjoyable. It has been my pleasure and honor to
serve as your head teaching assistant for many years. To that end, I am also thankful for
the advice and guidance given to me by Dr. Janet Olsen for succeeding in that position.
I would also like to thank the incredible faculty, staff, and support in the Chemistry
Department, the Loker Hydrocarbon Research Institute, and the University of Southern
California for all their immense help and assistance through the years, including Michele
Dea, Katie McKissick, David Hunter, Prof. Ralf Haiges, Bruno Herreros, Magnolia
Benitez, Frank Devlin, Allan Kershaw, Ross Lewis, Michael Nonezyan, Dr. Robert
Aniszfeld, Jessy May, the Aramark custodial staff, Shane Daywalt, Kevin Rust, Ralph Pan,
viii
Corey Shultz, Phillip Sliwoski, Jaime Avila, Carole Phillips, Mike Godinez, Donald
Wiggins, Ramón Delgadillo, and William Rivera.
It would be truly inattentive to not recognize my first steps in real science, which
would have never been possible without my undergraduate advisor at Syracuse University,
Prof. Yan-Yeung Luk, who took a chance on a freshman undergraduate chemistry major,
and guided me through four years of undergraduate research. Special thanks to Dr. Debjoyti
Bandyopadhyay, Dr. Nisha Varghese, Dr. Karen Simon, and Dr. Sri Kamesh Narasimhan
for their mentorship, which truly accelerated my entire scientific career and provided me
with an excellent research education. To that end I would also like to thank my professors
at Syracuse University as well as Dean Susan Wadley and the Coronat Scholars Program.
I also owe tremendous thanks to my high school chemistry teacher, Dr. Eloise Malinksy,
who provided an incredible AP Chemistry experience and started me on this journey. Truly,
I owe much thanks to all my teachers, from my start at Nate Perry Elementary through to
Pine View School—thank you for teaching me.
In the end, it is those who are closest to you that lift us. I would also like to thank
my friends, Chris and Clara Walter, who are always there for me. It was the honor of my
life to officiate your wedding. In addition to my family, I would like to thank Jillian Ellis
and her family, who have always encouraged me and supported me with kindness and
warmth. A special thanks to Nancy Jones, Robert Ellis, Julie Kay Ellis, Dave Requarth,
Stephanie Ellis, and Alex Gomez.
Last, but certainly not least, I am forever grateful to Jillian Ellis for her love,
patience, and support. Thank you for everything. The challenges and tribulations of moving
to Los Angeles and undertaking graduate school were infinitely alleviated by your presence
ix
and support. Thank you for our adventures, and here’s to many more. There is not a single
day you haven’t made me smile but more than anything, thank you for always believing in
me.

x
Table of Contents

Epigraph .............................................................................................................................. ii
Dedication .......................................................................................................................... iii
Preface................................................................................................................................ iv
Acknowledgements ..............................................................................................................v
List of Tables ................................................................................................................... xiv
List of Figures .................................................................................................................. xix
List of Schemes .......................................................................................................... xxxviii
Abstract .......................................................................................................................... xlvii

Chapter 1: Direct Arylation Polymerization ....................................................................1
1.1. Introduction .............................................................................................................. 1
1.2. Development of Direct Arylation Polymerization: Considerations for Well-Defined
Conjugated Polymers .......................................................................................................... 3
1.3. Strategies for Achieving Well-Defined Copolymers via DArP ............................. 62
1.4. Evaluating Structure-Function Relationships of DArP Polymers Through Practical
Performance ............................................................................................................... 115
1.5. Catalytic Oxidative Direct Arylation Polymerization .......................................... 153
1.6. Summary and Outlook .......................................................................................... 169
1.7. References ............................................................................................................ 171

Chapter 2: Analysis of Diverse Direct Arylation Polymerization (DArP) Conditions
Toward the Efficient Synthesis of Polymers Converging with Stille Polymers in Organic
Solar Cells ....................................................................................................................200
2.1. Introduction .......................................................................................................... 200
2.2. Experimental ........................................................................................................ 207
2.3. Results and Discussion ......................................................................................... 210
2.4. Conclusions .......................................................................................................... 232
2.5. References ............................................................................................................ 233

Chapter 3: Carbazole-Based Copolymers via Direct Arylation Polymerization (DArP)
for Suzuki-Convergent Polymer Solar Cell Performance ................................................240
3.1. Introduction .......................................................................................................... 240
3.2. Materials & Methods ............................................................................................ 242
3.3. Results and Discussion ......................................................................................... 248
xi
3.4. Conclusion ............................................................................................................ 264
3.5. References ............................................................................................................ 265

Chapter 4: Conjugated Polymers via Direct Arylation Polymerization in Continuous
Flow: Minimizing the Cost and Batch-to-Batch Variations for High-Throughput Energy
Conversion ....................................................................................................................269
4.1. Introduction .......................................................................................................... 269
4.2. Experimental ........................................................................................................ 274
4.3. Results and discussion .......................................................................................... 278
4.4. Conclusion ............................................................................................................ 291
4.5. References ............................................................................................................ 291

Chapter 5: Evaluating Structure-Function Relationships Toward Three-Component
Conjugated Polymers via Direct Arylation Polymerization (DArP) for Stille-Convergent
Solar Cell Performance ....................................................................................................296
5.1. Introduction .......................................................................................................... 296
5.2. Results and Discussion ......................................................................................... 300
5.3. Conclusions .......................................................................................................... 328
5.4. References ............................................................................................................ 329

Chapter 6: Palladium-catalyzed oxidative direct arylation polymerization (Oxi-DArP)
of an ester-functionalized thiophene ................................................................................336
6.1. Introduction .......................................................................................................... 336
6.2. Experimental ........................................................................................................ 341
6.3. Results and Discussion ......................................................................................... 343
6.4. Conclusions .......................................................................................................... 356
6.5. References ............................................................................................................ 357

Chapter 7: Synthesis of Random Poly(Hexyl Thiophene-3-Carboxylate) Copolymers
via Oxidative Direct Arylation Polymerization (Oxi-DArP) ...........................................364
7.1. Introduction .......................................................................................................... 364
7.2. Experimental ........................................................................................................ 367
7.3. Results and Discussion ......................................................................................... 370
7.4. Conclusion ............................................................................................................ 385
7.5. References ............................................................................................................ 385

Bibliography ....................................................................................................................391
xii
Appendix 1: Analysis of Diverse Direct Arylation Polymerization (DArP) Conditions
Toward the Efficient Synthesis of Polymers Converging with Stille Polymers in Organic
Solar Cells ................................................................................................................420
A1.1 Materials and Methods ......................................................................................... 420
A1.2 NMR Spectra ........................................................................................................ 425
A1.3 CV of the polymers .............................................................................................. 443
A1.4 DSC profiles of the polymers ............................................................................... 447
A1.5 GIXRD patterns of the polymers .......................................................................... 449
A1.6 Tabulated Overview of Polymer Properties from CV Traces, Absorption Profiles,
DSC, and GIXRD Patterns ............................................................................................. 453
A1.7 Spectral Mismatch Determination ........................................................................ 455
A1.8 Solar Cell Data ..................................................................................................... 456
A1.9 Mobility Measurements ........................................................................................ 463
A1.10 References ............................................................................................................ 463

Appendix 2: Carbazole-Based Copolymers via Direct Arylation Polymerization (DArP)
for Suzuki-Convergent Polymer Solar Cell Performance ................................................465
A2.1 NMR Spectra ........................................................................................................ 465
A2.2 CV Data 480
A2.3 Solar Cell Data ..................................................................................................... 482

Appendix 3: Conjugated Polymers via Direct Arylation Polymerization in Continuous
Flow: Minimizing the Cost and Batch-to-Batch Variations for High-Throughput Energy
Conversion ................................................................................................................485
A3.1 CV Data ............................................................................................................... 485

Appendix 4: Evaluating Structure-Function Relationships Toward Three-Component
Conjugated Polymers via Direct Arylation Polymerization (DArP) for Stille-Convergent
Solar Cell Performance ....................................................................................................486
A4.1 Materials & Methods ............................................................................................ 486
A4.2 Small Molecule NMR Spectra ............................................................................. 500
A4.3 Polymer NMR Spectra ......................................................................................... 511
A4.4 CV Traces ............................................................................................................. 532
A4.5 DSC Traces ........................................................................................................... 536
A4.6 Thin Film Measurements ...................................................................................... 539
A4.7 Tabulated Polymer Data from GIXRD and UV-Vis Measurements .................... 541
A4.8 Polymer OPV Data ............................................................................................... 543
A4.9 References ............................................................................................................ 549

xiii
Appendix 5: Palladium-catalyzed oxidative direct arylation polymerization (Oxi-DArP)
of an ester-functionalized thiophene ................................................................................551
A5.1 Synthetic Procedures ............................................................................................ 551
A5.2 NMR Data ............................................................................................................ 555
A5.3 CV Traces ............................................................................................................. 579
A5.4 UV-Vis Data ......................................................................................................... 582
A5.5 GIXRD Data ......................................................................................................... 586
A5.6 Mobility Measurements ........................................................................................ 590
A5.7 References ............................................................................................................ 591

Appendix 6: Synthesis of Random Poly(Hexyl Thiophene-3-Carboxylate) Copolymers
via Oxidative Direct Arylation Polymerization (Oxi-DArP) ...........................................592
A6.1 NMR Spectra ........................................................................................................ 592
A6.2 CV Traces ............................................................................................................. 608
A6.3 UV-Vis Data ......................................................................................................... 612
A6.4 Thin Film Measurements ...................................................................................... 614
A6.5 Data Table ............................................................................................................ 616
A6.6 References ............................................................................................................ 617

xiv
LIST OF TABLES

Table 1.1. Comparison of routes (Scheme 1.23), DArP classification (Figure 1.7),
conditions, and the resulting polymer properties, including yields, molecular weight, and
homocoupling quantification (hc) as reported by either Wang et al.
220
or Sommer et al.
226
........................................................................................................................................... 74

Table 1.2. Analysis of three polymers, including ubiquitous homopolymer P3HT,
120
the
popular DPP acceptor in an alternating copolymer PDPPTPT,
227
and heavily investigated
PCDTBT.
285
For P3HT, a mere 0.16% BDC results in a 41% decrease in performance while
a 1.41% BDC (with a small decrease in regioregularity) results in a 69% decrease in
performance. Similarly, 5% homocoupling defects in PDPPTPT results in a 28% decrease
in performance while a 2.4% homocoupling content can result in a 36% decrease, though
small differences in molecular weight may contribute somewhat to this latter disparity.
......................................................................................................................................... 117

Table 1.3. Polymers, Method, SCLC Hole Mobilities, and Photovoltaic Performance of
DArP and Stille P3HT-CNT by Thompson et al.
189
....................................................... 125

Table 1.4. Synthesis of random copolymers of 3-hexylthiophene with 3-hexyl-4-
fluorothiophene via DArP and resulting OPV performance by Coughlin, et al.
50
......... 126

Table 1.5. Performance of PPDTBT polymers synthesized via different DArP conditions
utilized in ITO-free flexible substrates or glass ITO substrates for OPVs as investigated by
Livi et al.
83
...................................................................................................................... 140

Table 1.6. Performance of DArP and Stille alternating copolymers evaluated by Marks et
al.
51
Molecular weights were comparable. ...................................................................... 141

xv
Table 1.7. OFET Performance (TGBC) observed by Leclerc et al.
225
for DPP-based
polymers as outlined in Scheme 1.47. ............................................................................ 148

Table 1.8. OFET performance (TGBC), annealed at different temperatures, as observed by
Li et al.
229
for DPP/BTz copolymers via different functionalization strategies, previously
outlined in Scheme 1.26. ................................................................................................. 149

Table 2.1. Reaction conditions for each DArP/Stille method, yields (after Soxhlet
extraction), molecular weight, dispersity, and presence of defects in NMR analysis. ... 213

Table 2.2. Electrochemical HOMO values, Optical Band Gaps, SCLC hole mobilities, and
d100 Lattice Spacing. ........................................................................................................ 224

Table 2.3. ITO-free flexible PSC characteristics of highest quality DArP PPDTBT
compared to Stille reference polymers. .......................................................................... 228

Table 2.4. Spin-coated ITO PSC device performance of highest quality DArP PPDTBT
compared to Stille reference polymers. .......................................................................... 231

Table 3.1. Reaction Parameters for the Synthesis of PCDTBT and the Yield, Molecular
Weight, and Dispersity after Soxhlet Extraction ............................................................ 250

Table 3.2. Optoelectronic Properties of PCDTBT, including HOMO energy levels, SCLC
hole mobilities, optical bandgaps, and polymer solar cell performance. ........................ 251

Table 3.3. Optoelectronic Properties of PCDTB, including HOMO energy levels, SCLC
hole mobilities, optical bandgaps, and polymer solar cell performance. ........................ 259

Table 4.1. Reaction conditions, molecular weight and photovoltaic parameters for DArP
and Stille in continuous flow polymerizations................................................................ 283

xvi
Table 4.2. Electrochemical HOMO Values, Optical Band Gaps, SCLC hole mobilities, and
d100 Lattice Spacing......................................................................................................... 285

Table 5.1. Reaction Parameters for the Synthesis of P3HT for Baseline Evaluation of
Polymer Properties and the Molecular Weight, Dispersity, Yield, and Regioregularity after
Soxhlet Extraction. .......................................................................................................... 301

Table 5.2. Optoelectronic Properties of Stille P3HT (A1) and DArP P3HT (A2-A6) after
Soxhlet Extraction, including HOMO energy level, SCLC Hole Mobility, Peak Absorption
Coefficient, Optical Bandgap, Melt and Crystallization Temperatures, d100 Spacing, and
Polymer Solar Cell Performance. ................................................................................... 303

Table 5.3. Synthetic Method (Adopted from Table 5.1), Route (Described in Scheme 5.1),
and Molecular Weight, Dispersity, and Yield after Soxhlet Purification for Stille (B1) and
DArP (B2-B7) P3HTT-DPP Semi-Random Copolymers............................................... 310

Table 5.4. Optoelectronic Properties of Stille P3HTT-DPP (B1) and DArP P3HTT-DPP
(B2-B6) after Soxhlet Extraction, including HOMO energy level, SCLC Hole Mobility,
Optical Bandgap, d100 spacing, Melt and Crystallization Temperatures, and Polymer Solar
Cell Performance. ........................................................................................................... 318

Table 5.5. Polymer Properties (Molecular weight and yield) and Optoelectronic Properties
of DArP P3HT Semi-Random Copolymers (P1-P8) with varying spacers or acceptors after
Soxhlet Extraction, including HOMO energy level, SCLC Hole Mobility, Peak Absorption
Coefficient, Optical Bandgap, d100 Spacing, and Polymer Solar Cell Performance. ...... 324

Table 6.1. Conditions, Regioregularity, Molecular Weight, Dispersity, and Yield for
Oxidative Direct Arylation Polymerization on 3-hexylthiophene and 3-
hexylesterthiophene ........................................................................................................ 347

xvii
Table 6.2. Electrochemical HOMO values, Optical Bandgaps, Space-Charge Limited
Current (SCLC) Mobilities of Oxi-DArP, DArP, and Stille polymers. .......................... 355

Table 7.1. Screening of reaction parameters for the synthesis of P3HET via oxidative direct
arylation polymerization. ................................................................................................ 371

Table 7.2. Molecular weights, dispersity, yields, electrochemical HOMO energy levels,
d100 spacings as determined by GIXRD, crystallite size, λmax, absorption coefficients, and
SCLC hole mobilities of P3HET-BTz and P3HET-TPD family of random copolymers with
oxi-DArP P3HET (P7) as reference. ............................................................................... 376

Table A1.1. Electrochemical HOMO, absorption onset in thin films, optical band gaps,
optical LUMO, λmax,abs , and absorption coefficients at peak wavelengths for class A, class
B, and class C DArP polymers as well as both Stille references, PPDTBT X and PPDTBTY.
......................................................................................................................................... 453

Table A1.2. 2θ, GIXRD intensities, interchain distances (100), peak widths at half
maximum (FWHM), crystallite size, melt, and glass transition temperatures (from DSC) of
class A, class B, and class C DArP polymers as well as both Stille references, PPDTBT X
and PPDTBTY. ................................................................................................................ 454

Table A1.3. Raw short-circuit current densities (JSC), spectral mismatch factor (M),
spectral mismatch-corrected short-circuit current densities (JSC,CORR), and integrated
short-circuit current densities (JSC,EQE) for select polymers as referenced in Table 2.1.
......................................................................................................................................... 457

Table A1.4. PSC characteristics of A2, B1, C1, C2, and both Stille references, PPDTBTX
and PPDTBTY. ................................................................................................................ 460

xviii
Table A 2.1. Summary of raw short-circuit current densities (Jsc,raw), spectral-mismatch
factor (M), spectral mismatch-corrected short-circuit current densities (Jsc,corr) and
integrated shortcircuit current densities (Jsc,EQE) for BHJ solar cells .............................. 483

Table A 2.2. Averages and Standard Deviations for Polymer Solar Cell Data.............. 483

Table A 4.1. Data Table of electrochemical oxidative HOMO levels, peak absorption, peak
absorption coefficient, optical bandgaps, 2θ, GIXRD reflection intensity, d100 spacing, full
width at half the maximum (FWHM), and crystallite size as estimated from Scherrer’s
equation. .......................................................................................................................... 541

Table A 4.2. Summary of raw short-circuit current densities (Jsc,raw), spectral-mismatch
factor (M), spectral mismatch-corrected short-circuit current densities (Jsc,corr) and
integrated shortcircuit current densities (Jsc,EQE) for BHJ solar cells based on semi-random
copolymers ...................................................................................................................... 545

Table A4.3. Averages and Standard Deviations for Polymer Solar Cell Data ............... 548

Table A5.1. Polymers (Entry as Designated in Table 1 of the Main Text), λmax,abs (nm),
absorption coefficient (cm
-1
), RR (%) as determined by peak ratios in
1
H-NMR, 2θ from
GIXRD, interchain distances (d) (Å), GIXRD intensities (a.u.), peak widths at half
maximum (FWHM), and crystallite size of neat polymers in thin films spin coated from o-
DCB. ............................................................................................................................... 589

Table A6.1. Data Table of electrochemical oxidative HOMO levels, peak absorption, peak
absorption coefficient, optical bandgaps, 2θ, GIXRD reflection intensity, d100 spacing, full
width at half the maximum (FWHM), and crystallite size as estimated from Scherrer’s
equation for P5, P6, P7, P3HET-BTz Family, and P3HET-TPD Family Polymers ....... 616

xix
LIST OF FIGURES

Figure 1.1. Chemical structures of some conjugated polymers, which include (a)
polyacetylene, (b) polyaniline, (c) polyphenylene vinylene, (d) polypyrrole, and (e)
polythiophene. ..................................................................................................................... 6

Figure 1.2. Some considerations when selecting a synthetic method for the generation of
polymers. ............................................................................................................................. 8

Figure 1.3. Simplified mechanistic overview of the synthesis of head-to-tail 3-
hexylthiophene couplings via (a) palladium-catalyzed Stille cross-coupling and (b)
palladium-catalyzed direct arylation with a carboxylic acid additive. Direct arylation
typically requires a carbonate can also operate without a carboxylate additive via
arylpalladium complexes.
113
............................................................................................. 18

Figure 1.4. For the coupling of 3-hexylthiophene, an unsymmetrical monomer, via
palladium-catalyzed cross-couplings there is the potential for electrophile homocoupling
that lead to head-to-head (HH) couplings and nucleophile homocoupling tail-to-tail (TT)
couplings despite cross-coupling toward head-to-tail (HT) couplings being most favorable.
........................................................................................................................................... 19

Figure 1.5. A comparison of the modes of operation and transition states for electrophilic
substitution (top), Heck-type coupling, σ-bond metathesis, and carboxylate-assisted
concerted metalation-deprotonation (CMD) for C−H activation of thiophene. Transition
state energy is highest for electrophilic substitution and lowest for the CMD pathway. . 21

Figure 1.6. As a consequence of C−H activation via CMD pathway, unselective side-
reactions may occur more prevalently. The free energy of activation of the β-position is
comparatively higher but can occur in small quantities over the course of a polymerization.
........................................................................................................................................... 23

xx
Figure 1.7. Classification of the DArP conditions for discussion in this review. ............ 27

Figure 1.8. Branching defects that may occur in addition to head-to-head homocoupling
as identified by Thompson et al.
118,119
for rr-P3HT via DArP. ......................................... 37

Figure 1.9. (a) Reaction conditions toward P3HT without β-defects and regioregularity
and properties that converge with Stille P3HT, (b) Comparison of pivalic acid with
neodecanoic acid, and (c) Cartoon mechanism illustrating bulky carboxylate ligands
preventing activation of the β-positions due to steric bulk while being not inhibiting α-
coupling............................................................................................................................. 39

Figure 1.10. Fragments of the
1
H NMR spectra of a DArP P3HT polymer exhibiting 0.75%
β-defect concentration. Observing the broad peaks for identifying small quantities of
branching content require significant magnification to be visible, which is not always
provided in the literature. .................................................................................................. 42

Figure 1.11. Example of a branched P3HT polymer possessing both bent units and
dendritic units.................................................................................................................... 44

Figure 1.12. Carboxylic acids additives (Left) and amide solvents (Right) investigated by
Thompson et al.
161,162
to evaluate their influence on the properties of DArP P3HT. ....... 47

Figure 1.13. (a) Equilibrium between an inactive palladium species, which consists of a
polymeric catalyst and a monomeric active catalyst as observed by Ozawa et al..
113
The
bulky aryl substituent (2,6-dimethylphenyl) the less bulky acetate (Me) provided the most
increase in reactivity and (b) generation of the dimeric but inactive palladium species and
the subsequent equilibrium between it and the monomeric active catalyst with the P(o-
OMePh)3 ligand utilized in Ozawa-derived DArP conditions.
187
Here they observed that a
bulky aryl substituent, less bulky acetate, and an electron-poor phosphine ligand provided
the highest reactivity for electron-rich thiophenes. ........................................................... 56

xxi
Figure 1.14. Expanding from (a) homopolymers to (b) alternating copolymers, (c) random
copolymers, (d) semi-random copolymers with random monomers but discrete acceptors,
or (e) semi-alternating copolymers with alternating monomers and discrete acceptors will
require additional considerations when utilizing DArP. ................................................... 64

Figure 1.15. Free energy of activation (ΔG298K, kcal mol
−1
) for various C−H bond
metalations by a Pd(C6H5)(PMe3)(OAc) complex of each arene by density functional
theory (DFT) with the B3LYP
233,234
exchange-correlation functional (top row) as reported
by Fagnou et al.,
102
or at the B3LYP/TZVP (DZVP for palladium) level using Gaussian 09
package and structure optimization in the gas phase as reported by Leclerc et al.,
55,232,235

where alkyl chains were reduced to methyl to simplify calculation times. ...................... 83

Figure 1.16. Simplified mechanism for Aryl−Aryl cross-coupling and homocoupling as
proposed by Ozawa et al.
158
All steps except reductive elimination are reversible. While
the cis route reliably leads to cross-coupling, the trans route is capable of essentially
debrominating one aryl species (enabling homocoupling via cross-coupling with the
corresponding aryl halide species, and homocoupling of the other aryl species. Utilizing
TMEDA was shown to reduce homocoupling by competing with the carboxylate ligand in
the trans configuration, thus inhibiting the trans route. .................................................... 91

Figure 1.17. Chemical structures of phosphines explored by Leclerc et al.
232
for
suppression of homocoupling defects and some β-branching defects. ............................. 93

Figure 1.18. Compatibility of electron-poor substrates with Class C conditions with
Pd(OAc)2 and 1-AdCOOH in DMA (left) and with electron-rich substrates with Class B
conditions with Pd(OAc)2, PCy 3HBF4, and PivOH in toluene as explored by Kanbara et
al.
243
................................................................................................................................... 93

Figure 1.19. Model reaction to evaluate potential end-capping reactions with solvent via
Class B DArP conditions as investigated by Sommer et al.
132
......................................... 96

xxii
Figure 1.20. Synthesis of PCPDTBT via DArP for OPVs as detailed by Horie, et al.
151
......................................................................................................................................... 128

Figure 1.21. Synthesis of PEDOTF via DArP (with microwave (B
MW
) and conventional
heating) for OPVs and OFETs by Kanbara, et al.
142
....................................................... 131

Figure 1.22. Synthesis of IDT-TQ Polymer (P3) via DArP (with microwave (P3B
MW
) and
conventional heating for OPVs and SCLC Hole Mobilities by Yang and Li, et al.
306
... 133

Figure 1.23. Synthesis of HXS-1 (P4) and PDFCDTBT (P5) via DArP for OPVs by
Zhishan Bo, et al.
307
........................................................................................................ 134

Figure 1.24. Synthesis of TPD and Bithiophene (P6) and Terthiophene (P7) copolymers
by Heeger, et al.
310
.......................................................................................................... 136

Figure 1.25. Synthesis of TPD and bisthienylselenophene copolymer (P8) for OPVs by
Heeger, et al.
313
............................................................................................................... 136

Figure 1.26. Synthesis of phenanthridinone-based copolymers with DPP for OPVs by
Leclerc, et al.
256
............................................................................................................... 138

Figure 1.27. Alternating copolymer P15 consisting of DPP and TFB, often referred to as
PDPPTFB, PDPPTB, PDPPF4B or PDPPTh2F4, where the R-group utilized is (a) 2-
hexyldecyl as explored by Jo et al.,
219
(b) 2-octyldodecyl as explored by Sommer et al.
226

and Wang et al.
220
........................................................................................................... 146

Figure 1.28. Synthesis of DPP and 4FTVT copolymers via DArP for OFETs by Geng,
Tian, and Zhang, et al.
330
................................................................................................ 150

Figure 1.29. Comparison of the synthetic steps toward monomers compatible with specific
polymerization methods and the effective, stoichiometric side byproducts of the
xxiii
polymerization. Barring termination events, the potential end groups of these eventual
polymers are also noted. ................................................................................................. 154

Figure 1.30. Monomers explored for oxi-DArP as reported by Chen, Li, and Lu et al.
360
......................................................................................................................................... 160

Figure 1.31. Monomers explored for oxi-DArP as reported by Li and Lu et al.
361
....... 161

Figure 2.1. (Top) General Direct Arylation scheme with AB and AA-BB type monomers
and the final polymer structures and end groups, as well as structural considerations not
typically considered for OPV performance. (Middle) The three general classes of DArP
polymers and the groups that have achieved quality polymers from the associated methods.
(Bottom) Practical considerations for DArP and variables that can affect final polymer
quality. ............................................................................................................................ 204

Figure 2.2.
1
H NMR spectra (600 MHz, CDCl3, 25 °C) of Stille PPDTBT X, A2, B1, C1,
C2, and Stille PPDTBTY which were observed to be the polymers with the most minimal
defects. The red alpha (α) corresponds to acceptor-acceptor homocoupling defects while
the blue delta(δ) corresponds to donor-donor homocoupling defects. The stars (*)
correspond to potential end-chain signals. The route is as outlined in Scheme 2.2. ..... 219

Figure 2.3. GIXRD patterns for, as detailed in Table 1, A1 (red line), A2 (purple line), B1
(blue line), C1 (teal line), C2 (green line), Stille PPDTBTX (black line), and Stille
PPDTBTY (yellow line). ................................................................................................. 222

Figure 2.4. UV-Vis spectra for all polymers reported in Table 1. Thicknesses of films were
obtained via GIXRD measurements in reflectivity mode. (Top) Class A DArP polymers
(A1 (red line), A2 (blue line), A3 (purple line), A4 (green line), with Stille PPDTBT X
(black line) for reference. (Middle) Class B DArP polymers (B1 (red line), B2 (blue line),
B3 (purple line), B4 (green line), with Stille PPDTBTX (black line) for reference. (Bottom)
xxiv
Class C DArP polymers (C1 (red line), C2 (blue line), with Stille PPDTBTX (black line)
and PPDTBTY (yellow line) for reference. ..................................................................... 227

Figure 3.1. UV-Vis Absorption Profile (a) and External Quantum Efficiency (EQE)
Measurement Data (b) for Suzuki PCDTBT (P1) and DArP PCDTBT as provided in Table
3.1.................................................................................................................................... 254

Figure 3.2. Section of aromatic region for PCDTBT couplings (a), peak assignments (b),
and inset overlay showing lack of homocoupling defects for both P1 and P3 (c).
1
H NMR
was acquired at 80°C in C2D2Cl4. Full NMR spectra are provided in the Appendix. .... 255

Figure 3.3. UV-Vis Absorption Profile (a) and External Quantum Efficiency (EQE)
Measurement Data (b) for DArP Carbazole-Based Copolymers as designated in Table 3.3.
......................................................................................................................................... 262

Figure 4.1. Schematic representation of copolymerizations using Stille and direct arylation
(DArP) cross coupling polymerization. .......................................................................... 270

Figure 4.2: Schematic presentation of the DArP flow synthesis setup. BPR: Back pressure
regulator. ......................................................................................................................... 281

Figure 4.3. Pictures of the commercially available glass column reactor from Vapourtec
and the in-house built stainless steel reactor. .................................................................. 282

Figure 4.4. (a) UV-Vis spectra and (b) GIXRD patterns for polymers reported in Table 2.
......................................................................................................................................... 286

Figure 5.1. (a) Direct arylation polymerization (DArP) enables the synthesis of conjugated
polymers without the need for metalation; however, (b) C-H activation of unselective
positions is a shortcoming that can be overcome by using (c) bulky carboxylic acids such
as neodecanoic acid......................................................................................................... 297
xxv

Figure 5.2. For key features of semi-random P3HT analogs, namely discrete secondary
components and high performance, to be preserved via DArP, minimizing defects,
balancing C-H reactivity, and determining optimal functional group assignment become
increasingly important considerations. ........................................................................... 300

Figure 5.3. (a) UV-Vis absorption profile for P3HT series of polymers. Thicknesses are
determined from x-ray reflectivity. (b) GIXRD patterns for neat polymer films. (c) EQE
spectra of BHJ PSCs. ...................................................................................................... 306

Figure 5.4. Fragments of the
1
H NMR spectra (Full Spectra available in the Appendix) of
B1-B3 and B6-B7 showing the aromatic coupling peak of DPP (proton highlighted by blue
circle in structures at top), where the # symbol corresponds to DPP coupling to the 5-
position of 3HT that is predominant in route X coupling (Scheme 1b), the ◊ symbol
corresponds to DPP coupling to the 2-position of 3HT predominantly in route Y coupling
(Scheme 5.1c), the ● symbol corresponds to DPP coupling to the thiophene monomer, and
the * symbol denotes DPP end groups that would predominantly occur in route Y. The
insets show superimposed fragments of (a) B7 and B2, (b) B7 and B3, as well as (c) B1
and B6. ............................................................................................................................ 312

Figure 5.5. (a) UV-Vis absorption profiles for P3HTT-DPP series of polymers.
Thicknesses are determined from x-ray reflectivity. (b) GIXRD patterns for neat polymer
films. (c) EQE spectra of BHJ PSCs. .............................................................................. 316

Figure 5.6. (a) UV-Vis absorption profiles for the P3HT Semi-Random series of polymers.
Thicknesses are determined from x-ray reflectivity. (b) GIXRD patterns for neat polymer
films. (c) EQE spectra of BHJ PSCs. .............................................................................. 325

Figure 6.1. Comparison of the prerequisite synthetic steps toward monomers compatible
with specific polymerization methods and the eventual end groups of these polymers. 338

xxvi
Figure 6.2.
1
H NMR spectra of the region used to determine regioregularity in Poly(3-
esterhexylthiophene) as synthesized by different methods. References to Entry are for
polymers made via conditions outlined in Table 6.1. ..................................................... 351

Figure 6.3 Comparison of (a) GIXRD and (b) UV-Vis spectra of P3HET made via Stille
(black line), DArP (red line), and Oxi-DArP (blue line) (Entry 18 of Table 6.1). Additional
GIXRD and UV-Vis spectra for other select Oxi-DArP polymers, as well as Stille, DArP,
and Oxi-DArP P3HT can be found in the Appendix. ..................................................... 356

Figure 7.1. Illustration of the need for bromination and metalation steps in order to make
a monomer suitable for traditional cross-coupling methods. Oxi-DArP enables both steps
to be bypassed en route to conjugated polymers while also providing benign end groups.
......................................................................................................................................... 365

Figure 7.2. Superimposed traces of the lower field aliphatic portion of the
1
H NMR spectra
(x-axis in ppm referenced to residual chloroform signal) of P2 (red trace) and P3 (blue
trace) showing (a) the majority head-to-tail coupling (δ4.30), (b) the corresponding
penultimate proton (δ4.25), (c) the head-to-head coupling (δ4.13), (d) the tail-to-tail
coupling (δ4.09), and (e) the β-coupling (δ3.90). Utilization of neodecanoic acid as an
additive suppresses this peak. Full NMR spectra are provided in the Appendix. .......... 374

Figure 7.3. GIXRD Patterns of the (a) P3HET-BTz family and (b) P3HET-TPD family of
copolymers with P7 as a reference.................................................................................. 380

Figure 7.4. UV-Vis absorption profiles of the (a) P3HET-BTz family and (b) P3HET-TPD
family of copolymers with P7 as a reference. Absorption coefficients are calculated from
thickness estimates acquired by GIXRD in the reflectivity mode. ................................. 382

Figure A1.1. Monomers prepared for the synthesis of DArP and Stille polymers. ....... 425

Figure A1.2.
1
H NMR spectrum of S1. (X) denotes solvent residues. .......................... 426
xxvii

Figure A1.3.
1
H NMR spectrum of S2. .......................................................................... 427

Figure A1.4.
1
H NMR spectrum of S3. (X) denotes solvent residues. .......................... 428

Figure A1.5.
1
H NMR spectrum of S4. .......................................................................... 429

Figure A1.6.
1
H NMR spectrum of S5. .......................................................................... 430

Figure A1.7. Stacked
1
H NMR Spectrum of the aromatic region for all polymers reported
in this work. Red alpha (α) denotes acceptor-acceptor couplings, blue delta (δ) denotes
donor-donor coupling, (*) denotes end-chain signals, and (§) denotes potential signals from
low molecular weight oligomeric material. .................................................................... 431

Figure A1.8.
1
H NMR spectrum of PPDTBTX. ............................................................. 432

Figure A1.9.
1
H NMR spectrum of A1. ......................................................................... 433

Figure A1.10.
1
H NMR spectrum of A2. ....................................................................... 434

Figure A1.11.
1
H NMR spectrum of A3. ....................................................................... 435

Figure A1.12.
1
H NMR spectrum of A4. ....................................................................... 436

Figure A1.13.
1
H NMR spectrum of B1. ....................................................................... 437

Figure A1.14.
1
H NMR spectrum of B2. ....................................................................... 438

Figure A1.15.
1
H NMR spectrum of B3. ....................................................................... 439

Figure A1.16.
1
H NMR spectrum of B4. ....................................................................... 440
xxviii

Figure A1.17.
1
H NMR spectrum of C1. ....................................................................... 441

Figure A1.18.
1
H NMR spectrum of C2. ....................................................................... 442

Figure A1.19.
1
H NMR spectrum of PPDTBTY. ........................................................... 443

Figure A1.20. CV traces for the electrochemical oxidation of class A DArP polymers as
identified in Table 1 of the main text. ............................................................................. 444

Figure A1.21. CV traces for the electrochemical oxidation of class B DArP polymers as
identified in Table 1 of the main text. ............................................................................. 445

Figure A1.22. CV traces for the electrochemical oxidation of class C DArP polymers and
Stille PPDTBT as identified in Table 1 of the main text. ............................................... 446

Figure A1.23. DSC profiles for polymers as outlined in Table 2.1. .............................. 447

Figure A1.24. DSC profiles for polymers as outlined in Table 2.1. .............................. 448

Figure A1.25. GIXRD patterns for class A DArP polymers as outlined in Table 2.1. .. 450

Figure A1.26. GIXRD patterns for class B DArP polymers as outlined in Table 2.1. .. 451

Figure A1.27. GIXRD patterns for class C DArP polymers and Stille PPDTBT as
identified in Table 1 of the main text. ............................................................................. 452

Figure A1.28. I-V Curves for polymers detailed in Table A1.2. ................................... 458

Figure A1.29. External quantum efficiency of the BHJ solar cells based on DArP PPDTBT
and Stille PPDTBT under optimized conditions for device fabrication. ........................ 459
xxix

Figure A1.30. I-V Curves for solar cells fabricated from o-DCB as detailed in Table S2.
......................................................................................................................................... 461

Figure A1.31. I-V Curves for solar cells fabricated from o-DCB/CB solvent mixtures as
detailed in Table S2. ....................................................................................................... 462

Figure A 2.1
1
H NMR of 2,7-dibromo-9-(heptadecan-9-yl)-9H-carbazole in CDCl3 ... 465

Figure A 2.2.
1
H NMR of 2,5-diethylhexyl-3,6-di(thiophen-2-yl)-2,5-dihydropyrrolo[3,4-
c]pyrrole-1,4-dione in CDCl3.......................................................................................... 466

Figure A2.3.
1
H NMR of 4,10-bis(diethylhexyl)-thieno[2',3':5,6]pyrido[3,4-g]thieno[3,2-
c]isoquinoline-5,11-dione in CDCl3 ............................................................................... 467

Figure A2.4.
1
H NMR of 5-octyl-1,3-di(thiophen-2-yl)-4H-thieno[3,4-c]pyrrole-4,6(5H)-
dione in CDCl3 ................................................................................................................ 468

Figure A2.5.
1
H NMR of 2,5-bis(2,3-dihydrothieno[3,4-b][1,4]dioxin-5-yl)pyridine in
CDCl3 .............................................................................................................................. 469

Figure A2.6. High Temperature
1
H NMR of P1 in C2D2Cl4.......................................... 470

Figure A2.7. High Temperature
1
H NMR of P3 in C2D2Cl4.......................................... 471

Figure A2.8.
1
H NMR of P1 in CDCl3 ........................................................................... 472

Figure A2.9.
1
H NMR of P2 in CDCl3 ........................................................................... 473

Figure A2.10.
1
H NMR of P3 in CDCl3 ......................................................................... 474
xxx

Figure A2.11.
1
H NMR of P4 in CDCl3 ......................................................................... 475

Figure A2.12.
1
H NMR of A1 in CDCl3 ........................................................................ 476

Figure A2.13.
1
H NMR of A2 in CDCl3 ........................................................................ 477

Figure A2.14.
1
H NMR of A3 in CDCl3 ........................................................................ 478

Figure A2.15.
1
H NMR of A4 in CDCl3 ........................................................................ 479

Figure A2.16. CV Traces for PCDTBT Series of Copolymers ..................................... 480

Figure A2.17. CV Traces for DArP Carbazole Series of Copolymers, where A1 is
PCDTDPP, A2 is PCTPTI, A3 is PCDTTPD, and A4 is PCBEDOT-Pyr. .................... 481

Figure A2.18. JV-Curves for PCDTBT Series of Copolymers...................................... 482

Figure A2.19. JV-Curves for Carbazole Series of Copolymers with Various Acceptors
......................................................................................................................................... 482

Figure A3.1. CV Traces for PPDTBT polymers ............................................................ 485

Figure A4.1.
1
H NMR for monomer, 2-bromo-3-hexylthiophene (2Br-3HT), in CDCl3.
......................................................................................................................................... 500

Figure A4.2.
1
H NMR for monomer, 2-bromo-5-trimethyltin-3-hexylthiophene, in CDCl3.
......................................................................................................................................... 501

Figure A4.3.
1
H NMR for monomer, 2,5-bis(trimethyltin)thiophene, in CDCl3. .......... 502

xxxi
Figure A4.4.
1
H NMR for monomer, 2,5-diethylhexyl-3,6-di(thiophen-2-yl)-2,5-
dihydropyrrolo[3,4-c]pyrrole-1,4-dione (EH-DPP), in CDCl3. ...................................... 503

Figure A4.5.
1
H NMR for monomer, 2,5-diethylhexyl-3,6-bis(5-bromothiophene-2-
yl)pyrrolo[3,4-c]-pyrrole-1,4-dione (Br-DPP), in CDCl3. .............................................. 504

Figure A4.6.
1
H NMR for monomer, 4,4'-dimethyl-2,2'-bithiazole (BTz), in CDCl3. .. 505

Figure A4.7.
1
H NMR for monomer, (E)-2-(2-(thiophen-2-yl)vinyl)thiophene (TvT), in
CDCl3. ............................................................................................................................. 506

Figure A4.8.
1
H NMR for monomer, 2,8-dibromo-4,10-bis(2-ethylhexyl)thieno
[2',3':5,6]pyrido[3,4-g]thieno[3,2-c]isoquinoline-5,11(4H,10H)-dione (Br-TPTI), in
CDCl3. ............................................................................................................................. 507

Figure A4.9.
1
H NMR for monomer, 5,8-dibromo-2,3-bis(3-(octyloxy)phenyl)
quinoxaline (Br-QX), in CDCl3. ..................................................................................... 508

Figure A4.10.
1
H NMR for monomer, 4,7-bis(5-bromo-4-hexylthiophen-2-
yl)benzo[c][1,2,5]thiadiazole (Br-BTD), in CDCl3. ....................................................... 509

Figure A4.11.
1
H NMR for monomer, 1,3-dibromo-5-octayl-4H-thieno[3,4-c]pyrrole-
4,6(5H)-dione (Br-TPD), in CDCl3. ............................................................................... 510

Figure A4.12.
1
H NMR Spectra of Stille P3HT (A1). ................................................... 511

Figure A4.13.
1
H NMR Spectra of DArP P3HT (A2). .................................................. 512

Figure A4.14.
1
H NMR Spectra of DArP P3HT (A3). .................................................. 513
Figure A4.15.
1
H NMR Spectra of DArP P3HT (A4). .................................................. 514

xxxii
Figure A4.16.
1
H NMR Spectra of DArP P3HT (A5). .................................................. 515

Figure A4.17.
1
H NMR Spectra of DArP P3HT (A6). .................................................. 516

Figure A4.18.
1
H NMR Spectra of Stille P3HTT-DPP (B1). ........................................ 517

Figure A4.19.
1
H NMR Spectra of DArP P3HTT-DPP (B2). ........................................ 518

Figure A4.20.
1
H NMR Spectra of DArP P3HTT-DPP (B3). ........................................ 519

Figure A4.21.
1
H NMR Spectra of DArP P3HTT-DPP (B4). ....................................... 520

Figure A4.22.
1
H NMR Spectra of DArP P3HTT-DPP (B5). ....................................... 521

Figure A4.23.
1
H NMR Spectra of DArP P3HTT-DPP (B6). ....................................... 522

Figure A4.24.
1
H NMR Spectra of DArP P3HTT-DPP (B7). ....................................... 523

Figure A4.25.
1
H NMR Spectra of DArP P3HT-BT-DPP (P1). Peaks for b-d overlap with
the 3HT couplings (around 6.98 ppm). ........................................................................... 524

Figure A4.26.
1
H NMR Spectra of DArP P3HT-TvT-DPP (P2). Peaks for b-e overlap with
the 3HT couplings (around 6.98 ppm). ........................................................................... 525

Figure A4.27.
1
H NMR Spectra of DArP P3HT-BTz-DPP (P3). .................................. 526

Figure A4.28.
1
H NMR Spectra of DArP P3HT-EDOT-DPP (P4). .............................. 527

Figure A4.29.
1
H NMR Spectra of DArP P3HTT-TPTI (P5). Peaks for b-c overlap with
the 3HT couplings (around 6.98 ppm). ........................................................................... 528
xxxiii

Figure A4.30.
1
H NMR Spectra of DArP P3HTT-QX (P6). Peaks for b-e overlap with
majority 3HT couplings (around 6.98 ppm). .................................................................. 529

Figure A 4.31.
1
H NMR Spectra of DArP P3HTT-BTD (P7). ...................................... 530

Figure A4.32.
1
H NMR Spectra of DArP P3HTT-TPD (P8)......................................... 531

Figure A4.33. Cyclic voltammetry traces of P3HT Series. ........................................... 532

Figure A4.34. Cyclic voltammetry traces of P3HTT-DPP Series. ................................ 533

Figure A4.35. Cyclic Voltametry of the P3HT-X-DPP Series. ..................................... 534

Figure A4.36. Cyclic Voltametry of the P3HTT-Y Series. ........................................... 535

Figure A4.37. DSC Traces of the P3HT Series ............................................................. 536

Figure A4.38. DSC Traces of P3HTT-DPP Series ........................................................ 537

Figure A4.39. DSC Traces of DArP Semi-Random P3HT Analogs ............................. 538

Figure A4.40. J-V Curves for P3HT (A1-A6), P3HTT-DPP (B1-B7), and Semi-Random
P3HT Analogs (P1-P8). .................................................................................................. 547

Figure A5.1.
1
H-NMR of 3-hexylesterthiophene in CDCl3. .......................................... 555

Figure A5.2.
1
H-NMR of 2-bromo-3-hexylesterthiophene in CDCl3. ........................... 556

Figure A5.3.
1
H-NMR of 2-bromo-5-trimethylstannyl-3-hexylthiophene in CDCl3..... 557

xxxiv
Figure A5.4.
1
H-NMR of Stille P3HET in CDCl3. ........................................................ 558

Figure A5.5.
1
H-NMR of DArP P3HET in CDCl3. ....................................................... 559

Figure A5.6.
1
H-NMR of 2-bromo-3-hexylthiophene in CDCl3. .................................. 560

Figure A5.7.
1
H-NMR of 2-bromo-3-trimethylstannyl-3-hexylthiophene in CDCl3..... 561

Figure A5.8.
1
H-NMR of Stille P3HT in CDCl3............................................................ 562

Figure A5.9.
1
H-NMR of DArP P3HT in CDCl3. .......................................................... 563

Figure A5.10.
1
H-NMR of Oxi-DArP P3HT (Entry 3) in CDCl3. ................................. 564

Figure A5.11.
1
H-NMR of Oxi-DArP P3HET (Entry 4) in CDCl3. .............................. 565

Figure A5.12.
1
H-NMR of Oxi-DArP P3HT (Entry 7) in CDCl3. ................................. 566

Figure A5.13.
1
H-NMR of Oxi-DArP P3HET (Entry 8) in CDCl3. .............................. 567

Figure A5.14.
1
H-NMR of Oxi-DArP P3HT (Entry 11) in CDCl3. ............................... 568

Figure A5.15.
1
H-NMR of Oxi-DArP P3HET (Entry 12) in CDCl3. ............................ 569

Figure A5.16.
1
H-NMR of Oxi-DArP P3HXT (Entry 13) in CDCl3. ............................ 570

Figure A5.17.
1
H-NMR of Oxi-DArP P3HET (Entry 16) in CDCl3. ............................ 571

Figure A5.18.
1
H-NMR of Oxi-DArP P3HET (Entry 17) in CDCl3. ............................ 572

Figure A5.19.
1
H-NMR of Oxi-DArP P3HET (Entry 18) in CDCl3. ............................ 573
xxxv

Figure A5.20.
1
H-NMR of Oxi-DArP P3HET (Entry 23) in CDCl3. ............................ 574

Figure A5.21.
1
H-NMR of Oxi-DArP P3HET (Entry 24) in CDCl3. ............................ 575

Figure A5.22.
13
C-NMR of Stille P3HET in CDCl3. ..................................................... 576

Figure A5.23.
13
C-NMR of DArP P3HET in CDCl3. .................................................... 577

Figure A5.24.
13
C-NMR of Oxi-DArP P3HET (Entry 16) in CDCl3. ........................... 578

Figure A5.25. CV Traces for the electrochemical oxidation of Stille P3HET (a), DArP
P3HET (b), Stille P3HT (c), and DArP P3HT (d). ......................................................... 579

Figure A5.26. CV Traces for the electrochemical oxidation of Entry 4 (a), Entry 7 (b),
Entry 8 (c), and Entry 12 (d). .......................................................................................... 580

Figure A5.27. CV Traces for the electrochemical oxidation of Entry 16 (a), Entry 18 (b),
Entry 24 (c). .................................................................................................................... 581

Figure A5.28. UV-Vis Spectra for Stille P3HET (i), DArP P3HET (ii), DArP P3HT (iii),
and Stille P3HT (iv). ....................................................................................................... 582

Figure A5.29. UV-Vis Spectra for Oxi-DArP P3HET Entry 4 (i), Oxi-DArP P3HT Entry
7 (ii), and Oxi-DArP P3HET Entry 8 (iii). ..................................................................... 583

Figure A5.30. UV-Vis Spectra for Oxi-DArP P3HET Entry 12 (i), Oxi-DArP P3HET
Entry 16 (ii), Oxi-DArP P3HET Entry 18 (iii), and Oxi-DArP P3HET Entry 24 (iv). .. 584

Figure A5.31. Comparison of the UV-Vis Spectra for Stille P3HET (i), DArP P3HET (ii),
and Oxi-DArP P3HET Entry 18 (iii). ............................................................................. 585
xxxvi

Figure A5.32. GIXRD Spectra for Stille P3HET (i), DArP P3HET (ii), DArP P3HT (iii),
Stille P3HT (iv), and Oxi-DArP P3HT Entry 7 ( v). The regioregularity of the
corresponding polymers is provided as well. .................................................................. 586

Figure A5.33. GIXRD Spectra for Oxi-DArP P3HET Entry 4 (i), Oxi-DArP P3HET Entry
8 (ii), Oxi-DArP P3HET Entry 12 (iii), and Oxi-DArP P3HET Entry 16 (iv), Oxi-DArP
P3HET Entry 18 (v), Oxi-DArP P3HET Entry 24 (vi). The regioregularity of the
corresponding polymers is provided as well. .................................................................. 587

Figure A5.34. Comparison of GIXRD Spectra for Stille P3HET (i), DArP P3HET (ii), and
optimized Oxi-DArP P3HET Entry 18 (iii). The regioregularity of the corresponding
polymers is provided as well........................................................................................... 588

Figure A6.1.
1
H NMR Spectrum of 3-hexylesterthiophene ........................................... 592

Figure A6.2.
1
H NMR Spectrum of 4,4’-dimethyl-2,2’-bithiazole (BTz) ..................... 593

Figure A6.3.
1
H NMR Spectrum of thieno[3,4-c]pyrrole-4,6-dione (TPD) .................. 594

Figure A6.4.
1
H NMR Spectrum of P1 .......................................................................... 595

Figure A6.5.
1
H NMR Spectrum of P2 .......................................................................... 596

Figure A6.6.
1
H NMR Spectrum of P3 .......................................................................... 597

Figure A6.7.
1
H NMR Spectrum of P4 .......................................................................... 598

Figure A6.8.
1
H NMR Spectrum of P5 .......................................................................... 599

Figure A6.9.
1
H NMR Spectrum of P6 .......................................................................... 600
xxxvii

Figure A6.10.
1
H NMR Spectrum of P7 ........................................................................ 601

Figure A6.11.
1
H NMR Spectrum of P3HET-BTz-5% ................................................. 602

Figure A6.12.
1
H NMR Spectrum of P3HET-BTz-10% ............................................... 603

Figure A6.13.
1
H NMR Spectrum of P3HET-BTz-15% ............................................... 604

Figure A6.14.
1
H NMR Spectrum of P3HET-TPD-5% ................................................. 605

Figure A6.15.
1
H NMR Spectrum of P3HET-TPD-10% ............................................... 606

Figure A6.16.
1
H NMR Spectrum of P3HET-TPD-15% ............................................... 607

Figure A6.17. CV Traces for P1-P4 ............................................................................... 608

Figure A6.18. CV Traces for P5-P7 ............................................................................... 609

Figure A6.19. CV Traces of P3HET-BTz Random Copolymers .................................. 610

Figure A6.20. CV Traces of P3HET-TPD Random Copolymers .................................. 611

Figure A6.21. UV-Vis of P5, P6, and P7. ...................................................................... 612

Figure A6.22. GIXRD Patterns of P5, P6, and P7. ........................................................ 613

Figure A6.23. X-ray reflectivity profiles of samples in thin films spin-coated from o-DCB.
The spacing between the Kiessig fringes is linked to film thickness, while response from
the background determines film roughness.
4,5
................................................................ 616

xxxviii
LIST OF SCHEMES

Scheme 1.1. Some traditional C−C forming reactions toward aryl-aryl (Ar-Ar) bonds for
conjugated materials, which include (1) Stille, (2) Suzuki, (3) Negishi, (4) Kumada, (5)
Murahashi, and (6) Yamamoto. .......................................................................................... 2

Scheme 1.2. Homopolymerization of a single arene or heteroarene (Ar) monomer or
alternating copolymerization of two monomers toward π-conjugated polymers via DArP.
............................................................................................................................................. 4

Scheme 1.3. Example of a synthetic route toward poly(3-hexylthiophene) (P3HT) via
traditional cross-coupling method, Stille polycondensation, which generates stoichiometric
quantities of toxic tin byproducts. Direct arylation polymerization (DArP) bypasses an
undesirable lithiation-metalation synthetic step en route to P3HT. .................................. 11

Scheme 1.4. Synthesis of PPDTBT via DArP and Stille polymerization methods, where
the DArP route, which utilizes both small molecule direct arylation and DArP, requires
only 4 steps while the synthesis via Stille requires 6 steps as well as two steps with
organolithium and trimethyltin reagents. .......................................................................... 14

Scheme 1.5. Illustration of (a) examples of the types of small molecule direct arylation
couplings observed by Lemaire, et al.,
111
which include targeted cross-coupling reactions
between C−H/C−Br functionalities, homocoupling events, and β-coupling between
unselective C−H and C−Br functionalities. (b) When applied to polymerizations, these
defects are embedded in the main chain and cannot be removed. .................................... 16

Scheme 1.6. Some representative Class A conditions and substrates, as noted in Figure 1.7,
which are characterized by a coordinating polar solvent and their lack of carboxylic acid
additive or their utilization of a phase transfer agent, which include (a) poly(3-
octylthiophene) via conditions reported by Lemaire, et al.,
136
(b) PDOF-TP via conditions
reported by Kanbara, et al.,
122
(c) ProDOT-based copolymers via conditions reported by
xxxix
Kumar, et al.,
139
and (d) bislactam-based bisthiophene copolymer reported by Kim, et al.
149
........................................................................................................................................... 29

Scheme 1.7. Some representative Class B conditions and substrates, as noted in Figure 1.7,
which are characterized by their Fagnou-derived phosphine-free conditions with a
carboxylic acid additive, such as PivOH, which include (a) P3HT via conditions reported
by Thompson et al.,
118
(b) PCPDTBT via conditions reported by Horie et al.
151
in aromatic
solvents, (c) PEDOTF via conditions reported by Kanbara, et al.
146
with a bulky carboxylic
acid, 1-AdCO2H, and (d) PNDITF4T via conditions in mesitylene (among other aromatic
solvents) reported by Sommer, et al.
132
............................................................................ 31

Scheme 1.8. Some representative Class C conditions and substrates, as noted in Figure 1.7,
which are characterized as Fagnou-derived DArP conditions with both a carboxylic acid
and a phosphine ligand, which include (a) a dithienobenzotropone-based copolymer
synthesized by Swager et al.,
152
(b) a thienyl-flanked benzothiadiazole (BTD) and
diketopyrrolopyrrole (DPP) copolymer reported by Ling et al.,
153
and (c) a carbazole/BTD
copolymer, PCDTBT, reported by Sommer, et al.
53
......................................................... 32

Scheme 1.9. Some representative Class D conditions, as noted in Figure 1.7, which are
characterized as Ozawa-derived DArP conditions with a phosphine ligand and the absence
of a carboxylic acid additive, which include (a) the original conditions employed by Ozawa
et al.
141
for P3HT, (b) modified conditions toward isoindigo and thienopyrroledione (TPD)
utilized by Leclerc et al.
156
, and (c) conditions toward PEDOT derivatives reported by
Hsiao et al.
157
.................................................................................................................... 33

Scheme 1.10. Some representative Class E conditions, as noted in Figure 1.7, which are
characterized as Ozawa-derived DArP conditions with a phosphine ligand and a carboxylic
acid additive, which include (a) conditions toward P3HT executed by Coughlin et al.
50
, (b)
conditions toward polythiophene derivatives developed by Leclerc et al.,
121
and (c)
conditions toward dithienosilole and TPD alternating copolymers developed by Ozawa et
al.
52,158
............................................................................................................................... 34
xl

Scheme 1.11. Synthesis of PQT12 via double β-unprotected thienyl-flanked monomer
evaluated by Leclerc et al.
121
The authors observed the formation of β-defects without the
utilization of the bulky carboxylic acid, neodecanoic acid (NDA). ................................. 41

Scheme 1.12. Ultra-low loading phosphine-free DArP conditions (Class B) reported by
Thompson et al.
163
............................................................................................................. 45

Scheme 1.13. Sequential bromination of 3-hexylthiophene and DArP in one-pot with only
evaporation of the DCM solvent in between reactions as explored by Kanbara et al. ..... 50

Scheme 1.14. Palladium reduction from Pd(II) to Pd(0) via C−H/C−H homocoupling of
bithiophene under phosphine-free conditions. .................................................................. 52

Scheme 1.15. End-capping P3HT chains through utilization of an aryl palladium complex
initiator as reported by Ozawa et al.
188
............................................................................. 58

Scheme 1.16. (a) Synthesis of PDOPT via DArP as reported by Sommer et al. and (b) the
resulting end groups observed by various solvents, including 1,2,4-trimethylbenzene, o-
dichlorobenzene, chlorobenzene, mesitylene, p-xylene, and toluene with various phenyl-
based end groups with degrees of chlorination. ................................................................ 59

Scheme 1.17. Synthesis of P3HT-CNT via DArP as reported by Thompson et al.
189
The
Stille compatible monomer of 3-cyanothiophene is challenging to prepare, which makes
DArP an attractive route toward this random copolymer. ................................................ 60

Scheme 1.18. Synthesis of P3HT-F via DArP as reported by Coughlin et al.
50
The Stille
compatible monomer is 3-hexyl-4-fluorothiophene is challenging to isolate, which makes
DArP an attractive route toward random copolymers. ..................................................... 61

xli
Scheme 1.19. Two different viable functionalization strategies, explored by Route A and
Route B by Sirringhaus et al.
208
and Dodabalapur et al.
209
respectively, toward DPP and
BTZ copolymer. ................................................................................................................ 66

Scheme 1.20. Synthesis of polythiophene via two different monomer functionalization
strategies as reported by Leclerc et al.
55
........................................................................... 67

Scheme 1.21. Synthesis via direct arylation of small molecules featuring
pentafluorobenzene and 2-hexylthiophene units via two different functionalization
strategies (top) and the subsequent application of optimized conditions on the
polymerization of a model fluorinated copolymer via DArP (bottom). Denoted as −OHD
is an hexyldecyloxy side-chain. The authors observed that dibromotetrafluorobenzene only
resulted in oligomers via DArP Class A conditions. ........................................................ 68

Scheme 1.22. Most commonly, DPP is brominated for utilization in Stille or Suzuki
polymerizations because the stannylation requires more challenging purification and the
resulting tin-functionalized DPP monomer can be a viscous oil.
221,222
An advantage of
DArP is that either the unfunctionalized DPP or the easier to achieve dibrominated DPP
are both viable monomers. Given the low molecular weights that have generally been
achieved with stannylated DPP, DArP may enable high quality polymers that have
previously been inaccessible. ............................................................................................ 69

Scheme 1.23. Exploration of different functionalization strategies on two electron-poor
monomers via two different DArP classifications as reported by Wang et al.
220
In an
concurrent study, Sommer et al.
226
also evaluated both routes and provided detailed defect
analysis of this polymer via Route A using Class E conditions. ...................................... 71

Scheme 1.24. Observation by Wang et al.
220
that Class E conditions generate nearly defect-
free copolymers when utilizing Route A but no polymers via Route B. Conversely, Class
C conditions generate oligomers with significant defects via Route A but high molecular
weight copolymers with homocoupling defects via Route B. .......................................... 73
xlii

Scheme 1.25. Functionalization strategy utilized by Coughlin et al.
228
for the generation of
well-defined DPP copolymers via DArP Class E conditions. .......................................... 76

Scheme 1.26. Synthesis of PDBTz-A and PDBTz-B, DArP with two different monomer
functionalization strategies, under Class E conditions as reported by Li et al.
229
............ 77

Scheme 1.27. Comparison of two different substitution routes toward the generation of
PPDTBT as reported by Livi et al.
83
For the Stille compatible monomers, the thienyl-
containing substrate would be stannylated. ...................................................................... 79

Scheme 1.28. Synthesis of three-component semi-random copolymer, P3HTT-DPP via
DArP by Thompson et al.
118,231
......................................................................................... 80

Scheme 1.29. Comparison of two different substitution routes toward the generation of
ternary semi-random alternating copolymer PBDT-BTD-BTZ via DArP by Farinola et al.
77

Attempts at C−H activation of the benzene-like substrates was unsuccessful for Class E
conditions. Several classifications of DArP conditions generated polymer via the ......... 81

Scheme 1.30. Utilization of a directing group to avoid formation of β-defects for pyrrole-
based copolymers with a Ru-catalyzed DArP method as reported by Kanbara et al.
236
.. 86

Scheme 1.31. (a) Synthesis of model copolymer, PBDTBTD, via a variety of reaction
parameters explored for Class E conditions as reported by Wang et al.
240
(b) Solvents and
bases explored. For parameters that provided greater than 13 kDA, numbering ranks them
from highest molecular weight to lowest. ......................................................................... 88

Scheme 1.32. Minimization of homocoupling defects via utilized of mixed-ligand catalytic
system as explored by Ozawa et al.
241
.............................................................................. 90

xliii
Scheme 1.33. Combination of N,N-diethylpropanamide for solubilizing power and
Pd(Cy 3)2 P(0) pre-catalyst employed by Kanbara et al.
249
for minimizing homocoupling
and improving molecular weight for bithiazole-based copolymers. ................................. 95

Scheme 1.34. Synthesis of PNDIT2 via DArP in MeTHF or toluene as explored by
Sommer et al.
133
................................................................................................................ 98

Scheme 1.35. Biphasic conditions utilized by Leclerc et al.
251
for the synthesis of various
copolymers via DArP. Some representative examples of the explored substrates are
provided. ........................................................................................................................... 99

Scheme 1.36. Random copolymers based on dioctyl fluorene and benzothiadiazole with
either 3-hexylthiophene (R = hexyl), thiophene (R = H), or with this shown unit replaced
by EDOT as explored by Wang et al.
254
......................................................................... 102

Scheme 1.37. Semi-random ternary copolymers based on quinoline and benzothiadiazole
with a cyclopentadithiophene donor explored by Jacob et al.
255
.................................... 103

Scheme 1.38. Synthesis of semi-random ternary copolymers with phenanthridinone-based
monomers as reported by Leclerc et al.
256
...................................................................... 104

Scheme 1.39. With regiounsymmetric monomers like dithieno[3,2-b:2′,3′-d]pyridin-
5(4H)-one, random orientation of the monomers can lead to considerably different
optoelectronic properties compared to regioregular polymers, as explored by Cao et al.
257
......................................................................................................................................... 105

Scheme 1.40. Synthesis of all-conjugated donor/acceptor block copolymers containing
P3HT and PNDIT2, achieved via DArP of Br-NDI and bithiophene in the presence of end-
capped P3HT for in situ formation of P3HT-b-PNDIT2. ............................................... 106

xliv
Scheme 1.41. Fluorinated porous organic polymers via DArP as explored by Chen, Qi, and
Han et al.
260
and by Feng et al.
261
.................................................................................... 108

Scheme 1.42. Synthesis of networked fluoroarene porous polymers via DArP as reported
by Koizumi et al.
262
......................................................................................................... 108

Scheme 1.43. Synthesis of 3-component networked random copolymers via DArP as
explored by Koizumi et al.
263
.......................................................................................... 110

Scheme 1.44. Synthesis of a phenazine-based microporous polymer as reported by Wang
et al.
264
............................................................................................................................. 111

Scheme 1.45. Synthesis of thienthiadiazole-based (TTD) conjugated porous polymers via
DArP as reported by Wang et al.
265
................................................................................ 112

Scheme 1.46. Synthesis of hyperbranched DPP polymers via DArP as reported by Wang
et al.
266
............................................................................................................................. 113

Scheme 1.47. Synthesis of DPP-based homopolymers, P16-P19, via DArP of two distinct
DPP monomers as reported by Leclerc et al.
225
P18 and P19 are synthesized via two
different functionalization strategies............................................................................... 147

Scheme 1.48. A plausible generalized mechanism for oxidative DArP (oxi-DArP) using a
palladium catalyst.
351
...................................................................................................... 157

Scheme 1.49. Synthesis of P3HT via oxi-DArP as reported by Ogino et al.
359
............. 158

Scheme 1.50. Synthesis of polybenzodiimidazoles via copper-catalyzed oxi-DArP as
reported by You and Lan et al.
362
.................................................................................... 162

xlv
Scheme 1.51. Synthesis of poly(hexyl thiophene-3-carboxylate), referred to as poly(3-
hexylesterthiophene) (P3HET) via oxi-DArP, DArP, and Stille as reported by Thompson
et al.,
363
which was the first report of each synthetic method toward this polymer from their
respective monomers. ..................................................................................................... 164

Scheme 1.52. Conditions employed by Thompson et al.
369
for the synthesis of P3HET and
two random copolymer analogs, consisting of 5, 10, or 15% of the secondary comonomer.
......................................................................................................................................... 166

Scheme 1.53. Combination of small molecule direct arylation and oxi-DArP toward 2,2’-
bithiazole-based copolymers as reported by You and Wu et al.
371
................................. 166

Scheme 1.54. Synthesis of various 5,5’-bithiazole-based derivatives via oxi-DArP utilizing
oxygen as the sole oxidant as reported by You and Wu et al.
373
.................................... 167

Scheme 1.55. Synthesis poly(arylenevinylene)s via Rh-catalyzed direct alkenylation as
reported by Kanbara et al.
374
........................................................................................... 169

Scheme 2.1. Total synthesis of PPDTBT via DArP and Stille polymerization methods. The
synthesis of PPDTBT via DArP includes the application of small molecule direct arylation
to generate on of the monomers for the DArP route. This enables the synthesis of DArP
PPDTBT in only four steps while the synthesis of Stille PPDTBT requires six steps (though
through the utilization of direct arylation, even the Stille route can have a step saved).
Conditions are as follows: (i) 1. nBuLI, THF, -78°C; 2. SnMe3Cl; (ii) P(o-tol)3, Pd2(dba)3;
(iii) 1. nBuLi, THF, -78°C; 2. SnMe3Cl; (iv) Br2, AcOH; (v) C16H33Br, K2CO3, DMF,
reflux; (vi) PivOH, K2CO3, Pd(OAc)2, DMA, 80°C; (vii) DArP Protocol (See main text);
(viii) P(o-tol)3, Pd2(dba)3. ............................................................................................... 206

Scheme 2.2. Comparison of Route X and Route Y toward generation of DArP PPDTBT.
The thiophene-containing substrate is stannylated for the corresponding Stille route. .. 212

xlvi
Scheme 3.1. Overview of the Synthesis to PCDTBT utilizing traditional methods as well
as direct arylation. ........................................................................................................... 244

Scheme 3.2. Synthesis of DArP Carbazole-Based Alternating Copolymers ................. 258

Scheme 4.1. Total synthesis of PPDTBT. (i) Toluene, PdCl2(PPh3)2, (90%). (ii) THF,
LDA, trimethyltinchloride, (65%). (iii) Toluene, Pd2dba3/P(o-tolyl). (iv) DMSO, sodium
hydroxide, 2-hexyldecanyl bromide (60%). (v) Acetic acid/CHCl3 (1:1), Br2, (95%). (vi)
Toluene, Pd2dba3/P(o-anisyl), Cs2CO3, NDA. ................................................................ 279

Scheme 5.1. Synthesis of P3HTT-DPP-10% by Stille and DArP Polymerization Methods.
Determining whether halogenation of the acceptor or not halogenating the acceptor results
in minimal defects is a consideration in DArP. .............................................................. 308

Scheme 5.2. Synthesis of P3HT Semi-Random Analogs by DArP Polymerization.
Optimized Conditions from Model System P3HTT-DPP are Applied to a variety of systems
with different spacers and acceptors to determine the applicability of DArP with various
substrates. ........................................................................................................................ 323

Scheme 6.1. Synthesis of 2-bromo-5-trimethyltin-3-hexylesterthiophene and the
intermediates utilized for Oxi-DArP, DArP, and Stille polymerizations for generation of
poly(3-hexylesterthiophene). .......................................................................................... 345

Scheme 7.1. Overview of the synthesis of (a) P3HET, (b) random copolymer family
P3HET-BTz, and (c) random copolymer family P3HET-TPD via palladium-catalyzed
oxidative direct arylation polymerization (oxi-DArP), which do not require preactivation
of the monomers. ............................................................................................................ 366

xlvii
ABSTRACT
The rapid increase in the breadth and scope of transformations that involve metal-
promoted activation of C−H bonds is fundamentally changing the field of synthetic
chemistry. Direct arylation polymerization (DArP) is a newly established synthetic
protocol for atom economical, effective, and affordable preparation of conjugated
polymers, which continue to be incredibly advantageous as operative materials for a
diverse and continually evolving array of applications. This route toward conjugated
polymers for high performance materials is particularly appealing because it circumvents
the preparation of organometallic derivatives and the associated cryogenic air- and water-
free reactions. Although a broad range of monomers are now readily polymerizable, direct
arylation polymerization is known to produce defects in the chemical structure, which have
a strong impact on the optical, electronic, and thermal properties of conjugated polymers.
Fundamental understanding of the underlying considerations of this method is required to
truly enable a broad reaching platform. In Chapter One, a comprehensive review of the
development and exploration of DArP is provided, including obstacles and strategies for
overcoming them as well as a thorough analysis of practical performance and the expansion
to oxidative C−H/C−H coupling.
In Chapter Two, ten DArP protocols across the major classes of DArP are reported
en route toward generating poly[(2,5-bis(2-hexyldecyloxy)phenylene)-alt-(4,7-
di(thiophen-2-yl)benzo[c][1,2,5]thiadiazole)] (PPDTBT). Through evaluation of the
method and resulting photophysical and electronic properties, it is shown that not all DArP
methods are suitable for generating device-quality alternating copolymers. When DArP
PPDTBT was synthesized in superheated THF with Cs2CO3, neodecanoic acid, and P(o-
xlviii
anisyl)3, it generated polymers of exceptional quality that performed comparably to Stille
counterparts in both roll coated ITO-free and spin-coated ITO devices.
In Chapter Three, although direct arylation polymerization (DArP) has recently
emerged as an alternative to traditional cross-coupling methods like Suzuki
polymerization, the evaluation of DArP polymers in practical applications like polymer
solar cells (PSCs) is limited. Because even the presence of minute quantities of defects can
dramatically influence the solar cell, performance of DArP polymers offers critical insight
alongside other structural and optoelectronic comparisons. Even via traditional methods,
carbazole-based donors are frequently prone to homocoupling defects, which has been
shown to—along with β-defects—compromise performance. Through defect minimization
with the bulky and affordable neodecanoic acid (NDA) mixture, the synthesis of DArP
poly[(9-(heptadecan-9-yl)-9H-carbazole)-alt-(4,7-di(thiophen-2-
yl)benzo[c][1,2,5]thiadiazole)] (PCDTBT) that outperforms Suzuki PCDTBT with similar
molecular weights is reported. Expanding beyond this model system, carbazole-based
polymers featuring 2,5-diethylhexyl-3,6-di(thiophen-2-yl)-2,5-dihydropyrrolo[3,4-
c]pyrrole-1,4-dione (DPP), 4,10-bis(diethylhexyl)-thieno[2',3':5,6]pyrido[3,4-
g]thieno[3,2-c]isoquinoline-5,11-dione (TPTI), 5-octyl-1,3-di(thiophen-2-yl)-4H-
thieno[3,4-c]pyrrole-4,6(5H)-dione (DT-TPD), and 2,5-bis(2,3-dihydrothieno[3,4-
b][1,4]dioxin-5-yl)pyridine (EDOT-Pyr) are generated. Polymers are characterized by
1
H
NMR, cyclic voltammetry, UV-Vis, GIXRD, SCLC hole mobilities, and are implemented
into polymer solar cells fabricated in air under ambient humidity. We demonstrate that
DArP polymers perform comparably to Suzuki in practical applications.
xlix
In Chapter Four, continuous flow methods are utilized in conjunction with DArP
for the generation of roll-to-roll (R2R) compatible polymer, PPDTBT, for combined high-
throughput polymer synthesis and energy conversion from simple, inexpensive, and
scalable monomers. Utilization of thienyl-flanked benzothiadiazole as the acceptor marks
the first evaluation of a β-unprotected substrate in continuous flow via DArP, which
enables critical evaluation of the suitability of this emerging synthetic method for
minimizing defects for the generation of high performance materials. Subsequently, DArP
PPDTBT via continuous flow is implemented into ITO-free and flexible R2R solar cells to
achieve PCE of 3.5%, which is comparable to the performance of Stille PPDTBT. These
efforts demonstrate the distinct advantages of the continuous flow protocol with DArP for
reducing the associated costs of polymer upscaling and minimzing batch-to-batch
variations for quality material.
Subsequently, in Chapter Five, through a comparative analysis of conditions on
increasingly complex model systems ranging from P3HT (where highly successful but
distinct conditions are compared for the first time herein) to a three-component polymer
architecture featuring ubiquitous diketopyrrolopyrrole (DPP), reaction conditions are
optimized to generate polymers that perform similarly to Stille reference polymers in solar
cells. Subsequently, these optimized conditions are then applied to the synthesis of several
novel semi-random polymers, exploring a variety of both electron-poor and electron-rich
substrates, such as (E)-2-(2-(thiophen-2-yl)vinyl)thiophene (TvT), 4,4’-dimethyl-2,2’-
bithiazole (BTz), and 3,4-ethylenedioxythiophene (EDOT) as well as distinct acceptor
units, such as pentacyclic aromatic lactam, 4,10-bis(2-
ethylhexyl)thieno[2',3':5,6]pyrido[3,4-g]thieno[3,2-c]isoquinoline-5,11(4H,10H)-
l
dione(TPTI) and 2,3-bis(3-(octyloxy)phenyl)quinoxaline (QX), further demonstrating the
broad compatibility of these DArP conditions and expanding the semi-random toolkit
toward achieving polymers with a variety of highly tunable optoelectronic properties.
Polymers are characterized by NMR analysis, electrochemical HOMO level determination,
UV-Vis, GIXRD, DSC, SCLC hole mobilities, and are also implemented into polymer
solar cells.
In Chapter Six, poly(hexyl thiophene-3-carboxylate), an alkyl ester side-chain
functionalized thiophene polymer herein referred to as poly(3-hexylesterthiophene)
(P3HET), is synthesized via a novel palladium-catalyzed oxidative dehydrogenative
polycondensation method. The ester promotes the generation of high molecular weight
polymers as a directing group, enabling direct hetero C-H/C-H coupling and bypassing the
functionalization requirements of traditional direct arylation (halogenation) and transition
metal-catalyzed cross-coupling (halogenation and metalation) methods. Despite lacking
functional groups in the 2- and 5-position, these unique reaction conditions achieve good
regioregularity through the utilization of a phosphine ligand. To evaluate this new
polymerization method, poly(hexyl thiophene-3-carboxlates) and poly(3-hexylthiophene)
polymers are synthesized via Oxi-DArP, traditional DArP, and Stille polycondensation and
subsequently characterized by electrochemical HOMO determination, UV-Vis, GIXRD,
and space-charge limited current (SCLC) hole mobilities. High quality polymers via Oxi-
DArP were only acquired when the ester functional group was present, whereas molecular
weight, regioregularity, and yields suffered with 3-hexylthiophene. Optimized Oxi-DArP
P3HET exhibited absorption coefficients, electrochemical HOMO levels, and semi-
crystallinity comparable to DArP and Stille P3HET as limited by its resulting
li
regioregularity. This work expands on an emerging synthetic method and develops
attractively simple and mild conditions toward the generation of high quality polymers
promoted by carbonyl directing groups.
Finally, in Chapter Seven, Oxi-DArP is further explored. Two random copolymer
families of poly(hexyl thiophene-3-carboxylate), herein referred to as poly(3-
hexylesterthiophene) (P3HET), featuring either thieno[3,4-c]pyrrole-4,6-dione (TPD) or
4,4’-dimethyl-2,2’-bithiazole (BTz) comonomers are synthesized by oxidative direct
arylation polymerization (oxi-DArP) conditions that enable high regioregularities despite
the lack of preactivation of the monomers. Through refinement of the reaction parameters
and minimization of auxiliary reagent loadings, polymers with good molecular weights are
achieved and the feed ratio is closely correlated to the polymer composition. These random
copolymers are evaluated by
1
H NMR, SEC, UV-Vis, GIXRD, and SCLC hole mobility
analyses to determine the compatibility of this emerging synthetic method with
increasingly popular random copolymer architectures.

1
CHAPTER 1: DIRECT ARYLATION POLYMERIZATION

1.1. Introduction

Conjugated polymers are operative materials for a diverse range of applications,
including photovoltaics,
1
field-effect transistors,
2
light-emitting diodes,
3
sensors,
4,5

electrochromic devices,
6,7
bioimaging materials,
8,9
drug delivery,
10
and as photosensitizers
in photodynamic therapy.
11
They have steadily improved since their discovery in the
1970s
12
through strategic and rational design modifications of the polymer backbone,
13

utilization of side-chains and other functional groups,
14,15
and evaluation of unique
structural motifs and application-based design enhancements.
16,17
Coupled with their
distinct advantages of being lightweight, solution processable, and compatible with flexible
substrates, polymers have inspired high throughput industrial-scale and low-cost flexible
roll-to-roll printed plastic optoelectronic devices
18–20
with recyclable components.
21
With
the steady development of increasingly finely-tuned aromatic backbones, the demand for
convenient, reliable, and efficient methods of generating these materials also grows.
For high performance conjugated polymers with well-defined structures from a
broad array of substrates, a transition metal-catalyzed cross-coupling polycondensation is
typically utilized, such as Migita-Kosugi-Stille,
22
Suzuki-Miyaura,
23,24
Kumada-Corriu,
25

Negishi,
26
Murahashi,
27
and Yamamoto
28
methods, which necessitate the functionalization
of one coupling site with a halogen (often brominated or iodinated) and another coupling
site with an organotin, organoboron, organomagnesium, organozinc, organolithium, or
organohalide species respectively (Scheme 1.1). While these methods have steadily
2
developed (and continue to develop) into a powerful arsenal of protocols in the toolkit of
synthetic chemistry, the past fifteen years have witnessed the emergence of metal-
promoted C−H activation toward C−C bonds from an aryl halide, thus requiring the pre-
activation of only one coupling partner, which has proven to be incredibly attractive for
improving atom economy, providing targets in fewer synthetic steps, generating more
benign byproducts, and decreasing the overall cost of transformations. Although C−H
activation methods have been known for over half a century,
29
they have only recently been
explored for the synthesis of π-conjugated polymers, with some pertinent reviews having
been written on the topic.
30–48
A deeper discussion of the implications, considerations, and
strategies for achieving well-defined polymers is necessary for the broad applicability of
this method, which would include not only selective and reactive methods but also
evaluation of the structure-function relationships of the resulting materials.

Scheme 1.1. Some traditional C−C forming reactions toward aryl-aryl (Ar-Ar) bonds for
conjugated materials, which include (1) Stille, (2) Suzuki, (3) Negishi, (4) Kumada, (5)
Murahashi, and (6) Yamamoto.
3
In this Chapter, recent advances directed toward the optimization of the direct
arylation polymerization protocol are critically discussed in the context of how they have
motivated the development and refinement of conditions. Specifically, how they have
analyzed and minimized unselective side reactions and expanded substrate scope.
Additionally, an evaluation of this protocol as a viable method toward practical
applications as it correlates to defect-content will be undertaken. Fully understanding the
reactivity and limitations of the method, as well as evaluating the quality of the resulting
polymers, can encourage and motivate future improvements and utility, with the goal of
direct arylation polymerization becoming a superlative cross-coupling method for the
broad generation of exceptional polymers.

1.2. Development of Direct Arylation Polymerization: Considerations for Well-
Defined Conjugated Polymers

Reactions that can substitute one preactivated species with a simple arene have
become highly prevalent, often broadly referred to as C−H (bond) activation and C−H
(bond) functionalization but also others. To describe these processes succinctly, avoid
unnecessarily broad terminology, and emphasize the arene being functionalized rather than
the bond being transformed, the term “catalytic direct arylation” has emerged to label
reactions with both arenes and heteroarenes.
49
When applied to the generation of polymers
through consecutive direct arylation reactions, this method should simply be referred to as
direct arylation polymerization (Scheme 1.2). This method is often abbreviated as
DArP,
40,50–52
which fittingly emphasizes the arene, typically abbreviated “Ar” (even when
referring to a heteroarene) and provides a suitable cadence. It is also sometimes abbreviated
4
more succinctly as DAP.
53,54
In an effort to emphasize the distinction between arenes in
general and heteroarenes, as well as broaden the terminology, this method is sometimes
also referred to as direct (hetero)arylation polymerization (DHAP).
55
Regardless, the
advantages of such a method that can directly activate C−H bonds without the need for pre-
functionalization beforehand cannot be understated, as it significantly simplifies the
synthesis of materials and could potentially enable monomers that are not compatible with
organometallic functional groups (either from difficulty in isolating pure monomers or
chemical instability). Furthermore, it would further solidify the notion of organic
electronics as less toxic, more environmentally friendly, and more sustainable than their
inorganic counterparts.

Scheme 1.2. Homopolymerization of a single arene or heteroarene (Ar) monomer or
alternating copolymerization of two monomers toward π-conjugated polymers via DArP.
In the following section, the evaluation of the advantages that make DArP
particularly attractive, the mechanistic considerations for this emerging method, and the
classifications of the immense variety of DArP parameters and the themes they encompass
with be discussed, concluding with case studies of ubiquitous reference polymer P3HT
toward addressing the perceived limitations. This section will be followed by a critical
5
discussion of the strategies toward well-defined copolymers, an evaluation of structure-
function relationships toward high performance practical materials, and ultimately
conclude with efforts in oxidative direct arylation polymerization toward direct C−H/C−H
coupling and an outlook for the future of DArP.

1.2.1. Practical Considerations for Motivating Direct Arylation Polymerization

Conjugated polymers, much like other classes of polymers that preceded and now
coexist with them, have properties that are intrinsically linked to parameters like molecular
weight (chain length), mass dispersity, structural defects, composition, and arrangement,
which includes alternating, block, statistical/random, gradient, and branched
configurations but can also include microstructural organization like regioregularity
(commonly measured for regiounsymmetric aryl substrates) or tacticity (relative
stereochemistry of chiral centers), which will impact their performance in applications.
Increasingly, highly tailored polymeric architectures are pursued for precisely tuning
optical, electronic, and physical properties. Because conjugated polymers can exhibit
discernible differences in optoelectronic properties that vary with molecular weight,
arrangement, and defects, methods to generate these materials in a predictable manner is
of utmost importance. Although Ziegler-Natta catalysts or ring-opening metathesis
polymerization (ROMP) are most commonly employed to synthesize polyacetylene, the
field of conjugated polymers has shifted toward other electroactive polymers, such as
polyphenylene vinylene and other benzene-based aryl motifs but especially polythiophenes
(Figure 1.1), which have typically been achieved via electropolymerization, chemical
oxidative polymerization, or metal-catalyzed cross-coupling reactions.
6

Figure 1.1. Chemical structures of some conjugated polymers, which include (a)
polyacetylene, (b) polyaniline, (c) polyphenylene vinylene, (d) polypyrrole, and (e)
polythiophene.
In preparing conjugated polymers, several considerations are prudent (Figure 1.2).
The first is the reliability of the synthetic method. Although methods like
electropolymerization and chemical oxidative polymerization are convenient for
generating some conjugated polymers, such as polyphenylenes, polypyrroles,
polythiophenes, and polyanilines,
56–60
they often exhibit poor structural control and
embedded defects, as well as potential metal/halide backbone impurities,
61
all of which
contribute to polymers that perform poorly in some targeted applications.
62
They are also
not broadly compatible with all substrates, particularly electron-poor systems with higher
electrochemical oxidation potentials.
63
Catalyzed cross-coupling methods tend to provide
better control but can still be vulnerable to side reactions and byproducts. Whereas with
small molecule couplings, these impurities or byproducts can usually be separable by
purification, these undesirable couplings are permanently embedded in the polymer when
extending these methods. Inevitably, this can alter polymer properties. Such undesired
7
couplings may include either homocoupling or couplings to other sites, which may lead to
branching polymers. Another consideration is what end groups will ultimately be present,
as end groups may impact polymer optoelectronic properties.
64
At the very least,
inconsistent end groups from poorly defined termination events can lead to variability in
polymer quality. When using a catalyst, residual metal residue, which are usually
physically entrapped in polymers or bound to polymers by some metal-ligand complex can
also significantly impact optoelectronic performance.
65–68
While traditional polymer
purification (extraction, filtration, precipitation, centrifugation, etc.) can remove some
metal residue and treatment with metal scavengers may remove even more, sometimes
metal residue will remain—which introduces considerations for heterogeneous or low
catalyst loading reactions. Lastly, due to the molecular weight dependence of polymer
properties, achieving suitable molecular weights are critical. For step-growth
polymerization, achieving high degrees of polymerization depends on stochiometric
balance of the reactive functional groups and the extent of the reaction at a given time, as
proposed by Carothers.
69,70

8

Figure 1.2. Some considerations when selecting a synthetic method for the generation of
polymers.
As briefly highlighted in the Introduction, the desire for well-defined, high
molecular weight, reliable, and convenient methods for generating π-conjugated polymers
has gradually led to the widespread and ubiquitous use of organometallic cross-coupling
reactions (Scheme 1.1). Although nickel-catalyzed polycondensations like Negishi and
Kumada have been quite popular for the synthesis of P3HT, much conjugated polymer
research now entails expanding from simple homopolymers like P3HT to more complex
9
multi-component alternating or random copolymers. With the increasing library of
structural motifs and complex polymer designs, the need for greater functional group
tolerance, isolable monomers to maximize purity, and reliable polymerization methods has
grown, all of which are provided by the Suzuki and Stille methods. Both Suzuki and Stille
enable isolation and purification of the active monomer species, whereas Negishi
(organozinc) and Kumada (organomagnesium) generate the active species in situ prior to
the polymerization, which works well for producing some homopolymers but can be
impractical for more complicated systems. It has also been observed that with Kumada-
based polymerizations, the monomer feed ratio does not always correlate to the polymer
composition, which makes this method unattractive for targeting statistically random
copolymers with specific compositions.
71
For these reasons, both Stille and Suzuki are
considered superior methods for generating high polymerization yields and reliably high
molecular weights with a wide variety of substrates with excellent correlation between feed
ratios and polymer compositions. However, while the Suzuki polycondensation uses an
organoboron group, the stability of these functional groups with thiophene-based substrates
can be limited. Likewise, the stannylation of benzene-like substrates for compatibility with
Stille can be challenging. Since Suzuki and Stille require one halogenated and one
organometallic coupling partner, both methods can be viable with strategic
functionalization (i.e. boronating a benzene-like substrate and stannylating a thiophene-
like substrate). However, in instances where two benzene-like substrates, such as such as
carbazole, fluorenes, and phenyl-based substrates, are copolymerized, Suzuki is the most
logical choice. When two thiophene-based substrates are utilized, Stille would typically be
more viable. Although benzene-like substrates are quite common in conjugated polymers,
10
the thiophene motif is unparalleled in its employment in high performance optoelectronic
applications.
72,73
Consequently, the Stille polymerization is the most widely utilized
synthetic method for state-of-the-art polymers in OPVs.
34
Together, the study of
conjugated polymers and the development of synthetic methods that have eventually been
employed to make conjugated polymers have ultimately resulted in two Nobel Prizes, first
for Chemistry in 2000 for doped polyacetylene and conducting polymers and then in 2010
for palladium-catalyzed cross couplings.
Although incredibly effective, the Stille method requires a toxic and relatively
unstable alkyltin functional group (−SnR3),
74
which is achieved via a lithiation-metalation
step under cryogenic air- and water-free conditions with highly flammable reagents.
Although organotin reagents are generally air-stable and easily stored, these reaction
parameters make Stille monomers somewhat unattractive for industrial-scale synthesis,
37

which is compounded by the fact that costly organotin functional groups are subsequently
generated as stoichiometric toxic waste byproducts during the polycondensation.
Additionally, the purification of Stille monomers can be quite difficult because the
organotin functional group is readily stripped on silica-based columns and is often too high
boiling for convenient distillations, often requiring a Kugelrohr distillation. To lower
boiling points or to achieve a solid that can be recrystallized, typically trimethyltin is
utilized; however, organotin toxicity is inversely related to alkyl chain length, which means
trimethyltin is the most toxic while a higher boiling but less toxic tributyltin may be too
challenging to purify.
75
Critically, the purity of the monomer can influence the molecular
weight of the resulting polymers.
76
Indeed, challenges in purifying the organotin
compounds may hinder the utilization of novel and interesting substrates. Elimination of
11
this particular step (Scheme 1.3), arguably the most challenging en route to Stille-
compatible monomers, would be a distinct advantage and major benefit for industrial-scale
polymer production.
77

Scheme 1.3. Example of a synthetic route toward poly(3-hexylthiophene) (P3HT) via
traditional cross-coupling method, Stille polycondensation, which generates stoichiometric
quantities of toxic tin byproducts. Direct arylation polymerization (DArP) bypasses an
undesirable lithiation-metalation synthetic step en route to P3HT.
The need for organometallic functional groups is the most significant hurdle for
labeling conjugated polymers and their resulting organic electronics as environmentally-
friendly and less toxic alternatives to inorganic materials, such as gallium arsenide or lead
perovskites. Stille requires excess stochiometric trialkyltin chloride derivatives to even
append the functional group to the substrate, which is then subsequently produced as a
waste byproduct during the polymerization. Calculations carried out by Farinola et al.
37

suggests that toward a relatively accessible alternating copolymer, poly([5-(2-ethylhexyl)-
4,6-dioxo-5,6-dihydro-4H-thieno[3,4-c]pyrrole-1,3-diyl]{4,8-bis[(2-ethylhexyl)oxy
]benzo(1,2-b:4,5-b’) dithiophene-2,6-diyl }) (PBDTTPD), 0.34 kg of tin waste would be
produced for every 1 kg of polymer generated. Furthermore, it is particularly uncommon
for synthetic accessibility to be discussed or emphasized when targeting new conjugated
polymers in the race for record-breaking mobilities in field-effect transistors (OFETs) or
12
efficiencies in OPVs. For instance, the production of common monomers such as carbazole
derivatives requires highly corrosive sulfuric acid and nitric acid, production of certain
diones requires corrosive and reactive thionyl chloride, corrosive and toxic bromines are
required for a number of substrates, any stannylated monomers require spontaneously
flammable organolithium reagents and toxic trialkyltin derivatives, and all polymerizations
require expensive palladium complexes.
37
For the synthesis of many semiconducting
polymers, these reactions are quite deleterious for the environment. Furthermore, some
high performance polymers require numerous steps, which has been shown to linearly
increase the cost per gram and all but dismiss their commercial viability.
78
This dissonance
between the desire for high performance polymers and the untenable costs of achieving
them must be resolved for polymers to be both effective and broadly applicable materials.
Polymers offer the distinct advantages of being aesthetically pleasant colored materials for
organic electronics capable of multicolored and/or semitransparent designs that are readily
implemented into flexible and lightweight devices via high throughput manufacturing
processes
19,79–81
but as identified by Lipomi, et al.
74
the energy- and cost-intensive nature
of organic electronics demands the production of polymers that minimize stochiometric
organotin waste, utilize heterogeneous catalysis, proceed through C-H activation, and can
adopt biofeedstock-derived starting materials.
Estimates by Sommer et al.
82
have suggested that DArP can reduce the cost of high
mobility polymer, poly{[N,N′-bis(2-octyldodecyl)-naphthalene-1,4,5,8-
bis(dicarboximide)-2,6-diyl]-alt-5,5′-(2,2′-bithiophene)} (PNDIT2) by about 35%
compared to the Stille route. For many conjugated polymers, it may be possible to even
combine small molecule direct arylation with DArP for minimizing the costs even further.
13
For example, Livi et al.
83
synthesized poly[(2,5-bis(2-hexyldecyloxy)phenylene)-alt-(4,7-
di(thiophen-2-yl)benzo[c][1,2,5]thiadiazole)] (PPDTBT) via a combination of small
molecule direct arylation and DArP that saved two steps compared to the Stille route
(Scheme 1.4). The fluorinated version of this polymer has achieved over 9% efficiency in
OPVs,
84
while the non-fluorinated version generates high performing large area, roll-
coated OPVs. This latter system exemplifies the direction that must be pursued for
economically and commercially viable energy conversion technology. With regards to the
OPV architecture, the devices were produced on an indium tin oxide(ITO)-free semi-
transparent substrate called Flextrode, developed by Krebs et al.
19,85
which consists of a
PET substrate layered with a silver grid, PEDOT:PSS, and ZnO.
86
Considering the absence
of ITO, which is particularly expensive and that the silver can be recycled,
21
these device
substrates are incredibly cost-effective compared to traditional OPVs. Indeed, one of the
major concerns for this technology is producing polymers on the scale necessary to produce
these roll-to-roll (R2R) OPVs, which has motivated the applications of continuous flow
chemistry to produce materials for R2R-coated high throughput OPVs by Stille,
80
as well
as DArP.
87
With regards to the materials employed, the work from Livi et al.
83
enabled the
synthesis of PPDTBT in 4 steps without the need for any organotin reagents or
organolithium reagents. For reference, ubiquitous state-of-the-art high performance
polymer, poly([2,6′-4,8-di(5-ethylhexylthienyl)benzo[1,2-b;3,3-b]dithiophene]{3-fluoro-
2[(2-ethylhexyl)carbonyl]thieno[3,4-b]thiophenediyl}) (PTB7-Th) can take up to 14 steps
to synthesize with four steps requiring organolithium reagents and one step requiring
trimethyltin reagents. Although PTB7-Th can achieve efficiencies exceeding 10% with
additives, fullerene acceptor PC71BM, and tailored interlayers
88
in small-area ITO devices,
14
it’s efficiency is under 2% when applied to realistic additive- and ITO-free R2R devices.
89

Conversely, 4-step PPDTBT via DArP can achieve OPV efficiencies above 3% in a similar
device.
83
However, the performance drops to below even 1% for polymers with defects.
83

For this reason, synthetic methods that can achieve well-defined copolymers will always
be preferential. And while this review will solely emphasize DArP as a synthetic method,
the materials that are pursued should always take the above considerations into account.
There is a need for both evaluating polymers for applications in a realistic and appreciable
way but also for selecting methods that can provide well-defined polymer structures.

Scheme 1.4. Synthesis of PPDTBT via DArP and Stille polymerization methods, where
the DArP route, which utilizes both small molecule direct arylation and DArP, requires
only 4 steps while the synthesis via Stille requires 6 steps as well as two steps with
organolithium and trimethyltin reagents.
It follows, then, from the discussion above that the development of direct
arylation—which has only recently emerged as a synthetic technique for conjugated
polymers—is critical for the sustainability and practicality of conjugated polymers as
operative materials but an overall emphasis on employing green chemistry, cost-effective
15
materials, and a rational commitment to sensible targets is also worth considering. It is the
collection of these practical considerations that ultimately motivates the development of
DArP.

1.2.2. Mechanistic Considerations for Minimizing Defects in Conjugated Polymers

Although this review will emphasize direct arylation conditions toward π-
conjugated polymers (Scheme 1.2), it must be emphatically noted that efforts in this
emerging field have been enabled by the incredible advances in small molecule carbon-
carbon bond formation toward the biaryl structural motifs that are increasingly relevant not
only for conjugated systems but for systems of relevance in pharmaceutical and biological
sciences.
29,90–104
These reports span nearly two decades and demonstrate how prevalent
direct arylation has become and continues to be.
35,105–110
Indeed, much of our understanding
of the DArP mechanism is derived from work on small molecule systems. Additionally,
much of our understanding of side reactions and associated byproducts is derived from
small molecule direct arylation. Such considerations are particularly important for the
application of small molecule direct arylation conditions toward polymeric systems
because byproducts via small molecule synthesis can usually be removed via purification
whereas such byproducts during a polymerization would be physically embedded in
polymeric chains (Scheme 1.5). Such structural differences induced by synthetic method
becomes critically important when considering the suitability of the resulting polymer for
practical applications, where homocoupling, branching content, residual metal
complexation, chain-termination reactions and resulting end groups, as well as physical
16
properties like degree of polymerization, mass dispersity, and yield will all inevitably
influence the optoelectronic properties or the eventual morphology.

Scheme 1.5. Illustration of (a) examples of the types of small molecule direct arylation
couplings observed by Lemaire, et al.,
111
which include targeted cross-coupling reactions
between C−H/C−Br functionalities, homocoupling events, and β-coupling between
unselective C−H and C−Br functionalities. (b) When applied to polymerizations, these
defects are embedded in the main chain and cannot be removed.
Because both DArP and Stille can achieve consecutive cross-couplings toward
conjugated polymers, many assumptions derived from the established Stille
polymerization, such as defect tendencies, functional group assignments, and substrate
scope are sometimes indiscriminately applied to DArP. It should not be overlooked that
DArP, although a member of the family of palladium-catalyzed cross-coupling reactions,
operates via a different mechanism. Understanding the scope and limitations of direct
arylation reactions, as well as how the resulting materials may differ compared to methods
like Stille, can only be aided by the evaluation of the pathways toward cross-couplings. As
17
illustrated in Figure 1.3a, which provides a simplified overview of the Stille mechanism
en route to 3-hexylthiophene couplings from the monomer, 2-bromo-5-trimethyltin-3-
hexylthiophene (as synthesized in Scheme 1.3), the general pathway involves the oxidative
addition of a Pd(0) to a C−halogen bond (most commonly bromides or iodides but also
pseudohalides like triflates).
112
This generates a Pd(II) intermediate with a Pd−Ar bond and
a bromide ligand which proceeds through a transmetalation step after nucleophilic attack
by an organometallic (M)-functionalized aryl bond, which for the Stille example in Figure
1.3a, is trimethyltin-functionalized thiophene bond (at the 5-position of the monomer). The
transmetalation of this intermediate from oxidative addition is the defining variable that
distinguishes the numerous cross-coupling reactions. The specific mechanism involved
will vary accordingly with the catalyst, the ligands, and the organometallic functional
group. Subsequently, the cycle begins anew with the regeneration of the active catalyst
species via reductive elimination of the cross-coupled aryl-aryl compounds, in this
example, coupled 3-hexylthiophene. While cross-coupling is the major reaction, side-
reactions can lead to other couplings.

