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Synthesis, photophysical and electrochemical characterization of 1,3-bis(2-pyridylimino)isoindole derivatives
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Synthesis, photophysical and electrochemical characterization of 1,3-bis(2-pyridylimino)isoindole derivatives
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Content
SYNTHESIS, PHOTOPHYSICAL AND ELECTROCHEMICAL
CHARACTERIZATION OF 1,3-BIS(2-PYRIDYLIMINO)ISOINDOLE
DERIVATIVES
by
Kenneth Hanson
________________________________________________________________________
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)
August 2010
Copyright 2010 Kenneth Hanson
ii
Epigraph
“It is a profound and necessary truth that the deep things in science are not found because
they are useful; they are found because it was possible to find them.”
-J. Robert Oppenheimer
iii
Dedication
Dedicated to my wife:
Debbie Hanson
iv
Acknowledgements
First and foremost like to thank my advisor and mentor, Prof. Mark E. Thompson,
for guiding me in my pursuit of knowledge and always encouraging me to pursue my
ideas. I would also like to thank Prof. Thomas Flood, Prof. Richard L. Brutchey, Prof.
Kyung W. Jung, Prof. Stephen B. Cronin, and Prof. Alan E. Willner for not only being
members of my qualifying examinations but also for helping me grow and develop as a
scientist.
I would like to thank my past and present colleagues for our many hours in lab
together with emphasis on those who were key in helping our lab maintain order among
the chaos: Alberto Bossi, Marco Curreli, Chao Wu, Cody Schlenker, Wei Wei, and
Dolores Perez. All of the members of team IR, Dr. Arnold Tamayo, Dr. Carsten Borek,
Dr. Laurent Griffe, Dr. Seogshin Kang, Dr. Matthew T. Whited and Dr. Slava Diev have
my gratitude for both the knowledge and the friendship they have shared with me.
Special thanks to Prof. Peter I. Djurovich for all of our conversations/arguments that have
made me both a better scientist and a better person.
It is important to mention our collaborators, Prof. Mark S. Gordon, Dr. Jeramy
Zimmerman, Dr. Xixi Xu, Prof. Stephen R. Forrest and Dr. Jason Brooks and
administrative/technical staff Judy Hom, Michele Dea, Heather Meunier, Marie de la
Torre and Jamie Avila and also the undergraduate members of team IR without whom
much progress would not have been possible.
Without the support and guidance of my undergraduate advisors my graduate
school experience and this thesis would not have been possible. Thanks to Prof. Daniel D.
Gregory, Prof. Mohammad Mahroof-Tahir, Prof. Mark Mechelke, Prof. Donald R. Neu,
v
Prof. Lakshmaiah Sreerama and the other faculty and staff at St. Cloud State University
whom I am forever indebted to for pushing my life in the direction best suited for me.
Also thanks to Prof. Slavi C. Sevov (University of Notre Dame) and Prof. Richard B.
Kaner (University of California, Los Angeles) for mentoring me during my first full time
research experiences. Also Prof. Shiou-Jyh Hwu (Clemson University) and the other
organizers of the National Science Foundations Summer Research in Solid State
Chemistry program for making that full time research experience possible.
Outside of lab, the support of my brother and his wife, Colin and Samantha
Hanson, my parents Kevin and Catherine Hanson, and my grandparents Jim and Connie
Hanson have made me the person I am today. And to my closest friends, Benjamin
Sorenson, Luke Roskop, Lance Pickens, Christopher Meyer and Richard Giles who have
always been there to support and challenge me through the years. And finally, thanks to
my best friend and wife who has been more than happy to put up with “the crazy” that is
Kenneth Hanson.