18

Figure 1.3. Simplified mechanistic overview of the synthesis of head-to-tail 3-
hexylthiophene couplings via (a) palladium-catalyzed Stille cross-coupling and (b)
palladium-catalyzed direct arylation with a carboxylic acid additive. Direct arylation
typically requires a carbonate can also operate without a carboxylate additive via
arylpalladium complexes.
113

The 3-hexylthiophene example for Stille cross-coupling polycondensation
exemplifies the consequences of homocoupling events in a polymer. For example,
regiosymmetric AB-type monomers would give the same polymer structure regardless of
whether cross-coupling or homocoupling events occurred; however, when it comes to
unsymmetrical monomers, such as 3-hexylthiophene, homocoupling linkages within the
polymer chains will change the polymer structure. For homopolymers generated from 3-
alkylthiophenes, this homocoupling content manifests itself as a decrease in the number of
so-called head-to-tail couplings. This is illustrated in Figure 1.4, which shows examples
of head-to-tail (HT) couplings achieved via successful cross-coupling, head-to-head (HH)
couplings achieved via nucleophile homocoupling, and tail-to-tail (TT) couplings achieved
19
via electrophile homocouplings. Cross-couplings, which consist of two functionalities that
will ultimately generate an aryl nucleophile and an aryl electrophile, may undergo side
reactions that lead to defects in the polymer chain. Although aryl nucleophiles in Stille and
Suzuki, namely aryltin and arylboron, do not undergo the common homocoupling-inducing
metal−halogen exchange that can occur with arylzinc (Kumada) or arylmagnesium
(Kumada) at unoptimized reaction temperatures, they are still prone to homocoupling
events. Commonly, residual oxygen or other oxidative impurities can oxidize Pd(0) to
Pd(II) and induce homocoupling via a double transmetallation; likewise, reducing
impurities can also induce homocoupling of electrophiles. This can even occur without
impurities via disproportionation, where essentially one arylpalladium species undergoes
transmetallation with another arylpalladium species instead of the nucleophile, which leads
to an electrophile homocoupling and the generation of Pd(II), which can then subsequently
result in nucleophile homocouplings.

Figure 1.4. For the coupling of 3-hexylthiophene, an unsymmetrical monomer, via
palladium-catalyzed cross-couplings there is the potential for electrophile homocoupling
20
that lead to head-to-head (HH) couplings and nucleophile homocoupling tail-to-tail (TT)
couplings despite cross-coupling toward head-to-tail (HT) couplings being most favorable.
Although DArP operates under a different mechanism, it is not immune to these
homocoupling events via disproportionation but acquires additional considerations.
Several mechanisms through which C−H activations occur have been proposed, including
electrophilic aromatic substitution, Heck-type coupling, and σ-bond metathesis, but the
concerted metalation-deprotonation (CMD) pathway has been the most supported
mechanism (Figure 1.5), which stems from the utilization of either carbonate or
carboxylate bases, though the carboxylate additive leads to a significant decrease in the
transition state energy.
102,114,115
Several reviews have been devoted to this seminal
discovery which will only be briefly discussed here.
98,116,117
A simplified overview of this
mechanism is provided in Figure 1.3b, which is distinguished from the Stille mechanism
by an anionic ligand exchange of the halogen ligand with a carboxylate anion, which assists
with the deprotonation of thiophene while simultaneously forming the second
arylpalladium bond, which undergoes reductive elimination to produce the aryl-aryl cross-
coupling bond. The importance of the CMD pathway highlights much of the advances in
the catalytic system for DArP. Investigations into direct arylation selectivity by Fagnou
and coworkers investigated CMD enthalpic contributions to the transition state energy and
ultimately determined that C−H acidity, though not directly proportional to the reactivity
of the C−H bond, can be used as a predictive trait for determining reactivity, suggesting
that electron-poor substrates are more reactive in general. For thiophene, the α-substitution
is electronically favored, which enables DArP to be utilized for the generation of polymers
with similar structural connectivity as Stille. Advantageously, when considering the
21
precursor to the Stille monomer, 2-bromo-3-hexylthiophene, the need to lithiate and
metalate to generate the organotin functional group can be bypassed via direct arylation of
the 5-position. Therefore, in theory Stille and DArP could achieve the same polymer
structures for polythiophenes.

Figure 1.5. A comparison of the modes of operation and transition states for electrophilic
substitution (top), Heck-type coupling, σ-bond metathesis, and carboxylate-assisted
concerted metalation-deprotonation (CMD) for C−H activation of thiophene. Transition
state energy is highest for electrophilic substitution and lowest for the CMD pathway.
Unfortunately, although the α-position is more reactive, the β-position is not
prohibitively unreactive. Observed by Thompson et al.
118–120
and subsequently by Leclerc
et al.,
121
β-coupling reactions can happen via DArP in small quantities with thiophene-
based polymers, though cross-linking has even been observed in polymers via MALDI-
TOF for benzene-like substrates as well by Kanbara et al.
122
which suggests unselective
22
C−H activation can occur on substrates such as carbazole in addition to thiophene. As
determined by Fagnou and Gorelsky,
114
the free energy of activation for direct arylation of
thiophene via the CMD pathway involving an acetate ligand for the α-position and β-
position is 25.6 kcal mol
-1
and 29.9 kcal mol
-1
respectively (Figure 1.6). For reference,
they observed the free energy of activation for benzene to be 33.9 kcal mol
-1
.
Consequently, with phosphine ligands, different solvents, and different substrates, the C−H
activation of unselective positions may occur more prevalently or could even be exploited
to happen in significantly higher qualities.
123
For example, electron-rich phosphine ligands
can increase the rate of oxidative addition but slow the kinetics of transmetalation steps or
reductive elimination; conversely, electron-poor ligands might improve the rate of
transmetalation.
124
This is exemplified in direct arylation, where electron-poor phosphines
increase the electrophilicity of the palladium center to further lower the transition energy
of the CMD process,
125
which can promote C−H bond cleavage, the rate-determining step
of direct arylation.
102,126
Additionally, coordinating solvents such as DMF and DMA can
behave as ligands in direct arylation,
127
lowering the activation barrier of C−H abstraction,
though DMA can lead to higher molecular weights and yields than DMF.
122
Optimizing
the catalytic system to overcome these limitations or exploit this potential is an emphasis
in section 3 of this Review. Indeed, the evaluation of β-defects is a major shortcoming in
the overall exploration of DArP as it often occurs in small quantities and depending on the
substrate, can be quite challenging to identify.
40

23

Figure 1.6. As a consequence of C−H activation via CMD pathway, unselective side-
reactions may occur more prevalently. The free energy of activation of the β-position is
comparatively higher but can occur in small quantities over the course of a polymerization.

The last two mechanistic influences on structural considerations accompany end
group defects and residual metal defects, which are not defects in the same vein as
homocoupling or branching but because they can result from inconsistent termination
events and vary from condition to condition, can be classified as defects.
40
This is because
polymer end groups have been shown to play an important role in the resulting properties
of respective conjugated polymers.
64,128–131
They are also critical for the formation of block
copolymers and control of end groups would also enable strategies for anchoring and
surface modification. For Stille- and Suzuki-prepared polymers, often the end group
functionalities (organotin, organoboron, and halide) are end-capped to remove them and
generate more benign terminal groups, such as benzene or thiophene, which is
24
accomplished via a two-step process with a mono-substituted aryltin or arylboron and then
subsequently an arylbromide to end-cap any tin or borom termini.
For DArP, it is generally surmised that because it operates through C−H activation,
more convenient H/Br end groups are produced. Although bromide terminal groups do also
affect performance, conveniently only one end-capping treatment would be necessary.
While this is true sometimes, however, it has been observed by Sommer et al.
132–134
that
C−H activation of the solvent medium can also occur, resulting in chain termination by the
solvent, most commonly observed with aromatic solvents, which like toluene and
chlorobenzene are generally quite good at solubilizing extended conjugated polymer chains
and are often employed as solvents. Additionally, depending on the additives employed in
the polymerization, these may also appear as end groups due to nucleophilic substitution
or debromination events.
Lastly, residual metal residues are quite underexplored, which result from catalyst
degradation during the polymerization, which can be bound as complexes or physically
entrapped in the polymer chains. Often, many of these residual metals can be considered
impurities; however, because they cannot all be removed by purification methods such as
extraction, filtration, metal scavengers, and precipitations, they may also be treated as
defects resulting from the synthetic method. For example, Reynolds et al.
135
reported the
synthesis of propylenedioxythiophene (ProDOT) via DArP and quantified the residual
metal defects by ICP-MS. While chemical oxidative polymerization with FeCl3 generated
polymer with significant iron content in the polymers (1000+ ppm), utilizing GRIM
resulted in significant magnesium (1600+ ppm) and nickel (900+ ppm) content.
Interestingly, DArP resulted in less than 20 ppm for both palladium and phosphorus. Such
25
observations can be traced to the lower catalyst loadings sometimes needed for DArP
compared to traditional methods like Stille or Suzuki.
In the preceding section, an overview of the different types of defects, origins of
these defects, and important considerations for achieving well-defined polymers are
summarized for both traditional cross-couplings as well as direct arylation. From here, the
discussion of DArP conditions and the resulting impact on the polymer structure will be
critical analyzed and potential solutions to these issues—which affect all synthetic
methods—will be discussed.

1.2.3. Cataloging Conditions for Strategic Optimization of Direct Arylation
Polymerization

With an understanding of the mechanistic considerations for DArP and the
attributes toward achieving well-defined conjugated polymers, evaluation of the various
DArP conditions is more readily undertaken. Despite the rich history of small molecule
direct arylation, the application of this method to polymers is relatively young. The first
reported attempt was the preparation of poly(3-alkylthiophene) (P3AT) via 2-iodo-3-
alkylthiophenes by Lemaire et al.
136
Although only oligomeric products (~3 kDa) were
achieved, the next ten years would result in only two more published works regarding
DArP.
137,138
It was in 2010, however, that the field would find its recrudescence—first with
the work from Kumar et al.
139
which reported the copolymerization of 3,4-
propylenedioxythiophenes with various side chains, and then with the relatively
unrecognized work from Sun et al.
140
which explored a variety of phase transfer agents,
catalysts, solvents, and bases for regioregular P3HT oligomers. However, the most
26
successful and influential report in 2010 was from Ozawa et al.,
141
which has motivated
and continues to inspire intense research in DArP, resulting in numerous publications in
the years that followed.
40,44
Since then, DArP has progressively developed into a
convenient and powerful synthetic tool.
32,33,35,36,40,42,142

The distinct advantages of DArP have spurred intense research these past few years,
specifically its substrate compatibility with established conditions
55,143,144
and optimization
of the reaction parameters for the generation of higher quality polymers.
40,52,83,119,121,145–147

One of the consequences of this rapid growth is the emergence of a broad array of different
conditions that are challenging to classify or fully categorize. At its most elementary state,
DArP mandates the presence of a transition metal-based catalyst (typically a palladium
species) and a base that can assist in C-H bond activation and ultimately neutralizes the
stoichiometric amount of acid that is formed by this method. Beyond this, numerous
combinations of a vast array of catalysts, bases, acids, phase-transfer agents, solvents,
temperatures, reaction times, ligands, concentrations, auxiliary reagent loadings, and
heating methods (oil bath, microwave) have emerged.
An emphasis of the present section is the classification of these numerous variations
of reaction parameters and components, which will facilitate the ensuing conversation.
Subsequently, the evolution of conditions will be analyzed and discussed for a more
nuanced and thoughtful examination of what improves DArP. This—in and of itself—is
worth discussing as well. Many reports judge the quality of polymers by DArP purely by
the molecular weight and yields; however, increasingly, the importance of structural
regularity and the minimization of defects or residual impurities has witnessed increased
emphasis.
40,53,148
Where applicable, the identification of well-defined polymer structures
27
that eliminate cross-linking or branching defects, as well as minimize homocoupling events
and other defects, will be considered important parameters of success in addition to
attributes such as molecular weight and yield.

Figure 1.7. Classification of the DArP conditions for discussion in this review.

In general, DArP conditions can be classified into a few different categories. These
are summarized in Figure 1.7. Class A is derived from the works of Lemaire et al.,
136–138

Sun et al.,
140
Kumar et al.,
139
and early DArP conditions employed by Kanbara et al.
122

These conditions are typically run in coordinating polar solvents like N,N-
dimethylformamide (DMF), N,N-dimethylacetamide (DMA), or N-methylpyrrolidone
28
(NMP) with a base (e.g. potassium carbonate (K2CO3)) with the optional addition of a
phase transfer agent or phosphine ligand but are defined by the absence of a carboxylic
acid additive (e.g. pivalic acid (PivOH)) which, as highlighted in the previous section and
further discussed below, are characteristic of Fagnou-derived DArP conditions. Where
applicable, the most common phase transfer agent utilized is tetra-n-butylammonium
bromide (TBAB). Some representative examples of these conditions are provided in
Scheme 1.6. In general, these conditions are compatible with C−H activation of electron-
poor and electron-rich moieties but tend to achieve higher molecular weights with C−H
activation of electron-poor substrates, which is reasonable considering the theorized
concerted metalation deprotonation (CMD) pathway via carbonate or carboxylate additives
that direct arylation operates through as discussed above.
114
For example, as can be seen in
Scheme 1.6b, utilization of tetrafluorobenzene resulted in number-averaged molecular
weights (Mn) that exceeded 31 kDa while C−H activation of bithiophene in Scheme 1.6d
resulted in Mn values of around 9 kDa when copolymerized with a large bislactam-based
monomer. Conversely, C−H activation with electron-rich EDOT or ProDOT monomers
resulted in Mn values of 4.6 kDa.

29

Scheme 1.6. Some representative Class A conditions and substrates, as noted in Figure
1.7, which are characterized by a coordinating polar solvent and their lack of carboxylic
acid additive or their utilization of a phase transfer agent, which include (a) poly(3-
octylthiophene) via conditions reported by Lemaire, et al.,
136
(b) PDOF-TP via conditions
reported by Kanbara, et al.,
122
(c) ProDOT-based copolymers via conditions reported by
Kumar, et al.,
139
and (d) bislactam-based bisthiophene copolymer reported by Kim, et al.
149

The next two classifications of DArP (Class B and Class C in Figure 1.7) are
derived from the pioneering work of Fagnou, et al. in 2006,
150
which were adopted for the
synthesis of conjugated polymers with little modification. The signature feature of these
conditions is the presence of a carboxylic acid, such as pivalic acid (PivOH), which after
deprotonation via a base, serves as a carboxylate ligand and proton shuttle. Indeed, the
signature difference in the Fagnou-derived conditions (Class B) and those employed by
Lemaire, et al.
136–138
(Class A) is the addition of the carboxylic acid, which may explain
why Class A can only achieve oligomers of P3HT,
136,140
while Class B can achieve much
30
higher molecular weights.
118,119
These reactions are typically run in coordinating polar
solvents, most commonly DMA, but have also been run in other aromatic solvents. Class
B and Class C are differentiated by utilization of a phosphine ligand. Fagnou-derived
conditions that are phosphine-free are designated Class B while those that utilized a
phosphine ligand are designated Class C. Representative examples of Class B conditions
are provided in Scheme 1.7. These conditions are generally attractive due to the utilization
of inexpensive, bench-stable reagents that allow the reaction to be conducted at ambient
pressure. For instance, reactions are typically well below the boiling point of commonly
used solvent, DMA (BP = 165°C). One consideration, however, is that because conditions
typically require DMA, which is less successful at solubilizing large aliphatic side-chains,
this solvent may not be ideal for certain large side-chains. Regardless, without the need for
phosphine ligands, which can be expensive and have poor air or thermal stability, this
method may be more attractive for industrial-scale synthesis. In general, Class B conditions
have been broadly applicable across a wide swath of different substrates and polymers and
are arguably the most attractive for their simplicity. Nonetheless, the utilization of
phosphine ligands can sometimes improve the resulting polymer quality. Representative
examples of Fagnou-derived conditions that utilize a phosphine ligand (Class C) are
provided in Scheme 1.8.

31

Scheme 1.7. Some representative Class B conditions and substrates, as noted in Figure
1.7, which are characterized by their Fagnou-derived phosphine-free conditions with a
carboxylic acid additive, such as PivOH, which include (a) P3HT via conditions reported
by Thompson et al.,
118
(b) PCPDTBT via conditions reported by Horie et al.
151
in aromatic
solvents, (c) PEDOTF via conditions reported by Kanbara, et al.
146
with a bulky carboxylic
acid, 1-AdCO2H, and (d) PNDITF4T via conditions in mesitylene (among other aromatic
solvents) reported by Sommer, et al.
132

32
Scheme 1.8. Some representative Class C conditions and substrates, as noted in Figure
1.7, which are characterized as Fagnou-derived DArP conditions with both a carboxylic
acid and a phosphine ligand, which include (a) a dithienobenzotropone-based copolymer
synthesized by Swager et al.,
152
(b) a thienyl-flanked benzothiadiazole (BTD) and
diketopyrrolopyrrole (DPP) copolymer reported by Ling et al.,
153
and (c) a carbazole/BTD
copolymer, PCDTBT, reported by Sommer, et al.
53

The last two classifications of DArP (Class D and Class E) are derived from the
seminal work of Ozawa, et al.
141
These conditions utilize the Herrmann-Beller catalyst
(trans-di( μ-acetato)bis[o-(di-o-tolyl-phosphino)benzyl]dipalladium(II)) with a phosphine
ligand and cesium carbonate (Cs2CO3) in superheated THF. These conditions are often
identified by the utilization of P(o-OMePh)3 and/or P(o-NMe2Ph)3 as the phosphine ligands
(though others have been used) most commonly with the Herrmann-Beller catalyst,
tris(dibenzylideneacetone)dipalladium(0) (Pd2dba3) (or its chloroform adduct,
Pd2dba3‧CHCl3) or bis(acetonitrile)dichloropalladium(II) (PdCl2(MeCN)2). Another
characteristic is the utilization of superheated THF or toluene (either superheated or very
near the boiling point). The utilization of superheated THF is particularly disadvantageous,
as for small-scale polymer batch synthesis, reproducibility can be challenging to achieve
due to solvent evaporation, high concentrations, and choosing the optimal high pressure
vessel size for minimizing vapor head space. Additionally, these reactions are often
prepared in a glove box prior to being removed, which may provide better molecular
weights and yields than attempts to prepare high pressure reactions on the benchtop,
especially considering the air-sensitive nature of the catalyst and ligands. In a stark contrast
to Fagnou-derived Class B and Class C reactions, the utilization of polar coordinating
33
solvents such as DMF or DMA generally do not work well with Ozawa-derived
conditions.
154,155
Additionally, these conditions sometimes do not utilize a carboxylic acid,
as was the case for Ozawa’s original DArP work, which will be referred to as Class D. The
presence of both a phosphine ligand and a carboxylic acid via Ozawa-derived conditions
will be referred herein as Class E conditions. Representative examples of Class D
conditions are provided in Scheme 1.9. Due to the utilization of superheated THF and air-
sensitive phosphine ligands, these DArP conditions are typically executed in a microwave
vial or another high-pressure flask, which is often prepared in a glovebox. Representative
examples of Class E conditions, which utilized a carboxylic acid, are provided in Scheme
1.10.

Scheme 1.9. Some representative Class D conditions, as noted in Figure 1.7, which are
characterized as Ozawa-derived DArP conditions with a phosphine ligand and the absence
of a carboxylic acid additive, which include (a) the original conditions employed by Ozawa
et al.
141
for P3HT, (b) modified conditions toward isoindigo and thienopyrroledione (TPD)
utilized by Leclerc et al.
156
, and (c) conditions toward PEDOT derivatives reported by
Hsiao et al.
157

34

Scheme 1.10. Some representative Class E conditions, as noted in Figure 1.7, which are
characterized as Ozawa-derived DArP conditions with a phosphine ligand and a carboxylic
acid additive, which include (a) conditions toward P3HT executed by Coughlin et al.
50
, (b)
conditions toward polythiophene derivatives developed by Leclerc et al.,
121
and (c)
conditions toward dithienosilole and TPD alternating copolymers developed by Ozawa et
al.
52,158

Although some reports explore conditions that may deviate from these broad
classifications, the overwhelming majority of DArP conditions can be described by these
few classes. The fundamental advantage of such a categorization rests in the observation
that not all conditions are broadly applicable to all substrates. Indeed, successful polymers
have been generated from each classification of conditions while at the same time, each
classification of conditions has also failed to produce polymers of adequate quality as well.
For example, Swager et al.
152
reported a dithienobenzotropone-based copolymer (Scheme
1.8a) that was challenging to brominate or iodinate in the alpha position for Stille-
compatible monomers. At first, they adopted Ozawa-derived Class D conditions but these
35
were unsuccessful for generating suitable polymers. Switching to Fagnou-derived Class C
conditions enabled better copolymers. The reasons for selecting a set of conditions can be
both broad and nuanced, which may include substrate reactivity, functional groups or their
assignment, and/or choice of catalytic system for the substrate but can also include
experimental parameters, such as concentration, solvent choice, preparation in a glovebox
or on the bench, and/or temperature.

1.2.4. Mechanistic Control of Homocoupling, β-Linkages, and End Groups in
Polythiophenes: Case Studies for the Optimization of DArP

Much of our understanding of the DArP mechanism and the quality of the resulting
polymers has come through experiments toward P3HT, the ubiquitous conjugated
homopolymer that enables facile quantification of regioregularity as well as β-coupling.
Indeed, as can be seen in the preceding section, a variety of conditions have been utilized
to synthesize P3HT via DArP (Classes A (Scheme 1.6a), B (Scheme 1.7a), D ( Scheme
1.9a), and E (Scheme 1.10a)). Few other polymers have been evaluated by such a variety
of DArP classifications, where numerous reaction parameters have been evaluated and
their influence analyzed with incredible detail. These reports, from a variety of groups, will
form the bases of this section, which utilizes a case-by-case evaluation of a variety of DArP
methods toward P3HT to evaluate how these resulting polymers may vary from condition
to condition. Of course—adopting these conditions to more complex systems will
inevitably introduce additional considerations but the evaluation of P3HT, which is perhaps
the most convenient conjugated polymer to analyze from a structural evaluation
perspective is invaluable.
36
In 1990, Ohta et al.
159
utilized tetrakis(triphenylphosphine)palladium(0)
(Pd(PPh3)4 with 1.5 equiv. of potassium acetate in DMA at 150°C in a sealed tube to
achieve cross-coupling of thiophene (BP = 84°C) with bromobenzene in what may be the
earliest reported direct arylation reaction of the thiophene heterocycle. However, the
mechanism of this reaction was not fully understood at the time but was classified as a
palladium-catalyzed regioselective cross-coupling in the same vein as the Heck coupling.
Eight years later, Lemaire et al.
111
adopted the conditions utilized by Jeffery
160
for Heck-
type cross-coupling of thiophene derivatives with iodobenzene using Pd(OAc)2, K2CO3,
DMF, and a phase transfer agent, tetra-n-butylammonium bromide (n-Bu4NBr or TBAB).
These conditions would then subsequently form the basis for their seminal work toward
the polymerization of alkylthiophenes (Scheme 1.6a).
136
These polymers only achieved
modest molecular weights. About ten years later, Sun et al.,
140
who also operated under the
assumption of a Heck-type mechanism, generated similar results by using a DMF/THF
solvent mixture, Pd(OAc)2, K2CO3, and TBAB, though they also explored a variety of
reaction parameters that were less successful. Together, these two reports demonstrate that
Class A conditions are compatible but not optimal for generating high molecular weight
P3HT homopolymers, though importantly, the selectivity for these types of reactions is still
quite high.
The reason for this can most likely be attributed to the lack of carboxylic acid
additive that was later observed by Fagnou et al.
150
(and discussed above) to be critically
important for promoting the CMD pathway for a lower transition state energy via proton
shuttling. Thompson et al.
118
reported the first application of Fagnou-derived Class B
conditions toward the synthesis of rr-P3HT (Scheme 1.7a). Indeed, the utilization of
37
PivOH enabled higher molecular weight polymers, surpassing 15 kDA but with a
regioregularity of 88%, which was lower than that of a Stille reference. Furthermore, they
observed fundamental differences in optoelectronic properties and structural characteristics
between the DArP and Stille polymers that was attributed to unselective C−H activation of
the 4-position that may result in branching of the polymer (Figure 1.8).

Figure 1.8. Branching defects that may occur in addition to head-to-head homocoupling
as identified by Thompson et al.
118,119
for rr-P3HT via DArP.
In a series of subsequent reports, Thompson et al.,
119,120,161–163
optimized their DArP
conditions with an emphasis on preserving the attractiveness and simplicity of the Fagnou-
derived conditions compared to the Ozawa-derived conditions. Specifically, they
attempted to preserve a phosphine-free catalytic system with relatively air-stable Pd(OAc)2
at reaction temperatures well-below the boiling point of the solvent (DMA, BP = 165°). At
the same time, they critically analyzed the reaction parameters, developing a thorough
causal relationship between parameters and resulting polymer properties. These
38
developments, as well as others for Class B conditions, are summarized below, which
include optimization en route to the ideal Class B conditions for rr-P3HT.
The first optimization of the reaction parameters was facile control over the reaction
temperature, catalyst loading, and reaction time. From the benchmark 88% regioregularity
with Mn of 22 kDa observed with 2% catalyst loading at 95°C, the authors observed the
regioregularity to increase from 83% to 89% by decreasing the temperature from 120°C to
20°C. The room-temperature polymerization had an Mn of 14 kDa but a low yield (9%).
Nonetheless, this is the lowest reported temperature ever to achieve suitably high molecular
weight polymers via DArP. Consequently, the authors observed that regioregularity
improved with decreasing catalyst loading. Through a compromise between reaction
temperature (70°C) and catalyst loading (0.25 mol %), the authors achieved an Mn of 16
kDa with 50% yield and a regioregularity of 93.5%. They then observed that substituting
pivalic acid (PivOH) with neodecanoic acid (NDA) improved the yields slightly and the
molecular weight to 20 kDa while preserving the regioregularity (Figure 1.9a). These
DArP conditions were ultimately highly attractive because they tuned the reaction
parameters instead of the catalytic system, preserving the simplicity and elegance of the
Fagnou conditions. Ultimately, the most critical variable however was the substitution of
PivOH with NDA (Figure 1.9b), which improved both physical and optoelectronic
properties.

39

Figure 1.9. (a) Reaction conditions toward P3HT without β-defects and regioregularity
and properties that converge with Stille P3HT, (b) Comparison of pivalic acid with
neodecanoic acid, and (c) Cartoon mechanism illustrating bulky carboxylate ligands
preventing activation of the β-positions due to steric bulk while being not inhibiting α-
coupling.
The utilization of a bulky carboxylic acid has proven to be critical for the
development of DArP for high performance materials. As reported by Thompson et
al.,
119,120
NDA is capable of completely suppressing β-couplings that traditional PivOH
could not (Figure 1.9c). As discussed above in Section 2.2, the low transition state energy
40
of the CMD pathway can lead to unselective C−H coupling and undesirable branching
defects, which can be removed by purification for small molecules but are embedded in
polymers. These branching defects were quantified by Thompson et al.
120
using
1
H NMR.
Using similar conditions, the authors evaluated the differences between NDA and PivOH
on the resulting polymer structures. Conditions with PivOH resulted in 0.16% β-defect
concentration (BDC) which was shown to negatively influence the solar cell
performance, crystallinity, and intensity of the vibronic shoulder in UV-Vis
absorption profiles. It is worth noting that identifying these defects would be even
more challenging with complex polymer structures. The utilization of a bulky
carboxylic acid has been a significant improvement to DArP conditions. Recently, Livi et
al.
83
and Marks et al.
51
determined a bulky carboxylic acid was necessary for Stille-
convergent polymer solar cell performance via DArP. These improvements toward
practical applications will be discussed in more detail in Section 4.
The potential for these types of β-defects with double unprotected β-positions was
later confirmed by Leclerc et al.
121
for Class E conditions. Utilizing a model system,
poly(3,3‴-didodecyl-2,2′:5′,2″:5″,2‴-quaterthiophene) (PQT12), the authors explored a
variety of reaction conditions and evaluated potential β-defects from two different
monomers that would generate PQT12. The quantification of these minute defects via
NMR was challenging, so the authors utilized UV-Vis and DSC measurements to indirectly
identify these defects. They observed NDA was necessary for the well-defined synthesis
of PQT12 from a β-unprotected monomer (Scheme 1.11), thus highlighting the broad
necessity for bulky carboxylic acids for both Fagnou-derived and Ozawa-derived
conditions.
41

Scheme 1.11. Synthesis of PQT12 via double β-unprotected thienyl-flanked monomer
evaluated by Leclerc et al.
121
The authors observed the formation of β-defects without the
utilization of the bulky carboxylic acid, neodecanoic acid (NDA).
Unfortunately, because such a small quantity of β-defects can alter performance,
the identification of these defects is of utmost importance; however, most reports in the
literature provide inadequate information regarding these defects. In Figure 1.10, a section
of a P3HT
1
H NMR spectrum between 2 and 3 ppm, where regioregularity can be
calculated through quantification of the head-to-tail couplings (2.80 ppm) and the head-to-
head couplings (2.58 ppm) is provided for an example of P3HT with 0.75% BDC. As
identified by Luscombe et al.
123
branching defects result in a broad peak between 2.2 and
2.4 ppm. As can be seen from the spectrum provided in Figure 1.10, defects are not clearly
visible between 2.2 and 2.4 on a traditionally provided NMR spectrum. In fact, this image
may appear larger than most spectra provided in the literature. It is only upon considerable
magnification of the region (provided in the inset), that the branching defects become
visible. Furthermore, if the aliphatic peaks are integrated to 2 protons, the value of this
branching peak would appear negligible with NMR software like MestReNova. For an
accurate measurement of BDC, the HT and HH regions should be integrated to a value of
100, where a branching peak region may then be quantified. In this case, this peak size
correlates to a BDC of 0.75%. Conveniently, the quantification of branching defects is
42
possible with P3HT; however, it becomes incredibly challenging with other more
complicated polymer systems because there are often many small, broad peaks that may
be unaccounted for, especially if the peak positions are in the aromatic region with other
peaks and chlorinated solvents or in the aliphatic region with alkyl chains and residual
solvents. Importantly, it is suggested that increased care be given to the proton NMR region
near 2.33 ppm for rr-P3HT prior before discounting the presence of potential β-defects.

Figure 1.10. Fragments of the
1
H NMR spectra of a DArP P3HT polymer exhibiting 0.75%
β-defect concentration. Observing the broad peaks for identifying small quantities of
branching content require significant magnification to be visible, which is not always
provided in the literature.
Although β-branching has been shown to be unfavorable for OPV
performance,
120,164–166
it is important to note that the general negativity surrounding the
term is not always warranted. There are many instances in which branched polymers may
43
be quite attractive. Nonlinear conjugated polymers may possess unique physical and
optoelectronic properties that make them particularly attractive for light-emitting devices
or nonlinear optical applications.
167–169
Toward that end, Luscombe et al.,
123
realized that
DArP could be advantageous for generating branched polymers compared to traditional
methods like Stille, reported Class A conditions toward increasing the branching content
of P3HT instead of suppressing it (Figure 1.11). Depending on the degree of branching, a
mixture of typical cross-couplings, bent (cross-coupling + β-coupling), and dendritic (two
cross-couplings + β-coupling) would occur. For linear polymers, the percentage of bent
units would be zero, while for hyperbranching, each thiophene would become a dendritic
unit. Utilizing a model system, the authors identified the branching peaks via NMR analysis
to quantify the degree of branching. They achieved a range of polymers with varying
branching content related to the phosphine ligand or catalyst, from 0% to 40%, with the
highest degrees of branching actually occurring with PdCl2 and no ligand. Utilizing
TMEDA or bidente ligand, 2,2’-bipypidyl, suppressed branching defects but, consistent
with Class A conditions, did not achieve high molecular weights. Thus, with catalyst
optimization, DArP may ultimately be compatible with unique targets and polymer
architectures.

44

Figure 1.11. Example of a branched P3HT polymer possessing both bent units and
dendritic units.
Although branching polymers are not well-explored in DArP, the capacity for high
β-selectivity has been reported. Itami et al.
170
reported a catalytic system with PdCl2,
P(OCH(CF3)2)3, Ag 2CO3, in m-xylene that can provided up to 99% β-selectivity for certain
functionalized thiophene substrates and even 88% selectivity for simple unfunctionalized
thiophene. Such strategies could be adopted to generate polymers with high branching
content, as several catalytic systems have demonstrated high β-selectivity.
171,172
Although
only briefly mentioned herein, the general explanation for this observation is the ability for
the P(OCH(CF3)2)3 phosphine ligand to promote a Heck-like reaction by elevating the
energy barrier of the CMD transition state through hydrogen bonding of the ligand with
the carbonate base.
173,174

Toward further optimization of the DArP conditions for linear P3HT, Thompson et
al.
163
reported the minimization of auxiliary reagent loadings on the synthesis of P3HT,
which includes reducing the loadings of all reagents, except the base (K2CO3), including
the catalyst, NDA, and the DMA solvent (resulting in higher concentrations). Through a
45
combination of minimizing the catalyst loading from the already low 0.25 mol % to an
ultra-low loading of 0.0313 mol %, decreasing the NDA loading from 30 to 3.75 mol %,
and increasing the concentration in DMA from 0.04 to 0.32 M along with a reaction
temperature increase to 160°C, which is still below the boiling point of DMA, the authors
were able to achieve molecular weights (24+ kDa), yields (>90%), and regioregularity
(96.5 %) that were superior not only to the previously evaluated DArP P3HT polymers but
also Stille reference polymers (Scheme 1.12). This is the highest regioregularity achieved
via phosphine-free DArP for high molecular P3HT to date. It rivals results achieved by
Ozawa et al.
141
with a more complicated catalytic system and with neodecanoic acid as a
carboxylate ligand, the authors observe a successful polymerization, whereas Ozawa
observed decomposition of the Pd(OAc)2 pre-catalyst at high temperatures without a
carboxylic acid, which forced them to utilize the Herrmann-Beller catalyst for temperature
stability. Additionally, the authors observed via MALDI-TOF and
1
H NMR that extensive
debromination occurs, though this did not affect the resulting molecular weights, which
suggests that debromination typically occurs after the polymer chains have stopped
growing. Importantly, the observation of fewer H/Br end groups for increased H/H end
groups is particularly beneficial when considering polymers for optoelectronic properties,
where end groups can negatively influence charge transport as discussed above,
64
further
highlighting the superiority of this method to Stille.

Scheme 1.12. Ultra-low loading phosphine-free DArP conditions (Class B) reported by
Thompson et al.
163

46
It is worth noting that P3HT is widely considered the most cost effective polymer
for its efficiency in OPVs
78,175
despite historically requiring organometallic functional
groups for its generation. While DArP is more sustainable and affordable overall, these
specific conditions are perhaps the most cost effective and attractive route toward rr-P3HT,
utilizing a mere 313 ppm of precious non-renewable palladium catalyst, are completely tin-
and phosphine-free, operate at high concentrations below the boiling point of the solvent,
and even use low quantities of NDA, which is already an affordable and industrially-
relevant material. As such, these conditions particularly embody the principles that
underscore DArP as a simple, inexpensive, and environmentally-friendly protocol toward
conjugated polymers.
As discussed above, the carboxylic acid is the signature feature of Fagnou-derived
Class B and C co nditions while the utilization of DMA as a solvent is thought to play a
critical role as a ligand or coordinating moiety in direct arylation. In two reports, Thompson
et al.
161,162
further evaluated the role of these important components. In the first, a
comprehensive library of 24 carboxylic acids was investigated, several for the first time,
which included linear, secondary, tertiary, secondary cyclic, tertiary cyclic, and secondary
bicyclic acids (Figure 1.12, Left). In the second report, amide solvents with alkyl
substituents on either the carbonyl group or the nitrogen atom were investigated (Figure
1.12, Right). In both reports, the optimized ultra-low loading reaction parameters were
utilized and only the acid additives or amide solvents were modified.

47

Figure 1.12. Carboxylic acids additives (Left) and amide solvents (Right) investigated by
Thompson et al.
161,162
to evaluate their influence on the properties of DArP P3HT.
Consistent with the previous observations with PivOH,
120
a bulky carboxylic acid
is often necessary for suppressing branching defects and improving molecular weight in
Class B DArP conditions. Linear, secondary, and even some tertiary aliphatic carboxylic
acids bulkier than PivOH (neoheptanoic and neoctanoic acid) do not prevent β-defects in
P3HT via optimized DArP conditions. The two most successful acids were neodecanoic
acid and neotridecanoic acid, both of which are neo-acids consisting of mixtures of isomers
but are overall more bulky than other carboxylic acids. Furthermore, they observed that
acid pKa values did not offer predictive power for determining effective carboxylic acid
additives, with no clear correlation between pKa and molecular weight, yield, or mass
dispersity; however, there was a correlation between increase in the number of carbon
atoms and the reactivity and selectivity of respective DArP catalytic systems. Specifically,
for linear, secondary, and tertiary acids, there was an increase in yield and molecular weight
with increasing carbon atoms for the acids. Nonetheless, of all the acids investigated it was
48
confirmed that NDA as an additive offered the best combination of high molecular weight,
yield, commercial availability, and well-defined chemical structure.
Subsequently, they evaluated several amide solvents (Figure 1.12), observing that
commercial (wet) amide solvents do not perform well, requiring dry solvents for the
generation of high molecular weight P3HT. Here, they observed that although DMA does
perform well (23.6 kDa), utilizing N,N-dimethylpropionamide or N,N-diethylacetamide
increased the molecular weights to 31.5 kDa and 32.5 kDA respectively. All other amide
solvents were less effective, generating lower regioregularities and molecular weights.
They concluded that solvent structure must be delicately balanced to promote high
reactivity but not inhibit association of the palladium and arene or ligation of palladium,
which may occur with more bulky amide solvents. This is consistent with some analogous
observations by Hartwig, et al.,
127
who observed that calculated CMD energy barriers were
much higher for palladium with P(
t
Bu)3 than when ligated by DMA solvent (under
phosphine-free conditions), due to the increased steric hindrance of the phosphine ligand.
They further observed that utilized an aromatic amide, such as N,N,-dimethylbenzamide
leads to incorporation of the aromatic amide in the polymer structure, highlighting a
potential C−H activation of the solvent. Furthermore, they observed that for the high
molecular weight polymers, complete removal of Br end groups was observed.
Additionally, although DMF, DMA, and NMP have all been utilized for Class A, B, and C
conditions, for the polymerization of P3HT, it was observed that DMF has suboptimal
performance while NMP does not work at all as a solvent. These experiments detail the
critical design principles that are necessary for DArP and highlight the need for further
fundamental exploration of DArP conditions.
49
To further improve the attractiveness of the DArP protocol, Kanbara et al.
176

reported the sequential bromination and DArP of rr-P3HT using slightly modified
phosphine-free conditions. Expanding on a previous study with one-pot reactions toward
alternating copolymers,
177
Kanbara and colleagues reported other alternating polymers in
addition to P3HT. Considering all the advantages that DArP can offer, providing one pot
access to rr-P3HT from 3-hexylthiophene would be quite convenient, especially for
industrial scale synthesis. As shown in Scheme 1.13, the authors utilized tetra-n-
butylammonium tribromide (TBA Br3) as a brominating reagent, which they observed to
generate less dibrominated product than benzyltrimethylammonium tribromide (BTMA
Br3). They observed that the presence of TBAB completely shut down the polymerization
in both Ozawa-derived Class D conditions and Fagnou-derived Class C conditions with
DMA. However, by switching the solvent from DMA to THF, TBAB was found to not
negatively influence the subsequent polymerization. Thus, the bromination was executed
with dichloromethane, which was subsequently evaporated before pivalic acid, potassium
carbonate, and THF were added prior to the addition of 0.10 mol % of Pd(OAc)2 in THF.
The polymerization was executed at 60°C for 96h. They achieved P3HT with 88% yield
with an Mn of 20 kDa and a regioregularity of 93%, which was slightly lower than
optimized DArP conditions, which they attributed to small amounts of 2,5-dibromo-3-
hexylthiophene. Interestingly, they observed no branching defects for their DArP P3HT,
which might be the result of utilizing THF as a solvent instead of DMA, which may lower
the reactivity of that position, or perhaps the lower reaction temperature. It is also uncertain
if that region was integrated or magnified to the extant suggested above.

50

Scheme 1.13. Sequential bromination of 3-hexylthiophene and DArP in one-pot with only
evaporation of the DCM solvent in between reactions as explored by Kanbara et al.
Given the success in developing phosphine-free Class B DArP conditions with
minimal auxiliary reagents, the exploration of Class C conditions toward rr-P3HT are
relatively unexplored. Koizumi, et al.
178
utilized heterogeneous catalysts for the synthesis
of rr-P3HT via DArP. They utilized Fagnou-derived Class B conditions (PivOH) or Class
C conditions (PivOH/PCy 3HBF4) with with Pd(OAc)2, Pd/C, or Pearlman’s catalyst,
Pd(OH)2/C in either DMA or NMP (Pd/C did not work in non-coordinating solvents,
toluene or THF). Consistent with observations by Fagnou, et al.,
179
the authors observed
that Pd(OH)2/C may terminate the polymerization prematurely via dehalogenation.
Interestingly, when utilizing Class C conditions they only generated insoluble and
branched material, suggesting that a phosphine ligand may promote unselective couplings.
Overall, the best results were achieved when they utilized Fagnou-derived Class B
conditions (PivOH) with Pd(OH)2/C in NMP at 1 00°C, which resulted in Mn values of 18.9
kDa, a regioregularity of 96%, and a yield of 99%. Increasing the temperature to 120°C
increased the molecular weight but lowered both the yield and regioregularity, presumably
due to defects. Decreasing the reaction time lowered the Mn to 18.4, but increased the
regioregularity to 97% with similar yields of 99%. Generally, yields and molecular weight
51
were improved with Pd(OH)2/C compared to Pd/C, and with NMP compared to DMA. This
catalytic system is particularly attractive because heterogenous catalysts
180
have been
shown to reduce the amount of residual palladium in the polymer, which can improve
charge transport.
181

For catalyst employment, N-heterocyclic carbenes (NHCs) have enjoyed increased
popularity as superior performers to traditional tertiary phosphanes. They have strong
electron donating ability for more facile oxidative insertion and the strong Pd−NHC bond
enables high stability even at low ligand/Pd ratios and high temperatures. Recently, 1,3-
bis(2,6-diisopropylphenyl)imidazol-2-ylidene](3-chloropyridyl)palladium(II) dichloride
(Pd-PEPPSI-iPr) was utilized for the chain-growth polymerization of P3HT via catalyst-
transfer Stille, observing a linear relationship between Mn and monomer conversion.
182

Cheng at al. explored the synthesis of P3HT via DArP utilizing a modified catalyst, Pd-iPr,
([1,3-bis(2,6-diisopropylphenyl)imidazol-2-ylidene]chloro[3-phenylallyl]palladium(II)).
At 140°C for 48h with pivalic acid, the authors achieved 57% yield after Soxhlet extraction
and a regioregularity of 94%. While the compatibility of Pd-NHC catalysts was confirmed,
the development and exploration of living behavior with DArP was not undertaken.
Although Class B conditions almost always utilize Pd(OAc)2, which is fairly air stable and
and one of the more affordable palladium precatalysts, the exploration of other catalysts,
especially heterogeneous, affordable, and highly stable ones, is desirable.
It is worth noting that for DArP, the precatalyst is often the air-stable Pd(OAc)2,
which is a Pd(II) species that, in the absence of a phosphine ligand, is thought to undergo
a homocoupling reaction in order to generate the active Pd(0) species.
183
Kanbara et al.
184

evaluated this on a model small molecule quarterthiophene system, generating C−H/C−H
52
homocoupling with Pd(OAc)2 that also resulted in the precipitation of palladium black.
This proposed reaction mechanism is provided in Scheme 1.14.

Scheme 1.14. Palladium reduction from Pd(II) to Pd(0) via C−H/C−H homocoupling of
bithiophene under phosphine-free conditions.
The observation by Thompson et al.
163
that lower catalyst loadings can improve the
regioregularity may be correlated to the reduction of this homocoupling event to generate
53
the active palladium species, which suggests that one route toward minimizing
homocoupling is the minimization of catalyst loading. This, coupled with a bulky
neodecanoic acid, which can prevent β-defects leads to polymers that are well-defined and
of higher molecular weight. Additionally, the utilization of strategic amide solvents can
result in the generation of only benign H/H end groups via Class B conditions. Finally,
with ultra-low loadings of the auxiliary reagents, these conditions are incredibly cost
effective and inherently have low residual metal content. Although it is possible that the
addition of phosphine ligands may further improve these conditions (toward Class C
conditions), the attractiveness of these elegantly simple conditions toward P3HT that is
superior to Stille counterparts in all facets should not be underappreciated.
The discussion thus far as entailed the development of the small molecule direct
arylation conditions for thiophenes first proposed by Ohta et al.
159
and Lemaire et al.
111
that
were subsequently improved by Fagnou et al.
49,150
prior to being applied and subsequently
refined by Thompson et al.
118–120,161–163
for the generation of rr-P3HT. It has also been
strategically employed for hyperbranched P3HT by Luscombe et al.
35
and various other
modifications of Class B conditions have been explored; however, the emergence of this
field and the first highly successful rr-P3HT synthesis via DArP is credited to the seminal
work of Ozawa et al.,
141
whose conditions are quite distinct from those reported by
Thompson et al.
163
These conditions, outlined above as Class D conditions, utilize
superheated THF with the Herrmann-Beller catalyst for high temperature stability with a
phopshine ligand and Cs2CO3 (Scheme 1.9a). When utilizing P(o-NMe2Ph)3 as the ligand,
Mn values greater than 30 kDa were achieved along with regioregularity exceeding 98%,
which is comparable to GRIM and better than typical Rieke or Stille P3HT. It is worth
54
highlighting that the authors observed an increase in regioregularity from 96% to 98% via
a decrease in catalyst loading from 2 to 1%, a similar trend which was also observed by
Thompson et al.
119
for phopshine-free Fagnou conditions, which suggests that in general,
homocoupling can be decreased by minimizing the catalyst loading, consistent with
reducing the opportunity for disproportionation. Another successful ligand was P(o-
OMePh)3, which also provided Mn values greater than 30 kDa but with a regioregularity of
93%, which is similar to that observed in Stille and Class D conditions.
119,120
In both cases,
yields after polymerization were 99%.
Most critically, however, they demonstrated that the choice of phosphine ligand is
vital to the performance of Class D and Class E conditions. Employment of a phosphine
with coordinating ability increases the regioregularity from 63% (for P(t-Bu)3) to 93%
(P(o-OMePh)3), with a 30-fold increase in molecular weight when all other parameters are
the same; however, the nature of the connectivity is also critical. While P(o-OMePh)3
generates a regioregularity of 93%, P(p-OMePh)3 only generates a regioregularity of 68%
as well as a much lower molecular weight. With regards to potential branching, the
presence of β-defects was not investigated until a subsequent work from Leclerc et al.
185

confirmed the absence of any branching defects and determining from detailed dyad
analysis that these conditions generate regioregularities exceeding 99.5% along with 0.5%
TT homocouplings. Furthermore, the authors observed dehalogenation as the primary
termination step. Further highlighting the advantages of DArP, the authors achieved highly
regioregular P3HT via two regioisomers, 2-bromo-3-hexylthiophene and 2-bromo-4-
hexylthiophene. Alhough the synthesis of 2-bromo-4-hexylthiophene required additional
55
steps and provided lower molecular weights, the high regioregularity demonstrated high
selectivity of the C−H bonds for either isomer.
Attempts to replicate these conditions and explore other ligands and parameters was
executed by Ma et al.
186
With the P(o-OMePh)3 ligand, which provided Ozawa et al. with
Mn of 30 kDa, 93% regioregularity, and 99% yield, the authors observed higher molecular
weights (37 kDa), but lower regioregularity and yields, 86% and 78%, respectively. The
authors attribute the decrease in regioregularity to poorer quality reagents. It is also
possible this difference could be attributed to the commercial source of the 2-bromo-3-
hexylthiophene they purchased, which may possess the regioisomer 2-bromo-4-
hexylthiophene, which may decrease the regioregularity because of selective couplings
with an isomeric monomer. Both the molecular weight increase and the yield decrease can
be attributed to the Soxhlet extraction with methanol and hexanes executed by Ma and
coworkers, which was only precipitated and centrifuged by Ozawa and coworkers. In
attempting other reagents, the authors generally observed that the optimal reagents were
Cs2CO3 (compared to potassium acetate (KOAc), potassium pivalate (KOPiv), cesium
fluoride (CsF), or potassium carbonate (K2CO3) and THF (compared to toluene, o-xylene,
or dioxane). They also observed that P(o-OMePh)3 was superior to bidente phosphine
ligands such as 1,2-bis(diphenylphosphino) ethane (dppe) and 1,1'-
Bis(diphenylphosphino)ferrocene (dppf), which confirms the reagent choices by Ozawa et
al.
141
but also again highlights the importance of the ligand choice for Class D and E
conditions.
Considering the lack of polar coordinating solvents for the Class D conditions,
Ozawa et al.
113
investigated the direct arylation mechanism on a small molecule system
56
with phosphine ligands. They observed that the catalyst can form dimeric or tetrameric
complexes but that ultimately it was increased steric bulk of the aryl substituents on the
palladium center that promoted the formation of the active species while utilizing pivalate
ligand reduces the reactivity compared to the acetate ligand (Figure 1.13a), with
triphenylphosphine as the ligand. In a follow-up report, Ozawa et al. evaluated the nature
of the phosphine ligand on direct arylation, observing that electron-poor phosphine ligands
promote direct arylation of electron-rich thiophenes while electron-rich phosphine ligands
promote direct arylation of electron-poor benzothiazole (Figure 1.13b). As mentioned
above, both Hartwig et al.
127
and Thompson et al.
162
observed that increased steric bulk of
the phosphine or steric bulk of the DMA solvent, respectively, effectively shuts down the
reaction through elevated CMD energy barriers. Together these reports suggest that
depending on the substrate and catalyst, the reactivity in DArP can vary significantly but
steric influences must be accounted for when optimizing the catalyst reactivity in addition
to electronic considerations.

Figure 1.13. (a) Equilibrium between an inactive palladium species, which consists of a
polymeric catalyst and a monomeric active catalyst as observed by Ozawa et al..
113
The
57
bulky aryl substituent (2,6-dimethylphenyl) the less bulky acetate (Me) provided the most
increase in reactivity and (b) generation of the dimeric but inactive palladium species and
the subsequent equilibrium between it and the monomeric active catalyst with the P(o-
OMePh)3 ligand utilized in Ozawa-derived DArP conditions.
187
Here they observed that a
bulky aryl substituent, less bulky acetate, and an electron-poor phosphine ligand provided
the highest reactivity for electron-rich thiophenes.
Expanding on their work for high quality rr-P3HT, Ozawa et al.
188
reported the
initiation of P3HT chains with a variety of aryl functionalities to control end groups from
an aryl palladium complex initiator, which is an analogous strategy to the widely reported
initiation of Kumada Catalyst Transfer Polymerization (KTCP); however, the authors
make clear distinctions between these two methods. The most obvious is that DArP may
not operate via a living polymerization, so once the chain is initiated, the palladium is
capable of detaching from the original chain to initiate another chain. The authors
generated an aryl palladium complex initiator prior to polymerizing P3HT, starting with
phenyl-based complex and then exploring other aryl groups (Scheme 1.15). They observed
initial end-capping percentage of 75% for their initiated P3HT which increased to 91-95%
with the addition of the end-capping reagent, phenylbromide (PhBr), though the molecular
weight suffered. End-capping ratios between 86 and 98% could be achieved with different
aryl groups, with para-substituted −NMe2 functionalized phenyl achieving 98% end
capping, with a regioregularity of 99% and Mn values greater than 11 kDa. Importantly,
the authors observed that smaller chains combine into larger chains toward the end of the
reaction, increasing both the molecular weight and the end-capping ratio, which is one of
the first reports to provide evidence for a step-growth polymerization mechanism.
58

Scheme 1.15. End-capping P3HT chains through utilization of an aryl palladium complex
initiator as reported by Ozawa et al.
188

With regards to end groups resulting from termination events, the influence of
solvent and chain termination was explored by Sommer et al. for Poly(3-(2,5-
dioctylphenyl)thiophene) (PDOPT), who observed that C−H activation of chlorinated
solvents (chlorobenzene, o-dichlorobenzene, and 1,2,4-trichlorobenzene) can occur,
resulting in chain termination by solvent moieties despite the higher reactivity of the
polymerization in chlorinated solvents (Scheme 1.16). This was not observed with non-
chlorinated methylated solvents, such as toluene, p-xylene, or mesitylene, which did not
undergo C−H to terminate chains. It is worth noting that they observed chain termination
to occur more frequently with lower monomer concentrations (0.05M) for Class E
conditions, leading only to oligomers, highlighting the importance of higher concentrations
for Class D and E DArP conditions, whereas Class B and Class C conditions are more
tolerant of lower monomer concentrations. The authors also attempted a bulk
59
polymerization under vacuum, achieving suitably high molecular weights (~9 kDa) despite
increased viscosity and the absence of solvent. Additionally, the authors observed for such
bulky side-chain containing polythiophenes via Class E conditions, internal tail-to-tail (TT)
defects occur, which are quite detrimental for chain ordering in these types of polymers,
whereas Kumada catalyst transfer polycondensation (KTCP) mostly exhibits terminal TT
units, which are less detrimental.

Scheme 1.16. (a) Synthesis of PDOPT via DArP as reported by Sommer et al. and (b) the
resulting end groups observed by various solvents, including 1,2,4-trimethylbenzene, o-
dichlorobenzene, chlorobenzene, mesitylene, p-xylene, and toluene with various phenyl-
based end groups with degrees of chlorination.
While P3HT is the quintessential reference conjugated polymer and is perhaps the
most studied polythiophene and can provide truly fundamental evaluations of the
mechanistic and structural considerations of the DArP methodology, increasing complex
structures have and continue to emerge frequently. Understanding the substrate scope and
limitations of this method will undoubtedly come from exploring other conjugated moieties
in DArP. To conclude this section, the expansion to 3HT-based conjugated random
60
copolymers will be critically evaluated to understand the potential substrate limitations of
this emerging method. The earliest example of such a derivative was the synthesis of
poly(3-hexylthiophene-co-cyanothiophene) by Thompson et al.
189
(Scheme 1.17). The
preparation of the Stille-compatible comonomer, 2-bromo-3-cyano-5-
trimethyltinthiophene is more challenging than the 3HT monomer, requiring the Knochel-
Hauser base and a more challenging purification, which makes DArP of this substrate
attractive. Critically, the monomer feed ratio matches the polymer composition—this is of
critical importance for the application of DArP to increasingly complex random
copolymers. As discussed in Section 2, this is not always possible with synthetic methods,
and so highlights the advantages of DArP. Polymers were regioregular but random, free of
any β-coupling defects, but subtle differences between the polymers was observed,
suggesting the way Stille and DArP randomly incorporate monomers may be different.

Scheme 1.17. Synthesis of P3HT-CNT via DArP as reported by Thompson et al.
189
The
Stille compatible monomer of 3-cyanothiophene is challenging to prepare, which makes
DArP an attractive route toward this random copolymer.
61
In a similar strategy, Coughlin et al.
50
generated random copolymers incorporating
3-hexyl-4-fluorothiophene into P3HT (Scheme 1.18). The Stille version of this monomer
has, to the best of our knowledge, not yet been isolated and this polymer has only been
synthesized via GRIM polymerization,
190
which is incompatible with random
copolymers,
71
or by electropolymerization with flanking thienyl moieties,
63
which also has
minimal control over structure. Incorporating 3H4FT at 0 (P3HT), 25, 50, 75, and 100%
(P3H4FT homopolymer), they observed a drop in the regioregularity, from 95% to 78%,
attributed to differences in monomer reactivity; however, molecular weights and yields
were good, all generally above 12 kDa except for P3H4FT, which had a lower molecular
weight most likely due to solubility. However, this is an exemplary example of the ability
for DArP to effectively generate materials that are incompatible with traditional methods.

Scheme 1.18. Synthesis of P3HT-F via DArP as reported by Coughlin et al.
50
The Stille
compatible monomer is 3-hexyl-4-fluorothiophene is challenging to isolate, which makes
DArP an attractive route toward random copolymers.
62

1.3. Strategies for Achieving Well-Defined Copolymers via DArP

In the preceding section, the utilization of polythiophene case studies enabled
fundamental exploration of the major considerations outlined in Section 1 for DArP,
including formation of defects like homocoupling, β-coupling, and end groups, as well
mechanistic considerations. P3HT also is one of the few substrates that has been broadly
synthesized by several different DArP classifications and it was demonstrated that Class A
and Class C have been the least successful in preparing rr-P3HT. Conversely, Class B, D,
and E have all generated quality P3HT. It is also the easiest substrate to quantify β-defects
with. Indeed, as demonstrated by Leclerc et al.,
121
even with thiophene-based
quarterthiophene polymers, quantification of β-defects is quite challenging, though it has
been observed via structure-function relationships that bulky carboxylic acids can mitigate
these defects.
40,51,121
With an understanding of the considerations for polythiophene model
systems at hand, the underlying endeavor of this section is the application of DArP to more
complex systems and the considerations that result from these more advanced systems.
This was briefly highlighted by the work from Leclerc et al.
185
through a comparison of
regioisomers 2-bromo-3-hexylthiophene and 2-bromo-4-hexylthiophene toward rr-P3HT
regarding optimal functionalization, as well as expanding to multiple diverse monomers as
exemplified by the works of Thompson et al.
189
and Coughlin et al.
50
Moving from
thiophene to other substrates will ultimately complicate the synthesis and introduce
additional considerations that must be addressed for DArP to become a superlative cross-
coupling method. The strategies for functionalization, which group should be halogenated
and which to undergo C−H activation, how to minimize defects and achieve well-defined
63
polymers when multiple monomers are copolymerized (either randomly or alternatingly),
and which classification of DArP conditions can be successful for different substrates will
be the emphasis of this section.
While P3HT is the quintessential reference conjugated polymer and is incredibly
well-explored, the current field of conjugated polymers is employing increasingly complex
polymer architectures for the generation of high performance materials.
34,72,191–194
The
desire for precisely adjusted optoelectronic properties in conjugated polymers has
promoted the so-called donor/acceptor (D/A) copolymer, which enables control over
polymer bandgaps and HOMO energy levels via finely-tuned electron-poor and electron-
rich moieties. This strategy has enabled truly high performance OPVs and OFETs, with
OPV performance now regularly exceeding 10%,
192
and sometimes as high as 12%
195
in
single-junction devices, which was long thought to be the efficiency needed for
commercialization. Similarly, OFETs have achieved electron mobilities exceeding 1 cm
2
V s.
196,197
Beyond the alternating D/A copolymers, other strategies including random
copolymers,
50,77,189,198
semi-random copolymers,
199–203
and semi-alternating
copolymers
204–207
have emerged as viable polymer architectures (Figure 1.14).
64

Figure 1.14. Expanding from (a) homopolymers to (b) alternating copolymers, (c) random
copolymers, (d) semi-random copolymers with random monomers but discrete acceptors,
or (e) semi-alternating copolymers with alternating monomers and discrete acceptors will
require additional considerations when utilizing DArP.
DArP is a way to ease the cost of synthesi s. Despite the increasing complexity of
structural designs for D/A polymers and the shift away from polythiophene, the thiophene
moiety is still the signature motif of conjugated polymers, which enables DArP to be viable
for generating these copolymers with optimization. In the follow section, the strategies
for achieving well-defined copolymers via DArP for these more complex systems will be
critically discussed to deconvolute substrate and DArP classification.

65
1.3.1. Influence of Functional Group Assignment on Polymer Structure

As outlined in Section 1, at minimum, direct arylation requires an acidic proton and
a halogenated leaving group; however, often there is some flexibility when both substrates
have acidic protons, as would be the case with coupling between two thiophene substrates
or with an acidic benzene-like proton, such as tetrafluorobenzene. As a result, converting
a monomer system from the Suzuki- and Stille-compatible versions to a system that can
work with DArP may open additional routes toward conjugated polymers. For example, in
two different reports, Sirringhaus et al.
208
and Dodabalapur et al.
209
synthesized copolymers
of DPP and benzotriazole (BTZ) derivatives from two different monomer functionalization
strategies, where Sirringhaus and coworkers utilized unhalogenated DPP and brominated
benzotriazole while Dodabalapur and coworkers utilized brominated DPP and
unhalogenasted BTZ (Scheme 1.19). Although Dodabalapur and coworkers did not
explicitly investigate defect content, Sirringhaus and coworkers observed defects to be
present in the DArP polymers. Regardless, these two reports demonstrate that different
potential avenues emerge for targeting new copolymers. This is especially relevant
considering the observation that some BTZ substrates may decompose in the presence of
organolithium reagents,
208
which would render the associated Suzuki polymerization route
more inaccessible than DArP.

66

Scheme 1.19. Two different viable functionalization strategies, explored by Route A and
Route B by Sirringhaus et al.
208
and Dodabalapur et al.
209
respectively, toward DPP and
BTZ copolymer.
One of the first DArP reports to compare the influence of selective bromination of
monomers was undertaken by Leclerc et al.
55
They synthesized a polythiophene polymer
from two bithiophene derivatives (PBTBT) (Scheme 1.20) as part of a larger study to
establish the broad applicability of Class E conditions with PivOH. In this case, conditions
were ineffective for generating polymers when the brominated monomer was double β-
unprotected bithiophene, 5,5'-dibromo-2,2'-bithiophene (Route A), resulting in lower
molecular weight polymers with structural defects. The authors determined via DFT
calculations that brominated thiophene lowers the free energy of activation of the β-
position, which can promote branching defects. Coupled with potential debromination
events, the combination of homocoupling and branching led to poorer quality polymers.
On the other hand, utilizing 5,5'-dibromo-4,4'-didodecyl-2,2'-bithiophene via Route B
generated suitable polymer that were to the Stille version, as identified by NMR analysis,
though β-linkages were not quantified.

67

Scheme 1.20. Synthesis of polythiophene via two different monomer functionalization
strategies as reported by Leclerc et al.
55

Another report to directly evaluate the influence of functionality on polymer quality
was undertaken by Livi et al.
145
They evaluated two distinct acidic C−H containing species,
thiophene and perfluorinated benzene. They evaluated selectivity on a small molecule
direct arylation system before applying their conditions toward the generation of a
copolymer (Scheme 1.21), utilizing several direct arylation conditions previously explored
for small molecule cross-couplings.
170,210–218
The authors observed that for perfluorinated
benzene, the utilization of Pd(OAc)2 with di-tert-butyl(methyl)phosphonium
tetrafluoroborate in DMA (Class A conditions) resulted in high selectivity of the small
molecule coupling, resulting in all the thiophene being functionalized (100% conversion)
and absence of the most common side-reaction, which was debromination of one coupling
partner and bromination of the second partner, which would generate 2-bromo-5-
hexylthiophene and 2-hexylthiophene respectively, which accounted for all the conversion
reactions. Utilizing the best conditions, which are modified Class A conditions that utilize
the above catalytic system with Ag2CO3 as the base in DMA at 100°C, the authors
synthesized model fluorinated copolymers (Scheme 1.21). Interestingly, they observed that
Route A generated only oligomers, resulting from debromination side reactions that
68
terminated the chain growth. Suitable molecular weights were achieved with a brominated
thiophene moiety (on an electron-rich system) and the unfunctionalized
tetrafluorobenzene. This early report was the first to emphasize two important aspects of
DArP: (1) the typical functionalization strategies derived from Stille and Suzuki may not
always be viable (halogenation of the acceptor), and (2) the catalytic system will ultimately
have significant control over which routes can be effective.

Scheme 1.21. Synthesis via direct arylation of small molecules featuring
pentafluorobenzene and 2-hexylthiophene units via two different functionalization
strategies (top) and the subsequent application of optimized conditions on the
polymerization of a model fluorinated copolymer via DArP (bottom). Denoted as −OHD
is an hexyldecyloxy side-chain. The authors observed that dibromotetrafluorobenzene only
resulted in oligomers via DArP Class A conditions.
69
For synthesizing the above polymer via Stille or Suzuki, the tetrafluorobenzene
would need to be boronated, which can be challenging, or stannylated, which is generally
low yielding.
219,220
Conversely, with Route A, the thiophene donor monomer would need
to be functionalized. Often, when considering functionalization strategies for Stille or
Suzuki, the major concern is the stability of the monomer to strong bases but also the ease
of purification of the resulting monomer. In general, it is considered difficult to stannylate
many acceptors that are utilized in conjugated copolymers. For example, it is much easier
to brominate ubiquitous acceptor diketopyrrolopyrrole (DPP) than it is to stannylate that
monomer (Scheme 1.22).
221,222
Despite its widespread application in copolymers, DPP is
rarely incorporated from a stannylated monomer, being overwhelmingly explored as a
halogenated monomer.
223,224
In the few reports that do utilize a tin-functionalized DPP
monomer, the molecular weights are often low.
221,222
This may be a result of the
challenging purification (an alumina column saturated with triethylamine to prevent
stripping of the tin groups that usually occurs with traditional silica column
chromatography) or the challenges in achieving stochiometric balance considering the
stannylated DPP with ethyl hexyl side chains was reported to be a viscous liquid.
221

Scheme 1.22. Most commonly, DPP is brominated for utilization in Stille or Suzuki
polymerizations because the stannylation requires more challenging purification and the
70
resulting tin-functionalized DPP monomer can be a viscous oil.
221,222
An advantage of
DArP is that either the unfunctionalized DPP or the easier to achieve dibrominated DPP
are both viable monomers. Given the low molecular weights that have generally been
achieved with stannylated DPP, DArP may enable high quality polymers that have
previously been inaccessible.
An advantage of DArP, subsequently, is that both the unfunctionalized and
halogenated DPP monomers would be viable and readily accessible candidates as
monomers, whereas Stille can be considered to only have one conveniently and realistically
accessible monomer route. One notable example was the synthesis of DPP homopolymers
by Leclerc et al.
225
with two DPP analogs, which will be discussed in Section 4 as a case
study for using OFET practical performance to gauge polymer quality. Extending on DPP
functionalization strategies, work by Wang et al.
220
(and Sommer et al.
226
discussed below)
explored the copolymerization of DPP with tetrafluorobenzene toward an ambipolar
copolymer via two functionalization strategies (Scheme 1.23), but instead of primarily
Class A conditions as explored by Livi and coworkers described above, the authors
compared Class C and Class E conditions. As part of their comprehensive study, they also
generated a Stille version, from brominated DPP (Br-DPP) and stannylated
tetrafluorobenzene (Sn-TFB), as well as a Suzuki version, from boronated DPP (B-DPP)
and brominated tetrafluorobenzene (Br-TFB). Additionally, they generated homopolymers
of DPP to analyze potential homocoupling defects. It is worth noting that the molecular
weights via Stille were quite low (Mn = 3.4 kDa) and the material via Suzuki had extensive
homocoupling defects originating from C−B/C−B homocoupling of the DPP monomer
(their first attempt to synthesize Suzuki failed completely, due to deboroylation), which is
71
reasonable considering that boroylated thiophenes can be unstable. Together, these results
demonstrate that both Stille and Suzuki have their limitations for achieving well-defined
copolymers, especially concerning challenges with organometallic functionalization of
some substrates, in this case, two electron-poor substrates.

Scheme 1.23. Exploration of different functionalization strategies on two electron-poor
monomers via two different DArP classifications as reported by Wang et al.
220
In an
concurrent study, Sommer et al.
226
also evaluated both routes and provided detailed defect
analysis of this polymer via Route A using Class E conditions.
Moving from Stille and Suzuki to DArP, Wang and coworkers
220
observed several
interesting details about the functionalization strategies and how they influence the
resulting polymer structure, especially how it relates to the DArP classifications. The
authors explored both Class C and Class E conditions utilizing Route A. Their
representative Class C conditions incorporated Pd(OAc)2 with PCy 3HBF4 and PivOH in a
1:1 DMA/xylene solvent mixture while the Class E conditions incorporated the Herrmann
Beller catalyst with P(o-OMePh)3 in superheated toluene. For Route A, the Class E
conditions were superior, generating Mn of 33 kDa and 99% yield while the Class C
72
conditions had lower yields and Mn values less than 10 kDa. Conversely, when using Route
B, the authors observed no polymer formation via the Class E conditions but achieve Mn
values of 80 kDa via Class C conditions with a modest yield of 45%. With slightly modified
Class C conditions, utilizing Pd(OAc)2 with P
t
Bu2Me-HBF4 in superheated THF, they
achieve a yield of 83% but with lower Mn values of 31 kDa. These observations are
summarized in Scheme 1.24. Via NMR analysis with a DPP homopolymer, the authors
confirm minimal homocoupling defects via Class E conditions with Route A and only a
very small peak corresponding to homocoupling via Class C conditions with Route B.
Potentially, the utilization of 10% catalyst and 1:2 phosphine ratio for their representative
Class C conditions may lead to these small homocoupling defects, as Sommer et al. have
observed that increasing phosphine ratio can minimize homocoupling. The authors also
comment on the tailing of the UV-Vis absorption onset as further evidence of potential
homocoupling, as the absorption shifts toward the DPP homopolymer with increasing
homocoupling defects. Such trends were also observed by Janssen et al.
227
Overall, Wang
and coworkers observe that Class E conditions, while only compatible with Route A for
these substrates, generate high quality polymers. Conversely, while Class C conditions are
compatible for Route B, they will lead to homocoupling defects. Thus, it is important to
take these considerations into account when strategizing the incorporation of monomeric
units in copolymers depending on the DArP classification.

73

Scheme 1.24. Observation by Wang et al.
220
that Class E conditions generate nearly defect-
free copolymers when utilizing Route A but no polymers via Route B. Conversely, Class
C conditions generate oligomers with significant defects via Route A but high molecular
weight copolymers with homocoupling defects via Route B.
Sommer et al.
226
in a concurrently published report evaluated the same
copolymerization of DPP with TFB as provided in Scheme 1.23. Consistent with the
observations from Wang et al.,
220
Sommer and coworkers observed Route B utilizing Class
E conditions did not result in polymers (Scheme 1.24), so focused their report on Route A.
Coincidently, they switched to Class B and Class C conditions with Route A before
revisiting it with Class E conditions. The results from select reactions from both reports
are summarized in Table 1.1. Sommer and coworkers observed that Class B and C
conditions with Route A could not suppress homocoupling defects; however, Class E
conditions—if the palladium to phosphine ligand ratio was 1:2 or larger—could suppress
homocoupling defects. Similar observations were made by Wang et al.
220
but the
74
homocoupling content was quantified by Sommer and coworkers. Although both Sommer
et al. and Wang et al. observed Class C to generally yield lower molecular weight material,
Sommer and coworkers observed that the utilization of pre-deprotonated potassium
pivalate (KOPiv) could achieve higher molecular weights (>12 kDa) but without reducing
the amount of homocoupling defects (11%). Interestingly, Sommer and coworkers could
achieve suitably high molecular weights via Route B using Class B conditions with 6%
homocoupling defects, suggesting that a phosphine ligand may not always be desirable for
minimizing defects and may even increase their likelihood for some substrates.

Table 1.1. Comparison of routes (Scheme 1.23), DArP classification (Figure 1.7),
conditions, and the resulting polymer properties, including yields, molecular weight, and
homocoupling quantification (hc) as reported by either Wang et al.
220
or Sommer et al.
226

Route
(Class)
Pd/P (Ratio) Base/Acid Solvent (M)
Temp.,
°C (t)
Yield
M n
(kDa)
hc (%) Ref.
A (B) Pd(OAc) 2
K 2CO 3 /
PivOH
Tol/DMA (0.3) 90 (72h) 65 22.0 6% Sommer
A (C)
Pd(OAc) 2 /
P
t
Bu 2Me-
HBF 4 (1:4)
K 2CO 3 /
PivOH
THF (0.5)
100
(24h)
75 6.7
n.d.
(significant)
Wang
A (C)
Pd(OAc) 2 /
PCy 3HBF 4
(1:1)
K 2CO 3 /
PivOH
Xylene/DMA
(0.5)
110
(24h)
30 2.9
n.d.
(significant)
Wang
A (C)
Pd(OAc) 2 /
PCy 3 (1:1)
K 2CO 3 /
PivOH
Tol/DMA (0.5) 90 (72h) 23 5.4 9% Sommer
A (C)
Pd(OAc) 2 /
PCy 3 (1:1)
KOPiv Tol/DMA (0.5) 90 (72h) 93 12.9 11% Sommer
75
A (E)
Herrmann-
Beller / P(o-
OMePh) 3 (1:4)
Cs 2CO 3 /
PivOH
Tol (0.5)
100
(24h)
99 33.2 n.d (minimal) Wang
A (E)
Pd 2dba 3 / P(o-
OMePh) 3 (1:2)
Cs 2CO 3 /
PivOH
Tol (0.5) 90 (72h) 86 16.5 0% Sommer
B (C)
Pd(OAc) 2 /
P
t
Bu 2Me-
HBF 4 (1:4)
K 2CO 3 /
PivOH
THF (0.5)
110
(24h)
83 31.0 n.d (some) Wang
B (E)
Herrmann-
Beller / P(o-
OMePh) 3 (1:4)
Cs 2CO 3 /
PivOH
Tol (0.5)
100
(24h)
0 -- -- Wang
B (E)
Pd 2dba 3 / P(o-
OMePh) 3 (1:2)
Cs 2CO 3 /
PivOH
Tol (0.5) 90 (72h) 0 -- -- Sommer

Highlighting the popularity of the DPP monomer, Coughlin et al.,
228
in a report
published around the same time as that of Sommer and coworkers and Wang and
coworkers, evaluated the influence of increasing degrees of fluorination on secondary
comonomer for DPP copolymers for OPVs and OFETs (Scheme 1.25). For consistency
and the high activation barrier of C−H bonds on benzene, the authors evaluated only the
so-called “Route A” monomer functionalization strategy, which would be compatible with
benzene. Consistent with the observations above, the Class E conditions lead to well-
defined polymers; however, Coughlin and coworkers observe that very small amounts of
DPP homocouplings may be present in the copolymer with benzene and may be present in
very slight amounts for the others, due to slight tailing of the absorption onset. They utilized
Class E conditions with the chloroform adduct of Pd2dba3 with a 1:4 ratio of P(o-OMePh)3
with PivOH/Cs2CO3 in a 10:1 toluene:DMF mixture with 0.05 M concentration of
monomers. With suitable palladium:phosphine ligand ratio, this observation of slight
76
homocoupling defects may originate from utilization of DMF instead of DMA as a solvent.
This report highlights the advantages of utilizing DPP as a model substrate, where
homocouplings can be readily identified via tailing of the absorption onset as proposed by
Janssen et al.
227
It also further confirms that Class E conditions are optimal for
unfunctionalized DPP monomers.

Scheme 1.25. Functionalization strategy utilized by Coughlin et al.
228
for the generation of
well-defined DPP copolymers via DArP Class E conditions.
More recently, Li et al.
229
also explored copolymerizations between two electron-
poor substrates. Copolymerization of DPP with 2,2’-bithiazole (BTz) was undertaken with
Class E conditions in toluene. A synthetic overview of the target polymer and the two
routes to achieve this polymer are provided in Scheme 1.26. The thiazole motif is one of
the more electron-poor five-member heterocycles, which makes BTz uniquely suited to
observe whether functionalization strategies can promote potential β-couplings due to
lower barriers for C−H activation. Indeed, with this system, β-linkages are possible with
both the DPP and BTz units. Between Route A and Route B pathways, the authors observe
both methods generate potential cross-linking of the polymers, induced by β-coupling.
Even with an incredibly strong solubilizing chain, which enabled solubility of the 10+ kDa
77
copolymers in hexanes, the authors observed insoluble material that could not be dissolved
in any solvent they tried. In contrast to the observations by Wang et al.
220
with
tetrafluorobenzene, the authors observe that Route B generates superior polymers, with
higher degrees of crystallinity, better practical performance, and less polymer defects
(branching and cross-linking). Interestingly, tailing of the absorption onset is visible for
the Route B polymer, which suggests it may exhibit more DPP homocoupling defects than
Route A. Regardless, the stark differences in polymer performance suggests that
functionalization strategy for DPP polymers is not universally applicable. Li and coworkers
observed that better performance can be achieved via Route B, suggesting that non-
bromination of DPP is not always preferential.

Scheme 1.26. Synthesis of PDBTz-A and PDBTz-B, DArP with two different monomer
functionalization strategies, under Class E conditions as reported by Li et al.
229

Another consideration with more complex monomer designs is the strategy for
achieving the desired couplings. In the above examples, DPP is synthesized via a
condensation reaction from a nitrile-functionalized substrate, most typically thiophene but
others have been explored as well.
230
As a result, the DPP “core” will almost always be
78
flanked with some aromatic system. For other acceptors, often the substrate is generated
by coupling two other substrates together. This was exemplified in Scheme 1.4 in Section
1, where an acceptor moiety, benzothiadiazole, was flanked with thienyl groups. Deciding
the strategy for equipping thienyl groups was undertaken as part of a larger study by Livi
et al.,
83
who were targeting poly[(2,5-bis(2-hexyldecyloxy)phenylene)-alt-(4,7-
di(thiophen-2-yl)benzo[c][1,2,5]thiadiazole)] (PPDTBT). The two different pairs of
monomers that could be utilized to generate the same copolymer via DArP are outlined in
Scheme 1.27. In this instance, the thiophenes could be equipped to the alkoxybenzene
donor (Route X) or the benzothiadiazole acceptor (Route Y). The authors observed that
Route X generated higher yields and molecular weights than Route Y when employing
DArP Class B or C conditions. Conversely, they observed that DArP Class E was most
compatible with Route Y, and generated lower molecular weights and yields via Route X.
This results suggest that Fagnou-derived conditions may work better with electron-poor
benzene-like C−Br bonds or thienyl groups on donors, while Ozawa-derived conditions
may perform better with electron-rich benzene-like C−Br bonds or thienyl groups on
acceptors. Despite the successful molecular weights, the authors observed that both Class
B and C conditions ultimately generated homocoupling defects via Route X, with
phosphine-free Class B conditions generating both acceptor/acceptor homocouplings as
well as donor/donor homocouplings while optimized Class C conditions suppress
donor/donor couplings but still exhibit some acceptor/acceptor couplings. Conversely,
optimized Class E conditions exhibited no homocoupling defects via Route Y. These
results highlight the need for careful monomer and halogenation strategies when pursuing
well-defined copolymers via DArP. The authors also noted that for the Stille compatible
79
monomers, the thienyl-containing substrates would be stannylated while the other group
would be halogenated. They noted that the purification of the stannylated thienyl-flanked
alkoxybenzene was significantly more challenging than the stannylated thienyl-flanked
benzothiadiazole (which can be recrystallized), resulting in large differences between Stille
Route X and Stille Route Y, which had four times greater Mn values. This highlights the
distinct flexibility that is evident when adopting the DArP methodology, though more work
is ultimately needed for broad applicability of the conditions across a variety of substrates.

Scheme 1.27. Comparison of two different substitution routes toward the generation of
PPDTBT as reported by Livi et al.
83
For the Stille compatible monomers, the thienyl-
containing substrate would be stannylated.
Thompson et al.
118,231
explored the synthesis of semi-random P3HT analogs via
DArP in two studies. In the first, they applied Fagnou-derived Class B conditions toward
the synthesis of P3HTT-DPP via Route X ( Scheme 1.28). The polymers possessed
considerable defects, including branching and homocoupling defects. In the second work,
they revisited the architecture but utilized both optimized Class B conditions and Class E
80
conditions. They ultimately observed that optimized Class B conditions suppressed
branching defects but lead to homocoupling defects; however, Class E conditions lead to
fewer homocoupling defects and convergence with Stille polymers. Interestingly, both
Route X and Route Y performed similarly, with small differences being attributed to DPP
coupling to the 2-position of 3HT instead of the 5-position, which may have led to slight
torsion in the backbone.

Scheme 1.28. Synthesis of three-component semi-random copolymer, P3HTT-DPP via
DArP by Thompson et al.
118,231

Although the exploration of other ternary copolymers will be discussed in more
detail later, it’s worth noting that functional group assignment was first identified as an
important parameter for ternary systems by Farinola et al.,
77
who attempted to generate
ternary random copolymers from benzo[1,2-b;4,5-b′]dithiophene as the donor moiety and
81
two acceptors, benzo[c][1,2,5]thiadiazole and benzo[d]-[1,2,3]triazole (Scheme 1.29). The
authors observed that attempts of C−H activation of benzothiadiazole acceptors did not
lead to polymers via Class E conditions. This was most likely due to inability of the
respective C−H bonds to undergo transformations due to high energy barriers, which is
usually only achieved for more acidic protons.

Scheme 1.29. Comparison of two different substitution routes toward the generation of
ternary semi-random alternating copolymer PBDT-BTD-BTZ via DArP by Farinola et al.
77

Attempts at C−H activation of the benzene-like substrates was unsuccessful for Class E
conditions. Several classifications of DArP conditions generated polymer via the
Considerations about C−H reactivity are an important parameter for DArP. To
conclude this section, the discussion will emphasize work toward understanding the role
of functionalization in promoting or demoting side-reactions, as C−H bond selectivity
remains one of the critical limitations of this synthetic method along with potential
dehalogenation reactions and chain termination events. Some reports have evaluated the
free energy of activation of various substrates via direct arylation (typically via DFT
82
studies), which is helpful for determining the likelihood of unselective C−H activation,
which may include β-activation in the case of thiophene, but will inevitably lead to other
C−H functionalization considerations with increasing complexity of substrates. In Figure
1.15, the free energy of activation for a variety of substrates under specific conditions is
provided, including both considerations for C−H activation as determined by Gorelsky,
Lapointe, and Fagnou
102
but also more recently by Leclerc, et al.
232
While the work from
Fagnou and coworkers emphasizes the C−H functionalization of various arenes, Leclerc
and coworkers extended the work into the evaluation of common arenes for conjugated
polymers. Additionally, they observed the differences between C−H activation when a
monomer is brominated. This may be useful for determining the likelihood that unselective
C−H couplings may occur depending on the selection of functionalization, which has been
the theme of this section. For example, as discussed earlier, Li and coworkers
229
observed
brominated BTz to perform more poorly than unhalogenated BTz, which is supported by
the DFT calculations performed by Leclerc et al.,
232
who observed β-activation of the
brominated BTz is 2.2 kcal mol
-1
lower than that of the alpha position of DPP, which may
not be effectively different enough to completely prevent branching.

83

Figure 1.15. Free energy of activation (ΔG298K, kcal mol
−1
) for various C−H bond
metalations by a Pd(C6H5)(PMe3)(OAc) complex of each arene by density functional
theory (DFT) with the B3LYP
233,234
exchange-correlation functional (top row) as reported
by Fagnou et al.,
102
or at the B3LYP/TZVP (DZVP for palladium) level using Gaussian 09
package and structure optimization in the gas phase as reported by Leclerc et al.,
55,232,235

where alkyl chains were reduced to methyl to simplify calculation times.
The compilation of these results into Figure 1.15 provides an opportunity to
observe potential trends as well. For example, looking at thiophene (top row, right) and
84
bithiophene (third row, left), it is observed that the free energy of activation of both the α-
and β-position decrease with extended conjugation. Likely, as the polymer chain extends
in conjugation length and the number of α-positions decreases and the number of β-
positions increases, the potential for unselective linkages increases. This becomes
especially true when halogenating thienyl groups, which can lower the free energy of β-
activation by as much as 2.5 kcal mol
-1
as observed between DPP and Br-DPP (last row,
left). Indeed, the β-activation of Br-DPP is low enough to be somewhat competitive with
that of the α-activation of benzodithiophene. These results highlight the need to further
optimize the catalytic system, particularly the incorporation of a bulky carboxylate ligands
as proposed by Thompson et al.,
120
which can potentially prevent these unselective linkages
and the need for catalytic systems that can minimize homocoupling defects as first
proposed by Sommer et al.
53

1.3.2. Improving Polymer Structure & Potential Scope Through Rational Design of
the Catalytic System

While judicious selection of the monomers ( β-protected or large differentials in free
energy of activation), β-linkages can sometimes be avoided; however, as has been shown
above in Section 2, the utilization of a bulky carboxylate ligand can also prevent defects.
In addition to careful consideration of monomer functionalization, numerous other tactics
and considerations have been adopted for achieving well-defined polymers beyond the
polythiophene case studies and alternating copolymers discussed above. Further efforts
toward minimizing β-linkages, homocoupling defects, controlling end groups, and
minimizing residual metal residues will be explored in this section, with the emphasis being
85
on potential mechanistic considerations and practical guidelines for achieving well-defined
copolymers.
Strategies for minimizing β-defects are typically limited to either blocking the β-
positions or the utilization of a bulky carboxylic acid additive as demonstrated by
Thompson et al.
119,120
and subsequently Leclerc et al.
121
Expanding on these observations,
Marks et al.
51
utilized 2,2-diethylhexanoic acid, a sterically demanding and bulky isomer
of the NDA mixture, which they envisioned may suppress β-defects even further,
especially considering the high reaction temperatures. They observed that the bulky acid
additive was critical for achieving high molecular weights. Both Thompson et al.
83
and
Marks et al.
51
observed that a bulky carboxylic acid was needed for Stille-convergent OPV
performance (discussed in more detail in Section 4). Another strategy for suppressing β-
defects is the utilization of directing groups, which was undertaken by Kanbara et al.
236,237

on a pyrrole and fluorene copolymerization (Scheme 1.30). This DArP reaction is notable
for its utilization of a ruthenium catalyst, which in combination with the directing group
(2-pyrimidinyl substituent), PivOH, K2CO3, and m-xylene as a solvent achieved Mn values
of 20 kDa with 86% yields. Subsequently, the directing group could be readily removed
with base treatment with 82% recovery. Importantly, the introduction of the 2-pyrimidinyl
substituent ensured selective α-proton activation, suppressing the formation of branched
and cross-linked structures, which enables pyrrole-based monomers, albeit somewhat
uncommon, as viable substrates for well-defined polymers via DArP.

86

Scheme 1.30. Utilization of a directing group to avoid formation of β-defects for pyrrole-
based copolymers with a Ru-catalyzed DArP method as reported by Kanbara et al.
236

Koizumi et al.
238
developed a novel thiol-modified silica gel, PITS, which they
used to immobile palladium catalysts for effective solid-supported catalysis. They
observed that this system suppressed β-defects when explored on unfunctionalized
bithiophenes with various brominated aryl species, including 2,5-dibromothiophene, which
suggests these supported systems can increase α-selectivity. Additionally, very low
residual palladium impurities were found in the resulting polymers, even as low as o.035
ppm, highlighting the attractiveness of supported or heterogenous catalysts, which are
worthy of further investigation in DArP.
239

Screening of conditions and exploration of different parameters is an important
endeavor for the realization of the true potential of synthetic methods, while also providing
insight into mechanistic and catalyst design principles. An early example of is exemplified
by an intense effort to understand the influence of various parameters by Wang et al.
240

who explored a variety of parameters for the synthesis of model copolymer from 4,8-di(2-
hexyldecyloxy)benzo[1,2-b:4,5-b’]-dithiophene and 4,7-dibromobenzothiadiazole
(Scheme 1.31a). They first explored Class B conditions, with Pd(OAc)2, against Class E
87
conditions, with either the Hermann-Beller catalyst or Pd2dba3. They observed the
Hermann-Beller catalyst was less effective than Pd2dba3. Although Class B and Class E
with Pd2dba3 generated polymers of similar molecular weights, Class B conditions
appeared to possess more defects. A similar observation would later be observed by
Thompson et al.,
83
discussed above, who screened a variety of DArP classifications,
including Class B, C, and E and also identified minimal defects with Pd2dba3 and Class E
conditions. Wang and coworkers, however, further explored a variety of solvents, bases,
acid additives, concentrations, and even phase transfer agents based on Class E conditions
(Scheme 1.31b). They observed that non-polar 1,2-dimethylbenzene (ODMB) generated
the highest molecular weight but that 1,4-dioxane was also quite successful. Increasing the
concentration of the monomers from 0.1M to 0.2M increased the molecular weight.
Consistent with other reports, they observed Class E conditions to fail without P(o-
OMePh)3. Additionally, they confirmed PivOH to be suitable as an additive and observed
phase transfer agents to hinder the polymerization. Interestingly, they observed the base,
K2CO3, to generate higher molecular weight polymers than Cs2CO3, and that increasing
the loading from 3 equiv. to 5 equiv. increased the molecular weight further. Other bases,
such as amine-type bases or group 2 alkaline bases did not work.

88

Scheme 1.31. (a) Synthesis of model copolymer, PBDTBTD, via a variety of reaction
parameters explored for Class E conditions as reported by Wang et al.
240
(b) Solvents and
bases explored. For parameters that provided greater than 13 kDA, numbering ranks them
from highest molecular weight to lowest.

Briefly described in the preceding section above, it has been observed to
occasionally be unfavorable to utilize Br-DPP via DArP, with Wang et al.,
220
Sommer et
al.,
226
Li et al.,
229
and Leclerc et al.
232
observing that Br-DPP can lead to some degree of
branching defects, homocoupling defects, or debromination events. Consequentially, it has
generally been surmised that unfunctionalized DPP is a more viable monomer. This truly
limits the broad capacity and enabling potential of DArP. Pioneering work from Ozawa, et
al.,
241
who developed a mixed-ligand approach,
52,158
has resulted in a novel catalytic system
that enables Br-DPP to be a more viable monomer for Class E conditions. Advantageously,
the secondary ligand is affordable and accessible tetramethylethylenediamine (TMEDA).
Through extensive study with model compounds and thorough NMR analysis, the authors
89
were able to quantify the polymer defects in great detail with DPP monomers. The
copolymer systems evaluated and the conditions utilized are provided in SCHEME. In a
copolymerization between DPP and 3,4-dicyanothiophene (DCNT) they observed that
traditional Class E conditions with the Hermann-Beller catalyst, P(o-OMePh)3, PivOH, and
Cs2CO3 in superheated toluene generated mostly insoluble materials (even with shorter
reaction times), which contrasts with a report from Leclerc et al.,
242
who achieved soluble
copolymers, which highlights potential disparities in polymer quality which may be the
result of batch-to-batch and experimental variations. Regardless, the incorporation of
TMEDA by Ozawa and coworkers into the catalytic system lead to completely soluble,
high-yielding, and high molecular weight copolymers. Furthermore, they observed
increased TMEDA to decrease homocoupling defects, from 14.1% total homocoupling
defects to 1.6%, minimizing both DPP/DPP homocoupling but also homocoupling between
DCNT. Quantifying homocoupling in the other copolymers was more challenging but it
was observed that copolymers with electron-rich 3,4-propylenedioxythiophene also
exhibited decrease in homocoupling defects, from 6.1% total homocoupling to less than
2%, highlighting the broad electron-density tolerance of this mixed ligand approach.

90
Scheme 1.32. Minimization of homocoupling defects via utilized of mixed-ligand catalytic
system as explored by Ozawa et al.
241

In developing this successful mixed-ligand approach, Ozawa and coworkers were
able to analyze a variety of defect tendencies and substrates across a series of
works,.
52,158,241
resulting in several invaluable conclusions. In the first report, they observed
that popular ligand P(o-NMe2Ph)3, which was highly successful for the synthesis of
exceptional-quality rr-P3HT (regioregularity > 98%), was less effective for
copolymerizations when used as the only ligand, which has set the precedent for P(o-
OMePh)3 being the most utilized phosphine ligand for DArP Class E conditions; however,
when both ligands are utilized, the likelihood of cross-linking is reduced. In the second
report, they first utilized diamines as secondary ligands, determining TMEDA to be
suitable for minimizing homocoupling defects to 1%. It was this optimized system that was
subsequently applied above for DPP monomers, which have generally been more prone to
defects. Ozawa and coworkers have proposed some mechanistic reasons for the
minimization of homocoupling and branching via incorporation of a TMEDA ligand
(Figure 1.16). As discussed earlier, the catalytic direct arylation cycle proceeds via an
arylpalladium carboxylate intermediate, which is formed after oxidative addition to an aryl
halide bond. Subsequently an anionic exchange with the carboxylate occurs, which
undergoes a metal-ligand activation of the C−H bond of the Ar’−H species. For the aryl-
aryl bond formation, the necessity for a three-center transition state mandates the cis
configuration; however, C−H can also happen in the trans configuration, resulting in the
diaryl species being unable to undergo reductive elimination. From here, the reverse
reaction can occur or an intramolecular protonation may also occur, leading to the
91
reduction of one aryl species, which in terms of the monomer functionality, is effectively
a debromination reaction of that aryl monomeric unit. This unit is now capable of
generating effective homocouplings via cross-coupling with a halogenated monomer.
Additionally, the remaining arylpalladium complex continues toward its own
homocoupling bond formation. TMEDA, which is more basic than the carboxylate ligand,
critically minimizes these homocouplings by competing with the carboxylate ligand,
inhibiting the trans route. On the other hand, in the cis configuration, TMEDA is too far
removed to prevent deprotonation. Finally, Ozawa and coworkers observed that while P(o-
OMePh)3 alone cannot prevent β-linkages, the combination of TMEDA and P(o-OMePh)3
prevents the formation of insoluble materials resulting from cross-linking.

Figure 1.16. Simplified mechanism for Aryl−Aryl cross-coupling and homocoupling as
proposed by Ozawa et al.
158
All steps except reductive elimination are reversible. While
92
the cis route reliably leads to cross-coupling, the trans route is capable of essentially
debrominating one aryl species (enabling homocoupling via cross-coupling with the
corresponding aryl halide species, and homocoupling of the other aryl species. Utilizing
TMEDA was shown to reduce homocoupling by competing with the carboxylate ligand in
the trans configuration, thus inhibiting the trans route.

Expanding on the work from Thompson et al.,
119,120
Leclerc et al.,
121
and Marks et
al.
51
that demonstrated a bulky carboxylate ligand is critical for positively influencing and
improving polymers via DArP, especially with regards to improving selectivity, Leclerc et
al.
232
explored the bulkiness of phosphine ligands as a method for suppressing potential
defects for Class E conditions, which frequently utilizes P(o-OMePh)3 as a ligand toward
alternating copolymers. From the reference methyl substituent, they explored isopropyl,
ethylhexyl, cyclopentane, cycloheptane, and methylcyclohexane substituents (Figure
1.17) and there influence on selectivity. They observed that increasingly bulkier phosphine
ligands exhibit suitable suppression of the homocoupling defects, even to a further extent
then employed Stille conditions; however, it was not enough to completely suppress defects
in all substrates, leading to potentially small quantities of β-defects for some brominated
aromatic units.

93
Figure 1.17. Chemical structures of phosphines explored by Leclerc et al.
232
for
suppression of homocoupling defects and some β-branching defects.
Although not typically considered as important as the palladium pre-catalyst,
phosphine ligand, or carboxylic acid additive, the solvent employed for DArP is often of
critical importance. Although Class A-C conditions typically employ an amide-derived
solvent, both aromatic and non-aromatic/non-coordinating solvents have been used as well.
Likewise, a variety of solvents have been explored for Class D and E conditions, though
as mentioned earlier, amide solvents are often less successful in those cases. Several reports
have evaluated the effect of solvents. A report from Kanbara et al.
243
evaluated several
thiophene-based monomers with varying electronics, which were copolymerized with 2,7-
dibromo-9,9-dioctylfluorene with either Class B conditions in DMA or Class C conditions
in toluene (Figure 1.18). They observed that electron-rich substrates were compatible with
Class B conditions in DMA while electron-poor substrates were compatible with Class C
conditions in toluene. Utilizing the reverse strategy (except for 3,4-dichlorothiophene,
which was compatible with both strategies), resulted in no polymer.

Figure 1.18. Compatibility of electron-poor substrates with Class C conditions with
Pd(OAc)2 and 1-AdCOOH in DMA (left) and with electron-rich substrates with Class B
94
conditions with Pd(OAc)2, PCy 3HBF4, and PivOH in toluene as explored by Kanbara et
al.
243

Expanding on that work, Kanbara and coworkers explored defects of the resulting
strategies.
244
Substituting thienyl groups into their fluorene substrate, they observed that
Class B conditions with DMA lead to homocoupling between the thienyl-flanked fluorene
and the electron-rich thiophene-derived monomers. Conversely, Class C conditions with
toluene lead to minimal homocoupling events when electron-poor thiophene-derived
monomers were copolymerized with thienyl-flanked fluorene, consistent with lowering the
activation energy barrier with increased proton acidity. They would subsequently apply
these conditions to the synthesis of benzo[1,2-b:4,5-b']dipyrrole-2,6(1H,5H)-dione
copolymers with TPD, achieving copolymers with n-type semiconducting behavior.
245

Expanding on their extensive work copolymerizing thiazole-based motifs via
DArP,
144,246–248
Kanbara et al.
249
explored employing their new Class C conditions for the
copolymerization of two electron-poor thiazole units (Scheme 1.33). Unfortunately, they
observed that toluene, which was thought to be suitable for electron-poor C−H activation,
was ineffective for generating bithiazole-based copolymers. Additionally, they observed
DMA to lack the solubilizing power for achieving more than oligomers. Utilizing the study
from Thompson et al.,
162
who evaluated numerous amide solvents for DArP, Kanbara and
coworkers confirmed that N,N-diethylpropanamide was a superior amide solvent for
generating higher molecular weight copolymers (Scheme 1.33 conditions). Although
technically Class C conditions, free phosphine ligands were not added. Instead, they
utilized Pd(0) precursor, Pd(PCy 3)2 in order to achieve higher initiation efficiencies of the
catalyst. As observed by Sommer et al.,
53,226
they observed PCy 3 and lower reaction
95
temperatures to minimize homocoupling defects in these polymers. The work from
Kanbara and coworkers highlights the advantages of the systematic studies employed on
model systems toward understanding structure-function relationships en route to better
copolymers. Indeed, much more basic optimization and condition screening is necessary
for DArP to become an established method.

Scheme 1.33. Combination of N,N-diethylpropanamide for solubilizing power and
Pd(Cy 3)2 P(0) pre-catalyst employed by Kanbara et al.
249
for minimizing homocoupling
and improving molecular weight for bithiazole-based copolymers.
While the solvent is not always directly a participant in the catalytic cycle (as DMA
is for Class A-C conditions), the solvents plays an important role in DArP not just as a
solubilizing medium for determining the upper limits of molecular weight but may also
serve as potential substrates for chain termination, which was investigated by Sommer et
al.
132–134
in a series of works. Utilizing some model reactions with monobrominated NDI
and various solvents Sommer and coworkers observed varying degrees of solvent end
groups, which are summarized in Figure 1.19. These results suggest that over the course
96
of the DArP reaction, solvent may inevitably terminate chain growth with phosphine-free
Class B conditions. They subsequently observed via copolymerizations of NDI with either
thiophene or dithienyltetrafluorobenzene (Scheme 1.7d) that mesitylene enabled the
highest molecular weights because it is largely C−H unreactive, where C−H reactivity
decreases with increasing substitution of the aromatic solvent, which was lowest for TCB
(chlorinated) and Mes (methylated). Ultimately, they determine that sometimes even
poorly solubilizing solvents may be beneficial for achieving high molecular weights due
to the reduction of solvent-induced chain termination.

Figure 1.19. Model reaction to evaluate potential end-capping reactions with solvent via
Class B DArP conditions as investigated by Sommer et al.
132

97
In a follow-up study, Sommer et al.
133
investigated green solvent, 2-
methyltetrahydrofuran (MeTHF), as a solvent for DArP reactions with NDI. This is the
first DArP report to utilize MeTHF, which is a less polar replacement for THF that is
derived in two steps from renewable feedstock, 2-furaldehyde, which is produced from
agricultural waste.
250
It is cost-effective, and more organic in nature than THF, which can
potentially enable higher molecular weights. Additionally, its higher boiling point
introduces less pressure when superheated at comparable temperatures, making it
potentially an attractive alternative solvent for DArP. Synthesis of their n-type NDI-based
copolymer via Class B conditions (Scheme 1.34) enabled suitable molecular weights once
optimized; however, they observed that polymerizations in MeTHF introduce a
hydroxylated NDI chain termini compared to a tolyl-terminated NDI when using toluene,
which slightly influenced the charge properties for field effect mobility. From their
optimization, several other valuable observations can be made. They observed that a
variety of carboxylate ligands work well via these DArP Class B conditions, with
cyclobutanecarboxylic acid, cyclohexanecarboxylic acid, and 1-adamantanecarboxylic
acid all achieving 14 kDa but PivOH providing the highest yield and molecular weight
(95% yield, 14.8 kDa). Increasing the catalyst loading (from 1 to 3%) increased the
molecular weight and they also observed that Na2CO3 worked better than K2CO3,
improving molecular weights from 16.2 kDa (3% catalyst) to 17.3 kDa. Lastly, they
synthesized a series of Pd2dba3 derivatives with various alkyl substitutions on the dba
ligand, with −H, −Me, −tBu, −OMe, and −F groups all improving the molecular weight but
found the best results with −OMe, which generated a PNDIT2 copolymer in 98% yield
with Mn values of 20 kDa with 2% catalyst loading. They compared this polymer to a
98
defect-free PNDIT2 polymer previously studied and found the polymer to be of high
quality, with minimal defects and comparable performance, only being slightly impacted
by hydroxylated chain termini.

Scheme 1.34. Synthesis of PNDIT2 via DArP in MeTHF or toluene as explored by
Sommer et al.
133

Most often, DArP is run in an anhydrous solvent but the cost of this method could
be reduced through establishing compatibility with wet or biphasic reagents. It has been
well-established that Suzuki is particularly user-friendly due to its general compatibility
with water. Considering that traditional DArP carbonate bases, like K2CO3 and Cs2CO3 are
generally insoluble in DMA or toluene, reactions are often vigorously stirred in order to
disperse the base in the reaction medium. Expanding to biphasic mixtures may promote
reactivity through solubilizing the base and increasing the interfacial area between the
aqueous phase and organic phase. Expanding on the report from Wang et al.
240
who
explored phase transfer agents and water additives for copolymerizations, Leclerc et al.
251

99
explored DArP in biphasic conditions, utilizing a toluene/water mixture to generate
copolymers from thienyl- or phenyl-based substrates. They successfully polymerized a
variety of substrates with biphasic conditions (Scheme 1.35), achieving good molecular
weights at ambient pressures, though a sealed microwave vial was still utilized for the
reactions. Employing PdCl2(PPh3)2 as the catalyst lead to robust and generally effective
copolymerizations below the boiling point of toluene. As an added benefit, K2CO3 was
utilized as the base, which is more cost-effective than Cs2CO3.

Scheme 1.35. Biphasic conditions utilized by Leclerc et al.
251
for the synthesis of various
copolymers via DArP. Some representative examples of the explored substrates are
provided.
100
En route to device quality polymers, the residual palladium content is a significant
consideration, as it has been shown to deteriorate device performance.
65–68
Although this
has been an issue for both Stille and Suzuki conjugated polymers, the attention DArP has
refocused on minimizing defects, controlling end groups, and minimizing residual
impurities has had the inherent benefit of refocusing attention on these issues. As discussed
earlier, Reynolds et al.
135
explored the synthesis of propylenedioxythiophene-based
(ProDOT) copolymers via DArP and quantified residual metal defects via ICP-MS,
demonstrating that DArP can lead to less than 20 ppm for both palladium and phosphine,
while other methods like GRIM and oxidative coupling with FeCL3 lead to significant
metal content. Strategies like those employed by Thompson et al.,
163
for utilizing 313 ppm
of palladium catalyst are one strategy but sometimes such low loadings are not feasible.
Ozawa et al.
241
were able to reduce the residual palladium content of DPP-based
copolymers (Scheme 1.32) via DArP by Soxhlet extraction with chlorobenzene containing
diethylammonium diethyldithiocarbamate. Consistent with the reports from Kettle et al.,
252

they were able to reduce residual palladium and phosphine content from over 1500 ppm to
under 60 ppm in most cases, sometimes as low as 11 and 15 ppm for Pd and P, respectively.
Such strategies are universally applicable to conjugated polymers but are highlighted here
as a strategy for improving conjugated polymers overall.

1.3.3. Non-Conventional Conjugated Polymeric Architectures via DArP

Thus far, the exploration of DArP has mostly consisted of linear homopolymers or
alternating copolymers, with the emphasis on minimizing defects toward increased
101
linearity or perfectly alternating systems. A few examples of strategic branching toward
hyperbranched polymers have been discussed. In this vein, the expansion to more
complicated polymer designs will be explored. These more complicated polymer
architectures, which are increasingly relevant to cutting edge conjugated polymer design,
are the next frontier for established DArP as a cutting-edge synthetic method for emerging
designs.
253
As mentioned earlier, Thompson et al.
118
(Scheme 1.28) and Farinola et al.
77

(Scheme 1.29) were the first to evaluate three-component copolymerizations via DArP,
with Farinola being the first to employ such DArP polymers in OPVs.
Other works have also explored multi-component copolymerizations including
work from Wang et al.
254
that also explore multichromophoric random copolymers from
halogenated dioctylfluorene, halogenated benzothiadiazole, and one of three
unfunctionalized thiophene-based monomers, including thiophene, 3-hexylthiophene, and
EDOT (Scheme 1.36). Often, a substrate-flanked benzothiadiazole is utilized as an
“acceptor” moiety in alternating copolymers, such as dithienylbenzothiadiazole. Utilizing
this three-component system, the need to pre-functionalize benzothiadiazole with
thiophene (or something else), then apply it to DArP or functionalize it further to apply to
Stille or Suzuki is bypassed, as benzothiadiazole cannot couple to the fluorene donor
without flanking; however, as the authors observed, such a strategy enables two
benzothiadiazole units (or two fluorene units) to share a single thienyl flanking unit, which
ultimately enables the generation of multichromophoric polymers compared to simple
alternating systems. Furthermore, beyond thiophene or EDOT, however, concerns
regarding regioselectivity emerge with regiounsymmetric units like 3-hexylthiophene in
this strategy.
102

Scheme 1.36. Random copolymers based on dioctyl fluorene and benzothiadiazole with
either 3-hexylthiophene (R = hexyl), thiophene (R = H), or with this shown unit replaced
by EDOT as explored by Wang et al.
254

Exploring methods for fine-tuning the HOMO energy level over a wide range of
values, Jacob et al.
255
synthesized random copolymers from halogenated benzothiadiazole,
halogenated biquinoline, and cyclopentadithiophene (Scheme 1.37), with random
copolymers exhibiting hole transport properties and smaller electrochemical bandgaps. It
is worth briefly highlighting that many groups define these types of polymers as random
copolymers, which—strictly-speaking—is only true if two or more AB monomeric
systems are utilized. More appropriately, these AA/BB/AA monomeric systems should be
referred to as semi-random, since due to the functionalization strategy, one or more of the
monomeric units will never couple to each other. Such discretely situated repeat units
renders these not truly random in the way AB systems enable coupling of identical
monomers.

103

Scheme 1.37. Semi-random ternary copolymers based on quinoline and benzothiadiazole
with a cyclopentadithiophene donor explored by Jacob et al.
255

Follow the above works, Leclerc et al.
256
adopted DArP for the synthesis of ternary
semi-random copolymers, which they explored in OPVs. They utilized 3,8-dibromo-6-
octyloxyphenanthridine and 3,8-dibromo-5-octylphenanthridin-6-one, which were
prepared conveniently from 2,7-dibromo-9-fluorenone via two-step procedure, where each
isomer can be separated column chromatography. Scheme 1.38 shows the generation of
the terpolymer they explored with DPP, though they also explored two alternating
copolymers from each donor. Although practical applications of DArP will be discussed in
detail in the following section, this work along with Farinola and coworkers’ efforts to
explore DArP ternary copolymers in OPVs, highlights the distinct advantages of DArP to
be compatible with emerging strategies.

104

Scheme 1.38. Synthesis of semi-random ternary copolymers with phenanthridinone-based
monomers as reported by Leclerc et al.
256

Such lactam moieties are increasingly popular in direct arylation. These types of
structures are unique in that they are unsymmetrical structures. Consequently, different
optoelectronic properties may emerge depending on the orientation of these substrates.
Extending from the phenanthridinone’s explored by Leclerc and coworkers above, Cao et
al.
257
explored the thiophene-derivative, dithieno[3,2-b:2′,3′-d]pyridin-5(4H)-one, via
DArP (Scheme 1.39). By tailoring the molecular structures, the authors could generate
regioregular polymers instead of polymers with a random orientation, which they observed
to generate different electronic structures. Defects were not identified but the regiorandom
copolymers exhibited stronger absorption coefficients, which suggests that “randomness”
of such head-to-head or tail-to-tail couplings can lead to more electron-rich and electron-
poor centers, thus exhibiting more push/pull behavior to improve absorption. Extending on
this, Wang et al.
258
explored another unsymmetrical unit, 5H-dithieno [3,2-b:2′,3'-d]pyran.
Although regioregularity was not evaluated, this work further highlights the advantages of
utilizing controlled randomness toward improved polymer performance.

105

Scheme 1.39. With regiounsymmetric monomers like dithieno[3,2-b:2′,3′-d]pyridin-
5(4H)-one, random orientation of the monomers can lead to considerably different
optoelectronic properties compared to regioregular polymers, as explored by Cao et al.
257

Expanding on their pioneering work investigating chain ends in DArP polymers,
Sommer et al.
259
exploited well-defined H-P3HT-Br end groups via DArP to generate H-
P3HT-T (thiophene) or H-P3HT-Mes (mesitylene) end groups, which provided either
suitable reactivity or lack of reactivity respectively, enabling the generation of fully
conjugated, crystalline block copolymers (Scheme 1.40) based on P3HT and PNDIT2.
Interestingly, they observed a “ring-walking”- like mechanism via kinectic resolution in
which Pd(0)dba intramolecularly undergoes oxidative addition into the second NDI-Br
bond of the same molecule. They observed thiophene end-capping enabled well-defined
block copolymers, minimizing individual homopolymers of P3HT or non-block
106
copolymers of PNDIT2, whereas the natural end groups or the mesitylene end groups were
less effective, resulting in high occurences of individual polymers (fewer blocks).

Scheme 1.40. Synthesis of all-conjugated donor/acceptor block copolymers containing
P3HT and PNDIT2, achieved via DArP of Br-NDI and bithiophene in the presence of end-
capped P3HT for in situ formation of P3HT-b-PNDIT2.

Beyond traditional linear conjugated polymers, the exploration of hyperbranched
and porous conjugated polymers is increasingly relevant for applications that can utilize
high porosity, interesting optoelectronic properties, and improved chemical stability, which
include gas storage, chemosensing, and photocatalysis. Like linear polymers, however,
they also demand broadly capable synthetic methods. This topic was briefly highlighted by
107
the work from Luscombe et al.
123
above in the section regarding polythiophene case studies
toward hyperbranched substrates. Some substrates are more inaccessible via traditional
Stille routes, as it can be exceedingly tedious to functionalize some structures with
organometallic functional groups and subsequently purify them. Exploiting the high
reactivity of the C−H bonds in tetrafluorobenzene, Chen, Qi, and Han et al.
260
synthesized
benzene-based porous polymers (Scheme 1.41) for both small gas molecule and solvent
absorption via DArP from 1,3,5-tribromobenzene and tetrakis(4-bromophenyl)methane.
Utilizing a similar strategy, Feng et al.
261
exploited the high reactivity of the C−H bonds in
tetrafluorobenzene to generate porous spirobifluoro-based copolymers (Scheme 1.41),
which exhibited suitable gas uptake capacities.

108
Scheme 1.41. Fluorinated porous organic polymers via DArP as explored by Chen, Qi, and
Han et al.
260
and by Feng et al.
261

In two reports, Koizumi et al.
262,263
further expanded the library of porous and
branched polymers via DArP. In this first, they employed 2,4,6-tris(4-bromophenyl)-1,3,5-
triazine with either tetrafluorobenzene or trifluorobenzene to generate three-arm networked
copolymers (Scheme 1.42), demonstrating that trifluorobenzene had higher CO2 capture
capacity than tetrafluorobenzene. These results ultimately also confirm that
trifluorobenzene also has sufficiently reactive C−H bonds for direct arylation via Class A
conditions.

Scheme 1.42. Synthesis of networked fluoroarene porous polymers via DArP as reported
by Koizumi et al.
262

109
In the second report, Koizumi and coworkers optimized conditions for
copolymerizations between tetrafluorobenzene and dioctylfluorene before applying the
conditions to other polymer architectures. From their evaluation of linear copolymers, they
observed that Ozawa-derived Class E conditions generated exceptional molecular weights
compared to Class C DArP conditions; however, when they subsequently adopted these
conditions for the synthesis of various branched polymer architectures, the results were
less favorable. As a result, they utilized Class C conditions with acetic acid (AcOH) for
generating a wide variety of different polymer architectures (Scheme 1.43), achieving
well-defined copolymers via detailed structural analysis with
19
F NMR.

110

Scheme 1.43. Synthesis of 3-component networked random copolymers via DArP as
explored by Koizumi et al.
263

111
Expanding to thiophene-containing substrates, Wang et al.
264
explored 8,11-
dibromodithieno[3,2-a:2’,3’-c]phenazine toward the synthesis of microporous polymers
(Scheme 1.44). The distinct advantage of this system is that it utilizes a single monomer
en route to a polymer system. The authors employed DArP Class E conditions in xylene at
various temperatures and reaction times. Naturally, the limited solubility of the porous
polymer makes characterization more difficult, but high temperature NMR of the
dispersion confirmed couplings with moderate end groups, elemental analysis confirmed
greater polymerization yields with increased time and temperature, and the red-shift of the
UV-Vis profile is consistent with extended conjugation.

Scheme 1.44. Synthesis of a phenazine-based microporous polymer as reported by Wang
et al.
264

112
Wang et al.
265
subsequently explored thienothiadiazole (TTD) as a monomer in
porous polymers with various halogenated branching arenes, including 1,3,5-
tribromobenzene, 2,2′,7,7′-tetrabromo-9,9′-spirobifluorene, and tris(4-bromophenyl)amine
(Scheme 1.45). Again, the others utilized Class E conditions in o-xylene, resulting in
polymers with extended conjugation and absorptions extending into the NIR-region.

Scheme 1.45. Synthesis of thienthiadiazole-based (TTD) conjugated porous polymers via
DArP as reported by Wang et al.
265

As discussed earlier, important considerations emerge regarding the
functionalization strategy for monomers, which was most evident with the body of DArP
literature emphasizing DPP. To generate a greater understanding of the potential for
113
branching polymers of DPP, Wang et al.
266
explored the synthesis of hyperbranched DPP
homopolymers from only Br-DPP (SCHEME). Via this single monomer, the only
accessible C−H bonds would be the β-positions on DPP, which would ultimately lead to
two main coupling pathways, homocoupling of the C−Br bonds or coupling of the β-
positions, leading to branched structures. The authors observed that Class C conditions in
either THF or DMA with a phosphine ligand lead to polymers while Class E conditions
generated no polymeric material. They confirmed that high temperatures were needed in
order to generate polymers and that THF lead to the best molecular weight upon the
screening of several different solvents, including various aromatic solvents and DMF. The
utilization of 1,2-bis(diphenylphopshino)ethane (dppe) with Pd(OAc)2 in THF with PivOH
(which outperformed AcOH and 1-AdCO2H) lead to the highest molecular weights and
yields. The authors identified homocoupling as the most significant coupling event in these
polymers, with reactions executed in DMA generating the highest branching content.
Utilizing bottom-gate/top-contact FETs, the authors observed that branching defects
significantly diminished the hold mobilities compared to well-defined homopolymers.

Scheme 1.46. Synthesis of hyperbranched DPP polymers via DArP as reported by Wang
et al.
266

114

With these observations in mind, the need to minimize defects for certain
applications like OPVs and OFETs becomes increasingly relevant. But these non-
conventional architectures highlight the advantages of the DArP method for broader
compatibility with underexplored conjugated polymer applications,
267,268
in such
applications as photoacoustic imaging or photothermal therapy.
269–271
The importance of
adapting DArP for applications not positioned in OPV or OFET technologies will
inevitably showcase the distinct advantages of this method, which has been shown to lead
to minimal metal residues. Taking advantage of this feature, Wang et al.
272
recently
explored a NIR photothermal-responsive hydrogel that undergoes structural changes in
response to NIR light based on a DArP-prepared narrow-bandgap alternating copolymer
based on DPP and EDOT. In a different report, they also explored brush copolymers for
biological imaging—noting that a 3,4-dihydro-2H-pyran protecting group was needed to
achieve good molecular weights with hydroxyl-containing side-chains.
54

Wang and coworkers application of DArP toward biomedical applications
highlights the potential scope of DArP, which avoids highly toxic organotin compounds,
but also exposes the limitations of functional groups that have been explored. Although the
next section will emphasize OPVs and OFETs, it is likely that with increased efforts, DArP
will become the superlative cross-coupling method for the generation of copolymers for a
truly broad and encompassing collection of applications in the same way that small
molecule direct arylation has led to a paradigm-shift in synthetic chemistry.

115
1.4. Evaluating Structure-Function Relationships of DArP Polymers Through
Practical Performance

DArP is often advertised as an alternative synthetic method to traditional cross-
coupling reactions for conjugated polymers for optoelectronic applications, such as
OPVs;
33,41,55
however, in many reports, DArP is seldom explored in these practical
applications or compared to benchmark materials. It is important to stress that while
conjugated polymers have been identified as excellent candidates for photovoltaics, it
cannot be said that all synthetic methods are suitable for generating polymers that are of
appropriate quality for organic electronics. It has been recognized, for example, that both
electropolymerization and chemical oxidative polymerization are both faster and more
scalable methods for achieving polymers than either Stille or DArP but generate polymers
that are unsuitable for electronic applications like OPVs.
62
Although high regioregularities
(>90%) and molecular weights (>65 kDa) can be achieved via chemical oxidative
polymerization of P3HT with ferric chloride at lower temperatures,
273
this method is not
typically used for high-quality P3HT as the residual chlorine impurities covalently
introduced into the backbone by FeCl3 can negatively influence performance.
61
Even
P3HT synthesized by different highly successful cross-coupling methods, including Stille,
Suzuki, GRIM, and Rieke, can perform differently from each other.
274
Methods that greatly
minimize homocoupling defects and produce very high regioregularities in P3HT (like
GRIM, >98%) actually do not perform much differently from lower regioregular (>94%)
P3HT in but have significantly worse thermal stability,
275–277
which is of critical
importance for commercial OPVs.
278

116
Of course—the collection of factors that influence organic electronic performance
is incredibly broad and nuanced, which include not only device architecture,
279
interlayer
materials,
280
acceptor type/loading,
281
and bulk heterojunction morphology optimization
but also polymer physical properties, such as regioregularity,
282
molecular weight,
76,283

polydispersity,
284
and end groups.
64
Nonetheless, for DArP to justifiably be considered a
viable alternative to highly prevalent and successful cross-coupling methods, its practical
performance should be evaluated more consistently overall. This is a missed opportunity
in most reports, as commonly the synthesis of existing or known polymers via DArP is
emphasized and not how these DArP polymers may differ or behave differently than Stille
or Suzuki polymers in optoelectronic devices, where subtle differences in molecular
structure may be compounded. Indeed, while many conditions have been reported, the
broad array of substrate scopes make it challenging to consistently analyze potential β-
defects and homocouplings; however, OPV or OFET performance can offer a critical
window into these nuanced differences between synthetic methods.
Work from Janssen, et al.
227
and Sommer, et al.
285
have demonstrated that
homocouplings defects are prevalent but underappreciated even in traditional (Suzuki and
Stille) polymerizations. Janssen and coworkers demonstrated that 5% homocoupling
content can dramatically diminish performance (Table 1.2). Critically, they observed many
reports in literature that may have the signatures of DPP homocoupling but are not
recognized as such, determining that 38 of 131 assessed publications may have polymers
with DPP homocoupling. Given that Stille and Suzuki are particularly well-established
synthetic methods, the observed widespread shortcomings should only further highlight the
need for thorough analysis of DArP polymers. Likewise, Sommer and coworkers
117
demonstrated that as little as 2.4% homocoupling defects can noticeably depreciate the
performance of PCDTBT (Table 1.2). It is here that we begin to observe the overall
challenges of defect analysis. While Janssen and coworkers highlight that the signature
trait of DPP homocoupling is tailing of the absorption onset, identifying potential
homocoupling defects in other substrates may certainly be more challenging. From the
work of Sommer and coworkers, it can be reasoned that traditional NMR methods (room
temperature with CDCl3) may be unable to observe these homocoupling defects and that
high temperature NMR is necessary for quantifying them, but this is not always possible
and can be complicated by signal overlap with chain termini and other peaks depending on
the substrates or extent of aggregation. A common feature of both works, however, is that
the subtle differences in the structural integrity of polymers will affect the resulting bulk
heterojunction (BHJ) morphology, which may alter optoelectronic properties in the solid
state but also likely depreciate device performance. Consequentially, the purely analytical
power of OPV or OFET device fabrication should be considered a supplement to traditional
basic optoelectronic and physical characterization for DArP polymers that may have these
defects but be challenging to identify or quantify.

Table 1.2. Analysis of three polymers, including ubiquitous homopolymer P3HT,
120
the
popular DPP acceptor in an alternating copolymer PDPPTPT,
227
and heavily investigated
PCDTBT.
285
For P3HT, a mere 0.16% BDC results in a 41% decrease in performance while
a 1.41% BDC (with a small decrease in regioregularity) results in a 69% decrease in
performance. Similarly, 5% homocoupling defects in PDPPTPT results in a 28% decrease
118
in performance while a 2.4% homocoupling content can result in a 36% decrease, though
small differences in molecular weight may contribute somewhat to this latter disparity.

Polymer
Mn
(kDa)
Homocoupling
Defects
β-
Defects
Jsc
(mA
cm-1)
Voc
(V)
FF
PCE
(%)
P3HT-
Stille
19
(Regioregularity =
93%)
0.00% 8.37 0.61 0.45 2.30
P3HT-
DArP
20
(Regioregularity =
93%)
0.00% 8.20 0.61 0.47 2.35
P3HT-
DArP
19
(Regioregularity =
92%)
0.16% 6.51 0.61 0.35 1.39
P3HT-
DArP
22
(Regioregularity =
88%)
1.41% 2.83 0.69 0.37 0.72
PDPPTPT 72
0% (“Near-
Perfect”)
0% 13.84 0.80 0.67 7.5
PDPPTPT 73 5% 0% 11.58 0.78 0.60 5.4
PCDTBT 8 0% 0% 12.15 0.86 0.50 5.22
PCDTBT 10 2.4% 0% 12.63 0.83 0.34 3.56
119
PCDTBT 23 0% 0% 13.12 0.87 0.60 6.85
PCDTBT 15 2.4% 0% 11.17 0.88 0.44 4.38

DArP is not immune to these homocoupling defects but has the added consideration
of being susceptible to unselective C-H arylation for β-coupling.
40,123
Studies by Thompson
et al.
120
have demonstrated that even as little as 0.16% β-defect concentration (BDC) can
negatively influence polymer solar cell performance. A summary of these quantified
defects and the effect on performance are provided in Table 1.2. While quantifying these
defects is possible with P3HT homopolymers and P3HT-based copolymers,
189
it can
become challenging with more complex polymers.
121
These underappreciated defects have
generally given DArP the reputation of being marginally inferior to Stille or Suzuki,
208

which stems from the side-reactions that can occur with any transition metal-catalyzed
C−H cross coupling. These reactions, which have been widely observed in small molecule
direct arylation, are troublesome for polymers due to the inability to purify or remove these
byproducts that are now embedded in the chain perpetually. Indeed, it is not uncommon to
avoid potential challenges with unselective C−H arylation and the resulting β-defects by
strategically selecting monomers that have those positions blocked. Unfortunately, such
strategies often lead to increased dihedral angles in the backbone, disrupting the
planarization, and affecting optoelectronic performance.
286
Subsequently, it is often the
strategic implementation of viable catalytic systems that will ultimately enable suitable
performance.
As discussed in Section 3, it is worth noting that—despite the negative
connotation—defects are not always undesirable. For example, β-branching is highly
120
attractive for achieving hyperbranched polymers, which are useful for applications like
light-emitting diodes.
123,169
In this case, end group defects are more detrimental.
287

Understanding the resulting physical properties of DArP polymers, especially how it
relates to synthetic methodology, can provide insight into how they perform for targeted
functions. In the following discussion, the exploration of DArP polymers in practical
applications will be further expounded and critically analyzed in order to deconvolute other
influential optoelectronic factors, such as molecular weight and device optimization.
Where applicable, performance as it relates to defect content will be emphasized. One of
the desired outcomes is a more critical investigation into the practical suitability of DArP
conditions with various substrates, where perhaps defect analysis is challenging or
insufficient but device performance can provide insight into the effectiveness of the
reaction parameters. It is worth briefly noting that small molecule direct arylation has
generated many small molecule materials for OPVs and OFETs but will not be discussed
here.
288–296
Additionally, DArP has been used for a variety of fascinating applications
beyond OPVs and OFETs, but these two popular evaluations enable better understanding
of the structure-function relationships. Beyond the work discussed above by Thompson et
al.,
120
who observed a bulky carboxylic acid can prevent β-defects and generate Stille-
convergent P3HT for OPVs (Table 1.2), investigations into the practical performance of
rr-P3HT made by DArP have been fairly limited considering the rich history of
polythiophenes.

1.4.1. Polythiophene-based Polymers via DArP for OPV and OFET Applications

121
Ma, et al.
186
reported DArP P3HT via several different conditions, mostly derived
from conditions reported from Ozawa, et al.
141
which included superheated THF, a
phosphine ligand, and Cs2CO3 (Class D). From their screening of conditions, it was
ascertained that only P(o-OMePh)3 as a ligand and Cs2CO3 as a base achieved suitably high
molecular weights (Mn = 32 kDa). Additionally, they observed that in THF as a solvent,
only H/H termini groups were detected via MALDI-TOF, suggesting C-Br/C-Br
homocoupling and dehalogenation eliminate all potential H/Br or Br/Br termini. Utilizing
a standard configuration of ITO/PEDOT:PSS/P3HT:PCBM (1:1 by weight)/LiF/Al, they
investigated P3HT in OPVs, which to the best of our knowledge, is the first evaluation of
Ozawa-derived DArP conditions in OPVs. They compared their most promising DArP
P3HT, which were synthesized by conditions analogous to Ozawa, et al.
141
except at
slightly higher temperatures (130°C) and higher catalyst loading (1.5%), with commercial
Rieke P3HT. This reference polymer performed comparably to the literature,
274
with a J sc
of 9.03 mA cm
-1
, a V oc of 0.60V, a FF of 0.58, and a PCE of 3.13%. However, DArP P3HT
had a lower Jsc of 7.98 mA cm
-1
, a V oc of 0.63V, a FF of 0.49, and a PCE of 2.46%. This
may result from the lower molecular weight of the DArP P3HT (32 kDa vs. 50 kDA), or
the lower regioregularity (90% vs. 95%), though the elevated Voc and low fill factor
suggests defects could be present.
120

In a report evaluating 4-fluorinated 3HT copolymers, Coughlin, et al.
50
generated a
P3HT homopolymer via DArP using Ozawa-derived Class E conditions with the
chloroform adduct of Pd2dba3 and PivOH. Although this was a reference polymer in an
interesting report of 4-fluorinated 3HT copolymers via DArP, this study includes one of
the few evaluations of DArP P3HT in OPVs. P3HT produced after 40h at 115°C had a
122
molecular weight of 13.0 kDa and a regioregularity of 95%. While the use of PivOH may
not prevent β-defects in Fagnou-derived Class B conditions,
119,120
it was observed by
Leclerc, et al.
121,185
that Ozawa-derived Class D conditions with 3HT prevent branching
defects, owing to the highly selective catalytic system, which comes at the cost of
superheated solvents and air-sensitive reagents compared to Fagnou-derived conditions.
Although Coughlin and coworkers do not compare this DArP P3HT to a reference P3HT,
they do observe good performance consistent with literature values.
297
With 1:1
P3HT:PC71BM ratios in a conventional device architecture of ITO/PEDOT:PSS/active
layer/Al, OPVs exhibited a Voc of 0.57V, a Jsc of 10.42 mA cm
-1
, a FF of o.61, and an
average PCE of 3.60%. Additionally, they observe SCLC hole mobilities of 9.7 x 10
-4

which is consistent with literature reports for Stille P3HT.
120,189
No EQE data was provided,
but although the PC71BM may contribute more than PC 61BM to the spectral response, these
OPV results would still suggest the polymers are of high quality, especially the fill factor.
The major difference between the work by Coughlin and coworkers and Ma and coworkers
is the presence of PivOH, which suggests a carboxylic acid additive may assist in the
generation of superior performing P3HT polymers.
Leclerc and Ozawa, et al.
185
produced DArP P3HT polymers (made via 2-bromo-
3-hexylthiophene and 2-bromo-4-hexylthiophene) via Ozawa’s conditions (Class D).
NMR analysis precluded the presence of β-defects and the polymers exhibited
exceptionally high regioregularities. Although OPV performance was not investigated,
they compare DArP P3HT to Rieke and GRIM P3HT in OFETs. Consistent with high
quality polymers, they observed mobilities for the DArP polymers to be comparable to
GRIM and Rieke P3HT. DArP P3HT from 2-bromo-3-hexylthiophene exhibited the
123
highest mobility, despite having less than half the molecular weight of the GRIM reference,
which suggests that it may exhibit superior solid state ordering (possibly enhanced by its
slightly higher regioregularity and potentially lower residual palladium and magnesium
content).
Utilizing a one pot synthesis of rr-P3HT from 3-hexylthiophene, Kanbara et al.
176

observed that the presence of TBAB—the byproduct of the bromination with TBABr3—
prevents the generation of P3HT via both Ozawa’s conditions
141
and Thompson’s
conditions.
163
They observed that modifying Thompson’s low-loading conditions to
increase catalyst loading to 0.1% and utilize THF instead of DMA did result in polymer
with PivOH as the additive. Furthermore, they achieved a regioregularity of 93% and
observed no branching defects. Although no reference P3HT was evaluated, they observed
an OPV PCE of 3.5% in an conventional configuration of ITO/PEDOT:PSS/P3HT:PCBM
(1:0.8)/LiF/Al with a BHJ thickness of 223 nm, resulting from a Jsc of 10.4 mA cm
-2
, a V oc
of 0.64 V, and a FF of 0.52. Despite the lower fill factors, the overall performance was
better than Rieke P3HT with similar thicknesses in a similar device architecture reported
by Tang et al.,
298
(Jsc = 7.6 mA cm
-2
, Voc = 0.58, FF = 0.61, PCE = 2.7%) who observed J sc
to decrease with thicker films (from 130 to 220 nm) in conventional architectures.
Although no Stille or Rieke reference was provided, this suggests that DArP P3HT via a
single-pot reaction can produce good OPV performance even with a lack of bulky
carboxylic acid as long as low reaction temperatures (60C) and low catalyst loadings
(0.1%) are employed.
Overall, work from Thompson et al.,
120
Coughlin, et al.,
50
and Kanbara et al.
176

demonstrated that well-performing OPVs comprising of DArP P3HT can be generated
124
either by Fagnou-derived Class B conditions or Ozawa-derived Class E conditions. The
performance of these polymers is consistent with minimizing molecular defects that would
negatively influencing morphology of the active layer. This is fortuitous but while it is true
P3HT is the most studied electroactive polymer, alternating copolymers, random
copolymers, and other multicomponent polymers have emerged as superior
performers.
34,192,200
Application of DArP to increasingly complicated systems, which may
be more susceptible to performance decreases that result from homocoupling or miniscule
branching, requires more careful consideration. Whereas P3HT of different homocoupling
content (regioregularity) can perform similarly to each other,
276
the same is not always true
for copolymers.
83,227,285

A report from Thompson et al.
189
demonstrated for the first time that P3HT random
analogs via DArP could perform comparably to Stille counterparts. They synthesized a
family of four P3HT-based copolymers featuring 5, 10, 15, and 20% 3-cyanothiophene
(CNT) loadings via DArP and Stille, which was outlined earlier in Scheme 1.17. They
utilized Fagnou-derived Class B conditions with bulky carboxylic acid, NDA, in DMA
with 0.25% Pd(OAc)2. Compared to DArP, the Stille polymerization required eight times
the catalyst loading to achieve similar molecular weights and it was noted that the
preparation of the corresponding CNT Stille monomer, 2-bromo-3-cyano-5-
trimethylstannylthiophene, was quite challenging with traditional methods of lithiation-
stannylation, requiring use of the Knöchel-Hauser base instead of traditionally utilized
LDA to generate a less reactive but more stable magnesiated species prior to quenching
with trimethyltin chloride.
299
The OPV results are summarized below in Table 1.3 and
show the close correlation between DArP and Stille copolymers, where DArP rivaled or
125
exceeded Stille counterparts. It is possible that more benign end groups (tin-free) and lower
residual palladium content enabled DArP contribute to improved performances. OPVs
could not be fabricated for 20% CNT loading due to low polymer solubility but hole
mobilities were comparable for the polymers.

Table 1.3. Polymers, Method, SCLC Hole Mobilities, and Photovoltaic Performance of
DArP and Stille P3HT-CNT by Thompson et al.
189

Polymer Method
μ
a
x 10
-4
,
cm
2
V
-1
s
-1

Jsc,
b
mA
cm
-1
Voc, V FF
PCE,
%
P3HT-CNT-5% Stille 1.51 7.02 0.72 0.58 2.96
P3HT-CNT-5% DArP 1.10 9.33 0.69 0.57 3.64
P3HT-CNT-10% Stille 1.03 8.16 0.75 0.55 3.33
P3HT-CNT-10% DArP 0.72 9.32 0.72 0.49 3.29
P3HT-CNT-15% Stille 0.85 7.56 0.81 0.55 3.28
P3HT-CNT-15% DArP 0.56 7.87 0.78 0.41 2.52
P3HT-CNT-20% Stille 0.62 -- -- -- --
P3HT-CNT-20% DArP 0.29 -- -- -- --
a
SCLC hole mobilities measured on neat polymer films.
b
Mismatch corrected.

Discussed above, Coughlin and coworkers
50
demonstrated the potential substrate
scope advantages of DArP, expanding the library of P3HT-analogs through the
incorporation of 3-hexyl-4-fluorothiophene (3H4FT). In terms of OPV performance, they
observed increasing Voc values corresponding with deepening of the HOMO energy up to
126
50% 3H4FT loading. These results are summarized in (Table 1.4). Due to the challenges
of synthesizing these polymers by other methods (only homopolymers via
GRIM/KTCP
190,300
or post-polymerization modification
301
have achieved anything
comparable), there was no available benchmark polymers to compare OPV performance.
Because the 3H4FT homopolymers via DArP could not make functioning devices due to
reduced solubility with the hexyl side-chain, comparing homopolymers was not feasible
either. This is certainly not a problem, as it highlights the ability for DArP to extend its
scope to interesting substrates that are challenging to produce by other methods, especially
for achieving polymer composition that closely matches the monomer feed ratio.

Table 1.4. Synthesis of random copolymers of 3-hexylthiophene with 3-hexyl-4-
fluorothiophene via DArP and resulting OPV performance by Coughlin, et al.
50

Polymer Jsc (mA cm
-1
) Voc (V) FF PCE (%)
P3HT75-co-3H4FT25 7.20 0.67 0.51 2.44
P3HT50-co-3H4FT50 4.72 0.70 0.37 1.21
P3HT25-co-3H4FT75 4.80 0.61 0.28 0.82

127
1.4.2. Analysis of OPV Performance of Conjugated Alternating Copolymers via
DArP

Recently, research efforts in conjugated polymers for photovoltaic applications
have focused on perfectly alternating copolymers or other multi-component copolymers.
The most successful conjugated polymer architecture is the perfectly alternating donor-
acceptor (D/A) copolymer, which allows for very finely-tuned electron-rich moieties and
electron-poor moieties to achieve precise control over the HOMO and LUMO, and thus,
Voc. Due to this finely-tuned nature, they may be more prone to diminished performance
resulting from homocoupling or branching defects compared to the homopolymers and
random copolymers discussed above.
An earlier but pioneering report on correlation between DArP polymers and OPV
performance for alternating copolymers was undertaken by Horie, et al.
151
They evaluated
19 distinct DArP conditions toward PCPDTBT (Figure 1.20) and compared it to a Suzuki
analog, evaluating a broad selection of phosphine ligands and solvents with traditional
Fagnou-derived conditions, including Class B (no phosphine ligand) and Class C (with
phosphine ligand) in DMA or NMP solvents. They also generated polymer with suitable
molecular weights via Class A (no acid/ligand), though no solar cells were reported. In this
case, the benzene-like BTD acceptor was halogenated. With this system, both unselective
C-H activation of the β-position and homocoupling are potential defects. Analysis of the
polymers by NMR provide evidence for possible cross-linking as well as homocoupling
defects of the CPDT donor unit. Via MALDI-TOF mass spectroscopy, the authors
confirmed the presence of homocoupling and branching defects in the polymer. It is worth
noting that Scherf et al.
302
also synthesized PCPDTBT via DArP; however, they utilized
128
acid-free Class A conditions with PCy 3HBF4 but also observed potential cross-linking
and/or homocoupling, and observed a slightly blue-shifted absorption profile compared to
a Stille analog. However, OPVs were not investigated. The PCE values reported by Horie,
et al., summarized in Figure 1.20 show that P1B and Suzuki PCDPDTBT perform
similarly in devices and the P1C polymer underperforms. When the device performance
parameters are analyzed further, it was observed that P1B exhibits a higher Jsc value but a
lower fill factor compared to the Suzuki analog. P1C on the other hand exhibits an
increased Voc value (0.64V compared to 0.61V) but lower Jsc values.

Figure 1.20. Synthesis of PCPDTBT via DArP for OPVs as detailed by Horie, et al.
151

Likely, the four-fold increase in molecular weight of the P1B polymer may
contribute to the increased Jsc compared to the Suzuki analog. Despite this significantly
elevated molecular weight, however, the P1B polymer merely performed similarly to the
Suzuki version. Consistent with other polymer trends, PCPDTBT has been shown to
provide higher charge mobilities with higher molecular weights (>30 kDa).
303
Since higher
129
molecular weights are expected to improve performance
76
but homocoupling defects and
branching defects were still observed, this suggests that defects may be the reason P1B
does not outperform Suzuki. Similarly, P1C, which had similar defects to P1B but a
comparable molecular weight to the Suzuki analog, has decreased performance. This
invaluable work from Horie and coworkers suggests that DArP, while capable of producing
high molecular weights, may generate defects that can affect practical performance. It is
worth noting that of the homocoupling defects observed, only CPDT homocouplings were
observed. This C−H/C−H coupling may be promoted by the catalyst, as the Pd(OAc)2
loadings were 10% in all cases, which may produce homocoupling events in order to form
the active palladium species (Scheme 1.14)
184
or lead to increased opportunities for
disproportionation.
Kanbara et al.
142
also compared the practical performance of DArP polymers
against a Suzuki analog. The target polymer in this case was PEDOTF, a polymer
composed of EDOT copolymerized with dioctyl-fluorene (Figure 1.21). Fluorene-based
copolymers are attractive for OPVs for their high charge carrier mobilities and high
absorption coefficients in alternating systems.
304
The optimization of this polymer consists
of four reports by Kanbara and coworkers.
142,146,148,305
The first emphasized optimization
of the catalytic system via conventional heating in an oil bath, with low Pd(OAc)2 loadings
of 1% with 1-adamantanecarboxylic acid (1-AdCO2H) as an additive in a Fagnou-derived
phosphine-free DArP (Class B).
146
They achieved polymers with a molecular weight
greater than 45 kDa. This was followed by optimization of the reaction via microwave
heating with temperatures below the boiling point of the solvent, DMA.
305
Switching from
a traditional mix of base and carboxylic acid, they utilized potassium pivalate (PivOK),
130
which they found advantageous as a base and a carboxylate ligand. With just 30 minutes
of microwave heating at 80°C, they achieved polymers with a molecular weight of 147
kDa with 1% Pd(OAc)2 after washing the polymer with DMF. In the third report, they
compared the best polymers from the first two reports in OFETs and OPVs.
142

Overwhelmingly, the microwaved DArP polymer outperformed both conventional DArP
and the Suzuki analog. P2B
MW
was over eight and half times as large as the Suzuki analog,
and correspondingly performs about eight and a half times better in solar cells. The authors
observed no homocoupling or branching defects in the DArP polymers, though did observe
homocoupling defects in the Suzuki analog. Due to the strategic selection of monomers,
some typical considerations for DArP are avoided here. Namely, unselective C-H
activation is unlikely due to the blocked β-positions via utilization of EDOT. Additionally,
the donor substrate does not have acidic C-H bonds for potential cross-linking. Importantly,
these conditions demonstrate that a phosphine ligand is not always necessary to suppress
homocoupling defects with careful selection of the reaction parameters and monomers.
Some additional advantages that are conveyed in this report are the lack of residual
phosphine in the DArP polymers compared to the Suzuki polymer and the reduced residual
palladium content due to the lower catalyst loading utilized for DArP (1% vs. 5%). What
remains unanswered is whether optimized Suzuki conditions, which may achieve fewer
homocoupling events and higher molecular weight, would still perform inferiorly
compared to DArP, as the molecular weight dependence of performance is a complicating
variable. But in merely achieving such high quality polymer via DArP, the potential
benefits of this method are highlighted.

131

Figure 1.21. Synthesis of PEDOTF via DArP (with microwave (B
MW
) and conventional
heating) for OPVs and OFETs by Kanbara, et al.
142

In the fourth report, the authors evaluate the effects of terminal structure, polymer
purity (residual palladium), and molecular weight of PEDOTF via DArP.
148
They observed
Br terminal groups to significantly decrease polymer performance from 4.6% to 2.9%.
Residual palladium had an influence on long-term stability. They ultimately confirmed
observations from others that—compared to C−Br end groups—C−H end groups can lead
to higher absorption coefficients, higher photoluminescence intensities, faster and less
dispersive charge recombination, and superior solar cell performance highlighted by
improved fill factors.
64
An advantage of DArP is that it could produce more benign C-H
end groups but the occurrence and influence of C−Br termini will also inevitably affect
performance.
134

Hoping to address the substrate limitations highlighted by Kanbara and coworkers
described above, Yang and Li, et al.
306
adopted microwave and conventional heating
conditions on two substrates with available β-positions. This indacenodithiophene-
132
quinoxaline copolymer (Figure 1.22) was generated via DArP with microwave heating,
DArP with conventional heating, and Stille polycondensation. The authors chose three
polymers that exhibited molecular weights that were comparable (ranging from 22 kDA to
27 kDa). In this case, they observed DArP with conventional heating and Stille to exhibit
limited defects as determined by NMR and MALDI-TOF as well as comparable OPV
performance and SCLC hole mobilities. With microwave heating, they observed both
insoluble material and defects—including both homocoupling and branching defects.
Additionally, the UV-Vis absorption profile of the P3B
MW
polymer is blue-shifted and
loses definition of the 425 nm peak. They conclude that microwave heating does
significantly accelerate the reaction rate but simultaneously stimulates β-activation,
yielding cross-linking and ill-defined structures. Consequently, the microwave P3B
MW

polymer exhibits lower efficiencies and low SCLC hole mobilities. On the other hand, the
conventional heating with DArP and Stille polymers perform comparably, with the P3B
polymer exhibiting slightly higher OPV performance and SCLC hole mobilities, consistent
with its suitable structure and slightly higher molecular weight. As can be seen from this
report, DArP is again capable of limited homocoupling defects with phosphine-free
conditions (Class B) but when C-H activation of β-positions is possible, microwave heating
may lead to suboptimal polymers due to its high reactivity.

133

Figure 1.22. Synthesis of IDT-TQ Polymer (P3) via DArP (with microwave (P3B
MW
) and
conventional heating for OPVs and SCLC Hole Mobilities by Yang and Li, et al.
306

Zhishan Bo, et al.,
307
who also noted the lack of practical evaluation of DArP
polymers, reported a comparison of DArP with Suzuki analogs. They utilized Pd(OAc)2-
catalyzed Class A DarP conditions with PCy 3HBF4 in DMA to generate two polymers,
HXS-1 and PDFCDTBT (Figure 1.23) with an Mn of 10 kDa and 11 kDa, respectively.
Via these conditions, the authors observed both potential cross-linking defects and
homocoupling in both polymers via DArP. Compared to the two Suzuki analogs,
308,309
the
DArP polymers also had lower molecular weights. In OPVs, they observed that Suzuki P4
had an efficiency of 3.60% while DArP P5C had an efficiency of 0.36%. While the
difference in molecular weight could contribute to this disparity, the dramatic drop that
was observed in Jsc, FF, and even Voc suggests the presence of significant defects.
Similarly, Suzuki P5 had an PCE of 2.88%, while the DArP version, P5C, had an efficiency
134
of 0.78%. In this case, the Voc and FF did not decrease as significantly; however, the Jsc
values dropped from 8.6 to 2.58 mA cm
-2
. Due to the comparable molecular weights, this
suggests structural defects are primarily the cause of this performance decrease.

Figure 1.23. Synthesis of HXS-1 (P4) and PDFCDTBT (P5) via DArP for OPVs by
Zhishan Bo, et al.
307

Heeger, et al.
310
reported a new conjugated polymer via DArP featuring
thienopyrrolodione (TPD) copolymerized with a terthiophene (Figure 1.24) for OPVs.
They also synthesized a copolymer with a bithiophene utilizing the same alkyl side-chains.
Both polymers were synthesized by Ozawa-derived Class D conditions, which utilized the
Herrmann-Beller catalyst, P(o-MeOPh)3, and Cs2CO3 in superheated THF without a
carboxylic acid. OPVs were fabricated in a glove box in a configuration with
ITO/PEDOT:PSS/Polymer:PC71BM/TiO2/Al prior to being encapsulated for measurement
in air. They opted to brominate the donor instead of the acceptor. The authors do not discuss
135
the possibility of either homocoupling or potential branching defects in this report;
however, in a related work, Leclerc, et al.
311
reported the copolymerization of a bithiophene
monomer with TPD via similar DArP conditions and observed potentially 2%
homocoupling content, though this homocoupling was also observed in Stille polymers.
Importantly, DArP generated polymers of superior molecular weight to Stille. As observed
in Figure 1.24, with additive-free processing conditions, the DArP polymers exhibit low
PCE values. The authors were able to dramatically enhance the performance with the
addition of 1-chloronathalene (CN). Although they did not compare these DArP polymers
to a Stille reference, Wei, et al.
312
reported a similar bithiophene-TPD copolymer via Stille
where the only difference was the branched chain on TPD. Although they produced devices
with PC61BM instead of PC71BM, they observed significantly higher fill factors and Jsc
values with additive-free OPVs; however, there are several possible reasons for this
disparity, which may include the selection of TPD side-chain, the TiO2 interlayer, or
homocoupling.

136
Figure 1.24. Synthesis of TPD and Bithiophene (P6) and Terthiophene (P7) copolymers
by Heeger, et al.
310

Heeger, et al.
313
subsequently reported a similar polymer but modified the central
heteroatom of the terthiophene from sulfur to selenium, generating a selenophene-
containing copolymer with TPD (Figure 1.25). This selenophene analog performed
considerably better than the terthiophene discussed above in OPVs, achieving high fill
factors and Jsc values without additives. It is worth noting that for these OPVs, no TiO2
layer was utilized as was previously incorporated as an electron-transfer layer (ETL),
which may contribute to the observed differences in performance.

Figure 1.25. Synthesis of TPD and bisthienylselenophene copolymer (P8) for OPVs by
Heeger, et al.
313

Leclerc, et al.
256
synthesized a series of phenanthridinone-based copolymers for
OPVs via DArP, which was touched on above regarding their pursuit for terpolymers. They
137
studied two copolymers and one terpolymer (terpolymer shown in Scheme 1.38). The two
alternating copolymers (Figure 1.26), consists of phenanthridinone-derived monomer
copolymerized with DPP. These were synthesized using conditions derived from another
work by Leclerc, et al.
55
which feature PdCl2(PPh3)2 instead of the traditional Herrmann-
Beller catalyst or Pd2dba3, but are otherwise analogous to Ozawa-derived Class E
conditions with PivOH. They also generated Suzuki analogs, which were compared to
DArP in OPVs. They generated OPVs in an inverted architecture with
ITO/PEI:GDE/Polymer:PC61BM/MoO3/Ag. They utilized Suzuki analogs for comparison
of the optoelectronic properties. For P9, the DArP and Suzuki copolymers performed
similarly, despite the Suzuki polymer having an Mn three times greater, a much narrower
PDI (Ð = 2.0 vs. 4.0), and was end-capped with phenyl boronic acid and bromobenzene.
This highlights the potential for DArP to yield exceptional quality polymers that might
outperform Suzuki due perhaps to minimal defects, more favorable end groups, and lower
residual palladium content. Interestingly, for P10, the DArP polymer outperformed the
Suzuki counterpart significantly. Upon inspection of the UV-Vis absorption profiles,
Suzuki P10 appears to exhibit tailing of the absorption onset, which may suggest possible
homocoupling defects via Suzuki polymerization. Regardless, both sets of devices
highlight the potential for DArP to exceed Suzuki in OPV performance.

138

Figure 1.26. Synthesis of phenanthridinone-based copolymers with DPP for OPVs by
Leclerc, et al.
256

To provide a more definitive evaluation of the influence of DArP conditions on
OPV polymer quality, Livi, et al.
83
evaluated a diverse set of DArP conditions, which
included both Fagnou- and Ozawa-derived conditions on a model system. The target
polymer was poly[(2,5-bis(2-hexyldecyloxy)phenylene)-alt-(4,7-di(thiophen-2-
yl)benzo[c][1,2,5]thiadiazole)], which was illustrated in Scheme 1.27 as part of the
discussion regarding optimal functional group assignment. The authors evaluated two
distinct routes toward PPDTBT, selecting the optimal route depending on the DArP
classification incorporated and subsequently evaluating the polymers for homocoupling
and branching defects. PPDTBT is closely related to a high OPV performance (>9%)
139
analog,
84
where the benzothiadiazole is fluorinated; however, this higher performance on
ITO did not translate to ITO-free large area roll-to-roll processed solar cells, where the
non-fluorinated analog performed better.
314
Thus, PPDTBT was evaluated for DArP.
As discussed above in Section 2, the functionalization strategy in DArP—which
component is halogenated and which component is C-H activated, can have a dramatic
influence on the resulting polymer physical properties. Whereas the discussion there
emphasized polymer molecular weight, yield, and quality, the emphasis in the work from
Livi and coworkers is the suitability for OPV-quality materials. Toward the synthesis of
this polymer, the authors utilized a combination of small molecule direct arylation and
DArP to achieve the target polymer in four steps instead of the six steps required for the
Still analog (Scheme 1.4). From a series of ten reaction protocols derived from a variety
of reported conditions in literature, the authors observed that Fagnou-derived Class B and
Class C conditions both generated some level of homocoupling defects in the main chain.
They observed Class B conditions to generate both acceptor/acceptor and donor/donor
homocouplings, while Class C conditions with PCy3HBF4 produced only acceptor/acceptor
couplings. These defects ultimately lowered the OPV performance of the resulting devices;
however, Ozawa-derived Class E conditions with NDA did not produce defects,
subsequently resulting in OPVs that rivaled or outperformed Stille counterparts. The OPV
results are summarized below in Table 1.5.

140
Table 1.5. Performance of PPDTBT polymers synthesized via different DArP conditions
utilized in ITO-free flexible substrates or glass ITO substrates for OPVs as investigated by
Livi et al.
83

Entry
a
Route
b
Mn
(kDa)
hc
c
β-
linkage
Method
d
Jsc
(mA
cm
-1
)
Voc
(V)
FF PCE
(%)
P11B X 14 A, D None R2R 3.61 0.79 0.30 0.85
ITO 7.98 0.81 0.49 3.22
P11C X 15 A
(min.)
None R2R 3.26 0.71 0.29 0.67
ITO 6.62 0.77 0.43 2.17
P11E Y 15 None None R2R 10.52 0.72 0.45 3.4
ITO 9.83 0.80 0.58 4.57
P11X X 16 N/A None R2R 8.88 0.72 0.46 2.9
ITO 9.63 0.80 0.58 4.45
P11Y Y 59 N/A None R2R 11.54 0.73 0.45 3.8
ITO 10.22 0.81 0.60 4.92
141
a
Entry regarding PPDTBT, letter is the DArP classification utilized.
b
Route is the
functionalization strategy as shown in Scheme 1.27.
c
Presence of homocoupling defects,
either acceptor (A) or donor (D) type defects.
d
Method of OPV fabrication, either roll-to-
roll (R2R) coated on ITO-free flexible substrates with 400 nm thick active-layers or glass
ITO substrates (ITO) via spin-coating for thicknesses around 100-110 nm.

Expanding on these findings, Marks et al.
51
explored the application of DArP Class
E conditions on polymers that have higher performance than PPDTBT in glass ITO OPVs.
They utilized 0.5% Pd2dba3‧CHCl3 with 2% P(o-OMePh)3 with 3 equiv. of Cs2CO3 and a
designer carboxylic acid additive, 2,2-diethylhexanoic acid, which they combined with
monomers in green solvent, MeTHF, to generate copolymers that rivaled or exceeded
DArP copolymers in OPVs, which is provided in Table 1.6. These general conditions
proved compatible with explored β-protected acceptor moieties and donors with available
β-positions. The donors were brominated, which lower the activation barrier of those
associated β-positions, highlighting the advantages of the bulky carboxylic acid for
minimizing these defects.

Table 1.6. Performance of DArP and Stille alternating copolymers evaluated by Marks et
al.
51
Molecular weights were comparable.
142

Entry Method Jsc (mA cm
-1
) Voc (V) FF PCE (%)
P12 DArP 15.5 0.77 0.68 8.19
Stille 15.0 0.78 0.70 8.24
P13 DArP 10.0 0.99 0.58 5.71
Stille 8.9 0.99 0.58 5.10
P14 DArP 12.9 0.81 0.66 6.86
Stille 13.0 0.79 0.70 7.20

These efficiencies are among the highest to be achieved via DArP polymers.
Importantly, the comparison with the ubiquitous Stille polymerization method enables
careful evaluation of the optoelectronic properties, importantly, the absence of β-defects
can be identified by suitable OPV performance, indicative of excellent morphology
derived from minimal defects in the polymeric structure. This success was—as
observed by Livi et al.
83
—in part due to the incorporation of a bulky carboxylic
ligand and the utilization of Class E conditions derived from by Ozawa et al.
154,155

However, the utilization of other reaction parameters have also recently led to
success. Expanding on their observations of optimal solvents for electron-rich and
143
electron-poor moieties discussed above, Kanbara et al.
244
utilized Pd(PCy3)2 with
PivOH in a toluene system to generated TPD/fluorene copolymers that exhibited a
PCE of 5.1% with a simple architecture, which was comparable to the 5.2% efficiency
reported in a separate report.
315
Similarly, Wang et al.
316
synthesized high-
performance poly(5,6-difluoro-2,1,3-benzo-thiadiazole-alt-quarternary
thiophene(Th4)) (denoted as PDFBT-Th4), which has recently achieved PCE values
of 10% in single-junction OPVs with hole mobilities of 1.92 cm
2
V
-1
s
-1
. Wang and
coworkers synthesized this polymer by Stille and DArP (Class E conditions with PivOH in
o-xylene), utilizing small molecule direct arylation to eliminate two steps as Livi et al.
83

did, and observed convergence of the optoelectronic properties; however, DArP
significantly outperformed Stille PDFBT-TH4 (4.1% vs. 3.1%), which resulted from a Voc
difference of 0.77 V for DArP and 0.52 V for Stille. Stille PDFBT-TH4 had a higher fill
factor but similar Jsc values. The reason for this large Voc difference is not clear but the
authors stated no branching evidence was visible via NMR. These works highlights that
attention to all details, from additives to catalyst to solvents, are all necessary for
the realization of good OPV performance by DArP materials.

1.4.3. Elucidating the Quality of DArP Conjugated Polymers via OFET
Performance

While the library of high mobility p-type conjugated polymers continues to expand,
the demand for n-type or ambipolar polymers also grows.
73,317
DArP has shown
considerable promise as a method toward well-performing organic field-effect transistors
(OFET) devices, often with some p-type character,
87,185,230,296,318
even for stretchable
144
electronics,
319
but also increasingly with n-type and ambipolar behavior.
48
As evident from
the evaluation of functional group assignment strategies discussed earlier, the DPP
structural motif is well-explored and is perhaps one of the most well-explored motifs in
OFETs,
320
with increased efforts in utilizing it for n-type and ambipolar materials. Indeed,
DPP-based copolymers have achieved excellent carrier mobilities through facile side-chain
engineering and strategic utilization of a secondary comonomer.
321–324
These materials,
with mobilities that can regularly exceed 10 cm
2
V
-1
s
-1
, are commonly prepared via Stille
or Suzuki polymerization. Already capable of matching or outperforming mobilities of
amorphous silicon FETs, the application of DArP for OFET materials would only further
enhance the attractiveness of these classes of polymers.
In the following section, impactful developments in the design and pursuit of DArP
materials for OFETs, particularly n-type or ambipolar polymers, will be evaluated. A
comparative analysis of OFETs via DArP can be challenging to perform without a Stille
or Suzuki references due to the differences in device architecture. Commonly, OFETs are
fabricated with the gate at the bottom (though top-gate is also widely used with orthogonal
solvents) but two major configurations exist for the source/drain, either top contact devices,
which can be achieved with shadow-masking of the substrate, or bottom contact devices
where electrodes are patterned first and the organic films are deposited on top.
325
The latter
is usually considered more attractive but differences can emerge, particularly with respect
to mobilities as noted by Street and Salleo.
326
For example, it has been observed that
mobilities achieved with a bottom-gate/bottom-contact (BGBC) geometry can be increased
considerably (from 0.025 to 0.87 cm
2
V
-1
s
-1
) by adopting a bottom-gate/top-contact
145
(BGTC) geometry.
327
Where applicable, the discussion of OFET performance will
emphasize its correlation to defects or with comparisons to benchmark materials.
Via Stille and Suzuki polymerization methods, W.H. Jo et al.
219
explored n-type
copolymers based on DPP and fluorinated benzene, generating four copolymers from
benzene, fluorobenzene, difluorobenzene, and tetrafluorobenzene. They achieved the best
electron mobilities (2.36 cm
2
V
-1
s
-1
) with tetrafluorobenzene-based copolymer P15
(Figure 1.27), in a BGTC transistor with gold source/drains and doped silicon and SiO2 as
the gate electrode and gate dielectric respectively. P15 derivatives with different side-
chains have since been generated via DArP by various groups. Sommer et al.
226
generated
a DArP (Class B) version with near double the molecular weight of the Stille version from
Jo and coworkers but observed average OFET electron mobilities of 0.5 cm
2
V
-1
s
-1
with
top-gate, bottom-contact (TGBC) transistors. They observed that mobilities improved with
molecular weight but the decreased performance compared to the Stille version could be
attributed to the presence of homocoupling defects, which may stem from debromination
events. Concurrently, Wang et al.
220
explored well-defined P15 by DArP Class E
conditions which generated minimal defects. Utilizing a BGTC geometry, the authors
observed ambipolar behavior, with balanced hole and electron mobilities of 1x10
-2
cm
2
V
-
1
s
-1
, where electron mobility could be improved to 3x10
-2
cm
2
V
-1
s
-1
at the cost of hole
mobility with thermal annealing. They attributed the poorer performance to the fabrication
of the OFETs in ambient conditions, which can dramatically diminish performance
compared to fabrication in a glove box.

146

Figure 1.27. Alternating copolymer P15 consisting of DPP and TFB, often referred to as
PDPPTFB, PDPPTB, PDPPF4B or PDPPTh2F4, where the R-group utilized is (a) 2-
hexyldecyl as explored by Jo et al.,
219
(b) 2-octyldodecyl as explored by Sommer et al.
226

and Wang et al.
220

The advantages of the DPP motif has cemented its popularity in conjugated and
small molecule systems. DPP-based polymers have previously been shown to provide high
electron mobilities exceeding 1 cm
2
V
-1
s
-1
, but require isolation of a organoboron-
functionalized DPP substrate.
328
Briefly mentioned early, Leclerc et al.
225
explored the
synthesis of three different DPP homopolymers via DArP, generating one species via two
distinct functionalization strategies in order to achieve four polymers. These monomers
and the resulting polymers are provided in Scheme 1.47. As particularly relevant to this
section, the authors noted that NMR characterization of defects was prohibitively
challenging, therefore they utilized optoelectronic properties and OFET performance to
gauge polymer quality. The authors first synthesized P16 from more practically accessible
brominated branched-chain DPP and an unfunctionalized straight-chain DPP. They
achieved Mn values of 16 kDa but observed poor solubility. Adding methyl groups to the
DPP monomers en route to P17 only lead to M n values of 6 kDa, which may stem from the
steric hindrance of the β-methyls. Subsequently, they evaluated which DPP methyl was
147
preventing effective polymerization, achieving Mn values for P19 that were three times
larger than P18. This suggests that either halogenation promotes β-activation en route to
P18 or C−H activation is less favorable with β-methyl steric influence. Indeed, both
theories have been supported by subsequent work from Leclerc et al.,
232
who determined
there are lower activation barriers for β-positions on halogenated substrates and from
Sommer et al.
259
who exploited this unfavorable steric interaction to generate block
copolymers.

Scheme 1.47. Synthesis of DPP-based homopolymers, P16-P19, via DArP of two distinct
DPP monomers as reported by Leclerc et al.
225
P18 and P19 are synthesized via two
different functionalization strategies.
The authors observed that P18 could possess homocoupling or branching defects
but NMR analysis was not helpful for identifying these defects. As a result, optoelectronic
properties were evaluated. Consistent with homocoupling, the authors observed tailing of
the absorption onset for P17 but other polymers were less conclusive. As a definitive
148
evaluation of polymer quality, the authors fabricated BGBC transistors for p-type mobility
and TGBC transistors for both n-type and p-type mobilities. These polymers demonstrated
ambipolar character, though P17 underperformed compared to the other polymers. The
results for TGBC transistors are summarized in Table 1.7. With similar molecular weights,
P16 and P18 had comparable performance; however, P19, which had about three times
higher molecular weight, achieved much higher hole mobilities (0.92 cm
2
V
-1
s
-1
), though
electron mobilities were correspondingly lower.

Table 1.7. OFET Performance (TGBC) observed by Leclerc et al.
225
for DPP-based
polymers as outlined in Scheme 1.47.
Polymer μh / cm
2
V
-1
s
-1
μe / cm
2
V
-1
s
-1

P16 0.13 0.19
P17 0.0055 0.0041
P18 0.27 0.083
P19 0.92 0.011

As discussed earlier, the functionalization strategy for DArP is of critical
importance. As briefly mentioned earlier in Scheme 1.26, Li et al.
229
observed dramatically
different OFET mobilities depending on the functionalization route. With brominated DPP
and unfunctionalized bithiazole (BTz), they observed significantly higher hole and electron
mobilities as outlined in Table 1.8. These differences were attributed to defects, which
were observed via both copolymers routes but were present to a greater degree in P20. A
similar polymer reported by Reichmanis et al.
329
where 5-decylheptadecyl side-chains were
149
employed was synthesized by Stille and gave an electron mobility up to 0.3 cm
2
V
-1
s
-1
in
OFETs. The reasons for the better performance via the DArP counterpart may be due to
the different side-chains but also the minimization of defects.

Table 1.8. OFET performance (TGBC), annealed at different temperatures, as observed by
Li et al.
229
for DPP/BTz copolymers via different functionalization strategies, previously
outlined in Scheme 1.26.

Polymer μh / cm
2
V
-1
s
-1
μe / cm
2
V
-1
s
-1

P20 (200°C) 0.00038 0.023
P20 (250°C) 0.0020 0.024
P21 (200°C) 0.0070 0.079
P21 (250°C) 0.048 0.42

Geng, Tian, and Zhang, et al.
330
also evaluated a DPP-based alternating polymer
for use in ambipolar OFETs. This polymer, copolymerized from DPP and (E)-1,2-bis(3,4-
difluorothien-2-yl)ethene (4FTVT), is provided in Figure 1.28. They synthesized this
polymer with Ozawa-derived Class E conditions with PivOH in Toluene. They observed
150
that the superior reactivity of 4FTVT enabled high molecular weights even when fairly
diluted (0.01M) compared to typical Ozawa conditions. They attempted to synthesize the
non-fluorinated analog via DArP but observed that the reaction did not work. As a result,
they studied the effect of fluorination by producing the analog via Stille. Although no Stille
analog of the 4FTVT copolymer was made, the authors observe that the mobilities were
among the best in the literature for any synthetic method,
193,219,331,332
suggesting polymer
quality via DArP was suitable. Interestingly, the DPP copolymer synthesized via Stille
exhibited tailing of the absorption onset, which may suggest homocoupling introduced by
Stille,
227
which was not observed for the DArP polymer.

Figure 1.28. Synthesis of DPP and 4FTVT copolymers via DArP for OFETs by Geng,
Tian, and Zhang, et al.
330

Moving beyond ubiquitous DPP, other dye-type structures have also been explored
in DArP, most notably isoindigo-based copolymers. Leclerc et al.
156
synthesized an
isoindigo and TPD copolymer via DArP, which were challenging to generate via Suzuki
151
methods. Although no direct comparisons were investigated, the electron mobilities for
isoindigo copolymerized with TPD and the bi-substituted version, bithienopyrroletetrone
(BTPD), were 0.0002 cm
2
V
-1
s
-1
and 0.0025 respectively in a BGBC geometry. In a
subsequent report, Leclerc et al.
87
generated copolymers of isoindigo and EDOT, which
achieved OFET hole mobilities of 0.003 cm
2
V
-1
s
-1
in a BGTC architecture. Wang et al.
296

explored the thiophene analogs of isoindigo, thienisoindigo, which they copolymerized
with a variety of substrates, three of which they explored in OFETs, tetrafluorobenzene
benzothiadiazole, and diflurobenzothiadiazole, which in a BGTC geometry achieved hole
mobilities of 0.0018, 0.17, and 0.001 respectively. They observed that the copolymer with
benzothiadiazole had previous been made via Suzuki and its hole mobility performance
was similar to the DArP version they investigated.
For achieving strong n-type polymers, few viable organic molecules are as popular
as naphthalene diimide (NDI),
194
which is the simplest structure of the rylene diimide
family,
333,334
which is increasingly explored in DArP.
335
It is most commonly synthesized
by Stille polycondensation. The first example of NDI-based copolymers via DArP was
reported by Horie et al.,
151
who applied their optimized Class B conditions described above
for the synthesis of an NDI copolymer with 4,4-bis(2-ethylhexyl)-4H-cyclopenta[2,1-b
;3,4-b′]dithiophene (CPDT) via Class B conditions. They generated low molecular weight
material and identified potential decomposition of the NDI unit, highlighting the need for
further optimization. Addressing this issue, Sommer, et al.
82,132,133,259,336,337
would explore
and optimize the DArP conditions toward the synthesis of well-defined NDI polymers in a
series of works. In particularly, they have had significant success utilizing bithiophene to
generate PNDIT2 (structure provided in Scheme 1.34) with both high and controllable
152
molecular weights, which were confirmed to be defect-free via detailed NMR studies.
82,132

Attractively, the conditions were phosphine-free Class B conditions, utilizing Pd2dba3,
PivOH, and an aromatic solvent, which ultimately also served as a chain termination
coupling and relatively benign end group. Furthermore, electron mobilities, which were
achieved via off-center spin-coating, achieved values near 3 cm
2
V
-1
s
-1
which were
achieved with TGBC geometry. These are among the highest reported for solution-
processed materials, and a two-fold improvement on their previously explored electron
mobility copolymer via DArP, a NDI and tetrafluorobenzene copolymer that achieved
electron mobilities of 1.3 cm
2
V
-1
s
-1
.
337
Subsequent reports would further optimize the
reaction parameters and further investigate this attractive motif. Much of this work has
been discussed in preceding sections, as the findings regarding solvent effects, chain
termination, and catalytic systems are applicable as general guidelines and considerations
for the application of DArP.
Other variations of NDI have been explored as well. Kanbara et al.
338

copolymerized EDOT-flanked NDI with dioctylfluorene via DArP Class B conditions,
observing ambipolar charge transfer behavior in OFETs, with a μh value of 5.3 x 10
-7
cm
2

V
-1
s
-1
and a μe value of 2.3 x 10
-6
cm
2
V
-1
s
-1
. Wang et al.
318
explored thienyl-flanked NDI
units, referred to herein as NDIT units that were copolymerized utilizing Class E
conditions, which generated suitably high molecular weight copolymers with EDOT, DPP,
and TTD (thienothiadiazole). They observed no OFET behavior with EDOT copolymers.
And despite the narrow bandgaps (<1.1 eV) for both DPP and TTD-based NDIT
copolymers, neither polymer exhibited electron mobility in bottom-gate, bottom-contact
153
(BGBC) OTFTs. The authors reasoned that this may be due to the architecture utilized, or
poor passivation of the SiO2/Si surface.
While novel NDI-derived substrates continue to emerge, the need to evaluate such
materials in electronic applications becomes more important for evaluating the potential of
DArP.
335,339
Nonetheless, DArP has been shown to be compatible with state-of-the-art
charge transport materials. Through these few case studies, the potential for high quality
and well-defined DArP polymers is abundant. Collectively, the results thus far demonstrate
that DArP polymers can perform quite well in OFETs and OPVs with careful selection of
the monomers and conditions. Continued effort is necessary to confirm superior
performance against Stille or Suzuki counterparts across a broader range of substrates.

1.5. Catalytic Oxidative Direct Arylation Polymerization

As evident from the preceding discussion, the emergence and application of direct
arylation as a viable synthetic method toward new C−C bonds has had a significant and
far-reaching impact on modern conjugated polymer chemistry. The advantages of directly
activating C−H bonds without pre-functionalization is extraordinarily attractive, provided
high selectivity and good reactivity are concurrently achieved. In the pursuit of increasingly
complex structural designs and novel materials, the development of expedient, dependable,
and efficient methods will always be vital. A distinct advantage of direct arylation is the
need to bypass the metalation, which is often accompanied by reactions with flammable
and dangerous organolithium reagents under air- and water-sensitive cryogenic conditions.
While certainly more convenient, the second coupling partner does need to be halogenated,
which is not always convenient either. Indeed, the most atom economical route toward new
154
C−C bonds is inevitably direct C−H/C−H activation, which would eliminate not only the
metalation step but also the halogenation step (Figure 1.29). Although DArP is
considerably more adherent to the principles of green chemistry, it should not go
unrecognized that organic halides and halogens themselves are also widely regarded as
environmental hazards, which would make the avoidance of such hazardous materials
particularly attractive. To this end, oxidative direct arylation toward consecutive bond
formation from unfunctionalized substrates would be the most atom economical route
toward conjugated polymers.

Figure 1.29. Comparison of the synthetic steps toward monomers compatible with specific
polymerization methods and the effective, stoichiometric side byproducts of the
polymerization. Barring termination events, the potential end groups of these eventual
polymers are also noted.
It is important to note that historically prevalent electrochemical and chemical
oxidative polymerization methods would be less likely to lead to well-defined materials
because they oxidize the substrate itself. Specifically, both ferric chloride
60
and
155
oxovanadium
340
have been used to generate polythiophenes but because they oxidize the
substrate,
341,342
defects are likely unpreventable and poor structural control is a
consequence of the method. It has been demonstrated that ferric chloride generates
polymers with both iron and chlorine impurities in the polymer backbone,
61
which will
assuredly affect its performance in organic electronics. Furthermore, many substrates are
not compatible with oxidative methods. For example, it was observed by Roncali et al.
63

that 3-fluoro-3-hexylthiophene is incompatible with electropolymerization with desired
substrates, requiring substitution with two flanking thienyl groups for polymerization. To
this end, a catalytic oxidative direct arylation is preferential, as it could provide better
control of polymer quality by oxidizing the catalyst as opposed to the substrate; however,
as identified by Fagnou et al.,
343
there exist significant challenges for cross-coupling that
does not feature preactivation of the substrate, namely issues with reactivity,
regioselectivity, and unwanted homocoupling defects which consume reagents.
Although recent efforts in applying this type of synthetic strategy toward
conjugated polymers will be emphasized, there is a considerable body of literature for small
molecule oxidative cross-coupling reactions for various aryl species,
100,101,344–350
with a
recent review from You et al.
351
covering oxidative C−H/C−H coupling reactions from
1960 through to mid-2016. As with DArP, much of the mechanistic understanding of this
method is derived from studies and theoretical work on small molecule systems.
Ultimately, oxidative direct arylation is another form of metal-mediated C−H activation,
which discussed above (Figure 1.5), has had several proposed mechanisms, which include
electrophilic aromatic substitution (SEAr),
352,353
concerted metalation-deprotonation
(CMD),
354,114,102
and σ-bond metathesis.
355,356
The key differences between this method
156
and direct arylation relate to the formation of the arylpalladium species, as an electrophilic
organohalide functionality is no longer available for oxidative addition of a palladium (o)
species. As a result, the active catalytic species is a palladium (II), which forms an
arylpalladium species via a C−H substitution, which may require a strong acid or
coordination to achieve (Scheme 1.48). Thus, it is generally surmised that harsher
conditions are necessary for achieving these transitions states. Additionally, upon reductive
elimination of the catalyst, the Pd(0) species must be re-oxidized to the active Pd(II)
species, lest it precipitate out as palladium black. Different strategies have emerged for
this, including utilizing stochiometric metals, employing a combination of oxygen and a
metal, where the metal (e.g. copper or silver) oxidizes the palladium to Pd(II) and is then
oxidized itself by oxygen, enabling catalytic amounts of the metal species. Recently, even
employing oxygen (O2) as the sole oxidant has proven successful, though special
consideration for the oxygen partial pressure, and the resulting influence of ligands,
catalysts, must be considered.
351
The need for an arylpalladium species without pre-
functionalization and the resulting need to re-oxidize the palladium species are the two
signature differences from DArP that have made the broad applicability of this method to
polymers more challenging.
It has been well-established that oxidative C−H/C−H coupling is compatible with
thiophene derivatives. Mori et al.
357
reported the selective homocoupling of thiophenes via
PdCl2(PhCN)2 with AgF as both the promoter and oxidant in DMSO as a solvent, which
they later improved with a combination of AgNO3 and KF.
358
Many functional groups were
tolerant under these conditions, including C−Br bonds and esters; however, expanding such
157
systems to polymers and the desire to achieve cross-couplings further complicates these
systems.

Scheme 1.48. A plausible generalized mechanism for oxidative DArP (oxi-DArP) using a
palladium catalyst.
351

With regards to selectivity, small molecule efforts have demonstrated several
successful strategies for achieving good site-selectivity, which include (a) utilization of a
directing group (referred to as chelation-directed control) to induce proximation of the
catalyst for a five- or six- memberered metallocycle, (b) utilizing particularly acidic C−H
bonds for more favorable activation, (c) incorporating sterically hindering groups to
improve C−H accessibility, and/or (d) fine-tuning of the catalytic system for control. In the
following section, successful attempts en route to polymers via catalyzed oxidative direct
158
arylation polymerization (oxi-DArP) are discussed. While there has been much success
with small molecule oxidative cross-couplings, the successful application of this long-
sought strategy to conjugated polymers is very limited. The earliest attempt was carried
out by Ogino et al.
359
who studied both 3-hexylthiophene (3HT) and 3,4-
ethylenedioxythiophene (EDOT) polymers via palladium-catalyzed polymerization
(Scheme 1.49). They observed that no coupling reactions occur without an acid. They
screened several acid additives to promote the polymerization, including acetic acid,
trifluoroacetic acid, methane sulfonic acid, and trifluoromethanesulfonic acid. They
observed good yields with methane sulfonic acid but higher molecular weight with
trifluoroacetic acid, which was further investigated with various catalyst loadings and
control studies. They best results were achieved with the loadings provided in Scheme
1.49. They observed double the molecular weight in oxygen atmosphere compared to air
and no yields without palladium catalyst; however, the P3HT contained significant
branching and head-to-head couplings.

Scheme 1.49. Synthesis of P3HT via oxi-DArP as reported by Ogino et al.
359

Investigating the scope of their conditions further, they evaluated several other
thiophene derivatives, including 3,4-dihexylthiophene, 3,4-bis(methoxy)thiophene, 3,4-
bis(hexyloxy)thiophene, and EDOT. Mn values under 1 kDa were observed for all samples
159
except EDOT, which could not be measured due to insolubility in the GPC solvent;
however, visually, they observed high yields and a stable dispersion that generated suitable
films that closely matched IR spectra of commercial PEDOT dispersions.
In the first oxi-DArP that generated high molecular weight polymers, Chen, Li, and
Lu et al.
360
explored symmetrical 5-alkyl[3,4-c]thienopyrrole-4,6-dione (TPD)-based
homopolymers. These monomer structures are provided in Figure 1.30. Based on the
preliminary results with Pd(OAc)2 (10%), excess oxidant, Cu(OAc)2 (210%), and K2CO3
in DMA under nitrogen, the authors further optimized conditions on the TPD-flanked
benzodithiophene monomer, which had the best molecular weights (18 kDa, 88% yield,
Đ=1.28); however, the optimization conditions lead to invaluable observations about this
new synthetic method. They demonstrated that the palladium catalyst and oxidant were
both necessary for successful polymerization. Although both Pd(dppf)Cl2 and
Pd(PhCN)2Cl2 worked, the molecular weights were lower than with Pd(OAc)2. Both NMP
and DMSO led to lower molecular weights, while Ag2CO3 as an oxidant performed
comparatively well. They demonstrated that traditional methods with ferric chloride did
not result in polymer, highlighting both the limitations of chemical oxidative
polymerization but also the potentially enabling scope of oxi-DArP for electron-poor
substrates. The authors proposed that the carbonyl group on TPD could form a six-member
ring by efficient coordination with the Pd(OAc)2 and the TPD substrate, resulting
homopolymers that exhibited optical bandgaps that were consistent with literature.

160

Figure 1.30. Monomers explored for oxi-DArP as reported by Chen, Li, and Lu et al.
360

Extending on their work, Li and Lu et al.
361
explored their conditions toward
polythiazole-based derivatives. In this work, they explored ester-functionalized thiazoles
which flanked thiophene, bithiophene, or terthiophene as shown in Figure 1.31. With the
side-chains on the terthiophene for enhanced solubility, the authors optimized conditions
on this system before applying it to the others. Compared to their previous work, the
authors explored different baseline conditions, with Ag2CO3 as the oxidant instead of
Cu(OAc)2 as well as KOAc instead of K 2CO3. They lowered the Pd(OAc)2 loading to 5%
and achieved Mn values of 13 kDa with a narrow dispersity (1.22) and high yields (98%).
Through the screening of a variety of conditions, the authors observed that catalyst loadings
low as 0.01% still generated polymer, albeit with lower molecular weight (7 kDa).
161
Additionally, they observed that PdCl2, Pd(PhCN)2Cl2, Pd(dppf)Cl2 and Pd(PPh3)4, a Pd(0)
species, all generated polymers (10, 12, 10, and 12 kDa respectively).

Figure 1.31. Monomers explored for oxi-DArP as reported by Li and Lu et al.
361

A report from You and Lan et al.
362
reported a copper-catalyzed polymerization of
benzodiimidazoles, which possessed identical C−H bonds but they also evaluated different
side-chain positions that could ultimately lead to polymers with regioregularity (Scheme
1.50). Azoles are vulnerable to palladium-catalyzed ring-opening isomerizations, so the
authors sought to develop a Cu-based catalytic system. Combining Cu(OAc)2 (20%) with
both Ag2CO3 (50%) and O2 (1 atm) as oxidants, the authors were able to achieve molecular
weights exceeding 22 kDa (and up to 45 kDa) for a variety of side-chains from C4 to C18
straight chains for BDI. Yields were also above 60% after Soxhlet extraction for all
polymers. With regioisomeric BDI’, which was only explored with the n-octyl side-chain,
the authors observed lower molecular weights (Mn = 6 kDa), which may suggest some
potential reactivity difference between the two monomers.

162

Scheme 1.50. Synthesis of polybenzodiimidazoles via copper-catalyzed oxi-DArP as
reported by You and Lan et al.
362

Extending on the work from Ogino et al.
359
Thompson et al.
363
sought to evaluate
unsymmetrical monomers for oxi-DArP. In the case of 3-hexylthiophene, the 2-position
and the 5-position have different reactivities due to the presence of the donating hexyl
chain, which is also a sterically hindering moiety; however, realizing the challenges of
utilizing alkyl chains as a potential directing group, the authors adopted the use of hexyl
thiophene-3-carboxylate, which—for consistency with the naming convention of 3HT—
was referred to as 3-hexylesterthiophene (3HET) (Scheme 1.51). The ester side chain has
been previously explored as an advantageous thermally cleavable side-chain for a variety
of applications.
15,364–367
As observed previously, the dione of TPD or an ester-
functionalized thiazole are both compatible with oxi-DArP but possess only one type of
C−H bond, which makes 3HET particularly attractive as a monomer. They screened several
conditions on both 3HT and 3HET in order to confirm the importance of the ester directing
group. Additionally, the authors synthesized the DArP version of the monomer as well as
163
the Stille version to compare potential defects and optoelectronic properties, which was the
first report of the utilization of DArP or Stille toward this polymer as well. Compared to
P3HT, P3HET synthesized by both DArP and Stille had higher regioregularities, which
suggests that the ester functionality likely improved the selectivity by coordination with
the palladium species.
368
With optimized conditions consisting of Pd(OAc)2, Ag2CO3, and
PCy 3HBF4 as a ligand in DMA, the authors were able to achieve 15 kDa polymers with
good yields. Although the yield decreased with decreasing catalyst, the regioregularity
increased slightly, from 84 to 86%. While these regioregularities are lower than that
achieved by either DArP or Stille, this substrate demonstrates that oxi-DArP is compatible
with unsymmetrical substrates, which indicates C−H activation can happen at a position
that is not adjacent to a carbonyl directing group; however, the lack of applicability to
P3HT confirms that either a directing group or an electron poor heterocycle is required for
oxi-DArP. Additionally, with a bulky phosphine ligand the regioregularity was increased
from about 75% to 85%, which suggests that homocoupling can be suppressed and
selectivity enhanced via optimization of the catalytic system.

164

Scheme 1.51. Synthesis of poly(hexyl thiophene-3-carboxylate), referred to as poly(3-
hexylesterthiophene) (P3HET) via oxi-DArP, DArP, and Stille as reported by Thompson
et al.,
363
which was the first report of each synthetic method toward this polymer from their
respective monomers.
In a subsequent report, Thompson et al.
369
explored the synthesis of random
copolymers via oxi-DArP. Extending the scope of the random benzodiimidazoles
copolymers explored by You and Lan et al.,
362
where C−H bonds were similar in reactivity,
the authors explored copolymers of 3HET with either 4,4’-dimethyl-2,2’-bithiazole (BTz)
or TPD ( Scheme 1.52). The emphasis of this work was evaluating whether oxi-DArP is
compatible with copolymerizations, though the authors further optimized their conditions
on P3HET first by utilizing PdCl2(PPh3)2 instead of Pd(OAc)2, lowering the catalyst
loading, and adding small amounts of NDA (20%) and I2 (5%), which enabled molecular
weights around 12 kDa for P3HET homopolymers but an increase in regioregularity to
almost 89%. They noted that the utilization of AcOH led to β-defects, suggestion that
165
unselective C−H activation can occur with a stronger acid, which was also observed by
Ogino et al.
359
in their pursuit of P3HT via oxi-DArP; however, such defects were not
noticeable with bulky neodecanoic acid. Recently, Sanford et al.
370
proposed that the silver
carboxylates, which may be formed during this reaction, can assist the metalation of
thiophenes, suggesting that initial metalation by Ag
I
carboxylates may be a plausible
pathway with reactions involving mixtures of Ag and Pd salts, which was the case here.
Adopting these optimized conditions toward the synthesis of random copolymers
consisting of 5, 10, or 15% BTz or TPD, the authors observed good correlation between
the monomer feed ratio and the polymer composition via NMR analysis. Observing a
combination of homocoupling peaks of the secondary components along with cross-
coupling to 3HET, the authors confirmed the randomness of the polymers. Additionally,
the authors confirmed that BTz, which does not have a directing group or an accessible
flanking nitrogen, is still compatible with oxi-DArP, suggesting that a directing group may
not always be necessary.

166
Scheme 1.52. Conditions employed by Thompson et al.
369
for the synthesis of P3HET and
two random copolymer analogs, consisting of 5, 10, or 15% of the secondary comonomer.
Highlighting the combined advantages of direct arylation and oxidative direct
arylation, You and Wu et al.
371
expanded the strategies toward conjugated polymers by
combining small molecule direct arylation toward 2,2’-bithiazole-based copolymers with
oxi-DArP, generating monomers with benzothiadiazole (BTD), benzotriazole (BTZ), and
dioctylfluorene (Scheme 1.53). The authors utilized a PdCl2 / CuCl co-catalyst with
Cu(OAc)2 as an oxidant to generate polymers with molecular weights near 70 kDa with
dioctylfluorene in a dioxane/DMSO mixture at 120°C.

Scheme 1.53. Combination of small molecule direct arylation and oxi-DArP toward 2,2’-
bithiazole-based copolymers as reported by You and Wu et al.
371

The most significant drawback of the conditions reported thus far is the utilization
of heavy metal salts as the terminal oxidant, which is economically unfeasible for scalable
synthesis via this route without recycling the silver. Ultimately, oxygen—the most
167
appealing oxidant—would make this method particularly attractive and scalable, which has
been explored in small molecules
351,372
and as discussed above, by Ogino and coworkers
and You, Lan, and coworkers as a co-oxidant.
359,362
Toward this goal, You and Wu et al.
373

reported the synthesis of 5,5’-bithiazole-based copolymers with oxygen as the sole oxidant,
avoiding the need for heavy metal salts like Cu(OAc)2 or Ag2CO3 (Scheme 1.54). Their
conditions utilized PdCl2, Cs2CO3, PivOH, and an O2 balloon in DMA/DMSO co-solvent.
These conditions, like ones explored by Thompson et al.
363
but with K2CO3 and NDA
(albeit toward lower regioregularities), are derived from DArP (Class B), with the simple
addition of oxygen via balloon. The authors observed a wide breadth of molecular weights,
from 6 kDa with simple bithiazole (no spacer) to 34 kDa with biphenyl, highlighting the
compatibility of oxygen with this catalytic system and its strong performance under mild
and attractive conditions.

Scheme 1.54. Synthesis of various 5,5’-bithiazole-based derivatives via oxi-DArP utilizing
oxygen as the sole oxidant as reported by You and Wu et al.
373

168
Although these advances show significant promise, more effort is ultimately
necessary for this method to emerge as a viable route toward conjugated polymers,
specifically improving the balance between reactivity and selectivity via optimization of
the catalytic system, broadening the substrate scope, and more detailed understanding the
mechanism. For example, clearly directing groups can assist in the polymerization but as
observed by Thompson and coworkers,
363,369
unsymmetrical groups are also compatible
with this method. Additionally, You and colleagues have demonstrated that—albeit with
different conditions—both 2,2’-bithiazole- and 5,5’-bithiazole-based monomers can both
generate high molecular weight homopolymers.
371,373
Likely, because electron-poor units
have been the most successful via this method, the need to minimize the C−H activation
barriers, which is loosely related to acidity, is critical for this method, as so far only 3HET,
TPD, and isomeric bithiazole species have been successfully polymerized.
It is worth highlighting that the employment of a directing group, which Kanbara
et al.
236
as discussed above (Scheme 1.30), utilized to generated well-defined linear
copolymers in DArP will inevitably play a larger role for oxi-DArP but also other emerging
methods that seek to eliminate the need for pre-functionalization. For example, expanding
on their system, Kanbara et al.
374
reported the synthesis of pyrrole-based polymers by a
dehydrogenative direct alkenylation with various aryl substrates (Scheme 1.55) with a
rhodium-based catalyst, achieving polymers even with generally inactive benzene-like
substrates through the use of a directing group, highlighting the strong potential of this
strategy for achieving high molecular weight polymers. These types of strategies—
expanding the viable catalytic systems, broadening substrate scope, and enabling the
169
potential of these synthetic methods should be pursued for the broad applicability of
emerging synthetic methods.

Scheme 1.55. Synthesis poly(arylenevinylene)s via Rh-catalyzed direct alkenylation as
reported by Kanbara et al.
374

1.6. Summary and Outlook

DArP has emerged as a viable alternative method to traditional cross-coupling
methods that require double pre-functionalization of substrates. The past seven years have
led to dramatic improvements in the fundamental understanding of this method, its
substrate scope and limitation, and strategies toward effective generation of conjugated
polymers through improve selectivity and reactivity. Direct arylation is manifestly
intertwined to increasingly relevant philosophies of green chemistry, as a method that
N
H H
N X
EH EH
+
[RuCl
2
(Cp
*
)]
2
(4%)
Cu(OAc)
2
•
H
2
O
DMF
(0.08M),
100°C, 4h
H H
Directing
Group
N X
Directing
Group
H H
H H
X
=
C,
N
--
or
--
+
--
or
--
OEH
EHO
H
H
N
N X
EH EH
X
=
C,
N
N X
EH EH
X
=
C,
N
n
n
N
N N
OEH
EHO
n
170
enables the avoidance of toxic organotin reagents, shorter syntheses that can avoid
lithiation-metalation reactions with hazardous reagents, and an atom economical, efficient,
and scalable method. Its immense attractiveness is countered by challenges with side-
reactions, including homocoupling and branching defects, which for many applications has
given DArP the reputation for being marginally inferior to traditional methods. To
overcome this stigma, greater attention to defects and limitations through careful and
detailed evaluation of the reaction parameters is necessary.
The major accomplishment has been the fine-tuning of the catalytic systems for
minimizing unselective C−H activation and homocoupling, which in many cases leads to
polymers that exhibit superior structural regularity compared to well-explored
homocoupling, which in many cases leads to polymers that can even exhibit superior
structural regularity compared to well-explored methods like Stille and Suzuki. Recently,
it has finally been recognized that with careful selection of the monomers and optimized
catalytic systems, DArP polymers can match or even outperform Stille or Suzuki due to
superior control over polymer structure and end groups. This is the culmination of many
studies and their important contributions to optimizing DArP, which has expanded from
just a handful of research groups to an increasingly broad community. But more work is
needed for the broad applicability of these various conditions.
The lessons learned from this intense collective research effort will inevitably assist
in the generation of increasingly complex polymer architectures with more expansive
substrate scope. To that end, the challenges for the future development of DArP will
emphasize continued broadening of the compatible functional groups and structural motifs,
while developing increasingly refined reaction parameters and catalytic systems, with the
171
hope of accessing systems that are generally incompatible with Stille or Suzuki. En route
to these systems, increased emphasis on the mechanism, the presence or absence of defects,
or the utilization of detailed optoelectronic characterization (such as OFET or OPVs) when
defect analysis is prohibitively challenging, must be undertaken for the collective
realization of DArP as a viable synthetic method with the selectivity, reactivity, and high-
quality of generated materials that are characteristic of traditional methods.
The next great challenge will be the application of catalyzed reactions toward
polymers from monomers without any pre-functionalization with environmentally-friendly
recyclable co-oxidants or oxygen as a sole oxidant, which has thus far been explored only
on electron-poor substrates but will need to be expanded to different substrates for
improved viability. The employment of directing groups, different catalysts than
palladium, and other optimization strategies will most likely ultimately lead to greater
success. New investigations, coupled with the discussions in this Review, may lead to
greater improvement of the generation of conjugated polymers from monomer synthesis
through to complex polymer architectures. While much room exists for improvement, the
pursuit of such optimizations will be a truly informative and empowering endeavor.