vi
Table of Contents
Epigraph ........................................................................................................................... ii
Dedication ....................................................................................................................... iii
Acknowledgements ...................................................................................................... iv
List of Tables .................................................................................................................. ix
List of Figures ............................................................................................................... xi
Abstract ........................................................................................................................ xvii
CHAPTER 1. Introduction ...........................................................................................1
1.1 Photochemistry vs. Photophysics.........................................................................1
1.2 Photophysics of Hydrogen ...................................................................................1
1.3 Molecular Photophysics .......................................................................................4
1.4 Electron-Electron Interactions .............................................................................6
1.5 Electron “Spin” ..................................................................................................12
1.6 Jablonski Diagram .............................................................................................15
1.6.1 Introduction ...............................................................................................15
1.6.2 Radiative Processes ...................................................................................16
1.6.3 Nonadiative Processes ..............................................................................18
1.6.4 Spin-Orbit Coupling..................................................................................21
1.7 Quantum Yield ...................................................................................................23
1.8 1,3-bis(2-pyridylimino)isoindole .......................................................................23
Chapter 1 References ...................................................................................................25
CHAPTER 2. Synthesis...............................................................................................27
2.1 Introduction ........................................................................................................27
2.2 Synthesis of alcohol/ethoxy substituted 1,3-bis(aryl or alkyl)isoindoline ........28
2.3 Substituted BPI platinum complex ligand precursors .......................................32
2.4 BPI platinum complexes ....................................................................................34
2.5 Benzannulated BPI platinum chloride complexes .............................................39
2.6 Experimental Section .........................................................................................42
2.6.1 General ......................................................................................................42
2.6.2 X-ray Crystallography ............................................................................64
Chapter 2 References ...................................................................................................65
CHAPTER 3. The Photophysics of Dihydroxy Substituted BPI
Derivatives ......................................................................................................................68
3.1 Introduction ........................................................................................................68
vii
3.2 Experimental Section .........................................................................................70
3.2.1 Photophysical Characterization ................................................................70
3.2.2 Computational Method .............................................................................70
3.3 Results and Discussion ......................................................................................71
3.3.1 Photophysics of BPI and hydroxyl/alkoxy substituted BPI ......................71
3.3.2 Absorption properties of dihydroxy bisiminoisoindole derivatives ..........77
3.3.3 Emissive properties of dihydroxy bisiminoisoindole derivatives .............82
3.4 Conclusion .........................................................................................................87
Chapter 3 References ...................................................................................................88
CHAPTER 4. Systematic Investigation of the Photophysical and
Electrochemical Properties of 1,3-bis(2-pyridylimino)isoindolate
Platinum(II) Derivatives ..............................................................................................89
4.1 Introduction ........................................................................................................89
4.2 Experimental Section .........................................................................................91
4.2.1 Electrochemical and Photophysical Characterization ...............................91
4.2.2 Computational Methods ............................................................................92
4.3 Results and Discussion ......................................................................................93
4.3.1 Computational Results ..............................................................................93
4.3.2 Electrochemistry .......................................................................................95
4.3.3 Electronic Spectroscopy ............................................................................98
4.3.4 Temperature Dependence .......................................................................111
4.4 Conclusion .......................................................................................................113
Chapter 4 References .................................................................................................115
CHAPTER 5. A Paradigm for Blue- or Red-Shifted Absorption
Depending on the Site of π-Extension as Exemplified in the
Photophysics of 1,3-Bis(2-pyridylimino)isoindolate Platinum(II)
Chloride and Others ....................................................................................................118
5.1 Introduction ......................................................................................................118
5.2 Experimental Section .......................................................................................119
5.2.1 Electrochemical and Photophysical Characterization .............................119
5.2.2 Computational Methods ..........................................................................120
5.3 Results and Discussion ....................................................................................121
5.3.1 Electrochemistry .....................................................................................121
5.3.2 Electronic Spectroscopy ..........................................................................124
5.3.3 Computational Results ............................................................................129
5.4 Conclusion .......................................................................................................141
Chapter 5 References .................................................................................................143
BIBLIOGRAPHY .......................................................................................................145
APPENDICES:
viii
APPENDIX 1: Efficient Dipyrrin-Centered Phosphorescence at
Room Temperature from Bis-Cyclometalated Iridium(III)
Dipyrrinato Complexes ........................................................................................155
A1.1 Introduction .............................................................................................155
A1.2 Experimental Section ..............................................................................157
A1.2.1 Synthesis ........................................................................................157
A1.2.2 X-ray Crystallography....................................................................161
A1.2.3 Electrochemical and Photophysical Characterization ....................163
A1.2.4 Computational Method ..................................................................163
A1.2.5 Device Fabrication .........................................................................164
A1.3 Results and Discussion............................................................................165
A1.3.1 Synthesis and Structure ..................................................................165
A1.3.2 DFT Calculations ...........................................................................171
A1.3.3 Electrochemistry ............................................................................173
A1.3.4 Electronic Spectroscopy .................................................................175
A1.3.5 OLED .............................................................................................183
A1.4 Conclusion ..............................................................................................185
Appendix 1 References ........................................................................................187
APPENDIX 2: The Synthesis of Near-infrared Absorbing Donor
/Acceptor Polymers and Their Application in Photodetectors .................190
A2.1 Introduction .............................................................................................190
A2.2 Synthesis .................................................................................................193
A2.3 Experimental Section ..............................................................................201
A2.3.1 General Information .......................................................................201
Appendix 2 References ........................................................................................209
APPENDIX 3: The Synthesis of 8,16-diphenyl-s-indaceno[1,2,3-
cd:5,6,7-c’d’]diphenalene for Application in Organic
Photodetectors ........................................................................................................211
A3.1 Introduction .............................................................................................211
A3.2 Synthesis .................................................................................................214
A3.3 Experimental Section ..............................................................................218
A3.3.1 General Information .......................................................................218
Appendix 3 References ........................................................................................224
APPENDIX 4: The Synthesis of PbS Quantum Dots ..................................225
A4.1 Introduction .............................................................................................225
A4.2 Synthesis .................................................................................................227
A4.3 Experimental Section ..............................................................................230
Appendix 4 References ........................................................................................231
ix
List of Tables
Table 2.1. The structure of alcohol/ethoxy substituted 1,3-bis(aryl or
alkyl)isoindoline dyes 3.1-7. ..............................................................................................29
Table 2.2. Select bond angles (°) and distances (Å) for BPI, 3.3 and 3.7. .......................31
Table 2.3. The structure of substituted BPI platinum complex ligand precursors. ...........32
Table 2.4. The structure of BPI platinum complexes 4.1-12. ...........................................34
Table 2.5. Crystallographic data for compounds 3.3 and 3.7. ...........................................65
Table 3.1. The structure of alcohol/ethoxy substituted 1,3-bis(aryl or
alkyl)isoindoline dyes 3.1-7. ..............................................................................................70
Table 3.2. Photoluminescent properties of 3.3 in various solvents at room
temperature. .......................................................................................................................73
Table 3.3. Absorption maxima and molar absorptivity of compounds 3.1-7.in
toluene, CH
2
Cl
2
and methanol. ..........................................................................................78
Table 3.4. Photophysical properties of BPI and 3.1-7 in various solvents and
PMMA. ..............................................................................................................................86
Table 4.1. TDDFT vertical excitation energies for the CPCM solvated complexes. ........94
Table 4.2. HOMO/LUMO energies for the CPCM solvated complexes. .........................94
Table 4.3. Electrochemical potentials for 4.1–4 reported in volts (V) relative to
Fc
+
/Fc.