1.7. References

(1) Thompson, B. C.; Fréchet, J. M. J. Angew. Chem. Int. Ed. 2008, 47 (1), 58.
(2) Sirringhaus, H.; Bird, M.; Zhao, N. Adv. Mater. 2010, 22 (34), 3893.
(3) Kabra, D.; Lu, L. P.; Song, M. H.; Snaith, H. J.; Friend, R. H. Adv. Mater. 2010, 22
(29), 3194.
(4) Thomas, S. W.; Joly, G. D.; Swager, T. M. Chem. Rev. 2007, 107 (4), 1339.
172
(5) McQuade, D. T.; Pullen, A. E.; Swager, T. M. Chem. Rev. 2000, 100 (7), 2537.
(6) Amb, C. M.; Dyer, A. L.; Reynolds, J. R. Chem. Mater. 2011, 23 (3), 397.
(7) Beaujuge, P. M.; Reynolds, J. R. Chem. Rev. 2010, 110 (1), 268.
(8) Li, J.; Liu, J.; Wei, C. -W.; Liu, B.; O’Donnell, M.; Gao, X. Phys. Chem. Chem. Phys.
2013, 15 (40), 17006.
(9) Feng, G.; Liu, J.; Geng, J.; Liu, B. J. Mater. Chem. B 2015, 3 (6), 1135.
(10) Feng, X.; Lv, F.; Liu, L.; Tang, H.; Xing, C.; Yang, Q.; Wang, S. ACS Appl. Mater.
Interfaces 2010, 2 (8), 2429.
(11) Chang, K.; Tang, Y.; Fang, X.; Yin, S.; Xu, H.; Wu, C. Biomacromolecules 2016.
(12) Chiang, C. K.; Fincher, C. R.; Park, Y. W.; Heeger, A. J.; Shirakawa, H.; Louis, E.
J.; Gau, S. C.; MacDiarmid, A. G. Phys. Rev. Lett. 1977, 39 (17), 1098.
(13) McCullough, R. D. Adv. Mater. 1998, 10 (2), 93.
(14) Ballauff, M. Angew. Chem. Int. Ed. Engl. 1989, 28 (3), 253.
(15) Mei, J.; Bao, Z. Chem. Mater. 2014, 26 (1), 604.
(16) Lee, J. K.; Ma, W. L.; Brabec, C. J.; Yuen, J.; Moon, J. S.; Kim, J. Y.; Lee, K.;
Bazan, G. C.; Heeger, A. J. J. Am. Chem. Soc. 2008, 130 (11), 3619.
(17) Yu, G.; Gao, J.; Hummelen, J. C.; Wudl, F.; Heeger, A. J. Science 1995, 270 (5243),
1789.
(18) Søndergaard, R. R.; Hösel, M.; Espinosa, N.; Jørgensen, M.; Krebs, F. C. Energy Sci
Eng 2013, 1 (2), 81.
(19) Angmo, D.; Krebs, F. C. J. Appl. Polym. Sci. 2013, 129 (1), 1.
(20) Søndergaard, R. R.; Hösel, M.; Krebs, F. C. J. Polym. Sci. B Polym. Phys. 2013, 51
(1), 16.
173
(21) Søndergaard, R. R.; Espinosa, N.; Jørgensen, M.; Krebs, F. C. Energy Environ. Sci.
2014, 7 (3), 1006.
(22) Carsten, B.; He, F.; Son, H. J.; Xu, T.; Yu, L. Chem. Rev. 2011, 111 (3), 1493.
(23) Sakamoto, J.; Rehahn, M.; Wegner, G.; Schlüter, A. D. Macromol. Rapid. Commun.
2009, 30 (9–10), 653.
(24) Sakamoto, J.; Schlüter, A. D. In Materials Science and Technology; Cahn, R. W.,
Haasen, P., Kramer, E. J., Eds.; Wiley-VCH Verlag GmbH & Co. KGaA:
Weinheim, Germany, 2013.
(25) Osaka, I.; McCullough, R. D. Acc. Chem. Res. 2008, 41 (9), 1202.
(26) Chen, T.-A.; Wu, X.; Rieke, R. D. J. Am. Chem. Soc. 1995, 117 (1), 233.
(27) Fuji, K.; Tamba, S.; Shono, K.; Sugie, A.; Mori, A. J. Am. Chem. Soc. 2013, 135
(33), 12208.
(28) Yamamoto, T.; Morita, A.; Miyazaki, Y.; Maruyama, T.; Wakayama, H.; Zhou, Z.
H.; Nakamura, Y.; Kanbara, T.; Sasaki, S.; Kubota, K. Macromolecules 1992, 25
(4), 1214.
(29) Alberico, D.; Scott, M. E.; Lautens, M. Chem. Rev. 2007, 107 (1), 174.
(30) Facchetti, A.; Vaccaro, L.; Marrocchi, A. Angew. Chem. Int. Ed. 2012, 51 (15),
3520.
(31) Wang, K.; Wang, M. Curr. Org. Chem. 2013, 17, 999.
(32) Kowalski, S.; Allard, S.; Zilberberg, K.; Riedl, T.; Scherf, U. Progress in Polymer
Science 2013, 38 (12), 1805.
(33) Mercier, L. G.; Leclerc, M. Acc. Chem. Res. 2013, 46 (7), 1597.
174
(34) Khlyabich, P. P.; Burkhart, B.; Rudenko, A. E.; Thompson, B. C. Polymer 2013, 54
(20), 5267.
(35) Okamoto, K.; Zhang, J.; Housekeeper, J. B.; Marder, S. R.; Luscombe, C. K.
Macromolecules 2013, 46 (20), 8059.
(36) Kuwabara, J.; Kanbara, T. J Syn. Org. Chem. Jpn. 2014, 72 (11), 1271.
(37) Marzano, G.; Ciasca, C. V.; Babudri, F.; Bianchi, G.; Pellegrino, A.; Po, R.;
Farinola, G. M. Eur. J. Org. Chem. 2014, No. 30, 6583.
(38) Segawa, Y.; Maekawa, T.; Itami, K. Angew. Chem. Int. Ed. 2015, 54 (1), 66.
(39) Morin, P.-O.; Bura, T.; Leclerc, M. Mater. Horiz. 2015, 3 (1), 11.
(40) Rudenko, A. E.; Thompson, B. C. J. Polym. Sci. A Polym. Chem. 2015, 53 (2), 135.
(41) Marrocchi, A.; Facchetti, A.; Lanari, D.; Petrucci, C.; Vaccaro, L. Energy Environ.
Sci. 2016, 9 (3), 763.
(42) Suraru, S.-L.; Lee, J. A.; Luscombe, C. K. ACS Macro Lett. 2016, 5 (6), 724.
(43) Bura, T.; Blaskovits, J. T.; Leclerc, M. J. Am. Chem. Soc. 2016, 138 (32), 10056.
(44) Pouliot, J.-R.; Grenier, F.; Blaskovits, J. T.; Beaupré, S.; Leclerc, M. Chem. Rev.
2016, 116 (22), 14225.
(45) Yu, S.; Liu, F.; Yu, J.; Zhang, S.; Cabanetos, C.; Gao, Y.; Huang, W. J. Mater.
Chem. C 2016, 5 (1), 29.
(46) Wu, W.; Xin, H.; Ge, C.; Gao, X. Tetrahedron Letters 2017, 58 (3), 175.
(47) Nitti, A.; Po, R.; Bianchi, G.; Pasini, D. Molecules 2016, 22 (1), 21.
(48) Bohra, H.; Wang, M. Journal of Materials Chemistry A 2017.
(49) Campeau, L.-C.; Fagnou, K. Chem. Commun. 2006, 12 (12), 1253.
175
(50) Homyak, P. D.; Liu, Y.; Harris, J. D.; Liu, F.; Carter, K. R.; Russell, T. P.; Coughlin,
E. B. Macromolecules 2016, 49 (8), 3028.
(51) Dudnik, A. S.; Aldrich, T. J.; Eastham, N. D.; Chang, R. P. H.; Facchetti, A.; Marks,
T. J. J. Am. Chem. Soc. 2016, 138 (48), 15699.
(52) Iizuka, E.; Wakioka, M.; Ozawa, F. Macromolecules 2015, 48 (9), 2989.
(53) Lombeck, F.; Komber, H.; Gorelsky, S. I.; Sommer, M. ACS Macro Lett. 2014, 3
(8), 819.
(54) Yang, C.; Liu, H.; Zhang, Y.; Xu, Z.; Wang, X.; Cao, B.; Wang, M.
Biomacromolecules 2016, 17 (5), 1673.
(55) Morin, P.-O.; Bura, T.; Sun, B.; Gorelsky, S. I.; Li, Y.; Leclerc, M. ACS Macro Lett.
2015, 4 (1), 21.
(56) Waltman, R. J.; Bargon, J. Can. J. Chem. 1986, 64 (1), 76.
(57) Roncali, J. Chem. Rev. 1992, 92 (4), 711.
(58) Toshima, N.; Hara, S. Progress in Polymer Science 1995, 20 (1), 155.
(59) Sadki, S.; Schottland, P.; Brodie, N.; Sabouraud, G. Chem. Soc. Rev. 2000, 29 (5),
283.
(60) Sugimoto, R.; Takeda, S.; Gu, H. B.; Yoshino, K. Chem. Exp. 1986, 1, 635.
(61) McCarley, T. D.; Noble, C. O.; DuBois, C. J.; McCarley, R. L. Macromolecules
2001, 34 (23), 7999.
(62) Cheng, Y.-J.; Yang, S.-H.; Hsu, C.-S. Chem. Rev. 2009, 109 (11), 5868.
(63) Gohier, F.; Frère, P.; Roncali, J. J. Org. Chem. 2013, 78 (4), 1497.
176
(64) Kim, Y.; Cook, S.; Kirkpatrick, J.; Nelson, J.; Durrant, J. R.; Bradley, D. D. C.;
Giles, M.; Heeney, M.; Hamilton, R.; McCulloch, I. J. Phys. Chem. C 2007, 111
(23), 8137.
(65) Troshin, P. A.; Susarova, D. K.; Moskvin, Y. L.; Kuznetsov, I. E.; Ponomarenko, S.
A.; Myshkovskaya, E. N.; Zakharcheva, K. A.; Balakai, A. A.; Babenko, S. D.;
Razumov, V. F. Adv. Funct. Mater. 2010, 20 (24), 4351.
(66) Bracher, C.; Yi, H.; Scarratt, N. W.; Masters, R.; Pearson, A. J.; Rodenburg, C.;
Iraqi, A.; Lidzey, D. G. Organic Electronics 2015, 27, 266.
(67) Nikiforov, M. P.; Lai, B.; Chen, W.; Chen, S.; Schaller, R. D.; Strzalka, J.; Maser,
J.; Darling, S. B. Energy Environ. Sci. 2013, 6 (5), 1513.
(68) Camaioni, N.; Tinti, F.; Franco, L.; Fabris, M.; Toffoletti, A.; Ruzzi, M.; Montanari,
L.; Bonoldi, L.; Pellegrino, A.; Calabrese, A.; Po, R. Organic Electronics 2012, 13
(4), 550.
(69) Cowie, J. M. G.; Arrighi, V. Polymers: Chemistry and Physics of Modern Materials,
Third Edition, Third.; CRC Press - Taylor & Francis Group, LLC.: Boca Raton, FL,
2007.
(70) Allcock, H. R.; Lampe, F. W.; Mark, J. E. Contemporary Polymer Chemistry (3rd
Edition), 3rd Edition.; Prentice Hall, Inc., 2003.
(71) Kozycz, L. M.; Gao, D.; Seferos, D. S. Macromolecules 2013, 46 (3), 613.
(72) Lu, L.; Zheng, T.; Wu, Q.; Schneider, A. M.; Zhao, D.; Yu, L. Chem. Rev. 2015, 115
(23), 12666.
(73) Sirringhaus, H. Adv. Mater. 2014, 26 (9), 1319.
(74) Burke, D. J.; Lipomi, D. J. Energy Environ. Sci. 2013, 6 (7), 2053.
177
(75) Cordovilla, C.; Bartolomé, C.; Martínez-Ilarduya, J. M.; Espinet, P. ACS Catal.
2015, 5 (5), 3040.
(76) Katsouras, A.; Gasparini, N.; Koulogiannis, C.; Spanos, M.; Ameri, T.; Brabec, C.
J.; Chochos, C. L.; Avgeropoulos, A. Macromol. Rapid Commun. 2015, 36 (20),
1778.
(77) Marzano, G.; Kotowski, D.; Babudri, F.; Musio, R.; Pellegrino, A.; Luzzati, S.; Po,
R.; Farinola, G. M. Macromolecules 2015, 48 (19), 7039.
(78) Osedach, T. P.; Andrew, T. L.; Bulović, V. Energy Environ. Sci. 2013, 6 (3), 711.
(79) Amb, C. M.; Craig, M. R.; Koldemir, U.; Subbiah, J.; Choudhury, K. R.; Gevorgyan,
S. A.; Jørgensen, M.; Krebs, F. C.; So, F.; Reynolds, J. R. ACS Appl. Mater.
Interfaces 2012, 4 (3), 1847.
(80) Helgesen, M.; Carlé, J. E.; dos Reis Benatto, G. A.; Søndergaard, R. R.; Jørgensen,
M.; Bundgaard, E.; Krebs, F. C. Adv. Energy Mater. 2015, 5 (9), 1401996.
(81) Krebs, F. C.; Nielsen, T. D.; Fyenbo, J.; Wadstrøm, M.; Pedersen, M. S. Energy
Environ. Sci. 2010, 3 (5), 512.
(82) Matsidik, R.; Komber, H.; Luzio, A.; Caironi, M.; Sommer, M. J. Am. Chem. Soc.
2015, 137 (20), 6705.
(83) Livi, F.; Gobalasingham, N. S.; Thompson, B. C.; Bundgaard, E. J. Polym. Sci., Part
A 2016, 54 (18), 2907.
(84) Nguyen, T. L.; Choi, H.; Ko, S.-J.; Uddin, M. A.; Walker, B.; Yum, S.; Jeong, J.-E.;
Yun, M. H.; Shin, T. J.; Hwang, S.; Kim, J. Y.; Woo, H. Y. Energy Environ. Sci.
2014, 7 (9), 3040.
178
(85) Espinosa, N.; García-Valverde, R.; Urbina, A.; Lenzmann, F.; Manceau, M.;
Angmo, D.; Krebs, F. C. Sol. Energ. Mat. Sol. Cells 2012, 97, 3.
(86) Hösel, M.; Søndergaard, R. R.; Jørgensen, M.; Krebs, F. C. Energy Technol. 2013,
1 (1), 102.
(87) Grenier, F.; Aïch, B. R.; Lai, Y.-Y.; Guérette, M.; Holmes, A. B.; Tao, Y.; Wong,
W. W. H.; Leclerc, M. Chem. Mater. 2015, 27 (6), 2137.
(88) Wan, Q.; Guo, X.; Wang, Z.; Li, W.; Guo, B.; Ma, W.; Zhang, M.; Li, Y. Adv. Funct.
Mater. 2016, 26 (36), 6635.
(89) Liu, K.; Larsen-Olsen, T. T.; Lin, Y.; Beliatis, M.; Bundgaard, E.; Jørgensen, M.;
Krebs, F. C.; Zhan, X. J. Mater. Chem. A 2016, 4 (3), 1044.
(90) Daugulis, O.; Zaitsev, V.; Shabashov, D.; Pham, Q.-N.; Lazareva, A. Synlett 2006,
2006 (20), 3382.
(91) Seregin, I. V.; Gevorgyan, V. Chem. Soc. Rev. 2007, 36 (7), 1173.
(92) Hachiya, H.; Hirano, K.; Satoh, T.; Miura, M. Org. Lett. 2009, 11 (8), 1737.
(93) Li, B.-J.; Yang, S.-D.; Shi, Z.-J. Synlett 2008, 2008 (7), 949.
(94) Kakiuchi, F.; Kochi, T. Synthesis 2008, 2008 (19), 3013.
(95) Chen, X.; Engle, K. M.; Wang, D.-H.; Yu, J.-Q. Angew. Chem. Int. Ed. 2009, 48
(28), 5094.
(96) Bellina, F.; Rossi, R. Tetrahedron 2009, 65 (50), 10269.
(97) Ackermann, L.; Vicente, R.; Kapdi, A. R. Angew. Chem. Int. Ed. 2009, 48 (52),
9792.
(98) Ackermann, L. Chem. Rev. 2011, 111 (3), 1315.
(99) Roger, J.; Gottumukkala, A. L.; Doucet, H. ChemCatChem 2010, 2 (1), 20.
179
(100) Lyons, T. W.; Sanford, M. S. Chem. Rev. 2010, 110 (2), 1147.
(101) Liu, C.; Zhang, H.; Shi, W.; Lei, A. Chem. Rev. 2011, 111 (3), 1780.
(102) Gorelsky, S. I.; Lapointe, D.; Fagnou, K. J. Org. Chem. 2012, 77 (1), 658.
(103) Schipper, D. J.; Fagnou, K. Chem. Mater. 2011, 23 (6), 1594.
(104) McGlacken, G. P.; Bateman, L. M. Chem. Soc. Rev. 2009, 38 (8).
(105) Hussain, I.; Singh, T. Adv. Synth. Catal. 2014, 356 (8), 1661.
(106) Della Ca’, N.; Fontana, M.; Motti, E.; Catellani, M. Acc. Chem. Res. 2016.
(107) Zhang, J.; Parker, T. C.; Chen, W.; Williams, L.; Khrustalev, V. N.; Jucov, E. V.;
Barlow, S.; Timofeeva, T. V.; Marder, S. R. J. Org. Chem. 2016, 81 (2), 360.
(108) Yuan, K.; Soulé, J.-F.; Doucet, H. ACS Catal. 2015, 5 (2), 978.
(109) Qiu, X.; Wang, M.; Zhao, Y.; Shi, Z. Angew. Chem. Int. Ed.
10.1002/anie.201703354.
(110) Moselage, M.; Li, J.; Kramm, F.; Ackermann, L. Angew. Chem. Int. Ed. 2017, 56
(19), 5341.
(111) Lavenot, L.; Gozzi, C.; Ilg, K.; Orlova, I.; Penalva, V.; Lemaire, M. Journal of
Organometallic Chemistry 1998, 567 (1–2), 49.
(112) Espinet, P.; Echavarren, A. M. Angew. Chem. Int. Ed. 2004, 43, 4704.
(113) Wakioka, M.; Nakamura, Y.; Wang, Q.; Ozawa, F. Organometallics 2012, 31 (13),
4810.
(114) Gorelsky, S. I.; Lapointe, D.; Fagnou, K. J. Am. Chem. Soc. 2008, 130 (33), 10848.
(115) Gorelsky, S. I. Coord. Chem. Rev. 2013, 257 (1), 153.
(116) Lapointe, D.; Fagnou, K. Chem. Lett. 2010, 39 (11), 1118.
(117) Livendahl, M.; Echavarren, A. M. Isr. J. Chem. 2010, 50 (5–6), 630.
180
(118) Rudenko, A. E.; Wiley, C. A.; Stone, S. M.; Tannaci, J. F.; Thompson, B. C. J.
Polym. Sci. A Polym. Chem. 2012, 50 (18), 3691.
(119) Rudenko, A. E.; Wiley, C. A.; Tannaci, J. F.; Thompson, B. C. J. Polym. Sci. A
Polym. Chem. 2013, 51 (12), 2660.
(120) Rudenko, A. E.; Latif, A. A.; Thompson, B. C. Nanotechnology 2014, 25 (1),
014005.
(121) Bura, T.; Morin, P.-O.; Leclerc, M. Macromolecules 2015, 48 (16), 5614.
(122) Lu, W.; Kuwabara, J.; Kanbara, T. Macromolecules 2011, 44 (6), 1252.
(123) Okamoto, K.; Housekeeper, J. B.; Michael, F. E.; Luscombe, C. K. Polym. Chem.
2013, 4 (12), 3499.
(124) Xue, L.; Lin, Z. Chem. Soc. Rev. 2010, 39 (5), 1692.
(125) Korenaga, T.; Suzuki, N.; Sueda, M.; Shimada, K. Journal of Organometallic
Chemistry 2015, 780, 63.
(126) Lafrance, M.; Lapointe, D.; Fagnou, K. Tetrahedron 2008, 64 (26), 6015.
(127) Tan, Y.; Hartwig, J. F. J. Am. Chem. Soc. 2011, 133 (10), 3308.
(128) Kim, J. S.; Lee, Y.; Lee, J. H.; Park, J. H.; Kim, J. K.; Cho, K. Adv. Mater. 2010, 22
(12), 1355.
(129) Park, J. K.; Jo, J.; Seo, J. H.; Moon, J. S.; Park, Y. D.; Lee, K.; Heeger, A. J.; Bazan,
G. C. Adv. Mater. 2011, 23 (21), 2430.
(130) Wang, Q.; Zhang, B.; Liu, L.; Chen, Y.; Qu, Y.; Zhang, X.; Yang, J.; Xie, Z.; Geng,
Y.; Wang, L.; Wang, F. J. Phys. Chem. C 2012, 116 (41), 21727.
(131) Mao, Z.; Vakhshouri, K.; Jaye, C.; Fischer, D. A.; Fernando, R.; DeLongchamp, D.
M.; Gomez, E. D.; Sauvé, G. Macromolecules 2013, 46 (1), 103.
181
(132) Matsidik, R.; Komber, H.; Sommer, M. ACS Macro Lett. 2015, 4 (12), 1346.
(133) Matsidik, R.; Luzio, A.; Hameury, S.; Komber, H.; McNeill, C. R.; Caironi, M.;
Sommer, M. J. Mater. Chem. C 2016, 4 (43), 10371.
(134) Schiefer, D.; Komber, H.; Mugwanga Keheze, F.; Kunz, S.; Hanselmann, R.; Reiter,
G.; Sommer, M. Macromolecules 2016, 49 (19), 7230.
(135) Estrada, L. A.; Deininger, J. J.; Kamenov, G. D.; Reynolds, J. R. ACS Macro Lett.
2013, 2 (10), 869.
(136) Se´vignon, M.; Papillon, J.; Schulz, E.; Lemaire, M. Tetrahedron Lett. 1999, 40 (32),
5873.
(137) Sévignon, M.; Hassan, J.; Gozzi, C.; Schulz, E.; Lemaire, M. Comptes Rendus de
l’Académie des Sciences - Series IIC - Chemistry 2000, 3 (7), 569.
(138) Hassan, J.; Schulz, E.; Gozzi, C.; Lemaire, M. J. Mol. Catal. A: Chemical 2003, 195
(1–2), 125.
(139) Kumar, A.; Kumar, A. Polym. Chem. 2010, 1 (3), 286.
(140) Zhang, J.; Li, J.; Sun, M. CIESC Journal 2010, 61 (6), 1587.
(141) Wang, Q.; Takita, R.; Kikuzaki, Y.; Ozawa, F. J. Am. Chem. Soc. 2010, 132 (33),
11420.
(142) Kuwabara, J.; Yasuda, T.; Choi, S. J.; Lu, W.; Yamazaki, K.; Kagaya, S.; Han, L.;
Kanbara, T. Adv. Funct. Mater. 2014, 24 (21), 3226.
(143) Guo, Q.; Dong, J.; Wan, D.; Wu, D.; You, J. Macromol. Rapid Commun. 2013, 34
(6), 522.
(144) Kuramochi, M.; Kuwabara, J.; Lu, W.; Kanbara, T. Macromolecules 2014, 47 (21),
7378.
182
(145) Livi, F.; Gobalasingham, N. S.; Bundgaard, E.; Thompson, B. C. J. Polym. Sci. A
Polym. Chem. 2015, 53 (22), 2598.
(146) Yamazaki, K.; Kuwabara, J.; Kanbara, T. Macromol. Rapid Commun. 2013, 34 (1),
69.
(147) Wakioka, M.; Nakamura, Y.; Montgomery, M.; Ozawa, F. Organometallics 2015,
34 (1), 198.
(148) Kuwabara, J.; Yasuda, T.; Takase, N.; Kanbara, T. ACS Appl. Mater. Interfaces
2016, 8 (3), 1752.
(149) Poduval, M. K.; Burrezo, P. M.; Casado, J.; López Navarrete, J. T.; Ortiz, R. P.;
Kim, T.-H. Macromolecules 2013, 46 (23), 9220.
(150) Lafrance, M.; Fagnou, K. J. Am. Chem. Soc. 2006, 128, 16496.
(151) Chang, S.-W.; Waters, H.; Kettle, J.; Kuo, Z.-R.; Li, C.-H.; Yu, C.-Y.; Horie, M.
Macromol. Rapid Commun. 2012, 33 (22), 1927.
(152) Weis, J. G.; Swager, T. M. ACS Macro Lett. 2015, 4 (1), 138.
(153) Sun, M.; Wang, W.; Lv, W.; Lu, M.; Yan, S.; Liang, L.; Ling, Q. Synthetic Metals
2015, 209, 412.
(154) Wakioka, M.; Kitano, Y.; Ozawa, F. Macromolecules 2013, 46 (2), 370.
(155) Wakioka, M.; Ichihara, N.; Kitano, Y.; Ozawa, F. Macromolecules 2014, 47 (2),
626.
(156) Grenier, F.; Berrouard, P.; Pouliot, J.-R.; Tseng, H.-R.; Heeger, A. J.; Leclerc, M.
Polym. Chem. 2013, 4 (6), 1836.
(157) Zhao, H.; Liu, C.-Y.; Luo, S.-C.; Zhu, B.; Wang, T.-H.; Hsu, H.-F.; Yu, H.
Macromolecules 2012, 45 (19), 7783.
183
(158) Iizuka, E.; Wakioka, M.; Ozawa, F. Macromolecules 2016, 49 (9), 3310.
(159) Ohta, A.; late) Yasuo Akita, (the; Ohkuwa, T.; Chiba, M.; Fukunaga, R.; Miyafuji,
A.; Nakata, T.; Tani, N.; Aoyagi, Y. Heterocycles 1990, 31 (11), 1951.
(160) Jeffery, T. Tetrahedron 1996, 52 (30), 10113.
(161) Rudenko, A. E.; Thompson, B. C. Macromolecules 2015, 48 (3), 569.
(162) Rudenko, A. E.; Thompson, B. C. J. Polym. Sci. A Polym. Chem. 2015, 53 (21),
2494.
(163) Rudenko, A. E.; Latif, A. A.; Thompson, B. C. J. Polym. Sci. A Polym. Chem. 2015,
53 (12), 1492.
(164) Tu, G.; Bilge, A.; Adamczyk, S.; Forster, M.; Heiderhoff, R.; Balk, L. J.;
Mühlbacher, D.; Morana, M.; Koppe, M.; Scharber, M. C.; Choulis, S. A.; Brabec,
C. J.; Scherf, U. Macromol. Rapid Commun. 2007, 28 (17), 1781.
(165) Mangold, H. S.; Richter, T. V.; Link, S.; Würfel, U.; Ludwigs, S. J. Phys. Chem. B
2012, 116 (1), 154.
(166) Qiao, J.; Yang, C.; He, Q.; Bai, F.; Li, Y. J. Appl. Polym. Sci. 2004, 92 (3), 1459.
(167) Varnavski, O.; Yan, X.; Mongin, O.; Blanchard-Desce, M.; Goodson, T. J. Phys.
Chem. C 2007, 111 (1), 149.
(168) Harpham, M. R.; Süzer, Ö.; Ma, C.-Q.; Bäuerle, P.; Goodson, T. J. Am. Chem. Soc.
2009, 131 (3), 973.
(169) Jakubiak, R.; Bao, Z.; Rothberg, L. Synth. Met. 2000, 114 (1), 61.
(170) Ueda, K.; Yanagisawa, S.; Yamaguchi, J.; Itami, K. Angew. Chem. Int. Ed. 2010, 49
(47), 8946.
(171) Tang, D.-T. D.; Collins, K. D.; Glorius, F. J. Am. Chem. Soc. 2013.
184
(172) Tang, D.-T. D.; Collins, K. D.; Ernst, J. B.; Glorius, F. Angew. Chem. Int. Ed. 2014,
53 (7), 1809.
(173) Tang, S.-Y.; Guo, Q.-X.; Fu, Y. Chem. Eur. J. 2011, 17 (49), 13866.
(174) Colletto, C.; Islam, S.; Juliá-Hernández, F.; Larrosa, I. J. Am. Chem. Soc. 2016, 138
(5), 1677.
(175) Po, R.; Bianchi, G.; Carbonera, C.; Pellegrino, A. Macromolecules 2015, 48 (3),
453.
(176) Saito, H.; Chen, J.; Kuwabara, J.; Yasuda, T.; Kanbara, T. Polymer Chemistry 2017,
8 (19), 3006.
(177) Saito, H.; Kuwabara, J.; Kanbara, T. J. Polym. Sci. Part A: Polym. Chem. 2015, 53
(19), 2198.
(178) Hayashi, S.; Kojima, Y.; Koizumi, T. Polym. Chem. 2015, 6 (6), 881.
(179) Parisien, M.; Valette, D.; Fagnou, K. J. Org. Chem. 2005, 70 (19), 7578.
(180) Cano, R.; Schmidt, A. F.; McGlacken, G. P. Chem. Sci. 2015, 6 (10), 5338.
(181) Liu, S.-Y.; Li, H.-Y.; Shi, M.-M.; Jiang, H.; Hu, X.-L.; Li, W.-Q.; Fu, L.; Chen, H.-
Z. Macromolecules 2012, 45 (22), 9004.
(182) Qiu, Y.; Mohin, J.; Tsai, C.-H.; Tristram-Nagle, S.; Gil, R. R.; Kowalewski, T.;
Noonan, K. J. T. Macromol. Rapid Commun. 2015, 36 (9), 840.
(183) Wei, C. S.; Davies, G. H. M.; Soltani, O.; Albrecht, J.; Gao, Q.; Pathirana, C.; Hsiao,
Y.; Tummala, S.; Eastgate, M. D. Angew. Chem. Int. Ed. 2013, 52 (22), 5822.
(184) Kuwabara, J.; Sakai, M.; Zhang, Q.; Kanbara, T. Org. Chem. Front. 2015, 2 (5),
520.
185
(185) Pouliot, J.-R.; Wakioka, M.; Ozawa, F.; Li, Y.; Leclerc, M. Macromol. Chem. Phys.
2016, 217 (13), 1493.
(186) Dou, J.; Chen, Z.; Ma, C. Synth. Met. 2014, 196, 117.
(187) Wakioka, M.; Nakamura, Y.; Hihara, Y.; Ozawa, F.; Sakaki, S. Organometallics
2014, 33 (21), 6247.
(188) Wang, Q.; Wakioka, M.; Ozawa, F. Macromol. Rapid Commun. 2012, 33 (14), 1203.
(189) Rudenko, A. E.; Khlyabich, P. P.; Thompson, B. C. ACS Macro Lett. 2014, 3, 387.
(190) Fei, Z.; Boufflet, P.; Wood, S.; Wade, J.; Moriarty, J.; Gann, E.; Ratcliff, E. L.;
McNeill, C. R.; Sirringhaus, H.; Kim, J.-S.; Heeney, M. J. Am. Chem. Soc. 2015,
137 (21), 6866.
(191) Hu, H.; Jiang, K.; Yang, G.; Liu, J.; Li, Z.; Lin, H.; Liu, Y.; Zhao, J.; Zhang, J.;
Huang, F.; Qu, Y.; Ma, W.; Yan, H. J. Am. Chem. Soc. 2015, 137 (44), 14149.
(192) Zhao, J.; Li, Y.; Yang, G.; Jiang, K.; Lin, H.; Ade, H.; Ma, W.; Yan, H. Nat. Energy
2016, 1 (2), 15027.
(193) Sun, B.; Hong, W.; Yan, Z.; Aziz, H.; Li, Y. Adv. Mater. 2014, 26 (17), 2636.
(194) Yan, H.; Chen, Z.; Zheng, Y.; Newman, C.; Quinn, J. R.; Dötz, F.; Kastler, M.;
Facchetti, A. Nature 2009, 457 (7230), 679.
(195) Zhao, F.; Dai, S.; Wu, Y.; Zhang, Q.; Wang, J.; Jiang, L.; Ling, Q.; Wei, Z.; Ma, W.;
You, W.; Wang, C.; Zhan, X. Adv. Mater. 2017, 29 (18), n/a.
(196) Nikolka, M.; Nasrallah, I.; Rose, B.; Ravva, M. K.; Broch, K.; Sadhanala, A.;
Harkin, D.; Charmet, J.; Hurhangee, M.; Brown, A.; Illig, S.; Too, P.; Jongman, J.;
McCulloch, I.; Bredas, J.-L.; Sirringhaus, H. Nat Mater 2017, 16 (3), 356.
186
(197) Nair, V. S.; Sun, J.; Qi, P.; Yang, S.; Liu, Z.; Zhang, D.; Ajayaghosh, A.
Macromolecules 2016, 49 (17), 6334.
(198) Howard, J. B.; Ekiz, S.; Cuellar De Lucio, A. J.; Thompson, B. C. Macromolecules
2016, 49 (17), 6360.
(199) Burkhart, B.; Khlyabich, P. P.; Cakir Canak, T.; LaJoie, T. W.; Thompson, B. C.
Macromolecules 2011, 44 (6), 1242.
(200) Khlyabich, P. P.; Burkhart, B.; Ng, C. F.; Thompson, B. C. Macromolecules 2011,
44 (13), 5079.
(201) Burkhart, B.; Khlyabich, P. P.; Thompson, B. C. J. Photon. Energy 2012, 2 (1),
021002.
(202) Burkhart, B.; Khlyabich, P. P.; Thompson, B. C. Macromol. Chem. Phys. 2013, 214
(6), 681.
(203) Howard, J. B.; Ekiz, S.; Noh, S.; Thompson, B. C. ACS Macro Lett. 2016, 977.
(204) Jung, J. W.; Liu, F.; Russell, T. P.; Jo, W. H. Energy Environ. Sci. 2013, 6 (11),
3301.
(205) Nielsen, C. B.; Ashraf, R. S.; Schroeder, B. C.; D’Angelo, P.; Watkins, S. E.; Song,
K.; Anthopoulos, T. D.; McCulloch, I. Chem. Commun. 2012, 48 (47), 5832.
(206) Li, J.; Ong, K.-H.; Lim, S.-L.; Ng, G.-M.; Tan, H.-S.; Chen, Z.-K. Chem. Commun.
2011, 47 (33), 9480.
(207) Duan, C.; Gao, K.; van Franeker, J. J.; Liu, F.; Wienk, M. M.; Janssen, R. A. J. J.
Am. Chem. Soc. 2016, 138 (34), 10782.
187
(208) Gruber, M.; Jung, S.-H.; Schott, S.; Venkateshvaran, D.; Kronemeijer, A. J.;
Andreasen, J. W.; McNeill, C. R.; Wong, W. W. H.; Shahid, M.; Heeney, M.; Lee,
J.-K.; Sirringhaus, H. Chem. Sci. 2015, 6 (12), 6949.
(209) Sonar, P.; Foong, T. R. B.; Dodabalapur, A. Phys. Chem. Chem. Phys. 2014, 16 (9),
4275.
(210) Zhang, J.; Chen, W.; Rojas, A. J.; Jucov, E. V.; Timofeeva, T. V.; Parker, T. C.;
Barlow, S.; Marder, S. R. J. Am. Chem. Soc. 2013, 135 (44), 16376.
(211) Battace, A.; Lemhadri, M.; Zair, T.; Doucet, H.; Santelli, M. Adv. Synth. Catal. 2007,
349 (16), 2507.
(212) Nakano, M.; Tsurugi, H.; Satoh, T.; Miura, M. Org. Lett. 2008, 10 (9), 1851.
(213) Okazawa, T.; Satoh, T.; Miura, M.; Nomura, M. J. Am. Chem. Soc. 2002, 124 (19),
5286.
(214) Požgan, F.; Roger, J.; Doucet, H. ChemSusChem 2008, 1 (5), 404.
(215) Roger, J.; Požgan, F.; Doucet, H. Green Chem. 2009, 11 (3), 425.
(216) Lafrance, M.; Rowley, C. N.; Woo, T. K.; Fagnou, K. J. Am. Chem. Soc. 2006, 128
(27), 8754.
(217) René, O.; Fagnou, K. Org. Lett. 2010, 12 (9), 2116.
(218) Chen, F.; Min, Q.-Q.; Zhang, X. J. Org. Chem. 2012, 77 (6), 2992.
(219) Park, J. H.; Jung, E. H.; Jung, J. W.; Jo, W. H. Adv. Mater. 2013, 25 (18), 2583.
(220) Wang, K.; Wang, G.; Wang, M. Macromol. Rapid Commun. 2015, 36 (24), 2162.
(221) Hu, X.; Zuo, L.; Fu, W.; Larsen-Olsen, T. T.; Helgesen, M.; Bundgaard, E.;
Hagemann, O.; Shi, M.; Krebs, F. C.; Chen, H. J. Mater. Chem. 2012, 22 (31),
15710.
188
(222) Hu, X.; Fu, W.; Zuo, L.; Shi, H.; Chen, M.; Liu, S.; Pan, J.; Fu, L.; Shi, M.; Chen,
H. Tetrahedron 2013, 69 (16), 3419.
(223) Bijleveld, J. C.; Gevaerts, V. S.; Di Nuzzo, D.; Turbiez, M.; Mathijssen, S. G. J.; de
Leeuw, D. M.; Wienk, M. M.; Janssen, R. A. J. Adv. Mater. 2010, 22 (35), E242.
(224) Li, W.; Hendriks, K. H.; Wienk, M. M.; Janssen, R. A. J. Acc. Chem. Res. 2016, 49
(1), 78.
(225) Pouliot, J.-R.; Sun, B.; Leduc, M.; Najari, A.; Li, Y.; Leclerc, M. Polym. Chem.
2014, 6 (2), 278.
(226) Broll, S.; Nübling, F.; Luzio, A.; Lentzas, D.; Komber, H.; Caironi, M.; Sommer,
M. Macromolecules 2015, 48 (20), 7481.
(227) Hendriks, K. H.; Li, W.; Heintges, G. H. L.; van Pruissen, G. W. P.; Wienk, M. M.;
Janssen, R. A. J. J. Am. Chem. Soc. 2014, 136 (31), 11128.
(228) Homyak, P.; Liu, Y.; Liu, F.; Russel, T. P.; Coughlin, E. B. Macromolecules 2015,
48 (19), 6978.
(229) Guo, C.; Quinn, J.; Sun, B.; Li, Y. Polym. Chem. 2016, 7 (27), 4515.
(230) Kuwabara, J.; Takase, N.; Yasuda, T.; Kanbara, T. J. Polym. Sci. Part A: Polym.
Chem. 2016, 54 (15), 2337.
(231) Gobalasingham, N.; Pankow, R.; Ekiz, S.; Thompson, B. J. Mater. Chem. A 2017.
(232) Bura, T.; Beaupré, S.; Légaré, M.-A.; Quinn, J.; Rochette, E.; Blaskovits, J. T.;
Fontaine, F.-G.; Pron, A.; Li, Y.; Leclerc, M. Chem. Sci. 2017, 8 (5), 3913.
(233) Lee, C.; Yang, W.; Parr, R. G. Phys. Rev. B 1988, 37 (2), 785.
(234) Becke, A. D. The Journal of Chemical Physics 1993, 98 (7), 5648.
189
(235) Roy, C.; Bura, T.; Beaupré, S.; Légaré, M.-A.; Sun, J.-P.; Hill, I. G.; Leclerc, M.
Macromolecules 2017.
(236) Lu, W.; Kuwabara, J.; Kanbara, T. Macromol. Rapid Commun. 2013, 34 (14), 1151.
(237) Kanbara, T.; Kuwabara, J.; Lu, W. IOP Conf. Ser.: Mater. Sci. Eng. 2014, 54.
(238) Hayashi, S.; Takigami, A.; Koizumi, T. ChemPlusChem 2016, 81 (9), 930.
(239) Kojima, Y.; Hayashi, S.; Koizumi, T. J. Polym. Sci. Part A: Polym. Chem. 2017, 55
(7), 1183.
(240) Wang, X.; Wang, M. Polym. Chem. 2014, 5 (19), 5784.
(241) Wakioka, M.; Takahashi, R.; Ichihara, N.; Ozawa, F. Macromolecules 2017, 50 (3),
927.
(242) Pouliot, J.-R.; Mercier, L. G.; Caron, S.; Leclerc, M. Macromol. Chem. Phys. 2013,
214 (4), 453.
(243) Kuwabara, J.; Yamazaki, K.; Yamagata, T.; Tsuchida, W.; Kanbara, T. Polym.
Chem. 2015, 6 (6), 891.
(244) Kuwabara, J.; Fujie, Y.; Maruyama, K.; Yasuda, T.; Kanbara, T. Macromolecules
2016, 49 (24), 9388.
(245) Wang, Z. A.; Kuwabara, J.; Ichige, A.; Yasuda, T.; Kanbara, T. Synthetic Metals
2016, 222, 383.
(246) Lu, W.; Kuwabara, J.; Kanbara, T. Polym. Chem. 2012, 3 (12), 3217.
(247) Lu, W.; Kuwabara, J.; Kuramochi, M.; Kanbara, T. J. Polym. Sci. Part A: Polym.
Chem. 2015, 53 (11), 1396.
(248) Yasuda, T.; Kuwabara, J.; Han, L.; Kanbara, T. Journal of Photopolymer Science
and Technology 2016, 29 (2), 347.
190
(249) Kuwabara, J.; Kuramochi, M.; Liu, S.; Yasuda, T.; Kanbara, T. Polym J 2017, 49
(1), 123.
(250) Aycock, D. F. Org. Process Res. Dev. 2007, 11 (1), 156.
(251) Grenier, F.; Goudreau, K.; Leclerc, M. J. Am. Chem. Soc. 2017, 139 (7), 2816.
(252) Kettle, J.; Horie, M.; Majewski, L. A.; Saunders, B. R.; Tuladhar, S.; Nelson, J.;
Turner, M. L. Solar Energy Materials and Solar Cells 2011, 95 (8), 2186.
(253) Hayashi, S.; Yamamoto, S.; Koizumi, T. Chem. Lett. 2016, 46 (2), 200.
(254) Wang, X.; Wang, K.; Wang, M. Polym. Chem. 2015, 6 (10), 1846.
(255) Tomar, M.; Ashar, A. Z.; Narayan, K. S.; Müllen, K.; Jacob, J. J Polym Res 2016,
23 (3), 50.
(256) Guérette, M.; Najari, A.; Maltais, J.; Pouliot, J.-R.; Dufresne, S.; Simoneau, M.;
Besner, S.; Charest, P.; Leclerc, M. Adv. Energy Mater. 2016, 6 (9), n/a.
(257) Huang, Y.; Zheng, N.; Wang, Z.; Ying, L.; Huang, F.; Cao, Y. Chemical
Communications 2017, 53 (12), 1997.
(258) Efrem, A.; Wang, K.; Wang, M. Dyes and Pigments.
(259) Nübling, F.; Komber, H.; Sommer, M. Macromolecules 2017, 50 (5), 1909.
(260) Liu, D.-P.; Chen, Q.; Zhao, Y.-C.; Zhang, L.-M.; Qi, A.-D.; Han, B.-H. ACS Macro
Lett. 2013, 2 (6), 522.
(261) Feng, L.-J.; Guo, J.-W.; Zhong, X.; Sun, Z.-Y. J. Macromol. Sci. A 2014, 51 (7),
604.
(262) Hayashi, S.; Togawa, Y.; Ashida, J.; Nishi, K.; Asano, A.; Koizumi, T. Polymer
2016, 90, 187.
(263) Hayashi, S.; Togawa, Y.; Kojima, Y.; Koizumi, T. Polym. Chem. 2016, 7 (36), 5671.
191
(264) Efrem, A.; Wang, K.; Amaniampong, P. N.; Yang, C.; Gupta, S.; Bohra, H.; Mushrif,
S. H.; Wang, M. Polym. Chem. 2016, 7 (30), 4862.
(265) Bohra, H.; Yu Tan, S.; Shao, J.; Yang, C.; Efrem, A.; Zhao, Y.; Wang, M. Polymer
Chemistry 2016, 7 (41), 6413.
(266) Wang, K.; Wang, M. J. Polym. Sci. Part A: Polym. Chem. 2017, 55 (6), 1040.
(267) Voit, B. I.; Lederer, A. Chem. Rev. 2009, 109 (11), 5924.
(268) Gao, C.; Yan, D. Progress in Polymer Science 2004, 29 (3), 183.
(269) Pu, K.; Mei, J.; Jokerst, J. V.; Hong, G.; Antaris, A. L.; Chattopadhyay, N.;
Shuhendler, A. J.; Kurosawa, T.; Zhou, Y.; Gambhir, S. S.; Bao, Z.; Rao, J. Adv.
Mater. 2015, 27 (35), 5184.
(270) Huang, S.; Upputuri, P. K.; Liu, H.; Pramanik, M.; Wang, M. J. Mater. Chem. B
2016, 4 (9), 1696.
(271) Huang, S.; Kannadorai, R. K.; Chen, Y.; Liu, Q.; Wang, M. Chem. Commun. 2015,
51 (20), 4223.
(272) Wu, Y.; Wang, K.; Huang, S.; Yang, C.; Wang, M. ACS Appl. Mater. Interfaces
2017, 9 (15), 13602.
(273) Amou, S.; Haba, O.; Shirato, K.; Hayakawa, T.; Ueda, M.; Takeuchi, K.; Asai, M.
J. Polym. Sci. A Polym. Chem. 1999, 37 (13), 1943.
(274) Marrocchi, A.; Lanari, D.; Facchetti, A.; Vaccaro, L. Energy Environ. Sci. 2012, 5
(9), 8457.
(275) Woo, C. H.; Thompson, B. C.; Kim, B. J.; Toney, M. F.; Fréchet, J. M. J. J. Am.
Chem. Soc. 2008, 130 (48), 16324.
192
(276) Sivula, K.; Luscombe, C. K.; Thompson, B. C.; Fréchet, J. M. J. J. Am. Chem. Soc.
2006, 128 (43), 13988.
(277) Mauer, R.; Kastler, M.; Laquai, F. Adv. Funct. Mater. 2010, 20 (13), 2085.
(278) Jørgensen, M.; Norrman, K.; Gevorgyan, S. A.; Tromholt, T.; Andreasen, B.; Krebs,
F. C. Adv. Mater. 2012, 24 (5), 580.
(279) Cao, W.; Xue, J. Energy Environ. Sci. 2014, 7 (7), 2123.
(280) Lim, K.-G.; Choi, M.-R.; Kim, J.-H.; Kim, D. H.; Jung, G. H.; Park, Y.; Lee, J.-L.;
Lee, T.-W. ChemSusChem 2014, 7 (4), 1125.
(281) Huang, W.; Gann, E.; Chandrasekaran, N.; Prasad, S. K. K.; Chang, S.-Y.; Thomsen,
L.; Kabra, D.; Hodgkiss, J. M.; Cheng, Y.-B.; Yang, Y.; McNeill, C. R. Adv. Energy
Mater. 2017, n/a.
(282) Kim, Y.; Cook, S.; Tuladhar, S. M.; Choulis, S. A.; Nelson, J.; Durrant, J. R.;
Bradley, D. D. C.; Giles, M.; McCulloch, I.; Ha, C.-S.; Ree, M. Nat. Mater. 2006, 5
(3), 197.
(283) Ballantyne, A. M.; Chen, L.; Dane, J.; Hammant, T.; Braun, F. M.; Heeney, M.;
Duffy, W.; McCulloch, I.; Bradley, D. D. C.; Nelson, J. Adv. Funct. Mater. 2008, 18
(16), 2373.
(284) Kohn, P.; Huettner, S.; Komber, H.; Senkovskyy, V.; Tkachov, R.; Kiriy, A.; Friend,
R. H.; Steiner, U.; Huck, W. T. S.; Sommer, J.-U.; Sommer, M. J. Am. Chem. Soc.
2012, 134 (10), 4790.
(285) Lombeck, F.; Komber, H.; Fazzi, D.; Nava, D.; Kuhlmann, J.; Stegerer, D.; Strassel,
K.; Brandt, J.; de Zerio Mendaza, A. D.; Müller, C.; Thiel, W.; Caironi, M.; Friend,
R.; Sommer, M. Adv. Energy Mater. 2016, 6 (21), 1601232.
193
(286) Oberhumer, P. M.; Huang, Y.-S.; Massip, S.; James, D. T.; Tu, G.; Albert-Seifried,
S.; Beljonne, D.; Cornil, J.; Kim, J.-S.; Huck, W. T. S.; Greenham, N. C.; Hodgkiss,
J. M.; Friend, R. H. The Journal of Chemical Physics 2011, 134 (11), 114901.
(287) Lee, J.-I.; Klaerner, G.; Miller, R. D. Chem. Mater. 1999, 11 (4), 1083.
(288) Chang, S.-W.; Waters, H.; Kettle, J.; Horie, M. Organic Electronics 2012, 13 (12),
2967.
(289) Liu, S.-Y.; Liu, W.-Q.; Xu, J.-Q.; Fan, C.-C.; Fu, W.-F.; Ling, J.; Wu, J.-Y.; Shi,
M.-M.; Jen, A. K.-Y.; Chen, H.-Z. ACS Appl. Mater. Interfaces 2014, 6 (9), 6765.
(290) Liu, S.-Y.; Fu, W.-F.; Xu, J.-Q.; Fan, C.-C.; Jiang, H.; Shi, M.; Li, H.-Y.; Chen, J.-
W.; Yong Cao; Chen, H.-Z. Nanotechnology 2014, 25 (1), 014006.
(291) Maglione, C.; Carella, A.; Centore, R.; Chávez, P.; Lévêque, P.; Fall, S.; Leclerc, N.
Dyes and Pigments 2017, 141, 169.
(292) Dong, D.; Fang, D.; Li, H.; Zhu, C.; Zhao, X.; Li, J.; Jin, L.; Xie, L.; Chen, L.; Zhao,
J.; Zhang, H.; Huang, W. Chem. Asian J. 2017, 12 (8), 920.
(293) Wu, W.; Li, J.; Zhao, Z.; Yang, X.; Gao, X. Organic Chemistry Frontiers 2017, 4
(5), 823.
(294) Payne, A.-J.; C. Welch, G. Organic & Biomolecular Chemistry 2017, 15 (15), 3310.
(295) McAfee, S. M.; Cann, J. R.; Josse, P.; Blanchard, P.; Cabanetos, C.; Welch, G. C.
ACS Sustainable Chem. Eng. 2016, 4 (6), 3504.
(296) Huang, J.; Wang, K.; Gupta, S.; Wang, G.; Yang, C.; Mushrif, S. H.; Wang, M. J.
Polym. Sci. Part A: Polym. Chem. 2016, 54 (13), 2015.
(297) Dang, M. T.; Hirsch, L.; Wantz, G. Adv. Mater. 2011, 23 (31), 3597.
(298) Zeng, L.; Tang, C. W.; Chen, S. H. Appl. Phys. Lett. 2010, 97 (5), 053305.
194
(299) Krasovskiy, A.; Krasovskaya, V.; Knochel, P. Angew. Chem., Int. Ed. 2006, 45 (18),
2958.
(300) Blaskovits, J. T.; Bura, T.; Beaupré, S.; Lopez, S. A.; Roy, C.; de Goes Soares, J.;
Oh, A.; Quinn, J.; Li, Y.; Aspuru-Guzik, A.; Leclerc, M. Macromolecules 2017, 50
(1), 162.
(301) Koo, B.; Sletten, E. M.; Swager, T. M. Macromolecules 2015, 48 (1), 229.
(302) Kowalski, S.; Allard, S.; Scherf, U. ACS Macro Lett. 2012, 1 (4), 465.
(303) Tsao, H. N.; Cho, D. M.; Park, I.; Hansen, M. R.; Mavrinskiy, A.; Yoon, D. Y.; Graf,
R.; Pisula, W.; Spiess, H. W.; Müllen, K. J. Am. Chem. Soc. 2011, 133 (8), 2605.
(304) Huang, J.-H.; Yang, C.-Y.; Ho, Z.-Y.; Kekuda, D.; Wu, M.-C.; Chien, F.-C.; Chen,
P.; Chu, C.-W.; Ho, K.-C. Organic Electronics 2009, 10 (1), 27.
(305) Choi, S. J.; Kuwabara, J.; Kanbara, T. ACS Sustainable Chem. Eng. 2013, 1 (8), 878.
(306) Chen, S.; Lee, K. C.; Zhang, Z.-G.; Kim, D. S.; Li, Y.; Yang, C. Macromolecules
2016, 49 (2), 527.
(307) Wei, H.; Lu, H.; Fang, T.; Bo, Z. Sci. China Chem. 2015, 58 (2), 286.
(308) Du, C.; Li, W.; Duan, Y.; Li, C.; Dong, H.; Zhu, J.; Hu, W.; Bo, Z. Polym. Chem.
2013, 4 (9), 2773.
(309) Qin, R.; Li, W.; Li, C.; Du, C.; Veit, C.; Schleiermacher, H.-F.; Andersson, M.; Bo,
Z.; Liu, Z.; Inganäs, O.; Wuerfel, U.; Zhang, F. J. Am. Chem. Soc. 2009, 131 (41),
14612.
(310) Jo, J.; Pron, A.; Berrouard, P.; Leong, W. L.; Yuen, J. D.; Moon, J. S.; Leclerc, M.;
Heeger, A. J. Adv. Energy Mater. 2012, 2 (11), 1397.
195
(311) Berrouard, P.; Najari, A.; Pron, A.; Gendron, D.; Morin, P.-O.; Pouliot, J.-R.;
Veilleux, J.; Leclerc, M. Angew. Chem. Int. Ed. 2012, 51 (9), 2068.
(312) Yuan, M.-C.; Chiu, M.-Y.; Liu, S.-P.; Chen, C.-M.; Wei, K.-H. Macromolecules
2010, 43 (17), 6936.
(313) Wang, D. H.; Pron, A.; Leclerc, M.; Heeger, A. J. Adv. Funct. Mater. 2013, 23 (10),
1297.
(314) Livi, F.; Zawacka, N. K.; Angmo, D.; Jørgensen, M.; Krebs, F. C.; Bundgaard, E.
Macromolecules 2015, 48 (11), 3481.
(315) Kim, H.; Lee, B. H.; Lee, K. C.; Kim, G.; Yu, J. Y.; Kim, N.; Lee, S. H.; Lee, K.
Adv. Energy Mater. 2013, 3 (12), 1575.
(316) Efrem, A.; Wang, K.; Jia, T.; Wang, M. J. Polym. Sci. Part A: Polym. Chem. 2017,
DOI: 10.1002/pola.28555.
(317) Zhao, Y.; Guo, Y.; Liu, Y. Adv. Mater. 2013, 25 (38), 5372.
(318) Shao, J.; Wang, G.; Wang, K.; Yang, C.; Wang, M. Polym. Chem. 2015, 6 (38),
6836.
(319) Li, Y.; Tatum, W. K.; Onorato, J. W.; Barajas, S. D.; Yang, Y. Y.; Luscombe, C. K.
Polym. Chem. 2017.
(320) Yi, Z.; Wang, S.; Liu, Y. Adv. Mater. 2015, 27 (24), 3589.
(321) Chen, S.; Sun, B.; Hong, W.; Aziz, H.; Meng, Y.; Li, Y. J. Mater. Chem. C 2014, 2
(12), 2183.
(322) Chen, H.; Guo, Y.; Yu, G.; Zhao, Y.; Zhang, J.; Gao, D.; Liu, H.; Liu, Y. Adv. Mater.
2012, 24 (34), 4618.
196
(323) Kang, I.; Yun, H.-J.; Chung, D. S.; Kwon, S.-K.; Kim, Y.-H. J. Am. Chem. Soc.
2013, 135 (40), 14896.
(324) Li, J.; Zhao, Y.; Tan, H. S.; Guo, Y.; Di, C.-A.; Yu, G.; Liu, Y.; Lin, M.; Lim, S. H.;
Zhou, Y.; Su, H.; Ong, B. S. Scientific Reports 2012, 2, srep00754.
(325) Islam, M. N.; Mazhari, B. In 2008 IEEE International Conference on Electron
Devices and Solid-State Circuits; 2008; pp 1–4.
(326) Street, R. A.; Salleo, A. Appl. Phys. Lett. 2002, 81 (15), 2887.
(327) Sun, J.; Devine, R.; Dhar, B. M.; Jung, B. J.; See, K. C.; Katz, H. E. ACS Appl.
Mater. Interfaces 2009, 1 (8), 1763.
(328) Kanimozhi, C.; Yaacobi-Gross, N.; Chou, K. W.; Amassian, A.; Anthopoulos, T.
D.; Patil, S. J. Am. Chem. Soc. 2012, 134 (40), 16532.
(329) Fu, B.; Wang, C.-Y.; Rose, B. D.; Jiang, Y.; Chang, M.; Chu, P.-H.; Yuan, Z.;
Fuentes-Hernandez, C.; Kippelen, B.; Brédas, J.-L.; Collard, D. M.; Reichmanis, E.
Chem. Mater. 2015, 27 (8), 2928.
(330) Gao, Y.; Zhang, X.; Tian, H.; Zhang, J.; Yan, D.; Geng, Y.; Wang, F. Adv. Mater.
2015, 27 (42), 6753.
(331) Lee, J.; Han, A.-R.; Kim, J.; Kim, Y.; Oh, J. H.; Yang, C. J. Am. Chem. Soc. 2012,
134 (51), 20713.
(332) Yun, H.-J.; Kang, S.-J.; Xu, Y.; Kim, S. O.; Kim, Y.-H.; Noh, Y.-Y.; Kwon, S.-K.
Adv. Mater. 2014, 26 (43), 7300.
(333) Suraru, S.-L.; Würthner, F. Angew. Chem. Int. Ed. 2014, 53 (29), 7428.
(334) Sommer, M. J. Mater. Chem. C 2014, 2 (17), 3088.
197
(335) Nakabayashi, K.; Yamada, M.; Mori, H. J. Polym. Sci. Part A: Polym. Chem. 2016,
54 (19), 3151.
(336) Matsidik, R.; Martin, J.; Schmidt, S.; Obermayer, J.; Lombeck, F.; Nübling, F.;
Komber, H.; Fazzi, D.; Sommer, M. J. Org. Chem. 2015, 80 (2), 980.
(337) Luzio, A.; Fazzi, D.; Nübling, F.; Matsidik, R.; Straub, A.; Komber, H.; Giussani,
E.; Watkins, S. E.; Barbatti, M.; Thiel, W.; Gann, E.; Thomsen, L.; McNeill, C. R.;
Caironi, M.; Sommer, M. Chem. Mater. 2014, 26 (21), 6233.
(338) Nohara, Y.; Kuwabara, J.; Yasuda, T.; Han, L.; Kanbara, T. J. Polym. Sci. A Polym.
Chem. 2014, 52, 1401.
(339) Bohra, H.; Shao, J.; Huang, S.; Wang, M. Tetrahedron Letters 2016, 57 (13), 1497.
(340) Haba, O.; Hayakawa, T.; Ueda, M.; Kawaguchi, H.; Kawazoe, T. React. Funct.
Polym. 1998, 37 (1–3), 163.
(341) Andersson, M. R.; Selse, D.; Berggren, M.; Jaervinen, H.; Hjertberg, T.; Inganaes,
O.; Wennerstroem, O.; Oesterholm, J.-E. Macromolecules 1994, 27 (22), 6503.
(342) Hayakawa, T.; Fukukawa, K.-I.; Morishima, M.; Takeuchi, K.; Asai, M.; Ando, S.;
Ueda, M. J. Polym. Sci. A Polym. Chem. 2001, 39 (13), 2287.
(343) Stuart, D. R.; Fagnou, K. Science 2007, 316 (5828), 1172.
(344) Yeung, C. S.; Dong, V. M. Chem. Rev. 2011, 111 (3), 1215.
(345) Wencel-Delord, J.; Dröge, T.; Liu, F.; Glorius, F. Chem. Soc. Rev. 2011, 40 (9),
4740.
(346) Satoh, T.; Miura, M. Chem. Eur. J. 2010, 16 (37), 11212.
(347) Colby, D. A.; Bergman, R. G.; Ellman, J. A. Chem. Rev. 2010, 110 (2), 624.
198
(348) Liu, C.; Yuan, J.; Gao, M.; Tang, S.; Li, W.; Shi, R.; Lei, A. Chem. Rev. 2015, 115
(22), 12138.
(349) Ashenhurst, J. A. Chem. Soc. Rev. 2010, 39 (2), 540.
(350) Cho, S. H.; Kim, J. Y.; Kwak, J.; Chang, S. Chem. Soc. Rev. 2011, 40 (10), 5068.
(351) Yang, Y.; Lan, J.; You, J. Chem. Rev. 2017.
(352) Lane, B. S.; Brown, M. A.; Sames, D. J. Am. Chem. Soc. 2005, 127 (22), 8050.
(353) Pivsa-Art, S.; Satoh, T.; Kawamura, Y.; Miura, M.; Nomura, M. BCSJ 1998, 71 (2),
467.
(354) García-Cuadrado, D.; de Mendoza, P.; Braga, A. A. C.; Maseras, F.; Echavarren, A.
M. J. Am. Chem. Soc. 2007, 129 (21), 6880.
(355) Thompson, M. E.; Baxter, S. M.; Bulls, A. R.; Burger, B. J.; Nolan, M. C.;
Santarsiero, B. D.; Schaefer, W. P.; Bercaw, J. E. J. Am. Chem. Soc. 1987, 109 (1),
203.
(356) Hennessy, E. J.; Buchwald, S. L. J. Am. Chem. Soc. 2003, 125 (40), 12084.
(357) Masui, K.; Ikegami, H.; Mori, A. J. Am. Chem. Soc. 2004, 126 (16), 5074.
(358) Takahashi, M.; Masui, K.; Sekiguchi, H.; Kobayashi, N.; Mori, A.; Funahashi, M.;
Tamaoki, N. J. Am. Chem. Soc. 2006, 128 (33), 10930.
(359) Tsuchiya, K.; Ogino, K. Polym J 2013, 45 (3), 281.
(360) Zhang, Q.; Wan, X.; Lu, Y.; Li, Y.; Li, Y.; Li, C.; Wu, H.; Chen, Y. Chem. Commun.
2014, 50 (83), 12497.
(361) Zhang, Q.; Li, Y.; Lu, Y.; Zhang, H.; Li, M.; Yang, Y.; Wang, J.; Chen, Y.; Li, C.
Polymer 2015, 68, 227.
199
(362) Huang, Q.; Qin, X.; Li, B.; Lan, J.; Guo, Q.; You, J. Chem. Commun. 2014, 50 (89),
13739.
(363) Gobalasingham, N. S.; Noh, S.; Thompson, B. C. Polym. Chem. 2016, 7 (8), 1623.
(364) Chen, H.-Y.; Hou, J.; Zhang, S.; Liang, Y.; Yang, G.; Yang, Y.; Yu, L.; Wu, Y.; Li,
G. Nat. Photon. 2009, 3 (11), 649.
(365) Liu, J.; Kadnikova, E. N.; Liu, Y.; McGehee, M. D.; Fréchet, J. M. J. J. Am. Chem.
Soc. 2004, 126 (31), 9486.
(366) Manceau, M.; Bundgaard, E.; Carlé, J. E.; Hagemann, O.; Helgesen, M.;
Søndergaard, R.; Jørgensen, M.; Krebs, F. C. J. Mater. Chem. 2011, 21 (12), 4132.
(367) Reeves, B. D.; Unur, E.; Ananthakrishnan, N.; Reynolds, J. R. Macromolecules
2007, 40 (15), 5344.
(368) Noh, S.; Gobalasingham, N. S.; Thompson, B. C. Macromolecules 2016, 49 (18),
6835.
(369) Gobalasingham, N. S.; Pankow, R. M.; Thompson, B. C. Polym. Chem. 2017, 8 (12),
1963.
(370) Lotz, M. D.; Camasso, N. M.; Canty, A. J.; Sanford, M. S. Organometallics 2017,
36 (1), 165.
(371) Guo, Q.; Jiang, R.; Wu, D.; You, J. Macromol. Rapid Commun. 2016, 37 (9), 794.
(372) Wang, D.; Izawa, Y.; Stahl, S. S. J. Am. Chem. Soc. 2014, 136 (28), 9914.
(373) Guo, Q.; Wu, D.; You, J. ChemSusChem 2016, 9 (19), 2765.
(374) Saito, H.; Kuwabara, J.; Yasuda, T.; Kanbara, T. Polym. Chem. 2016, 7 (16), 2775.

200
CHAPTER 2: ANALYSIS OF DIVERSE DIRECT ARYLATION
POLYMERIZATION (DARP) CONDITIONS TOWARD THE EFFICIENT
SYNTHESIS OF POLYMERS CONVERGING WITH STILLE POLYMERS
IN ORGANIC SOLAR CELLS

2.1. Introduction

The promise of scalable, flexible, lightweight, and solution processable polymer
solar cells (PSCs) as an inexpensive method of energy generation has motivated research
in the field for two decades.
1,2
In addressing polymer scalability for efficient production,
direct arylation polymerization (DArP)
3–18
has emerged as a simplifying synthetic
alternative to prevalent traditional cross-coupling polycondensation reactions, such as
Kumada,
19
Suzuki,
20
Negishi,
21
and Stille
22
polymerizations.
23
Although Stille
polymerization has been the most effective and widely-employed method toward state-of-
the-art polymers,
24
it necessitates the addition of a toxic
25
and often unstable alkyltin
functional group via a lithiation-metalation step under cryogenic air- and water-free
conditions. Because DArP proceeds through a C-H activation pathway,
26–28
it requires only
halogenation and available acidic protons to proceed, attractively bypassing the need for
stannylation. Elimination of this particular step, arguably the most challenging en route to
Stille-compatible monomers, is a major benefit for large-scale production.
However, it is important to establish the suitability of various synthetic methods
with their targeted application and not merely their large-scale synthetic considerations.
While conjugated polymers have been identified as excellent candidates for photovoltaics,
not all synthetic methods generate polymers of appropriate quality for PSCs. For example,
201
it is well known that some methods such as electropolymerization or chemical oxidative
polymerization, generate polymers that are unsuitable for PSC applications.
29
Although
these methods are faster and more scalable than either Stille or DArP, it is not a viable
method toward high quality PSC materials. Even P3HT synthesized by different highly
successful cross-coupling methods, including Stille, GRIM, and Rieke, can perform
differently from each other in PSCs,
30
particularly in regards to thermal stability
31,32
which
is of critical importance for commercial PSCs.
33
DArP offers the advantages of fewer
synthetic steps, easier purification of the monomers compared to Stille, more
environmentally benign synthesis (avoidance of stoichiometric organotin bromide
byproducts), tin-free end groups, and potentially the same or broader substrate scope—all
incredibly appealing for large scale synthesis. However, concerns about insoluble material
(which industrially is difficult to remove by leaching
34
), defects, low yields, and poor
performance are all significant obstacles for DArP to overcome in order to truly replace
Stille.
In terms of device performance, results vary from method to method for DArP;
however, for the great majority of reports, PSC device results are not provided despite the
widespread claim of DArP being an alternative route toward PSC materials. As a result, a
clear picture of DArP polymer performance in solar cells is limited. The most promising
report on correlation between perfectly alternating DArP polymers and PSC performance
is from Horie, et al.
35
which investigated a series of DArP PCPDTBT polymers in PSCs
and compared them to a Suzuki polymer. Almost all DArP polymers underperformed,
which is consistent with defects or residual impurities and this report remains one of only
a handful of practical evaluations of DArP polymers in PSCs. Ternary random copolymers
202
synthesized by Farinola, et al.
36
via DArP performed poorly compared to Stille
counterparts, consistent with defects. Kanbara, et al.
15
synthesized very high molecular
weight DArP polymers that outperformed Suzuki counterparts dramatically, though it is
uncertain if this is related to molecular weight or impurities in the Suzuki polymer. An
indacenodithiophene-quinoxaline copolymer prepared by Yang, et al.
37
exhibited similar
efficiencies between Stille and DArP, but microwave-assisted DArP performed poorly,
consistent with increased defects.
For DArP to be realized as a true alternative synthetic method for OPV materials,
there are two requirements that must be met: (1) the numerous variations of DArP must be
classified and evaluated on model systems, preferably one with both thiophene and
benzene-like substrates available to study selectivity and defects and (2) the optimal
conditions for each DArP classification should be used to generate polymers that are
compared in solar cell devices against Stille polymers. As outlined in Figure 2.1, DArP
can be generally categorized into three classes. The first class is derived from phosphine-
free direct arylation protocols optimized by Fagnou, et al.
26,27,38–40
that was first adapted to
polymerizations by Kanbara, et al.,
39
tested in devices by Horie, et al.
35
and later optimized
by our group.
8,41
This class typically features an amide such as N,N-dimethylacetamide
(DMA), or other nitrogen containing compound such as N-methyl-2-pyrrolidone (NMP),
35

as the reaction solvent or a major component of the solvent mixture. Pd(OAc)2 is generally
the precatalyst and an acid, such as pivalic acid (PivOH),
39
1-adamantanecarboxylic acid,
15

or neodecanoic acid (NDA)
3,8,11,41
is used in conjunction with a base (e.g. K2CO3) to
generate a carboxylate ligand in situ. The signature feature of this class is the absence of a
phosphine ligand. The second class is derived from studies by Scherf, et al.,
42
Sommer, et
203
al.
43
and Kanbara, et al.,
44
which are similar to Class A but feature a phosphine ligand, such
as PCy 3, and may or may not contain a carboxylic acid.
42
Furthermore, due to the
incorporation of a phosphine ligand, these conditions may utilize solvents other than DMA,
such as toluene, but generally the precatalyst is still Pd(OAc)2. The third class is derived
from the works of Ozawa, et al.
45
and Leclerc, et al.,
4,12
which feature superheated THF or
refluxing toluene, a Hermann-Beller Pd catalyst or Pd2(dba)3 (with or without chloroform
adduct), and a phosphine ligand such as P(o-anisyl)3. These methods most often feature
Cs2CO3 as a base and may or may not feature a carboxylic acid. Together, these three
classes roughly categorize the majority of DArP synthetic methods that are currently well-
explored. From these classifications, the basis for developing a comparative analysis of
DArP methods and their influence on device performance can begin to take shape.
204

Figure 2.1. (Top) General Direct Arylation scheme with AB and AA-BB type monomers
and the final polymer structures and end groups, as well as structural considerations not
typically considered for OPV performance. (Middle) The three general classes of DArP
polymers and the groups that have achieved quality polymers from the associated methods.
(Bottom) Practical considerations for DArP and variables that can affect final polymer
quality.
205

Of particular interest to this work is the alternating polymer based on phenylene
and 4,7-di(thiophene-2-yl)benzo[c][1,2,5]thiadiazole (DTBT), herein referred to as
PPDTBT.
46
With solubilizing hexyldecyl alkoxy (-OHD) chains on the benzene, PPDTBT
is an excellent candidate for DArP because its synthesis requires only a few steps and it
has performed well in PSCs, outperforming the historically dominant electroactive
reference polymer, regioregular poly(3-hexylthiophene) (rr-P3HT) in flexible PSCs
46
and
achieving respectable efficiencies in ITO spin-coated devices (5.08%).
47
It is worth noting
that PPDTBT stands apart from many other donor/acceptor polymers, because it is
successful without needing additives for optimal morphology,
48–51
or other impractical
treatments that reduce stability and lifetime,
52
not to mention challenges removing the high-
boiling additives from the blend in roll-to-roll processing.
53,54
Furthermore, as shown in
Scheme 2.1, direct arylation can be used to simplify the synthesis of the monomers, further
compounding the benefits of the direct arylation method and eliminating two steps en route
toward a high performance polymer.

206

Scheme 2.1. Total synthesis of PPDTBT via DArP and Stille polymerization methods. The
synthesis of PPDTBT via DArP includes the application of small molecule direct arylation
to generate on of the monomers for the DArP route. This enables the synthesis of DArP
PPDTBT in only four steps while the synthesis of Stille PPDTBT requires six steps (though
through the utilization of direct arylation, even the Stille route can have a step saved).
Conditions are as follows: (i) 1. nBuLI, THF, -78°C; 2. SnMe3Cl; (ii) P(o-tol)3, Pd2(dba)3;
(iii) 1. nBuLi, THF, -78°C; 2. SnMe3Cl; (iv) Br2, AcOH; (v) C16H33Br, K2CO3, DMF,
reflux; (vi) PivOH, K2CO3, Pd(OAc)2, DMA, 80°C; (vii) DArP Protocol (See main text);
(viii) P(o-tol)3, Pd2(dba)3.

In this work, we prepare PPDTBT via ten DArP protocols derived from the above
mentioned three synthetic classes in order to analyse thepolymer structures and—most
importantly—determine their suitability in PSCs. We analysed the effect of functionality
on these polymers by synthesizing DArP PPDTBT via two different routes and reporting
the most efficient route toward each class of polymer. Four reaction conditions are adopted
from class A, four from class B, and two from class C. To simplify the descriptions of these
DArP PPDTBT polymers, the class letter is provided with a number to facilitate the
207
discussion of DArP polymers across their classification (e.g. A4, B3, or C1). In order to
definitively compare these polymers to Stille PPDTBT, several batches of Stille PPDTBT
were synthesized and the two highest performing batches were used for comparisons.
These two Stille polymers were generated from different monomers, though the final
polymer has the same repeat unit. This is further explained in the results and discussion but
this was done to ensure parity between DArP polymers generated by two different synthetic
routes. For the two Stille PPDTBT reference polymers that were chosen, one had similar
molecular weight to the DArP polymers (which were between 10 and 20 kDa), and one
higher molecular weight batch which we consider a high performance comparison.
Likewise, sometimes multiple batches of DArP PPDTBT were synthesized across all ten
protocols but the best batches are reported here. Of all the conjugated polymer synthetic
methods to emerge these past several decades, DArP offers the most promise for the
generation of high quality polymers with fewer steps and meaningfully smaller
environmental effects. But for mainstream success, DArP must overcome its reputation for
inferior photovoltaic performance en route to potential industrial scale synthesis.

2.2. Experimental

2.2.1. Materials

Unless otherwise noted, all reagents were purchased and used as received from
Sigma Aldrich. All reactions were performed under dry N2, unless otherwise noted. All dry
reactions were performed with glassware that was oven-dried and then flamed under high
208
vacuum before being backfilled with N2. Conditions for small molecule synthesis of the
monomers are provided in Scheme 2.1 as reported in Ref. 46.

2.2.2. Measurements

NMR spectra were recorded at 25°C using CDCl3. Polymer
1
H NMRs were
obtained on a Varian 600 MHz NMR spectrometer. For polymer molecular weight
determination, polymer samples were dissolved in HPLC grade o-dichlorobenzene (o-
DCB) at a concentration of 0.5 mg ml
−1
, briefly heated and then allowed to turn to room
temperature prior to filtering through a 0.2 μm PTFE filter. SEC was performed using
HPLC grade o-dichlorobenzene at a flow rate of 0.6 ml min
−1
on one 300 × 8.0 mm
LT6000L Mixed High Org column (Viscotek) at 60 °C using a Viscotek GPC Max VE
2001 separation module and a Viscotek TDA 305 RI detector. The instrument was
calibrated vs. polystyrene standards (1050–3,800,000 g mol
−1
) and data was analyzed using
OmniSec 4.6.0 software.

2.2.3. Device Fabrication and Characterization

Roll-Coated ITO-Free Flextrode Method
All processing steps were carried out under ambient conditions using coating and
printing techniques that are directly applicable to large-scale roll-to-roll processing. The
devices (with an active area of approximately 1 cm
2
) were fabricated on a lab-scale mini-
roll coater.
55
Devices were prepared on Flextrode, an ITO-free semi-transparent substrate
composed of PET/Ag-grid/PEDOT:PSS/ZnO.
56
In this study, all polymer:PC61BM (>
209
99.0% purity) ratios were kept 1:1.5 (w/w) and active layers were slot die coated at 70°C
from a 40 mg/mL solution in o-DCB, 3:2 v/v o-DCB/CB (chlorobenzene), or 4:1 v/v o-
DCB/CB. Films with thicknesses of about 400 nm were generated by adjusting the flow
rate of the solution and the web speed. Afterwards, the back PEDOT:PSS was slot die
coated on the active layer followed by screen-printing of a silver current collecting comb
structure on top. The device fabrication was completed by annealing the solar cells in an
oven for 5 min at 100°C.

Spin-Coated ITO Method
All steps of device fabrication and testing were performed in air. ITO-coated glass
substrates (10Ω/□) were sequentially cleaned by sonication in detergent solution, deionized
water, tetrachloroethylene, acetone, and isopropyl alcohol, and dried under nitrogen
stream. A thin layer of PEDOT:PSS (Clevios™ PH 500), filtered with a 0.45μm PVDF
syringe filter (Pall Life Sciences) was first spin-coated on the cleaned glass/ITO substrate
and then placed in an oven at 125°C for 50 minutes under vacuum. Separate solutions of
polymers and PC61BM were prepared in o-dichlorobenzene, which were stirred for 24h
before being mixed at the appropriate ratios (1:1.5 w/w) and stirred an additional 24h to
form homogenous mixture. The final polymer concentration just prior to spin-coating was
10.5 mg/mL. The polymer: PC61BM active layer was spin-coated with a 0.45 PTFE syringe
filter (Pall Life Sciences) on top of the PEDOT:PSS layer. The active-layer thickness was
105-115 nm. After spin-coating of the active layer, the films were first placed into a N2
cabinet for 30 minutes and then placed in a vacuum chamber (Denton Benchtop Turbo IV
Coating System), which was pumped down under high vacuum (< 9x10
-7
torr) after which
210
a 100nm thick layer of aluminium was thermally evaporated at 2-4 Å/sec onto the active
layer through shadow masks to define the active area of the devices as 5.1 mm
2
. Devices
were thermally annealed for a few minutes at 150°C under N2 and allowed to cool to room
temperature before testing.

2.3. Results and Discussion

2.3.1. Synthetic methodology

Synthetic details for the ten DArP protocols and the two reference Stille
polymerizations are summarized in Table 1. Of particular importance in DArP is the
influence of functionality on synthetic performance. Recently, our group
16
and Wang, et
al.
57
made critical observations about which coupling partner should be halogenated for
optimal DArP performance with highly fluorinated substrates. Though the system
presented here is very different because only thiophene has sufficiently acidic protons, it is
worth noting that given these two substrates (phenylene and BT), there are two routes that
can be used to generate the same polymer. In Route X, the thiophene-providing substrate
is 2,2'-(2,5-bis((2-hexyldecyl)oxy)-1,4-phenylene)dithiophene, which is coupled with 4,7-
dibromobenzo[c][1,2,5]thiadiazole to generate PPDTBTX. In Route Y, the thiophene-
containing substrate is 4,7-di(thiophene-2-yl)benzo[c][1,2,5]thiadiazole, which is coupled
with 1,4-dibromo-2,5-bis((2-hexyldecyl)oxy)benzene. These routes are illustrated in
Scheme 2. In our hands, Route Y generates the cleanest monomers and can be considered
the easiest route in terms of purification with either DArP or Stille; however, for achieving
high molecular weight material, it was observed that Route X works best for DArP
211
reactions based on class A and class B, but Route Y works best for reactions based on class
C. Thus, Route X was adopted for Entries A1-A4 and B1-B4, while Route Y was adopted
for Entries C1-2. It is for this reason we report two reference Stille PPDTBT polymers, one
utilizing Route X and one utilizing Route Y with the substrate bifunctionalized with
thiophenes being stannylated. These were prepared via traditional methods in refluxing
toluene with P(o-tol)3 and Pd2(dba)3. The polymers were generated without end-capping in
order to highlight differences originating from natural end groups in devices. Stille
PPDTBTX exhibited molecular weights similar to DArP polymers whereas PPDTBTY has
a much higher molecular weight. Through the use of small molecule direct arylation, the
route toward DArP PPDTBT requires only four steps compared to Stille PPDTBT, which
needs six steps (Scheme 2.1). Traditional Stille cross-coupling requires first the
stannylation of thiophene followed by the coupling to acquire 4,7-di(thiophene-2-
yl)benzo[c][1,2,5]thiadiazole (DTBT). This is then distannylated in order to generate the
monomer for Stille polymerization; however, for DArP, direct arylation of thiophene with
dibromobenzothiadiazole yields DArP-ready DTBT and bypasses two organotin steps in
achieving PPDTBT.

212

Scheme 2.2. Comparison of Route X and Route Y toward generation of DArP PPDTBT.
The thiophene-containing substrate is stannylated for the corresponding Stille route.
213
Table 2.1. Reaction conditions for each DArP/Stille method, yields (after Soxhlet
extraction), molecular weight, dispersity, and presence of defects in NMR analysis.
a
Note that class A and class B were executed from Route X (See Scheme 2), while class C
was generated from Route Y. PPDTBT denotes Stille reference, where subscript indicates
the route.
b
Denotes reaction temperature.
c
Denotes reaction time.
d
Solvent concentration
refers to monomer concentration in determined volume of solvent; mixtures of solvents (i.e
DMA/Toluene) were always 1:1 v/v.
e
Acid refers to the carboxylic acid, if applicable,
which was always neodecanoic in this study. For class A, loading was 0.6 equivalents; for
Entry
a
RT
b

(°C)
T
c

(h)
Solvent (Conc.
M)
d
Acid
e,f
Catalyst
(Loading)
Ligand
(Loading)
Mn
g
(kDa)
Đ
g

Yield
h

(%)
Defects
i

A1 70 48 DMA (0.04) NDA Pd(OAc) 2 (2%) None 11 2.5 25 A,D
A2 90 48 DMA (0.04) NDA Pd(OAc) 2 (2%) None 14 3.9 28 A,D
A3 90 48
DMA/Toluene
(0.04)
NDA Pd(OAc) 2 (4%) None 15 2.5 25 A,D
A4 110 48 DMA (0.04) NDA Pd(OAc) 2 (2%) None 15 4.1 24 A,D
B1 90 72 DMA (0.27) NDA Pd(OAc) 2 (2%) PCy 3 (4%) 15 3.9 25 A (min.)
B2 90 72
DMA/Toluene
(0.18)
NDA Pd(OAc) 2 (4%) PCy 3 (8%) 11 3.6 67 A
B3 90 72 DMA (0.27) None Pd(OAc) 2 (2%) PCy 3 (4%) 6.5 1.7 16 A,D
B4 90 72
DMA/Toluene
(0.18)
None Pd(OAc) 2 (4%) PCy 3 (8%) 8.6 2.1 6.3 A,D
C1 100 48 Toluene (0.4) NDA
Pd 2(dba) 3▪CHCl 3
(0.5%)
P(o-
anisyl) 3
(4%)
9.5 3.7 67 D
C2 120 12 THF (0.4) NDA Pd 2(dba) 3 (2%)
P(o-
anisyl) 3
(16%)
15 2.1 78 N/A
PPDTBT X 110 48 Toluene (0.04) None Pd 2(dba) 3 (2%) P(o-tol) 3 16 2.1 70 N/A
PPDTBT Y 110 48 Toluene (0.04) None Pd 2(dba) 3 (2%) P(o-tol) 3 59 3.3 79 N/A
214
all other classes, loading was 1.0 equivalent.
f
In addition to acid, a base (except for
PPDTBT and PPDTBT via Stille) was always used at 3.0 equivalents, which was K2CO3
for all entries except C1 and C2, which utilized Cs2CO3.
g
As estimated from GPC.
h
After
Soxhlet extraction.
i
Presence of acceptor-acceptor homocouplings denoted with “A” and
presence of donor-donor homocouplings denoted with “D” as determined by
1
H NMR.

Across the significant body of work in DArP, a variety of different carboxylic acids
have been used as proton shuttles. For all experiments where an acid is necessary, we have
chosen to implement neodecanoic acid (NDA), which has had success in our DArP
conditions,
3,8,41,58
as well as conditions reported by Leclerc, et al.,
11
in eliminating β-
defects, which negatively influence rr-P3HT crystallinity and device performance. DArP
P3HT with RR up to 96% were achieved by across-the-board minimization of auxiliary
reagents, including 313 ppm catalyst loading, 0.32M monomer concentration (up from
0.04M), and 3.75% of NDA.
6
Throughout the optimization of DArP P3HT, the reaction
temperature was always kept below the boiling point of DMA. For all of these reasons,
these DArP protocols are incredibly attractive and convenient, and form the bases for our
studies of class A (A1-A4) on the synthesis of DArP PPDTBT.
Applying these homopolymer conditions to PPDTBT copolymer required
increasing the equivalents of both the base and carboxylic acid and tuning the reaction
temperature. We maintained traditional monomer concentrations of 0.04M in DMA (or
DMA/Toluene 1:1 v/v). All polymers reported via class A were prepared via Route X
because the molecular weights surpassed those of Route Y. In all our efforts, however,
keeping the catalyst loading below 2% was not possible. This may indicate low reactivity
215
of the system as no color change was observed multiple times when catalyst loading did
not exceed 2%. This is potentially the signature drawback of applying these conditions to
copolymers, as Kanbara, et al.
59
have suggested that in order for the Pd(0) species to be
generated, homocoupling events must occur first. We too observed the quality of DArP
P3HT decreased with increased catalyst loading.
41
Thus, with higher Pd(OAc)2 loadings,
the occurrence of homocoupling defects may increase proportionally. DArP PPDTBT was
purified by first an initial precipitation of the reaction mixture into methanol, followed by
filtration and Soxhlet extraction by methanol, hexanes, and then chloroform, which was
subsequently concentrated and re-precipitated into methanol. In addition to an overview of
the reaction conditions, Table 1 (A1-A4) provides the yields after purification, the number-
averaged molecular weights as determined by GPC, and the polydispersity.
Although the molecular weights acquired were satisfactory (Mn > 10 kDa) in all
cases, the yields were relatively low. Increasing the temperature from 70°C to 90°C (A2)
improved molecular weight but ultimately did not improve yields significantly.
Incorporating a solvent mixture of DMA/Toluene (1:1 v/v, Entry A3) decreased the
reactivity of the system, therefore higher catalyst loadings (4%) were needed to acquire
good molecular weights. Although toluene has better solubilizing power this result
encourages the reasoning that DMA may play a role as a supporting ligand in the direct
arylation mechanism in phosphine-free DArP.
7
Lastly, A4 was reacted at 110°C, the same
as Stille reaction temperatures, but still well below the boiling point of DMA. This polymer
left insoluble material in the extraction thimble, potentially containing branched structures
due to undesired C-H activation of β-protons at high temperatures. From these
observations, and optoelectronic observations that will be discussed in more detail later,
216
the application of class B DArP conditions were subsequently executed (Entry B1-B4).
These conditions are similar to the catalytic system to class A but feature a phosphine
ligand and optionally include a carboxylic acid.
As observed with class A, Route X was observed to generate higher molecular
weight polymers than Route Y for B1-B4 so those are reported here. For these sets of
reactions, the DArP protocol described by Sommer, et al.
43
was followed. The ligand
incorporated was PCy 3 at a 2:1 ratio with Pd(OAc)2 in all cases and when a carboxylic acid
was used, again NDA was incorporated due to its established advantages. For this set of
experiments, 90°C was chosen to ensure high molecular weights but minimal potential
defects. Unlike entries A1-A4, the concentration of the monomers for these next four
entries was increased to 0.25M, nearly six times as concentrated than A1-A4. Despite the
higher temperatures and more concentrated solution, B3 and B4 exhibited low molecular
weights and yields, reaffirming the role that carboxylic acids play in generating a highly
active catalytic species even in a system with a phosphine ligand.
27
B1 and B2 generated
polymers with good molecular weights but the yields were quite different. Whereas B1 led
to similar molecular weights and yields as class A, B2 had yields near 70%; however, it
was again observed that DMA/Toluene mixture did not generate appreciable color change
in the reaction mixture, so that catalyst loading was doubled to 4% to acquire polymers.
Lastly, the final two DArP conditions continue to feature phosphine ligands but
from protocols derived from Ozawa, et al.
45
Both Leclerc, et al. and Ozawa, et al. have
shown success with P(o-NMe2Ph3)3 as an effective ligand for the synthesis of defect-free
copolymers.
11,60
Through the incorporation of two ligands, P(o-NMe2Ph3)3 and P(o-
anisyl)3, Ozawa, et al. produced copolymers based on dithienosilole and
217
thienopyrroledione without defects.
61
Despite the success of the dual ligand approach, P(o-
anisyl)3 has been successfully incorporated into different catalytic systems as the lone
ligand.
12,62
This is pertinent to this study because the emphasis in this work is the use of
relatively cheap and accessible materials that align with the vision of DArP polymers.
Since P(o-NMe2Ph3)3 is not commercially available, it was not considered for this work
despite its high performance in DArP. As a result, P(o-anisyl)3 was used for entries C1 and
C2. Even alone, however, these conditions are unique because they incorporate NDA
instead of PivOH, which can further elucidate the effect of NDA with P(o-anisyl)3.
Additionally, although both are commercially available, the Herrmann-Beller catalyst was
eschewed for Pd2(dba)3 (or its chloroform adduct) for its relative accessibility, cost, and
abundance.
For class C, it was observed—contrary to class A and B—that Route Y outperforms
Route X, therefore the monomers utilized differ from those used in class A and class B
reactions. This is advantageous because, as previously mentioned, the monomer
purification for Route Y is easier and thus more suitable for large-scale polymer synthesis.
For these remaining studies, entry C1 is based on a study from Ozawa, et al.
61
and was run
in toluene with 0.5% Pd2(dba)3·CHCl3 loading, P(o-anisyl)3, NDA, and Cs2CO3. The
phosphine:catalyst ratio was 8:1 and the monomer concentration was 0.40M in toluene and
reacted for 48h at 100°C. Although similar to C1, including ligand, acid, and base, entry
C2 has some key differences as was inspired from the protocol by Leclerc, et al.
12
Instead
of toluene, the reaction was run in superheated THF (120°C) with a monomer concentration
of 0.40M in a pressurized vessel. The catalyst loading was increased to 2% and the
phosphine:catalyst ratio was maintained at 8:1. It was reacted for the shortest time of all
218
reactions in this study (12h) and the reaction mixture became an appropriate color
(consistent with visual observations of other polymerizations) after only a few minutes.
Certainly, the high temperature and pressure lead to a significant increase in catalytic
efficiency.
These ten DArP protocols across three classes of DArP methodology offer a good
breadth of polymers to analyse. Our studies also indicate that with class A and class B
DArP methods, it is beneficial for the thiophenes to be electron-rich, whereas for class C
methods, electron-poor thiophenes generate higher molecular weight polymers.
Conclusively, however, the presence of NDA—with its combination of good reactivity,
abundance and affordability, its ability to prevent of β-defects, and its compatibility with
all three classes of DArP make it an invaluable additive and proton shuttle worthy of
widespread incorporation into this emerging polymerization method. In the following
sections, our observations regarding structural analyses and electronic properties will be
elucidated.

2.3.2. Structural analysis of DArP PPDTBT

Polymer structure and regularity, whether it manifests as homocoupling content in
alternating copolymers or as regioregularity in unsymmetrical homopolymers, plays a
critical role in the properties of polymers. Several approaches exist to study defects in
polymer chains. Since most polymers are challenging to dissolve in high concentrations,
13
C NMR is generally considered ineffective for detailed polymer characterization;
however, much information can be acquired via
1
H NMR analysis, especially when
comparing several of the same polymers made via different methods. Recently, Sommer,
219
et al.
43
reported a strategic method for analysing homocoupling defects in perfectly
alternating polymers made via DArP by generating homopolymers based on the individual
monomers. These homopolymer peak assignments are useful for identifying homocoupling
defects. In this study, donor-donor homocoupling defects were identified by comparing
DArP PPDTBT spectrum to that of the donor homopolymer reported in a previous work.
16

Figure 2.2 shows stacked NMR of the DArP PPDTBT polymers that exhibited the smallest
quantity of defects from each class, compared to the
1
H NMR spectrum of Stille PPDTBTX
which was of comparable molecular weight. Comparisons within each class are provided
in the Appendix. In Figure 2, these donor-donor couplings are labelled with a blue delta
(δ). Signals corresponding to acceptor-acceptor homocouplings are labelled with a red
alpha (α). These signals were correlated to a similar polymer, poly(4TBB4T), reported in
the literature.
63

Figure 2.2.
1
H NMR spectra (600 MHz, CDCl3, 25 °C) of Stille PPDTBT X, A2, B1, C1,
C2, and Stille PPDTBTY which were observed to be the polymers with the most minimal
defects. The red alpha (α) corresponds to acceptor-acceptor homocoupling defects while
220
the blue delta(δ) corresponds to donor-donor homocoupling defects. The stars (*)
correspond to potential end-chain signals. The route is as outlined in Scheme 2.2.
For entries A1-A4, homocoupling defects were observed in all cases at varying
intensities but all in greater quantities than the Stille PPDTBT reference. Specifically,
higher occurrences of acceptor-acceptor couplings were detected than donor-donor
couplings. Due to being synthesized via Route X, we can reason that increased amounts of
C-Br/C-Br homocouplings occurred. The mechanistic details of these homocoupling
reactions is not fully understood
43
but these may occur from the reduction of C-Br bonds
to C-H bonds promoted by the palladium catalyst or disproportionation of the catalyst to
form dimers.
41,61
A1, generated at the lowest temperatures, showed the lowest content of
homocoupling defects in class A. A3 had the most homocoupling defects, consistent with
the highest catalyst loading (4%). Although temperature plays a role, as observed by AB-
type homopolymers like rr-P3HT, catalyst loading may be more important for generating
defects in DArP methods via class A. With regards to class B, B1 very closely resembles
Stille PPDTBTX. It has the lowest defects of any polymer generated from class A or B.
This is in agreement with the report from Sommer, et al.
43
which shows that PCy 3 and a
carboxylic acid can dramatically reduce homocoupling defects. B2, generated with NDA
in DMA/toluene solvent mixture, did exhibit acceptor-acceptor homocouplings while B3
and B4 (both generated without NDA) exhibited both donor-donor and acceptor-acceptor
homocoupling defects. Of all the polymers produced in this study, B4 showed the most
homocoupling defects. Ultimately, the reaction protocols investigated in class B reveal that
both NDA and PCy3 are necessary to achieve low homocoupling content, consistent with
221
reports from Sommer, et al.
43
but now expanded in scope to include the substrates presented
here.
Although C1 and C2 were generated via Route Y, the Stille counterpart, PPDTBTY,
was not a suitable NMR comparison due to its very high molecular weight, which resulted
in broad
1
H NMR peaks that were indist inguishable from each other. Furthermore, because
of the monomer design for this route, it is more challenging to prepare model
homopolymers to assign homocoupling peaks. Possible donor-donor homocoupling
defects derived from the small molecule 2,2’,5,5’-tetramethoxy-1,1’-biphenyl
64
suggest
that donor-donor homocouplings are present in C1 but not C2. Ultimately, other
characterization techniques would be needed to fully elucidate the quality of C2.

222

Figure 2.3. GIXRD patterns for, as detailed in Table 1, A1 (red line), A2 (purple line),
B1 (blue line), C1 (teal line), C2 (green line), Stille PPDTBTX (black line), and Stille
PPDTBTY (yellow line).
To further characterize the structural considerations of DArP PPDTBT, both DSC
and GIXRD analyses were carried out on the polymers. GIXRD diffraction patterns
(Figure 2.3, additional patterns provided in Figure A1.25-27) show that only a handful of
223
DArP PPDTBT polymers exhibited (100) diffraction peaks, which correlated to
semicrystallinity of thermally annealed pristine polymer films. These specific polymers
(A1, A2, B1, C1, and C2) exhibit strong diffraction peaks comparable to each other;
however, A4, B2, and B3 show diffraction peaks but these have weaker intensities.
Compared to Stille PPDTBT, the interchain distances (See Table 2.2) of A1 and
A2 are similar (about 19.2 Å) but the interchain distances for B1, C1, and C2 are slightly
larger, indicating these polymers do not pack together as tightly as the Stille and class A.
It is possible that the end groups of these polymers may influence this interchain packing.
65

This may relate to the ultimate termination events of these four classes of polymerizations.
Additionally, DSC analysis was carried out on each polymer (Figure A1.23 & 24). Of all
the polymers tested, only the Stille polymers and C2 exhibited endothermic and exothermic
peaks, corresponding to Tm and Tc, respectively (Figure A1.24). This is consistent with
NMR defect analysis though it is interesting that B1, which exhibited minimal acceptor-
acceptor defects, as well as other polymers which showed diffraction peaks via GIXRD
(A1-2, C1) showed no DSC peaks. Since DSC is a bulk polymer measurement, these results
may be more sensitive to structural defects or lower molecular weight features but are not
indicative of thin film quality. For PPDTBTX, PPDTBTY, and C2, the Tm was found to be
265°C, 236°C, and 223°C while Tc was 247°C, 220°C, and 207°C, respectively. The
molecular weight or potential defects could influence these values.

224
Table 2.2. Electrochemical HOMO values, Optical Band Gaps, SCLC hole mobilities, and
d100 Lattice Spacing.
Entry
a
HOMO
b
(eV) Eg
c
(nm/eV) Μ (cm
2
V
-1
s
-1
) d100 (Å)
d
A1 5.43 711/1.74 7.54 x 10
-5
19.23
A2 5.42 708/1.75 7.04 x 10
-5
19.19
A3 5.44 706/1.76 0.63 x 10
-5
N/A
A4 5.42 709/1.75 7.26 x 10
-5
20.48
B1 5.43 700/1.77 8.14 x 10
-5
19.57
B2 5.48 712/1.74 0.88 x 10
-5
19.83
B3 5.52 704/1.76 1.06 x 10
-5
19.79
B4 5.55 705/1.76 0.70 x 10
-5
N/A
C1 5.45 710/1.75 3.56 x 10
-5
20.81
C2 5.45 705/1.76 8.81 x 10
-5
20.29
PPDTBTX 5.43 705/1.76 8.86 x 10
-5
19.02
PPDTBTY 5.44 715/1.73 10.5 x 10
-5
19.15
a
Note that class A and class B were executed from Route X (See Scheme 2), while class C
was generated from Route Y. PPDTBT denotes Stille reference, where subscript indicates
the route.
b
Determined from cyclic voltammetry (vs. Fc/Fc
+
) of the film in acetonitrile with
0.1M TBAPF6. notes reaction temperature.
c
Calculated from the absorption band edge in
thin films, Eg = 1240/λedge.
d
Interchain distances (100) as determined by GIXRD.

2.3.3. Electronic properties and device performance

225
Electronic properties, including electrochemical HOMO levels, absorption band
edges, optical band gaps, space-charge limited current (SCLC) hole mobilities, as well as
d100 interchain spacings as determined by GIXRD are provided in Table 2.2 for DArP
PPDTBT and Stille reference polymers. Optical LUMO, peak absorption information, 2θ,
crystallite size, and additional information can be found in the Appendix (Table A1.1 &
Table A1.2). HOMO levels are similar to Stille reference polymers for all DArP PPDTBT
regardless of the method from which it was generated except for B3 and B4, which had
deeper HOMOs consistent with lower molecular weights
66
and the presence of increased
acceptor-acceptor homocoupling defects. But in all cases, similar optical band gaps were
observed. The similarities in band edge of the absorption profiles result in very similar
optical band gaps for all polymers studied. In general, crystallinity of the polymers
translated into higher SCLC hole mobilities.
67
Polymers with GIXRD diffraction peaks,
like A1, A2, B1, and C1 generally had higher hole mobilities than polymers that did not
show strong diffraction peaks, like A3, B2-B4. The Stille polymers and C2 exhibited the
highest hole mobilities. In most instances, a lack of diffraction peaks and a corresponding
lack of vibronic shoulder in the UV-Vis profile (Figure 2.4) led to lower hole mobilities.
Although the NMR analysis at a cursory glance indicates only subtle differences in
the polymers since defects appear in fairly small quantities, significant differences in both
UV-Vis absorption profiles and PSC performance are observed. With regards to UV-Vis
characterization, all polymers absorb light in two distinct regions: (1) a low coefficient
absorption peak around 425 nm and (2) a more intense absorption between 600 and 660
nm. Stille PPDTBTX and PPDTBTY both show a strong, clear vibronic shoulder around
655nm. Compared to class A DArP polymers, the Stille references are redshifted slightly;
226
however, the most obvious difference is the clear lack of intense vibronic shoulders in
DArP polymers. This is most noticeable in A3 and A4, which have no shoulder, though A3
also exhibits very low absorption coefficients compared to the other DArP polymers (i.e.
A1, A2, and A4). Although not as intense, both A1 and A2 do exhibit subtle peaks near
650 nm, potentially representative of higher structural regularity than other class A DArP
polymers.
11

The same trend is observed for class B DArP polymers, as all absorption profiles
differ significantly from Stille reference polymers. The most promising polymer, B1, does
exhibit a vibronic band around 650 nm, which is more intense than that peak closer to 600
nm. This is an improvement on the best class A DArP polymer absorptions, which may
indicate that B1 has better structural integrity than any other polymer from either class A
or B, emphasizing the potential benefits of PCy 3 to reduce defects. However, absorption
profiles of B2, B3, and B4 are markedly worse than B1. This can be attributed to a
combination of lack of NDA (B3 and B4) and defects introduced with higher catalyst
loadings in DMA/toluene mixtures (B2 and B4).
Lastly, C1 and C2 were also characterized by UV-Vis. C1, like those polymers of
class A and class B, again did not match well with Stille reference polymers and was both
blue-sifted and lacking in a vibronic peak near 650 nm; however, contrary to all observed
DArP polymers, C2 exhibited excellent overlap with Stille reference polymers, showcasing
a strong vibronic shoulder with a more intense peak than even higher molecular weight
Stille PPDTBTY. This optimal overlap suggests that C2 conditions generate polymers that
may have better structural integrity than even their Stille counterparts.
227

Figure 2.4. UV-Vis spectra for all polymers reported in Table 1. Thicknesses of films were
obtained via GIXRD measurements in reflectivity mode. (Top) Class A DArP polymers
(A1 (red line), A2 (blue line), A3 (purple line), A4 (green line), with Stille PPDTBT X
(black line) for reference. (Middle) Class B DArP polymers (B1 (red line), B2 (blue line),
228
B3 (purple line), B4 (green line), with Stille PPDTBTX (black line) for reference. (Bottom)
Class C DArP polymers (C1 (red line), C2 (blue line), with Stille PPDTBTX (black line)
and PPDTBTY (yellow line) for reference.
While these absorption profiles can offer a predictive insight into the potential of
these polymers, it is ultimately the device performance that determines the capacity for
DArP polymers to replace their Stille equivalents. Since it has been postulated that
homocoupling and branching defects originating from unwanted side reactions in DArP
can negatively influence device performance,
8,36,37,68
only DArP PPDTBT polymers that
showed similar characteristics to Stille polymers were considered for device fabrication.
The device results on roll-coated ITO-free substrates for A2, B1, C1, C2, PPDTBTX, and
PPDTBTY are provided in Table 3. To establish their general performance, all polymer
active layers were processed from o-DCB first. The best performing polymers were further
optimized through solvent mixtures, specifically o-DCB:CB 3:2 v/v and o-DCB:CB 4:1
v/v blends.

Table 2.3. ITO-free flexible PSC characteristics of highest quality DArP PPDTBT
compared to Stille reference polymers.
Polymer
a
Solv.
b
JSC
c
(mA cm
-1
) VOC
c
, V FF
c
, (%) η
c
, % (Max)
A2 1 3.61 0.79 30 0.85
B1 1 3.26 0.71 29 0.67
C1 1 1.80 0.80 26 0.37
C2 1 8.84 0.75 47 3.1
229
PPDTBTX 1 8.02 0.72 46 2.7
PPDTBTY 1 10.41 0.75 48 3.7
C2 2 7.66 0.74 53 3.0
PPDTBTX 2 7.58 0.72 47 2.6
PPDTBTY 2 10.2 0.72 42 3.1
C2 3 10.52 0.72 45 3.4
PPDTBTX 3 8.88 0.72 46 2.9
PPDTBTY 3 11.54 0.73 45 3.8
Devices were fabricated on ITO-free flexible substrates from a 40 mg/mL o¬-DCB solution
of 1:1.5 w/w polymer:PC61BM to generate ~400 nm thick active-layer
. a
Entry is as noted
in Table 1.
b
Solvent mixtures for processing are as follows: (1) o-DCB; (2) o-DCB/CB 3:2
v/v; (3) o-DCB/CB 4:1 v/v.
c
Values correspond to the highest performing PSC from each
polymer sample. Average values and ITO-substrate PSCs are provided in the Appendix.

Devices fabricated from polymers A2, B1, and C1 all showed poor performance
that diverged significantly from Stille reference polymers, most likely due to potential
structural defects, which had previously manifested themselves in absorption profiles and
NMR analysis but are now confirmed in both ITO-free and ITO substrates. Although B1
had very few defects per NMR analysis, it still performed poorly, confirming observations
from Leclerc, et al. that NMR analysis is not a definitive method for determining polymer
quality.
11
Stille PPDTBTX, with similar molecular weights to DArP PPDTBT, offers the
best comparison. Both B1 and C2 exhibited a similar VOC (0.71 V and 0.75 V) to that of
the Stille polymers (0.72 – 0.75 V) but increased VOC was observed for A2 and C1.
230
Although the VOC values vary, a potential correlation to electrochemically-determined
oxidative HOMO values cannot be made due to the observed HOMOs being fairly
consistent with one another. A2 and B1 exhibited significantly lower JSC values compared
to PPDTBTX but a higher VOC resulted in A2 exhibiting a higher efficiency (0.85%) than
B1 (0.67%). C1 was the most ineffective material studied in devices, having the lowest JSC
(1.80 mA/cm
-1
) and lowest fill factor (0.26), with a modest efficiency of 0.37%. C2 vastly
outperformed all DArP polymers and proved to be an effective material for PSC active
layers. From o-DCB slot die coating, C2 exhibited higher JSC, VOC, and FF—achieving a
PCE of 3.1% compared to PPDTBTX which achieved 2.7%. Through optimization with
solvent mixing, it is apparent that device performance is sensitive to processing conditions.
For example, roll coating from 3:2 v/v o-DCB/CB solution improved fill factors for C2
devices to as high as 53%, which was the highest fill factor achieved in roll coated devices.
By roll coating from 4:1 v/v o-DCB/CB solution, higher short-circuit currents (10.52
mA/cm
2
) were observed in C2 compared to PPDTBTX (8.88 mA/cm
2
). This increased
short-circuit current of C2 translates into a PCE of nearly 3.4%. PPDTBTX (2.9%) and
PPDTBTY (3.8%) also exhibited their best PCE with the 4:1 solvent ratio, indicating that
in roll coating devices, small amounts of CB can improve device performance significantly.
Although PPDTBTY outperformed its DArP counterpart, the high molecular weight of the
material (roughly a four times larger Mn estimation by GPC) could be responsible for this
disparity. Since it is well known that molecular weight can have a powerful influence on
device performance,
69–71
it is expected that PPDTBTY may exhibit higher performance.
Regardless, the performance of C2 compared to PPDTBTX and its comparable
performance to a PPDTBTY provides further evidence that C2 is structurally superior to
231
other DArP methods and perhaps even superior to the Stille method, which is known to
exhibit some frequency of homocoupling defects.
72–74

Additionally, devices fabricated on glass/ITO are also provided in Table 4 for
additional insight. Again, the polymers evaluated were A2, B1, C1, C2, and the Stille
reference polymers. Solvent mixtures were found to slightly decrease performance, so
devices reported here are all spin-coated from o-DCB. EQE data (acquired on these ITO
substrates), spectral mismatch, and J-V curves for both Flextrode and ITO are also provided
in the Appendix.

Table 2.4. Spin-coated ITO PSC device performance of highest quality DArP PPDTBT
compared to Stille reference polymers.
Polymer
a
JSC
b,c
(mA cm
-1
) VOC
c
, V FF
c
, (%) η
c
, %
A2 7.98 0.81 0.49 3.22
B1 6.62 0.77 0.43 2.17
C1 6.04 0.82 0.36 1.77
C2 9.83 0.80 0.58 4.57
PPDTBTX 9.63 0.80 0.58 4.45
PPDTBTY 10.22 0.81 0.60 4.92
a
Entry as noted in Table 1. Devices as fabricated in the experimental section, active-layer
thickness of 100-110 nm.
b
Mismatch corrected.
c
Results are the average of at least eight
pixels. Raw data, standard deviations, EQE data, and J-V curves provided in the Appendix.
Similar trends are observed in spin-coated ITO devices; however, the VOC does not vary as
much in these devices (0.77 to 0.82 V). The most obvious differences in polymer
232
performance are related to the JSC and FF, with A2, B1, and C1 exhibiting below 50% FF
and a JSC under 8 mA/cm
2
. Conversely, C2 outperformed PPDTBTX slightly (PCE = 4.6%
vs. 4.5%) and was only marginally worse than PPDTBTY (PCE = 4.9%) despite the
differences in molecular weight. It should be noted that although roll-coated polymer
devices are highly challenging to optimize and the upscaling of miniature ITO substrate
performance to large area performance comes with numerous considerations and
challenges, the results for flexible ITO-free solar cells are only marginally worse than ITO-
coated devices reported here and in the literature.
47
This is an impressive achievement that
is a testament to the potential scalability of large area solar cells with scalable polymers,
which as iterated earlier, is an important property for the realization of readily deployable
PSC technology.

2.4. Conclusions

Direct arylation polymerization has been touted as a shorter, simpler route toward
conjugated polymers but the synthetic method has historically been critically important to
the quality of polymers for specific applications. DArP polymers are not often evaluated
in solar cells, generating some uncertainty about their potential ability to actually replace
traditional methods like Stille polycondensation. Through the evaluation of several classes
of DArP synthetic methodology, including the analysis of defects, photophysical
properties, and electronic properties, we determined the suitability of PPDTBT synthesized
via DArP in solar cells compared to high performance Stille counterparts. It was observed
that even within different classes of DArP, polymer quality and solar cell performance can
vary significantly. When DArP PPDTBT was synthesized in superheated THF with
233
Cs2CO3, neodecanoic acid, and P(o-anisyl)3, it generated polymers of exceptional quality
that performed comparably to Stille counterparts in both roll coated ITO-free and ITO
devices. Given similar molecular weights, C2 actually outperformed the Stille reference
polymer. Although not as convenient as other DArP methods which react well-below the
boiling point of the solvent, this superheated method generates polymers of practical value.
As a result, further efforts are encouraged in order for Fagnou-derived DArP conditions to
generate alternating copolymers that perform comparatively to Stille polymers in PSCs.

2.5. References

(1) Yu, G.; Gao, J.; Hummelen, J. C.; Wudl, F.; Heeger, A. J. Science 1995, 270 (5243),
1789.
(2) Thompson, B. C.; Fréchet, J. M. J. Angew. Chem. Int. Ed. 2008, 47 (1), 58.
(3) Rudenko, A. E.; Thompson, B. C. J. Polym. Sci. A Polym. Chem. 2015, 53 (2), 135.
(4) Mercier, L. G.; Leclerc, M. Acc. Chem. Res. 2013, 46 (7), 1597.
(5) Rudenko, A. E.; Thompson, B. C. Macromolecules 2015, 48 (3), 569.
(6) Rudenko, A. E.; Latif, A. A.; Thompson, B. C. J. Polym. Sci. A Polym. Chem. 2015,
53 (12), 1492.
(7) Rudenko, A. E.; Thompson, B. C. J. Polym. Sci. A Polym. Chem. 2015, 53 (21),
2494.
(8) Rudenko, A. E.; Latif, A. A.; Thompson, B. C. Nanotechnology 2014, 25 (1),
014005.
(9) Wakioka, M.; Nakamura, Y.; Hihara, Y.; Ozawa, F.; Sakaki, S. Organometallics
2013, 32 (15), 4423.
234
(10) Wakioka, M.; Kitano, Y.; Ozawa, F. Macromolecules 2013, 46 (2), 370.
(11) Bura, T.; Morin, P.-O.; Leclerc, M. Macromolecules 2015, 48 (16), 5614.
(12) Morin, P.-O.; Bura, T.; Sun, B.; Gorelsky, S. I.; Li, Y.; Leclerc, M. ACS Macro Lett.
2015, 4 (1), 21.
(13) Kuramochi, M.; Kuwabara, J.; Lu, W.; Kanbara, T. Macromolecules 2014, 47 (21),
7378.
(14) Kuwabara, J.; Nohara, Y.; Choi, S. J.; Fujinami, Y.; Lu, W.; Yoshimura, K.; Oguma,
J.; Suenobu, K.; Kanbara, T. Polym. Chem. 2013, 4 (4), 947.
(15) Kuwabara, J.; Yasuda, T.; Choi, S. J.; Lu, W.; Yamazaki, K.; Kagaya, S.; Han, L.;
Kanbara, T. Adv. Funct. Mater. 2014, 24 (21), 3226.
(16) Livi, F.; Gobalasingham, N. S.; Bundgaard, E.; Thompson, B. C. J. Polym. Sci. A
Polym. Chem. 2015, 53 (22), 2598.
(17) Wang, K.; Wang, M. Curr. Org. Chem. 2013, 17, 999.
(18) Wang, X.; Wang, M. Polym. Chem. 2014, 5 (19), 5784.
(19) Osaka, I.; McCullough, R. D. Acc. Chem. Res. 2008, 41 (9), 1202.
(20) Wu, W.-C.; Liu, C.-L.; Chen, W.-C. Polymer 2006, 47 (2), 527.
(21) Chen, T.-A.; Wu, X.; Rieke, R. D. J. Am. Chem. Soc. 1995, 117 (1), 233.
(22) Carsten, B.; He, F.; Son, H. J.; Xu, T.; Yu, L. Chem. Rev. 2011, 111 (3), 1493.
(23) Morin, P.-O.; Bura, T.; Leclerc, M. Mater. Horiz. 2015, 3 (1), 11.
(24) Khlyabich, P. P.; Burkhart, B.; Rudenko, A. E.; Thompson, B. C. Polymer 2013, 54
(20), 5267.
(25) Burke, D. J.; Lipomi, D. J. Energy Environ. Sci. 2013, 6 (7), 2053.
(26) Gorelsky, S. I.; Lapointe, D.; Fagnou, K. J. Am. Chem. Soc. 2008, 130 (33), 10848.
235
(27) Lafrance, M.; Fagnou, K. J. Am. Chem. Soc. 2006, 128, 16496.
(28) Campeau, L.-C.; Fagnou, K. Chem. Commun. 2006, 12 (12), 1253.
(29) Cheng, Y.-J.; Yang, S.-H.; Hsu, C.-S. Chem. Rev. 2009, 109 (11), 5868.
(30) Marrocchi, A.; Lanari, D.; Facchetti, A.; Vaccaro, L. Energy Environ. Sci. 2012, 5
(9), 8457.
(31) Woo, C. H.; Thompson, B. C.; Kim, B. J.; Toney, M. F.; Fréchet, J. M. J. J. Am.
Chem. Soc. 2008, 130 (48), 16324.
(32) Sivula, K.; Luscombe, C. K.; Thompson, B. C.; Fréchet, J. M. J. J. Am. Chem. Soc.
2006, 128 (43), 13988.
(33) Jørgensen, M.; Norrman, K.; Gevorgyan, S. A.; Tromholt, T.; Andreasen, B.; Krebs,
F. C. Adv. Mater. 2012, 24 (5), 580.
(34) Marzano, G.; Ciasca, C. V.; Babudri, F.; Bianchi, G.; Pellegrino, A.; Po, R.;
Farinola, G. M. Eur. J. Org. Chem. 2014, No. 30, 6583.
(35) Chang, S.-W.; Waters, H.; Kettle, J.; Kuo, Z.-R.; Li, C.-H.; Yu, C.-Y.; Horie, M.
Macromol. Rapid Commun. 2012, 33 (22), 1927.
(36) Marzano, G.; Kotowski, D.; Babudri, F.; Musio, R.; Pellegrino, A.; Luzzati, S.; Po,
R.; Farinola, G. M. Macromolecules 2015, 48 (19), 7039.
(37) Chen, S.; Lee, K. C.; Zhang, Z.-G.; Kim, D. S.; Li, Y.; Yang, C. Macromolecules
2016, 49 (2), 527.
(38) Liégault, B.; Lapointe, D.; Caron, L.; Vlassova, A.; Fagnou, K. J. Org. Chem. 2009,
74 (5), 1826.
(39) Fujinami, Y.; Kuwabara, J.; Lu, W.; Hayashi, H.; Kanbara, T. ACS Macro Lett.
2012, 1 (1), 67.
236
(40) Rudenko, A. E.; Wiley, C. A.; Stone, S. M.; Tannaci, J. F.; Thompson, B. C. J.
Polym. Sci. A Polym. Chem. 2012, 50 (18), 3691.
(41) Rudenko, A. E.; Wiley, C. A.; Tannaci, J. F.; Thompson, B. C. J. Polym. Sci. A
Polym. Chem. 2013, 51 (12), 2660.
(42) Kowalski, S.; Allard, S.; Scherf, U. ACS Macro Lett. 2012, 1 (4), 465.
(43) Lombeck, F.; Komber, H.; Gorelsky, S. I.; Sommer, M. ACS Macro Lett. 2014, 3
(8), 819.
(44) Kuwabara, J.; Yamazaki, K.; Yamagata, T.; Tsuchida, W.; Kanbara, T. Polym.
Chem. 2015, 6 (6), 891.
(45) Wang, Q.; Takita, R.; Kikuzaki, Y.; Ozawa, F. J. Am. Chem. Soc. 2010, 132 (33),
11420.
(46) Livi, F.; Zawacka, N. K.; Angmo, D.; Jørgensen, M.; Krebs, F. C.; Bundgaard, E.
Macromolecules 2015, 48 (11), 3481.
(47) Nguyen, T. L.; Choi, H.; Ko, S.-J.; Uddin, M. A.; Walker, B.; Yum, S.; Jeong, J.-E.;
Yun, M. H.; Shin, T. J.; Hwang, S.; Kim, J. Y.; Woo, H. Y. Energy Environ. Sci.
2014, 7 (9), 3040.
(48) Lee, J. K.; Ma, W. L.; Brabec, C. J.; Yuen, J.; Moon, J. S.; Kim, J. Y.; Lee, K.;
Bazan, G. C.; Heeger, A. J. J. Am. Chem. Soc. 2008, 130 (11), 3619.
(49) Lou, S. J.; Szarko, J. M.; Xu, T.; Yu, L.; Marks, T. J.; Chen, L. X. J. Am. Chem. Soc.
2011, 133 (51), 20661.
(50) Rogers, J. T.; Schmidt, K.; Toney, M. F.; Bazan, G. C.; Kramer, E. J. J. Am. Chem.
Soc. 2012, 134 (6), 2884.
237
(51) Rogers, J. T.; Schmidt, K.; Toney, M. F.; Kramer, E. J.; Bazan, G. C. Adv. Mater.
2011, 23 (20), 2284.
(52) Wang, D. H.; Pron, A.; Leclerc, M.; Heeger, A. J. Adv. Funct. Mater. 2013, 23 (10),
1297.
(53) Søndergaard, R.; Hösel, M.; Angmo, D.; Larsen-Olsen, T. T.; Krebs, F. C. Mater.
Today 2012, 15 (1–2), 36.
(54) Søndergaard, R. R.; Hösel, M.; Krebs, F. C. J. Polym. Sci. B Polym. Phys. 2013, 51
(1), 16.
(55) Carlé, J. E.; Andersen, T. R.; Helgesen, M.; Bundgaard, E.; Jørgensen, M.; Krebs,
F. C. Sol. Energ. Mat. Sol. Cells 2013, 108, 126.
(56) Hösel, M.; Søndergaard, R. R.; Jørgensen, M.; Krebs, F. C. Energy Technol. 2013,
1 (1), 102.
(57) Wang, K.; Wang, G.; Wang, M. Macromol. Rapid Commun. 2015, 36 (24), 2162.
(58) Rudenko, A. E.; Khlyabich, P. P.; Thompson, B. C. ACS Macro Lett. 2014, 3, 387.
(59) Kuwabara, J.; Sakai, M.; Zhang, Q.; Kanbara, T. Org. Chem. Front. 2015, 2 (5),
520.
(60) Wakioka, M.; Ishiki, S.; Ozawa, F. Macromolecules 2015, 48 (22), 8382.
(61) Iizuka, E.; Wakioka, M.; Ozawa, F. Macromolecules 2015, 48 (9), 2989.
(62) Wakioka, M.; Ichihara, N.; Kitano, Y.; Ozawa, F. Macromolecules 2014, 47 (2),
626.
(63) Anant, P.; Mangold, H.; Lucas, N. T.; Laquai, F.; Jacob, J. Polymer 2011, 52 (20),
4442.
238
(64) Ishida, T.; Aikawa, S.; Mise, Y.; Akebi, R.; Hamasaki, A.; Honma, T.; Ohashi, H.;
Tsuji, T.; Yamamoto, Y.; Miyasaka, M.; Yokoyama, T.; Tokunaga, M.
ChemSusChem 2015, 8 (4), 695.
(65) Koldemir, U.; Puniredd, S. R.; Wagner, M.; Tongay, S.; McCarley, T. D.; Kamenov,
G. D.; Müllen, K.; Pisula, W.; Reynolds, J. R. Macromolecules 2015, 48 (18), 6369.
(66) Verilhac, J.-M.; Pokrop, R.; LeBlevennec, G.; Kulszewicz-Bajer, I.; Buga, K.;
Zagorska, M.; Sadki, S.; Pron, A. J. Phys. Chem. B 2006, 110 (27), 13305.
(67) Kokil, A.; Yang, K.; Kumar, J. J. Polym. Sci. B Polym. Phys. 2012, 50 (15), 1130.
(68) Homyak, P.; Liu, Y.; Liu, F.; Russel, T. P.; Coughlin, E. B. Macromolecules 2015,
48 (19), 6978.
(69) Ballantyne, A. M.; Chen, L.; Dane, J.; Hammant, T.; Braun, F. M.; Heeney, M.;
Duffy, W.; McCulloch, I.; Bradley, D. D. C.; Nelson, J. Adv. Funct. Mater. 2008, 18
(16), 2373.
(70) Goh, C.; Kline, R. J.; McGehee, M. D.; Kadnikova, E. N.; Fréchet, J. M. J. Appl.
Phys. Lett. 2005, 86 (12), 122110.
(71) Katsouras, A.; Gasparini, N.; Koulogiannis, C.; Spanos, M.; Ameri, T.; Brabec, C.
J.; Chochos, C. L.; Avgeropoulos, A. Macromol. Rapid Commun. 2015, 36 (20),
1778.
(72) Hong, W.; Chen, S.; Sun, B.; Arnould, M. A.; Meng, Y.; Li, Y. Chem. Sci. 2015, 6
(5), 3225.
(73) Lu, L.; Zheng, T.; Xu, T.; Zhao, D.; Yu, L. Chem. Mater. 2015, 27 (2), 537.
239
(74) Vangerven, T.; Verstappen, P.; Drijkoningen, J.; Dierckx, W.; Himmelberger, S.;
Salleo, A.; Vanderzande, D.; Maes, W.; Manca, J. V. Chem. Mater. 2015, 27 (10),
3726.

240
CHAPTER 3: CARBAZOLE-BASED COPOLYMERS VIA DIRECT
ARYLATION POLYMERIZATION (DARP) FOR SUZUKI-CONVERGENT
POLYMER SOLAR CELL PERFORMANCE

3.1. Introduction

Direct arylation polymerization (DArP)
1–6
has recently emerged as a simplifying synthetic
alternative to traditional cross-coupling polymerizations toward conjugated polymers,
which have promise as solution-processable materials for a variety of applications,
including as active layer materials in organic photovoltaics (OPVs); however, it is valuable
to also establish the suitability of various synthetic methods with their targeted application
instead of simply their synthetic feasibility. For example, it is well known that
electropolymerization and chemical oxidative polymerization methods generate materials
that are generally unsuitable for solar cell applications. Although these methods are faster
and more scalable than any traditional method, such as Suzuki or Stille, it is not a viable
method toward high quality OPV materials. In the same way, DArP must be evaluated for
its suitability for generating performance materials. Ultimately, most state-of-the-art
conjugated polymers are synthesized by Stille or Suzuki polycondensation, with Stille
being the most popular method. Recently, increased emphasis has finally been placed on
evaluating DArP polymers practical performance in realistic applications, including as
field-effect transistors and active layer materials in OPVs.
2,7
Generally, these reports have
demonstrated that not all DArP conditions and materials are suitable for good performance.
Whether it is a result of increased homocoupling defects or potential β-defects, more effort
is necessary for evaluating DArP polymers in OPVs.
241
Although a comparison of DArP conditions against a Suzuki model systems for
carbazole-based copolymers has not yet been undertaken, we recently demonstrated DArP
to be a suitable alternative to Stille polycondensation toward both random P3HT
analogues
8
and in perfectly-alternating copolymers
9
for implementation into OPVs;
however, the exploration of DArP as an alternative to Suzuki polycondensation is
uncommon, especially when comparing their performance in OPVs. For carbazole-based
polymers, Suzuki is the most prevalent method due to the instability of tin-functionalized
benzene-like substrates. Thus, the carbazole species is most commonly boronated while
the secondary component (i.e. an acceptor) is halogenated. A goal of the present work is
the evaluation of distinct but successful DArP conditions toward carbazole-based polymers
that are traditionally made via Suzuki polymerization. In this case, the assessment of DArP
conditions will emphasize a direct comparison of practical performance in OPVs against a
Suzuki model polymer, which has yet to be undertaken for the most promising DArP
conditions.
Herein we report the development and comparison of distinct DArP conditions on
the final properties of carbazole-based perfectly alternating copolymer model system,
poly[(9-(heptadecan-9-yl)-9H-carbazole)-alt-(4,7-di(thiophen-2-
yl)benzo[c][1,2,5]thiadiazole)] (PCDTBT). PCDTBT is widely explored and advantageous
for a number of reasons, including its incredibly high internal quantum efficiency with
PC71BM (near 100%)
10
and its thermal stability.
11
From this model system, suitable DArP
conditions are then utilized to expand the polymer family and investigate other carbazole-
based alternating copolymers, including 2,5-diethylhexyl-3,6-di(thiophen-2-yl)-2,5-
dihydropyrrolo[3,4-c]pyrrole-1,4-dione (DPP), 4,10-bis(diethylhexyl)-
242
thieno[2',3':5,6]pyrido[3,4-g]thieno[3,2-c]isoquinoline-5,11-dione (TPTI), 5-octyl-1,3-
di(thiophen-2-yl)-4H-thieno[3,4-c]pyrrole-4,6(5H)-dione (TPD), and 2,5-bis(2,3-
dihydrothieno[3,4-b][1,4]dioxin-5-yl)pyridine (BEDOT-Pyr). These respective polymers,
PCDPP, PCTPTI, PCDTTPD, and PCBEDOT-Pyr, are fully characterized and
implemented in PSCs under ambient conditions with PC61BM to evaluate their raw
performance, which were comparable to Suzuki polymers.

3.2. Materials & Methods

Unless otherwise noted, all reagents were purchased and used as received from
commercial sources. Solvents were purchased from VWR and used without purification
except for tetrahydrofuran (THF), which was dried over sodium/benzophenone before
distillation. All reactions were performed under dry N2 in glassware that was pre-dried in
an oven, unless otherwise noted. Flash chromatography was performed on a Teledyne
CombiFlash Rf instrument with RediSep Rf normal phase disposable columns.
1
H NMR
spectra were recorded in CDCl3 on a Varian Mercury 400 NMR Spectrometer (small
molecules) or a Varian Mercury 600 NMR spectrometer (polymers). N,N-
dimethylacetamide (anhydrous DMA, 99.9%), neodecanoic acid (NDA), thiophene,
cesium carbonate (Cs2CO3), and potassium carbonate (K2CO3) were purchased from Alfa
Aesar. Palladium acetate (Pd(OAc)2 was purchased from TCI (USA).
Tris(dibenzylideneacetone) dipalladium(0) (Pd2dba3) and Tetrakis(triphenylphosphine)
palladium(0) (Pd(PPh3)4 were purchased from Strem Chemicals Inc.
The overall synthesis for DArP and Suzuki PCDTBT are provided in Scheme 1.
The synthesis of the monomers, 2,7-dibromo-9-(heptadecan-9-yl)-9H-carbazole (for
243
DArP), 9-(heptadecan-9-yl)-2,7-bis(4,4,5,5-tetramethyl-1,3,2-dioxaborolan-2-yl)-9H-
carbazole (for Suzuki) and 4,7-bis(5-bromothiophen-2-yl)benzo[c][1,2,5]thiadiazole (for
Suzuki) were performed without modification as reported in the literature.
12
The synthesis
of 4,7-di(thiophen-2-yl)benzo[c][1,2,5]thiadiazole (for DArP) was performed as reported
in the literature, except for substitution of PivOH with NDA.
9
The synthesis of monomers
2,5-diethylhexyl-3,6-di(thiophen-2-yl)-2,5-dihydropyrrolo[3,4-c]pyrrole-1,4-dione
(DPP), 4,10-bis(diethylhexyl)-thieno[2',3':5,6]pyrido[3,4-g]thieno[3,2-c]isoquinoline-
5,11-dione (TPTI), 5-octyl-1,3-di(thiophen-2-yl)-4H-thieno[3,4-c]pyrrole-4,6(5H)-dione
(TPD), and 2,5-bis(2,3-dihydrothieno[3,4-b][1,4]dioxin-5-yl)pyridine (BEDOT-Pyr) were
synthesized without modification as reported in the literature.
13–17

Number average molecular weight (Mn) and polydispersity (Ð) were determined by
size exclusion chromatography (SEC) using a Viscotek GPC Max VE 2001 separation
module and a Viscotek Model 2501 UV detector, with 70 °C HPLC grade 1,2-
dichlorobenzene (o-DCB) as eluent at a flow rate of 0.6 mL/min on one 300 × 7.8 mm
TSK-Gel GMHHR-H column (Tosoh Corp). The instrument was calibrated vs. polystyrene
standards (1050−3,800,000 g/mol), and data were analyzed using OmniSec 4.6.0 software.
Polymer samples for SEC measurements were prepared by dissolving a polymer in hot
HPLC grade o-DCB at a concentration of 0.5 mg/mL and allowed to cool to room
temperature prior to filtering through a 0.2 μm PTFE filter.

Cyclic voltammetry (CV) was performed on Princeton Applied Research
VersaStat3 potentiostat under the control of VersaStudio Software. A standard three-
electrode cell based on a Pt wire working electrode, a silver wire pseudo reference electrode
244
(calibrated vs Fc/Fc
+
which is taken as 5.1 eV vs vacuum),
18,19
and a Pt wire counter
electrode was purged with nitrogen and maintained under a nitrogen atmosphere during all
measurements, which were executed at a scan rate of 0.05 V/s. Polymer films were made
by drop-casting an o-DCB solution of polymer (10 mg/mL) and tetrabutylammonium
hexafluorophosphate (TBAPF6) (30 mg/mL) directly onto the Pt wire and dried under
nitrogen prior to measurement. Acetonitrile was distilled over CaH2 prior to use, and
TBAPF6 (0.1 M) was used as the supporting electrolyte.

Scheme 3.1. Overview of the Synthesis to PCDTBT utilizing traditional methods as well
as direct arylation.
For polymer thin-film measurements, solutions were spin-coated onto pre-cleaned
glass slides from o-dichlorobenzene (o-DCB) solutions at 7 mg/mL. UV−vis absorption
spectra were obtained on a Perkin-Elmer Lambda 950 spectrophotometer. Thicknesses of
the samples and grazing incidence X-ray diffraction (GIXRD) measurements were
obtained using Rigaku diffractometer Ultima IV using a Cu Kα radiation source (λ = 1.54
Å) in the reflectivity and grazing incidence X-ray diffraction mode, respectively.
245

3.2.1. General Procedure for Polymerization via Suzuki PCDTBT (Polymer P1)

Monomers, 2,7-(bis(4,4,5,5-tetramethyl-1,3,2-dioxaboralan-2-yl)-n-9-
heptadecanylcarbazole (0.3 mmol) and 3,6-Bis-(5-bromo-thiophen-2-yl)-2,5-di-n-octyl-
pyrrolo[3,4-c]pyrrole-1,4-dione (0.3 mmol) were dissolved in 15mL THF and 5mL of
water. Tetrakis(triphenylphosphine)palladium(0) (1 mol %) was added along with 8.5
equivalents (relative to total monomer loading) of K 2CO3. The reaction mixture was
vigorously stirred at 85°C for 24h, then precipitated into methanol, filtered, and purified
by Soxhlet extraction with methanol, hexanes, and then chloroform, this final fraction
subsequently being concentrated and precipitated into methanol before being filtered and
dried overnight.

3.2.2. General Procedure for Polymerization via Fagnou DArP (Polymer P2)

Monomers were dissolved in dry DMA to yield a monomer concentration of 0.04M.
Subsequently, 1 equiv. of neodecanoic acid and 1.5 equiv. K2CO3 were added to the
reaction mixture. The solution was degassed with nitrogen flow for 10 minutes before
Pd(OAc)2 was added and the reaction mixture was further degassed for 20 minutes. Then
the reaction was immersed into a pre-heated oil bath at 80°C and stirred rigorously to
disperse the insoluble base under nitrogen atmosphere for 48 hours. Then the reaction was
cooled, a small amount of chlorobenzene was added to the reaction mixture and it was
precipitated into methanol, filtered, and purified by Soxhlet extraction with methanol,
hexanes, and finally chloroform. The final chloroform fraction was concentrated in vacuo
246
and precipitated into methanol. The polymers were filtered and dried overnight under high
vacuum.

3.2.3. General Procedure for Polymerization via Ozawa DArP (Polymer P3, A1-
A4)

Monomers, neodecanoic acid (1 equiv.), Cs2CO3 (3 equiv.), were
dissolved/suspended in dry THF to yield a monomer concentration of 0.4M in a high
pressure vessel. This was degassed with nitrogen for 5 minutes before P(o-anisyl)3 (16
mol%) and Pd2dba3 (2 mol%) were added and the vessel was further degassed for 5 minutes
before the flask was sealed via Teflon screw cap and heated to 120°C for 12h (under
pressure). Then the reaction was cooled, a small amount of chlorobenzene was added to
the reaction mixture and it was precipitated into methanol, filtered, and purified by Soxhlet
extraction with methanol, hexanes, and finally chloroform. The final chloroform fraction
was concentrated in vacuo and precipitated into methanol. The polymers were filtered and
dried overnight under high vacuum.

3.2.4. General Procedure for Polymerization via Biphasic DArP (Polymer P4)

Monomers, neodecanoic acid (1 equiv.), K2CO3 (40 equiv.), were
dissolved/suspended in toluene in a high pressure vessel to yield a monomer concentration
of 0.2M. An equal volume of water was added to the flask along with P(o-anisyl)3 (16
mol%) and PdCl2(PPh3)2 (2 mol%). With nitrogen flow, the bisphasic mixture was
degassed for several minutes before the reaction was heated to 100°C for 12h. Then the
reaction was cooled, a small amount of chlorobenzene was added to the reaction mixture
247
and it was precipitated into methanol, filtered, and purified by Soxhlet extraction with
methanol, hexanes, and finally chloroform. The final chloroform fraction was concentrated
in vacuo and precipitated into methanol. The polymers were filtered and dried overnight
under high vacuum.

3.2.5. Device Fabrication Procedure

All steps of device fabrication and testing were performed in air. ITO-coated glass
substrates (Thin Film Devices, Inc.; 10Ω/□) were sequentially cleaned by sonication in
detergent solution, deionized water, tetrachloroethylene, acetone, and isopropyl alcohol,
and dried under nitrogen stream. A thin layer of PEDOT:PSS (Heraeus Clevios™ PH
1000), filtered with a 0.45μm PVDF syringe filter (Pall Life Sciences) was spin-coated on
the cleaned glass/ITO substrate and then placed in an oven at 125°C for 50 minutes under
high vacuum. Separate solutions which were stirred for 8h before being mixed at the
appropriate ratios (1:1.3 or 1:1.5 w/w) and stirred overnight to form an homogenous
mixture. The final polymer concentration just prior to spin-coating was 11 mg/mL. The
polymer: PC61BM active layer was spin-coated with a 0.45 PTFE syringe filter (Pall Life
Sciences) on top of the PEDOT:PSS layer. The active-layer thickness was 80-105 nm.
After spin-coating of the active layer, the films were first placed into a N2 cabinet for 30
minutes and then placed in a vacuum chamber (Denton Benchtop Turbo IV Coating
System), which was pumped down under high vacuum (< 9x10
-7
torr) after which a 100nm
thick layer of aluminium was thermally evaporated at 3-5 Å/sec onto the active layer
through shadow masks to define the active area of the devices as 5.1 mm
2
. Devices were
allowed to cool to room temperature after deposition and tested immediately.
248
The current density–voltage (J–V) characteristics of the photovoltaic devices were
measured under ambient conditions using a Keithley 2400 source-measurement unit. An
Oriel® Sol3A class AAA S11 solar simulator with a Xenon lamp (450 W) and an AM 1.5G
filter was used as the solar simulator. An Oriel PV reference cell system 91150 V was used
as the reference cell to calibrate the light intensity of the solar simulator (to 100 mW/cm
2
),
achieved by making the Jsc of the reference cell under simulated sunlight as high as it was
under the calibration condition. External quantum efficiency (EQE) measurements were
performed using a 300 W Xenon arc lamp (Newport Oriel), chopped and filtered
monochromatic light (250 Hz, 10 nm FWHM) from a Cornerstone 260 1/4 M double
grating monochromator (Newport 74125) together with a light bias lock-in amplifier. A
silicon photodiode calibrated at Newport was utilized as the reference cell.
Mobility was measured using a hole-only device configuration of
ITO/PEDOT:PSS/Polymer/Al in the space charge limited current regime as described in
literature.
20
The device preparation for a hole-only device was the same as that described
above for solar cells and film thicknesses were determined by GIXRD in the reflectivity
mode. The dark current was measured under ambient conditions and humidity.

3.3. Results and Discussion

The synthetic route toward poly[(9-(heptadecan-9-yl)-9H-carbazole)-alt-(4,7-
di(thiophen-2yl)benzo[c][1,2,5]thiadiazole)] (PCDTBT) by Suzuki polymerization and
DArP is provided in Scheme 3.1 as well as the associated monomer synthesis required to
achieve those polymers. Ultimately, because of the need to stannylate the thiophene to
generate the benzothiadiazole acceptor monomer, the need to brominate that monomer, and
249
boronate the carbazole, direct arylation effectively enables the avoidance of three synthetic
steps en route to PCDTBT. Despite Suzuki being considered a greener and less toxic
alternative to Stille, the traditional route to Suzuki PCDTBT generates tin waste (via the
acceptor synthesis) and utilizes a significant quantity of organolithium reagents.
Consequently, direct arylation makes the synthesis of PCDTBT completely tin-free, while
eliminating a lithiation-boronation step and a bromination step, which make this route
significantly more appealing. It is important to note that the synthesis of DArP PCDTBT
has been previously reported by Leclerc, et al.,
21
but without a bulky carboxylic acid and
was not evaluated in OPVs. Additionally, small molecule direct arylation has been used to
synthesize the BTD monomer (tin-free), but en route to Suzuki PCDTBT.
22
Herein, we
generate PCDTBT via a combination of small molecule direct arylation and DArP—
highlighting the advantages of direct arylation overall.
Both Fagnou- and Ozawa-derived DArP methodologies have generated suitable
polymers for OPVs when compared to Stille;
2,7–9,23,24
however, in the majority of DArP
reports, OPVs are typically not reported. A report from Horie et al.
25
demonstrated that
DArP polymers may behave different in devices owing to defects, which we also
observed.
23
More efforts are necessary to evaluate the substrate scope of DArP for high
performing polymers in practical applications. DArP has a reputation for generating
marginally inferior polymers due to the presence of defects, either homocoupling or β-
defects which result from unselective C-H activation. Even very small amounts of defects
have been shown to negatively influence performance
7,9,23,26
despite comparable
optoelectronic properties. Of particular interest is carbazole-based donors, which have been
shown to generate homocoupling defects even via Suzuki polycondensation, depending on
250
the conditions.
26
The work, from Sommer, et al., demonstrates that even with well-
established Suzuki conditions, different reaction parameters must constantly be evaluated.
Thus, for DArP to be realized as a viable alternative to Stille and Suzuki
polycondensations, different varieties of DArP protocols should be evaluated not only for
their physical and optelectronic properties but for their practical performance, which can
be influenced by minute differences. To that end, this work comprises of the evaluation of
highly promising DArP conditions on the model PCDTBT system prior to exploring
optimized conditions on a variety of carbazole-based alternating copolymers. These
reaction parameters and resulting physical polymer properties are provided in Table 3.1.
These include both traditional Fagnou- and Ozawa-derived DArP conditions that we
previously reported for non-carbazole substrates as well as biphasic conditions adapted
from Leclerc, et al,
27
which utilize toluene/water solvent mixtures but are modified here to
include bulky carboxylic acid, neodecanoic acid (NDA), which is an affordable and
prevalent additive for minimizing defects compared to PivOH. Ultimately, these three
conditions were selected because of their capacity for generating high quality polymers but
with limited comparative analysis in devices.

Table 3.1. Reaction Parameters for the Synthesis of PCDTBT and the Yield, Molecular
Weight, and Dispersity after Soxhlet Extraction
Entry
a
Pd (Load.)
b
P (Load.)
c
Solvent
d
Conc.
e

(M)
Acid
f
Base
g

Temp.,
h

°C
Time,
i
h
Yield,
j
%
M n,
k
kDa
Ð
l
P1
Pd(PPh 3) 4
(1%)
None THF/H 2O 0.04 None K 2CO 3 85 24 76 11.8 2.43
251
P2
Pd(OAc) 2
(2%)
None DMA 0.04 NDA Cs 2CO 3 90 48 44 5.1 2.28
P3
Pd 2dba 3
(2%)
P(o-anisyl) 3
(16%)
THF 0.40 NDA Cs 2CO 3 120 12 70 11.1 3.04
P4
PdCl 2(PPh 3) 2
(2%)
P(o-anisyl) 3
(16%)
Toluene/
H 2O
0.20 NDA K 2CO 3 100 12 64 7.1 2.56
a
Polymers are PCDTBT.
b
Palladium catalyst employed as well as percent loading.
c
Phosphine, if applicable, incorporated as well as percent loading.
d
Solvent or solvent
mixture that was utilized. When mixture is denoted, the v/v ratio was 1:1 in all cases.
e
Concentration of monomers relative to solvent.
f
Carboxylic acid, if applicable,
incorporated, which was always one equiv.
g
Base incorporated, if applicable, which was 3
equiv. for Cs2CO3 or either 8.5 equiv. (Suzuki) or 40 equiv. (DArP) for K2CO3.
h
Temperature of the oil bath.
i
Reaction time.
j
Yield after Soxhlet extraction with methanol,
hexanes, and reprecipitation from chloroform fraction.
k
Molecular weight as determined
by SEC calibrated to polystyrene standards after purification by Soxhlet extraction.
l
As
determined by SEC.

Table 3.2. Optoelectronic Properties of PCDTBT, including HOMO energy levels, SCLC
hole mobilities, optical bandgaps, and polymer solar cell performance.
Entry
a
HOMO
,
b
eV
µ,
c
x 10
-4
cm
2
V
-1
s
-1

Eg,
d

eV

Polymer:
PC61BM
e
Jsc,
f,g
mA cm
-1

Voc,
h
V
FF
i

η,
j
%
P1 5.43 2.34 1.89 1:1.3 6.17 0.87 0.35 1.88
P2 5.58 0.35 1.87 1:1.3 -- -- -- --
P3 5.41 1.46 1.90 1:1.3 6.76 0.88 0.35 2.08
P4 5.44 0.57 1.91 1:1.5 4.15 0.87 0.31 1.12
252
a
Entry as provided in Table 1, where P1 is Suzuki PCDTBT and P2-P5 are DArP PCDTBT.
b
Determined by cyclic voltammetry (vs. Fc/Fc
+
) in 0.1M TBAPF6, where HOMO = 5.1 +
Eox.
c
Measured on neat polymer films.
d
Calculated from the absorption band edge in thin
films, Eg = 1240/λedge.
e
For solar cell data, polymers were spin-coated from
Polymer:PC61BM mixtures dissolved in o-dichlorobenzene (o-DCB) (except for P2 which
was dissolved in chloroform) and dried under N2 for 30 min. prior to aluminum deposition
f
Mismatch corrected.
g
Standard deviations of less than 0.3 mA/cm2 were observed in all
cases averaged over eight pixels.
h
Standard deviations of less than 0.01 V were observed
in all cases averaged over eight pixels.
i
Standard deviations of less than 0.02 were observed
in all cases averaged over eight pixels.
j
Standard deviations of less than 0.2% were
observed in all cases averaged over at least eight pixels.

These iterations of DArP conditions were compared to PCDTBT produced by
Suzuki polymerization (P1), which is the dominant route toward a variety of carbazole-
based copolymers.
28
Conditions for P2 are adopted from Fagnou conditions,
29
which utilize
Pd(OAc)2, are phosphine-free, and incorporate K2CO3 as an insoluble base in DMA at
temperatures below the boiling point. In order to prevent potential β-defects, NDA is
utilized as the acid (to facilitate the C-H activation as a proton shuttle) instead of PivOH.
9,23

P3 is synthesized via high pressure conditions that utilize superheated THF with Pd2dba3,
Cs2CO3, P(o-OMePh)3, and NDA. These conditions were previously demonstrated to
generate polymers that perform comparably to Stille with an alkoxy benzene-based donor
9

and are included here to observe performance compared to Suzuki. Lastly, P4 is derived
from biphasic conditions described above that were recently evaluated by Leclerc, et al.
27

253
but with PivOH replaced with NDA. These conditions also utilize more affordable K2CO3
instead of Cs2CO3 in high loadings (40 equiv.).
Yields, number-averaged molecular weights, and dispersity are provided in Table
1 in addition to the reaction parameters. Both P3 (70%) and P4 (64%) have yields
comparable to the Suzuki reference, P1 (76%), but conditions for P2 result in lower yields
(44%). Most likely, this can be attributed to the lower molecular weights and larger fraction
of material being removed in the hexanes fraction of the Soxhlet extraction, as crude yields
were generally high for all conditions. Both P1 and P3 exhibited similar molecular weights,
which exceed 11 kDa, (though P3 exhibited a higher dispersity) while P2 and P4 were
similar in molecular weight but less than 8 kDa. For P4, it was observed that some material
remained in the Soxhlet extractor thimble after the chloroform fraction. Upon soaking in
hot chlorobenzene, some of this material was dissolved, subsequently concentrated, and
corresponded to about a 9% yield. Per SEC, the molecular weight of this small
chlorobenzene fraction was about 14.5 kDa. Because it constituted such a small part of the
overall polymer yield (from the chloroform fraction), it was not further characterized or
included with the yield of the main fraction. It was also observed that some insoluble
material remained in the thimble for P4, which was the only instance of residual insoluble
material observed for PCDTBT, as P1-P3 were fully solubilized by the hot chloroform
Soxhlet extraction.
254

Figure 3.1. UV-Vis Absorption Profile (a) and External Quantum Efficiency (EQE)
Measurement Data (b) for Suzuki PCDTBT (P1) and DArP PCDTBT as provided in Table
3.1.
255

Figure 3.2. Section of aromatic region for PCDTBT couplings (a), peak assignments (b),
and inset overlay showing lack of homocoupling defects for both P1 and P3 (c).
1
H NMR
was acquired at 80°C in C2D2Cl4. Full NMR spectra are provided in the Appendix.
Polymers in Table 3.1 were subsequently characterized via electrochemical
HOMO energy level determination, SCLC hole mobilities, and UV-Vis absorption
measurements, where optical bandgap for these materials were derived. The thin film
absorption profiles are provided in Figure 3.1a. These observations, along with polymer
solar cell data acquired in a simple and conventional
ITO/PEDOT:PSS/Polymer:PC61BM/Al device architecture, are provided in Table 3.2.
HOMO energy levels for P1, P3, and P4 are consistent and within experimental error (all
around ~5.43 eV) while P2 has a deeper HOMO consistent with its lower molecular weight.
Likewise, optical bandgaps derived from the absorption onset are comparable (1.9 eV),
consistent with other studies of this ubiquitous wide-band gap polymer.
12
Small but
256
significant differences can be observed in the SCLC hole mobility data acquired on these
polymers as neat films in a hole-only device configuration of
ITO/PEDOT:PSS/PCDTBT/Al. Both P1 and P3 exhibit hole mobilities that are greater in
magnitude than P2 or P4, suggesting better organization of the polymer films perhaps due
to higher molecular weight.
30

For Suzuki PCDTBT solar cell data, we note that higher PCE values have been
achieved through modification of the fullerene (utilizing PC71BM to improve spectral
response), higher isolated molecular weights, and other processing enhancements but
emphasize here polymers of comparable molecular weights to facilitate discussion. To that
end, our batch of Suzuki PCDTBT exhibits a PCE of 1.88%, stemming from a short-circuit
current (Jsc) of 6.17 mA cm
-1
, an open-circuit voltage (Voc) of 0.87 V, and a fill factor of
35%. This performance is consistent with a comparable molecular weight Suzuki PCDTBT
made by Leclerc, et al.
31
with PC61BM, which exhibited an efficiency of 2.26%, though
they utilized an etchant, UV-ozone cleaner, a LiF layer, and an end-capped PCDTBT
polymer, which has been shown to improve performance.
32,33
We elected not to end cap
this Suzuki PCDTBT in order to provide a more comprehensive comparison to DArP
polymers, which have an inherent advantage in natural end groups. Additionally, the
optimized PCDTBT:PC61BM ratios are lower than reported elsewhere,
11
possibly because
of different processing conditions and the molecular weights of the polymer used.
Ultimately, our best OPV performance was achieved with a PCDTBT:PC 61BM ratio of
1:1.3, which is consistent with optimized ratios previously observed by our group.
12,28
P2,
via a potential combination of defects and low molecular weight, did not produce a suitable
film for a functioning device. P4, most likely because of its lower molecular weight,
257
performed more poorly than P1. The most promising of the conditions, used to generate
P3, have previously demonstrated compatibility with Stille-convergent DArP polymer
performance.
9
Here, P3 exhibits similar Voc and FF values compared to Suzuki but a higher
Jsc value, resulting in a higher but comparable performance to the Suzuki model polymer.
To further evaluate the solar cell performance, external quantum efficiency (EQE)
measurements were carried out to study the spectral response of the respective PCDTBT
polymers. This data is provided in Figure 3.1b. P1 exhibits the strongest response in the
400 nm region of the polymers studied herein while P3 exhibits the strongest response in
the 600 nm region, though both profiles are fairly similar. P4 is markedly weaker in spectral
response in the 600 nm region.
Because PCDTBT is an amorphous polymer, other indicators of polymer quality
that can be derived from semicrystalline polymers such as GIXRD diffraction peaks and
the lattice spacing, crystallite size, or DSC thermal transitions are not feasible with
PCDTBT. To further evaluate the backbone regularity between P1 and P3, high-
temperature NMR was undertaken in C2D2Cl4 at 80°C for that pair. Full NMR spectra are
provided in the Appendix while a section of the aromatic region for P1 and P3 are provided
in Figure 3.2. Overall, the NMR regions shown in Figure 3.2 not only closely match each
other but also are consistent with those observed by Leclerc, et al.
21
and Sommer, et al.,
3

who produced homocoupling-free PCDTBT polymers. Additionally, as observed by
Sommer et al.
26
the utilization of Pd(PPh3)4 produces Suzuki polymers without
homocoupling defects. Thus, for the P3 to exhibit such a similar profile to P1, it can be
inferred to also exhibit no homocoupling defects. Sommer et al. observed two sets of
doublets that emerge between the main peaks at 8.16 and 8.26 ppm that occupy the “well”
258
region from 8.20 to 8.24 ppm where we observe no signals. It is likely the peaks at 8.19
and 8.24 are related to TBT-H end groups, which they too observed gave signals in that
region and which they deconvoluted to quantify the homocoupling content. Ultimately, the
similarity in NMR spectra between the P1 and P3 polymers suggest the absence of
homocoupling defects and the established evidence for the suppression of β-defects with a
bulky carboxylic acid
7,23,34,35
suggests P3 is defect-free at least to the same extent as the
Suzuki model system.

Scheme 3.2. Synthesis of DArP Carbazole-Based Alternating Copolymers

With the optimal conditions for DArP PCDTBT as utilized in P3, the synthesis of
several carbazole-based copolymers was undertaken. These targets are expounded in
Scheme 3.2 and feature a variety of previously investigated but also relatively unexplored
or novel carbazole-based copolymers, which include 2,5-diethylhexyl-3,6-di(thiophen-2-
yl)-2,5-dihydropyrrolo[3,4-c]pyrrole-1,4-dione (DPP), 4,10-bis(diethylhexyl)-
thieno[2',3':5,6]pyrido[3,4-g]thieno[3,2-c]isoquinoline-5,11-dione (TPTI), 5-octyl-1,3-
di(thiophen-2-yl)-4H-thieno[3,4-c]pyrrole-4,6(5H)-dione (TPD), and 2,5-bis(2,3-
dihydrothieno[3,4-b][1,4]dioxin-5-yl)pyridine (BEDOT-Pyr). The polymer physical
259
properties after Soxhlet extraction and their resulting optoelectronic properties are
provided in Table 3.3. As observed from Table 3.3, yields were generally good for these
carbazole-based copolymers, with A2 giving a consistent yield after Soxhlet extraction to
P3 above, and the other three copolymers giving higher yields. A1 had the highest yields,
molecular weight, and dispersity, which may result from the two branched chains on the
DPP monomer, which could enhance the solubility for reaching higher molecular weights
that resulted in less material being lost in the hexanes fraction. The TPTI monomer, which
also has two branched ethyl hexyl chains, did not reach comparable molecular weights to
A1 but did exceed 12 kDa. Both A3 and A4, which do not have strong solubilizing
functionalities, both exceeded 11 kDa. It is worth noting that a small amount of solid
remained in the thimble for A3, which was not soluble even in hot chlorobenzene and
detracted from the overall yield. Nonetheless, DArP continues to show fairly broad
substrate scope which can now be extended to lactam-containing TPTI-like substrates in
addition to push-pull, nitrogen-containing substrate BEDOT-Pyr, which has been explored
for electrochromics.
17,36

Table 3.3. Optoelectronic Properties of PCDTB, including HOMO energy levels, SCLC
hole mobilities, optical bandgaps, and polymer solar cell performance.
Entry
a
#
b
Yield,
c

%
M n,
d
kDa
Ð
e
HOMO,
f

eV
µ,
g
x
10
-5
cm
2
V
-1
s
-1

E g,
h

eV

Polymer:
PC 61BM
i
Jsc,
j,k
mA
cm
-1

Voc,
l
V
FF
m

η,
n

%
PCBTDPP A1 91 18.7 3.12 5.44 1.48 1.68 1:1.5 7.84 0.83 0.38 2.44
PCTPTI A2 69 12.1 2.26 5.57 0.62 2.25 1:1.5 6.62 0.96 0.47 2.98
PCDTTPD A3 80 10.4 2.07 5.59 1.06 2.09 1:1.5 4.93 0.88 0.42 1.68
260
PCBEDOT-
Pyr
A4 77 11.9 2.51 5.53 0.55 2.31 1:1.5 3.51 0.61 0.33 0.71
a
Entry as illustrated in Scheme 1.
b
Designation as referred to in the main text and Appendix.
c
Yield after Soxhlet extraction with methanol, hexanes, and reprecipitation from
chloroform fraction.
d
Molecular weight as determined by SEC calibrated to polystyrene
standards after purification by Soxhlet extraction.
e
As determined by SEC.
f
Determined by
cyclic voltammetry (vs. Fc/Fc
+
) in 0.1M TBAPF6, where HOMO = 5.1 + Eox.
g
Measured
on neat polymer films.
h
Calculated from the absorption band edge in thin films, Eg =
1240/λedge.
i
Ratio of polymer to fullerene (by weight) used in solar cells. For solar cell data,
polymers were spin-coated from Polymer:PC61BM mixtures dissolved in o-
dichlorobenzene (o-DCB) and dried under N2 for 30 min. prior to aluminum deposition
j
Mismatch corrected.
k
Standard deviations of less than 0.4 mA/cm2 were observed in all
cases averaged over four pixels.
l
Standard deviations of less than 0.004 V were observed
in all cases averaged over four pixels.
m
Standard deviations of less than 0.1 were observed
in all cases averaged over four pixels.
n
Standard deviations of less than 0.2% were observed
in all cases averaged over at least four pixels.

In the discussion of polymer properties, it is worth highlighting works that explore
some of these materials’ Suzuki analogues. For instance, A1 was previously synthesized
by Suzuki polycondensation,
37
which achieved a current density of 5.2 mA cm
-2
along with
an open-circuit voltage (Voc) of 0.85V and a fill factor of 0.37 (PCE=1.6%). With spectral
mismatch correction, we observed similar results in a previous work with non-endcapped
polymer, with a V oc of 0.83V and a fill factor of 0.40 in addition to a corrected Jsc value of
7.99 mA cm
-2
(PCE = 2.64%).
28
Although a DArP PCBTDPP polymer has been reported,
21

261
it was neither synthesized with a bulky carboxylic acid to prevent β-defects nor tested in
solar cells to gauge its practical performance compared to the Suzuki counterpart. Here,
A1 performs quite similarly to our reported Suzuki counterpart, with a Jsc of 7.84 mA cm
-
2
, a V oc of 0.83V, and a fill factor of 0.38 (PCE = 2.44%) despite having a more modest
molecular weight, which may influence the current density and fill factor. An
1
H NMR
spectrum for A1 is provided in the Appendix (Figure A2.12), which has a similar profile
to a Suzuki analogue reported recently,
28
suggesting minimal defects. Additional
properties, including HOMO energy level, hole mobility, and optical bandgap are
consistent with our previously reported Suzuki analogue.
28
The UV-Vis absorption profiles
as well as EQE spectral response measurements are provided in Figure 3.3 for the
carbazole-based series of copolymers. Notably, DPP-containing A1 possesses the lowest
bandgap and absorbs the furthest into the near-IR region.

262

Figure 3.3. UV-Vis Absorption Profile (a) and External Quantum Efficiency (EQE)
Measurement Data (b) for DArP Carbazole-Based Copolymers as designated in Table 3.3.
For A2, we report a DArP version of PCTPTI for the first time here, which like A1
exhibited similar optoelectronic properties to the Suzuki counterpart.
28
This includes
comparable HOMO energy levels, which are quite deep thanks to the TPTI motif, hole
mobilities, and optical bandgaps. Interestingly, in this work we observe higher current
density for the A2 than the Suzuki counterpart; however, this comes at a slight cost to fill
263
factor, resulting in comparable PCE values (PCE of 2.98% compared to 3.06% previously
observed for Suzuki PCTPTI
28
). Notably, this TPTI-containing copolymer possesses the
highest Voc of the polymers studied in this work and one of the widest bandgaps. These
comparable optoelectronic properties are further correlated by close
1
H NMR spectra
profiles between the DArP version reported here (Figure A2.13) and a Suzuki analogue
recently evaluated,
28
though the TPTI unit may promote aggregation that leads to broad,
ill-defined NMR peaks in both cases.
A3 is the DArP analogue to the Suzuki polymer first reported by Leclerc, et al.
16

TPD units are known for deepening the HOMO energy levels and increasing the Voc.
Compared to that report, A3 exhibits slightly higher currents and fill factors but a somewhat
depreciated Voc value, which was reported to be 1.07 V for Suzuki PCDTTPD but observed
to be 0.88 V in our devices. Differences in device fabrication, synthetic method,
endcapping, purification, and processing may contribute to these differences. There have
been other reports of correspondingly lower Voc values as well.
38,39
Their Suzuki
PCDTTPD was rigorously purified for 18h with a palladium scavenger, which was not
undertaken here, and residual palladium content may contribute to diminished Voc values.
40

Additionally, as noted by Sommer et al.,
26
utilization of Suzuki conditions with Pd2dba3
and the phosphine ligand SPHOS can lead to 2-4% carbazole homocoupling defects, which
may have influenced the polymer performance observed.
16
Although a figure of the
1
H
NMR spectrum was not provided in that report, the reported peaks are quite similar to the
ones observed herein (Figure A2.14), which include a broad peak corresponding to 2H
near 8.15 ppm from the carbazole unit and a broad region between 7.59 – 7.10 ppm
corresponding to 8H, which includes the carbazole and dithienyl TPD aromatic protons,
264
highlighting the challenges of good peak resolution with this polymer even at molecular
weights below 13 kDa.
A4 to the best of our knowledge does not have a Suzuki analogue, though the
BEDOT-Pyr motif has been incorporated into polymers for electrochromics,
36
as a push-
pull monomer for electropolymerization. An
1
H NMR spectrum is provided in the
Appendix (Figure A2.15), which shows significant overlap between the carbazole and
pyridine moiety peaks between 8.10-7.26 ppm, which may be exacerbated by the
unsymmetrical BEDOT-Pyr unit, which may result in the significant peak splitting
observed in that region. Despite the promise of an exceptionally wide bandgap and a deep
HOMO energy level, the Voc of this polymer in solar cells is modest. Additional
optimization of the processing conditions may improve these results but as evidenced from
the strong absorption coefficients and high molecular weights and isolated yields, DArP
offers promise as a route toward unexplored polymers with challenging to purify or more
inaccessible substrates. This effort highlights the compatibility of a variety of different
acceptors with the carbazole monomer via DArP.

3.4. Conclusion

In summary, suitable DArP conditions were identified through screening on
ubiquitous model alternating copolymer, poly[(9-(heptadecan-9-yl)-9H-carbazole)-alt-
(4,7-di(thiophen-2-yl)benzo[c][1,2,5]thiadiazole)] (PCDTBT). A variety of DArP
conditions from several classes of reaction protocols were evaluated and compared to their
Suzuki counterpart for the first time. These include biphasic DArP conditions utilizing
water and toluene with bulky carboxylic acid, neodecanoic acid, as well as traditional
265
Fagnou-derived DArP conditions and Ozawa-derived DArP conditions. Through a
combination of suitable molecular weight and solar cell performance, we identify optimal
conditions for screening a series of carbazole-based polymers with a variety of
electronically interesting acceptors to evaluate the substrate scope and their compatibility
with DArP.

3.5. References

(1) Pouliot, J.-R.; Grenier, F.; Blaskovits, J. T.; Beaupré, S.; Leclerc, M. Chem. Rev.
2016, 116 (22), 14225.
(2) Efrem, A.; Wang, K.; Jia, T.; Wang, M. J. Polym. Sci. Part A: Polym. Chem. 2017,
DOI: 10.1002/pola.28555.
(3) Lombeck, F.; Komber, H.; Gorelsky, S. I.; Sommer, M. ACS Macro Lett. 2014, 3
(8), 819.
(4) Iizuka, E.; Wakioka, M.; Ozawa, F. Macromolecules 2015, 48 (9), 2989.
(5) Kuwabara, J.; Yasuda, T.; Choi, S. J.; Lu, W.; Yamazaki, K.; Kagaya, S.; Han, L.;
Kanbara, T. Adv. Funct. Mater. 2014, 24 (21), 3226.
(6) Rudenko, A. E.; Thompson, B. C. J. Polym. Sci. A Polym. Chem. 2015, 53 (2), 135.
(7) Dudnik, A. S.; Aldrich, T. J.; Eastham, N. D.; Chang, R. P. H.; Facchetti, A.; Marks,
T. J. J. Am. Chem. Soc. 2016, 138 (48), 15699.
(8) Rudenko, A. E.; Khlyabich, P. P.; Thompson, B. C. ACS Macro Lett. 2014, 3, 387.
(9) Livi, F.; Gobalasingham, N. S.; Thompson, B. C.; Bundgaard, E. J. Polym. Sci., Part
A 2016, 54 (18), 2907.
266
(10) Park, S. H.; Roy, A.; Beaupré, S.; Cho, S.; Coates, N.; Moon, J. S.; Moses, D.;
Leclerc, M.; Lee, K.; Heeger, A. J. Nat Photon 2009, 3 (5), 297.
(11) Beaupré, S.; Leclerc, M. J. Mater. Chem. A 2013, 1 (37), 11097.
(12) Khlyabich, P. P.; Rudenko, A. E.; Street, R. A.; Thompson, B. C. ACS Appl. Mater.
Interfaces 2014, 6 (13), 9913.
(13) Khlyabich, P. P.; Burkhart, B.; Ng, C. F.; Thompson, B. C. Macromolecules 2011,
44 (13), 5079.
(14) Cao, J.; Liao, Q.; Du, X.; Chen, J.; Xiao, Z.; Zuo, Q.; Ding, L. Energy Environ. Sci.
2013, 6 (11), 3224.
(15) Berrouard, P.; Dufresne, S.; Pron, A.; Veilleux, J.; Leclerc, M. J. Org. Chem. 2012,
77 (18), 8167.
(16) Najari, A.; Berrouard, P.; Ottone, C.; Boivin, M.; Zou, Y.; Gendron, D.; Caron, W.-
O.; Legros, P.; Allen, C. N.; Sadki, S.; Leclerc, M. Macromolecules 2012, 45 (4),
1833.
(17) Irvin, D. J.; Jr, C. J. D.; Reynolds, J. R. Chem. Commun. 1999, No. 20, 2121.
(18) Cardona, C. M.; Li, W.; Kaifer, A. E.; Stockdale, D.; Bazan, G. C. Adv. Mater. 2011,
23 (20), 2367.
(19) Thompson, B. C.; Kim, Y.-G.; McCarley, T. D.; Reynolds, J. R. J. Am. Chem. Soc.
2006, 128 (39), 12714.
(20) Kokil, A.; Yang, K.; Kumar, J. J. Polym. Sci. B Polym. Phys. 2012, 50 (15), 1130.
(21) Morin, P.-O.; Bura, T.; Sun, B.; Gorelsky, S. I.; Li, Y.; Leclerc, M. ACS Macro Lett.
2015, 4 (1), 21.
267
(22) Lombeck, F.; Matsidik, R.; Komber, H.; Sommer, M. Macromol. Rapid Commun.
2015, 36 (2), 231.
(23) Rudenko, A. E.; Latif, A. A.; Thompson, B. C. Nanotechnology 2014, 25 (1),
014005.
(24) Chen, S.; Lee, K. C.; Zhang, Z.-G.; Kim, D. S.; Li, Y.; Yang, C. Macromolecules
2016, 49 (2), 527.
(25) Chang, S.-W.; Waters, H.; Kettle, J.; Kuo, Z.-R.; Li, C.-H.; Yu, C.-Y.; Horie, M.
Macromol. Rapid Commun. 2012, 33 (22), 1927.
(26) Lombeck, F.; Komber, H.; Fazzi, D.; Nava, D.; Kuhlmann, J.; Stegerer, D.; Strassel,
K.; Brandt, J.; de Zerio Mendaza, A. D.; Müller, C.; Thiel, W.; Caironi, M.; Friend,
R.; Sommer, M. Adv. Energy Mater. 2016, 6 (21), 1601232.
(27) Grenier, F.; Goudreau, K.; Leclerc, M. J. Am. Chem. Soc. 2017, 139 (7), 2816.
(28) Ekiz, S.; Thompson, B. C. J. Polym. Sci. A Polym. Chem. 2017, doi:
10.1002/pola.28680.
(29) Rudenko, A. E.; Wiley, C. A.; Tannaci, J. F.; Thompson, B. C. J. Polym. Sci. A
Polym. Chem. 2013, 51 (12), 2660.
(30) Verilhac, J.-M.; Pokrop, R.; LeBlevennec, G.; Kulszewicz-Bajer, I.; Buga, K.;
Zagorska, M.; Sadki, S.; Pron, A. J. Phys. Chem. B 2006, 110 (27), 13305.
(31) Wakim, S.; Beaupré, S.; Blouin, N.; Aich, B.-R.; Rodman, S.; Gaudiana, R.; Tao,
Y.; Leclerc, M. J. Mater. Chem. 2009, 19 (30), 5351.
(32) Koldemir, U.; Puniredd, S. R.; Wagner, M.; Tongay, S.; McCarley, T. D.; Kamenov,
G. D.; Müllen, K.; Pisula, W.; Reynolds, J. R. Macromolecules 2015, 48 (18), 6369.
268
(33) Park, J. K.; Jo, J.; Seo, J. H.; Moon, J. S.; Park, Y. D.; Lee, K.; Heeger, A. J.; Bazan,
G. C. Adv. Mater. 2011, 23 (21), 2430.
(34) Rudenko, A. E.; Thompson, B. C. Macromolecules 2015, 48 (3), 569.
(35) Bura, T.; Morin, P.-O.; Leclerc, M. Macromolecules 2015, 48 (16), 5614.
(36) Du Bois, C. J.; Larmat, F.; Irvin, D. J.; Reynolds, J. R. Synthetic Metals 2001, 119
(1), 321.
(37) Zou, Y.; Gendron, D.; Badrou-Aïch, R.; Najari, A.; Tao, Y.; Leclerc, M.
Macromolecules 2009, 42 (8), 2891.
(38) Uddin, M. A.; Kim, T.; Yum, S.; Choi, H.; Hwang, S.; Kim, J. Y.; Woo, H. Y.
Current Applied Physics 2015, 15 (5), 654.
(39) Song, K. W.; Choi, M. H.; Lee, J. Y.; Moon, D. K. J. Ind. Eng. Chem. 2014, 20 (1),
290.
(40) Bracher, C.; Yi, H.; Scarratt, N. W.; Masters, R.; Pearson, A. J.; Rodenburg, C.;
Iraqi, A.; Lidzey, D. G. Organic Electronics 2015, 27, 266.

269
CHAPTER 4: CONJUGATED POLYMERS VIA DIRECT ARYLATION
POLYMERIZATION IN CONTINUOUS FLOW: MINIMIZING THE COST
AND BATCH-TO-BATCH VARIATIONS FOR HIGH-THROUGHPUT
ENERGY CONVERSION

4.1. Introduction

Organic photovoltaic (OPV)
1-3
technology differentiates itself from all other PV
technologies by enabling preparation under ambient conditions using low temperature roll-
to-roll (R2R) coating and printing of liquid inks onto flexible substrates. Together with
potentially low material cost and usage, these R2R solution processing techniques allow
large scale manufacturing at extreme rates outperforming any known energy resource with
respect to manufacturing rate, energy pay-back time and energy return factor.
4
For large
scale fabrication of organic electronics, conjugated polymers are especially attractive
because they have proven to be compatible with R2R processing techniques and allow for
the formation of flexible high performance devices for both organic field effect transistors
and OPVs. In addition, they are strong absorbers of visible light, in even <100 nm thick
film devices, and the power conversion efficiency (PCE) of polymeric based OPVs has
now reached over 11% for small scale record laboratory devices (1-10 mm
2
).
5
High
performance polymers are generally adapted to an ideal combination between spectral
coverage and morphological properties by simple modification of solubilizing sidechains
and the conjugated backbone.
270
Conjugated polymers are typically synthesized by copolymerizing two
electronically distinct monomeric units and the most common reaction methodology
employed is the palladium catalyzed Stille cross coupling polymerization of bromide-
terminated and trimethylstannyl-terminated monomers (Figure 4.1). The advantages of the
Stille polymerization are its broad scope and high reliability, i.e. compatible with a wide
variety of functional groups, demonstrated high yield and the possibility for synthesis of
conjugated polymers with high molecular weight. These attributes have made the Stille
reaction very popular in laboratory scale synthesis of functional polymer materials.

Br Br
Stille
+ Sn Sn
DArP
Br Br
Sn Br
H H
+
Ar
1
Ar
1
Ar
1
Ar
1
Ar
2
Ar
2
Ar
2
Ar
2
n
n
HBr

Figure 4.1. Schematic representation of copolymerizations using Stille and direct arylation
(DArP) cross coupling polymerization.
However, the Stille reaction has some significant drawbacks that increase in
severity as scale is increased. The major challenge is the stoichiometric amounts of the
highly toxic organotin byproduct, in terms of trialkyltin derivatives, making this reaction
impractical for production in industrial scale. Moreover, stannylated monomers are
synthesized via multistep organometallic processes that require challenging purification
271
steps and more often the metallated monomers are unstable and problematic to purify.
However, developments in organic synthetic methodologies can address these issues by
providing new synthetic tools. In recent years direct arylation polymerization (DArP) of
non-preactivated arenes with aryl halides has attracted much attention as an alternative to
the Stille reaction (and Suzuki coupling) and several reports have shown that high quality
conjugated polymers can be synthesized via this route and successfully be applied in
organic electronic devices.
6,7
In its simplest form, DArP is carried out by coupling one
aromatic C-H bond with an aryl halide C-X bond creating a C-C bond (Figure 4.1).
Compared to the Stille polymerization, which requires lithiation and stannylation of one
monomer, the DArP reaction does not require preparation of the toxic stannylated
monomer and thus a complex and toxic synthetic step can elegantly be discarded. From an
industrial point of view, the DArP protocol bears many advantages, i.e. simple synthetic
route with reduced steps, reduced waste production and it provides a better atom economy
since use of organometallic reactants are avoided. Together with reduced cost for waste
disposal, synthetic routes with fewer steps require smaller quantities of reactants, solvents,
reagents and man hours. Therefore, the overall cost of the target conjugated polymer is
expected to be lowered as the materials cost is known to increase linearly with the number
of synthetic steps.
8,9
The use of the DArP reaction as a protocol for the preparation of
conjugated polymers has already been exploited and there has been several successful
reports in the literature where conjugated polymers have been synthesized in high yield,
high quality (i.e. defect free) and with high molecular weight.
7,10,11

Besides synthetic complexity, upscaling from milligram scale, which is the
standard scale when testing and producing record semiconducting polymers, to the
272
kilogram scale needed in a mass production can be a major issue in terms of reproducibility.
While it is possible to produce large quantities of conjugated polymer materials using
traditional batch synthesis, problems such as variability from synthesis to synthesis leads
to batch-to-batch variations in yield, molecular weight and distribution which can be a
crucial parameter for most polymer systems in terms of delivering uniform high
performance in organic electronics such as OPVs. Due to mass and heat-transfer issues,
batch-to-batch variations are especially a challenge when scaling up polymerizations,
which most often makes it difficult to reproduce the degree of polymerization just by
copying reaction conditions from a small scale polymerization protocol to a larger scale.
Thus, when upscaling a batch reaction one typically has to optimize the reaction conditions
on a large scale which is time consuming, requires new large scale equipment and large
amounts of reactants for optimization. On the other hand, if the polymerization could be
optimized with small scale equipment and the reactor could be automatically filled and
emptied at the end of the reaction; up-scaling would be extremely straightforward and
efficient. This highlights some of the attractive features of continuous flow synthesis where
the reaction conditions always are almost exactly the same, regardless of scale. By using a
reactor with fixed internal diameter the scaling of a flow process can be done without
altering the reaction volume and thereby it is possible to keep the reaction conditions
constant. The reactant solution is simply pumped into a preheated reactor at a constant
continuous flow where the flow and reactor volume regulate the reaction time. Upscaling
of a reaction is basically realized by pumping larger amounts of reactant solution through
the reactor.
12

273
There has been recent interest in conjugated polymer synthesis using continuous flow
methods and various polymerization reactions (i.e., Stille coupling, Suzuki coupling,
Grignard metathesis and Kumada coupling) have indeed been translated to the continuous
flow process with success.
12-15
However, there has only been one report where the DArP
reaction has been studied in continuous flow where the polymer poly[isoindigo-alt-EDOT]
was synthesized and tested in OPVs, though on a small scale.
16
One concern in DArP is
the potential for unselective C-H activation towards branching defects, which is often
mitigated by selecting substrates with blocked β-positions (as is the case with EDOT).
Thus, a goal of the present work is to evaluate C-H selectivity in a continuous flow system
with DArP and the resulting structure-function relationship of defects and solar cell
performance. Herein, we report the continuous flow synthesis of the copolymer PPDTBT,
based on dialkoxyphenylene and dithienylbenzothiadiazole (see Scheme 4.1), using DArP,
including optimization experiments in order to combine DArP chemistry with a continuous
flow process.
To ensure high solubility and molecular weight, 2-hexyldecyloxy sidechains were
incorporated on the benzene and the total synthesis of DArP PPDTBT can be reduced to 4
simple steps which are very appealing for low cost synthesis on an industrial scale.
Furthermore, PPDTBT has outperformed the state-of-the-art material poly(3-
hexylthiophene) (P3HT) in roll coated flexible OPVs
7
which designate it as a convincing
future candidate for high-throughput roll-to-roll OPV production.
The polymers generated from the DArP experiments in continuous flow were
evaluated by UVvis, GIXRD, SCLC hole mobility, and through the preparation of bulk
heterojunction (BHJ) OPVs. Fabrication of the solar cells was carried out on a previously
274
reported compact coating/printing machine,
17
which enables the preparation of OPVs in a
directly scalable manner. PCEs > 3% could be reached with ITO-free roll-coated solar
cells, based on DArP PPDTBT, where all layers were deposited by solution processing.

4.2. Experimental

4.2.1. Materials

Unless otherwise noted, all chemicals and reagents were purchased and used as
received from Sigma Aldrich or TCI. Synthesis of the monomers 2, 3 and 5 were carried
out following the procedure reported in the literature.
18

4.2.2. Continuous Flow Polymerization

Stille continuous flow polymerization was performed on a commercially available
flow chemistry system (the E-Series) from Vapourtec with a Std Tube Reactor Assembly
with 20 mL SS. A monomer solution of 0.150 M together with the catalyst system
Pd2dba3/P(o-tolyl)3 (3mol%) was dissolved in toluene and applied with a flow rate of 0.33
mL min
−1
at 160 °C under 20 bars back-pressure. The product was collected by discharging
the reaction mixture into a stirring solution of methanol/NH4OH(aq) 10:1 (v/v), followed
by Soxhlet extraction with methanol, hexane, dichloromethane and chlorobenzene. The
chlorobenzene fraction was precipitated in methanol, filtered and dried in vacuum to give
the final product.
DArP continuous flow polymerization was performed on a commercially available
flow chemistry system (the E-Series) from Vapourtec with an in-house built stainless steel
275
column reactor. A monomer solution of 0.150 M together with the catalyst system
Pd2dba3/P(o-anisyl) (3% mol), and neodecanoic acid (NDA) (1 eq.) was dissolved in
toluene and applied to the prepacked reactor, as described by Grenier et al.
17
, containing
cesium carbonate and carboxylate additive dispersed in celite with a flow rate between 0.1-
0.2 mL min
−1
at 100-160 °C under 7-20 bars back-pressure. The product was collected by
discharging the reaction mixture into a stirring solution of methanol/NH4OH(aq) 10:1
(v/v), and worked up in the same manner as for the Stille polymerization.

4.2.3. Polymer molecular weight

For polymer molecular weight determination, polymer samples were fully
dissolved in HPLC grade o-dichlorobenzene at a concentration of 0.5 mg/ml, briefly heated
and then allowed to return to room temperature prior to filtering through a 0.2 μm PTFE
filter. SEC was performed using HPLC grade o-dichlorobenzene at a flow rate of 0.6
ml/min on one 300 × 8.0 mm LT6000L Mixed High Org column (Viscotek) at 60°C using
a Viscotek GPC Max VE 2001 separation module and a Viscotek TDA 305 RI detector.
The instrument was calibrated versus polystyrene standards (1,050 – 3,800,000 g/mol) and
data was analyzed using OmniSec 4.6.0 software.

4.2.4. Cyclic Voltammetry (CV)

CV was executed on a Princeton Applied Research VersaStat3 potentiostat under
the control of VersaStudio Software. A standard three electrode cell based on a Pt wire
working electrode, a Pt wire counter electrode, and a silver wire pseudo reference electrode
276
(calibrated vs. Fc/Fc+ which is taken as 5.1 eV vs. vacuum)
19
was purged with nitrogen
and maintained under nitrogen atmosphere during all measurements. For CV, acetonitrile
was distilled over CaH2 prior to use and tetrabutyl ammonium hexafluorophosphate (0.1
M) was used as the supporting electrolyte. Polymer films were made by applying a
10mg/mL o-DCB solution via drop-casting directly onto the working electrode under a
nitrogen umbrella and thoroughly dried prior to measurement.

4.2.5. Thin Film Measurements (UV-Vis, GIXRD, Crystallite Size, SCLC Hole
Mobilities)

For thin film measurements, solutions were spin-coated onto pre-cleaned 2.5 cm
2

glass slides (sonicated for 10 minutes in water, acetone, and isopropyl alcohol then dried
under high N2 flow) from 7 mg/mL o-dichlorobenzene solutions. UV-vis absorption
spectra were obtained on a Perkin-Elmer Lambda 950 spectrophotometer. The thickness of
thin films and GIXRD measurements were obtained using Rigaku Diffractometer Ultima
IV using Cu Kα radiation source (λ = 1.54 Å) in the reflectivity and grazing-incidence X-
ray diffraction mode, respectively.

Crystallite size was estimated using Scherrer’s equation
20,21
:
τ = Kλ/(β cosθ) (1)
where τ is the mean size of the ordered domains, K is the dimensionless shape factor (K =
0.9), λ is the x-ray wavelength, β is the line broadening at half the maximum intensity
(FWHM) in radians, and θ is the Bragg angle.
277
Mobility was measured using a hole-only device configuration of
ITO/PEDOT:PSS/Polymer/Al in the space charge limited current regime (SCLC).
22
ITO-
coated glass substrates (10 Ω/square) were sequentially cleaned by sonication in detergent
solution, deionized water, tetrachloroethylene, acetone, and isopropyl alcohol, and dried
under nitrogen stream. A thin layer of PEDOT:PSS (Clevios™ PH 500), filtered with a
0.45μm PVDF syringe filter (Pall Life Sciences) was first spin-coated on the cleaned
glass/ITO substrate and then placed in an oven at 125°C for 50 minutes under vacuum.
Polymer was spin-coated onto the PEDOT:PSS layer from 7 mg/mL o-dichlorobenzene
solutions with a 0.45 PTFE syringe filter (Pall Life Sciences). After spin-coating of the
polymer layer, the films were first placed into a N2 cabinet for 30 minutes and then placed
in a vacuum chamber (Denton Benchtop Turbo IV Coating System), which was pumped
down under high vacuum (< 9x10-7 torr) after which a 100nm thick layer of aluminium
was thermally evaporated at 2-4 Å/sec onto the active layer through shadow masks to
define the active area of the devices as 5.1 mm
2
. Thicknesses were measured on a Rigaku
Diffractometer Ultima IV using Cu Kα radiation source (λ = 1.54 Å) in the reflectivity
mode. The dark current was measured under ambient conditions. At sufficient potential the
mobilities of charges in the device can be determined by fitting the dark current to the
model of SCL current and described by equation 2:
2
0 3
9
8
SCLC R
V
J
L
ε εµ =
(2),
where JSCLC is the current density, ε0 is the permittivity of space, εR is the dielectric constant
of the polymer (assumed to be 3), μ is the zero-field mobility of the majority charge
carriers, V is the effective voltage across the device (V = Vapplied – Vbi – Vr), and L is the
polymer layer thickness. The series and contact resistance of the hole-only device (18 – 23
278
Ω) was measured using a blank (ITO/PEDOT/Al) configuration and the voltage drop due
to this resistance (Vr) was subtracted from the applied voltage. The built-in voltage (Vbi),
which is based on the relative work function difference of the two electrodes, was also
subtracted from the applied voltage. The built-in voltage can be determined from the
transition between the ohmic region and the SCL region and is found to be about 1 V.

4.2.6. OPV Fabrication

ITO free roll coated OPV devices were prepared on a substrate consisting of
PET/Ag grid/hole transport layer/ZnO as reported in the literature,
23
using an earlier
reported mini roll coater.
17
The active layer solution, consisting of PPDTBT:PCBM (1:1.5
by weight) dissolved in ODCB (40 mg ml
-1
) was slot-die coated at 80 °C with a flow rate
of 0.16 mL min
−1
and a web speed of 0.8 m min
−1
giving a wet thickness of 13 μm
corresponding to a dry thickness of ≈400 nm.

4.2.7. Device Testing

IV-characteristics were measured with a Keithley 2400 source meter under 100 mW
cm
−2
white light source (AM1.5G) from a Steuernagel KHS1200 solar simulator. The
active area was accurately measured using ultrafast light beam induced current (LBIC)
mapping.[24]

4.3. Results and discussion

279
Monomer synthesis: The preparations of the monomers 2 and 5, on a scale up to 0.5 kg, is
outlined in Scheme 1 starting from low cost materials, 1,4-dihydroxybenzene and 4,7-
Dibromobenzo[c]-1,2,5-thiadiazole. 1,4-dihydroxybenzene was dialkylated with 2-
hexyldecyl bromide in the presence of sodium hydroxide in DMSO to afford the
dialkoxybenzene 4 in reasonable yield (50-60%). 4 was then subjected to quantitative
bromination giving the 2,5-dibromo-1,4- dialkoxy-benzene 5. The benzothiadiazole
monomer 2 was prepared in one step by introducing the flanking thiophenes through a
Stille coupling with 2-tributyltin-thiophene. Purification of 2 was simply done by flushing
the reaction solution through a short plug of silica, to remove palladium residues, followed
by concentration in vacuum and recrystallization to afford fine orange needle-like crystals
in high yield (90%).

O
S S
N
S
N
+
O
N
S
N
Br Br
S
Sn R
R
R
S S
N
S
N
Sn Sn
HD
HD OH
HO
O
O HD
HD Br
Br
S
S
N
S
N
O
O
HD
HD
(i) (ii)
(iii)
(v) (iv) (vi)
1 2 3
4 5
PPDTBT
n
Stille
H H
DArP

Scheme 4.1. Total synthesis of PPDTBT. (i) Toluene, PdCl2(PPh3)2, (90%). (ii) THF,
LDA, trimethyltinchloride, (65%). (iii) Toluene, Pd2dba3/P(o-tolyl). (iv) DMSO, sodium
hydroxide, 2-hexyldecanyl bromide (60%). (v) Acetic acid/CHCl3 (1:1), Br2, (95%). (vi)
Toluene, Pd2dba3/P(o-anisyl), Cs2CO3, NDA.

280
Polymer synthesis: In terms of DArP, reported work from Thompson, et al.,
25
Leclerc, et
al.,
26
and Marks, et al.
6
highlight the importance of a bulky carboxylic acid, such as
neodecanoic acid (NDA), for improving polymer quality. Small amounts of β-defects (~1%
or less) are possible with pivalic acid (PivOH) even in optimized DArP conditions[27] due
to unselective C-H activation and may have a noticeable effect on performance.[25] In our
previous work, we optimized the batch synthesis of PPDTBT using DArP methods
including the analysis of defects, photophysical properties, and electronic properties to
determine the suitability of PPDTBT synthesized via DArP in OPVs. Under optimized
conditions DArP PPDTBT was synthesized in superheated THF with Cs2CO3 as base,
bulky NDA as additive and Pd2dba3/P(o-anisyl) as catalytic system. Under the optimized
reaction conditions polymers of exceptional quality were generated showing PCEs > 3%
in roll coated OPVs which was comparable to Stille counterparts. Though, when translating
the DArP batch reaction to continuous flow several considerations have to be taken into
account. First of all, the HPLC pump which is used to pump the reaction solution into the
reactor does not tolerate solid particles so the carbonate base has to be loaded on a column
reactor as a stationary phase. Unfortunately, NDA, which is a liquid even when
deprotonated (unlike PivOH), can be washed out of the column with solvents. As a result,
it was included with the feed solution as the mobile phase. Though, to achieve higher
molecular weights pivalate (Piv) was also utilized in the column reactor as a stationary
phase, whereby the mobile phase, containing the rest of the reactants (i.e. monomers, NDA
and catalyst), can be pumped through in a continuous flow (Figure 4.2). Secondly, in our
initial continuous flow experiments we tried to use THF as solvent but without success.
Whereas hot THF is an excellent solvent for PPDTBT it also dissolved and flushed out the
281
stationary phase over time. While it only involved smaller quantities it was enough to
inhibit the degree of polymerization and also lead to shut down of the flow chemistry
system due to precipitation of solid particles in the back pressure regulator (BPR). For these
reasons, we switched to toluene which is a very poor solvent for the base and pivalate
additive and thus a truly insoluble stationary phase could be preserved.

Figure 4.2: Schematic presentation of the DArP flow synthesis setup. BPR: Back pressure
regulator.
In a typical fl ow experiment the monomer units, 2 and 5 (Scheme 4.1), together
with the catalyst system Pd2dba3/P(o-anisyl) and NDA was dissolved in toluene and
pumped (Knauer HPLC Pump) into a column reactor with a flow speed ranging from 0.1
to 0.2 mL*min
−1
, resulting in a reaction time of 60-120 min, keeping the pressure around
7 bars with a BPR. We used column reactors filled with cesium carbonate and carboxylate
additive dispersed in celite as described by Leclerc.
16
As described above, the highest
degree of polymerization was afforded when we used carboxylate additive both in the feed
solution and packed in the column reactor to ensure that the polymerization proceeded all
through the reactor. Initially we used a commercially available glass column reactor from
Vapourtec (Figure 4.3) but unfortunately the column pressure limit was not compatible
282
with our reaction conditions which resulted in bursting of the column. Apparently a high
pressure can build up inside the reactor along with the polymerization reaction and thus it
would be more sensible to use a stainless steel reactor with a higher pressure limit. A
stainless steel column reactor with a 12 ml volume (after solid packing) was built in house
and all DArP experiments in continuous flow were performed in this reactor, as seen in
figure 3. To diminish diffusion of reaction solution on the column we did not run reactions
below 150 mM concentration because when diluted, the polymerization rate is reduced for
the diluted fractions at the start and finish of the flow experiment resulting in a lower yield.
These concentrations typically consume about 2 grams of monomer, which afforded yields
around 40-50% after Soxhlet purification with minor batch-to-batch variation in molecular
weight.

Figure 4.3. Pictures of the commercially available glass column reactor from Vapourtec
and the in-house built stainless steel reactor.
283
Table 4.1. Reaction conditions, molecular weight and photovoltaic parameters for DArP
and Stille in continuous flow polymerizations.
Entry
Reaction
time
(min)
Temp.
(C°)
Mn
(kDa)/PDI
a

Jsc (mA/cm2) Voc (V)
FF
(%)
PCE
(%)
1 60 160 24/2.2 6.7±1.3 0.76±0.00 33±3 1.7±0.4
2 60 140 32/2.0 9.5±0.1 0.78±0.00 38±1 2.8±0.1
3 60 120 25/2.1 9.1±0.0.1 0.79±0.00 45±1 3.2±0.1
4 80 120 27/2.0 9.6±0.2 0.78±0.00 41±2 3.0±0.1
5 120 120 28/2.3 10.5±0.2 0.78±0.00 42±2 3.5±0.2
6
(0.17M)
120 120 60/2.9 8.4±0.2 0.78±0.00 37±2 2.40±0.1
7
(Stille)
1440 160 53/3.2 10.5±0..3 0.80±0.00 46±0.8 3.90±0.1
a
As estimated from GPC after Soxhlet extraction using polystyrene standards.

The reaction time (related to flow rate), temperature, and resulting molecular
weight of the polymers are provided in Table 1. We first studied the influence of the
reaction temperature on the polymerization rate by running the DArP reaction at
temperatures from 160 °C down to 120 °C while keeping the reaction time at 60 min. No
significant change in number average molecular weight (Mn) was observed between the
160 °C reaction (Table 4.1, entry 1) and the 120 °C reaction (Table 4.1, entry 3) though a
284
minor increase in Mn, from 24 kDa to 32 kDa, was observed when going from 160 °C to
140 °C indicating that temperature has a restricted influence on the polymerization rate
around 120-140 °C. We also tried to run the reaction at 100-110 °C but this only resulted
in low molecular weight oligomers. Subsequently, we increased the reaction time, by
lowering the flow from 0.2 ml/min to 0.1 ml/min, from 60 min to 120 min which resulted
in a small enhancement of the molecular weight from 25 kDa to 28 kDa (Table 4.1, entry
3-5). To avoid longer reaction times on this flow system and in order to increase the
molecular weight further we tried to enhance the concentration of the monomers from 150
mM to 170 mM while keeping the reaction time at 120 min. A clear enhancement of the
molecular weight from 28 kDa to 60 kDa, though with a slightly higher PDI, is detected
which is actually higher than a reference polymer batch prepared by a Stille
copolymerization in continuous flow on a similar scale (Table 4.1, (entry 6-7). Though, it
should be mentioned that a significant pressure build-up was observed due to increased
viscosity of the polymer solution inside the column reactor. This issue could complicate
the flow synthesis in a future polymer scale up process and thus alternative materials for
the column packing should be explored in order to ease the flow of the polymer solution.
Due to the high molecular weights, good peak resolution could not be achieved via
1
H NMR. While this may make the analysis of potential defects less straightforward, recent
work from Janssen, et al.
28
and Sommer, et al.
29
suggests that structure-function
relationships can offer insight into polymer quality when NMR analysis is not
straightforward or challenging. Optoelectronic properties, such as HOMO energy level,
absorption coefficients, optical band gaps, SCLC hole mobilities, and d100 spacing derived
from GIXRD diffraction peaks are provided in Table 4.2.
285

Table 4.2. Electrochemical HOMO Values, Optical Band Gaps, SCLC hole mobilities, and
d100 Lattice Spacing.
Entry
HOMO
a

(eV)
α
b
(λmax)
(cm
-1
)
Eg
c

(eV)
µ
(cm2 V
-1
s
-
1
)
d100
d

(Å)
Crystallite size
(nm)
1 5.47 96584 1.72 1.76 x 10
-5
18.82 13.74
2 5.49 95833 1.72 3.37 x 10
-5
18.94 13.06
3 5.50 102020 1.72 4.21 x 10
-5
18.78 13.28
4 5.49 110289 1.71 5.19 x 10
-5
18.82 13.74
5 5.48 107965 1.73 6.68 x 10
-5
18.82 13.98
6 (0.17M) 5.47 94964 1.72 1.26 x 10
-5
18.90 12.07
7 (Stille) 5.50 87331 1.71 7.86 x 10
-5
18.82 13.74
a
Determined from cyclic voltammetry (vs. Fc/Fc+) of the film in acetonitrile with 0.1M
TBAPF6.
b
Extinction coefficients determined from thin film thickness measurements by
GIXRD in the reflectivity mode.
c
Calculated from the absorption band edge in thin films,
Eg = 1240/λedge.
e
Interchain distances (100) as determined by GIXRD.

Through optoelectronic properties, the presence or lack of defects can be
postulated. For example, previous evaluations of DArP PPDTBT (from batch synthesis)
that generated even minimal amounts of homocoupling defects, including no donor/donor
homocoupling but a small amount of acceptor/acceptor coupling, demonstrated loss of the
vibronic shoulder in the UV-Vis absorption profile, even when molecular weights were
286
comparable.
30
None of the polymers reported here lose the distinctive vibronic shoulder
characteristic of the semicrystalline PPDTBT polymer (Figure 4.4a). Both Janssen, et al.
and Sommer, et al. also observed changes in the UV-Vis absorption profiles resulting from
differences in thin film behavior of polymers with homocoupling defects, namely
weakening of absorption peaks or slanting of the absorption onset. This was true even for
amorphous polymers, where defects in PPDTBT may have a more pronounced effect. In
fact, the intensity of the vibronic shoulder suggests the DArP polymers may have greater
ordering in the solid state than the Stille reference. This improved ordering may result from
more benign end groups via DArP or possibly fewer homocoupling defects.

Figure 4.4. (a) UV-Vis spectra and (b) GIXRD patterns for polymers reported in Table 2.
287

GIXRD measurements were executed to further evaluate crystallinity. The (100)
diffraction peak position for these polymers are similar, suggesting that all polymers
produced via flow are semicrystalline in nature with similar d100 spacings (Table 4.2 and
Figure 4.4b). This suggests that—if defects are indeed present for the DArP polymers—
they are present in very small quantities. Indeed, as was observed with the vibronic
shoulders in UV-Vis absorption profiles, the intensity of the diffraction peaks for DArP
polymers are generally stronger than that of the Stille reference. Additionally, crystallite
size was estimated utilizing Scherrer’s equation to determine the crystalline correlation
lengths (CCL) of the polymers. In most cases, the full width at half the maximum (FWHM)
values were similar, resulting in CCL values that ranged between 12.07 and 13.98 nm
(Table 4.2).
Beyond these subtle differences in vibronic shoulder and crystallinity, other properties are
quite similar between the various PPDTBT polymers as seen in Table 4.2. HOMO energy
levels are comparable and within measurement error. The optical band gaps, as determined
from the onset, are quite similar at around 1.7 eV for all polymers. Together, this data
suggests that the polymers are of high quality overall and if defects are present, they are in
small enough quantities to not significantly affect thin film optoelectronic properties.
The lack of indicators for suggesting defects suggests that—consistent with
previous observations with this high performing DArP catalytic system—the presence of
significant homocoupling defects may be mitigated. However, the evaluation of potential
β-defects is less straightforward and can be challenging to quantify for substrates more
complex than P3HT. It has been speculated that cross-linking can result in insoluble
288
polymer, which is sometimes observed in DArP. However, due to the challenges of
extracting all the polymer from the column, determining what is insoluble from the
Celite/carboxylate/Cs2CO3 mixture is prohibitively challenging. Observations from
Thompson, et al.
25
have suggested that small amounts of β-defects (<1%) are still readily
soluble and can have a minimal effect on GIXRD and optoelectronic properties, but still
diminish solar cell performance. Most likely, due to the optimal morphology required for
OPVs, small amounts of β-defects may not dramatically diminish optoelectronic properties
but could influence interactions with fullerene and charge transport.
Thus, the only true metric for identifying small quantities of β-defects is through
either NMR analysis or evaluation in a practical application, where minute differences in
structure are compounded through increased complexity of the supramolecular
morphology. It has been observed with P3HT:PC61BM OPVs that even 0.16% β-defect
content in P3HT can diminish fill factors (FF) by up to 25%.
25
OPV performance can offer
a critical window into the nuanced differences between synthetic methods. As a
performance reference, PPDTBT prepared via Stille cross coupling in continuous flow is
provided as Entry 7 in Table 4.1. As can be seen from Table 4.1, the reaction at 160°C
(Entry 1) results in good molecular weight polymer that underperforms in both Jsc and FF.
It has been observed that lower temperatures can reduce defects,
31
which suggests that
reacting at such high temperatures may generate polymers of poorer quality. Reducing the
reaction temperature to 140°C improves the performance, consistent with generating fewer
defects; however, the fill factor is still diminished. Lowering the temperature further, to
120°C, generates polymer that performs quite well in devices, achieving a PCE of 3.2%. It
is critical to note here that the Stille reference polymer has almost double the molecular
289
weight of this DArP analog while both Voc and FF are comparable and the Jsc differs by
about 1.4 mA cm
-2
. The molecular weight influence on device performance has been well-
established.
32
For example, Xiao, et al. observed—albeit with a different polymer—a Jsc
increase from 3.5 mA cm
-2
to 7.4 mA cm
-2
with an M n increase from 17 to 32 kDa, although
Voc and FF did not change significantly. This is a 111% increase in Jsc for a polymer of
double the molecular weight. They also observed an increase from 7.4 to 9.9 mA cm
-2
for
an increase from 32 to 73 kDa (34% increase), most likely due to polymer optoelectronic
properties saturating at some intermediate molecular weight.
33
Thus, it can be reasoned that
for Entry 3, the lower Jsc compared to the Stille reference may most likely be attributable
to lower molecular weight.
Continuing the optimization of the DArP in flow experiments, which emphasized
keeping the temperature at 120°C, the flow rate was reduced for Entry 4 to 0.150 mL/min,
and then reduced further to 0.100 mL/min for Entry 5, hereby increasing the reaction time
to 90 min and 120 min, respectively. Reducing the flow rate modestly increased the
molecular weight, from 25 kDA up to 28 kDA, but this corresponded to an increase in Jsc
from 9.1 to 10.5 mA cm
-2
, which is comparable to the Stille reference polymer. Some
variations in Voc and FF were observed, which may stem from small quantities of defects
but could potentially be attributed to residual palladium content or slight differences in
polydispersity. Regardless, this result validates the potential for continuous flow DArP
methods to rival Stille counterparts, owing to superior end groups and minimal defects;
however, achieving higher molecular weights may also yield better results.
Increasing the monomer feed concentration to its saturation point (for the solid
BTD monomer) in room temperature toluene (0.17M) produced considerably higher
290
molecular weights; however, significant pressure buildup in the column resulted from the
viscosity of polymer/toluene elution. This higher pressure may have led to undesirable
defects because despite the polymer’s exceptional molecular weight, the performance is
modest. Correspondingly, certain optoelectronic properties are inconsistent. For example,
it possesses one of the smaller vibronic shoulders of the DArP family of copolymers
(Figure 4.4a) as well as somewhat lower SCLC hole mobilities (Table 4.2) compared to
both the higher performing but lower molecular weight counterparts and the Stille
reference. These observations suggest polymer of poorer overall quality despite the high
molecular weights.
Overall, the device performance suggests that DArP may be a viable method toward
quality polymers, when accounting for molecular weight, but some limitations are observed
when tuning the parameters. Entry 3, which operates at the lowest temperature and shortest
reaction time, produces good fill factors and suitable Jsc values for the molecular weight.
Decreasing the flow rate increases the molecular weight and J sc (Entry 4 and 5) but at the
cost of slightly lower fill factors (45 vs. 42 or 41), which may suggest that longer time
spent in the column may generate extremely small quantities of β-defects, since the
performance is not dramatically diminished as observed in the reports from Thompson et
al.
25
and Leclerc et al.
26
Indeed, it can generally be surmised that—aside from differences
that could be attributable to molecular weight differences—DArP polymers from Entries 3
to 5 all perform comparatively well while Entries 1, 2, and 6 may have small quantities of
defects. Balancing the need for lower temperatures, shorter reaction times, and higher
molecular weight becomes more challenging, especially considering the potential for
possible β-defects. Regardless, Entry 3 and Entry 5 demonstrate that quality polymers can
291
be generated via DArP that perform comparatively to the Stille counterpart, despite the
differences in molecular weight. However, there is not a readily accessible solid bulky
carboxylic acid available, and more effort is ultimately necessary to achieve high molecular
weights with minimal defects when β-positions are available.

4.4. Conclusion

Direct arylation polymerization enables the generation of conjugated polymers in
fewer synthetic steps with less toxic byproducts. When coupled with continuous flow
methods, which lower costs and minimize batch-to-batch variations, facile upscaling of
polymers is enabled. Coupled with roll-to-roll processing methods, this approach is
particularly appealing for industrial scalability of affordable energy conversion. Despite
achieving lower molecular weights than Stille batch polymerization, the DArP PPDTBT
polymers perform comparatively well in roll-coated flexible solar cells. Furthermore, the
practical performance of polymers can give insight into the quality of polymerization
methods, as some substrates may be prone to homocoupling or unselective β-coupling
defects, which may happen in extremely small quantities but still influence performance.

4.5. References

[1] A. Facchetti, Chem. Mater. 2011, 23, 733.
[2] R. Søndergaard, M. Hösel, D. Angmo, T. T. Larsen-Olsen, F. C. Krebs, Mater.
Today 2012, 15, 36.
292
[3] H. Kang, G. Kim, J. Kim, S. Kwon, H. Kim, K. Lee, Adv. Mater. 2016, 28, 7821.
[4] F. C. Krebs, N. Espinosa, M. Hösel, R. R. Søndergaard, M. Jørgensen, Adv. Mater.
2014, 26, 29.
[5] M. A. Green, K. Emery, Y. Hishikawa, W. Warta, E. D. Dunlop, D. H. Levi, A. W.
Y. Ho-Baillie, Prog. Photovolt: Res. Appl. 2017, 25, 3.
[6] A. S. Dudnik, T. J. Aldrich, N. D. Eastham, R. P. H. Chang, A. Facchetti, T. J.
Marks, J. Am. Chem. Soc. 2016, 138, 15699.
[7] F. Livi, N. S. Gobalasingham, B. C. Thompson, E. Bundgaard, J. Polym. Sci. , Part
A: Polym. Chem. 2016, 54, 2907.
[8] T. P. Osedach, T. L. Andrew, V. Bulovic, Energy Environ. Sci. 2013, 6, 711.
[9] L. A. Estrada, J. J. Deininger, G. D. Kamenov, J. R. Reynolds, ACS Macro Lett.
2013, 2, 869.
[10] P. O. Morin, T. Bura, M. Leclerc, Mater. Horiz. 2016, 3, 11.
[11] M. Guérette, A. Najari, J. Maltais, J. R. m. Pouliot, S. p. Dufresne, M. Simoneau,
S. Besner, P. Charest, M. Leclerc, Adv. Energy Mater. 2016, 6, 1502094.
[12] M. Helgesen, J. E. Carle, G. A. dos Reis Benatto, R. R. Søndergaard, M. Jørgensen,
E. Bundgaard, F. C. Krebs, Adv. Energy Mater. 2015, 5, 1401996.
293
[13] J. H. Bannock, S. H. Krishnadasan, A. M. Nightingale, C. P. Yau, K. Khaw, D.
Burkitt, J. J. M. Halls, M. Heeney, J. C. de Mello, Adv. Funct. Mater. 2013, 23,
2123.
[14] H. Seyler, J. Subbiah, D. J. Jones, A. B. Holmes, W. W. H. Wong, Beilstein J. Org.
Chem. 2013, 9, 1492.
[15] H. Seyler, D. J. Jones, A. B. Holmes, W. W. H. Wong, Chem. Commun. 2012, 48,
1598.
[16] F. Grenier, B. R. Aïch, Y. Y. Lai, M. Guérette, A. B. Holmes, Y. Tao, W. W. H.
Wong, M. Leclerc, Chem. Mater. 2015, 27, 2137.
[17] J. E. Carlé, T. R. Andersen, M. Helgesen, E. Bundgaard, M. Jørgensen, F. C. Krebs,
Sol. Energy Mater. Sol. Cells 2013, 108, 126.
[18] J. E. Carlé, J. Wenzel Andreasen, M. Jørgensen, F. C. Krebs, Sol. Energy Mater.
Sol. Cells 2010, 94, 774.
[19] C. M. Cardona, W. Li, A. E. Kaifer, D. Stockdale, G. C. Bazan, Adv. Mater. 2011,
23, 2367.
[20] H. Yang, S. W. LeFevre, C. Y. Ryu, Z. Bao, Appl. Phys. Lett. 2007, 90, 172116.
[21] A. Sharenko, N. D. Treat, J. A. Love, M. F. Toney, N. Stingelin, T. Q. Nguyen, J.
Mater. Chem. A 2014, 2, 15717.
[22] A. Kokil, K. Yang, J. Kumar, J. Polym. Sci. B Polym. Phys. 2012, 50, 1130.
294
[23] M. Hösel, R. Søndergaard, M. Jørgensen, F. C. Krebs, Energy Technol. 2013, 1,
102.
[24] F. C. Krebs, M. Jørgensen, Adv. Opt. Mater. 2014, 2, 465.
[25] A. E. Rudenko, A. A. Latif, B. C. Thompson, Nanotechnology 2014, 25, 014005.
[26] T. Bura, P. O. Morin, M. Leclerc, Macromolecules 2015, 48, 5614.
[27] A. E. Rudenko, B. C. Thompson, Macromolecules 2015, 48, 569.
[28] K. H. Hendriks, W. Li, G. H. L. Heintges, G. W. P. van Pruissen, M. M. Wienk, R.
A. J. Janssen, J. Am. Chem. Soc. 2014, 136, 11128.
[29] F. Lombeck, H. Komber, D. Fazzi, D. Nava, J. Kuhlmann, D. Stegerer, K. Strassel,
J. Brandt, A. D. de Zerio Mendaza, C. Müller, W. Thiel, M. Caironi, R. Friend, M.
Sommer, Adv. Energy Mater. 2016, 6, 1601232.
[30] F. Livi, N. S. Gobalasingham, B. C. Thompson, E. Bundgaard, J. Polym. Sci. , Part
A: Polym. Chem. 2016, 54, 2907.
[31] F. Lombeck, H. Komber, S. I. Gorelsky, M. Sommer, ACS Macro Lett. 2014, 3,
819.
[32] Z. Xiao, K. Sun, J. Subbiah, T. Qin, S. Lu, B. Purushothaman, D. J. Jones, A. B.
Holmes, W. W. H. Wong, Polym. Chem. 2015, 6, 2312.
[33] C. Müller, E. Wang, L. M. Andersson, K. Tvingstedt, Y. Zhou, M. R. Andersson,
O. Inganäs, Adv. Funct. Mater. 2010, 20, 2124.
295

296
CHAPTER 5: EVALUATING STRUCTURE-FUNCTION RELATIONSHIPS
TOWARD THREE-COMPONENT CONJUGATED POLYMERS VIA
DIRECT ARYLATION POLYMERIZATION (DARP) FOR STILLE-
CONVERGENT SOLAR CELL PERFORMANCE

5.1. Introduction

Conjugated polymers (CPs), which offer promise as scalable, flexible, lightweight,
and solution-processable materials,
1–3
are attractive for an array of applications, including
photovoltaics,
4–7
field-effect transistors,
8,9
and electrochromic devices.
10,11
With their
emergence, the demand for convenient, reliable, and effective methods for generating these
materials also grows.
12,13
Direct arylation polymerization (DArP)
14–16
has emerged as a
simplifying synthetic alternative to traditional cross-coupling polycondensation reactions,
such as Kumada,
17
Negishi,
18
Suzuki,
19
and Stille
20
polymerizations. Although the Stille
polycondensation is typically employed for state-of-the-art conjugated polymers for
OPVs,
6
it necessitates the addition of a toxic
21
and often unstable alkyltin functional group
via a lithiation-metalation step under cryogenic air- and water-free conditions.
22
DArP
attractively bypasses the need for stannylation by proceeding through a C-H activation
pathway that requires only a halogenated leaving group and an acidic proton (Figure
5.1a).
23–25
Compared to Stille, DArP offers the advantages of fewer synthetic steps, easier
purification of monomers, and more environmentally benign synthesis with no tin waste or
end groups—all of which are quite advantageous for industrial scale synthesis; however,
concerns about defects, substrate limitations, and poor performance are all significant
297
obstacles that DArP must overcome in order to be a viable alternative to Stille
polymerization.
26

Figure 5.1. (a) Direct arylation polymerization (DArP) enables the synthesis of conjugated
polymers without the need for metalation; however, (b) C-H activation of unselective
positions is a shortcoming that can be overcome by using (c) bulky carboxylic acids such
as neodecanoic acid.
There exist two main classifications of DArP conditions that have been successful
for the synthesis of CPs. The first is inspired by the pioneering work of Fagnou, et al.
24
that
typically utilizes an amide solvent (such as DMA), an insoluble base, and most importantly,
a carboxylic acid as a proton shuttle. The second family of conditions are derived from
Ozawa, et al.,
27
in which phosphine ligands and organic solvents such as toluene or
superheated THF or are utilized. These conditions may or may not utilize a carboxylic acid.
Recently, we reported optimized Fagnou-derived DArP conditions for high performance
rr-P3HT homopolymers and analogues (AB monomer systems).
28,29
Subsequently, we
298
reported Ozawa-derived conditions for donor/acceptor (DA) alternating polymers (AA/BB
systems).
26
In both instances, DArP polymers demonstrated Stille-convergent or DArP-
superior polymer solar cell (PSC) performance. Although each condition is unique, they
share a bulky carboxylic acid additive, neodecanoic acid (NDA). Carboxylic acids have
previously been deemed advantageous as a proton shuttle for effective C-H arylation.
24

Observed originally by our group,
26,29–32
and confirmed by others,
33,34
the bulky carboxylic
acid is critical for minimization of defects, particularly unselective C-H activation (Figure
5.1b), which even in incredibly small quantities can have dramatic influence over
performance in PSCs.
29,34–36

With these important developments in mind, the application of DArP to
increasingly complex polymer strategies necessitates methodological evaluation of
functional group assignment, C-H reactivity, defect tendencies, and practical performance.
Recently, copolymers that feature three or more components have emerged as viable
strategies for achieving improved performance and desired material properties.
37–46
This
includes both random and semi-random rr-P3HT analogs that preserve the most attractive
attributes of rr-P3HT (affordability,
47
miscibility with PC61BM
48
at favorable mixing ratios
(P3HT:PC61BM; 1:0.8),
49
high hole mobility, semicrystallinity, and high peak absorption
coefficients) while improving performance through the distribution of discrete acceptors
throughout the polymer backbone.
50–59
Additionally, (semi)alternating DA polymers with
discrete acceptors but randomly incorporated donors (or vice-versa) can have beneficial
structural, electrical, and photovoltaic properties.
35,45,46,60–62
All of these architectures
demand a synthetic method that minimizes potential defects that can negatively influence
polymer quality and performance.
63–65
Previous attempts by Rudenko et al.
66
and Farinola
299
et al.,
35
to generate three-component polymers via DArP for OPVs have demonstrated that
minute defects can lead to diminished performance.
Herein, we briefly evaluate a variety of successful DArP conditions on model
system P3HT to confirm their compatibility for effective OPV performance of thiophene-
based polymer architectures before evaluating both Fagnou- and Ozawa-derived conditions
on a model three-component semi-random P3HT analogue, poly(3-hexylthiophene—
thiophene—diketopyrolopyrole) (P3HTT-DPP). As a multi-component system, semi-
random polymers are uniquely suited for observing the influence of functional group
assignment on homocoupling and β-defects as it pertains to electron-rich and electron-poor
heteroarenes. This polymer architecture is unique in that it possesses a combination of AB-
type polymerization with a concurrent alternating copolymerization, resulting in discrete
acceptors in the polymer backbone that consists of three comonomers (Figure 5.2).
Particularly, such systems enable evaluation of whether C-H reactivity differences alter
polymer composition. A goal of the present work is the unity between structural regularity
and optimal polymer performance in solar cells. Ultimately, it is demonstrated that not all
DArP conditions generate polymers that perform similarly to Stille in PSCs and that the
functional group assignment and synthetic method are both critically important for
achieving high quality polymers.
300

Figure 5.2. For key features of semi-random P3HT analogs, namely discrete secondary
components and high performance, to be preserved via DArP, minimizing defects,
balancing C-H reactivity, and determining optimal functional group assignment become
increasingly important considerations.
5.2. Results and Discussion

5.2.1. P3HT Synthetic Methodology

With the numerous iterations of DArP conditions available, several select
conditions were—as a baseline study—utilized for the synthesis of rr-P3HT and are
compared to Stille P3HT. Stille was chosen because it is the most convenient method for
generating three-component copolymers explored herein. These include successful
conditions from both Fagnou-derived DArP conditions as well as Ozawa-derived
conditions and are provided in Table 5.1. To the best of our knowledge, this is the first
report to compare ultra-low loading Fagnou DArP conditions with Ozawa-derived DArP
conditions against a Stille reference. Ma et al. observed Ozawa-derived DArP P3HT to
301
underperform compared to Rieke P3HT.
67
In Table 5.1, A1 is generated by Stille
polymerization, and is provided as a reference. Conditions for A2 are derived from
traditional Fagnou conditions, utilizing PivOH. A3 and A4 are optimized Fagnou
conditions developed in our group, the former having been successful for Stille-convergent
P3HT analogues without β-defects,
28,68
and the latter having been recently optimized to
dramatically minimize reagent loadings.
31
Conditions for A5 are adopted from the Ozawa-
derived DArP conditions utilized by Leclerc, et al.,
69
which we modified with NDA to
generate high performance perfectly alternating copolymers.
26
Lastly, A6 is a similar set
of reaction parameters but with a lower catalyst loading and replacement of the solvent
with 2-methyltetrahydrofuran (MeTHF), which was first utilized in DArP by Sommer et
al.
70
and is considered a cost-effective green alternative to THF since it originates from
renewable feedstock, furfural.
71
Similar conditions to A6 were utilized by Marks, et al.
34

with bulky carboxylic acid, 2,2-diethylhexanoic acid, which is one of the isomers of the
more affordable neodecanoic acid (NDA) mixture. For this work, however, 2,2-
diethylhexanoic acid was cost-prohibitive for effective screening of conditions; therefore,
in all instances where a bulky carboxylic acid is investigated, neodecanoic acid was
incorporated.

Table 5.1. Reaction Parameters for the Synthesis of P3HT for Baseline Evaluation of
Polymer Properties and the Molecular Weight, Dispersity, Yield, and Regioregularity after
Soxhlet Extraction.
302

P3HT
Catalyst
(Load.)
a

Solvent
(Conc.)
b

Temp.,
°C
Carboxylic
Acid, %
Base
c

Phosphine
Ligand
e

Mn,
f

kDa
(Ð)
Yield,
g
%
rr,
h
%
A1
Pd(PPh 3) 4
(4%)
DMF
(0.04M)
95 None None None
17.9
(2.40)
68 92.9
A2
i

Pd(OAc) 2
(0.25%)
DMA
(0.04M)
70
PivOH
(30%)
K 2CO 3 None
17.1
(3.11)
55 93.1
A3
Pd(OAc) 2
(0.25%)
DMA
(0.04M)
70
NDA
(30%)
K 2CO 3 None
18.2
(2.77)
60 93.4
A4
Pd(OAc) 2
(0.03%)
DMA
(0.3M)
160
NDA
(3.8%)
K 2CO 3 None
21.6
(3.47)
88 95.0
A5
Pd 2dba 3
(2%)
THF
(0.4M)
120
NDA
(100%)
Cs 2CO 3
P(o-
MeOPh) 3
14.5
(2.03)
81 93.8
A6
Pd 2dba 3
(1%)
MeTHF
(0.4M)
120
NDA
(100%)
Cs 2CO 3
P(o-
MeOPh) 3
19.7
(2.11)
74 96.2
a
Catalyst loading relative to monomer loading (1 mmol).
b
Concentration of the monomer
in the solvent.
c
Where applicable, 1.5 equiv. of respective base was utilized.
e
Where
applicable, phosphine ligand loading was 16% (A5) or 8% (A6).
f
As determined by SEC
calibrated to polystyrene standards after purification by Soxhlet extraction.
g
Yield after
purification by Soxhlet extraction, precipitation, and drying under high vacuum overnight.
h
Regioregularity was calculated as the NMR peak integration ratio of the head-to-tail
coupling (δ2.81) vs. the head-to-head and tail-to-tail couplings (δ2.55 and—if applicable—
δ2.52, respectively). Of the polymers in this table, only A2 contained β-defects (0.2%) after
Soxhlet extraction.
303
Polymer properties in Table 5.1 demonstrate that a broad range of reaction
conditions can achieve good molecular weights and yields for P3HT homopolymers, which
in all cases exceeded 14 kDa and 50% yields after Soxhlet extraction. Regioregularities
generally varied between 93 and 96%, with DArP conditions for A2, A3, and A5 generally
having a similar regioregularity with A1; however, both A4 and A6 have higher
regioregularities at 95.0% and 96.2% respectively, which could be correlated to the lower
catalyst loadings, as higher catalyst loadings are attributed to increased homocoupling
events.
31,72
Importantly, in all instances where NDA was utilized, no β-defects were
observed via
1
H NMR analysis. NMR spectra of the polymers are provided in the Appendix
(Figure A4.12-17), Consistent with previous reports, we observe 0.2% β-defect
concentration (BDC) when PivOH is utilized (Figure A4.13).
29
Polymers in Table 5.1
were subsequently characterized for their optoelectronic properties and then employed in
bulk heterojunction solar cells with PC61BM. Optoelectronic properties are outlined in
Table 5.2, which includes HOMO energy levels, SCLC hole mobility measurements, peak
absorption coefficients, optical bandgaps, melt and crystallization temperatures as
determined by DSC, and d100 lattice spacings as determined by GIXRD on thin films. CV
and DSC traces are provided in Figure A4.33 and Figure A4.37, respectively, while UV-
Vis absorption profiles and GIXRD patterns are provided in Figure 5.3a and b
respectively. Additionally, the PSC performance, including the Jsc, Voc, FF, and PCE are
provided in Table 5.2. Raw data, standard deviations, and the J-V curves are provided in
the Appendix. EQE spectral response measurements are provided in Figure 5.3c.
Table 5.2. Optoelectronic Properties of Stille P3HT (A1) and DArP P3HT (A2-A6) after
Soxhlet Extraction, including HOMO energy level, SCLC Hole Mobility, Peak Absorption
304
Coefficient, Optical Bandgap, Melt and Crystallization Temperatures, d100 Spacing, and
Polymer Solar Cell Performance.
P3HT
a

HOMO,
b

eV
µ,
c
x 10
-4

cm
2
V
-1
s
-1

Abs.
Coeff.
d

cm
-1

E g,
e

eV
T m, °C
(T c, °C)
f

d 100,
g

Å
Jsc,
h,i

mA cm
-1

Voc,
j

V
FF
k

η,
l
%
A1 5.22 2.28 104039 1.9 221 (190) 17.2 8.34 0.59 0.581 2.86
A2 5.29 1.81 102776 1.9 215 (181) 17.3 5.85 0.59 0.464 1.60
A3 5.22 2.11 110500 1.9 216 (181) 16.9 8.22 0.61 0.556 2.79
A4 5.24 2.23 104206 1.9 213 (180) 17.1 8.61 0.60 0.578 2.99
A5 5.24 2.19 109489 1.9 211 (187) 17.0 8.50 0.60 0.573 2.92
A6 5.23 2.47 121110 1.9 223 (191) 17.1 9.40 0.59 0.591 3.28
a
Entry as provided in Table 1, where A1 is Stille P3HT and A2-A6 are DArP P3HT. For
solar cell data, polymers were spin-coated from Polymer:PC61BM mixtures (1:0.8 by mass)
dissolved in chlorobenzene (CB) and dried under N2 for 30 min. prior to aluminum
deposition and we subsequently annealed for 30 minutes under nitrogen at 150°C after
deposition of the electrodes.
b
Determined by cyclic voltammetry (vs. Fc/Fc
+
) in 0.1M
TBAPF6, where HOMO = 5.1 + E ox.
c
Measured on neat polymer films.
d
Determined from
UV-Vis absorption profiles of thin films where thickness is estimated from GIXRD in
reflectivity mode.
e
Calculated from the absorption band edge in thin films, Eg = 1240/λedge.
f
Measured by DSC.
g
Calculated from GIXRD diffraction peaks in thin films.
h
Mismatch
corrected.
i
Standard deviations of less than 0.3 mA/cm2 were observed in all cases
averaged over eight pixels.
j
Standard deviations of less than 0.004 V were observed in all
cases averaged over eight pixels.
k
Standard deviations of less than 0.02 were observed in
all cases averaged over eight pixels.
l
Standard deviations of less than 0.2% were observed
in all cases averaged over at least six pixels.
305

Optoelectronic properties provided in Table 5.2 are comparable across all methods.
HOMO energy levels are within measurement error and are similar for all polymers.
Absorption profiles exhibit similar absorption breadth regardless of synthetic method
(Figure 5.3a). The absorption onset is similar for all DArP polymers. Consequently, all
polymers have an optical Eg of 1.9 eV, consistent with A1. Additionally, peak extinction
coefficients are all comparable to A1, with most DArP polymers exceeding Stille, but as
observed in Figure 5.3a, polymers that have higher regioregularity than Stille also
demonstrate a stronger vibronic shoulder, suggesting stronger ordering in the solid state
and higher degree of crystallinity. Both DSC and GIXRD measurements were undertaken
to further evaluate crystallinity. DSC scans generally demonstrate similar melting and
crystallization temperatures for all P3HT batches, with the highest temperature peaks being
observed in A6, which has the highest regioregularity. GIXRD patterns (Figure 5.3b)
demonstrate that peak position and intensity do not vary dramatically. Interchain distances
are similar (ranging from ~16.9-17.2Å) for all polymers, with A2 having the largest
interchain distance (17.3Å) but also the only β-defects.
29
Furthermore, the full widths at
half the maximum (FWHM) were quantified (see Table S1). Estimating correlation lengths
(CCL) from the FWHM via Scherrer’s equation reveals that crystallite size is generally the
same for all P3HT polymers, though all DArP P3HT CCL values are greater than Stille.
As shown in Table 5.2, this semicrystallinity and high regioregularity translates into high
hole mobilities for all P3HT polymers evaluated herein. These values are generally
consistent with previous reports for P3HT.
29

306

Figure 5.3. (a) UV-Vis absorption profile for P3HT series of polymers. Thicknesses are
determined from x-ray reflectivity. (b) GIXRD patterns for neat polymer films. (c) EQE
spectra of BHJ PSCs.
As a measure of practical polymer performance, DArP and Stille P3HT were
incorporated in bulk heterojunction polymer solar cells (BHJ PSCs) with PC61BM in a
conventional device architecture of ITO/PEDOT:PSS/Active Layer/Al. All processing
steps were executed in air under ambient temperatures and humidity. The active layer was
spin-coated from a polymer and PC61BM blend in CB at 10 mg/mL polymer concentration
at 1:0.8 polymer:PC61BM ratio. It is critically important to note that despite A2 having only
0.2% β-defects concentration and similar optoelectronic properties, the device performance
is dramatically diminished compared to the other routes. While Voc values are generally
consistent across all polymers, both the Jsc and FF are markedly lower for A2. Compared
to A1, DArP P3HT polymers A3, A4, and A5 all perform similarly with suitably high
currents and fill factors. A6, which has the highest regioregularity and peak absorption
coefficients, also exhibits the highest Jsc. As observed in Figure 5.3c, external quantum
efficiency (EQE) measurements show similar photocurrent response for all polymers
consistent with their absorption profiles. In general, photocurrent response near 400 nm
can be attribute to PC61BM while the polymer is responsible elsewhere. A2 exhibits much
307
poorer spectral response after 450 nm. Given how similar the optoelectronic properties are
for A2 compared to the other P3HT polymers, this diminished response can be attribute to
negative morphological impacts of β-defects in this polymer when blended with fullerene.
For many years, DArP polymers were considered marginally inferior to Stille polymers
despite close correlation of optoelectronic properties—including crystallinity, absorption
profiles, and other critical properties.
26,34,35
The solar cells results reported herein
demonstrate that even nearly undetectable quantities of β-defects can significantly diminish
polymer performance, consistent with previous observations.
29,34,35
Possibly, the
observation that A2 does not pack together as closely as the other P3HT polymers may
lead to decreased charge transport or increased recombination, lowering both the fill factor
and short-circuit current. Lower FF may be observed due to branching defects negatively
influencing the supramolecular morphology of the BHJ system.
5.2.2. P3HTT-DPP Synthetic Methodology

In expanding from a simple AB homopolymer to a more complex three-component
AB-AA-BB semi-random copolymer, additional considerations come into play. Whereas
multiple conditions were suitable for homopolymer P3HT, this has not been the case when
expanding to two-component systems
26
or for three-component systems.
35
Recently, a
handful of reports have emerged debating the optimal functionalization strategy for
minimizing C-Br/C-Br homocoupling events (i.e., which coupling partner should be
brominated in alternating copolymers).
73–76
Because DArP is often considered an
alternative to Stille, the former C-Sn functionality typically becomes the C-H functionality
(consistent with avoiding the associated lithiation-metalation step). But this is also
308
sometimes done because some acceptors are often challenging to both metalate and purify.
From these reports that evaluate functionalization strategy, stark contrasts emerge in terms
of resulting polymer quality and structural integrity.
73–75
Three-component systems offer
the opportunity to evaluate the role of functionality and its consequences. Thus, for the
application of DArP to semi-random polymers, we have elected to study the role of C-Br
functionalization on a model system, poly(3-hexylthiophene-thiophene-
diketopyrrolopyrrole) (P3HTT-DPP), where either the DPP monomer or the thiophene
spacer will be brominated. The traditional Stille route is illustrated in Scheme 5.1a, while
these two DArP routes are illustrated in Scheme 5.1b and c.

Scheme 5.1. Synthesis of P3HTT-DPP-10% by Stille and DArP Polymerization Methods.
Determining whether halogenation of the acceptor or not halogenating the acceptor results
in minimal defects is a consideration in DArP.

It is important to stress here that this functionalization strategy shown in Scheme
5.1b and c is purely for observing which DArP protocols generate fewer defects for
ensuring discrete acceptor distribution in the polymer backbone. The two resulting
polymers will be inherently different, as DPP should predominately couple to the 5-
309
position of 3HT for Route X, but the 2-position for Route Y, which is in and of itself an
interesting investigation into the influence of coupling in P3HT semi-random analogues.
This is because the Stille method only essentially allows for one route due to general
difficulties of stannylating acceptors and purifying them, including DPP which is much
easier to brominate than stannylate.
77,78
Additionally, the synthesis of the reverse
functionalized 3HT DArP monomer, 2-bromo-4-hexylthiophene,
76
which would achieve
the same type of coupling in Route Y as the original monomers, requires additional
synthetic steps and introduces two variables (and distinct thiophene C-H reactivity issues),
which convolute the analysis of these systems.
Based on the results of the P3HT screening, select DArP conditions (Table 5.3)
were applied to the synthesis of P3HTT-DPP (Scheme 5.1). These polymers are listed in
Table 5.3 where the method, designated as A#, references the conditions that were adopted
in Table 5.1. Additionally, the route utilized is provided as referenced in Scheme 5.1.
Because of the lower boiling point of thiophene (84°C), conditions utilized for A4 (at
160°C) were not included for generating DArP P3HTT-DPP to be consistent with the
Fagnou DArP conditions, which are convenient because reactions proceed below the
boiling point of the reagents. Therefore, conditions for A3 were the only representative
Fagnou conditions to be applied to the synthesis of P3HTT-DPP. On the other hand,
conditions for both A5 and A6 were included because the reaction is executed in a
pressurized vessel consistent with the Ozawa DArP conditions.

310
Table 5.3. Synthetic Method (Adopted from Table 5.1), Route (Described in Scheme 5.1),
and Molecular Weight, Dispersity, and Yield after Soxhlet Purification for Stille (B1) and
DArP (B2-B7) P3HTT-DPP Semi-Random Copolymers.
Entry Method
a
Route
b
Mn,
c
kDa (Ð) Yield,
d
%
B1 A1 -- 13.8 (2.89) 60
B2 A3 X 9.1 (3.43) 41
B3 A3 Y 4.4 (1.45) 18
B4 A5 X 9.7 (2.26) 62
B5 A5 Y 9.8 (1.97) 68
B6 A6 X 15.8 (2.51) 77
B7 A6 Y 16.7 (2.44) 71
a
Method refers to conditions utilized to synthesize the corresponding P3HT polymer in
Table 1 of the main text.
b
Route refers to functionalization strategy of DPP as outlined in
Scheme 5.1a (route X) and Scheme 5.1b (route Y).
c
As determined by SEC calibrated to
polystyrene standards after purification by Soxhlet extraction.
d
Yield after purification by
Soxhlet extraction, precipitation, and drying under high vacuum overnight.

As shown in Table 5.3, the expansion of DArP to semi-random copolymers is more
complicated compared to simple homopolymers—whereas multiple conditions were viable
for generating Mn values greater than 15 kDa for P3HT, the same is not true for P3HTT-
DPP. Most notably, only B1, B6, and B7 exceed 10 kDa, though the respective values of
B6 and B7 (~16 kDa) both exceed their Stille counterpart, B1. These molecular weights
are consistent for P3HT-based three-component semi-random copolymers via Stille,
50,53,79

311
which generally vary between 10 and 20 kDa. While this range of molecular weights for
Stille may result from insufficient stoichiometry optimization, the consumption of
monomers via undesirable side reactions or debromination/ destannylation events,
80
we
consider the relatively parity of the molecular weights to still provide invaluable
comparisons for unearthing structure-function relationships between DArP polymers and
their performance. It is also important to note that 3-hexylthiophene is comparatively
lighter as a monomer than most other donors reported in literature, and so these lower
molecular weights can translate into higher degrees of polymerization than other larger
monomers. However, rigorous stochiometric optimization may improve the molecular
weights across all synthetic methods. Compared to homopolymer synthesis, Fagnou-
derived conditions appear to be less effective for generating three-component copolymers.
The molecular weight for B3 is modest (< 5 kDa), which ultimately resulted in much of
the oligomers being removed by hexanes fraction of the Soxhlet extraction and a low final
isolated yield. Although not as low, B2 also had a comparatively lower molecular weight
(9.1 kDa) and yield (41%) than other conditions. Although they did not exceed 10 kDa,
B2, B4, and B5 do achieve values near this value and produce good thin films when spin-
coated from o-dichlorobenzene solutions.

312

Figure 5.4. Fragments of the
1
H NMR spectra (Full Spectra available in the Appendix) of
B1-B3 and B6-B7 showing the aromatic coupling peak of DPP (proton highlighted by blue
circle in structures at top), where the # symbol corresponds to DPP coupling to the 5-
position of 3HT that is predominant in route X coupling (Scheme 1b), the ◊ symbol
313
corresponds to DPP coupling to the 2-position of 3HT predominantly in route Y coupling
(Scheme 5.1c), the ● symbol corresponds to DPP coupling to the thiophene monomer, and
the * symbol denotes DPP end groups that would predominantly occur in route Y. The
insets show superimposed fragments of (a) B7 and B2, (b) B7 and B3, as well as (c) B1
and B6.
Consistent with the synthesis of DArP P3HT in the presence of bulky carboxylic
acid, NDA,
1
H NMR analysis of all DArP P3HTT -DPP polymers confirmed the absence
of any quantifiable β-defects; however, with the addition of two secondary components,
additional considerations emerge regarding how these monomers incorporate into the
backbone and what variations exist in the final polymer structure. Figure 5.4 provides a
comparison of the proton shifts that correspond to DPP coupling in B1, B2, B3, B6, and
B7, which occurs downfield of the other thiophene aromatic peaks. B4 and B5 are omitted
from Figure 5.4 because they resemble B6 and B7 respectively. Full
1
H NMR spectra of
all P3HTT-DPP polymers are provided in Figure A4.18-24. B1, which is analogous to
DArP route X, provides a good reference spectrum. The peak at δ8.94 corresponds to DPP
coupling to the 5-position of 3HT (indicated by # in Figure 5.4), while the shoulder at
δ8.96 corresponds to DPP coupling to thiophene (indicated by ● in Figure 5.4).
Considering 3HT constitutes 80% of the polymer chain while thiophene has a 10% loading,
the difference in peak integrations are statistically reasonable. For B2, which is capable of
the same types of couplings as B1, significant differences are visible. While there is still
significant DPP coupling to the 5-position of 3HT, there is also some coupling to the 2-
position, which occurs at δ9.07. Furthermore, there is a broader and more intense peak than
B1 for the associated DPP/thiophene coupling at δ8.96. Interestingly, despite the relative
314
monomer loadings being just 10% for both thiophene and DPP, there appears to be a higher
occurrence of DPP/thiophene coupling in B2 than in B1. Previous studies of DPP
homopolymers suggest that, in CDCl3, peaks downfield near δ 9.23 would correspond to
DPP/DPP homocoupling;
81
however, no such peaks are observed in the P3HTT-DPP series
reported herein. Possibly, due to the relatively low loadings of the DPP monomer (10%)
compared to thiophene and 3HT (90% total), C-Br/C-Br homocouplings are more likely to
occur with 3HT. Regardless, the presence of C-Br/C-Br coupling of DPP to the 2-position
of 3HT suggests that Fagnou-derived DArP via route X (B2) is unsuitable for minimizing
homocoupling events. For B3, which had a lower molecular weight, Figure 5.4b shows
that although coupling to the 2-position and thiophene are most prevalent, the broad
shoulder that extends from δ8.96 to 8.90 suggests some homocoupling to the 5-position of
3HT may occur but not to the same extent as B2 exhibits homocoupling. Compared to B3,
B7 also demonstrates coupling primarily to the 2-position of 3HT and to thiophene, though
due to the broad thiophene coupling peak, it is again difficult to preclude the presence of
5-position 3HT/DPP homocouplings but the shoulder from δ8.96 to 8.90 is not as
pronounced as in B3 (Figure 5.4b).
Despite producing the same couplings via route X, Stille (B1), Fagnou (B2), and
Ozawa (B6) methods lead to noticeable differences in how the monomers incorporate into
the polymer backbone as evident in Figure 5.4. B1 exhibits a narrow peak with a distinct
shoulder corresponding to thiophene coupling (● in Figure 5.4). B2 has a broader
DPP/3HT coupling peak, with a strong DPP/thiophene coupling peak in addition to the
previously mentioned homocoupling defects. B6 lacks a distinct DPP/thiophene shoulder
but overall features a broad DPP/3HT peak compared to B1 and B2. Importantly, compared
315
to B2, B6 does not show evidence for unselective C-Br/C-Br DPP coupling to the 2-
position. As seen in Figure 5.4c, the region associated with DPP/thiophene couplings (●
in Figure 5.4) is more intense for B6 than B1, and a shoulder is visible, though neither
shoulder is as intense as B2. These differences contrast with route Y, where B3 and B7
exhibit comparable quantities of coupling to either thiophene (● in Figure 5.4) or 3HT (◊
in Figure 5.4). The likely reasoning for this distinction is the reaction temperature of
Fagnou conditions (70°C) and Ozawa conditions (120°C) versus the boiling point of the
route X thiophene monomer (84°C) and the route Y 2,5-dibromothiophene (211°C). B3
and B7 exhibit similar quantities of couplings because all monomers have boiling points
well above the reaction temperatures. Differences in polymers (molecular weight, yield,
and performance) can be attributed to the method employed. On the other hand, whereas
B2 conditions operated below the boiling point of thiophene, B6 is above the boiling point.
As a result, monomers may react at different rates and incorporate into the polymer
differently. B2, operating below the boiling point of thiophene, exhibits the most
DPP/thiophene couplings. Conversely, B6—well above the boiling point of thiophene—
exhibits fewer DPP/thiophene couplings than B2. Eventually, however, all monomers do
incorporate into the polymer chains, as observed by integrating thiophene aromatic peaks
(around δ 7.0), which correlate well amongst Stille (B1), Fagnou DArP (B2), and Ozawa
DArP (B6).
Additionally, the broadness of the DPP coupling peak in B6 compared to B1 and
B2 (# in Figure 5.4) suggests differences in monomer connectivity. B2, which has greater
variations in term of monomer connectivity, has a sharper resonance at δ8.92 and a more
defined shoulder at δ8.95. Thus, B6 may have comparatively greater 3HT couplings,
316
leading to it being sterically shielded and having a broader resonance from reduced
relaxation pathways. Whereas the narrowness of the Stille polymer NMR suggests DPP
could be dispersed broadly in the polymer backbone (i.e. DPP surrounded by stretches of
3HT), the B6 spectrum indicates DPP may not be as dispersed in the polymer backbone as
in B1 or even B2. Lastly, although B3 and B7 feature H-DPP monomer and so are expected
to feature that end group at δ8.88, it is worth noting that B6 has a nearly indistinguishable
peak there as well, suggesting that dehalogentation may occur during the polymerization.
Overall, NMR evidence suggests that both route X and route Y can generate polymers with
minimal homocouplings but only when utilizing phosphine ligand-incorporated Ozawa-
derived conditions. These results confirm previous observations by Sommer, et al., but now
for systems featuring three components.
64,82

Figure 5.5. (a) UV-Vis absorption profiles for P3HTT-DPP series of polymers.
Thicknesses are determined from x-ray reflectivity. (b) GIXRD patterns for neat polymer
films. (c) EQE spectra of BHJ PSCs.
Additional support for homocoupling or the lack thereof is evident in the UV-Vis
absorption profiles, which are provided in Figure 5.5a. As observed by Janssen, et al.
63

homocoupling defects may contribute to tailing of the absorption onset. This is distinctly
visible for B2. B3 exhibits weaker polymer absorption overall compared to other P3HTT-
317
DPP polymers. B4-B7 all exhibit comparable absorption profiles, though B5 has weaker
absorption near 700 nm, which is attributed to DPP, despite NMR evidence showing
similar DPP content for all DArP P3HTT-DPP polymers. Nonetheless, other than B2 which
exhibits a smaller bandgap due to tailing, all P3HTT-DPP polymers have an optical
bandgap of 1.5 eV. Despite the different linkage patterns (2-position vs. 5-position of 3HT),
the optoelectronic properties share several similarities as outlined in Table 5.4, which
includes HOMO energy levels, SCLC hole mobility measurements, optical bandgaps, melt
and crystallization temperatures as determined by DSC, and d 100 lattice spacings as
determined by GIXRD on thin films. CV and DSC traces are provided in Figure A4.34
and Figure A4.38, respectively, and GIXRD patterns are provided in Figure 5.5b.
Additionally, the PSC performance, including the Jsc, Voc, FF, and PCE are provided in
Table 5.4. Raw data, standard deviations, mismatch determination, and the J-V curves are
provided in the Appendix. EQE spectral response measurements are provided in Figure
5.5c.
Overall, electrochemical HOMO energy levels are slightly deeper compared to
P3HT, with lower molecular weight polymers having a deeper HOMO than higher
molecular weight polymers (Table 5.4). Both B6 and B7 are consistent with B1, while B4
and B5 are reasonable given their lower molecular weight, though all are within
experimental error. Additionally, SCLC hole mobilities vary but are consistent with P3HT-
based polymers. Except for B2 and B3 which exhibit comparatively lower mobilities,
DArP polymers demonstrate mobilities comparable to B1, consistent with the high
regioregularity and semicrystallinity of the polymers. Evidence for their crystallinity is
provided by GIXRD and DSC measurements. Except for B3, all polymers exhibit
318
diffraction peaks via GIXRD (Figure 5.5b), where d100 spacings are similar across the
P3HTT-DPP series, ranging from 16.2 to 16.5 Å (Table 5.4). DSC measurements
demonstrate that all P3HTT-DPP polymers except B3 exhibit both melt and crystallization
transitions. Although all DArP P3HTT-DPP polymers exhibit melt and crystallization
temperatures below B1, the temperatures do increase with increasing molecular weight for
the DArP series. Additionally, as observed in the DSC traces (Figure A4.38), the thermal
transitions for B2, B4, and B5 are generally broader and more shallow than B1.
Interestingly, despite the higher molecular weights (Table 5.3) of B6 and B7, both the melt
and crystallization temperatures are below that of B1, though the crystallite sizes are more
than 50% larger (Table S1).

Table 5.4. Optoelectronic Properties of Stille P3HTT-DPP (B1) and DArP P3HTT-DPP
(B2-B6) after Soxhlet Extraction, including HOMO energy level, SCLC Hole Mobility,
Optical Bandgap, d100 spacing, Melt and Crystallization Temperatures, and Polymer Solar
Cell Performance.
P3HTT-
DPP
a

HOMO,
b
eV µ,
c
x 10
-4

cm
2
V
-1
s
-1

Eg,
d

eV
Tm, °C
(Tc, °C)
e

d100,
f

Å
Jsc,
g,h

mA cm
-1

Voc,
i

V
FF
j

η,
k
%
B1 5.29 2.31 1.5 209 (193) 16.36 13.06 0.60 0.590 4.62
B2 5.36 0.86 1.4 185 (183) 16.22 5.21 0.58 0.520 1.57
B3 5.40 0.59 1.5 -- (--) -- 4.41 0.57 0.449 1.13
B4 5.33 1.46 1.5 177 (162) 16.36 10.17 0.60 0.585 3.57
B5 5.34 1.88 1.5 178 (173) 16.37 9.08 0.59 0.580 3.11
B6 5.28 2.40 1.5 187 (167) 16.31 13.24 0.61 0.597 4.82
B7 5.29 2.17 1.5 184 (171) 16.47 12.23 0.60 0.567 4.16
319
a
Entry as provided in Table 3, where B1 is Stille P3HTT-DPP and B2-B7 are DArP
P3HTT-DPP. For solar cell data, polymers were spin-coated from Polymer:PC61BM
mixtures (1:1.3 by mass) dissolved in o-dichlorobenzene (o-DCB) and dried under N2 for
30 min. prior to aluminum deposition.
b
Determined by cyclic voltammetry (vs. Fc/Fc
+
) in
0.1M TBAPF6, where HOMO = 5.1 + Eox.
c
Measured on neat polymer films.
d
Calculated
from the absorption band edge in thin films, Eg = 1240/λedge.
e
Measured by DSC.
f

Calculated from GIXRD diffraction peaks in thin films.
g
Mismatch corrected.
h
Standard
deviations of less than 0.3 mA/cm
2
were observed in all cases averaged over eight pixels.
i
Standard deviations of less than 0.009 V were observed in all cases averaged over eight
pixels.
j
Standard deviations of less than 0.02 were observed in all cases averaged over eight
pixels.
k
Standard deviations of less than 0.3% were observed in all cases averaged over
eight pixels.

Solar cell data detailed in Table 5.4 shows further disparity between DArP methods
than was evident for P3HT series. Processing conditions were kept consistent across all
polymers, which were all spin-coated from 10 mg/mL o-DCB solutions at 1:1.3
polymer:PC61BM ratios in air under ambient temperature and humidity. Here, A3
conditions (toward B2 and B3) with low operating temperatures and catalyst loading
derived from Fagnou DArP generate comparatively ineffectual P3HTT-DPP regardless of
whether Route X or Route Y were utilized. A5 conditions (toward B4 and B5)
underperformed somewhat compared to Stille (B1) but this may most likely be attributed
to the lower molecular weights, as similar conditions utilized in A6 with MeTHF resulted
in higher molecular weights that performed significantly better in devices (Table 5.4). An
320
interesting observation from the solar device data is that route X and route Y do not
dramatically alter the polymer performance. Although we observed a slight reduction in Jsc
between route X and route Y (e.g. between B4 and B5 or B6 and B7), the Voc and FF are
comparatively unchanged. EQE spectral response measurements show that this Jsc loss is
from a lower response in the 700 nm region. This is interesting as both B5 and B7 exhibit
slightly higher spectral responses in the 500 nm region. Likely, these differences can be
attributed to DPP primarily coupling to the 2-position of 3HT, with the hexyl side chain of
3HT potentially having some steric interaction with the ethyl hexyl of the DPP unit.
Because of the thienyl moiety that flanks the DPP “core” and the overall low loading of
DPP, this interaction may be lessened, resulting in comparatively well-performing devices
with minimal Jsc loss.
Ultimately, B6 and B7 both performed the best of the DArP family of copolymers,
with B6 outperforming B1. Interestingly, EQE measurements show that Stille P3HTT-DPP
and DArP P3HTT-DPP have different photocurrent responses. Despite the similar Jsc
currents observed between B1 and B6, the differences in spectral response may be
attributable to differences in how the monomer units incorporate into the rr-P3HT
backbone as discussed earlier. B1 and B2, with larger quantities of DPP/thiophene
couplings, exhibit variations in spectral response compared to B6. Additionally,
differences in possible end groups between B1 and B6 polymerization methods could
influence Jsc, as chain termini may influence charge transport, interchain packing, and film
morphology in the bulk heterojunction.
83,84
Lastly, it is also possible that these differences
can occur due to variations in the degree of semicrystallinity. Differences in the EQE
between Stille and DArP polymers have been previously observed,
28
but this is rare
321
because DArP is overwhelming utilized for perfectly alternating polymers where polymer
chain composition is inflexible unless defects occur. Our model system herein is interesting
because it suggests that given the chance to randomly incorporate in a P3HT backbone,
DArP and Stille may do so in different ways. The differences between B1 and B6, including
the broadening of the DPP coupling peak (Figure 5.4) observed in the proton NMR for B6,
the loss of a strongly distinct vibronic shoulder in UV-Vis profiles (Figure 5.5a) despite
higher peak intensity via GIXRD (Figure 5.5b), the lower DSC melt and crystallization
temperatures despite higher molecular weights, and the stronger 700 nm spectral response
of B6 ultimately suggest that DArP and Stille can yield distinct copolymers when
randomness is pursued, even if defects are suppressed.

5.2.3. Semi-Random P3HT Analogues Synthetic Methodology

While the conditions reported herein have generated suitable P3HT and P3HTT-
DPP polymers, further evaluation of the substrate scope and limitations would be
beneficial. To this end, the optimized conditions for B6 and the corresponding route X were
subsequently applied to the screening of four different spacer units (to replace thiophene)
and four unique acceptors (to replace DPP). These polymers are outlined in Scheme 5.2,
where the synthetic route, the structures of the monomers, and the resulting polymer
naming designations are provided. Scheme 5.2a shows the four spacers utilized to make
corresponding P3HT-X-DPP type semi-random copolymers with 10% DPP loading. All
four of the polymers via Scheme 5.2a are novel and feature two different thiophene-type
units with extended conjugation, an electron-poor bithiazole unit, and an electron-rich
EDOT unit, which provides an opportunity to consider the influence of these types of
322
motifs via DArP in three-component semi-random copolymers. It is worth noting that
bithiazole is challenging to lithiate and stannylate, so offers promise to DArP as a method
for expanding potential substrate scope and polymer compositions. Scheme 5.2b features
replacement of the model DPP monomer with one of four acceptors, two of which possess
a thienyl moiety attached to the electron-poor core (fused TPTI and BTD) and two which
are halogenated directly on the electron-poor core, one that is benzene-based (QX) and one
that is thiophene-based (TPD). These four different types of acceptors enable evaluation of
the relative effectiveness of DArP with other substrates. Polymer properties are provided
in Table 5.5, which show that replacement of the thiophene with other substrates does not
diminish the molecular weight and yields compared to model system P3HTT-DPP;
however, molecular weights are generally lower than DArP P3HTT-DPP for the four
different acceptor substrates. This is especially true for BTD and TPD polymers. This could
potentially result for suboptimal stochiometric balance, especially considering thiophene
is added to the reaction vessel with microliter syringe and can be challenging to weight.
Regardless, although lower molecular weights overall led to diminished yields for the
acceptor series of polymers after Soxhlet extraction, the polymers still produce interesting
optoelectronic properties and suitably good films for measuring thin film performance.

323

Scheme 5.2. Synthesis of P3HT Semi-Random Analogs by DArP Polymerization.
Optimized Conditions from Model System P3HTT-DPP are Applied t o a variety of systems
with different spacers and acceptors to determine the applicability of DArP with various
substrates.
In all cases for P3HT-X-DPP series (Scheme 5.2a) of copolymers, feed ratios
correlated well with polymer compositions.
1
H NMR spectra of these four polymers are
provided in Figure A4.25-28. Incorporation of BT or TvT ultimately led to polymers that
resembled P3HTT-DPP, with the dominant DPP coupling observed in NMR to occur at the
5-position of 3HT but subtle broadening of the peaks (Figure A4.25) or small shoulders
(Figure A4.26) can be attributed to coupling with BT or TvT respectively. With the
strongly electron-withdrawing BTz motif (P3), which features two methyl groups,
resolution of the aliphatic peaks is enhanced compared to the other substrates investigated.
Interestingly, the typically strong peak associated with the DPP/3HT is obfuscated by the
emergence of other distinct peaks of high intensity (Figure A4.27). This suggests that
324
despite the significant presence of 3HT monomers, DPP coupling to BTz happens more
frequently. Likewise, for P4, a strong peak emerges for DPP/EDOT coupling (Figure
A4.28). These results suggest that DPP may be preferentially reactive via C-H arylation
with EDOT and BTz than 3HT. For the acceptor series of polymers, P3HTT-A (Scheme
5.2b), feed ratios generally correlate well to polymer composition, though P6 has a slightly
lower QX composition (~8%) than the monomer feed loading of 10%. For this series of
polymers, all are novel semi-random polymers except for P3HTT-TPD, which was
previously investigated by Stille polymerization.
85
It is worth noting that the NMR for that
polymer matches closely with the one reported here (Figure A4.32). Semi-random
polymers with TPTI, QX, and this BTD monomer are novel but the BTD unit has been
previously explored directly for both Stille and DArP semi-random polymers.
50,66

Table 5.5. Polymer Properties (Molecular weight and yield) and Optoelectronic Properties
of DArP P3HT Semi-Random Copolymers (P1-P8) with varying spacers or acceptors after
Soxhlet Extraction, including HOMO energy level, SCLC Hole Mobility, Peak Absorption
Coefficient, Optical Bandgap, d100 Spacing, and Polymer Solar Cell Performance.
Polymer
a

Mn,
f
kDa
(Ð)
Yield,
g
%
HOMO,
b

eV
µ,
c
x 10
-4

cm
2
V
-1
s
-1

E g,
d

eV
T m, °C
(T c, °C)
e

d 100,
f

Å
Jsc,
g,h

mA cm
-1

Voc,
i

V
FF
j

η,
k

%
P1 16.3 (2.33) 76 5.23 0.29 1.50 187 (183) 15.8 10.3 0.59 0.55 3.34
P2 14.2 (2.27) 63 5.21 0.44 1.48 198 (182) 16.0 11.2 0.58 0.56 3.64
P3 15.8 (2.56) 73 5.40 0.16 1.47 184 (172) 15.7 7.4 0.57 0.44 1.86
P4 17.7 (3.10) 71 5.18 0.17 1.29 196 (170) 16.3 5.1 0.49 0.32 0.80
P5 10.0 (2.05) 49 5.36 0.39 1.91 -- 16.8 9.6 0.67 0.59 3.79
P6 9.1 (1.88) 36 5.11 0.51 1.77 183 (156) 17.2 4.7 0.58 0.49 1.34
P7 8.6 (2.14) 52 5.17 1.25 1.63 155 (113) 16.4 3.1 0.60 0.44 0.82
P8 7.6 (1.97) 46 5.29 0.31 1.81 156 (115) 18.2 5.8 0.73 0.51 2.16
325
a
Entry as provided in Scheme 5.2. For solar cell data, polymers were spin-coated from
Polymer:PC61BM mixtures (1:1.3 by mass) dissolved in o-dichlorobenzene (o-DCB) and
dried under N2 for 30 min. prior to aluminum deposition.
b
Determined by cyclic
voltammetry (vs. Fc/Fc
+
) in 0.1M TBAPF6, where HOMO = 5.1 + E ox.
c
Measured on neat
polymer films.
d
Calculated from the absorption band edge in thin films, Eg = 1240/λedge.
e

Measured by DSC.
f
Calculated from GIXRD diffraction peaks in thin films.
g
Mismatch
corrected.
h
Standard deviations of less than 0.3 mA/cm2 were observed in all cases
averaged over eight pixels.
i
Standard deviations of less than 0.01 V were observed in all
cases averaged over eight pixels.
j
Standard deviations of less than 0.01 were observed in
all cases averaged over eight pixels.
k
Standard deviations of less than 0.3% were observed
in all cases averaged over eight pixels

Figure 5.6. (a) UV-Vis absorption profiles for the P3HT Semi-Random series of polymers.
Thicknesses are determined from x-ray reflectivity. (b) GIXRD patterns for neat polymer
films. (c) EQE spectra of BHJ PSCs.

Optoelectronic properties and PSC characterization provided in Table 5.5 confirm
that the semi-random polymer architecture is an invaluable strategy toward unique material
326
properties. Additionally, absorption profiles, GIXRD patterns, and EQE spectral response
measurements are provided in Figure 5.6. Electrochemical oxidative via CV experiments
demonstrates that deeper HOMOs of 5.4 eV and shallow HOMOs of 5.11 eV can be
achieved with small loadings (10%) of electron-poor BTz motif or QX respectively.
Indeed, small secondary and tertiary component loadings provide several different HOMO
energy levels and optical bandgaps, as observed in Table 5.5. All polymers demonstrated
some level of preservation of rr-P3HT qualities. This includes crystallinity—as all
polymers exhibited diffraction peaks via GIXRD measurements in thin films (Figure 5.6b)
and all except P5 via DSC measurements (Figure A4.39) of bulk polymers. This translates
into high hole mobilities for all polymers (Table 5.5). Additionally, absorption profiles
demonstrate a variety of unique changes via incorporation of just a small amount of
secondary component loading. Incorporation of BT (P1) and TvT (P2) (Figure 5.6a)
improve the vibronic shoulder of respective copolymers compared to model system
P3HTT-DPP (Figure 5.5a). Incorporation of electron-poor BTz (P3) moderately blue
shifts the peak absorption in the 500-nm region without changing the optical bandgap
compared to other DPP copolymers. On the other hand, replacing the thiophene with
electron-rich EDOT (P4) not only red shifts the absorption but significantly extends its
absorption into the near-IR region, lowering the optical bandgap from 1.5 typically
observed for P3HTT-DPP down to 1.29 eV. Conversely, replacing the 10% DPP loading
with various acceptors narrows the absorption but provides a range of distinct optical
bandgaps, from 1.6 eV for BTD (P7) to 1.91 for TPTI (Table 5.5). While the DPP unit is
widely employed because of its capacity for broadly absorbing photons, the need for wide
bandgap polymers for ternary or tandem solar cells should not be underappreciated. Both
327
TPTI (P5) and QX ( P6) semi-random polymers provide high bandgaps compared to
P3HTT-DPP but P5 features strong peak coefficients and P6 demonstrates strong
crystallinity. Unfortunately, both BTD and TPD copolymers have weaker absorption
coefficients, which is consistent with previous reports.
50,66,85

As a practical measure of polymer performance, PSCs were fabricated for all semi-
random polymers outlined in Scheme 5.2 and Table 5.5. Processing conditions were kept
consistent across all polymers, which were all spin-coated from 10 mg/mL o-DCB
solutions at 1:1.3 polymer:PC61BM ratios in air under ambient temperature and humidity.
As a result, the PSCs reported herein can be considered baseline studies and further
optimization is required to determine the maximum efficiency that can be achieved in these
novel polymers. Regardless, we can gleam important qualities from these unoptimized
devices. For example, where P3HTT-TPD exhibits weaker absorptions, it demonstrates the
highest Voc values of the polymers explored in this work. P3HTT-QX (P6) and P3HTT-
BTD (P7) exhibits modest performance, the latter of which is consistent with previous
reports.
50
P3HTT-TPTI (P5) exhibits strong peak absorption coefficients and
correspondingly strong spectral response at 500 nm (Figure 5.6c). For the P3HT-X-DPP
series of copolymers, both P1 (BT) and P2 (TvT) exhibit properties that resemble the model
P3HTT-DPP system. Interestingly, as discussed earlier, the absorption profiles both exhibit
a vibronic shoulder that resembles Stille P3HTT-DPP more so than DArP P3HTT-DPP.
The solar cell performance, however, more closely resembles B4 and B5 (Table 5.4,
Figure 5.5c) than either Stille or B6. Despite the promise of the absorption profiles and
optoelectronic properties, both P3 (BTz) and P4 (EDOT) underperform compared to other
328
DPP-based copolymers, though P4 exhibits very broad but weak spectral response as seen
in Figure 5.6.
This collection of semi-random copolymers expands on an increasingly popular
design strategy approach of random copolymers toward materials with finely tuned
optoelectronic properties. Recently, it was reported that thiophene and
diketopyrrolopyrrole (DPP) are some of the most synthetically accessible substrates.
Strategies toward novel semi-random polymers, incorporating strategically accessible
motifs with the advantages of randomness, are a pathway toward affordable polymers. The
ability to utilize DArP toward these materials further improves this attractiveness.

5.3. Conclusions

Ultimately, this work demonstrates a comprehensive methodological evaluation of
several distinct but successful DArP conditions on two unique model systems. The
application of DArP to three-component copolymers is exceedingly rare due to problems
with defects and poor performance, which are overcome herein through the combination
of 2-methyltetrahydrofuran (MeTHF) and affordable neodecanoic acid (NDA), which have
not been utilized together for DArP. This report details an uncommon instance of DArP
polymers performing well in solar cells, and further expands DArP to be compatible with
high quality three-component polymers. Optimized DArP conditions are subsequently
utilized to generate seven novel semi-random P3HT analogues, highlighting the
advantages of the semi-random architecture and demonstrating the broad compatibility of
DArP with challenging to stannylate monomers and a broad range of acceptors. After years
of DArP being considered a marginally inferior method to Stille for practical applications,
329
the need for bulky carboxylic acids and careful consideration of functional group
assignment and conditions is confirmed herein. Future work should explore DArP on
increasingly complex and varied structures and multi-component copolymers with an
emphasis on employing green solvents and affordable reagents.

5.4. References

(1) Krebs, F. C.; Tromholt, T.; Jørgensen, M. Nanoscale 2010, 2 (6), 873.
(2) Angmo, D.; Krebs, F. C. J. Appl. Polym. Sci. 2013, 129 (1), 1.
(3) Shown, I.; Ganguly, A.; Chen, L.-C.; Chen, K.-H. Energy Sci Eng 2015, 3 (1), 2.
(4) Bundgaard, E.; Livi, F.; Hagemann, O.; Carlé, J. E.; Helgesen, M.; Heckler, I. M.;
Zawacka, N. K.; Angmo, D.; Larsen-Olsen, T. T.; dos Reis Benatto, G. A.; Roth, B.;
Madsen, M. V.; Andersson, M. R.; Jørgensen, M.; Søndergaard, R. R.; Krebs, F. C.
Adv. Energy Mater. 2015, 5 (10), DOI: 10.1002/aenm.201402186.
(5) Thompson, B. C.; Fréchet, J. M. J. Angew. Chem. Int. Ed. 2008, 47 (1), 58.
(6) Khlyabich, P. P.; Burkhart, B.; Rudenko, A. E.; Thompson, B. C. Polymer 2013, 54
(20), 5267.
(7) Benten, H.; Mori, D.; Ohkita, H.; Ito, S. J. Mater. Chem. A 2016, 4 (15), 5340.
(8) Nikolka, M.; Nasrallah, I.; Rose, B.; Ravva, M. K.; Broch, K.; Sadhanala, A.; Harkin,
D.; Charmet, J.; Hurhangee, M.; Brown, A.; Illig, S.; Too, P.; Jongman, J.; McCulloch,
I.; Bredas, J.-L.; Sirringhaus, H. Nat Mater 2017, 16 (3), 356.
(9) Kim, N.-K.; Jang, S.-Y.; Pace, G.; Caironi, M.; Park, W.-T.; Khim, D.; Kim, J.; Kim,
D.-Y.; Noh, Y.-Y. Chem. Mater. 2015, 27 (24), 8345.
330
(10) Ponder, J. F.; Österholm, A. M.; Reynolds, J. R. Macromolecules 2016, 49 (6),
2106.
(11) Li, W.; Guo, Y.; Shi, J.; Yu, H.; Meng, H. Macromolecules 2016, 49 (19), 7211.
(12) Helgesen, M.; Carlé, J. E.; dos Reis Benatto, G. A.; Søndergaard, R. R.; Jørgensen,
M.; Bundgaard, E.; Krebs, F. C. Adv. Energy Mater. 2015, 5 (9), 1401996.
(13) Angmo, D.; Gevorgyan, S. A.; Larsen-Olsen, T. T.; Søndergaard, R. R.; Hösel, M.;
Jørgensen, M.; Gupta, R.; Kulkarni, G. U.; Krebs, F. C. Org. Electron. 2013, 14 (3),
984.
(14) Bura, T.; Blaskovits, J. T.; Leclerc, M. J. Am. Chem. Soc. 2016, 138 (32), 10056.
(15) Rudenko, A. E.; Thompson, B. C. J. Polym. Sci. A Polym. Chem. 2015, 53 (2), 135.
(16) Pouliot, J.-R.; Grenier, F.; Blaskovits, J. T.; Beaupré, S.; Leclerc, M. Chem. Rev.
2016, 116 (22), 14225.
(17) Osaka, I.; McCullough, R. D. Acc. Chem. Res. 2008, 41 (9), 1202.
(18) Chen, T.-A.; Wu, X.; Rieke, R. D. J. Am. Chem. Soc. 1995, 117 (1), 233.
(19) Wu, W.-C.; Liu, C.-L.; Chen, W.-C. Polymer 2006, 47 (2), 527.
(20) Carsten, B.; He, F.; Son, H. J.; Xu, T.; Yu, L. Chem. Rev. 2011, 111 (3), 1493.
(21) Burke, D. J.; Lipomi, D. J. Energy Environ. Sci. 2013, 6 (7), 2053.
(22) Marzano, G.; Ciasca, C. V.; Babudri, F.; Bianchi, G.; Pellegrino, A.; Po, R.;
Farinola, G. M. Eur. J. Org. Chem. 2014, No. 30, 6583.
(23) Gorelsky, S. I.; Lapointe, D.; Fagnou, K. J. Am. Chem. Soc. 2008, 130 (33), 10848.
(24) Lafrance, M.; Fagnou, K. J. Am. Chem. Soc. 2006, 128, 16496.
(25) Campeau, L.-C.; Fagnou, K. Chem. Commun. 2006, 12 (12), 1253.
331
(26) Livi, F.; Gobalasingham, N. S.; Thompson, B. C.; Bundgaard, E. J. Polym. Sci.,
Part A 2016, 54 (18), 2907.
(27) Wang, Q.; Takita, R.; Kikuzaki, Y.; Ozawa, F. J. Am. Chem. Soc. 2010, 132 (33),
11420.
(28) Rudenko, A. E.; Khlyabich, P. P.; Thompson, B. C. ACS Macro Lett. 2014, 3, 387.
(29) Rudenko, A. E.; Latif, A. A.; Thompson, B. C. Nanotechnology 2014, 25 (1),
014005.
(30) Rudenko, A. E.; Wiley, C. A.; Tannaci, J. F.; Thompson, B. C. J. Polym. Sci. A
Polym. Chem. 2013, 51 (12), 2660.
(31) Rudenko, A. E.; Latif, A. A.; Thompson, B. C. J. Polym. Sci. A Polym. Chem. 2015,
53 (12), 1492.
(32) Rudenko, A. E.; Thompson, B. C. Macromolecules 2015, 48 (3), 569.
(33) Bura, T.; Morin, P.-O.; Leclerc, M. Macromolecules 2015, 48 (16), 5614.
(34) Dudnik, A. S.; Aldrich, T. J.; Eastham, N. D.; Chang, R. P. H.; Facchetti, A.; Marks,
T. J. J. Am. Chem. Soc. 2016, 138 (48), 15699.
(35) Marzano, G.; Kotowski, D.; Babudri, F.; Musio, R.; Pellegrino, A.; Luzzati, S.; Po,
R.; Farinola, G. M. Macromolecules 2015, 48 (19), 7039.
(36) Chang, S.-W.; Waters, H.; Kettle, J.; Kuo, Z.-R.; Li, C.-H.; Yu, C.-Y.; Horie, M.
Macromol. Rapid Commun. 2012, 33 (22), 1927.
(37) Huang, X.; Zhang, G.; Zhou, C.; Liu, L.; Jin, Y.; Liu, S.; Ying, L.; Huang, F.; Cao,
Y. Polym. Chem. 2015, 6 (22), 4154.
(38) Hu, L.; Han, J.; Qiao, W.; Wang, Z. Y. Polymer 2016, 99, 427.
332
(39) Heo, H.; Kim, H.; Lee, D.; Jang, S.; Ban, L.; Lim, B.; Lee, J.; Lee, Y.
Macromolecules 2016, 49 (9), 3328.
(40) Howard, J. B.; Ekiz, S.; Cuellar De Lucio, A. J.; Thompson, B. C. Macromolecules
2016, 49 (17), 6360.
(41) Li, A.; Amonoo, J.; Huang, B.; Goldberg, P. K.; McNeil, A. J.; Green, P. F. Adv.
Funct. Mater. 2014, 24 (35), 5594.
(42) Nair, V. S.; Sun, J.; Qi, P.; Yang, S.; Liu, Z.; Zhang, D.; Ajayaghosh, A.
Macromolecules 2016, 49 (17), 6334.
(43) Nielsen, C. B.; Ashraf, R. S.; Schroeder, B. C.; D’Angelo, P.; Watkins, S. E.; Song,
K.; Anthopoulos, T. D.; McCulloch, I. Chem. Commun. 2012, 48 (47), 5832.
(44) Li, J.; Ong, K.-H.; Lim, S.-L.; Ng, G.-M.; Tan, H.-S.; Chen, Z.-K. Chem. Commun.
2011, 47 (33), 9480.
(45) Kang, T. E.; Choi, J.; Cho, H.-H.; Yoon, S. C.; Kim, B. J. Macromolecules 2016,
49 (6), 2096.
(46) Kang, T. E.; Kim, K.-H.; Kim, B. J. J. Mater. Chem. A 2014, 2 (37), 15252.
(47) Po, R.; Bianchi, G.; Carbonera, C.; Pellegrino, A. Macromolecules 2015, 48 (3),
453.
(48) Bakulin, A. A.; Hummelen, J. C.; Pshenichnikov, M. S.; van Loosdrecht, P. H. M.
Adv. Funct. Mater. 2010, 20 (10), 1653.
(49) Dang, M. T.; Hirsch, L.; Wantz, G.; Wuest, J. D. Chem. Rev. 2013, 113 (5), 3734.
(50) Burkhart, B.; Khlyabich, P. P.; Cakir Canak, T.; LaJoie, T. W.; Thompson, B. C.
Macromolecules 2011, 44 (6), 1242.
333
(51) Burkhart, B.; Khlyabich, P. P.; Thompson, B. C. J. Photon. Energy 2012, 2 (1),
021002.
(52) Burkhart, B.; Khlyabich, P. P.; Thompson, B. C. Macromolecules 2012, 45 (9),
3740.
(53) Burkhart, B.; Khlyabich, P. P.; Thompson, B. C. Macromol. Chem. Phys. 2013, 214
(6), 681.
(54) Khlyabich, P. P.; Burkhart, B.; Ng, C. F.; Thompson, B. C. Macromolecules 2011,
44 (13), 5079.
(55) Khlyabich, P. P.; Rudenko, A. E.; Thompson, B. C. J. Polym. Sci. A Polym. Chem.
2014, 52 (8), 1055.
(56) Howard, J. B.; Noh, S.; Beier, A. E.; Thompson, B. C. ACS Macro Lett. 2015, 4
(7), 725.
(57) Noh, S.; Gobalasingham, N. S.; Thompson, B. C. Macromolecules 2016, 49 (18),
6835.
(58) Xu, B.; Noh, S.; Thompson, B. C. Macromolecules 2014, 47 (15), 5029.
(59) Kozycz, L. M.; Gao, D.; Seferos, D. S. Macromolecules 2013, 46 (3), 613.
(60) Lee, Y.-S.; Lee, J. Y.; Bang, S.-M.; Lim, B.; Lee, J.; Na, S.-I. J. Mater. Chem. A
2016, 4 (29), 11439.
(61) Jung, J. W.; Liu, F.; Russell, T. P.; Jo, W. H. Energy Environ. Sci. 2013, 6 (11),
3301.
(62) Beaupré, S.; Shaker-Sepasgozar, S.; Najari, A.; Leclerc, M. Journal of Materials
Chemistry A 2017, 5 (14), 6638.
334
(63) Hendriks, K. H.; Li, W.; Heintges, G. H. L.; van Pruissen, G. W. P.; Wienk, M. M.;
Janssen, R. A. J. J. Am. Chem. Soc. 2014, 136 (31), 11128.
(64) Lombeck, F.; Komber, H.; Gorelsky, S. I.; Sommer, M. ACS Macro Lett. 2014, 3
(8), 819.
(65) Lombeck, F.; Komber, H.; Fazzi, D.; Nava, D.; Kuhlmann, J.; Stegerer, D.; Strassel,
K.; Brandt, J.; de Zerio Mendaza, A. D.; Müller, C.; Thiel, W.; Caironi, M.; Friend,
R.; Sommer, M. Adv. Energy Mater. 2016, 6 (21), 1601232.
(66) Rudenko, A. E.; Wiley, C. A.; Stone, S. M.; Tannaci, J. F.; Thompson, B. C. J.
Polym. Sci. A Polym. Chem. 2012, 50 (18), 3691.
(67) Dou, J.; Chen, Z.; Ma, C. Synth. Met. 2014, 196, 117.
(68) Gobalasingham, N. S.; Noh, S.; Thompson, B. C. Polym. Chem. 2016, 7 (8), 1623.
(69) Morin, P.-O.; Bura, T.; Sun, B.; Gorelsky, S. I.; Li, Y.; Leclerc, M. ACS Macro
Lett. 2015, 4 (1), 21.
(70) Matsidik, R.; Luzio, A.; Hameury, S.; Komber, H.; McNeill, C. R.; Caironi, M.;
Sommer, M. J. Mater. Chem. C 2016, 4 (43), 10371.
(71) Aycock, D. F. Org. Process Res. Dev. 2007, 11 (1), 156.
(72) Kuwabara, J.; Sakai, M.; Zhang, Q.; Kanbara, T. Org. Chem. Front. 2015, 2 (5),
520.
(73) Livi, F.; Gobalasingham, N. S.; Bundgaard, E.; Thompson, B. C. J. Polym. Sci. A
Polym. Chem. 2015, 53 (22), 2598.
(74) Wang, K.; Wang, G.; Wang, M. Macromol. Rapid Commun. 2015, 36 (24), 2162.
(75) Guo, C.; Quinn, J.; Sun, B.; Li, Y. Polym. Chem. 2016, 7 (27), 4515.
335
(76) Pouliot, J.-R.; Wakioka, M.; Ozawa, F.; Li, Y.; Leclerc, M. Macromol. Chem. Phys.
2016, 217 (13), 1493.
(77) Hu, X.; Zuo, L.; Fu, W.; Larsen-Olsen, T. T.; Helgesen, M.; Bundgaard, E.;
Hagemann, O.; Shi, M.; Krebs, F. C.; Chen, H. J. Mater. Chem. 2012, 22 (31), 15710.
(78) Hu, X.; Fu, W.; Zuo, L.; Shi, H.; Chen, M.; Liu, S.; Pan, J.; Fu, L.; Shi, M.; Chen,
H. Tetrahedron 2013, 69 (16), 3419.
(79) Howard, J. B.; Ekiz, S.; Noh, S.; Thompson, B. C. ACS Macro Lett. 2016, 977.
(80) Schiefer, D.; Komber, H.; Mugwanga Keheze, F.; Kunz, S.; Hanselmann, R.;
Reiter, G.; Sommer, M. Macromolecules 2016, 49 (19), 7230.
(81) Guo, Q.; Dong, J.; Wan, D.; Wu, D.; You, J. Macromol. Rapid Commun. 2013, 34
(6), 522.
(82) Broll, S.; Nübling, F.; Luzio, A.; Lentzas, D.; Komber, H.; Caironi, M.; Sommer,
M. Macromolecules 2015, 48 (20), 7481.
(83) Park, J. K.; Jo, J.; Seo, J. H.; Moon, J. S.; Park, Y. D.; Lee, K.; Heeger, A. J.; Bazan,
G. C. Adv. Mater. 2011, 23 (21), 2430.
(84) Kim, Y.; Cook, S.; Kirkpatrick, J.; Nelson, J.; Durrant, J. R.; Bradley, D. D. C.;
Giles, M.; Heeney, M.; Hamilton, R.; McCulloch, I. J. Phys. Chem. C 2007, 111 (23),
8137.
(85) Burkhart, B.; Khlyabich, P. P.; Thompson, B. C. ACS Macro Lett. 2012, 1 (6), 660.

336
CHAPTER 6: PALLADIUM-CATALYZED OXIDATIVE DIRECT ARYLATION
POLYMERIZATION (OXI-DARP) OF AN ESTER-FUNCTIONALIZED
THIOPHENE

6.1. Introduction

An impressive toolkit exists for the generation of conjugated polymers, which have
been explored for a broad range of material applications, including organic photovoltaics,
1,2

electrochromic devices,
3,4
field-effect transistors,
5
and more recently for biomedical
imaging, therapy, and drug delivery.
6
This toolkit has encompassed a variety of synthetic
methods, from electropolymerization
7
and chemical oxidative polymerization
8
to ring-
opening metathesis polymerization (ROMP)
9
and photopolymerization;
10
however, the
most popular strategies toward conjugated polymers have generally consisted of cross-
coupling polycondensations, such as Stille,
11
Suzuki,
12
Kumada,
13
and Negishi
14

polymerizations. While these methods are highly prevalent and useful, these classic
transition metal-catalyzed cross-coupling reactions typically require both halogenated and
metallic functional groups. These metalated monomers can be both challenging to purify
due to their instability but also quite toxic,
15
as is the case with organotin functional groups
via Stille polymerization, which has been the method of choice for almost every top
performing polymer in OPV applications.
16
As research intensifies in the pursuit of
increasingly complex structural designs and novel materials applications, the development
of expedient, dependable, and efficient methods for the preparations of these materials is
vital.
337
Direct arylation polymerization (DArP)
17–25
has emerged recently as an alternative
to these highly prevalent transition metal-catalyzed polycondensations for the generation
of high quality conjugated polymers. DArP is considered a greener and more sustainable
alternative to the traditional Stille polymerization because it eliminates the need for toxic
organotin functional groups, as well as the associated lithiation-metalation step (which
requires cryogenic conditions with highly flammable reagents). Because DArP enables
quality polymers from less toxic reagents in fewer steps, the overall synthesis of conjugated
polymers is more amenable to industrial-scale manufacturing.
26

Ultimately, the most atom economical route toward conjugated polymers is direct
C-H/C-H activation, which would eliminate not only the metalation step but also the
halogenation en route to conjugated polymers (Figure 6.1). By avoiding organic halides,
which are widely recognized as environmental hazards, this method would be more earth-
friendly while also generating polymers with benign end groups. It has been observed that
bromine and organotin functionalities, which would be the end groups in a typical Stille
polymerization, negatively influence performance—by charge trapping, varying interchain
packing, and altering the film morphology in optoelectronic applications.
27,28
However,
methods in the same vein as historically prominent electrochemical or chemical oxidative
polymerizations with ferric chloride
29,30
or oxovanadium
31
typically oxidize the
substrate
29,32
, which can result in defects, poor structural control, and—in polymers made
via ferric chloride—both iron and chlorine impurities in the polymer backbone.
33

Furthermore, these methods are not always compatible with desired substrates
34
because
they operate by oxidizing the monomer itself, which introduces additional variables such
as cation or radical stability. Ideally, a catalyzed oxidative direct arylation would provide
338
better control over polymer quality by oxidizing the catalyst as opposed to the substrate;
however, as previously identified by Fagnou, there exist significant challenges for cross-
coupling that does not feature preactivation of the substrate, namely issues with reactivity,
regioselectivity, and unwanted homocoupling defects which consume reagents.
35
While
there is a considerable body of literature for small molecule oxidative cross-coupling
reactions of arenes,
36–40
the successful application of this long-sought synthetic strategy in
polymers is limited.

Figure 6.1. Comparison of the prerequisite synthetic steps toward monomers compatible
with specific polymerization methods and the eventual end groups of these polymers.
To the best of our knowledge, the first reported palladium-catalyzed oxidative
polymerization of thiophene derivatives was carried out by Ogino, et al.,
41
featuring
palladium (II) acetate as a catalyst and a combination of copper (II) acetate and
trifluoroacetic acid under oxygen. Polymers were generally of modest molecular weight
(<7 kDa), were regiorandom, and potentially contained β-defects. Recently, You and Lan,
et al.
42
reported a copper catalyzed polymerization of benzodiimidazoles and Lu and Li, et
al.
43
reported palladium-catalyzed oxidative direct arylation polymerization conditions
which feature Pd(OAc)2 as a catalyst, K2CO3 as a base, DMA as a solvent, but also feature
339
Cu(OAc)2 or Ag2CO3 as an oxidant; however, the conditions were reported to only work
on heterocycles featuring a symmetrical dione, such as thieno[3,4-c]pyrrole-4,6-dione
(TPD), to generate homopolymers. It was proposed that the dione is necessary for
coordination with the palladium center and likely the carbonyl serves as a directing group
in this system. Recently, they expanded this method to polymerize homopolymers based
on symmetrical carbonyl-containing thiazole-flanked thiophene units with Pd(OAc)2,
KOAc as a base, DMA as a solvent, and Ag 2CO3 as an oxidant.
44
While these reports are
interesting, the monomers contain only one type of C-H bond. More fundamental
exploration of this method is necessary.
A goal of the present work is to expand the substrate scope and report the first
palladium-catalyzed oxidative direct arylation polymerization (Oxi-DArP) of an
unsymmetrical thiophene monomer with an ester directing group to generate poly(hexyl
thiophene-3-carboxylate), herein referred to as poly(3-hexylesterthiophene) (P3HET) for
simplicity and consistency with abbreviations of 3-substituted thiophenes, such as 3-
hexylthiophene (3HT). The alkyl ester functional group is an increasingly popular side-
chain in polymers.
45
As an electron withdrawing group, it can lower a material’s HOMO
while maintaining good solubility comparable to alkyl chains, which contrasts with
fluoroalkyl side-chains which are also electron withdrawing but often have limited
solubility in common organic solvents.
46
Furthermore, ester functionalities have been
explored for various side-chain engineering applications. Fréchet, et al.
47
observed
improved solar cell performance in polymers with thermally cleavable solubilizing ester
groups. Additionally, Krebs, et al.
48
have reported that polymer solar cells which featured
a thermally cleaved ester side-chain improves device operating lifetime and stability.
340
Reynolds, et al.
49
utilized alkyl ester functionalities to synthesize high molecular weight
polymers in organic solvents, then chemically defunctionalized the alkyl ester side chains
to generate carboxylate salts that were readily soluble in water. Indeed, while much
research has focused on the development of novel conjugated backbones, side-chain
engineering is not adequately considered or pursued, despite the dramatic influence it can
have on conjugated polymers.
46,50
If these interesting side-chain structures can be
simultaneously utilized as directing groups, the synthesis of conjugated polymers via Oxi-
DArP would not only be significantly more atom economical and more synthetically
efficient but could also enable side-chains that are incompatible with halogenation or
metalation reactions, either from instability or challenges in purification.
Here two substrates were explored as model systems for Oxi-DArP, 3-
hexylthiophene and 3-hexylesterthiophene. These model systems enable fundamental
exploration of Oxi-DArP for a variety of reasons. The first is to evaluate the observations
made by Lu and Li, et al.
43,44
, that a carbonyl directing group facilitates this mechanism.
Toward this end, we expect 3-hexylesterthiophene to outperform 3-hexylthiophene for
optimized conditions; however, by utilizing an unsymmetrical directing group, this system
also evaluates the observation that symmetrical diones or esters are required for C-H/C-H
activation toward polymer generation (that the palladium center is coordinated to carbonyls
on both coupling partners prior to reductive elimination). If this is the case, we would
expect significant amounts of head-to-head coupling of 3-hexylesterthiophene or at the
very extreme, generation of only dimers. A further advantage of these substrates is the
availability of protons in both the α- and β-positions of the thiophene rings which can be
used to evaluate selectivity, and through
1
H-NMR analysis both regioregularity and defects
341
can be conveniently explored. Finally, both substrates are compatible upon bromination
with traditional DArP synthesis, and with metallation, Stille polycondensation. This allows
for a more comparative analysis of the quality of the polymers generated and insight into
the potential for polymers generated via Oxi-DArP to be competitive with DArP or Stille
polymers, especially considering the advantages of avoiding both halogenation and
metalation of the monomers.

6.2. Experimental

6.2.1. Materials & Methods

Unless otherwise noted, all reagents were purchased and used as received from
Sigma Aldrich. N,N-dimethylacetamide (anhydrous DMA, 99.9%), N-bromosuccinimide
(NBS, 99%), neodecanoic acid (NDA), and potassium carbonate were purchased from Alfa
Aesar. NBS was recrystallized from H2O and dried under vacuum (1 mmHg), potassium
carbonate was dried at 110°C under vacuum (1mmHg). Palladium acetate (98%) was
purchased from TCI (USA). PCy 3-HBF4 and silver carbonate were purchased from Strem
Chemicals. Dimethylformamide (DMF) Dri-Solve (99%), Toluene Dri-Solv (99%), and
THF were purchased from EMD Chemicals. THF was refluxed over sodium and
benzophenone prior to distillation.
NMR spectra were recorded at 25°C using CDCl3 on a Varian 400 MHz NMR
Spectrometer (small molecules), Varian 500 MHz NMR Spectrometer (small molecules),
or Varian 600 MHz NMR Spectrometer (polymers). Chemical shifts are given in parts per
342
million (ppm) and are referenced to residual solvent signals in commercial deuterated
chloroform (δ = 7.26 ppm).
For polymer molecular weight determination, polymer samples were dissolved in
HPLC grade o-dichlorobenzene at a concentration of 0.5 mg/ml, briefly heated and then
allowed to turn to room temperature prior to filtering through a 0.2 μm PTFE filter. SEC
was performed using HPLC grade o-dichlorobenzene at a flow rate of 0.6 ml/min on one
300 × 8.0 mm LT6000L Mixed High Org column (Viscotek) at 60°C using a Viscotek GPC
Max VE 2001 separation module and a Viscotek TDA 305 RI detector. The instrument was
calibrated vs. polystyrene standards (1,050 – 3,800,000 g/mol) and data was analyzed using
OmniSec 4.6.0 software.
For thin film measurements, solutions were spin-coated onto pre-cleaned glass
slides (sonicated for 10 minutes in water, acetone, and isopropyl alcohol then dried under
high N2 flow) from o-dichlorobenzene solutions at 7mg/mL. UV-vis absorption spectra
were obtained on a Perkin-Elmer Lambda 950 spectrophotometer. The thickness of thin
films and GIXRD measurements were obtained using Rigaku Diffractometer Ultima IV
using Cu Kα radiation source (λ = 1.54 Å) in the reflectivity and grazing-incidence X-ray
diffraction mode, respectively.
Cyclic voltammetry was executed on a Princeton Applied Research VersaStat3
potentiostat under the control of VersaStudio Software. A standard three electrode cell
based on a Pt wire working electrode, a Pt wire counter electrode, and a silver wire pseudo
reference electrode (calibrated vs. Fc/Fc
+
which is taken as 5.1 eV vs. vacuum)
51,52
was
purged with nitrogen and maintained under nitrogen atmosphere during all measurements.
For cyclic voltammetry, acetonitrile was distilled over CaH2 prior to use and tetrabutyl
343
ammonium hexafluorophosphate (0.1 M) was used as the supporting electrolyte. Polymer
films were made by applying a 10mg/mL o -DCB solution via dropcasting directly onto the
working electrode under a nitrogen umbrella and thoroughly dried prior to measurement.

6.2.2. General Procedure for the Synthesis of Polymers (P3HT, P3HET) via Oxi-
DArP

Small molecule synthesis, Stille polymerization methods, and direct arylation
polymerization (DArP) are provided in the Appendix. The general procedure for Oxi-DArP
is as follows: Respective monomers (3HT or 3HET) (0.5 mmol) were dissolved in
anhydrous DMA to yield a 0.05M solution. To the reaction mixture, the appropriate ratio
of oxidant, additive, or ligand (See Table 6.1) was added and the reaction mixture was
degassed for 15 minutes with nitrogen flow. Then Pd(OAc)2 (loading detailed in Table
6.1) was added to the reaction mixture, which was further degassed for 10 minutes. Then
the reaction was immersed into a pre-heated oil bath at the appropriate temperature and
stirred under nitrogen atmosphere for 72 hours. Then the reaction mixture was cooled,
precipitated into methanol, filtered, and purified via Soxhlet extraction with methanol,
hexanes, and lastly chloroform; this final fraction was concentrated in vacuo and
precipitated into methanol. Upon filtering, the polymers were dried under high vacuum
overnight. P3HET
1
H NMR (600 MHz, CDCl3, δ ppm): δ7.86 (m, 1H), 4.30 (t, 2H), 1.75
(m, 2H), 1.44 (br, 6H), 0.89 (t, 3H). P3HT
1
H NMR (600 MHz, CDCl3, δ ppm): δ 6.96
(m, 1H), 2.79 (b, 2H), 1.71 (m, 2H), 1.26 (m, 6H), 0.88 (t, 3H)

6.3. Results and Discussion

344
6.3.1. Synthetic Methodology

Synthesis of 2-bromo-5-trimethylstannyl-3-hexylesterthiophene as a monomer for
Stille polycondensation is provided in Scheme 6.1 while intermediates 3-
hexylesterthiophene (1) and 2-bromo-3-hexylesterthiophene (2) were utilized for Oxi-
DArP and DArP respectively. The synthesis of P3HT via Stille polycondensation is well-
established
53
, and likewise, intermediates 3-hexylthiophene and 2-bromo-3-
hexylthiophene were used for Oxi-DArP and DArP respectively. The synthesis of 3 was
achieved through the Steglich esterification to generate 1, which was isolated and then
subsequently treated with LDA and carbon tetrabromide to acquire 2. To avoid inseparable
isomers via 5-lithiated intermediate, treatment of 2 with the Knochel-Hauser base
54,55
for a
5-magnesiated intermediate quenched by trimethyltin chloride afforded 3. Indeed, for 3-
hexylesterthiophene, both the bromination and metalation are non-trivial synthetic steps
requiring flammable reagents, cryogenic conditions, and air- and water-sensitive reagents
that are all attractively bypassed via Oxi-DArP.

345

Scheme 6.1. Synthesis of 2-bromo-5-trimethyltin-3-hexylesterthiophene and the
intermediates utilized for Oxi-DArP, DArP, and Stille polymerizations for generation of
poly(3-hexylesterthiophene).
It is worth noting that in pursuit of this comparative analysis, we report the first
synthesis of poly(3-hexylesterthiophene) via traditional DArP, further underscoring the
broad compatibility of DArP with electron-withdrawing side-groups.
56
This substrate is
compatible with our traditional Fagnou-derived DArP conditions, which utilize very low
palladium acetate Pd(OAc)2 loadings of 0.25 mol%, 1.5 equiv. of potassium carbonate
(K2CO3), and 30 mol% of neodecanoic acid (NDA). It is believed that NDA is deprotonated
346
in situ by K 2CO3 to serve as a bulky carboxylate ligand-base which limits the formation of
β-defects
21
and facilitates a faster
57
and more effective direct arylation.
18
As an alternative
to the commonly used pivalic acid (PivOH), our group introduced the inexpensive and
environmentally benign
58
NDA and has demonstrated increased polymer yields and
molecular weight in addition to decreased quantities of polymer defects.
59
Among all DArP
conditions, these specific parameters are very attractive due to their low-cost, bench
stability, and mild operating parameters, particularly reaction temperatures well below the
boiling point of the solvent.
It is in this spirit that we hope to develop Oxi-DArP as a mild but effective method
for the generation of polymers. Table 6.1 provides the conditions employed for various
Oxi-DArP runs and whether 3-hexylthiophene (3-HT) or 3-hexylesterthiophene (3-HET)
was employed. The catalyst employed was almost always Pd(OAc) 2 (though Pd2(dba)3 was
used for Entry 24 and 25, while Pd(PPh3)4 was used for Stille) but the catalyst loading was
varied. All Oxi-DArP runs were executed with a monomer concentration of 0.05M in N,N-
dimethylacetamide (DMA) at varying temperatures between 70
o
C and 130
o
C, all below the
boiling point of DMA. Early efforts supported the viability of Cu(OAc)2 as an oxidant but
Ag2CO3 was found to outperform Cu(OAc)2
44
and became the oxidant of choice for
optimization studies. Table 6.1 also provides the regioregularity of the polymers acquired
as determined by
1
H-NMR peaks ratios (Figure A5.4-5.5, A5.8-A5.21), the molecular
weights as determined by SEC, and the yields after Soxhlet extraction with methanol,
hexanes, and chloroform followed by reprecipitation. Additionally, data for P3HT and
P3HET synthesized via traditional DArP and Stille are also provided as the last four entries
347
in Table 6.1 as a point of reference for gauging the quality of the acquired polymers via
Oxi-DArP.

Table 6.1. Conditions, Regioregularity, Molecular Weight, Dispersity, and Yield for
Oxidative Direct Arylation Polymerization on 3-hexylthiophene and 3-
hexylesterthiophene
Entry Substrate Catalyst
a

Loading
(mol %)
Oxidant &
Loading (mol%)
Additive (equiv) or
Ligand (mol%)
Temp
b

(
o
C)
RR
c

(%)
Mn
d

(kDa)
Đ
e
Yield
f

(%)
1 3-HT 10 Cu(OAc)2 (10%) K2CO3 (2.2 equiv) 110 -- -- -- --
2 3-HET 10 Cu(OAc)2 (10%) K2CO3 (2.2 equiv) 110 -- -- -- --
3 3-HT 10 Cu(OAc)2 (210%) K2CO3 (2.2 equiv) 110 45 0.9 1.9 9
4 3-HET 10 Cu(OAc)2 (210%) K2CO3 (2.2 equiv) 110 75 6.5 2.6 33
5 3-HT 0 Cu(OAc)2 (210%) K2CO3 (2.2 equiv) 110 -- -- -- --
6 3-HET 0 Cu(OAc)2 (210%) K2CO3 (2.2 equiv) 110 -- -- -- --
7 3-HT 10 Ag2CO3 (210%) K2CO3 (2.2 equiv) 110 45 1.5 1.6 16
8 3-HET 10 Ag2CO3 (210%) K2CO3 (2.2 equiv) 110 75 10.4 2.0 68
9 3-HT 0 Ag2CO3 (210%) K2CO3 (2.2 equiv) 110 -- -- -- --
10 3-HET 0 Ag2CO3 (210%) K2CO3 (2.2 equiv) 110 -- -- -- --
11 3-HT 10 Ag2CO3 (210%) K2CO3 (2.2 eq.);
NDA (0.3 eq.)
110 45 1.1 1.2 14
12 3-HET 10 Ag2CO3 (210%) K2CO3 (2.2 eq.);
NDA (0.3 eq.)
110 79 11.1 2.4 62
13 3-HET 10 Ag2CO3 (210%) None 110 78 4.9 1.8 24
14 3-HT 0 FeCl3 None 45
g
55 12.0 3.1 40
15 3-HET 0 FeCl3 None 45
g
-- -- -- --
16 3-HET 10 Ag2CO3 (210%) PCy3-HBF4 (20%) 110 84 15.1 2.5 77
17 3-HET 8 Ag2CO3 (210%) PCy3-HBF4 (20%) 110 85 14.6 2.3 68
348
18 3-HET 6 Ag2CO3 (210%) PCy3-HBF4 (20%) 110 86 14.9 2.4 44
19 3-HET 4 Ag2CO3 (210%) PCy3-HBF4 (20%) 110 -- -- -- Trace
20 3-HET 2 Ag2CO3 (210%) PCy3-HBF4 (20%) 110 -- -- -- Trace
21 3-HET 2 Ag2CO3 (210%) PCy3-HBF4 (20%) 130 -- -- -- Trace
22 3-HET 10 Ag2CO3 (210%) PCy3-HBF4 (20%) 70 -- -- -- --
23 3-HET 10 Ag2CO3 (210%) PCy3-HBF4 (20%) 90 88 5.1 1.9 34
24 3-HET 8
h
Ag2CO3 (210%) K2CO3 (2.2 eq.);
NDA (0.3 eq.)
110 68 12.2 2.7 82
25 3-HET 8
h
Ag2CO3 (210%) PCy3-HBF4 (20%) 110 -- -- -- --
DArP 3-HT 0.25 N/A K2CO3 (1.5 eq.);
NDA (0.3 eq.)
70 93 19.2 2.8 60
DArP 3-HET 0.25 N/A K2CO3 (1.5 eq.);
NDA (0.3 eq.)
70 96 11.7 2.9 55
Stille 3-HT 4
i
N/A N/A 95
j
94 22.3 2.2 78
Stille 3-HET 4
i
N/A N/A 95
j
98 11.3 2.7 69
a
Pd(OAc)2 was the catalyst utilized in all runs unless otherwise noted.
b
DMA was used in
all runs except for Stille polymerization as noted. Temperature applied to the reaction
mixture by oil bath under vigorous stirring.
c
As determined by
1
H-NMR as a percentage of
head-to-tail (HT) couplings (δ=4.30ppm for P3HET and δ=2.80ppm for P3HT) as
calculated from peak integrations of observable couplings (HT and HH).
d
As determined
by SEC.
e
(Mw/Mn).
f
After Soxhlet extraction with methanol, hexanes, and chloroform, and
subsequent reprecipitation and filtration.
g
Solvent was CHCl3.
h
Catalyst was Pd2(dba)3.
i
Catalyst was Pd(PPh3)4.
j
Solvent was DMF.

6.3.2. Structural Analysis of P3HET

349
For unsymmetric side-chain containing monomers, regioregularity is a critical
property of the resulting polymers, influencing a number of electronic properties, such as
electrical conductivity, electroluminescence, and absorption but also physical properties
such as semicrystallinity and thermal stability.
8,60–62
For 3-alkylthiophenes, it is well-
established that the head-to-tail (HT), head-to-head (HH), and tail-to-tail (TT) content of
linkages can be readily determined by
1
H NMR.
14,63,64
Similarly, the linkage content for
ester-functionalized thiophenes can also be determined conveniently through NMR via the
–O-CH2– groups in the side-chain, as reported by Pomerantz.
65,66

The regioregularity provided in Table 6.1 is determined from the percentage of
head-to-tail couplings as calculated from peak integrations of all observable couplings (HT
and HH). For P3HT, the HT shift is located at δ=2.80 ppm while it is δ=4.30 ppm in P3HET
(See Figure 6.2). As attributed to Pomerantz, et al,
65
the HH coupling in P3HET can be
identified from the O-CH2 group, as the steric repulsion between side chains causes a
polymer chain twist, leading to a peak at higher field, δ=4.13 ppm. Stille and DArP P3HET,
which exhibit primarily HT couplings, show a small triplet here, signaling homocoupling
defects. We observe, as did Pomerantz, et al.,
65
that with increased homocoupling defects,
as observed in Oxi-DArP, these peaks broaden. While regioregularity is important, it is
often overvalued, as demonstrated by Fréchet, et al.,
62
who concluded that P3HT
regioregularities of 86, 90, and 96 all perform similarly in OPVs but lower regioregularities
exhibit higher thermal stability in bulk heterojunction devices.
It can be determined based on the aromatic region of proton NMRs (Figure A5.4-
5.5, A5.8-A5.21) that Stille P3HET polymers exhibit the fewest defects, followed by
DArP, which exhibits slightly more defects. As determined by Pomerantz, et al.,
67
the
350
aromatic region for ester side-chain thiophene polymers can have four significant peaks,
which correspond to triads of linkages (HT-HT, HT-HH, HT-TT, HH-TT). We observe
HT-HT triads at δ=7.86 ppm, which is the dominant aromatic peak in Stille and DArP
P3HET. Despite the high regioregularity of Stille and DArP polymers, there are two other
aromatic peaks that can be attributed to HH-TT triads and HT -HH triads.
65,67,68
These peaks
are naturally more obvious in Oxi-DArP P3HET, which have more head-to-head coupling
defects than either Stille or DArP, and so exhibits higher quantities of HT-HH triads, which
occur around δ=7.60 ppm, as well as HT-TT triads, which occur around δ=7.92 ppm.
65,68

351
Figure 6.2.
1
H NMR spectra of the region used to determine regioregularity in Poly(3-
esterhexylthiophene) as synthesized by different methods. References to Entry are for
polymers made via conditions outlined in Table 6.1.
As presented in the following section, the tuning of conditions plays an important
role in increasing the regioregularity of P3HET via Oxi-DArP, and we show that with
incorporation of a phosphine ligand, we can achieve regioregularities around 85% with
good yields and molecular weights.

6.3.3. Role of Reaction Parameters

From the results in Table 6.1, it becomes evident that the ester functionality plays
a critical role in the oxidative direct arylation mechanism as a directing group that
coordinates with the palladium center (although it is possible that the electron-withdrawing
effect of the ester group could better facilitate C-H activation of the 2-position). Across all
conditions, only oligomers are ever acquired with 3-hexylthiophene, while molecular
weights even higher than DArP or Stille are acquired in some instances for 3-
hexylesterthiophene. Importantly, no polymers were ever acquired without a palladium
catalyst. This is evidence that the substrate itself is not oxidized to polymerize through a
cationic or radical pathway, as would occur in a chemical oxidative polymerization but
rather a palladium-catalyzed polymerization occurs. From proposed mechanistic
evaluations,
35,43
it is posited that a base is necessary for the catalytic cycle. Our early efforts
focused on potassium carbonate as utilized by Li and Lu, et al.
43,44
but we observe that
replacement of base with a phosphine ligand, tricyclohexylphosphine tetrafluoroborate
352
(PCy 3-HBF4), resulted in a significant increase in regioregularity even at loadings of only
20 mol %. The reason for this is not fully understood but the availability of silver carbonate
as a base may render potassium carbonate as an unnecessary extra base additive. This is
supported by Entry 13 and the observation by Li and Lu, et al.
43,44
that the polymerization
does proceed even without potassium carbonate, though we observe lower yields and
molecular weight. Our best yields and regioregularity occur when potassium carbonate is
replaced by PCy 3-HBF4 (Entry 16) which we can conclude better promotes C-H/C-H cross-
coupling of the substrate, and limits homocoupling. We observe minor improvements in
regioregularity with decreased catalyst loading (Entry 16-18) but no reproducible
polymerization after reaching 4% catalyst loading (Entry 19-20). This may be because
there is competition between the precipitation of palladium black from the reaction mixture
and the re-oxidation of Pd
0
to Pd
II
. Although reaction temperatures of 110
o
C generate
higher molecular weight polymers, we observe the best regioregularity at 90
o
C (Entry 23)
but at the cost of reduced molecular weight and yield. At 70
o
C, we acquire no polymer
(Entry 22). Conversely, the reaction also fails when elevated to 130
o
C (Entry 21). This
could be attributed to decomposition of the palladium catalyst
69
or silver carbonate
70
. We
attempted to replicate Oxi-DArP with a Pd
0
species, Pd2(dba)3, to see if regioregularity
could be improved but we observed no polymer formation with PCy 3-HBF4 (Entry 25) and
although good yields and molecular weight were achieved with K2CO3 and NDA,
regioregularity diminished significantly (Entry 24). Interestingly, as observed in previous
reports,
43,44
the carbonyl-containing heterocycle is incompatible with chemical oxidative
polymerization with ferric chloride (Entry 15). These reports observed that electron-
withdrawing groups or electron-poor rings are unable to be oxidatively polymerized with
353
ferric chloride, and potentially gives promise for Oxi-DArP to be compatible with
substrates incompatible with ferric chloride, while being generally superior to chemical
oxidative polymerization. Overall, we observed the best results in Entry 16-18, with good
regioregularity, molecular weights, and yields. Generally, Oxi-DArP P3HET polymers
exhibited lower regioregularity compared to Stille and DArP versions but both electronic
and physical characteristics were comparable. Yields after Soxhlet extraction and
molecular weights are similar (e.g. Entry 8, 17, 24), or even better than DArP or Stille in
some instances (Entry 16-18). Broad peaks upfield of the diagnostic head-to-head coupling
(δ4.12) in P3HET (e.g. Figure A5.17), which could be indicative of β-defects or branching
points,
21,71,72
are not observed in the
1
H NMR spectra of Oxi -DArP P3HET made with
NDA or ligands but may be present in Entry 13 (Figure A5.16) which featured no
additives.

6.3.4. Electronic Properties of Oxi-DArP Polymers

Electronic properties, including electrochemical HOMO levels, absorption band
edges, optical band gaps, and space-charge limited current (SCLC) mobilities are provided
in Table 6.2 for a selection of Oxi -DArP polymers. HOMO levels are similar for all P3HET
regardless of the method from which it was generated, which provides a much deeper
HOMO compared to P3HT. Due to low molecular weight, low regioregularity, and
potential defects, Oxi-DArP P3HT exhibits outlying properties compared to DArP and
Stille P3HT. UV-vis spectra (Figure A5.28-31), GIXRD patterns (Figure A5.32-34), and
associated content (peak absorption coefficients, peak absorption wavelengths,
interlamellar d100 distances) for the polymers provided in Table 6.2 can be found in the
354
Appendix (Table A5.1). Peak absorption coefficients greater than 1 x 10
5
cm
-1
are acquired
for DArP and Stille polymers. Oxi-DArP polymers vary but for the highest quality P3HET
made via Oxi-DArP (Entry 16 & 18), peak absorption coefficients are only about 10% less
than their DArP and Stille counterparks (~9 x 10
4
cm
-1
) as shown in Figure 3, with
corresponding loss of vibronic shoulders, which may be indicative of reduced crystallinity
as a result of reduced regioregularity. Along these lines, GIXRD patterns (Figure A5.32-
34) show that Oxi-DArP P3HET polymers with regioregularity less than 80% exhibit
decreased or absent intensities of the (100) diffraction peak; however, regioregularities of
85% or more do exhibit diffraction peak intensities comparable to DArP and Stille P3HET
(Figure 6.3). We observe crystallite sizes for Stille and DArP P3HET to be slightly larger
than corresponding P3HT polymers (Table A5.1), while Oxi-DArP polymers exhibit an
increase in crystallite size (from 14.8 nm in Stille to 19.4 nm for Entry 18). Compared to
P3HT, the interchain distances (Table A5.1) for P3HET polymers is larger, indicating they
do not pack as tightly as P3HT. This observed difference in semicrystallinity and packing
consequently translates into SCLC hole mobilities, with Stille and DArP P3HT exhibiting
the highest hole mobilities (Table 6.2). Among the P3HET polymers, Stille and DArP
demonstrate higher hole mobilities than Oxi-DArP but values generally vary closely with
regioregularity, namely, Entry 16 and 18 which have higher regioregularity also have
higher hole mobilities more closely comparable to Stille and DArP P3HET. It can be
generally summated that Oxi-DArP P3HET makes polymers with comparable electronic
properties as limited by its resulting diminished regioregularity.

355
Table 6.2. Electrochemical HOMO values, Optical Bandgaps, Space-Charge Limited
Current (SCLC) Mobilities of Oxi-DArP, DArP, and Stille polymers.
Entry
a
HOMO
b
, eV Eg
c
, nm/eV µ
d
, cm
2
V
-1
s
-1

Stille-P3HET 5.98 570 / 2.17 2.09 x 10
-5

DArP-P3HET 6.00 568 / 2.18 1.17 x 10
-5

Stille-P3HT 5.28 648 / 1.91 2.44 x 10
-4

DArP-P3HT 5.27 651 / 1.90 2.13 x 10
-4

7 (P3HT) 5.61 558 / 2.22 2.59 x 10
-7

4 (P3HET) 5.96 521 / 2.38 1.16 x 10
-6

8 (P3HET) 5.97 605 / 2.05 9.87 x 10
-5

12 (P3HET) 5.97 590 / 2.10 9.63 x 10
-5

16 (P3HET) 5.97 596 / 2.08 5.71 x 10
-5

18 (P3HET) 5.96 603 / 2.05 5.26 x 10
-5

24 (P3HET) 5.97 575 / 2.15 1.98 x 10
-6

a
Entry designation as referenced in Table 6.1 of the main text.
b
Determined by cyclic
voltammetry (vs. Fc/Fc
+
) in 0.1M TBAPF6 in acetonitrile solution.
c
Calculated from the
absorption band edge in thin films, Eg = 1240/λedge.
d
Measured on neat polymer films.

356

Figure 6.3 Comparison of (a) GIXRD and (b) UV-Vis spectra of P3HET made via Stille
(black line), DArP (red line), and Oxi-DArP (blue line) (Entry 18 of Table 6.1).
Additional GIXRD and UV-Vis spectra for other select Oxi-DArP polymers, as well as
Stille, DArP, and Oxi-DArP P3HT can be found in the Appendix.

6.4. Conclusions

357
We have reported the first polymerization toward P3HET without preactivation of
the monomer, the first traditional DArP of the corresponding monomer, and the first
palladium-catalysed regioregular Oxi-DArP of an unsymmetrical monomer, which offers
insight into the role of C-H selectivity in this new synthetic method. We provide a strategic
and unique model substrate that is easily scalable and offers fundamental evaluation of this
method through convenient
1
H-NMR analysis. Through replacement of a base salt with a
bench-stable phosphine ligand, we observe critical improvements in the quality of the
acquired polymers, which exhibit regioregularity up to 86%, good yields, molecular
weight, and electronic characteristics along with limited defects and the distinct advantage
of bypassing both the halogenation and metalation of the monomers, which can be
challenging. We can posit that Oxi-DArP of P3HET generates polymers with comparable
electronic properties as limited by its resulting regioregularity. The results presented here
give promise to this new synthetic method as a new route toward conjugated polymers for
a variety of materials applications.

6.5. References

(1) Bundgaard, E.; Livi, F.; Hagemann, O.; Carlé, J. E.; Helgesen, M.; Heckler, I. M.;
Zawacka, N. K.; Angmo, D.; Larsen-Olsen, T. T.; dos Reis Benatto, G. A.; Roth, B.;
Madsen, M. V.; Andersson, M. R.; Jørgensen, M.; Søndergaard, R. R.; Krebs, F. C.
Adv. Energy Mater. 2015, 5 (10), DOI: 10.1002/aenm.201402186.
(2) Thompson, B. C.; Fréchet, J. M. J. Angew. Chem. Int. Ed. 2008, 47 (1), 58.
(3) Thompson, B. C.; Abboud, K. A.; Reynolds, J. R.; Nakatani, K.; Audebert, P. New
J. Chem. 2005, 29 (9), 1128.
358
(4) Kerszulis, J. A.; Amb, C. M.; Dyer, A. L.; Reynolds, J. R. Macromolecules 2014,
47 (16), 5462.
(5) Kola, S.; Kim, J. H.; Ireland, R.; Yeh, M.-L.; Smith, K.; Guo, W.; Katz, H. E. ACS
Macro Lett. 2013, 2 (8), 664.
(6) Zhu, C.; Liu, L.; Yang, Q.; Lv, F.; Wang, S. Chem. Rev. 2012, 112 (8), 4687.
(7) Yassin, A.; Mallet, R.; Leriche, P.; Roncali, J. Chem. Electro. Chem 2014, 1 (7),
1219.
(8) Roncali, J. Chem. Rev. 1992, 92 (4), 711.
(9) Mäker, D.; Maier, C.; Brödner, K.; Bunz, U. H. F. ACS Macro Lett. 2014, 3 (5), 415.
(10) Kim, J.-M.; Lee, J.-S.; Choi, H.; Sohn, D.; Ahn, D. J. Macromolecules 2005, 38 (22),
9366.
(11) Carsten, B.; He, F.; Son, H. J.; Xu, T.; Yu, L. Chem. Rev. 2011, 111 (3), 1493.
(12) Wu, W.-C.; Liu, C.-L.; Chen, W.-C. Polymer 2006, 47 (2), 527.
(13) Osaka, I.; McCullough, R. D. Acc. Chem. Res. 2008, 41 (9), 1202.
(14) Chen, T.-A.; Wu, X.; Rieke, R. D. J. Am. Chem. Soc. 1995, 117 (1), 233.
(15) Burke, D. J.; Lipomi, D. J. Energy Environ. Sci. 2013, 6 (7), 2053.
(16) Khlyabich, P. P.; Burkhart, B.; Rudenko, A. E.; Thompson, B. C. Polymer 2013, 54
(20), 5267.
(17) Rudenko, A. E.; Thompson, B. C. J. Polym. Sci. A Polym. Chem. 2015, 53 (2), 135.
(18) Rudenko, A. E.; Thompson, B. C. Macromolecules 2015, 48 (3), 569.
(19) Mercier, L. G.; Leclerc, M. Acc. Chem. Res. 2013, 46 (7), 1597.
(20) Rudenko, A. E.; Thompson, B. C. J. Polym. Sci. A Polym. Chem. 2015, 53 (21),
2494.
359
(21) Rudenko, A. E.; Latif, A. A.; Thompson, B. C. Nanotechnology 2014, 25 (1),
014005.
(22) Wakioka, M.; Nakamura, Y.; Hihara, Y.; Ozawa, F.; Sakaki, S. Organometallics
2013, 32 (15), 4423.
(23) Lombeck, F.; Komber, H.; Gorelsky, S. I.; Sommer, M. ACS Macro Lett. 2014, 3
(8), 819.
(24) Kuwabara, J.; Yasuda, T.; Choi, S. J.; Lu, W.; Yamazaki, K.; Kagaya, S.; Han, L.;
Kanbara, T. Adv. Funct. Mater. 2014, 24 (21), 3226.
(25) Livi, F.; Gobalasingham, N. S.; Bundgaard, E.; Thompson, B. C. J. Polym. Sci. A
Polym. Chem. 2015, 53 (22), 2598.
(26) Grenier, F.; Aïch, B. R.; Lai, Y.-Y.; Guérette, M.; Holmes, A. B.; Tao, Y.; Wong,
W. W. H.; Leclerc, M. Chem. Mater. 2015, 27 (6), 2137.
(27) Park, J. K.; Jo, J.; Seo, J. H.; Moon, J. S.; Park, Y. D.; Lee, K.; Heeger, A. J.; Bazan,
G. C. Adv. Mater. 2011, 23 (21), 2430.
(28) Kim, Y.; Cook, S.; Kirkpatrick, J.; Nelson, J.; Durrant, J. R.; Bradley, D. D. C.;
Giles, M.; Heeney, M.; Hamilton, R.; McCulloch, I. J. Phys. Chem. C 2007, 111
(23), 8137.
(29) Andersson, M. R.; Selse, D.; Berggren, M.; Jaervinen, H.; Hjertberg, T.; Inganaes,
O.; Wennerstroem, O.; Oesterholm, J.-E. Macromolecules 1994, 27 (22), 6503.
(30) Sugimoto, R.; Takeda, S.; Gu, H. B.; Yoshino, K. Chem. Exp. 1986, 1, 635.
(31) Haba, O.; Hayakawa, T.; Ueda, M.; Kawaguchi, H.; Kawazoe, T. React. Funct.
Polym. 1998, 37 (1–3), 163.
360
(32) Hayakawa, T.; Fukukawa, K.-I.; Morishima, M.; Takeuchi, K.; Asai, M.; Ando, S.;
Ueda, M. J. Polym. Sci. A Polym. Chem. 2001, 39 (13), 2287.
(33) McCarley, T. D.; Noble, C. O.; DuBois, C. J.; McCarley, R. L. Macromolecules
2001, 34 (23), 7999.
(34) Gohier, F.; Frère, P.; Roncali, J. J. Org. Chem. 2013, 78 (4), 1497.
(35) Stuart, D. R.; Fagnou, K. Science 2007, 316 (5828), 1172.
(36) Yeung, C. S.; Dong, V. M. Chem. Rev. 2011, 111 (3), 1215.
(37) Wencel-Delord, J.; Dröge, T.; Liu, F.; Glorius, F. Chem. Soc. Rev. 2011, 40 (9),
4740.
(38) Satoh, T.; Miura, M. Chem. Eur. J. 2010, 16 (37), 11212.
(39) Lyons, T. W.; Sanford, M. S. Chem. Rev. 2010, 110 (2), 1147.
(40) Colby, D. A.; Bergman, R. G.; Ellman, J. A. Chem. Rev. 2010, 110 (2), 624.
(41) Tsuchiya, K.; Ogino, K. Polym J 2013, 45 (3), 281.
(42) Huang, Q.; Qin, X.; Li, B.; Lan, J.; Guo, Q.; You, J. Chem. Commun. 2014, 50 (89),
13739.
(43) Zhang, Q.; Wan, X.; Lu, Y.; Li, Y.; Li, Y.; Li, C.; Wu, H.; Chen, Y. Chem. Commun.
2014, 50 (83), 12497.
(44) Zhang, Q.; Li, Y.; Lu, Y.; Zhang, H.; Li, M.; Yang, Y.; Wang, J.; Chen, Y.; Li, C.
Polymer 2015, 68, 227.
(45) Chen, H.-Y.; Hou, J.; Zhang, S.; Liang, Y.; Yang, G.; Yang, Y.; Yu, L.; Wu, Y.; Li,
G. Nat. Photon. 2009, 3 (11), 649.
(46) Mei, J.; Bao, Z. Chem. Mater. 2014, 26 (1), 604.
361
(47) Liu, J.; Kadnikova, E. N.; Liu, Y.; McGehee, M. D.; Fréchet, J. M. J. J. Am. Chem.
Soc. 2004, 126 (31), 9486.
(48) Manceau, M.; Bundgaard, E.; Carlé, J. E.; Hagemann, O.; Helgesen, M.;
Søndergaard, R.; Jørgensen, M.; Krebs, F. C. J. Mater. Chem. 2011, 21 (12), 4132.
(49) Reeves, B. D.; Unur, E.; Ananthakrishnan, N.; Reynolds, J. R. Macromolecules
2007, 40 (15), 5344.
(50) Howard, J. B.; Noh, S.; Beier, A. E.; Thompson, B. C. ACS Macro Lett. 2015, 4 (7),
725.
(51) Cardona, C. M.; Li, W.; Kaifer, A. E.; Stockdale, D.; Bazan, G. C. Adv. Mater. 2011,
23 (20), 2367.
(52) Thompson, B. C.; Kim, Y.-G.; McCarley, T. D.; Reynolds, J. R. J. Am. Chem. Soc.
2006, 128 (39), 12714.
(53) Burkhart, B.; Khlyabich, P. P.; Cakir Canak, T.; LaJoie, T. W.; Thompson, B. C.
Macromolecules 2011, 44 (6), 1242.
(54) Krasovskiy, A.; Krasovskaya, V.; Knochel, P. Angew. Chem., Int. Ed. 2006, 45 (18),
2958.
(55) Khlyabich, P. P.; Rudenko, A. E.; Thompson, B. C. J. Polym. Sci. A Polym. Chem.
2014, 52 (8), 1055.
(56) Rudenko, A. E.; Khlyabich, P. P.; Thompson, B. C. ACS Macro Lett. 2014, 3, 387.
(57) Lafrance, M.; Fagnou, K. J. Am. Chem. Soc. 2006, 128, 16496.
(58) Fefer, M.; Rutkowski, A. J. J. Am. Oil Chem. Soc. 1968, 45 (1), 5.
(59) Rudenko, A. E.; Wiley, C. A.; Tannaci, J. F.; Thompson, B. C. J. Polym. Sci. A
Polym. Chem. 2013, 51 (12), 2660.
362
(60) Kim, Y.; Cook, S.; Tuladhar, S. M.; Choulis, S. A.; Nelson, J.; Durrant, J. R.;
Bradley, D. D. C.; Giles, M.; McCulloch, I.; Ha, C.-S.; Ree, M. Nat. Mater. 2006, 5
(3), 197.
(61) Mauer, R.; Kastler, M.; Laquai, F. Adv. Funct. Mater. 2010, 20 (13), 2085.
(62) Woo, C. H.; Thompson, B. C.; Kim, B. J.; Toney, M. F.; Fréchet, J. M. J. J. Am.
Chem. Soc. 2008, 130 (48), 16324.
(63) Amou, S.; Haba, O.; Shirato, K.; Hayakawa, T.; Ueda, M.; Takeuchi, K.; Asai, M.
J. Polym. Sci. A Polym. Chem. 1999, 37 (13), 1943.
(64) McCullough, R. D.; Lowe, R. D.; Jayaraman, M.; Anderson, D. L. J. Org. Chem.
1993, 58, 904.
(65) Pomerantz, M.; Cheng, Y.; Kasim, R. K.; Elsenbaumer, R. L. Synth. Met. 1999, 101
(1–3), 162.
(66) Pomerantz, M.; Cheng, Y.; Kasim, R. K.; Elsenbaumer, R. L. J. Mater. Chem. 1999,
9 (9), 2155.
(67) Pomerantz, M.; Yang, H.; Cheng, Y. Macromolecules 1995, 28 (17), 5706.
(68) Pomerantz, M.; Cheng, Y.; Kasim, R. K.; Elsenbaumer, R. L. Synth. Met. 1997, 85
(1–3), 1235.
(69) Wang, Q.; Takita, R.; Kikuzaki, Y.; Ozawa, F. J. Am. Chem. Soc. 2010, 132 (33),
11420.
(70) Norby, P.; Dinnebier, R.; Fitch, A. N. Inorg. Chem. 2002, 41 (14), 3628.
(71) Rudenko, A. E.; Wiley, C. A.; Stone, S. M.; Tannaci, J. F.; Thompson, B. C. J.
Polym. Sci. A Polym. Chem. 2012, 50 (18), 3691.
363
(72) Okamoto, K.; Housekeeper, J. B.; Michael, F. E.; Luscombe, C. K. Polym. Chem.
2013, 4 (12), 3499.

364
CHAPTER 7: SYNTHESIS OF RANDOM POLY(HEXYL THIOPHENE-3-
CARBOXYLATE) COPOLYMERS VIA OXIDATIVE DIRECT ARYLATION
POLYMERIZATION (OXI-DARP)

7.1. Introduction

Conjugated polymers have been explored for a variety of materials applications,
including organic photovoltaics,
1,2
electrochromic devices,
3,4
field-effect transistors,
5
light-
emitting diodes,
6
and more recently for biomedical imaging, therapy, and drug delivery.
7

Consequently, there is growing demand for straightforward and diverse strategies for
achieving these materials. Popular strategies have generally utilized transition metal-
catalyzed polycondensations, such as Stille,
8
Kumada,
9
Negishi,
10
and Suzuki
11

polymerizations. These typically require both halogenated and metallic functional groups;
however, metalated monomers can be challenging to purify, potentially unstable, and
toxic.
12
Direct arylation polymerization (DArP)
13–20
has emerged recently as an alternative,
while being considered a greener and more sustainable substitute, as it eliminates the need
for metalation and the associated synthetic step (i.e. lithiation-metalation).
Ultimately, the most atom economical route toward conjugated polymers is direct
C-H/C-H coupling, which would eliminate two steps en route to conjugated polymers.
Such routes are exemplified by historically prevalent methods such as electrochemical and
chemical oxidative polymerizations with ferric chloride
21,22
or oxovanadium;
23
however,
not all substrates are compatible
24
with these methods because they operate by oxidizing
the monomer itself, which introduces other variables such as cation and radical stability
365
and inevitably lead to poor structural control and—in the case of ferric chloride oxidation—
both iron and chlorine backbone impurities.
25

Figure 7.1. Illustration of the need for bromination and metalation steps in order to make
a monomer suitable for traditional cross-coupling methods. Oxi-DArP enables both steps
to be bypassed en route to conjugated polymers while also providing benign end groups.

Catalysed oxidative direct arylation has emerged as a route toward overcoming
these limitations by oxidizing a catalyst as opposed to the substrate.
26–30
This strategy has
been widely utilized in small molecule couplings; however, the application to polymers is
relatively limited. Pioneering studies from a handful of research groups have established a
range of effective conditions and catalysts for generating polymers.
31–37
In general, this
method requires a catalyst (typically palladium), a coordinating solvent such as N,N-
dimethylacetamide (DMA), and an oxidant (such as copper acetate, silver carbonate, or in
specific instances, oxygen). For the most part, this method has only been investigated for
the generation of homopolymers, often with monomers that contain only one type of C-H
bond.

366

Scheme 7.1. Overview of the synthesis of (a) P3HET, (b) random copolymer family
P3HET-BTz, and (c) random copolymer family P3HET-TPD via palladium-catalyzed
oxidative direct arylation polymerization (oxi-DArP), which do not require preactivation
of the monomers.
Recently, we demonstrated the first palladium-catalysed oxidative direct arylation
polymerization (oxi-DArP) of an unsymmetrical thiophene with an ester containing
directing group (Figure 7.1).
35
This substrate, hexyl thiophene-3-carboxylate, herein
referred to as 3-hexylesterthiophene (3HET) for simplicity and consistency with
abbreviations of 3-substituted thiophenes, such as 3-hexylthiophene (3HT), is an
increasingly popular motif
38–42
that offers the advantages of three distinct C-H bonds for
evaluating selectivity in the polymerization method. Subsequently, the resulting cross-
coupling, homocoupling, or β-coupling defects can be conveniently explored through
1
H-
NMR analysis. 3HET is incompatible with both chemical oxidative polymerization and
electropolymerization, while its synthesis via Stille requires two steps with flammable
reagents, cryogenic conditions, and air- and water-sensitive reagents.
35,43
Oxi-DArP
367
attractively overcomes or bypasses these limitations. A goal of the present work is to
further improve the regioregularity that can be achieved with this substrate through
refinement of the reaction conditions and minimization of auxiliary reagents.
Subsequently, these optimized conditions are utilized for the synthesis of two families of
random copolymers featuring thieno[3,4-c]pyrrole-4,6-dione (TPD) or 4,4’-dimethyl-2,2’-
bithiazole (BTz), designated P3HET-TPD-X% and P3HET-BTz-X% respectively, where
X% is the secondary monomer content, which was 5, 10, or 15% in this work (Scheme
7.1). Through minimization of the catalyst loading enabled by incorporation of acid
additives, we achieve polymers with fewer homocoupling defects, good molecular weights,
and acquire random copolymers where the feed ratio is closely correlated to polymer
composition. The influence of secondary acceptor content on an already deep HOMO
P3HET is investigated and the capacity for oxi-DArP to be utilized in systems more
complex than simple homopolymers is established.

7.2. Experimental

7.2.1. Materials & Methods

Unless otherwise noted, all reagents were purchased and used as received from
commercial sources. N,N-dimethylacetamide (anhydrous DMA, 99.9%) and neodecanoic
acid (NDA) were purchased from Alfa Aesar. Palladium acetate (98%) was purchased from
TCI (USA). PCy 3-HBF4 and silver carbonate (Ag2CO3) were purchased from Strem
Chemicals. The synthesis of small molecule monomers 3-hexylesterthiophene,
35

thieno[3,4-c]pyrrole-4,6-dione (TPD),
44
and 4,4’-dimethyl-2,2’-bithiazole (BTz)
45
were
368
executed without modification as reported in the literature.
1
H NMR spectra of the
monomers are provided in the Appendix.
NMR spectra were recorded at 25°C using CDCl3 on a 400 MHz NMR
Spectrometer (small molecules) or Varian 600 MHz NMR Spectrometer (polymers).
Chemical shifts are given in parts per million (ppm) and are referenced to residual solvent
signals in commercial deuterated chloroform (δ = 7.26 ppm).
For polymer molecular weight determination, polymer samples were dissolved in
HPLC grade o-dichlorobenzene at a concentration of 0.5 mg/ml, briefly heated and then
allowed to turn to room temperature prior to filtering through a 0.2 μm PTFE filter. SEC
was performed using HPLC grade o-dichlorobenzene at a flow rate of 0.6 ml/min on one
300 × 8.0 mm LT6000L Mixed High Org column (Viscotek) at 60°C using a Viscotek GPC
Max VE 2001 separation module and a Viscotek TDA 305 RI detector. The instrument was
calibrated versus polystyrene standards (1,050 – 3,800,000 g/mol) and data was analysed
using OmniSec 4.6.0 software.
For thin film measurements, solutions were spin-coated onto pre-cleaned
glass slides (sonicated for 10 minutes in water, acetone, and isopropyl alcohol then
dried under high N2 flow) from o-dichlorobenzene solutions at 7mg/mL. UV-vis
absorption spectra were obtained on a Perkin-Elmer Lambda 950
spectrophotometer. The thickness of thin films and GIXRD measurements were
obtained using Rigaku Diffractometer Ultima IV using Cu Kα radiation source (λ =
1.54 Å) in the reflectivity and grazing-incidence X-ray diffraction mode,
respectively. Mobility measurements were measured using hole-only device
369
configuration of ITO/PEDOT:PSS/Polymer/Al in the space charge limited current
regime, which is expounded in the Appendix.
Cyclic voltammetry was executed on a Princeton Applied Research VersaStat3
potentiostat under the control of VersaStudio Software. A standard three electrode cell
based on a Pt wire working electrode, a Pt wire counter electrode, and a silver wire pseudo
reference electrode (calibrated vs. Fc/Fc
+
which is taken as 5.1 eV vs. vacuum)
46,47
was
purged with nitrogen and maintained under nitrogen atmosphere during all measurements.
For cyclic voltammetry, acetonitrile was distilled over CaH2 prior to use and tetrabutyl
ammonium hexafluorophosphate (0.1 M) was used as the supporting electrolyte. Polymer
films were made by applying a 10mg/mL o-DCB solution via drop-casting directly onto
the working electrode under a nitrogen umbrella and thoroughly dried prior to
measurement.

7.2.2. General Procedure for Synthesis of Polymers via Oxi-DArP

The general procedure for oxi-DArP is as follows: Respective monomers (1 mmol
total) were dissolved in anhydrous DMA to yield a specific concentration (See Table 7.1).
To the reaction mixture, the appropriate equivalents of oxidant (2.1 equivalents of Ag2CO3
in all cases), additive, and/or ligand (See Table 7.1) was added and the reaction mixture
was degassed for 10 minutes with nitrogen flow. Then the catalyst (Pd(OAc)2 or
PdCl2(PPh3)2) (loading detailed in Table 7.1) was added to the reaction mixture, which
was further degassed for 10 minutes before the reaction vessel was immersed into a pre-
heated oil bath at 110°C and stirred under nitrogen atmosphere for 72 hours. Then the
reaction mixture was cooled, a small amount of chlorobenzene was added, and the mixture
370
was precipitated into methanol, filtered, and purified via Soxhlet extraction with methanol,
hexanes, and lastly chloroform; this final fraction was filtered through Celite, then
concentrated in vacuo and precipitated into methanol. Upon filtering, the polymers were
dried under high vacuum overnight. P3HET
1
H NMR (600 MHz, CDCl3, δ ppm): δ7.86
(m, 1H), 4.30 (t, 2H), 1.75 (m, 2H), 1.44 (br, 6H), 0.89 (t, 3H).

7.3. Results and Discussion

7.3.1. Synthetic Methodology

The synthesis of P3HET homopolymers, P3HET-BTz copolymers, and P3HET-
TPD copolymers are illustrated in Scheme 7.1. In this study, the synthesis of P3HET via
oxi-DArP was optimized via screening of several conditions to improve regioregularity
compared to our previously reported conditions; however, maintaining comparable
molecular weights and yields was also emphasized.
35
The best conditions for the synthesis
of P3HET were then subsequently applied to generate two families of random P3HET
copolymers. As previously identified by Fagnou, there exist significant challenges for
cross-coupling that does not feature preactivation of the monomer, specifically issues with
reactivity, regioselectivity, and unwanted homocoupling defects that consume reagents.
48

Indeed, the effect of a secondary monomer on the oxi-DArP synthetic method is to the best
of our knowledge unexplored. Random copolymers are viewed as a valuable strategy
toward unique material properties but it is important that the synthetic method utilized
enables targeted incorporation of secondary components.
43,49–54
Whereas methods such as
Stille and DArP typically have excellent correlation between the feed ratio of monomers
371
and the polymer composition,
43,49,50,55
other methods such as GRIM often exhibit poor
correlation.
54,56
Evaluating the nature of oxi-DArP with regards to this characteristic is
important for both the development of this emerging method and for understanding its
limitations.

Table 7.1. Screening of reaction parameters for the synthesis of P3HET via oxidative direct
arylation polymerization.
#
Catalyst
(Loading)
Ligand
(Loading)
Additives
(Loading)
M
a

( mol/L)
M n
b

(kDa)
Ð
c

Yield
d

(%)
RR
e

(%)
P1
Pd(OAc) 2
(1%)
PCy 3HBF 4
(8%)
AcOH
(1.0 equiv.)
0.05 4.71 1.33 28 93.3
P2
Pd(OAc) 2
(2%)
PCy 3HBF 4
(8%)
AcOH
(0.2 equiv.)
0.10 5.66 1.58 33 92.1
P3
Pd(OAc) 2
(2%)
PCy 3HBF 4
(8%)
NDA
(0.2 equiv.)
0.10 6.64 1.93 45 90.6
P4
Pd(OAc) 2
(2%)
PCy 3HBF 4
(8%)
NDA
(0.2 equiv.)
0.15 5.09 1.79 37 89.9
P5
Pd(OAc) 2
(2%)
PCy 3HBF 4
(8%)
NDA
(0.2 equiv.),
I 2 (5%)
0.10 8.11 1.99 41 90.8
P6
Pd(OAc) 2
(3%)
PCy 3HBF 4
(16%)
NDA
(0.2 equiv.),
I 2 (5%)
0.10 10.74 2.06 49 88.5
372
P7
PdCl 2(PPh 3) 2
(3%)
PCy 3HBF 4
(16%)
NDA
(0.2 equiv.),
I 2 (5%)
0.10 11.67 2.07 68 88.9
a
Concentration of the monomer in the solvent (DMA).
b,c
As determined by SEC calibrated
to polystyrene standards.
d
Yield after precipitation, Soxhlet extraction, filtration through
Celite, and re-precipitation followed by drying overnight under high vacuum (100 mtorr).
e
Regioregularity was calculated as the NMR peak integration ratio of the head-to-tail
coupling (δ4.30) vs. the head-to-head and tail-to-tail couplings (δ4.13 and—if applicable—
δ4.11, respectively).

Previously, we reported regioregularities as high as 86% with good molecular
weights under optimized conditions.
35
Attempts to maintain good molecular weights and
improve the regioregularity further were ineffective; however, it was observed that with
decreased catalyst loading, the regioregularity improved gradually. Similarly,
regioregularity improved with lower operating temperatures. Unfortunately, both strategies
led to lower molecular weights or no polymer formation. Because of a competing tendency
for palladium black to precipitate out prior to being re-oxidized, oxi-DArP typically
requires large catalyst loadings for achieving suitable molecular weights;
33,35,36
however,
the inverse relationship between catalyst loading and regioregularity demands an
alternative solution. Efforts in DArP have demonstrated that the optimization of the
catalytic system and minimization of auxiliary reagent loadings could improve molecular
weights and regioregularity.
57

Inspired by this, Table 7.1 outlines the strategy for achieving this outcome. Work
in oxidative palladium catalysis has suggested that acid additives can help keep the
373
palladium in solution.
58
Entry P1 features—for the oxi-DArP synthesis of P3HET—the
lowest catalyst loading that achieves chloroform-soluble polymer (Soxhlet), 1% Pd(OAc)2.
When reacted with a monomer concentration of 0.05M in DMA with the phosphine ligand
salt, PCy 3HBF4, the addition of one equivalent of acetic acid enables the synthesis of
P3HET. Although the molecular weight was relatively low, the polymer exhibited a very
high regioregularity (93.3%). Unfortunately, in addition to the traditional head-to-tail
coupling NMR peak at δ4.30 and the head-to-head coupling at δ4.13, there was an
additional peak at δ3.90 (Figure A6.4). Its position (given its similar upper field shift
observed in P3HT
59
)suggests that this peak corresponds to coupling of the β-position,
indicating the presence of branching defects in P1. From NMR integrations (Figure A6.4),
this branching defect concentration (BDC) was 3.2%. Doubling the monomer
concentration, increasing the catalyst loading, and reducing the acetic acid loading to 0.2
equivalents increased the molecular weight and maintained a high regioregularity (P2 in
Table 7.1). Although minimizing the acetic acid loading reduces the branching defects
(0.9% BDC), it does not eliminate them (Figure A6.5).
Branching defects were shown to have a negative influence on DArP polymers but
our group has had success utilizing bulky neodecanoic acid (NDA) to prevent C-H
activation of the β-position in DArP.
20,59
When incorporated instead of AcOH in oxi-DArP
(P3), the molecular weights improve and the NMR peak associated with branching
disappears (Figure A6.6). This is demonstrated in Figure 7.2, which shows superimposed
NMR spectra of the lower field aliphatic region of P2 and P3, where different couplings
can be identified. Here, P2 has a distinct peak near δ3.90 that is not present in P3,
potentially indicative of a lack of β-couplings. It is also worth noting that utilization of
374
NDA seems to reduce the quantity of tail-to-tail couplings (δ4.09) as well. Although
regioregularity decreases slightly (90.6%) with NDA, the overall quality of the polymer
structure improves in addition to yields and molecular weights (Table 7.1).

Figure 7.2. Superimposed traces of the lower field aliphatic portion of the
1
H NMR spectra
(x-axis in ppm referenced to residual chloroform signal) of P2 (red trace) and P3 (blue
trace) showing (a) the majority head-to-tail coupling (δ4.30), (b) the corresponding
penultimate proton (δ4.25), (c) the head-to-head coupling (δ4.13), (d) the tail-to-tail
coupling (δ4.09), and (e) the β -coupling (δ3.90). Utilization of neodecanoic acid as an
additive suppresses this peak. Full NMR spectra are provided in the Appendix.

375
Attempting to increase the monomer concentration further (P4) did not improve the
molecular weight, most likely a result of reduced solubilizing medium. Although not
detailed in Table 7.1, several reaction temperatures were also explored with the conditions
listed for P3. Molecular weights were generally lower with reduced temperatures and the
reaction did not proceed above 120°C in our hands, possibly due to catalyst or silver
carbonate degradation. Thus, the reaction temperature for most conditions was 110°C. It
was also observed that lowering the catalyst loading below 2% generally improved the
regioregularity slightly but at the cost of reduced reaction yields and decreased molecular
weight. Alternative phosphine ligand salts, di-tert-butyl(methyl)phosphonium
tetrafluoroborate and tri-tert-butylphosphonium tetrafluoroborate, were investigated but
did not improve the regioregularity. Lastly, molecular oxygen (via balloon) was substituted
for Ag2CO3 as an oxidant (with and without Cs2CO3 base added as an alternative base) but
no polymer was observed with these lower catalyst loadings. During screening of
conditions, it was observed that a catalytic amount of iodine (5%) added to the reaction
improved molecular weights and yields. The reason for this is not fully realized but may
be related to potential iodination of the 3HET substrate or participation in the oxidative
catalytic cycle.
Ultimately, molecular weights greater than 10 kDa were achieved by increasing the
catalyst loading (though at the cost of some regioregularity), maintaining 0.1M monomer
concentration, and utilizing a catalytic amount of iodine in addition to maintaining the other
reaction parameters. As shown in Table 7.1, P6 has better molecular weights but slightly
lower regioregularity compared to P1-P5. These conditions offered the best compromise
in molecular weight and regioregularity. During the optimization of these conditions,
376
several catalysts were also evaluated (Bis(tri-tert-butylphosphine)palladium(0),
Bis(dibenzylideneacetone)palladium(0)) but ultimately, PdCl2(PPh3)2 performed the best,
improving the molecular weight slightly but significantly improving the polymer yield after
purification. This result is summarized as P7, and provided the best combination of
molecular weight, yield, and regioregularity.

Table 7.2. Molecular weights, dispersity, yields, electrochemical HOMO energy levels,
d100 spacings as determined by GIXRD, crystallite size, λmax, absorption coefficients, and
SCLC hole mobilities of P3HET-BTz and P3HET-TPD family of random copolymers with
oxi-DArP P3HET (P7) as reference.
Polymer
a

Mn
(kDa)
b

Ð
c

Yield
d

(%)
HOMO
e

(eV)
d100
f

(Å)
λmax
g

(nm)
Eg
h
,
nm/eV
µ
i
, cm
2
V
-1
s
-1

P7 11.7 2.07 68 5.95 20.20 494
597 /
2.08
2.27 x
10
-6

P3HET-
BTz-5%
11.1 2.06 60 6.01 19.44 488
601 /
2.06
3.56 x
10
-6

P3HET-
BTz-10%
8.6 2.11 64 6.00 18.78 480
595 /
2.08
1.05 x
10
-6

P3HET-
BTz-15%
5.6 1.89 58 6.07 18.39 467
580 /
2.14
1.97 x
10
-7

P3HET-
TPD-5%
13.9 2.04 54 6.01 20.57 495
604 /
2.05
2.58 x
10
-6

377
P3HET-
TPD-10%
10.1 2.44 67 6.05 21.32 494
608 /
2.04
6.99 x
10
-8

P3HET-
TPD-15%
8.2 3.03 63 5.99 21.58 491
607 /
2.04
5.26 x
10
-8

a
Polymers were measured after purification. P7 molecular weight, dispersity, yield as
shown in Table 7.1.
b
Molecular weight as determined by SEC calibrated to polystyrene
standards.
c
Dispersity as determined by GPC.
d
Yield after precipitation from reaction
mixture, Soxhlet extraction with methanol, hexanes, and chloroform, which was filtered
through Celite and precipitated into methanol, filtered and dried overnight under high
vacuum.
e
Determined by cyclic voltammetry (vs. Fc/Fc
+
) in 0.1M TBAPF6 in acetonitrile
solution.
f
Determined from GIXRD measurements.
g
Extracted from UV-Vis absorption
profile.
h
Calculated from the absorption band edge in thin films, Eg = 1240/ λedge.
I

Measured on neat polymer films.

7.3.2. P3HET Random Copolymers via Oxi-DArP

The conditions utilized for P7 were subsequently applied for the synthesis of two
families of copolymers, P3HET-BTz (Scheme 1b) and P3HET-TPD (Scheme 7.1c). Both
BTz and TPD-based homopolymers have previously been synthesized by oxi-DArP and so
were logical choices for evaluating copolymers.
33,36
Furthermore, both substrates are
unique—as BTz does not contain a directing group but features electron-poor thiazole
while TPD contains a carbonyl directing group. Although it does not provide the strong
solubilizing power of longer chains, the methyl group was targeted for BTz to ensure steric
hindrance of the side chains would not be a major factor in influencing the potential
378
coupling to the 2- or 5-position of 3HET. A summary of the polymer characteristics are
provided in Table 7.2, including molecular weights, dispersity, yields, electrochemical
HOMO energy levels, d100 spacings as determined by GIXRD, λmax and optical bandgaps
as extracted from UV-Vis data, and hole mobilities. Overall, molecular weights decreased
with increasing secondary component loadings, which is expected considering the limited
solubility of the acceptors; however dispersity remains close to 2 across the P3HET-BTz
family while it increases with increasing TPD content in the P3HET-TPD series. Yields
after purification are provided in Table 7.2 and were relatively good overall. Crude yields
were generally very high but low molecular weight material was lost in the hexanes fraction
of the Soxhlet. It is worth noting that polymers were generally soluble in the chloroform
fraction and no insoluble material except residual metal (palladium or silver) was observed
in the Soxhlet extractor thimble after purification.
Based on
1
H-NMR spectra (Figure A6.11-16), the feed ratio closely matched the
polymer composition for all polymers in the P3HET-BTz series. Because the BTz unit
contains two methyl groups (6H), resolution of the peaks was easier than with the P3HET-
TPD series (2H). Nonetheless, integration of the methylene peak associated with the octyl
chain on TPD (δ3.68) does show correlation between the feed ratio and the final
composition as well (Figure A6.14-16). Neither BTz or TPD contributes to integrations in
the aromatic region (except for possible end group signals), but splitting of the 3HET
aromatic peaks at δ7.86 and δ7.60 in that region can be attributed to the presence of
secondary components dispersed in the backbone. Additional support is provided by the
ester side-chain of P3HET, whose methylene peaks can be used to estimate regioregularity.
The head-to-tail cross-coupling shift is located at δ4.30 while the head-to-head
379
homocoupling is located at δ4.13. Another peak is visible at δ4.20 when BTz content
increases, or correspondingly at δ4.18 for TPD. This new peak can be attributed to 3HET
coupling with respective comonomers. With regards to the P3HET-BTz family (Figure
A6.11-13), the methyl signal of the BTz repeat unit is split in the random copolymers when
compared to the BTz monomer (Figure A6.2), likely attributed to BTz coupling to either
the 2- or the 5-position (δ2.69 and 2.44 respectively) of the majority 3HET backbone. A
small signal in between these two peaks (δ2.52 in Figure A6.11-13), which increases with
increasing BTz content, can most likely be attributed to BTz-BTz homocoupling. This
suggests that the BTz monomer is incorporated throughout the backbone to some extent
even if homocoupling occurs. We elect to describe this combination of cross-coupling and
homocoupling as “randomness” though we expect C-H reactivity or steric hindrance of the
3-alkylester to play some role. The NMR is somewhat less clear for the P3HET -TPD series
of copolymers (Figure A6.14-16). At 15% TPD content, the signal (δ3.68) associated with
the methylene peak of the octyl side-chain is better defined (compared to 5 and 10% TPD
loadings), and shows excellent correlation between the feed ratio and the polymer
composition (Figure A6.16). Broadly integrating the region does show correlation for
P3HET-TPD-5% and P3HET-TPD-10% but structural characterization in the same vein as
the BTZ family by
1
H NMR is not as straightforward, due in part to the fewer protons of
the methylene compared to the two methyl groups and the distance of the octyl chain on
TPD from the backbone. Due to the broadness of the TPD methylene peak (δ3.68),
homocouplings may be hidden; however, the emergence of a peak at δ4.18 suggests cross-
coupling does occur.
380

Figure 7.3. GIXRD Patterns of the (a) P3HET-BTz family and (b) P3HET-TPD family
of copolymers with P7 as a reference.

381
Further evidence for the incorporation of the acceptors was observed in GIXRD
patterns (Figure 7.3). Despite the random incorporation of secondary components, all
copolymers maintained their semicrystallinity. For the P3HET-BTz family of copolymers,
the (100) diffraction peaks gradually shifted to higher 2θ values (Figure 7.3a) with
increasing BTz content, which suggests that interchain distances for P3HET-BTz
copolymers is smaller and the polymers pack together more tightly. Given the lack of long
solubilizing chains on the BTz studied herein, it is reasonable that increasing the BTz
content would promote tighter packing. Consequently, interchain distances decrease from
about 20.2Å to 18.4Å as BTz content increases. The opposite trend is observed for the
P3HET-TPD family of copolymers (Figure 7.3b). In this case, interchain distances
increase from about 20.2Å to 21.6Å as higher TPD content shifts the (100) diffraction peak
toward smaller 2θ values. This is consistent with previous reports as larger secondary
components are added to the polymer backbone.
43,62

382

Figure 7.4. UV-Vis absorption profiles of the (a) P3HET-BTz family and (b) P3HET-
TPD family of copolymers with P7 as a reference. Absorption coefficients are calculated
from thickness estimates acquired by GIXRD in the reflectivity mode.

UV-Vis spectra of the random copolymers are provided in Figure 7.4 with P7 as a
reference. Absorption coefficients were determined from thicknesses estimated by GIXRD
in the reflectivity mode (Appendix). For the P3HET-BTz family of copolymers, the λmax
383
peak position blue shifts with increased BTz content, moving from 494 nm for P3HET to
467 nm for P3HET-BTz-15% (Table 7.2). Correspondingly, the optical bandgap, as
determined from the absorption onset, increases slightly with BTz content, from 2.08 eV
(P3HET) to 2.14 ev (P3HET-BTz-15%). Such trends are not observed with P3HET-TPD
copolymers as both the λmax peak position and the optical bandgap remains relatively
constant compared to P7. These differences in behaviour could be attributed to the strongly
electron-poor nature of the thiazole motif compared to TPD when dispersed in the
exceptionally electron-poor P3HET backbone but also to the low molecular weight of
P3HET-BTz-15%, which was the lowest amongst the random copolymers.
36
Additionally,
HOMO energy levels (Table 7.2), which were determined via electrochemical oxidation
(Figure A6.17-20), were generally consistent regardless of the secondary monomer
loading, with values roughly the same as P3HET. Considering the 3-hexylesterthiophene
motif alone can produce homopolymers that have incredibly deep HOMO energy
levels,
35,43
it is unsurprising that secondary acceptors at low loadings do not dramatically
alter the electrochemical oxidation, as all these systems can be considered random
acceptor-acceptor copolymers.
Additional data, including the absorption coefficients at max absorption, FWHM,
and the crystallite size as estimated by Scherrer’s equation,
60,61
can be found in Table A6.1.
Generally, P3HET homopolymers and random copolymer analogs featured similar
absorption coefficients, though lower molecular weight polymers generally had weaker
absorption coefficients. This is most obvious with P3HET-BTz-15%, which contains
significant loading of the weakly soluble BTz motif and only achieved Mn values of 5.6
kDa. Furthermore, the full width at half the maximum (FWHM) intensity of the GIXRD
384
peaks have been quantified (see Table A6.1). Compared to P7, the random polymer
analogues exhibit larger FWHM values, suggesting that the incorporation of a secondary
component reduces crystallite size but not significantly. Estimating correlation lengths
(CCL) from the FWHM via Scherrer’s equation (Table A6.1) reveals the CCL in random
copolymers is smaller than the crystallites of P3HET homopolymers. In general, random
P3HET-BT copolymers exhibited higher CCL values than P3HET-TPD copolymers.
Additional analysis of the polymers comes from hole mobilities measured by the
space-charge limited current (SCLC) method (Table 7.2). Compared to high mobility
polymers like P3HT, P3HET generally exhibits a lower mobility,
35
even though it is
semicrystalline, which is consistent with the results herein. The P3HET-TPD family of
random copolymers exhibited hole mobilities that were similar to that of P3HET; however,
the P3HET-BTz family exhibit lower mobilities, which is consistent with the lower
molecular weights of P3HET-BTz-10% and P3HET-BTz-15%. The consistency of the hole
mobilities of P3HET-TPD-5%, P3HET-TPD-10%, and P3HET-BTz-5% demonstrate
that—given sufficient molecular weights—the hole mobilities of random P3HET
copolymers does not dramatically depart from P3HET homopolymers.
Collectively, the investigation of oxi-DArP conditions has enabled improved
regioregularities without significantly diminished molecular weights. Oxi-DArP P3HET-
based random copolymers maintain their crystallinity and optoelectronic properties, and
exhibit good molecular weights despite the incorporation of a secondary monomer feed.
Importantly, the polymer composition correlates well to the monomer feed ratio, which
enables oxi-DArP to be compatible with the increasingly popular random copolymer
385
strategy for achieving tailored material properties, though more work is needed to expand
the substrate scope and enable a broad-reaching platform.

7.4. Conclusion

We have reported the optimization of conditions for the synthesis of regioregular
P3HET without any preactivation of the monomer, and the first catalysed regioregular
copolymerization toward P3HET random copolymers, which offers additional insight into
the compatibility of this method with copolymerizations and the role of C-H selectivity in
this emerging synthetic method. This study offers additional insight into the role of C-H
selectivity in this new synthetic method. We also confirm the compatibility of thieno[3,4-
c]pyrrole-4,6-dione (TPD) and 4,4’-dimethyl-2,2’-bithiazole (BTz) with oxi-DArP and
importantly their ability to be incorporated into a random copolymer architecture in a
predictable and controlled manner. Oxi-DArP offers the distinct advantage of bypassing
both the halogenation and metalation of the monomers, which can be challenging. Future
work should emphasize broadening of the substrate scope and utilizing oxi-DArP
conjugated polymers in application-focused studies.

7.5. References

(1) Bundgaard, E.; Livi, F.; Hagemann, O.; Carlé, J. E.; Helgesen, M.; Heckler, I. M.;
Zawacka, N. K.; Angmo, D.; Larsen-Olsen, T. T.; dos Reis Benatto, G. A.; Roth, B.;
Madsen, M. V.; Andersson, M. R.; Jørgensen, M.; Søndergaard, R. R.; Krebs, F. C.
Adv. Energy Mater. 2015, 5 (10), DOI: 10.1002/aenm.201402186.
386
(2) Benten, H.; Mori, D.; Ohkita, H.; Ito, S. J. Mater. Chem. A 2016, 4 (15), 5340.
(3) Österholm, A. M.; Shen, D. E.; Kerszulis, J. A.; Bulloch, R. H.; Kuepfert, M.; Dyer,
A. L.; Reynolds, J. R. ACS Appl. Mater. Interfaces 2015, 7 (3), 1413.
(4) Ponder, J. F.; Österholm, A. M.; Reynolds, J. R. Macromolecules 2016, 49 (6), 2106.
(5) Sirringhaus, H. Adv. Mater. 2014, 26 (9), 1319.
(6) Lombeck, F.; Di, D.; Yang, L.; Meraldi, L.; Athanasopoulos, S.; Credgington, D.;
Sommer, M.; Friend, R. H. Macromolecules 2016, 49 (24), 9382.
(7) Zhu, C.; Liu, L.; Yang, Q.; Lv, F.; Wang, S. Chem. Rev. 2012, 112 (8), 4687.
(8) Carsten, B.; He, F.; Son, H. J.; Xu, T.; Yu, L. Chem. Rev. 2011, 111 (3), 1493.
(9) Osaka, I.; McCullough, R. D. Acc. Chem. Res. 2008, 41 (9), 1202.
(10) Chen, T.-A.; Wu, X.; Rieke, R. D. J. Am. Chem. Soc. 1995, 117 (1), 233.
(11) Wu, W.-C.; Liu, C.-L.; Chen, W.-C. Polymer 2006, 47 (2), 527.
(12) Burke, D. J.; Lipomi, D. J. Energy Environ. Sci. 2013, 6 (7), 2053.
(13) Pouliot, J.-R.; Grenier, F.; Blaskovits, J. T.; Beaupré, S.; Leclerc, M. Chem. Rev.
2016, 116 (22), 14225.
(14) Bura, T.; Blaskovits, J. T.; Leclerc, M. J. Am. Chem. Soc. 2016, 138 (32), 10056.
(15) Suraru, S.-L.; Lee, J. A.; Luscombe, C. K. ACS Macro Lett. 2016, 5 (6), 724.
(16) Rudenko, A. E.; Thompson, B. C. J. Polym. Sci. A Polym. Chem. 2015, 53 (2), 135.
(17) Wang, K.; Wang, M. Curr. Org. Chem. 2013, 17, 999.
(18) Wakioka, M.; Nakamura, Y.; Hihara, Y.; Ozawa, F.; Sakaki, S. Organometallics
2013, 32 (15), 4423.
(19) Kuwabara, J.; Yasuda, T.; Choi, S. J.; Lu, W.; Yamazaki, K.; Kagaya, S.; Han, L.;
Kanbara, T. Adv. Funct. Mater. 2014, 24 (21), 3226.
387
(20) Livi, F.; Gobalasingham, N. S.; Thompson, B. C.; Bundgaard, E. J. Polym. Sci., Part
A 2016, 54 (18), 2907.
(21) Andersson, M. R.; Selse, D.; Berggren, M.; Jaervinen, H.; Hjertberg, T.; Inganaes,
O.; Wennerstroem, O.; Oesterholm, J.-E. Macromolecules 1994, 27 (22), 6503.
(22) Sugimoto, R.; Takeda, S.; Gu, H. B.; Yoshino, K. Chem. Exp. 1986, 1, 635.
(23) Haba, O.; Hayakawa, T.; Ueda, M.; Kawaguchi, H.; Kawazoe, T. React. Funct.
Polym. 1998, 37 (1–3), 163.
(24) Gohier, F.; Frère, P.; Roncali, J. J. Org. Chem. 2013, 78 (4), 1497.
(25) McCarley, T. D.; Noble, C. O.; DuBois, C. J.; McCarley, R. L. Macromolecules
2001, 34 (23), 7999.
(26) Yeung, C. S.; Dong, V. M. Chem. Rev. 2011, 111 (3), 1215.
(27) Wencel-Delord, J.; Dröge, T.; Liu, F.; Glorius, F. Chem. Soc. Rev. 2011, 40 (9),
4740.
(28) Satoh, T.; Miura, M. Chem. Eur. J. 2010, 16 (37), 11212.
(29) Lyons, T. W.; Sanford, M. S. Chem. Rev. 2010, 110 (2), 1147.
(30) Colby, D. A.; Bergman, R. G.; Ellman, J. A. Chem. Rev. 2010, 110 (2), 624.
(31) Tsuchiya, K.; Ogino, K. Polym J 2013, 45 (3), 281.
(32) Huang, Q.; Qin, X.; Li, B.; Lan, J.; Guo, Q.; You, J. Chem. Commun. 2014, 50 (89),
13739.
(33) Zhang, Q.; Wan, X.; Lu, Y.; Li, Y.; Li, Y.; Li, C.; Wu, H.; Chen, Y. Chem. Commun.
2014, 50 (83), 12497.
(34) Zhang, Q.; Li, Y.; Lu, Y.; Zhang, H.; Li, M.; Yang, Y.; Wang, J.; Chen, Y.; Li, C.
Polymer 2015, 68, 227.
388
(35) Gobalasingham, N. S.; Noh, S.; Thompson, B. C. Polym. Chem. 2016, 7 (8), 1623.
(36) Guo, Q.; Wu, D.; You, J. ChemSusChem 2016, 9 (19), 2765.
(37) Guo, Q.; Jiang, R.; Wu, D.; You, J. Macromol. Rapid Commun. 2016, 37 (9), 794.
(38) Qiu, Y.; Worch, J. C.; Fortney, A.; Gayathri, C.; Gil, R. R.; Noonan, K. J. T.
Macromolecules 2016, 49 (13), 4757.
(39) Mei, J.; Bao, Z. Chem. Mater. 2014, 26 (1), 604.
(40) Liu, J.; Kadnikova, E. N.; Liu, Y.; McGehee, M. D.; Fréchet, J. M. J. J. Am. Chem.
Soc. 2004, 126 (31), 9486.
(41) Manceau, M.; Bundgaard, E.; Carlé, J. E.; Hagemann, O.; Helgesen, M.;
Søndergaard, R.; Jørgensen, M.; Krebs, F. C. J. Mater. Chem. 2011, 21 (12), 4132.
(42) Reeves, B. D.; Unur, E.; Ananthakrishnan, N.; Reynolds, J. R. Macromolecules
2007, 40 (15), 5344.
(43) Noh, S.; Gobalasingham, N. S.; Thompson, B. C. Macromolecules 2016, 49 (18),
6835.
(44) Berrouard, P.; Dufresne, S.; Pron, A.; Veilleux, J.; Leclerc, M. J. Org. Chem. 2012,
77 (18), 8167.
(45) Pellet-Rostaing, S.; Regnouf-de-Vains, J.-B.; Lamartine, R. Tetrahedron Letters
1996, 37 (33), 5889.
(46) Cardona, C. M.; Li, W.; Kaifer, A. E.; Stockdale, D.; Bazan, G. C. Adv. Mater. 2011,
23 (20), 2367.
(47) Thompson, B. C.; Kim, Y.-G.; McCarley, T. D.; Reynolds, J. R. J. Am. Chem. Soc.
2006, 128 (39), 12714.
(48) Stuart, D. R.; Fagnou, K. Science 2007, 316 (5828), 1172.
389
(49) Xu, B.; Noh, S.; Thompson, B. C. Macromolecules 2014, 47 (15), 5029.
(50) Howard, J. B.; Ekiz, S.; Cuellar De Lucio, A. J.; Thompson, B. C. Macromolecules
2016, 49 (17), 6360.
(51) Duan, C.; Gao, K.; van Franeker, J. J.; Liu, F.; Wienk, M. M.; Janssen, R. A. J. J.
Am. Chem. Soc. 2016, 138 (34), 10782.
(52) Khlyabich, P. P.; Rudenko, A. E.; Thompson, B. C. J. Polym. Sci. A Polym. Chem.
2014, 52 (8), 1055.
(53) Marzano, G.; Kotowski, D.; Babudri, F.; Musio, R.; Pellegrino, A.; Luzzati, S.; Po,
R.; Farinola, G. M. Macromolecules 2015, 48 (19), 7039.
(54) Kozycz, L. M.; Gao, D.; Seferos, D. S. Macromolecules 2013, 46 (3), 613.
(55) Howard, J. B.; Noh, S.; Beier, A. E.; Thompson, B. C. ACS Macro Lett. 2015, 4 (7),
725.
(56) Shi, C.; Yao, Y.; Yang; Pei, Q. J. Am. Chem. Soc. 2006, 128 (27), 8980.
(57) Rudenko, A. E.; Latif, A. A.; Thompson, B. C. J. Polym. Sci. A Polym. Chem. 2015,
53 (12), 1492.
(58) Piera, J.; Bäckvall, J.-E. Angewandte Chemie International Edition 2008, 47 (19),
3506.
(59) Rudenko, A. E.; Latif, A. A.; Thompson, B. C. Nanotechnology 2014, 25 (1),
014005.
(60) Khlyabich, P. P.; Burkhart, B.; Ng, C. F.; Thompson, B. C. Macromolecules 2011,
44 (13), 5079.
(61) Yang, H.; LeFevre, S. W.; Ryu, C. Y.; Bao, Z. Appl. Phys. Lett. 2007, 90 (17),
172116.
390
(62) Sharenko, A.; Treat, N. D.; Love, J. A.; Toney, M. F.; Stingelin, N.; Nguyen, T.-Q.
J. Mater. Chem. A 2014, 2 (38), 15717.

391
BIBLIOGRAPHY
Ackermann, L., 2011. Chem. Rev. 111, 1315–1345.
Ackermann, L., Lygin, A.V., 2011. Org. Lett. 13, 3332–3335.
Ackermann, L., Vicente, R., Kapdi, A.R., 2009. Angew. Chem. Int. Ed. 48, 9792–9826.
Adam, G., Pivrikas, A., Ramil, A.M., Tadesse, S., Yohannes, T., Sariciftci, N.S., Egbe,
D.A.M., 2011. J. Mater. Chem. 21, 2594–2600.
Ahmadi, Z., McIndoe, J.S., 2013. Chem. Commun. 49, 11488–11490.
A. Johnson, S., 2015. Dalton Transactions 44, 10905–10913.
Alberico, D., Scott, M.E., Lautens, M., 2007. Chem. Rev. 107, 174–238.
Alexandris, S., Franczyk, A., Papamokos, G., Marciniec, B., Matyjaszewski, K., Koynov,
K., Mezger, M., Floudas, G., 2015. Macromolecules.
Allard, N., Najari, A., Pouliot, J.-R., Pron, A., Grenier, F., Leclerc, M., 2012. Polym.
Chem. 3, 2875–2879.
Allcock, H.R., Lampe, F.W., Mark, J.E., 2003. Contemporary Polymer Chemistry (3rd
Edition), 3rd Edition. ed. Prentice Hall, Inc.
Alunni, S., Linda, P., Marino, G., Santini, S., Savelli, G., 1972. J. Chem. Soc., Perkin
Trans. 2 2070–2073.
Amb, C.M., Chen, S., Graham, K.R., Subbiah, J., Small, C.E., So, F., Reynolds, J.R., 2011.
J. Am. Chem. Soc. 133, 10062–10065.
Amb, C.M., Craig, M.R., Koldemir, U., Subbiah, J., Choudhury, K.R., Gevorgyan, S.A.,
Jørgensen, M., Krebs, F.C., So, F., Reynolds, J.R., 2012. ACS Appl. Mater. Interfaces
4, 1847–1853.
Ames, D.E., Bull, D., 1982. Tetrahedron 38, 383–387.
Ames, D.E., Opalko, A., 1984. Tetrahedron 40, 1919–1925.
An, Q., Zhang, F., Zhang, J., Tang, W., Deng, Z., Hu, B., 2016. Energy Environ. Sci. 9,
281–322.
Ananthakrishnan, N., Padmanaban, G., Ramakrishnan, S., Reynolds, J.R., 2005.
Macromolecules 38, 7660–7669.
Andersen, T.R., Dam, H.F., Burkhart, B., Angmo, D., Corazza, M., Thompson, B.C.,
Krebs, F.C., 2014. J. Mater. Chem. C 2, 9412–9415.
Andersen, T.R., Larsen-Olsen, T.T., Andreasen, B., Böttiger, A.P.L., Carlé, J.E.,
Helgesen, M., Bundgaard, E., Norrman, K., Andreasen, J.W., Jørgensen, M., Krebs,
F.C., 2011. ACS Nano 5, 4188–4196.
Andrew, T.L., Bulović, V., 2012. ACS Nano 6, 4671–4677.
Angmo, D., Bjerring, M., Nielsen, N.C., Thompson, B.C., Krebs, F.C., 2015. J. Mater.
Chem. C 3, 5541–5548.
Ashcroft, C.P., Dunn, P.J., Hayler, J.D., Wells, A.S., 2015. Org. Process Res. Dev. 19,
740–747.
Ashenhurst, J.A., 2010. Chem. Soc. Rev. 39, 540–548.
Aycock, D.F., 2007. Org. Process Res. Dev. 11, 156–159.
Bakhmutov, V.I., Berry, J.F., Cotton, F.A., Ibragimov, S., Murillo, C.A., 2005. Dalton
Transactions.
Bakulin, A.A., Martyanov, D., Paraschuk, D.Y., Loosdrecht, P.H.M. van, Pshenichnikov,
M.S., 2009. Chemical Physics Letters 482, 99–104.
392
Balerna, M., Fosset, M., Chicheportiche, R., Romey, G., Lazdunski, M., 1975.
Biochemistry 14, 5500–5511.
Ballantyne, A.M., Chen, L., Dane, J., Hammant, T., Braun, F.M., Heeney, M., Duffy, W.,
McCulloch, I., Bradley, D.D.C., Nelson, J., 2008. Adv. Funct. Mater. 18, 2373–2380.
Bannock, J.H., Treat, N.D., Chabinyc, M., Stingelin, N., Heeney, M., Mello, J.C. de,
2016a. Scientific Reports 6, 23651.
Bannock, J.H., Xu, W., Baïssas, T., Heeney, M., de Mello, J.C., 2016b. European Polymer
Journal 80, 240–246.
Barbarella, G., Bongini, A., Zambianchi, M., 1994. Macromolecules 27, 3039–3045.
Barlow, J.W., 1993. Makromolekulare Chemie. Macromolecular Symposia 70–71, 235–
244.
Barlow, J.W., Paul, D.R., 1981. Polym Eng Sci 21, 985–996.
Battace, A., Lemhadri, M., Zair, T., Doucet, H., Santelli, M., 2007. Adv. Synth. Catal.
349, 2507–2516.
Beaupré, S., Leclerc, M., 2013. J. Mater. Chem. A 1, 11097–11105.
Beaupré, S., Pron, A., Drouin, S.H., Najari, A., Mercier, L.G., Robitaille, A., Leclerc, M.,
2012. Macromolecules 45, 6906–6914.
Beaupré, S., Shaker-Sepasgozar, S., Najari, A., Leclerc, M., 2017. Journal of Materials
Chemistry A 5, 6638–6647.
Becke, A.D., 1993. The Journal of Chemical Physics 98, 5648–5652.
Beller, M., Fischer, H., Herrmann, W.A., Öfele, K., Brossmer, C., 1995. Angew. Chem.,
Int. Ed. 34, 1848–1849.
Berrouard, P., Dufresne, S., Pron, A., Veilleux, J., Leclerc, M., 2012a. J. Org. Chem. 77,
8167–8173.
Berrouard, P., Najari, A., Pron, A., Gendron, D., Morin, P.-O., Pouliot, J.-R., Veilleux, J.,
Leclerc, M., 2012b. Angew. Chem. Int. Ed. 51, 2068–2071.
Betancur, R., Romero-Gomez, P., Martinez-Otero, A., Elias, X., Maymó, M., Martorell,
J., 2013. Nat Photon 7, 995–1000.
Bhattacharya, S., Gupta, R.K., Bhattacharya, S.N., 2010. Polym Eng Sci 50, 1350–1357.
Bin, H., Zhang, Z.-G., Gao, L., Chen, S., Zhong, L., Xue, L., Yang, C., Li, Y., 2016. J.
Am. Chem. Soc. 138, 4657–4664.
Biniek, L., Chochos, C.L., Leclerc, N., Boyron, O., Fall, S., Lévèque, P., Heiser, T., 2012.
J. Polym. Sci. A Polym. Chem. 50, 1861–1868.
Bishara, A., Shaban, H.I., 2006. J. Appl. Polym. Sci. 101, 3565–3571.
Blaskovits, J.T., Bura, T., Beaupré, S., Lopez, S.A., Roy, C., de Goes Soares, J., Oh, A.,
Quinn, J., Li, Y., Aspuru-Guzik, A., Leclerc, M., 2017. Macromolecules 50, 162–
174.
Böhm, V.P.W., Herrmann, W.A., 2001. Chem. - Eur. J. 7, 4191–4197.
Bohra, H., Shao, J., Huang, S., Wang, M., 2016a. Tetrahedron Letters 57, 1497–1501.
Bohra, H., Wang, M., 2017. Journal of Materials Chemistry A.
Bohra, H., Yu Tan, S., Shao, J., Yang, C., Efrem, A., Zhao, Y., Wang, M., 2016b. Polymer
Chemistry 7, 6413–6421.
Brabec, C.J., Durrant, J.R., 2011. MRS Bull. 33, 670–675.
Bracher, C., Yi, H., Scarratt, N.W., Masters, R., Pearson, A.J., Rodenburg, C., Iraqi, A.,
Lidzey, D.G., 2015. Organic Electronics 27, 266–273.
Brady, M.A., Su, G.M., Chabinyc, M.L., 2011. Soft Matter 7, 11065–11077.
393
Brain, E.G., Doyle, F.P., Hardy, K., Long, A.A.W., Mehta, M.D., Miller, D., Nayler,
J.H.C., Soulal, M.J., Stove, E.R., Thomas, G.R., 1962. Journal of the Chemical
Society (Resumed).
Bras, J., Pepin-Donat, B., 2001. Magn. Reson. Chem. 39, 57–67.
Broll, S., Nübling, F., Luzio, A., Lentzas, D., Komber, H., Caironi, M., Sommer, M., 2015.
Macromolecules 48, 7481–7488.
Bronstein, H., Hurhangee, M., Fregoso, E.C., Beatrup, D., Soon, Y.W., Huang, Z.,
Hadipour, A., Shakya Tuladhar, P., Rossbauer, S., Sohn, E.-H., Shoaee, S., Dimitrov,
S.D., Frost, J.M., Ashraf, R.S., Kirchartz, T., Watkins, S.E., Song, K., Anthopoulos,
T.D., Nelson, J., Rand, B.P., Durrant, J.R., McCulloch, I., 2013. Chem. Mater. 4239–
4249.
Brookins, R.N., Schanze, K.S., Reynolds, J.R., 2007. Macromolecules 40, 3524–3526.
Bryan, Z.J., McNeil, A.J., 2013. Macromolecules 46, 8395–8405.
Bubnova, O., Khan, Z.U., Malti, A., Braun, S., Fahlman, M., Berggren, M., Crispin, X.,
2011. Nat Mater 10, 429–433.
Buchwald, S.L., Bolm, C., 2009. Angew. Chem. Int. Ed. 48, 5586–5587.
Bugaut, X., Glorius, F., 2011. Angew. Chem. Int. Ed. 50, 7479–7481.
Bulloch, R.H., Kerszulis, J.A., Dyer, A.L., Reynolds, J.R., 2015. ACS Appl. Mater.
Interfaces 7, 1406–1412.
Bundgaard, E., Krebs, F.C., 2007. Sol. Energ. Mat. Sol. Cells, Low Band Gap Polymer
Materials for Organic Solar Cells 91, 954–985.
Bundgaard, E., Livi, F., Hagemann, O., Carlé, J.E., Helgesen, M., Heckler, I.M., Zawacka,
N.K., Angmo, D., Larsen-Olsen, T.T., dos Reis Benatto, G.A., Roth, B., Madsen,
M.V., Andersson, M.R., Jørgensen, M., Søndergaard, R.R., Krebs, F.C., 2015. Adv.
Energy Mater. 5, DOI: 10.1002/aenm.201402186.
Bura, T., Beaupré, S., Légaré, M.-A., Quinn, J., Rochette, E., Blaskovits, J.T., Fontaine,
F.-G., Pron, A., Li, Y., Leclerc, M., 2017. Chem. Sci. 8, 3913–3925.
Bura, T., Blaskovits, J.T., Leclerc, M., 2016. J. Am. Chem. Soc. 138, 10056–10071.
Burke, D.J., Lipomi, D.J., 2013. Energy Environ. Sci. 6, 2053–2066.
Burkhart, B., Khlyabich, P.P., Cakir Canak, T., LaJoie, T.W., Thompson, B.C., 2011.
Macromolecules 44, 1242–1246.
Burkhart, B., Khlyabich, P.P., Thompson, B.C., 2012a. J. Photon. Energy 2, 021002-1.
Burkhart, B., Khlyabich, P.P., Thompson, B.C., 2012b. Macromolecules 45, 3740–3748.
Burkhart, B., Khlyabich, P.P., Thompson, B.C., 2012c. ACS Macro Lett. 1, 660–666.
Burkhart, B., Khlyabich, P.P., Thompson, B.C., 2013. Macromol. Chem. Phys. 214, 681–
690.
Cai, M., Bao, X., Wang, X., Zhang, H., Qiu, M., Yang, R., Yang, C., Wan, X., 2016.
Chem. Mater.
Caldwell, G., Renneboog, R., Kebarle, P., 1989. Canadian Journal of Chemistry 67, 611–
618.
Calò, V., Nacci, A., Monopoli, A., Cotugno, P., 2009. Chem. - Eur. J. 15, 1272–1279.
Camaioni, N., Tinti, F., Franco, L., Fabris, M., Toffoletti, A., Ruzzi, M., Montanari, L.,
Bonoldi, L., Pellegrino, A., Calabrese, A., Po, R., 2012. Organic Electronics 13, 550–
559.
Campeau, L.-C., Fagnou, K., 2006. Chem. Commun. 12, 1253–1264.
394
Campeau, L.-C., Parisien, M., Jean, A., Fagnou, K., 2006. J. Am. Chem. Soc. 128, 581–
590.
Campo, B., Oosterbaan, W.D., Gilot, J., Cleij, T.J., Lutsen, L., Janssen, R.A.J.,
Vanderzande, D., 2009. Design and synthesis of side-chain functionalized
regioregular poly(3-hexylthiophene)-based copolymers and application in
polymer:fullerene bulk heterojunction solar cells, in: Kafafi, Z.H., Lane, P.A. (Eds.),
SPIE 7416, Organic Photovoltaics X. p. 74161G–74161G–11.
Canaani, E., Aaronson, S.A., 1979. Proc. Natl. Acad. Sci. U.S.A. 76, 1677–1681.
Cano, R., Schmidt, A.F., McGlacken, G.P., 2015. Chem. Sci. 6, 5338–5346.
Cao, J., Liao, Q., Du, X., Chen, J., Xiao, Z., Zuo, Q., Ding, L., 2013. Energy Environ. Sci.
6, 3224–3228.
Cardona, C.M., Li, W., Kaifer, A.E., Stockdale, D., Bazan, G.C., 2011. Adv. Mater. 23,
2367–2371.
Carril, M., Correa, A., Bolm, C., 2008. Angew. Chem. Int. Ed. 120, 4940–4943.
Carsten, B., He, F., Son, H.J., Xu, T., Yu, L., 2011. Chem. Rev. 111, 1493–1528.
Chakrabarti, R., Chakraborty, D., 2006. J. Appl. Polym. Sci. 102, 3698–3703.
Chang, M.-Y., Chen, Y.-F., Tsai, Y.-S., Chi, K.-M., 2009. J. Electrochem. Soc. 156,
B234–B237.
Chang, S.-W., Waters, H., Kettle, J., Horie, M., 2012a. Organic Electronics 13, 2967–
2974.
Chang, S.-W., Waters, H., Kettle, J., Kuo, Z.-R., Li, C.-H., Yu, C.-Y., Horie, M., 2012b.
Macromol. Rapid Commun. 33, 1927–1932.
Chavez, C.A., Choi, J., Nesterov, E.E., 2014. Macromolecules 47, 506–516.
Chen, C.-C., Dou, L., Zhu, R., Chung, C.-H., Song, T.-B., Zheng, Y.B., Hawks, S., Li, G.,
Weiss, P.S., Yang, Y., 2012. ACS Nano 6, 7185–7190.
Chen, C.-H., Cheng, Y.-J., Dubosc, M., Hsieh, C.-H., Chu, C.-C., Hsu, C.-S., 2010a.
Chem. Asian J. 5, 2483–2492.
Chen, C.-H., Hsieh, C.-H., Dubosc, M., Cheng, Y.-J., Hsu, C.-S., 2010b. Macromolecules
43, 697–708.
Chen, F., Min, Q.-Q., Zhang, X., 2012. J. Org. Chem. 77, 2992–2998.
Chen, H., Choi, J.-H., Salas-de la Cruz, D., Winey, K.I., Elabd, Y.A., 2009.
Macromolecules 42, 4809–4816.
Chen, H., Guo, Y., Yu, G., Zhao, Y., Zhang, J., Gao, D., Liu, H., Liu, Y., 2012. Adv.
Mater. 24, 4618–4622.
Chen, S., Small, C.E., Amb, C.M., Subbiah, J., Lai, T., Tsang, S.-W., Manders, J.R.,
Reynolds, J.R., So, F., 2012. Adv. Energy Mater. 2, 1333–1337.
Chen, S., Sun, B., Hong, W., Aziz, H., Meng, Y., Li, Y., 2014. J. Mater. Chem. C 2, 2183–
2190.
Chen, T.-A., Wu, X., Rieke, R.D., 1995. J. Am. Chem. Soc. 117, 233–244.
Cheng, Y.-J., Hsieh, C.-H., Li, P.-J., Hsu, C.-S., 2011. Adv. Funct. Mater. 21, 1723–1732.
Cheng, Y.-J., Yang, S.-H., Hsu, C.-S., 2009. Chem. Rev. 109, 5868–5923.
Chiechi, R.C., Hummelen, J.C., 2012. ACS Macro Lett. 1, 1180–1183.
Cho, S.H., Kim, J.Y., Kwak, J., Chang, S., 2011. Chem. Soc. Rev. 40, 5068–5083.
Cho, Y.J., Lee, J.Y., Chin, B.D., Forrest, S.R., 2013. Organic Electronics 14, 1081–1085.
Chochos, C.L., Choulis, S.A., 2011. Prog. Polym. Sci. 36, 1326–1414.
Choi, M.-G., Ho, T.C., Angelici, R.J., 2008. Organometallics 27, 1098–1105.
395
Choi, S.J., Kuwabara, J., Kanbara, T., 2013. ACS Sustainable Chem. Eng. 1, 878–882.
Christophersen, C., Begtrup, M., Ebdrup, S., Petersen, H., Vedsø, P., 2003. J. Org. Chem.
68, 9513–9516.
Ciana, C.-L., Phipps, R.J., Brandt, J.R., Meyer, F.-M., Gaunt, M.J., 2011. Angew. Chem.
Int. Ed. 50, 458–462.
Coffin, R.C., Peet, J., Rogers, J., Bazan, G.C., 2009. Nat. Chem. 1, 657–661.
Colby, D.A., Bergman, R.G., Ellman, J.A., 2010. Chem. Rev. 110, 624–655.
Colletto, C., Islam, S., Juliá-Hernández, F., Larrosa, I., 2016. J. Am. Chem. Soc. 138,
1677–1683.
Cooling, N., Burke, K.B., Zhou, X., Lind, S.J., Gordon, K.C., Jones, T.W., Dastoor, P.C.,
Belcher, W.J., 2011. Solar Energy Materials and Solar Cells 95, 1767–1774.
Cordovilla, C., Bartolomé, C., Martínez-Ilarduya, J.M., Espinet, P., 2015. ACS Catal. 5,
3040–3053.
Cosnier, S., Karyakin, A., 2010. Electropolymerization: Concepts, Materials and
Applications. Wiley-CVH, Weinheim, Germany.
Cowie, J.M.G., Arrighi, V., 2007. Polymers: Chemistry and Physics of Modern Materials,
Third Edition, Third. ed. CRC Press - Taylor & Francis Group, LLC., Boca Raton,
FL.
Cristau, H.-J., Cellier, P.P., Spindler, J.-F., Taillefer, M., 2004. Chem. - Eur. J. 10, 5607–
5622.
Cui, X., Li, J., Zhang, Z.-P., Fu, Y., Liu, L., Guo, Q.-X., 2007. J. Org. Chem. 72, 9342–
9345.
Cui, X., Li, Z., Tao, C.-Z., Xu, Y., Li, J., Liu, L., Guo, Q.-X., 2006. Org. Lett. 8, 2467–
2470.
Curzons, A.D., Mortimer, D.N., Constable, D.J.C., Cunningham, V.L., 2001. Green
Chem. 3, 1–6.
Dang, M.T., Hirsch, L., Wantz, G., 2011. Adv. Mater. 23, 3597–3602.
Dang, M.T., Hirsch, L., Wantz, G., Wuest, J.D., 2013. Chem. Rev. 113, 3734–3765.
Dao-Huy, T., Haider, M., Glatz, F., Schnürch, M., Mihovilovic, M.D., 2014. Eur. J. Org.
Chem. 36, 8119–8125.
Das, S., Khlyabich, P.P., Burkhart, B., Roberts, S.T., Couderc, E., Thompson, B.C.,
Bradforth, S.E., 2014. J. Phys. Chem. C.
Dembitsky, V.M., 2006. Lipids 41, 309–340.
Demir, G.E., Yıldırım, M., Cengiz, U., Kaya, İ., 2015. React. Funct. Polym. 97, 63–68.
Dhar, P., Khlyabich, P.P., Burkhart, B., Roberts, S.T., Malyk, S., Thompson, B.C.,
Benderskii, A.V., 2013. J. Phys. Chem. C 117, 15213–15220.
Diliën, H., Chambon, S., Cleij, T.J., Lutsen, L., Vanderzande, D., Adriaensens, P.J., 2011.
Macromolecules 44, 4711–4720.
Do, H.-Q., Daugulis, O., 2008. J. Am. Chem. Soc. 130, 1128–1129.
Do, H.-Q., Khan, R.M.K., Daugulis, O., 2008. J. Am. Chem. Soc. 130, 15185–15192.
Dong, D., Fang, D., Li, H., Zhu, C., Zhao, X., Li, J., Jin, L., Xie, L., Chen, L., Zhao, J.,
Zhang, H., Huang, W., 2017. Chem. Asian J. 12, 920–926.
Dong, J.J., Roger, J., Doucet, H., 2009a. Tetrahedron Lett. 50, 2778–2781.
Dong, J.J., Roger, J., Požgan, F., Doucet, H., 2009b. Green Chem. 11.
Dou, J., Chen, Z., Ma, C., 2014. Synth. Met. 196, 117–124.
396
Du Bois, C.J., Larmat, F., Irvin, D.J., Reynolds, J.R., 2001. Synthetic Metals, Proceedings
of the International Conference on Science and technology of Synthetic Metals 119,
321–322.
Du, C., Li, W., Duan, Y., Li, C., Dong, H., Zhu, J., Hu, W., Bo, Z., 2013. Polym. Chem.
4, 2773–2782.
Du, Z.-J., Gao, L.-X., Lin, Y.-J., Han, F.-S., 2013. ChemCatChem n/a-n/a.
Duan, C., Furlan, A., van Franeker, J.J., Willems, R.E.M., Wienk, M.M., Janssen, R.A.J.,
2015. Adv. Mater. 27, 4461–4468.
Duan, C., Gao, K., van Franeker, J.J., Liu, F., Wienk, M.M., Janssen, R.A.J., 2016. J. Am.
Chem. Soc. 138, 10782–10785.
Dudnik, A.S., Aldrich, T.J., Eastham, N.D., Chang, R.P.H., Facchetti, A., Marks, T.J.,
2016. J. Am. Chem. Soc. 138, 15699–15709.
Dutta, J., Naskar, K., 2014. RSC Adv. 4, 60831–60841.
Efrem, A., Wang, K., Amaniampong, P.N., Yang, C., Gupta, S., Bohra, H., Mushrif, S.H.,
Wang, M., 2016. Polym. Chem. 7, 4862–4866.
Efrem, A., Wang, K., Jia, T., Wang, M., 2017. J. Polym. Sci. Part A: Polym. Chem. DOI:
10.1002/pola.28555.
Efrem, A., Wang, K., Wang, M., n.d. Dyes and Pigments.
Eggert Carlé, J., Wenzel Andreasen, J., Jørgensen, M., Christian Krebs, F., 2010. Sol.
Energ. Mat. Sol. Cells 94, 774–780.
Ekiz, S., Thompson, B.C., 2017. J. Polym. Sci. A Polym. Chem. doi: 10.1002/pola.28680.
Ekiz, S., Thompson, B.C., n.d. J. Polym. Sci. Part A: Polym. Chem. doi:
10.1002/pola.28680.
El Kassmi, A., Fache, F., Lemaire, M., 1994. Journal of Electroanalytical Chemistry 373,
241–244.
Ellison, S.L.R., Robinson, M.J.T., 1983. Journal of the Chemical Society, Chemical
Communications.
Elumalai, N.K., Uddin, A., 2016. Energy Environ. Sci. 9, 391–410.
Engelmann, G., Jugelt, W., Kossmehl, G., Welzel, H.-P., Tschuncky, P., Heinze, J., 1996.
Macromolecules 29, 3370–3375.
Engle, K.M., Yu, J.-Q., 2013. J. Org. Chem.
Enthaler, S., Junge, K., Beller, M., 2008. Angew. Chem. Int. Ed. 47, 3317–3321.
Erb, T., Zhokhavets, U., Gobsch, G., Raleva, S., Stühn, B., Schilinsky, P., Waldauf, C.,
Brabec, C.J., 2005. Adv. Funct. Mater. 15, 1193–1196.
Espinet, P., Echavarren, A.M., 2004. Angew. Chem. Int. Ed. 43, 4704–4734.
Espinosa, N., García-Valverde, R., Urbina, A., Lenzmann, F., Manceau, M., Angmo, D.,
Krebs, F.C., 2012. Sol. Energ. Mat. Sol. Cells 97, 3–13.
Espinosa, N., Lenzmann, F.O., Ryley, S., Angmo, D., Hösel, M., Søndergaard, R.R., Huss,
D., Dafinger, S., Gritsch, S., Kroon, J.M., Jørgensen, M., Krebs, F.C., 2013. J. Mater.
Chem. A 1, 7037–7049.
Estrada, L.A., Deininger, J.J., Kamenov, G.D., Reynolds, J.R., 2013. ACS Macro Lett. 2,
869–873.
Facchetti, A., Vaccaro, L., Marrocchi, A., 2012. Angew. Chem. Int. Ed. 51, 3520–3523.
Fairlamb, I.J.S., 2007. Chem. Soc. Rev. 36, 1036–1045.
Fefer, M., 1978. J. Am. Oil Chem. Soc. 55, A342–A348.
Fefer, M., Rutkowski, A.J., 1968. J. Am. Oil Chem. Soc. 45, 5–10.
397
Feng, L.-J., Guo, J.-W., Zhong, X., Sun, Z.-Y., 2014. J. Macromol. Sci. A 51, 604–609.
Ferrari, M., Mucci, A., Schenetti, L., Malmusi, L., 1995. Magnetic Resonance in
Chemistry 33, 657–663.
Forrest, S. r., Bradley, D. d. c., Thompson, M. e., 2003. Adv. Mater. 15, 1043–1048.
Fors, B.P., Hawker, C.J., 2012. Angew. Chem. Int. Ed. 51, 8850–8853.
Fournier Dit Chabert, J., Joucla, L., David, E., Lemaire, M., 2004. Tetrahedron 60, 3221–
3230.
Freitas, J.N. de, Grova, I.R., Akcelrud, L.C., Arici, E., Sariciftci, N.S., Nogueira, A.F.,
2010. J. Mater. Chem. 20, 4845–4853.
Fritz, H.P., Gordon, I.R., Schwarzhans, K.E., Venanzi, L.M., 1965. Journal of the
Chemical Society (Resumed).
Fu, B., Wang, C.-Y., Rose, B.D., Jiang, Y., Chang, M., Chu, P.-H., Yuan, Z., Fuentes-
Hernandez, C., Kippelen, B., Brédas, J.-L., Collard, D.M., Reichmanis, E., 2015.
Chem. Mater. 27, 2928–2937.
Fuji, K., Tamba, S., Shono, K., Sugie, A., Mori, A., 2013. J. Am. Chem. Soc. 135, 12208–
12211.
Fujie, Y., Kuwabara, J., Kanbara, T., 2015. Molecular Crystals and Liquid Crystals 622,
14–18.
Fujinami, Y., Kuwabara, J., Lu, W., Hayashi, H., Kanbara, T., 2012. ACS Macro Lett. 1,
67–70.
Gao, C., Yan, D., 2004. Progress in Polymer Science 29, 183–275.
Gao, Y., Zhang, X., Tian, H., Zhang, J., Yan, D., Geng, Y., Wang, F., 2015. Adv. Mater.
27, 6753–6759.
García-Cuadrado, D., de Mendoza, P., Braga, A.A.C., Maseras, F., Echavarren, A.M.,
2007. J. Am. Chem. Soc. 129, 6880–6886.
García-Melchor, M., Braga, A.A.C., Lledós, A., Ujaque, G., Maseras, F., 2013. Acc.
Chem. Res.
García-Valverde, R., Cherni, J.A., Urbina, A., 2010. Prog. Photovolt: Res. Appl. 18, 535–
558.
Gendron, D., Leclerc, M., 2011. Energy Environ. Sci. 4, 1225–1237.
Gilbert, M.D., Pendergrass, A., Isenberg, F.M., Lisk, D.J., 1974. J. Agric. Food Chem. 22,
589–592.
Gobalasingham, N. S.; Ekiz, S.; Pankow, R. M.; Livi, F.; Thompson, B. C.; Bundgaard,
E.
Polymer Chemistry, 2017, DOI: 10.1039/C7PY00859G
Gobalasingham, N., Pankow, R., Ekiz, S., Thompson, B., 2017. J. Mater. Chem. A. DOI:
10.1039/C7TA03980H
Gobalasingham, N.S., Noh, S., Howard, J.B., Thompson, B.C., 2016. ACS Appl. Mater.
Interfaces 8, 27931–27941.
Gobalasingham, N.S., Noh, S., Thompson, B.C., 2016. Polym. Chem. 7, 1623–1631.
Gobalasingham, N.S., Pankow, R.M., Thompson, B.C., 2017. Polym. Chem. 8, 1963–
1971.
Goh, C., Kline, R.J., McGehee, M.D., Kadnikova, E.N., Fréchet, J.M.J., 2005. Appl. Phys.
Lett. 86, 122110.
Goh, S.H., Paul, D.R., Barlow, J.W., 1982. Polym Eng Sci 22, 34–39.
Goldsmith, P.J., Teat, S.J., Woodward, S., 2005. Angew. Chem., Int. Ed. 44, 2235–2237.
398
Goodson, F.E., Wallow, T.I., Novak, B.M., 1997. J. Am. Chem. Soc. 119, 12441–12453.
Goodson, F.E., Wallow, T.I., Novak, B.M., 1998. Macromolecules 31, 2047–2056.
Gorelsky, S.I., 2013. Coord. Chem. Rev., A Tribute to Edward I. Solomon on his 65th
Birthday: Part 1 257, 153–164.
Gorelsky, S.I., Lapointe, D., Fagnou, K., 2008. J. Am. Chem. Soc. 130, 10848–10849.
Gorelsky, S.I., Lapointe, D., Fagnou, K., 2012. J. Org. Chem. 77, 658–668.
Gozzi, C., Lavenot, L., Ilg, K., Penalva, V., Lemaire, M., 1997. Tetrahedron Lett. 38,
8867–8870.
Granado, A., Iturriza, L., Eguiazábal, J.I., 2014. J. Appl. Polym. Sci. 131, n/a-n/a.
Greaney, M.J., Araujo, J., Burkhart, B., Thompson, B.C., Brutchey, R.L., 2013. Chem.
Commun. 49, 8602–8604.
Gregory, A., Stenzel, M.H., 2012. Progress in Polymer Science 37, 38–105.
Grenier, F., Aïch, B.R., Lai, Y.-Y., Guérette, M., Holmes, A.B., Tao, Y., Wong, W.W.H.,
Leclerc, M., 2015. Chem. Mater. 27, 2137–2143.
Grenier, F., Berrouard, P., Pouliot, J.-R., Tseng, H.-R., Heeger, A.J., Leclerc, M., 2013.
Polym. Chem. 4, 1836–1841.
Grenier, F., Goudreau, K., Leclerc, M., 2017. J. Am. Chem. Soc. 139, 2816–2824.
Greve, D.R., Apperloo, J.J., Janssen, R.A.J., 2001. Eur. J. Org. Chem. 2001, 3437–3443.
Grimsdale, A.C., Leok Chan, K., Martin, R.E., Jokisz, P.G., Holmes, A.B., 2009. Chem.
Rev. 109, 897–1091.
Gruber, M., Jung, S.-H., Schott, S., Venkateshvaran, D., Kronemeijer, A.J., Andreasen,
J.W., McNeill, C.R., Wong, W.W.H., Shahid, M., Heeney, M., Lee, J.-K.,
Sirringhaus, H., 2015. Chem. Sci. 6, 6949–6960.
Grushin, V.V., Marshall, W.J., 2009. J. Am. Chem. Soc. 131, 918–919.
Grzybowski, M., Gryko, D.T., 2015. Advanced Optical Materials 3, 280–320.
Gu, C., Fei, T., Yao, L., Lv, Y., Lu, D., Ma, Y., 2011. Adv. Mater. 23, 527–530.
Guérette, M., Najari, A., Maltais, J., Pouliot, J.-R., Dufresne, S., Simoneau, M., Besner,
S., Charest, P., Leclerc, M., 2016. Adv. Energy Mater. 6, n/a-n/a.
Guerlin, A., Dumur, F., Dumas, E., Miomandre, F., Wantz, G., Mayer, C.R., 2010. Org.
Lett. 12, 2382–2385.
Guihaumé, J., Clot, E., Eisenstein, O., Perutz, R.N., 2010. Dalton Trans. 39, 10510–10519.
Guillerez, S., Bidan, G., 1998. Synth. Met. 93, 123–126.
Guo, B., Guo, X., Li, W., Meng, X., Ma, W., Zhang, M., Li, Y., 2016. J. Mater. Chem. A
4, 13251–13258.
Guo, B., Zhou, W., Wu, M., Lv, J., Yu, C., Li, F., Hu, Z., 2016. J. Mater. Chem. A 4,
9644–9652.
Guo, C., Quinn, J., Sun, B., Li, Y., 2016. Polym. Chem. 7, 4515–4524.
Guo, Q., Dong, J., Wan, D., Wu, D., You, J., 2013. Macromol. Rapid Commun. 34, 522–
527.
Guo, Q., Jiang, R., Wu, D., You, J., 2016a. Macromol. Rapid Commun. 37, 794–798.
Guo, Q., Wu, D., You, J., 2016b. ChemSusChem 9, 2765–2768.
Gurau, M.C., Delongchamp, D.M., Vogel, B.M., Lin, E.K., Fischer, D.A., Sambasivan,
S., Richter, L.J., 2007. Langmuir 23, 834–842.
Han, W., Mayer, P., Ofial, A.R., 2011. Angew. Chem. Int. Ed. 50, 2178–2182.
Harder, S., Feil, F., 2002. Organometallics 21, 2268–2274.
399
Harpham, M.R., Süzer, Ö., Ma, C.-Q., Bäuerle, P., Goodson, T., 2009. J. Am. Chem. Soc.
131, 973–979.
Harris, J.R., Roos, C., Djalali, R., Rheingans, O., Maskos, M., Schmidt, M., 1999. Micron
30, 289–298.
Hasell, T., Wood, C.D., Clowes, R., Jones, J.T.A., Khimyak, Y.Z., Adams, D.J., Cooper,
A.I., 2010. Chem. Mater. 22, 557–564.
Hassan, J., Schulz, E., Gozzi, C., Lemaire, M., 2003. J. Mol. Catal. A: Chemical 195, 125–
131.
Hayashi, S., Kojima, Y., Koizumi, T., 2015. Polym. Chem. 6, 881–885.
Hayashi, S., Kojima, Y., Koizumi, T., 2017. Polymer 113, 214–220.
Hayashi, S., Takigami, A., Koizumi, T., 2016a. ChemPlusChem 81, 930–934.
Hayashi, S., Togawa, Y., Ashida, J., Nishi, K., Asano, A., Koizumi, T., 2016b. Polymer
90, 187–192.
Hayashi, S., Togawa, Y., Kojima, Y., Koizumi, T., 2016c. Polym. Chem. 7, 5671–5686.
Hayashi, S., Yamamoto, S., Koizumi, T., 2016d. Chem. Lett. 46, 200–203.
He, C.-Y., Fan, S., Zhang, X., 2010. J. Am. Chem. Soc. 132, 12850–12852.
He, C.-Y., Min, Q.-Q., Zhang, X., 2012. Organometallics 31, 1335–1340.
He, C.-Y., Wu, C.-Z., Qing, F.-L., Zhang, X., 2014. J. Org. Chem. 79, 1712–1718.
He, G., Liu, J., Li, Y., Yang, Y., 2002. Appl. Phys. Lett. 80, 1891–1893.
He, Z., Zhong, C., Su, S., Xu, M., Wu, H., Cao, Y., 2012. Nat. Photon. 6, 593–597.
Heckmann, G., Niemeyer, M., 2000. J. Am. Chem. Soc. 122, 4227–4228.
Heeger, A.J., 1998. Solid State Commun. 107, 673–679.
Helgesen, M., Carlé, J.E., dos Reis Benatto, G.A., Søndergaard, R.R., Jørgensen, M.,
Bundgaard, E., Krebs, F.C., 2015. Adv. Energy Mater. 5, 1401996.
Hennessy, E.J., Buchwald, S.L., 2003. J. Am. Chem. Soc. 125, 12084–12085.
Heo, H., Kim, H., Lee, D., Jang, S., Ban, L., Lim, B., Lee, J., Lee, Y., 2016.
Macromolecules 49, 3328–3335.
Herrmann, W.A., Brossmer, C., Öfele, K., Reisinger, C.-P., Priermeier, T., Beller, M.,
Fischer, H., 1995. Angew. Chem., Int. Ed. 34, 1844–1848.
Heyer, E., Retailleau, P., Ziessel, R., 2014. Org. Lett. 16, 2330–2333.
Higashihara, T., Goto, E., Ueda, M., 2012. 167–170.
Hollinger, J., Jahnke, A.A., Coombs, N., Seferos, D.S., 2010. J. Am. Chem. Soc. 132,
8546–8547.
Honda, S., Ohkita, H., Benten, H., Ito, S., 2010. Chem. Commun. 46, 6596–6598.
Honda, S., Ohkita, H., Benten, H., Ito, S., 2011a. Adv. Energy Mater. 1, 588–598.
Honda, S., Yokoya, S., Ohkita, H., Benten, H., Ito, S., 2011b. J. Phys. Chem. C 115,
11306–11317.
Horie, M., Shen, I.-W., Tuladhar, S.M., Leventis, H., Haque, S.A., Nelson, J., Saunders,
B.R., Turner, M.L., 2010. Polymer 51, 1541–1547.
Horowitz, G., 1998. Adv. Mater. 10, 365–377.
Hoth, C.N., Choulis, S.A., Schilinsky, P., Brabec, C.J., 2009. J. Mater. Chem. 19.
Howard, J.B., Ekiz, S., Cuellar De Lucio, A.J., Thompson, B.C., 2016. Macromolecules
49, 6360–6367.
Howard, J.B., Noh, S., Beier, A.E., Thompson, B.C., 2015. ACS Macro Lett. 4, 725–730.
Hu, L., Han, J., Qiao, W., Wang, Z.Y., 2016. Polymer 99, 427–433.
400
Hu, X., Fu, W., Zuo, L., Shi, H., Chen, M., Liu, S., Pan, J., Fu, L., Shi, M., Chen, H., 2013.
Tetrahedron 69, 3419–3424.
Hu, X., Zuo, L., Fu, W., Larsen-Olsen, T.T., Helgesen, M., Bundgaard, E., Hagemann, O.,
Shi, M., Krebs, F.C., Chen, H., 2012. J. Mater. Chem. 22, 15710–15716.
Huang, J., Li, G., Wu, E., Xu, Q., Yang, Y., 2006. Adv. Mater. 18, 114–117.
Huang, J., Wang, K., Gupta, S., Wang, G., Yang, C., Mushrif, S.H., Wang, M., 2016. J.
Polym. Sci. Part A: Polym. Chem. 54, 2015–2031.
Huang, J.-H., Yang, C.-Y., Ho, Z.-Y., Kekuda, D., Wu, M.-C., Chien, F.-C., Chen, P.,
Chu, C.-W., Ho, K.-C., 2009. Organic Electronics 10, 27–33.
Huang, S., Kannadorai, R.K., Chen, Y., Liu, Q., Wang, M., 2015. Chem. Commun. 51,
4223–4226.
Huang, S., Upputuri, P.K., Liu, H., Pramanik, M., Wang, M., 2016. J. Mater. Chem. B 4,
1696–1703.
Huang, W., Gann, E., Chandrasekaran, N., Prasad, S.K.K., Chang, S.-Y., Thomsen, L.,
Kabra, D., Hodgkiss, J.M., Cheng, Y.-B., Yang, Y., McNeill, C.R., 2017. Adv.
Energy Mater. n/a-n/a.
Huang, X., Zhang, G., Zhou, C., Liu, L., Jin, Y., Liu, S., Ying, L., Huang, F., Cao, Y.,
2015. Polym. Chem. 6, 4154–4161.
Huang, Y., Zheng, N., Wang, Z., Ying, L., Huang, F., Cao, Y., 2017. Chemical
Communications 53, 1997–2000.
Huckett, S.C., Miller, L.L., Jacobson, R.A., Angelici, R.J., 1988. Organometallics 7, 686–
691.
Iitsuka, T., Schaal, P., Hirano, K., Satoh, T., Bolm, C., Miura, M., 2013. J. Org. Chem.
Iizuka, E., Wakioka, M., Ozawa, F., 2016. Macromolecules 49, 3310–3317.
Ilangovan, A., Satish, G., 2013. Org. Lett.
Iraqi, A., Barker, G.W., 1998. J. Mater. Chem. 8, 25–29.
Irvin, D.J., Jr, C.J.D., Reynolds, J.R., 1999. Chem. Commun. 2121–2122.
Islam, M.N., Mazhari, B., 2008. Comparison of top and bottom-contact organic thin film
transistors for analog circuit applications, in: 2008 IEEE International Conference on
Electron Devices and Solid-State Circuits. Presented at the 2008 IEEE International
Conference on Electron Devices and Solid-State Circuits, pp. 1–4.
Ito, M., Kubo, H., Itani, I., Morimoto, K., Dohi, T., Kita, Y., 2013. J. Am. Chem. Soc.
135, 14078–14081.
Jackson, C.L., Chanzy, H.D., Booy, F.P., Drake, B.J., Tomalia, D.A., Bauer, B.J., Amis,
E.J., 1998. Macromolecules 31, 6259–6265.
Jakubiak, R., Bao, Z., Rothberg, L., 2000. Synth. Met. 114, 61–64.
Jeffery, T., 1996. Tetrahedron 52, 10113–10130.
Jeffries-El, M., Sauvé, G., McCullough, R.D., 2005. Macromolecules 38, 10346–10352.
Jenkins, I.H., Salzner, U., Pickup, P.G., 1996. Chem. Mater. 8, 2444–2450.
Jensen, J., Dam, H.F., Reynolds, J.R., Dyer, A.L., Krebs, F.C., 2012. J. Polym. Sci., Part
B: Polym. Phys. 50, 536–545.
Jensen, J., Madsen, M.V., Krebs, F.C., 2013. Journal of Materials Chemistry C 1, 4826–
4835.
Jia, P., Argun, A.A., Xu, J., Xiong, S., Ma, J., Hammond, P.T., Lu, X., 2009. Chem. Mater.
21, 4434–4441.
Jiang, M., Huang, T., Xie, J., 1995. Macromol. Chem. Phys. 196, 803–813.
401
Jin, S.-H., Park, H.-J., Kim, J.Y., Lee, K., Lee, S.-P., Moon, D.-K., Lee, H.-J., Gal, Y.-S.,
2002. Macromolecules 35, 7532–7534.
Jin, W., Wong, W.-T., Law, G.-L., 2014. ChemCatChem n/a-n/a.
Jo, J., Pron, A., Berrouard, P., Leong, W.L., Yuen, J.D., Moon, J.S., Leclerc, M., Heeger,
A.J., 2012. Adv. Energy Mater. 2, 1397–1403.
Jo, W.H., Park, S.J., Kwon, I.H., 1992. Polym. Int. 29, 173–178.
Johansson, E.M.J., Yartsev, A., Rensmo, H., Sundström, V., 2009. J. Phys. Chem. C 113,
3014–3020.
Joshi, S., Grigorian, S., Pietsch, U., 2008. Phys. Status Solidi A 205, 488–496.
Ju, L., Yao, J., Wu, Z., Liu, Z., Zhang, Y., 2013. J. Org. Chem.
Jung, J.W., Liu, F., Russell, T.P., Jo, W.H., 2013. Energy Environ. Sci. 6, 3301–3307.
Jurow, M.J., Mayr, C., Schmidt, T.D., Lampe, T., Djurovich, P.I., Brütting, W.,
Thompson, M.E., 2016. Nat Mater 15, 85–91.
Kabra, D., Lu, L.P., Song, M.H., Snaith, H.J., Friend, R.H., 2010. Adv. Mater. 22, 3194–
3198.
Kanbara, T., Kuwabara, J., Lu, W., 2014. IOP Conf. Ser.: Mater. Sci. Eng. 54.
Kang, I., Yun, H.-J., Chung, D.S., Kwon, S.-K., Kim, Y.-H., 2013. J. Am. Chem. Soc.
135, 14896–14899.
Kang, T.E., Choi, J., Cho, H.-H., Yoon, S.C., Kim, B.J., 2016. Macromolecules 49, 2096–
2105.
Kang, T.E., Kim, K.-H., Kim, B.J., 2014. J. Mater. Chem. A 2, 15252–15267.
Kanimozhi, C., Yaacobi-Gross, N., Chou, K.W., Amassian, A., Anthopoulos, T.D., Patil,
S., 2012. J. Am. Chem. Soc. 134, 16532–16535.
Kapdi, A., 2013. Dalton Transactions.
Karakawa, M., Ie, Y., Aso, Y., 2011. Semicond. Sci. Technol. 26.
Kawano, T., Yoshizumi, T., Hirano, K., Satoh, T., Miura, M., 2009. Org. Lett. 11, 3072–
3075.
Kerszulis, J.A., Amb, C.M., Dyer, A.L., Reynolds, J.R., 2014. Macromolecules 47, 5462–
5469.
Kettle, J., Horie, M., Majewski, L.A., Saunders, B.R., Tuladhar, S., Nelson, J., Turner,
M.L., 2011. Solar Energy Materials and Solar Cells, Photovoltaics, Solar Energy
Materials & Thin Films, IMRC 2009-Cancun 95, 2186–2193.
Khan, M.T., Bhargav, R., Kaur, A., Dhawan, S.K., Chand, S., 2010. Thin Solid Films,
Biomolecular Electronics and Organic Nanotechnology for Environmental
Preservation 519, 1007–1011.
Khan, Z.U., Edberg, J., Hamedi, M.M., Gabrielsson, R., Granberg, H., Wågberg, L.,
Engquist, I., Berggren, M., Crispin, X., 2016. Adv. Mater. 28, 4556–4562.
Khlyabich, P.P., Burkhart, B., Ng, C.F., Thompson, B.C., 2011a. Macromolecules 44,
5079–5084.
Khlyabich, P.P., Burkhart, B., Rudenko, A.E., Thompson, B.C., 2013. Polymer 54, 5267–
5298.
Khlyabich, P.P., Burkhart, B., Thompson, B.C., 2011b. J. Am. Chem. Soc. 133, 14534–
14537.
Khlyabich, P.P., Burkhart, B., Thompson, B.C., 2012. J. Am. Chem. Soc. 134, 9074–9077.
Khlyabich, P.P., Rudenko, A.E., Burkhart, B., Thompson, B.C., 2015a. ACS Appl. Mater.
Interfaces 7, 2322–2330.
402
Khlyabich, P.P., Rudenko, A.E., Street, R.A., Thompson, B.C., 2014a. ACS Appl. Mater.
Interfaces 6, 9913–9919.
Khlyabich, P.P., Rudenko, A.E., Thompson, B.C., 2014b. J. Polym. Sci. A Polym. Chem.
52, 1055–1058.
Khlyabich, P.P., Rudenko, A.E., Thompson, B.C., Loo, Y.-L., 2015b. Adv. Funct. Mater.
25, 5557–5563.
Kim, A., Lee, D.H., Um, H.A., Shin, J., Cho, M.J., Choi, D.H., 2015. Polym. Chem. 6,
5478–5486.
Kim, H., Lee, B.H., Lee, K.C., Kim, G., Yu, J.Y., Kim, N., Lee, S.H., Lee, K., 2013. Adv.
Energy Mater. 3, 1575–1580.
Kim, H.J., 2009. SPIE Newsroom.
Kim, H.J., Kim, J.-J., Lee, H.H., n.d. X-ray measurement of real-time variations at an
organic interface | SPIE Homepage: SPIE [WWW Document]. URL
http://spie.org/newsroom/1680-x-ray-measurement-of-real-time-variations-at-an-
organic-interface (accessed 2.20.17).
Kim, H.J., Lee, H.H., Kim, J.-J., 2009. Real time measurement of the structural change in
P3HT:PCBM thin films and the relation with device performance in OPV cells, in:
Kafafi, Z.H., Lane, P.A. (Eds.), . p. 74160O.
Kim, J.H., An, B.-K., Yoon, S.-J., Park, S.K., Kwon, J.E., Lim, C.-K., Park, S.Y., 2014.
Adv. Funct. Mater. 24, 2746–2753.
Kim, J.S., Lee, Y., Lee, J.H., Park, J.H., Kim, J.K., Cho, K., 2010. Adv. Mater. 22, 1355–
1360.
Kim, N.-K., Jang, S.-Y., Pace, G., Caironi, M., Park, W.-T., Khim, D., Kim, J., Kim, D.-
Y., Noh, Y.-Y., 2015. Chem. Mater. 27, 8345–8353.
Kim, Y., Cook, S., Kirkpatrick, J., Nelson, J., Durrant, J.R., Bradley, D.D.C., Giles, M.,
Heeney, M., Hamilton, R., McCulloch, I., 2007. J. Phys. Chem. C 111, 8137–8141.
Kim, Y., Cook, S., Tuladhar, S.M., Choulis, S.A., Nelson, J., Durrant, J.R., Bradley,
D.D.C., Giles, M., McCulloch, I., Ha, C.-S., Ree, M., 2006. Nat. Mater. 5, 197–203.
Kim, Y., Shin, M., Kim, H., Ha, Y., Ha, C.-S., 2008. J. Phys. D: Appl. Phys. 41, 225101.
Kiriy, A., Senkovskyy, V., Sommer, M., 2011. Macromol. Rapid Commun. 32, 1503–
1517.
Kitahara, M., Umeda, N., Hirano, K., Satoh, T., Miura, M., 2011. J. Am. Chem. Soc. 133,
2160–2162.
Ko, S.-J., Lee, W., Choi, H., Walker, B., Yum, S., Kim, S., Shin, T.J., Woo, H.Y., Kim,
J.Y., 2015. Adv. Energy Mater. 5, n/a-n/a.
Koch, F.P.V., Smith, P., Heeney, M., 2013. J. Am. Chem. Soc. 135, 13695–13698.
Kohn, P., Huettner, S., Komber, H., Senkovskyy, V., Tkachov, R., Kiriy, A., Friend, R.H.,
Steiner, U., Huck, W.T.S., Sommer, J.-U., Sommer, M., 2012. J. Am. Chem. Soc.
134, 4790–4805.
Kojima, Y., Hayashi, S., Koizumi, T., 2017. J. Polym. Sci. Part A: Polym. Chem. 55,
1183–1188.
Kokil, A., Yang, K., Kumar, J., 2012. J. Polym. Sci. B Polym. Phys. 50, 1130–1144.
Kola, S., Kim, J.H., Ireland, R., Yeh, M.-L., Smith, K., Guo, W., Katz, H.E., 2013. ACS
Macro Lett. 2, 664–669.
Koo, B., Sletten, E.M., Swager, T.M., 2015. Macromolecules 48, 229–235.
403
Koppe, M., Egelhaaf, H.-J., Clodic, E., Morana, M., Lüer, L., Troeger, A., Sgobba, V.,
Guldi, D.M., Ameri, T., Brabec, C.J., 2013. Adv. Energy Mater. 3, 949–958.
Koppolu, V.R., Gupta, M.C., Bagienski, W., Shen, Y., Shu, C., Gibson, H.W., Dorn, H.C.,
2009. Organic solar cells with a blend of two solution processable electron acceptors,
C60(CN)2 and PCBM, in: 2009 34th IEEE Photovoltaic Specialists Conference
(PVSC). Presented at the 2009 34th IEEE Photovoltaic Specialists Conference
(PVSC), pp. 001252–001257.
Korenaga, T., Suzuki, N., Sueda, M., Shimada, K., 2015. Journal of Organometallic
Chemistry 780, 63–69.
Kotlarski, J.D., Moet, D.J.D., Blom, P.W.M., 2011. J. Polym. Sci., Part B: Polym. Phys.
49, 708–711.
Kotowski, D., Luzzati, S., Bianchi, G., Calabrese, A., Pellegrino, A., Po, R., Schimperna,
G., Tacca, A., 2013. J. Mater. Chem. A 1, 10736–10744.
Kowalski, S., Allard, S., Scherf, U., 2012. ACS Macro Lett. 1, 465–468.
Kowalski, S., Allard, S., Zilberberg, K., Riedl, T., Scherf, U., 2013. Progress in Polymer
Science, Topical issue on Conductive Polymers 38, 1805–1814.
Krasovskiy, A., Krasovskaya, V., Knochel, P., 2006. Angew. Chem., Int. Ed. 45, 2958–
2961.
Krebs, F.C., 2009. Sol. Energ. Mat. Sol. Cells, Processing and Preparation of Polymer and
Organic Solar Cells 93, 394–412.
Krebs, F.C., Fyenbo, J., Tanenbaum, D.M., Gevorgyan, S.A., Andriessen, R., van
Remoortere, B., Galagan, Y., Jørgensen, M., 2011. Energy Environ. Sci. 4, 4116–
4123.
Krebs, F.C., Gevorgyan, S.A., Gholamkhass, B., Holdcroft, S., Schlenker, C., Thompson,
M.E., Thompson, B.C., Olson, D., Ginley, D.S., Shaheen, S.E., Alshareef, H.N.,
Murphy, J.W., Youngblood, W.J., Heston, N.C., Reynolds, J.R., Jia, S., Laird, D.,
Tuladhar, S.M., Dane, J.G.A., Atienzar, P., Nelson, J., Kroon, J.M., Wienk, M.M.,
Janssen, R.A.J., Tvingstedt, K., Zhang, F., Andersson, M., Inganäs, O., Lira-Cantu,
M., de Bettignies, R., Guillerez, S., Aernouts, T., Cheyns, D., Lutsen, L.,
Zimmermann, B., Würfel, U., Niggemann, M., Schleiermacher, H.-F., Liska, P.,
Grätzel, M., Lianos, P., Katz, E.A., Lohwasser, W., Jannon, B., 2009. Sol. Energ.
Mat. Sol. Cells 93, 1968–1977.
Krebs, F.C., Nielsen, T.D., Fyenbo, J., Wadstrøm, M., Pedersen, M.S., 2010. Energy
Environ. Sci. 3, 512–525.
Krebs, F.C., Nyberg, R.B., Jørgensen, M., 2004. Chem. Mater. 16, 1313–1318.
Kularatne, R.S., Magurudeniya, H.D., Sista, P., Biewer, M.C., Stefan, M.C., 2013. J.
Polym. Sci. A Polym. Chem. 51, 743–768.
Kumada, T., Nohara, Y., Kuwabara, J., Kanbara, T., 2015. BCSJ 88, 1530–1535.
Kumar, Anshu, Kumar, Anil, 2010. Polym. Chem. 1, 286–288.
Kuramochi, M., Kuwabara, J., Lu, W., Kanbara, T., 2014. Macromolecules 47, 7378–
7385.
Kuwabara, J., Fujie, Y., Maruyama, K., Yasuda, T., Kanbara, T., 2016a. Macromolecules
49, 9388–9395.
Kuwabara, J., Kuramochi, M., Liu, S., Yasuda, T., Kanbara, T., 2017. Polym J 49, 123–
131.
404
Kuwabara, J., Nohara, Y., Choi, S.J., Fujinami, Y., Lu, W., Yoshimura, K., Oguma, J.,
Suenobu, K., Kanbara, T., 2013. Polym. Chem. 4, 947–953.
Kuwabara, J., Takase, N., Yasuda, T., Kanbara, T., 2016b. J. Polym. Sci. Part A: Polym.
Chem. 54, 2337–2345.
Kuwabara, J., Yasuda, T., Choi, S.J., Lu, W., Yamazaki, K., Kagaya, S., Han, L., Kanbara,
T., 2014. Adv. Funct. Mater. 24, 3226–3233.
Kuwabara, J., Yasuda, T., Takase, N., Kanbara, T., 2016c. ACS Appl. Mater. Interfaces
8, 1752–1758.
Lafrance, M., Fagnou, K., 2006a. J. Am. Chem. Soc. 128, 16496–16497.
Lafrance, M., Fagnou, K., 2006b. J. Am. Chem. Soc. 128, 16496–16497.
Lafrance, M., Lapointe, D., Fagnou, K., 2008. Tetrahedron, Catalytic Aromatic C-H
Activation 64, 6015–6020.
Lafrance, M., Rowley, C.N., Woo, T.K., Fagnou, K., 2006. J. Am. Chem. Soc. 128, 8754–
8756.
Lai, Y.-Y., Tung, T.-C., Liang, W.-W., Cheng, Y.-J., 2015. Macromolecules 48, 2978–
2988.
Lane, B.S., Brown, M.A., Sames, D., 2005. J. Am. Chem. Soc. 127, 8050–8057.
Lanke, V., Ramaiah Prabhu, K., 2013. Org. Lett.
Lanni, E.L., McNeil, A.J., 2009. J. Am. Chem. Soc. 131, 16573–16579.
Lanni, E.L., McNeil, A.J., 2010. Macromolecules 43, 8039–8044.
Lapointe, D., Fagnou, K., 2010. Chem. Lett. 39, 1118–1126.
Larsson, P.-F., Correa, A., Carril, M., Norrby, P.-O., Bolm, C., 2009. Angew. Chem. Int.
Ed. 121, 5801–5803.
Lavenot, L., Gozzi, C., Ilg, K., Orlova, I., Penalva, V., Lemaire, M., 1998. Journal of
Organometallic Chemistry 567, 49–55.
Lee, C., Yang, W., Parr, R.G., 1988. Phys. Rev. B 37, 785–789.
Lee, H.-J., Lee, B.R., Choi, S.-W., Song, M.H., 2012. Optics Express 20, 24472.
Lee, J., Chen, H.-F., Batagoda, T., Coburn, C., Djurovich, P.I., Thompson, M.E., Forrest,
S.R., 2016. Nat Mater 15, 92–98.
Lee, J., Han, A.-R., Kim, J., Kim, Y., Oh, J.H., Yang, C., 2012. J. Am. Chem. Soc. 134,
20713–20721.
Lee, J.-I., Klaerner, G., Miller, R.D., 1999. Chem. Mater. 11, 1083–1088.
Lee, J.Y., Jo, J.W., Jo, W.H., n.d. Org. Electron.
Lee, Y.-S., Lee, J.Y., Bang, S.-M., Lim, B., Lee, J., Na, S.-I., 2016. J. Mater. Chem. A 4,
11439–11445.
Lei, T., Dou, J.-H., Cao, X.-Y., Wang, J.-Y., Pei, J., 2013. J. Am. Chem. Soc. 135, 12168–
12171.
Leong, W.L., Cowan, S.R., Heeger, A.J., 2011. Adv. Energy Mater. 1, 517–522.
Leong, W.L., Welch, G.C., Kaake, L.G., Takacs, C.J., Sun, Y., Bazan, G.C., Heeger, A.J.,
2012. Chem. Sci. 3, 2103–2109.
Lewis, N.S., Nocera, D.G., 2006. PNAS 103, 15729–15735.
Li, B., Darcel, C., Dixneuf, P.H., 2013. ChemCatChem n/a-n/a.
Li, G., Shrotriya, V., Huang, J., Yao, Y., Moriarty, T., Emery, K., Yang, Y., 2005. Nat.
Mater. 4, 864–868.
Li, G., Zhu, R., Yang, Y., 2012. Nat. Photon. 6, 153–161.
405
Li, J., Liu, J., Wei, C.-W., Liu, B., O’Donnell, M., Gao, X., 2013. Phys. Chem. Chem.
Phys. 15, 17006–17015.
Li, J., Ong, K.-H., Lim, S.-L., Ng, G.-M., Tan, H.-S., Chen, Z.-K., 2011. Chem. Commun.
47, 9480–9482.
Li, J., Zhao, Y., Tan, H.S., Guo, Y., Di, C.-A., Yu, G., Liu, Y., Lin, M., Lim, S.H., Zhou,
Y., Su, H., Ong, B.S., 2012. Scientific Reports 2, srep00754.
Li, K., Khlyabich, P.P., Li, L., Burkhart, B., Thompson, B.C., Campbell, J.C., 2013. J.
Phys. Chem. C 117, 6940–6948.
Li, K., Li, L., Khlyabich, P.P., Burkhart, B., Sun, W., Lu, Z., Thompson, B.C., Campbell,
J.C., 2014. Journal of Applied Physics 115, 223104.
Li, N.-N., Zhang, Y.-L., Mao, S., Gao, Y.-R., Guo, D.-D., Wang, Y.-Q., 2014. Org. Lett.
Li, P., Chai, Z., Zhao, G., Zhu, S.-Z., 2009. Tetrahedron 65, 1673–1678.
Li, S., Ye, L., Zhao, W., Zhang, S., Mukherjee, S., Ade, H., Hou, J., 2016. Adv. Mater.
DOI: 10.1002/adma.201602776.
Li, W., An, Y., Wienk, M.M., Janssen, R.A.J., 2015a. J. Mater. Chem. A.
Li, Weishuo, Guo, Y., Shi, J., Yu, H., Meng, H., 2016. Macromolecules 49, 7211–7219.
Li, W., Hendriks, K.H., Furlan, A., Wienk, M.M., Janssen, R.A.J., 2015b. J. Am. Chem.
Soc. 137, 2231–2234.
Li, Weiwei, Hendriks, K.H., Wienk, M.M., Janssen, R.A.J., 2016. Acc. Chem. Res. 49,
78–85.
Li, W., Roelofs, W.S.C., Turbiez, M., Wienk, M.M., Janssen, R.A.J., 2014. Adv. Mater.
26, 3304–3309.
Li, Y., Tatum, W.K., Onorato, J.W., Barajas, S.D., Yang, Y.Y., Luscombe, C.K., 2017.
Polym. Chem.
Liang, J., Zhao, S., Jiang, X.-F., Guo, T., Yip, H.-L., Ying, L., Huang, F., Yang, W., Cao,
Y., 2016. ACS Appl. Mater. Interfaces 8, 6164–6173.
Liégault, B., Petrov, I., Gorelsky, S.I., Fagnou, K., 2010. J. Org. Chem. 75, 1047–1060.
Lilliu, S., Agostinelli, T., Pires, E., Hampton, M., Nelson, J., Macdonald, J.E., 2011.
Macromolecules 44, 2725–2734.
Lim, J., Chong, M.S.K., Teo, E.Y., Chen, G.-Q., Chan, J.K.Y., Teoh, S.-H., 2013. J.
Biomed. Mater. Res. 101B, 752–761.
Lim, K.-G., Choi, M.-R., Kim, J.-H., Kim, D.H., Jung, G.H., Park, Y., Lee, J.-L., Lee, T.-
W., 2014. ChemSusChem 7, 1125–1132.
Lin, S., Herbert, D.E., Velian, A., Day, M.W., Agapie, T., 2013. J. Am. Chem. Soc.
Lin, Y., Zhao, F., He, Q., Huo, L., Wu, Y., Parker, T.C., Ma, W., Sun, Y., Wang, C., Zhu,
D., Heeger, A.J., Marder, S.R., Zhan, X., 2016. J. Am. Chem. Soc. 138, 4955–4961.
Liu, C., Yuan, J., Gao, M., Tang, S., Li, W., Shi, R., Lei, A., 2015. Chem. Rev. 115,
12138–12204.
Liu, D., Liu, C., Li, H., Lei, A., 2013. Angew. Chem. Int. Ed. 52, 4453–4456.
Liu, D.-P., Chen, Q., Zhao, Y.-C., Zhang, L.-M., Qi, A.-D., Han, B.-H., 2013. ACS Macro
Lett. 2, 522–526.
Liu, H., Shi, G., Pan, S., Jiang, Y., Zhang, Y., 2013. Org. Lett.
Liu, H.-W., Chang, D.-Y., Chiu, W.-Y., Rwei, S.-P., Wang, L., 2012. J. Mater. Chem. 22,
15586–15591.
Liu, K., Larsen-Olsen, T.T., Lin, Y., Beliatis, M., Bundgaard, E., Jørgensen, M., Krebs,
F.C., Zhan, X., 2016. J. Mater. Chem. A 4, 1044–1051.
406
Liu, L., Wang, Z., Zhang, H., Wang, W., Zhang, J., Tang, Y., 2015. Chem. Commun.
Liu, P.M., Frost, C.G., 2013. Org. Lett.
Liu, S.-Y., Fu, W.-F., Xu, J.-Q., Fan, C.-C., Jiang, H., Shi, M., Li, H.-Y., Chen, J.-W.,
Yong Cao, Chen, H.-Z., 2014a. Nanotechnology 25, 014006.
Liu, S.-Y., Li, H.-Y., Shi, M.-M., Jiang, H., Hu, X.-L., Li, W.-Q., Fu, L., Chen, H.-Z.,
2012. Macromolecules 45, 9004–9009.
Liu, S.-Y., Liu, W.-Q., Xu, J.-Q., Fan, C.-C., Fu, W.-F., Ling, J., Wu, J.-Y., Shi, M.-M.,
Jen, A.K.-Y., Chen, H.-Z., 2014b. ACS Appl. Mater. Interfaces 6, 6765–6775.
Liu, W., Cao, H., Lei, A., 2010. Angew. Chem. Int. Ed. 122, 2048–2052.
Liu, X.-W., Shi, J.-L., Yan, J.-X., Wei, J.-B., Peng, K., Dai, L., Li, C.-G., Wang, B.-Q.,
Shi, Z.-J., 2013. Org. Lett.
Livendahl, M., Echavarren, A.M., 2010. Isr. J. Chem. 50, 630–651.
Livi, F., Gobalasingham, N.S., Bundgaard, E., Thompson, B.C., 2015. J. Polym. Sci. A
Polym. Chem. 53, 2598–2605.
Lizin, S., Van Passel, S., De Schepper, E., Vranken, L., 2012. Solar Energy Materials and
Solar Cells 103, 1–10.
Lo, C.-T., Chou, P.-W., 2014. J. Phys. Chem. B 118, 12763–12771.
Loewe, R.S., Ewbank, P.C., Liu, J., Zhai, L., McCullough, R.D., 2001. Macromolecules
34, 4324–4333.
Lohwasser, R.H., Thelakkat, M., 2011. Macromolecules 44, 3388–3397.
Lombeck, F., Di, D., Yang, L., Meraldi, L., Athanasopoulos, S., Credgington, D., Sommer,
M., Friend, R.H., 2016a. Macromolecules 49, 9382–9387.
Lombeck, F., Komber, H., Fazzi, D., Nava, D., Kuhlmann, J., Stegerer, D., Strassel, K.,
Brandt, J., de Zerio Mendaza, A.D., Müller, C., Thiel, W., Caironi, M., Friend, R.,
Sommer, M., 2016b. Adv. Energy Mater. 6, 1601232.
Lombeck, F., Matsidik, R., Komber, H., Sommer, M., 2015. Macromol. Rapid Commun.
36, 231–237.
López, L.A., López, E., 2015. Dalton Trans.
Lotz, M.D., Camasso, N.M., Canty, A.J., Sanford, M.S., 2017. Organometallics 36, 165–
171.
Lu, W., Kuwabara, J., Iijima, T., Higashimura, H., Hayashi, H., Kanbara, T., 2012a.
Macromolecules 45, 4128–4133.
Lu, W., Kuwabara, J., Kanbara, T., 2011. Macromolecules 44, 1252–1255.
Lu, W., Kuwabara, J., Kanbara, T., 2012b. Polym. Chem. 3, 3217–3219.
Lu, W., Kuwabara, J., Kanbara, T., 2013. Macromol. Rapid Commun. 34, 1151–1156.
Lu, W., Kuwabara, J., Kuramochi, M., Kanbara, T., 2015. J. Polym. Sci. Part A: Polym.
Chem. 53, 1396–1402.
Lukose, B., Bobbili, S.V., Clancy, P., 2017. Molecular Simulation 43, 743–755.
Luo, Y., Montarnal, D., Kim, S., Shi, W., Barteau, K.P., Pester, C.W., Hustad, P.D.,
Christianson, M.D., Fredrickson, G.H., Kramer, E.J., Hawker, C.J., 2015.
Macromolecules.
Luzio, A., Fazzi, D., Nübling, F., Matsidik, R., Straub, A., Komber, H., Giussani, E.,
Watkins, S.E., Barbatti, M., Thiel, W., Gann, E., Thomsen, L., McNeill, C.R.,
Caironi, M., Sommer, M., 2014. Chem. Mater. 26, 6233–6240.
Lyons, T.W., Sanford, M.S., 2010. Chem. Rev. 110, 1147–1169.
407
Ma, W., Kim, J.Y., Lee, K., Heeger, A.J., 2007. Macromol. Rapid. Commun. 28, 1776–
1780.
Ma, W., Shi, K., Wu, Y., Lu, Z.-Y., Liu, H.-Y., Wang, J.-Y., Pei, J., 2016. ACS Appl.
Mater. Interfaces 8, 24737–24743.
Ma, W., Yang, C., Gong, X., Lee, K., Heeger, A.J., 2005. Adv. Funct. Mater. 15, 1617–
1622.
Machui, F., Rathgeber, S., Li, N., Ameri, T., Brabec, C.J., 2012. J. Mater. Chem. 22,
15570–15577.
Madsen, M.V., Gevorgyan, S.A., Pacios, R., Ajuria, J., Etxebarria, I., Kettle, J., Bristow,
N.D., Neophytou, M., Choulis, S.A., Stolz Roman, L., Yohannes, T., Cester, A.,
Cheng, P., Zhan, X., Wu, J., Xie, Z., Tu, W.-C., He, J.-H., Fell, C.J., Anderson, K.,
Hermenau, M., Bartesaghi, D., Jan Anton Koster, L., Machui, F., González-Valls, I.,
Lira-Cantu, M., Khlyabich, P.P., Thompson, B.C., Gupta, R., Shanmugam, K.,
Kulkarni, G.U., Galagan, Y., Urbina, A., Abad, J., Roesch, R., Hoppe, H., Morvillo,
P., Bobeico, E., Panaitescu, E., Menon, L., Luo, Q., Wu, Z., Ma, C., Hambarian, A.,
Melikyan, V., Hambsch, M., Burn, P.L., Meredith, P., Rath, T., Dunst, S., Trimmel,
G., Bardizza, G., Müllejans, H., Goryachev, A.E., Misra, R.K., Katz, E.A., Takagi,
K., Magaino, S., Saito, H., Aoki, D., Sommeling, P.M., Kroon, J.M., Vangerven, T.,
Manca, J., Kesters, J., Maes, W., Bobkova, O.D., Trukhanov, V.A., Paraschuk, D.Y.,
Castro, F.A., Blakesley, J., Tuladhar, S.M., Alexander Röhr, J., Nelson, J., Xia, J.,
Parlak, E.A., Tumay, T.A., Egelhaaf, H.-J., Tanenbaum, D.M., Mae Ferguson, G.,
Carpenter, R., Chen, H., Zimmermann, B., Hirsch, L., Wantz, G., Sun, Z., Singh, P.,
Bapat, C., Offermans, T., Krebs, F.C., 2014. Sol. Energ. Mat. Sol. Cells 130, 281–
290.
Maglione, C., Carella, A., Centore, R., Chávez, P., Lévêque, P., Fall, S., Leclerc, N., 2017.
Dyes and Pigments 141, 169–178.
Mandoc, M.M., Kooistra, F.B., Hummelen, J.C., Boer, B. de, Blom, P.W.M., 2007.
Applied Physics Letters 91, 263505.
Mangold, H.S., Richter, T.V., Link, S., Würfel, U., Ludwigs, S., 2012. J. Phys. Chem. B
116, 154–159.
Mao, Z., Vakhshouri, K., Jaye, C., Fischer, D.A., Fernando, R., DeLongchamp, D.M.,
Gomez, E.D., Sauvé, G., 2013. Macromolecules 46, 103–112.
Marrocchi, A., Facchetti, A., Lanari, D., Petrucci, C., Vaccaro, L., 2016. Energy Environ.
Sci. 9, 763–786.
Marrocchi, A., Lanari, D., Facchetti, A., Vaccaro, L., 2012. Energy Environ. Sci. 5, 8457–
8474.
Masui, K., Ikegami, H., Mori, A., 2004. J. Am. Chem. Soc. 126, 5074–5075.
Matsidik, R., Komber, H., Luzio, A., Caironi, M., Sommer, M., 2015a. J. Am. Chem. Soc.
137, 6705–6711.
Matsidik, R., Komber, H., Sommer, M., 2015b. ACS Macro Lett. 4, 1346–1350.
Matsidik, R., Luzio, A., Hameury, S., Komber, H., McNeill, C.R., Caironi, M., Sommer,
M., 2016. J. Mater. Chem. C 4, 10371–10380.
Matsidik, R., Martin, J., Schmidt, S., Obermayer, J., Lombeck, F., Nübling, F., Komber,
H., Fazzi, D., Sommer, M., 2015c. J. Org. Chem. 80, 980–987.
Matyjaszewski, K., Tsarevsky, N.V., 2014. J. Am. Chem. Soc. 136, 6513–6533.
Mauer, R., Kastler, M., Laquai, F., 2010. Adv. Funct. Mater. 20, 2085–2092.
408
McAfee, S.M., Cann, J.R., Josse, P., Blanchard, P., Cabanetos, C., Welch, G.C., 2016.
ACS Sustainable Chem. Eng. 4, 3504–3517.
McCullough, R.D., 1998. Adv. Mater. 10, 93–116.
McCullough, R.D., Lowe, R.D., Jayaraman, M., Anderson, D.L., 1993. J. Org. Chem. 58,
904–912.
McGlacken, G.P., Bateman, L.M., 2009. Chem. Soc. Rev. 38.
McQuade, D.T., Pullen, A.E., Swager, T.M., 2000. Chem. Rev. 100, 2537–2574.
Mercier, L.G., Aïch, B.R., Najari, A., Beaupré, S., Berrouard, P., Pron, A., Robitaille, A.,
Tao, Y., Leclerc, M., 2013. Polym. Chem. 4, 5252–5260.
Mercier, L.G., Leclerc, M., 2013. Acc. Chem. Res. 46, 1597–1605.
Mihailetchi, V.D., Xie, H.X., de Boer, B., Koster, L.J.A., Blom, P.W.M., 2006. Adv.
Funct. Mater. 16, 699–708.
Mikroyannidis, J.A., Tsagkournos, D.V., Balraju, P., Sharma, G.D., 2011. Journal of
Power Sources 196, 2364–2372.
Ming, S., Zhen, S., Lin, K., Zhao, L., Xu, J., Lu, B., 2015. ACS Appl. Mater. Interfaces 7,
11089–11098.
Misra, R., Gautam, P., Maragani, R., 2015. Tetrahedron Lett. 56, 1664–1666.
Mori, A., Sugie, A., 2008. Bulletin of the Chemical Society of Japan 81, 548–561.
Morin, P.-O., Bura, T., Sun, B., Gorelsky, S.I., Li, Y., Leclerc, M., 2015. ACS Macro Lett.
4, 21–24.
Moselage, M., Li, J., Kramm, F., Ackermann, L., 2017. Angew. Chem. Int. Ed. 56, 5341–
5344.
Müller, C., Wang, E., Andersson, L.M., Tvingstedt, K., Zhou, Y., Andersson, M.R.,
Inganäs, O., 2010. Adv. Funct. Mater. 20, 2124–2131.
Murphy, K.P., Xie, D., Thompson, K.S., Amzel, L.M., Freire, E., 1994. Proteins:
Structure, Function, and Genetics 18, 63–67.
Muto, K., Yamaguchi, J., Lei, A., Itami, K., 2013. J. Am. Chem. Soc.
Naidu, B.V.K., Park, J.S., Kim, S.C., Park, S.-M., Lee, E.-J., Yoon, K.-J., Joon Lee, S.,
Wook Lee, J., Gal, Y.-S., Jin, S.-H., 2008. Solar Energy Materials and Solar Cells
92, 397–401.
Nair, V.S., Sun, J., Qi, P., Yang, S., Liu, Z., Zhang, D., Ajayaghosh, A., 2016.
Macromolecules 49, 6334–6342.
Najari, A., Berrouard, P., Ottone, C., Boivin, M., Zou, Y., Gendron, D., Caron, W.-O.,
Legros, P., Allen, C.N., Sadki, S., Leclerc, M., 2012. Macromolecules 45, 1833–
1838.
Nakabayashi, K., Mori, H., 2013. Chem. Lett. 42, 717–718.
Nakabayashi, K., Otsuki, N., Mori, H., n.d. J. Polym. Sci. Part A: Polym. Chem. n/a-n/a.
Nakabayashi, K., Yamada, M., Mori, H., 2016. J. Polym. Sci. Part A: Polym. Chem. 54,
3151–3158.
Nakano, M., Tsurugi, H., Satoh, T., Miura, M., 2008. Org. Lett. 10, 1851–1854.
Navarro, O., Marion, N., Mei, J., Nolan, S.P., 2006. Chem. - Eur. J. 12, 5142–5148.
Negishi, E., Okukado, N., King, A.O., Van Horn, D.E., Spiegel, B.I., 1978. J. Am. Chem.
Soc. 100, 2254–2256.
Newman, S.G., Lautens, M., 2010. J. Am. Chem. Soc. 132, 11416–11417.
Nielsen, C.B., Ashraf, R.S., Schroeder, B.C., D’Angelo, P., Watkins, S.E., Song, K.,
Anthopoulos, T.D., McCulloch, I., 2012. Chem. Commun. 48, 5832–5834.
409
Nielsen, K.T., Bechgaard, K., Krebs, F.C., 2005. Macromolecules 38, 658–659.
Nielsen, T.D., Cruickshank, C., Foged, S., Thorsen, J., Krebs, F.C., 2010. Solar Energy
Materials and Solar Cells 94, 1553–1571.
Nikiforov, M.P., Lai, B., Chen, W., Chen, S., Schaller, R.D., Strzalka, J., Maser, J.,
Darling, S.B., 2013. Energy Environ. Sci. 6, 1513–1520.
Nikolka, M., Nasrallah, I., Rose, B., Ravva, M.K., Broch, K., Sadhanala, A., Harkin, D.,
Charmet, J., Hurhangee, M., Brown, A., Illig, S., Too, P., Jongman, J., McCulloch,
I., Bredas, J.-L., Sirringhaus, H., 2017. Nat Mater 16, 356–362.
Nitti, A., Po, R., Bianchi, G., Pasini, D., 2016. Molecules 22, 21.
Noh, S., Gobalasingham, N.S., Thompson, B.C., 2016. Macromolecules 49, 6835–6845.
Nohara, Y., Kuwabara, J., Yasuda, T., Han, L., Kanbara, T., 2014. J. Polym. Sci. A Polym.
Chem. 52, 1401–1407.
Nübling, F., Komber, H., Sommer, M., 2017. Macromolecules 50, 1909–1918.
Oberhumer, P.M., Huang, Y.-S., Massip, S., James, D.T., Tu, G., Albert-Seifried, S.,
Beljonne, D., Cornil, J., Kim, J.-S., Huck, W.T.S., Greenham, N.C., Hodgkiss, J.M.,
Friend, R.H., 2011. The Journal of Chemical Physics 134, 114901.
Odani, R., Hirano, K., Satoh, T., Miura, M., 2013. J. Org. Chem.
Ohta, A., late) Yasuo Akita, (the, Ohkuwa, T., Chiba, M., Fukunaga, R., Miyafuji, A.,
Nakata, T., Tani, N., Aoyagi, Y., 1990. Heterocycles 31, 1951.
Okamoto, K., Housekeeper, J.B., Michael, F.E., Luscombe, C.K., 2013a. Polym. Chem.
4, 3499–3506.
Okamoto, K., Zhang, J., Housekeeper, J.B., Marder, S.R., Luscombe, C.K., 2013b.
Macromolecules 46, 8059–8078.
Okazawa, T., Satoh, T., Miura, M., Nomura, M., 2002. J. Am. Chem. Soc. 124, 5286–
5287.
Osaka, I., McCullough, R.D., 2008. Acc. Chem. Res. 41, 1202–1214.
Osedach, T.P., Andrew, T.L., Bulović, V., 2013. Energy Environ. Sci. 6, 711–718.
Oshima, T., Yamanaka, I., Kumar, A., Yamaguchi, J., Nishiwaki-Ohkawa, T., Muto, K.,
Kawamura, R., Hirota, T., Yagita, K., Irle, S., Kay, S.A., Yoshimura, T., Itami, K.,
2015. Angew. Chem. Int. Ed. n/a-n/a.
Österholm, A.M., Shen, D.E., Kerszulis, J.A., Bulloch, R.H., Kuepfert, M., Dyer, A.L.,
Reynolds, J.R., 2015. ACS Appl. Mater. Interfaces 7, 1413–1421.
Ottone, C., Berrouard, P., Louarn, G., Beaupré, S., Gendron, D., Zagorska, M., Rannou,
P., Najari, A., Sadki, S., Leclerc, M., Pron, A., 2012. Polym. Chem. 3, 2355–2365.
Ouattara, M.P., Lenfant, S., Vuillaume, D., Pézolet, M., Rioux-Dubé, J.-F., Brisson, J.,
Leclerc, M., 2013. Macromolecules 46, 6408–6418.
Palaniappan, K., Murphy, J.W., Khanam, N., Horvath, J., Alshareef, H., Quevedo-Lopez,
M., Biewer, M.C., Park, S.Y., Kim, M.J., Gnade, B.E., Stefan, M.C., 2009.
Macromolecules 42, 3845–3848.
Palermo, E.F., McNeil, A.J., 2012. Macromolecules 45, 5948–5955.
Pammer, F., Passlack, U., 2014. ACS Macro Lett. 3, 170–174.
Pan, C., Sugiyasu, K., Takeuchi, M., 2014. Chem. Commun. 50, 11814–11817.
Pantelic, R.S., Suk, J.W., Hao, Y., Ruoff, R.S., Stahlberg, H., 2011. Nano Lett. 11, 4319–
4323.
Parella, R., Gopalakrishnan, B., Babu, S.A., 2013. J. Org. Chem.
Parisien, M., Valette, D., Fagnou, K., 2005. J. Org. Chem. 70, 7578–7584.
410
Park, I., Lim, Y., Noh, S., Lee, D., Meister, M., Amsden, J.J., Laquai, F., Lee, C., Yoon,
D.Y., 2011. Organic Electronics 12, 424–428.
Park, J.H., Jung, E.H., Jung, J.W., Jo, W.H., 2013. Adv. Mater. 25, 2583–2588.
Park, J.K., Jo, J., Seo, J.H., Moon, J.S., Park, Y.D., Lee, K., Heeger, A.J., Bazan, G.C.,
2011. Adv. Mater. 23, 2430–2435.
Park, S.H., Roy, A., Beaupré, S., Cho, S., Coates, N., Moon, J.S., Moses, D., Leclerc, M.,
Lee, K., Heeger, A.J., 2009. Nat Photon 3, 297–302.
Paul, D.R., Barlow, J.W., 1980. Journal of Macromolecular Science, Part C 18, 109–168.
Payne, A.-J., C. Welch, G., 2017. Organic & Biomolecular Chemistry 15, 3310–3319.
Peet, J., Tamayo, A.B., Dang, X.-D., Seo, J.H., Nguyen, T.-Q., 2008. Applied Physics
Letters 93, 163306.
Pehk, T., Kiirend, E., Lippmaa, E., Ragnarsson, U., 1996. Journal of the Chemical Society,
Perkin Transactions 2.
Pellet-Rostaing, S., Regnouf-de-Vains, J.-B., Lamartine, R., 1996. Tetrahedron Letters 37,
5889–5892.
Penalva, V., Hassan, J., Lavenot, L., Gozzi, C., Lemaire, M., 1998. Tetrahedron Lett. 39,
2559–2560.
Phipps, R.J., Gaunt, M.J., 2009. Science 323, 1593–1597.
Phipps, R.J., Grimster, N.P., Gaunt, M.J., 2008. J. Am. Chem. Soc. 130, 8172–8174.
Pieber, B., Cantillo, D., Kappe, C.O., 2012. Chem. - Eur. J. 18, 5047–5055.
Piera, J., Bäckvall, J.-E., 2008. Angewandte Chemie International Edition 47, 3506–3523.
Pivsa-Art, S., Satoh, T., Kawamura, Y., Miura, M., Nomura, M., 1998. BCSJ 71, 467–
473.
Poduval, M.K., Burrezo, P.M., Casado, J., López Navarrete, J.T., Ortiz, R.P., Kim, T.-H.,
2013. Macromolecules 46, 9220–9230.
Poelking, C., Andrienko, D., 2013. Macromolecules 46, 8941–8956.
Politis, J.K., Nemes, J.C., Curtis, D.M., 2001. J. Am. Chem. Soc. 123, 2537–2547.
Ponder, J.F., Österholm, A.M., Reynolds, J.R., 2016. Macromolecules 49, 2106–2111.
Pouliot, J.-R., Grenier, F., Blaskovits, J.T., Beaupré, S., Leclerc, M., 2016a. Chem. Rev.
116, 14225–14274.
Pouliot, J.-R., Mercier, L.G., Caron, S., Leclerc, M., 2013. Macromol. Chem. Phys. 214,
453–457.
Pouliot, J.-R., Sun, B., Leduc, M., Najari, A., Li, Y., Leclerc, M., 2014. Polym. Chem. 6,
278–282.
Pouliot, J.-R., Wakioka, M., Ozawa, F., Li, Y., Leclerc, M., 2016b. Macromol. Chem.
Phys. 217, 1493–1500.
Požgan, F., Roger, J., Doucet, H., 2008. ChemSusChem 1, 404–407.
Prakash, A., Katiyar, M., 2012. White polymer light emitting diode using blend of
fluorescent polymers. pp. 854938-854938–6.
Pu, K., Mei, J., Jokerst, J.V., Hong, G., Antaris, A.L., Chattopadhyay, N., Shuhendler,
A.J., Kurosawa, T., Zhou, Y., Gambhir, S.S., Bao, Z., Rao, J., 2015. Adv. Mater. 27,
5184–5190.
Qi, B., Wang, J., 2013. Phys. Chem. Chem. Phys. 15, 8972–8982.
Qiao, J., Yang, C., He, Q., Bai, F., Li, Y., 2004. J. Appl. Polym. Sci. 92, 1459–1466.
411
Qin, R., Li, W., Li, C., Du, C., Veit, C., Schleiermacher, H.-F., Andersson, M., Bo, Z.,
Liu, Z., Inganäs, O., Wuerfel, U., Zhang, F., 2009. J. Am. Chem. Soc. 131, 14612–
14613.
Qiu, X., Wang, M., Zhao, Y., Shi, Z., n.d. Angew. Chem. Int. Ed.
10.1002/anie.201703354.
Qiu, Y., Worch, J.C., Fortney, A., Gayathri, C., Gil, R.R., Noonan, K.J.T., 2016.
Macromolecules 49, 4757–4762.
Rahimi, K., Botiz, I., Agumba, J.O., Motamen, S., Stingelin, N., Reiter, G., 2014. RSC
Adv. 4, 11121–11123.
Ramanathan, M., Kilbey, I., S. Michael, Ji, Q., Hill, J.P., Ariga, K., 2012. J. Mater. Chem.
22.
Ramani, T., Umadevi, P., Prasanth, K.L., Sreedhar, B., 2013. European Journal of Organic
Chemistry n/a-n/a.
Rampon, D.S., Wessjohann, L.A., Schneider, P.H., 2014. J. Org. Chem.
Reay, A.J., Neumann, L.K., Fairlamb, I.J.S., 2016. Synlett 27, 1211–1216.
Reetz, M.T., Westermann, E., Lohmer, R., Lohmer, G., 1998. Tetrahedron Lett. 39, 8449–
8452.
Reineke, S., Thomschke, M., Lüssem, B., Leo, K., 2013. Rev. Mod. Phys. 85, 1245–1293.
Remy, M.S., Cundari, T.R., Sanford, M.S., 2010. Organometallics 29, 1522–1525.
René, O., Fagnou, K., 2010a. Org. Lett. 12, 2116–2119.
René, O., Fagnou, K., 2010b. Adv. Synth. Catal. 352, 2116–2120.
Reynolds, J.R., Skotheim, T.A., Skotheim, T.A., 2007. Conjugated polymers processing
and applications. CRC, Boca Raton.
Ricci, P., Kramer, K., Cambeiro, X.C., Larrosa, I., 2013. J. Am. Chem. Soc.
Richards, J.J., Rice, A.H., Nelson, R.D., Kim, F.S., Jenekhe, S.A., Luscombe, C.K., Pozzo,
D.C., 2013. Adv. Funct. Mater. 23, 514–522.
Richter, T.V., Link, S., Hanselmann, R., Ludwigs, S., 2009. Macromol. Rapid Commun.
30, 1323–1327.
Rigby, D., Lin, J.L., Roe, R.J., 1985. Macromolecules 18, 2269–2273.
Robb, M.J., Montarnal, D., Eisenmenger, N.D., Ku, S.-Y., Chabinyc, M.L., Hawker, C.J.,
2013. Macromolecules 46, 6431–6438.
Roger, J., Požgan, F., Doucet, H., 2009. Green Chem. 11, 425–432.
Roman, D.S., Takahashi, Y., Charette, A.B., 2011. Org. Lett. 13, 3242–3245.
Romero-Gómez, P., Pastorelli, F., Mantilla-Pérez, P., Mariano, M., Martínez-Otero, A.,
Elias, X., Betancur, R., Martorell, J., 2015. J. Photon. Energy 5, 057212–057212.
Rossi, R., Bellina, F., Lessi, M., Manzini, C., 2014. Adv. Synth. Catal. 356, 17–117.
Roth, B., Rudenko, A.E., Thompson, B.C., Krebs, F.C., 2014. J. Photon. Energy 5,
0572051–0572059.
Roumen, L., Peeters, J.W., Emmen, J.M.A., Beugels, I.P.E., Custers, E.M.G., de Gooyer,
M., Plate, R., Pieterse, K., Hilbers, P.A.J., Smits, J.F.M., Vekemans, J.A.J., Leysen,
D., Ottenheijm, H.C.J., Janssen, H.M., Hermans, J.J.R., 2010. J. Med. Chem. 53,
1712–1725.
Roy, A.H., Hartwig, J.F., 2001. J. Am. Chem. Soc. 123, 1232–1233.
Roy, C., Bura, T., Beaupré, S., Légaré, M.-A., Sun, J.-P., Hill, I.G., Leclerc, M., 2017.
Macromolecules.
412
Rudenko, Andrey E., Khlyabich, P.P., Thompson, B.C., 2014. ACS Macro Lett. 3, 387–
392.
Rudenko, A.E., Khlyabich, P.P., Thompson, B.C., 2015. J. Polym. Sci. Part A: Polym.
Chem. n/a-n/a.
Rudenko, Andrey E, Latif, A.A., Thompson, B.C., 2014. Nanotechnology 25, 014005.
Rudenko, Andrey E, Noh, S., Thompson, B.C., 2013. Nanotechnology 24, 484002.
Rudenko, A.E., Thompson, B.C., 2015a. J. Polym. Sci. A Polym. Chem. 53, 135–147.
Rudenko, A.E., Thompson, B.C., 2015b. Macromolecules 48, 569–575.
Rudenko, A.E., Wiley, C.A., Stone, S.M., Tannaci, J.F., Thompson, B.C., 2012. J. Polym.
Sci. A Polym. Chem. 50, 3691–3697.
Rudenko, Andrey E., Wiley, C.A., Tannaci, J.F., Thompson, B.C., 2013. J. Polym. Sci. A
Polym. Chem. 51, 2660–2668.
Sadki, S., Schottland, P., Brodie, N., Sabouraud, G., 2000. Chem. Soc. Rev. 29, 283–293.
Saeed, M.A., Le, H.T.M., Miljanić, O.Š., 2014. Acc. Chem. Res. 47, 2074–2083.
Saito, H., Chen, J., Kuwabara, J., Yasuda, T., Kanbara, T., 2017. Polymer Chemistry 8,
3006–3012.
Saito, H., Kuwabara, J., Kanbara, T., 2015. J. Polym. Sci. Part A: Polym. Chem. 53, 2198–
2201.
Saito, H., Kuwabara, J., Yasuda, T., Kanbara, T., 2016. Polym. Chem. 7, 2775–2779.
Sakamoto, J., Rehahn, M., Wegner, G., Schlüter, A.D., 2009. Macromol. Rapid. Commun.
30, 653–687.
Sakamoto, J., Schlüter, A.D., 2013. Suzuki Polycondensation, in: Cahn, R.W., Haasen, P.,
Kramer, E.J. (Eds.), Materials Science and Technology. Wiley-VCH Verlag GmbH
& Co. KGaA, Weinheim, Germany.
Samanta, S.K., Fritsch, M., Scherf, U., Gomulya, W., Bisri, S.Z., Loi, M.A., 2014. Acc.
Chem. Res. 47, 2446–2456.
Samorí, P., 2011. Functional supramolecular architectures for organic electronics and
nanotechnology. 1. Wiley-VCH, Weinheim.
Sasabe, H., Kido, J., 2011. Chem. Mater. 23, 621–630.
Sasabe, H., Kido, J., 2013. J. Mater. Chem. C 1, 1699–1707.
Scharber, M.C., Mühlbacher, D., Koppe, M., Denk, P., Waldauf, C., Heeger, A.J., Brabec,
C.J., 2006. Adv. Mater. 18, 789–794.
Schiefer, D., Komber, H., Mugwanga Keheze, F., Kunz, S., Hanselmann, R., Reiter, G.,
Sommer, M., 2016. Macromolecules 49, 7230–7237.
Schilinsky, P., Asawapirom, U., Scherf, U., Biele, M., Brabec, C.J., 2005. Chem. Mater.
17, 2175–2180.
Schipper, D.J., Fagnou, K., 2011. Chem. Mater. 23, 1594–1600.
Schlenk, W., Schlenk, Wilh., 1929. Ber. Dtsch. Chem. Ges. 62, 920–924.
Schnapperelle, I., Bach, T., 2013. ChemCatChem n/a-n/a.
Schnurch, M., Dastbaravardeh, N., Ghobrial, M., Mrozek, B., D. Mihovilovic, M., 2011.
Current Organic Chemistry 15, 2694–2730.
Schrock, R.R., 2014. Acc. Chem. Res.
Scully, S.R., McGehee, M.D., 2006. J. Appl. Phys. 100, 034907.
Se´vignon, M., Papillon, J., Schulz, E., Lemaire, M., 1999. Tetrahedron Lett. 40, 5873–
5876.
Searle, M.S., Williams, D.H., 1992. J. Am. Chem. Soc. 114, 10690–10697.
413
Segawa, Y., Maekawa, T., Itami, K., 2015. Angew. Chem. Int. Ed. 54, 66–81.
Senkovskyy, V., Tkachov, R., Beryozkina, T., Komber, H., Oertel, U., Horecha, M.,
Bocharova, V., Stamm, M., Gevorgyan, S.A., Krebs, F.C., Kiriy, A., 2009. J. Am.
Chem. Soc. 131, 16445–16453.
Sévignon, M., Hassan, J., Gozzi, C., Schulz, E., Lemaire, M., 2000. Comptes Rendus de
l’Académie des Sciences - Series IIC - Chemistry 3, 569–572.
Seyferth, D., 2009. Organometallics 28, 1598–1605.
Shan, G., Yang, X., Zong, Y., Rao, Y., 2013. Angew. Chem. Int. Ed. n/a-n/a.
Sharma, B., Singh, A., Afroz, M.A., Iyer, P.K., Jacob, J., 2017. Synthetic Metals 226, 56–
61.
Sharma, S.S., Sharma, G.D., Mikroyannidis, J.A., 2011. Solar Energy Materials and Solar
Cells 95, 1219–1223.
Shen, X., Li, L., Wu, H., Yao, S.Q., Xu, Q.-H., 2011. Nanoscale 3, 5140–5146.
Shen, X., Li, S., Li, L., Yao, S.Q., Xu, Q.-H., 2015. Chem. Eur. J. 21, 2214–2221.
Sherry, B.D., Fürstner, A., 2008. Acc. Chem. Res. 41, 1500–1511.
Shih, P.-I., Tseng, Y.-H., Wu, F.-I., Dixit, A.K., Shu, C.-F., 2006. Adv. Funct. Mater. 16,
1582–1589.
Shimomura, M., Kaga, M., Nakayama, N., Miyauchi, S., 1995. Synth. Met. 69, 313–314.
Shirakawa, E., Itoh, K., Higashino, T., Hayashi, T., 2010. J. Am. Chem. Soc. 132, 15537–
15539.
Shonaike, G.O., Simon, G.P., 1999. Polymer Blends and Alloys. CRC Press.
Shrotriya, V., Li, G., Yao, Y., Moriarty, T., Emery, K., Yang, Y., 2006. Adv. Funct. Mater.
16, 2016–2023.
Shu, Y.-C., Hsiao, K.-J., Tsen, W.-C., 2009. J. Appl. Polym. Sci. 113, 265–273.
Shultz, G.V., Gere, A.R., 2015. J. Chem. Educ. 92, 1325–1329.
Sinha, J., Lee, S.J., Kong, H., Swift, T.W., Katz, H.E., 2013. Macromolecules 46, 708–
717.
Sirringhaus, H., 2014. Adv. Mater. 26, 1319–1335.
Sirringhaus, H., Bird, M., Zhao, N., 2010. Adv. Mater. 22, 3893–3898.
Sivaraman, P., Mishra, S.P., Bhattacharrya, A.R., Thakur, A., Shashidhara, K., Samui,
A.B., 2012. Electrochim. Acta 69, 134–138.
Sivula, K., Luscombe, C.K., Thompson, B.C., Fréchet, J.M.J., 2006. J. Am. Chem. Soc.
128, 13988–13989.
Small, C.E., Chen, S., Subbiah, J., Amb, C.M., Tsang, S.-W., Lai, T.-H., Reynolds, J.R.,
So, F., 2011. Nat. Photon. 6, 115–120.
Snaith, H.J., 2012. Energy Environ. Sci. 5, 6513–6520.
Sommer, M., 2014. J. Mater. Chem. C 2, 3088–3098.
Sonar, P., Foong, T.R.B., Dodabalapur, A., 2014. Phys. Chem. Chem. Phys. 16, 4275–
4283.
Sonar, P., Grimsdale, A.C., Heeney, M., Shkunov, M., McCulloch, I., Müllen, K., 2007.
Synth. Met. 157, 872–875.
Sonar, P., Williams, E.L., Singh, S.P., Dodabalapur, A., 2011. J. Mater. Chem. 21, 10532–
10541.
Song, K.W., Choi, M.H., Lee, J.Y., Moon, D.K., 2014. J. Ind. Eng. Chem. 20, 290–296.
Speros, J.C., Paulsen, B.D., Slowinski, B.S., Frisbie, C.D., Hillmyer, M.A., 2012. ACS
Macro Lett. 1, 986–990.
414
Stefan, M.C., Bhatt, M.P., Sista, P., Magurudeniya, H.D., 2012. Polym. Chem. 3, 1693–
1701.
Steinmetz, M., Ueda, K., Grimme, S., Yamaguchi, J., Kirchberg, S., Itami, K., Studer, A.,
2012. Chem. Asian J. 7, 1256–1260.
Street, R.A., Davies, D., Khlyabich, P.P., Burkhart, B., Thompson, B.C., 2013a. J. Am.
Chem. Soc. 135, 986–989.
Street, R.A., Hawks, S.A., Khlyabich, P.P., Li, G., Schwartz, B.J., Thompson, B.C., Yang,
Y., 2014a. J. Phys. Chem. C 118, 21873–21883.
Street, R.A., Khlyabich, P.P., Rudenko, A.E., Thompson, B.C., 2014b. J. Phys. Chem. C
118, 26569–26576.
Street, R.A., Khlyabich, P.P., Thompson, B.C., 2013b. Org. Electron. 14, 2932–2939.
Street, R.A., Salleo, A., 2002. Appl. Phys. Lett. 81, 2887–2889.
Street, R.A., Song, K.W., Northrup, J.E., Cowan, S., 2011. Phys. Rev. B 83, 165207.
Street, R.A., Yang, Y., Thompson, B.C., McCulloch, I., 2016. J. Phys. Chem. C 120,
22169–22178.
Stuart, D.R., Fagnou, K., 2007. Science 316, 1172–1175.
Su, M.-S., Kuo, C.-Y., Yuan, M.-C., Jeng, U.-S., Su, C.-J., Wei, K.-H., 2011. Adv. Mater.
23, 3315–3319.
Subramaniyan, S., Xin, H., Kim, F.S., Murari, N.M., Courtright, B.A.E., Jenekhe, S.A.,
2014. Macromolecules 47, 4199–4209.
Sun, B., Hong, W., Yan, Z., Aziz, H., Li, Y., 2014. Adv. Mater. 26, 2636–2642.
Sun, C.-L., Li, B.-J., Shi, Z.-J., 2011. Chem. Rev. 111, 1293–1314.
Sun, H.-Y., Gorelsky, S.I., Stuart, D.R., Campeau, L.-C., Fagnou, K., 2010. J. Org. Chem.
75, 8180–8189.
Sun, J., Devine, R., Dhar, B.M., Jung, B.J., See, K.C., Katz, H.E., 2009. ACS Appl. Mater.
Interfaces 1, 1763–1769.
Sun, M., Wang, W., Lv, W., Lu, M., Yan, S., Liang, L., Ling, Q., 2015. Synthetic Metals
209, 412–418.
Sun, Q.J., Hou, J.H., Yang, C.H., Li, Y.F., Yang, Y., 2006. Applied Physics Letters 89,
153501.
Sun, Y., Giebink, N.C., Kanno, H., Ma, B., Thompson, M.E., Forrest, S.R., 2006. Nature
440, 908–912.
Suraru, S.-L., Würthner, F., 2014. Angew. Chem. Int. Ed. 53, 7428–7448.
Suresh, P., Balraju, P., Sharma, G.D., Mikroyannidis, J.A., Stylianakis, M.M., 2009. ACS
Appl. Mater. Interfaces 1, 1370–1374.
Suzaki, Y., Osakada, K., 2003. Organometallics 22, 2193–2195.
Synooka, O., Kretschmer, F., Hager, M.D., Schubert, U., Gobsch, G., Hoppe, H., 2013.
Impact of methanol top-casting or washing on the polymer solar cell performance.
pp. 881117-881117–7.
Takacs, C.J., Sun, Y., Welch, G.C., Perez, L.A., Liu, X., Wen, W., Bazan, G.C., Heeger,
A.J., 2012. J. Am. Chem. Soc. 134, 16597–16606.
Takahashi, M., Masui, K., Sekiguchi, H., Kobayashi, N., Mori, A., Funahashi, M.,
Tamaoki, N., 2006. J. Am. Chem. Soc. 128, 10930–10933.
Tan, Y., Hartwig, J.F., 2011. J. Am. Chem. Soc. 133, 3308–3311.
Tang, D.-T.D., Collins, K.D., Ernst, J.B., Glorius, F., 2014. Angew. Chem. Int. Ed. 53,
1809–1813.
415
Tang, D.-T.D., Collins, K.D., Glorius, F., 2013. J. Am. Chem. Soc.
Tang, S.-Y., Guo, Q.-X., Fu, Y., 2011. Chem. Eur. J. 17, 13866–13876.
Tao, C., Liu, F., Zhu, Y., Liu, W., Cao, Z., 2013. Org. Biomol. Chem. 11.
Thomas, S.W., Joly, G.D., Swager, T.M., 2007. Chem. Rev. 107, 1339–1386.
Thompson, B.C., Abboud, K.A., Reynolds, J.R., Nakatani, K., Audebert, P., 2005. New J.
Chem. 29, 1128–1134.
Thompson, B.C., Fréchet, J.M.J., 2008. Angew. Chem. Int. Ed. 47, 58–77.
Thompson, B.C., Khlyabich, P.P., Burkhart, B., Aviles, A.E., Rudenko, A., Shultz, G.V.,
Ng, C.F., Mangubat, L.B., 2011. Green 1, 29–54.
Thompson, B.C., Kim, Y.-G., McCarley, T.D., Reynolds, J.R., 2006. J. Am. Chem. Soc.
128, 12714–12725.
Thompson, B.C., Schottland, P., Zong, K., Reynolds, J.R., 2000. Chem. Mater. 12, 1563–
1571.
Thompson, M.E., Baxter, S.M., Bulls, A.R., Burger, B.J., Nolan, M.C., Santarsiero, B.D.,
Schaefer, W.P., Bercaw, J.E., 1987. J. Am. Chem. Soc. 109, 203–219.
Thuy-Boun, P.S., Villa, G., Dang, D., Richardson, P.F., Su, S., Yu, J.-Q., 2013. J. Am.
Chem. Soc.
Tian, L.-H., Meng, J.-H., Wu, X.-N., Zhao, Y.-X., Ding, X.-L., He, S.-G., Ma, T.-M.,
2013. Chem. - Eur. J. n/a-n/a.
Tkachov, R., Senkovskyy, V., Beryozkina, T., Boyko, K., Bakulev, V., Lederer, A., Sahre,
K., Voit, B., Kiriy, A., 2014. Angew. Chem. Int. Ed. 53, 2402–2407.
Tolosa, J., Kub, C., Bunz, U.H.F., 2009. Angewandte Chemie International Edition 48,
4610–4612.
Tomar, M., Ashar, A.Z., Narayan, K.S., Müllen, K., Jacob, J., 2016. J Polym Res 23, 50.
Tomlinson, E.P., Willmore, M.J., Zhu, X., Hilsmier, S.W.A., Boudouris, B.W., 2015. ACS
Appl. Mater. Interfaces 7, 18195–18200.
Tong, L., Kushida, S., Kuwabara, J., Kanbara, T., Ishii, N., Saeki, A., Seki, S., Furumi, S.,
Yamamoto, Y., 2014. Polym. Chem. DOI:-10.1039/C4PY00023D.
Toshima, N., Hara, S., 1995. Progress in Polymer Science 20, 155–183.
Trent, J.S., Scheinbeim, J.I., Couchman, P.R., 1981. J. Polym. Sci. B Polym. Lett. Ed. 19,
315–319.
Trent, J.S., Scheinbeim, J.I., Couchman, P.R., 1983. Macromolecules 16, 589–598.
Troshin, P.A., Susarova, D.K., Moskvin, Y.L., Kuznetsov, I.E., Ponomarenko, S.A.,
Myshkovskaya, E.N., Zakharcheva, K.A., Balakai, A.A., Babenko, S.D., Razumov,
V.F., 2010. Adv. Funct. Mater. 20, 4351–4357.
Tsao, H.N., Cho, D.M., Park, I., Hansen, M.R., Mavrinskiy, A., Yoon, D.Y., Graf, R.,
Pisula, W., Spiess, H.W., Müllen, K., 2011. J. Am. Chem. Soc. 133, 2605–2612.
Tsoi, W.C., Spencer, S.J., Yang, L., Ballantyne, A.M., Nicholson, P.G., Turnbull, A.,
Shard, A.G., Murphy, C.E., Bradley, D.D.C., Nelson, J., Kim, J.-S., 2011.
Macromolecules 44, 2944–2952.
Tu, G., Bilge, A., Adamczyk, S., Forster, M., Heiderhoff, R., Balk, L.J., Mühlbacher, D.,
Morana, M., Koppe, M., Scharber, M.C., Choulis, S.A., Brabec, C.J., Scherf, U.,
2007. Macromol. Rapid Commun. 28, 1781–1785.
Uddin, M.A., Kim, T., Yum, S., Choi, H., Hwang, S., Kim, J.Y., Woo, H.Y., 2015. Current
Applied Physics 15, 654–661.
416
Ueda, K., Yanagisawa, S., Yamaguchi, J., Itami, K., 2010. Angew. Chem. Int. Ed. 49,
8946–8949.
Urien, M., Bailly, L., Vignau, L., Cloutet, E., de Cuendias, A., Wantz, G., Cramail, H.,
Hirsch, L., Parneix, J.-P., 2008. Polym. Int. 57, 764–769.
Urien, M., Wantz, G., Cloutet, E., Hirsch, L., Tardy, P., Vignau, L., Cramail, H., Parneix,
J.-P., 2007. Org. Electron. 8, 727–734.
Vakuliuk, O., Koszarna, B., Gryko, D.T., 2011. Adv. Synth. Catal. 353, 925–930.
Vallée, F., Mousseau, J.J., Charette, A.B., 2010. J. Am. Chem. Soc. 132, 1514–1516.
Van Aken, K., Strekowski, L., Patiny, L., 2006. Beilstein J. Org. Chem. 2.
Varnavski, O., Yan, X., Mongin, O., Blanchard-Desce, M., Goodson, T., 2007. J. Phys.
Chem. C 111, 149–162.
Veldman, D., İpek, Ö., Meskers, S.C.J., Sweelssen, J., Koetse, M.M., Veenstra, S.C.,
Kroon, J.M., van Bavel, S.S., Loos, J., Janssen, R.A.J., 2008. J. Am. Chem. Soc. 130,
7721–7735.
Vitali, R., Montani, E., 1980. Polymer 21, 1220–1222.
Voit, B.I., Lederer, A., 2009. Chem. Rev. 109, 5924–5973.
Wagner, A.M., Hickman, A.J., Sanford, M.S., 2013. J. Am. Chem. Soc.
Wakim, S., Beaupré, S., Blouin, N., Aich, B.-R., Rodman, S., Gaudiana, R., Tao, Y.,
Leclerc, M., 2009. J. Mater. Chem. 19, 5351–5358.
Wakioka, M., Ichihara, N., Kitano, Y., Ozawa, F., 2014a. Macromolecules 47, 626–631.
Wakioka, M., Ikegami, M., Ozawa, F., 2010. Macromolecules 43, 6980–6985.
Wakioka, M., Kitano, Y., Ozawa, F., 2013a. Macromolecules 46, 370–374.
Wakioka, M., Nakamura, Y., Hihara, Y., Ozawa, F., Sakaki, S., 2013b. Organometallics
32, 4423–4430.
Wakioka, M., Nakamura, Y., Hihara, Y., Ozawa, F., Sakaki, S., 2014b. Organometallics
33, 6247–6252.
Wakioka, M., Nakamura, Y., Montgomery, M., Ozawa, F., 2015. Organometallics 34,
198–205.
Wakioka, M., Nakamura, Y., Wang, Q., Ozawa, F., 2012. Organometallics 31, 4810–4816.
Wakioka, M., Takahashi, R., Ichihara, N., Ozawa, F., 2017. Macromolecules 50, 927–934.
Waltman, R.J., Bargon, J., 1986. Can. J. Chem. 64, 76–95.
Walvoord, R.R., Kozlowski, M.C., 2013. J. Org. Chem.
Wan, Q., Guo, X., Wang, Z., Li, W., Guo, B., Ma, W., Zhang, M., Li, Y., 2016. Adv.
Funct. Mater. 26, 6635–6640.
Wang, B., Nack, W.A., He, G., Zhang, S.-Y., Chen, G., 2014. Chem. Sci.
Wang, D., Izawa, Y., Stahl, S.S., 2014. J. Am. Chem. Soc. 136, 9914–9917.
Wang, D.H., Kim, D.Y., Choi, K.W., Seo, J.H., Im, S.H., Park, J.H., Park, O.O., Heeger,
A.J., 2011. Angew. Chem. Int. Ed. 50, 5519–5523.
Wang, D.H., Pron, A., Leclerc, M., Heeger, A.J., 2013. Adv. Funct. Mater. 23, 1297–1304.
Wang, K., Wang, M., 2013. Curr. Org. Chem. 17, 999–1012.
Wang, K., Wang, M., 2017. J. Polym. Sci. Part A: Polym. Chem. 55, 1040–1047.
Wang, M., Fan, T., Lin, Z., 2012. Organometallics 31, 560–569.
Wang, M., Zhang, X., Zhuang, Y.-X., Xu, Y.-H., Loh, T.-P., 2015. J. Am. Chem. Soc.
137, 1341–1347.
Wang, Q., Takita, R., Kikuzaki, Y., Ozawa, F., 2010. J. Am. Chem. Soc. 132, 11420–
11421.
417
Wang, Qifeng, Wakioka, M., Ozawa, F., 2012. Macromol. Rapid Commun. 33, 1203–
1207.
Wang, Qilin, Zhang, B., Liu, L., Chen, Y., Qu, Y., Zhang, X., Yang, J., Xie, Z., Geng, Y.,
Wang, L., Wang, F., 2012. J. Phys. Chem. C 116, 21727–21733.
Wang, S., Yang, J., Broch, K., Novák, J., Cao, X., Shaw, J., Tao, Y., Hu, Y., Huang, W.,
2016. RSC Adv. 6, 57163–57173.
Wang, X., Gu, X., Yuan, C., Chen, S., Zhang, P., Zhang, T., Yao, J., Chen, F., Chen, G.,
2004. J. Biomed. Mater. Res. 68A, 411–422.
Wang, X., Wang, M., 2014. Polym. Chem. 5, 5784–5792.
Wang, Z.A., Kuwabara, J., Ichige, A., Yasuda, T., Kanbara, T., 2016. Synthetic Metals
222, 383–387.
Wei, C.S., Davies, G.H.M., Soltani, O., Albrecht, J., Gao, Q., Pathirana, C., Hsiao, Y.,
Tummala, S., Eastgate, M.D., 2013. Angew. Chem. Int. Ed. 52, 5822–5826.
Wei, H., Lu, H., Fang, T., Bo, Z., 2015. Sci. China Chem. 58, 286–293.
Wei, Q., Nishizawa, T., Tajima, K., Hashimoto, K., 2008. Adv. Mater. 20, 2211–2216.
Weis, J.G., Swager, T.M., 2015. ACS Macro Lett. 4, 138–142.
Wencel-Delord, J., Glorius, F., 2013. Nat. Chem. 5, 369–375.
Woo, C.H., Thompson, B.C., Kim, B.J., Toney, M.F., Fréchet, J.M.J., 2008. J. Am. Chem.
Soc. 130, 16324–16329.
Woody, K.B., Henry, E.M., Jagtap, S., Collard, D.M., 2011. Macromolecules 44, 9118–
9124.
Wu, C.-G., Lu, M.-I., Tsai, P.-F., 2009. Macromol. Chem. Phys. 210, 1851–1855.
Wu, W., Li, J., Zhao, Z., Yang, X., Gao, X., 2017a. Org. Chem. Front. 4, 823–827.
Wu, W., Xin, H., Ge, C., Gao, X., 2017b. Tetrahedron Letters 58, 175–184.
Wu, W.-C., Liu, C.-L., Chen, W.-C., 2006. Polymer 47, 527–538.
Wu, Y., Wang, K., Huang, S., Yang, C., Wang, M., 2017. ACS Appl. Mater. Interfaces 9,
13602–13610.
Wu, Z., Chen, S., Hu, C., Li, Z., Xiang, H., Zhou, X., 2013. ChemCatChem n/a-n/a.
Würfel, P., Würfel, U., 2009. Physics of Solar Cells: From Basic Principles to Advanced
Concepts, 3rd ed. John Wiley & Sons, Weinheim, Germany.
Xia, N., Taillefer, M., 2008. Chem. - Eur. J. 14, 6037–6039.
Xiao, Z., Sun, K., Subbiah, J., Qin, T., Lu, S., Purushothaman, B., Jones, D.J., Holmes,
A.B., Wong, W.W.H., 2015. Polym. Chem. 6, 2312–2318.
Xu, B., Noh, S., Thompson, B.C., 2014. Macromolecules 47, 5029–5039.
Xu, L., Zhao, J., Cui, C., Liu, R., Liu, J., Wang, H., 2011. Electrochimica Acta 56, 2815–
2822.
Xue, B., Peng, J., Xin, Z., Kong, Y., Li, L., Li, B., 2005. Journal of Materials Chemistry
15, 4793.
Xue, L., Lin, Z., 2010. Chem. Soc. Rev. 39, 1692–1705.
Yagyu, T., Hamada, M., Osakada, K., Yamamoto, T., 2001. Organometallics 20, 1087–
1101.
Yamamoto, T., Komarudin, D., Arai, M., Lee, B.-L., Suganuma, H., Asakawa, N., Inoue,
Y., Kubota, K., Sasaki, S., Fukuda, T., Matsuda, H., 1998. J. Am. Chem. Soc. 120,
2047–2058.
418
Yamamoto, T., Morita, A., Miyazaki, Y., Maruyama, T., Wakayama, H., Zhou, Z.H.,
Nakamura, Y., Kanbara, T., Sasaki, S., Kubota, K., 1992. Macromolecules 25, 1214–
1223.
Yamamoto, Y., Tong, L., 2014. IOP Conf. Ser.: Mater. Sci. Eng. 54.
Yamazaki, K., Kuwabara, J., Kanbara, T., 2013. Macromol. Rapid Commun. 34, 69–73.
Yan, H., Chen, Z., Zheng, Y., Newman, C., Quinn, J.R., Dötz, F., Kastler, M., Facchetti,
A., 2009. Nature 457, 679–686.
Yang, C., Liu, H., Zhang, Y., Xu, Z., Wang, X., Cao, B., Wang, M., 2016.
Biomacromolecules 17, 1673–1683.
Yang, X., Zhou, G., Wong, W.-Y., 2014. J. Mater. Chem. C 2, 1760–1778.
Yang, Y., Lan, J., You, J., 2017. Chem. Rev.
Yang, Y.-F., Cheng, G.-J., Liu, P., Leow, D., Sun, T.-Y., Chen, P., Zhang, X., Yu, J.-Q.,
Wu, Y.-D., Houk, K.N., 2013. J. Am. Chem. Soc.
Yasuda, T., Kuwabara, J., Han, L., Kanbara, T., 2016. Journal of Photopolymer Science
and Technology 29, 347–352.
Yi, Z., Wang, S., Liu, Y., 2015. Adv. Mater. 27, 3589–3606.
Ying, L., Ho, C.-L., Wu, H., Cao, Y., Wong, W.-Y., 2014. Adv. Mater. 26, 2459–2473.
Yokoyama, A., Miyakoshi, R., Yokozawa, T., 2004. Macromolecules 37, 1169–1171.
Yoshizumi, T., Tsurugi, H., Satoh, T., Miura, M., 2008. Tetrahedron Lett. 49, 1598–1600.
Yu, S., Liu, F., Yu, J., Zhang, S., Cabanetos, C., Gao, Y., Huang, W., 2016. J. Mater.
Chem. C 5, 29–40.
Yuan, J., Ouyang, J., Cimrová, V., Leclerc, M., Najari, A., Zou, Y., 2017. J. Mater. Chem.
C 5, 1858–1879.
Yuan, M.-C., Chiu, M.-Y., Liu, S.-P., Chen, C.-M., Wei, K.-H., 2010. Macromolecules
43, 6936–6938.
Yue, D., Khatav, P., You, F., Darling, S.B., 2012. Energy Environ. Sci. 5, 9163–9172.
Yum, S., An, T.K., Wang, X., Lee, W., Uddin, M.A., Kim, Y.J., Nguyen, T.L., Xu, S.,
Hwang, S., Park, C.E., Woo, H.Y., 2014. Chem. Mater. 26, 2147–2154.
Yun, H.-J., Kang, S.-J., Xu, Y., Kim, S.O., Kim, Y.-H., Noh, Y.-Y., Kwon, S.-K., 2014.
Adv. Mater. 26, 7300–7307.
Zeng, Y., Qian, H., Chen, X., Li, Z., Yu, S., Xiao, X., 2010. Chinese Journal of Chemistry
28, 727–733.
Zhang, H.-H., Dong, J., Hu, Q.-S., 2014. Eur. J. Org. Chem. 2014, 1327–1332.
Zhang, J., Chen, W., Rojas, A.J., Jucov, E.V., Timofeeva, T.V., Parker, T.C., Barlow, S.,
Marder, S.R., 2013. J. Am. Chem. Soc. 135, 16376–16379.
Zhang, J., Kang, D.-Y., Barlow, S., Marder, S.R., 2012. J. Mater. Chem. 22, 21392–21394.
Zhang, K., Hu, Z., Duan, C., Ying, L., Huang, F., Cao, Y., 2013. Nanotechnology 24,
484003.
Zhang, X., Gao, Y., Li, S., Shi, X., Geng, Y., Wang, F., 2014. J. Polym. Sci. A Polym.
Chem. 52, 2367–2374.
Zhang, X., He, C.-Y., Wu, C.-Z., Zhu, Y.-L., 2013. Chem. Sci.
Zhang, Y., Chien, S.-C., Chen, K.-S., Yip, H.-L., Sun, Y., Davies, J.A., Chen, F.-C., Jen,
A.K.-Y., 2011. Chem. Commun. 47, 11026–11028.
Zhao, D., Wang, W., Yang, F., Lan, J., Yang, L., Gao, G., You, J., 2009. Angew. Chem.
Int. Ed. 48, 3296–3300.
419
Zhao, F., Dai, S., Wu, Y., Zhang, Q., Wang, J., Jiang, L., Ling, Q., Wei, Z., Ma, W., You,
W., Wang, C., Zhan, X., 2017. Adv. Mater. 29, n/a-n/a.
Zhao, H., Liu, C.-Y., Luo, S.-C., Zhu, B., Wang, T.-H., Hsu, H.-F., Yu, H., 2012.
Macromolecules 45, 7783–7790.
Zhao, J., Li, Y., Hunt, A., Zhang, Jianquan, Yao, H., Li, Z., Zhang, Jie, Huang, F., Ade,
H., Yan, H., 2016. Adv. Mater. 28, 1868–1873.
Zhao, J., Oniwa, K., Asao, N., Yamamoto, Y., Jin, T., 2013. J. Am. Chem. Soc.
Zhao, L., Bruneau, C., Doucet, H., 2013. Chem. Commun. 49.
Zhao, Y., Guo, Y., Liu, Y., 2013. Adv. Mater. 25, 5372–5391.
Zheng, B., Jia, T., Walsh, P.J., 2013. Org. Lett.
Zhokhavets, U., Erb, T., Gobsch, G., Al-Ibrahim, M., Ambacher, O., 2006. Chem. Phys.
Lett. 418, 347–350.
Zhou, C.Y., Yan, L.T., Zhang, L.N., Ai, X.D., Li, T.X., Dai, C.A., 2012. J. Macromol.
Sci., Part A: Pure Appl.Chem. 49, 293–297.
Zhou, E., Tan, Z. ’ao, Huo, L., He, Y., Yang, C., Li, Y., 2006. J. Phys. Chem. B 110,
26062–26067.
Zhou, H., Zhang, Y., Seifter, J., Collins, S.D., Luo, C., Bazan, G.C., Nguyen, T.-Q.,
Heeger, A.J., 2013. Adv. Mater. 25, 1646–1652.
Zhou, X., Liang, H., Jiang, P., Zhang, K.Y., Liu, S., Yang, T., Zhao, Q., Yang, L., Lv, W.,
Yu, Q., Huang, W., 2016. Adv. Sci. 3, n/a-n/a.
Zhou, Y., Sun, Q., Tan, Z. ’ao, Zhong, H., Yang, C., Li, Y., 2007. J. Phys. Chem. C 111,
6862–6867.
Zhu, E., Ni, B., Zhao, B., Hai, J., Bian, L., Wu, H., Tang, W., 2014. Macromol. Chem.
Phys. 215, 227–234.
Zou, Y., Gendron, D., Badrou-Aïch, R., Najari, A., Tao, Y., Leclerc, M., 2009.
Macromolecules 42, 2891–2894.

420
Appendix 1: Analysis of Diverse Direct Arylation Polymerization (DArP)
Conditions Toward the Efficient Synthesis of Polymers Converging with
Stille Polymers in Organic Solar Cells

A1.1 Materials and Methods

A1.1.1 Synthesis of Polymers via DArP: Class A Polymers

A three-necked flask was charged with 1 equiv. of 2,2'-(2,5-bis((2-
hexyldecyl)oxy)-1,4-phenylene)dithiophene, 1 equiv. of 4,7-
dibromobenzo[c][1,2,5]thiadiazole, 3 equiv. of K2CO3 and 1.2 equiv. of neodecanoic acid.
DMA (or a mixture DMA:Toluene 1:1 v/v) was subsequently added in order to have a
monomer concentration of 0.04 M. The reaction mixture was degassed with N2 and stirred
at 50
o
C for few minutes before 0.02 equiv. of Pd(OAc)2 (0.04 equiv. for the DMA:toluene
1:1 mixture) were added. The reaction mixture was heated up to 70, 90 or 110
o
C for 48 h
and then allowed to reach RT and subsequently precipitated into cold MeOH (and stirred
for few minutes) before Soxhlet extraction was carried out with MeOH, hexanes, and
chloroform. Finally, the polymer collected in chloroform was concentrated and precipitated
again into cold MeOH, subsequently filtered and dried under vacuum to yield the desired
polymer.
Poly[(2,5-bis(2-hexyldecyloxy)phenylene)-alt-(4,7-di(thiophen-2-
yl)benzo[c][1,2,5]thiadiazole)] (PPDTBT Class A Conditions)
1
H NMR ( 600 MHz,
421
CDCl3, ppm): δ 8.18 (br, 2H), 7.93 (br, 2H), 7.69 (br, 2H), 7.37 (br, 2H), 4.10 (br, 4H),
2.01 (br, 2H), 1.68 (br, 4H), 1.44−1.23 (m, 44H), 0.86−0.82 (br, 12H).
A1, 25% yield. Mn = 11 kDa (PDI = 2.5).
A2, 28% yield. Mn = 14 kDa (PDI = 3.9).
A3, 25% yield. Mn = 15 kDa (PDI = 2.5).
A4, 24% yield. Mn = 15 kDa (PDI = 4.1).

A1.1.2 Synthesis of Polymers via DArP: Class B Polymers

A 4 mL screw-capped vial was charged with 1 equiv. of 2,2'-(2,5-bis((2-hexyldecyl)oxy)-
1,4-phenylene)dithiophene, 1 equiv. of 4,7-dibromobenzo[c][1,2,5]thiadiazole, 3 equiv. of
K2CO3, 1 equiv. of neodecanoic acid and 0.04 equiv. of tricyclohexylphosphine. DMA (or
a mixture DMA:Toluene 1:1 v/v) was subsequently added in order to have a monomers
concentration of 0.18 M (or 0.27 M in the case of the DMA:Toluene 1:1 mixture). The
reaction mixture was degassed with N2 and stirred at 50
o
C for few minutes before 0.02
equiv of Pd(OAc)2 (0.04 equiv if a or a mixture DMA:Toluene 1:1 was used as a solvent)
were added. The reaction mixture was heated up to 90
o
C for 72 h and then allowed to
reach RT and subsequently precipitated into cold MeOH (and stirred for few minutes)
before Soxhlet extraction was carried out in MeOH, hexanes, and chloroform. Finally, the
chloroform fraction was concentrated and precipitated into cold MeOH, filtered and dried
under vacuum to yield the desired polymer.
422
Poly[(2,5-bis(2-hexyldecyloxy)phenylene)-alt-(4,7-di(thiophen-2-
yl)benzo[c][1,2,5]thiadiazole)]
(PPDTBT Class B Conditions)
1
H NMR (600 MHz, CDCl3, ppm): δ 8.18 (br, 2H), 7.93
(br, 2H), 7.69 (br, 2H), 7.37 (br, 2H), 4.10 (br, 4H), 2.01 (br, 2H), 1.68 (br, 4H), 1.44−1.23
(m, 44H), 0.86−0.82 (br, 12H).
B1, 25% yield. Mn = 15 kDa (PDI = 3.9).
B2, 67% yield. Mn = 11 kDa (PDI = 3.6).
B3, 16% yield. Mn = 6.5 kDa (PDI = 1.7).
B4, 6.3% yield. Mn = 8.6 kDa (PDI = 2.1).
A1.1.3 Synthesis of Polymers via DArP: Class C Polymers

(C1) A 8 mL screw -capped vial was charged with 1 equiv of 4,7-di(thiophen-2-
yl)benzo[c][1,2,5]thiadiazole, 1 equiv of 1,4-dibromo-2,5-bis((2-hexyldecyl)oxy)benzene,
3 equiv of Cs2CO3, 1 equiv. of neodecanoic acid and 0.04 equiv of tris(o-
methoxyphenyl)phosphine. Toluene was subsequently added in order to have a monomer
concentration of 0.40 M. The reaction mixture was degassed with N2 and stirred at 50
o
C
for few minutes before 0.005 equiv of Pd2(dba)3•CHCl3 were added. The reaction mixture
was heated up to 100
o
C for 48 h and then allowed to reach RT and subsequently
precipitated into cold MeOH (and stirred for few minutes) before Soxhlet extraction was
carried out in MeOH, hexanes, and chloroform. Finally, the polymer collected in
423
chloroform was precipitated again into cold MeOH, filtered and dried under vacuum to
yield the desired polymer.
(C2) A 10 mL round bottom microwave vial was charged with 1 equiv. of 4,7-di(thiophen-
2-yl)benzo[c][1,2,5]thiadiazole, 1 equiv. of 1,4-dibromo-2,5-bis((2-
hexyldecyl)oxy)benzene, 3 equiv. of Cs 2CO3, 1 equiv. of neodecanoic acid and 0.16 equiv.
of tris(o-methoxyphenyl)phosphine. THF was subsequently added in order to have a
monomers concentration of 0.40 M. The reaction mixture was degassed with N2 for few
minutes before 0.02 equiv. of Pd2(dba)3 were added and the reaction mixture was heated
up to 120
o
C for 12 h. The resulting mixture was then allowed to reach rt before 3-4 mL of
chlorobenzene were added. The mixture was subsequently precipitated into cold MeOH
and stirred for few minutes before Soxhlet extraction was carried out in MeOH, hexanes,
and chloroform. The chloroform fraction was concentrated and precipitated into cold
MeOH, filtered and dried under vacuum to yield the desired polymer.
Poly[(2,5-bis(2-hexyldecyloxy)phenylene)-alt-(4,7-di(thiophen-2-
yl)benzo[c][1,2,5]thiadiazole)]
(PPDTBT Class C Conditions)
1
H NMR (600 MHz, CDCl3, ppm): δ 8.18 (br, 2H), 7.93
(br, 2H), 7.69 (br, 2H), 7.37 (br, 2H), 4.10 (br, 4H), 2.01 (br, 2H), 1.68 (br, 4H), 1.44−1.23
(m, 44H), 0.86−0.82 (br, 12H).
C1, 67% yield. Mn = 9.5 kDa (PDI = 3.7).
C2, 78% yield. Mn = 15 kDa (PDI = 2.1).
424
A1.1.4 Synthesis of Polymers via Stille Polycondensation

A three-necked flask was charged with 1 equiv. of ((2,5-bis((2-hexyldecyl)oxy)-1,4-
phenylene)bis(thiophene-5,2-diyl))bis(trimethylstannane), 1 equiv. of 4,7-
dibromobenzo[c][1,2,5]thiadiazole (or 4,7-bis(5-(trimethylstannyl)thiophen-2-
yl)benzo[c][1,2,5]thiadiazole and 1,4-dibromo-2,5-bis((2-hexyldecyl)oxy)benzene) and
0,18 equiv. of tris(o-tolyl)phosphine. Toluene was subsequently added in order to have a
monomers concentration of 0.20 M. The reaction mixture was degassed with N 2 and stirred
at 50
o
C for few minutes before 0.03 equiv. of Pd2(dba)3 were added and the reaction
mixture was heated at 105
o
C for 48 h. The resulting mixture was then allowed to reach RT
and subsequently precipitated into cold MeOH and stirred for few minutes before Soxhlet
extraction was carried out in MeOH, h exanes, and chloroform. The chloroform fraction
was concentrated and precipitated into cold MeOH, filtered and dried under vacuum to
yield the desired polymer.
Poly[(2,5-bis(2-hexyldecyloxy)phenylene)-alt-(4,7-di(thiophen-2-
yl)benzo[c][1,2,5]thiadiazole)]
(PPDTBT Stille Conditions)
1
H NMR (600 MHz, CDCl3, ppm): δ 8.18 (br, 2H), 7.93 (br,
2H), 7.69 (br, 2H), 7.37 (br, 2H), 4.10 (br, 4H), 2.01 (br, 2H), 1.68 (br, 4H), 1.44−1.23 (m,
44H), 0.86−0.82 (br, 12H).
PPDTBTX, 70% yield. Mn = 16 kDa (PDI = 2.1).
PPDTBTY, 79% yield. Mn = 59 kDa (PDI = 3.3).
425
A1.2 NMR Spectra

A1.2.1
1
H NMR spectra of the monomers

Figure A1.1. Monomers prepared for the synthesis of DArP and Stille polymers.

426

Figure A1.2.
1
H NMR spectrum of S1. (X) denotes solvent residues.
427

Figure A1.3.
1
H NMR spectrum of S2.
428

Figure A1.4.
1
H NMR spectrum of S3. (X) denotes solvent residues.
429

Figure A1.5.
1
H NMR spectrum of S4.
430

Figure A1.6.
1
H NMR spectrum of S5.

431

Figure A1.7. Stacked
1
H NMR Spectrum of the aromatic region for all polymers reported
in this work. Red alpha (α) denotes acceptor-acceptor couplings, blue delta (δ) denotes
donor-donor coupling, (*) denotes end-chain signals, and (§) denotes potential signals from
low molecular weight oligomeric material.

432
A1.2.2
1
H NMR spectra of the polymers

Figure A1.8.
1
H NMR spectrum of PPDTBTX.

433

Figure A1.9.
1
H NMR spectrum of A1.
434
Figure A1.10.
1
H NMR spectrum of A2.

435

Figure A1.11.
1
H NMR spectrum of A3.
436

Figure A1.12.
1
H NMR spectrum of A4.
437

Figure A1.13.
1
H NMR spectrum of B1.
438

Figure A1.14.
1
H NMR spectrum of B2.
439

Figure A1.15.
1
H NMR spectrum of B3.
440

Figure A1.16.
1
H NMR spectrum of B4.
441

Figure A1.17.
1
H NMR spectrum of C1.

442

Figure A1.18.
1
H NMR spectrum of C2.
443

Figure A1.19.
1
H NMR spectrum of PPDTBTY.

A1.3 CV of the polymers

A1.3.1 Method

Cyclic voltammetry was executed on a Princeton Applied Research VersaStat3 potentiostat
under the control of VersaStudio Software. A standard three electrode cell based on a Pt
wire working electrode, a Pt wire counter electrode, and a silver wire pseudo reference
electrode (calibrated vs. Fc/Fc+ which is taken as 5.1 eV vs. vacuum)
1,2
was purged with
nitrogen and maintained under nitrogen atmosphere during all measurements. For cyclic
voltammetry, acetonitrile was distilled over CaH2 prior to use and tetrabutyl ammonium
444
hexafluorophosphate (0.1 M) was used as the supporting electrolyte. Polymer films were
made by applying a 10 mg mL
−1
o-DCB solution via dropcasting directly onto the working
electrode under a nitrogen umbrella and thoroughly dried prior to measurement.

Figure A1.20. CV traces for the electrochemical oxidation of class A DArP polymers as
identified in Table 1 of the main text.

445

Figure A1.21. CV traces for the electrochemical oxidation of class B DArP polymers as
identified in Table 1 of the main text.

446

Figure A1.22. CV traces for the electrochemical oxidation of class C DArP polymers and
Stille PPDTBT as identified in Table 1 of the main text.

447
A1.4 DSC profiles of the polymers
A1.4.1 Method
DSC profiles were recorded on a PerkinElmer DSC 8000 under N2 with a scan rate
of 10 °C/min. Sample size was about 8 mg, and polymers were used as obtained after
Soxhlet extraction.

Figure A1.23. DSC profiles for polymers as outlined in Table 2.1.
448

Figure A1.24. DSC profiles for polymers as outlined in Table 2.1.

449
A1.5 GIXRD patterns of the polymers
A1.5.1 Method

For thin film measurements, solutions were spin-coated onto pre-cleaned 2.5 cm
2

glass slides (sonicated for 10 minutes in water, acetone, and isopropyl alcohol then dried
under high N2 flow) from o-dichlorobenzene solutions at 7 mg mL
−1
. UV-vis absorption
spectra of neat polymer films were obtained on a Perkin-Elmer Lambda 950
spectrophotometer. The thickness of films and GIXRD measurements were obtained using
Rigaku Diffractometer Ultima IV using Cu Kα radiation source (λ = 1.54 Å) in the
reflectivity and grazing-incidence X-ray diffraction mode, respectively.
Crystallite size was estimated using Scherrer’s equation:
τ = Kλ/(β cosθ) (1)
where τ is the mean size of the ordered domains, K is the dimensionless shape factor (K =
0.9), λ is the x-ray wavelength, β is the line broadening at half the maximum intensity
(FWHM) in radians, and θ is the Bragg angle.

450

Figure A1.25. GIXRD patterns for class A DArP polymers as outlined in Table 2.1.

451

Figure A1.26. GIXRD patterns for class B DArP polymers as outlined in Table 2.1.

452

Figure A1.27. GIXRD patterns for class C DArP polymers and Stille PPDTBT as
identified in Table 1 of the main text.

453
A1.6 Tabulated Overview of Polymer Properties from CV Traces, Absorption
Profiles, DSC, and GIXRD Patterns

Table A1.1. Electrochemical HOMO, absorption onset in thin films, optical band gaps,
optical LUMO, λmax,abs , and absorption coefficients at peak wavelengths for class A, class
B, and class C DArP polymers as well as both Stille references, PPDTBT X and PPDTBTY.
Entry
HOMO
(eV)
Film
Onset
(nm)
Eg
(eV)
Optical
LUMO
(eV)
λmax,abs
(nm)
Abs.
Coeff.
(cm
-1
)
A1 5.43 711 1.74 3.69 605 67995
A2 5.42 708 1.75 3.67 644 67064
A3 5.44 706 1.76 3.68 602 50344
A4 5.42 709 1.75 3.67 605 63663
B1 5.43 700 1.77 3.66 642 69849
B2 5.48 712 1.74 3.74 599 57618
B3 5.52 704 1.76 3.76 599 53549
B4 5.55 705 1.76 3.79 600 49803
C1 5.45 710 1.75 3.70 602 61338
C2 5.45 705 1.76 3.69 657 88959
PPDTBTX 5.43 705 1.76 3.67 653 79335
PPDTBTY 5.44 715 1.73 3.71 659 82197

454
Table A1.2. 2θ, GIXRD intensities, interchain distances (100), peak widths at half
maximum (FWHM), crystallite size, melt, and glass transition temperatures (from DSC) of
class A, class B, and class C DArP polymers as well as both Stille references, PPDTBT X
and PPDTBTY.
Entry
2θ
(deg)
Intensity
(counts)
d100
(Å)
FWHM
a

(deg)
Crystallite
Size (nm)
Tm
(°C)
Tg
(°C)
A1 4.59 2240 19.23 0.505 15.78 -- --
A2 4.60 2120 19.19 0.494 16.13 -- --
A3 N/A -- -- -- -- -- --
A4 4.31
324
(negligible)
20.48 N/A N/A -- --
B1 4.51 2005 19.57 0.377 21.13 -- --
B2 4.45
176
(negligible)
19.83 N/A N/A -- --
B3 4.46
146
(negligible)
19.79 N/A N/A -- --
B4 N/A -- -- -- -- -- --
C1 4.24 1207 20.81 0.458 17.39 -- --
C2 4.35 3153 20.29 0.436 18.27 223 207
PPDTBTX 4.64 2597 19.02 0.469 16.99 236 220
PPDTBTY 4.61 2321 19.15 0.529 15.06 265 247
455
a
Although small peaks are visible for some polymers, due to inaccuracy as a result of these
low intensities (close to baseline), FWHM and crystallite size was not calculated for these
polymers, though the d100 lattice spacing is provided.

A1.7 Spectral Mismatch Determination

As emphasized by Shrotriya et al.,
3
there can be a spectral error in the measured short-
circuit current due to differences in the spectra irradiance of the light source and the
reference spectrum or differences in the spectral responses of the reference detector and
test cell. This error can be conveyed by a spectra mismatch correction factor (M)
4
which is
defined as:
22
11
22
11
() () () ()
() () () ()
Ref R S T
Ref T S R
E S dE S d
M
E S dE S d
λλ
λλ
λ λ
λ λ
λ λ λ λ λ λ
λ λ λ λ λ λ
=
∫∫
∫∫
(2),
where ERef (λ ) is the reference spectral irradiance; ES (λ ) is the source spectral irradiance;
SR (λ ) is the spectral responsivity; and ST (λ ) is the spectral responsivity of the test cell, each
as a function of wavelength ( λ). Spectral responsivities S(λ ) for the tested devices were
calculated based on the external quantum efficiency (EQE) values, according to equation
3:
() ()
q
S EQE
hc
λ
λ λ =
(3),
456
where the constant term q/hc equals 8.0655 x 10
5
for wavelength in units of meters and
S(λ ) in units of AW
-1
. Based on the spectral responsivities S(λ ) obtained using equation 3,
integrated short-circuit current densities (Jsc,EQE) can be obtained:
2
1
,
() ()
sc EQE Ref T
J E Sd
λ
λ
λ λ λ =
∫
(4).
In order to mismatch-correct the efficiencies of the BHJ solar cells, short-circuit current
densities (Jsc) were divided by the M, as defined in equation 5. The raw data (Jsc), spectral-
mismatch factor (M) and the spectral mismatch-corrected short-circuit current densities
(Jsc,corr) are summarized in Table A1.3.
,
sc
sc corr
J
J
M
=
(5).

A1.8 Solar Cell Data

The current-voltage (I-V) curves of the PSCs were measured in the voltage range -1
≤ V ≤ +1 (50 mV step size and 20 ms step time) with a Keithley 2400 source-meter under
a Steuernagel solar simulator (ambient conditions), which was previuosly calibrated with
a reference Si-photodiode providing 1000 W m
-1
AM 1.5G.
Spin-Coated ITO Substrates
The I-V characteristics were measured under ambient conditions using a Keithley
2400 source-meter. An Oriel® Sol3A class AAA solar simulator with a 450 watt xenon
lamp and an AM 1.5G filter was used as the solar simulator. An Oriel PV reference cell
system (91150V) was used as the reference cell. To calibrate the light intensity of the solar
simulator to 100 mW/cm
2
, the power of the xenon lamp was adjusted to make the short-
457
circuit current density (Jsc) of the reference cell under simulated sin light as high as it was
under the calibration condition.
External quantum efficiency measurements were performed using a 300 W xenon
arc lamp (Newport Oriel), chopped and filtered monochromatic light (250 Hz, 10 nm
FWHM) from a Cornerstone 260 ¼ m double grating monochromator (Newport 74125)
together with a light-bias lock-in amplifier. A silicon photodiode calibrated at Newport was
utilized as the reference cell. Spectr