a
Unless otherwise noted, electrochemical reductions are reversible and
oxidations are irreversible. .................................................................................................96
Table 4.4. The relative intensities and the orbitals involved in the 20 lowest
energy transitions of 4.6 found by TDDFT. ....................................................................101
Table 4.5. Photophysical properties of 4.7 in various solvents at room
temperature. .....................................................................................................................108
Table 4.6. Photophysical properties of complexes 4.1-14. .............................................110
Table 5.1. Electrochemical potentials for 5.1–5 reported in volts (V) relative to
Fc
+
/Fc. ..............................................................................................................................122
Table 5.2. Photophysical properties of complexes 5.1-5. ...............................................128
x
Table 5.3. Selected bond lengths (Å) and angles (degrees) for 5.1-5 from DFT
calculations and reported x-ray data of 5.2. .....................................................................130
Table 5.4. TDDFT and TDA vertical excitation energies for gas phase and CPCM
solvated complexes. .........................................................................................................131
Table 5.5. HOMO/LUMO energies and the Kohn-Sham Shifts (HOMO-LUMO
gap) for the gas phase and CPCM solvated complexes. ..................................................132
Table A1.1. Crystallographic data for compounds A1.3, A1.4 and A1.5(6’,6’). ............162
Table A1.2. Selected Bond Distances and Angles for A1.3, A1.4, A1.5(6’,6’),
(ppz)
2
Ir(bpy)
+
, and Zn(5-Ph-dpym)
2
. ...............................................................................168
Table A1.3. Calculated HOMO/LUMO values and oxidation/reduction potentials
for complexes A1.1–7. .....................................................................................................172
Table A1.4. Photophysical properties of complexes A1.1–7. .........................................182
xi
List of Figures
Figure 1.1. a) Bohr model representation of the photoexcitation of a hydrogen
atom. b) The absorption lines of hydrogen in the visible region of the
electromagnetic spectrum. ...................................................................................................2
Figure 1.2. Potential energy surface of the ground and first excited states with
absorption(abs), emission(em) and nonradiative(nr) transitions between states
labeled accordingly. .............................................................................................................5
Figure 1.3. Pictorial representation of the interaction between atomic orbitals
(AOs) of a) similar energies/symmetries, b) unequal energies and c) dissimilar
symmetries. ..........................................................................................................................8
Figure 1.4. a) the ground state and three possible excited state electron
configurations of a molecule, b) 1,3-bis(2-pyridylimino)isoindolate platinum(II)
chloride ((BPI)PtCl), c) the absorption spectrum of (BPI)PtCl in dichloromethane. ..........9
Figure 1.5. Possible orientations of electrons in the ground and the excited state. .........12
Figure 1.6. Pictorial representation of the four possible two electron interactions. ........13
Figure 1.7. A Jablonski diagram representing the ground (S
0
), singlet excited
(S
1
) and triplet excited (T
1
) states of a molecule and the transitions between them.
1) Singlet to singlet absorption (S
0
+ hν→ S
1
); 2) fluorescence (S
1
→ S
0
+ hν);
3) internal conversion (S
1
→ S
0
+ heat); 4) intersystem crossing (S
1
→ T
1
+ heat);
5) Singlet to triplet absorption (S
0
+ hν→ T
1
); 6) phosphorescence (T
1
→ S
0
+
hν); 7) intersystem crossing (T
1
→ S
0
+ heat). ..................................................................15
Figure 1.8. A pictorial representation of the absorption and emission process for
a TICT molecule. ...............................................................................................................18
Figure 2.1. Structure of 1,3-bis(2-pyridylimino)isoindoline (BPI). .................................27
Figure 2.2. Standard reaction conditions for the synthesis of BPI and related
compounds. ........................................................................................................................28
Figure 2.3. ORTEP drawings of compounds 3.3 and 3.7. (carbon (black),
nitrogen (blue), oxygen (red)) ............................................................................................31
Figure 2.4. Reaction scheme for the platination of BPI with (COD)PtCl
2
. ......................35
Figure 2.5. Reaction scheme for the synthesis of (BPI)PtMe. ..........................................37
Figure 2.6. Monitored decomposition of (BPI)PtMe
1
H NMR (CDCl
3
). .........................38
xii
Figure 2.7. Reaction scheme for the synthesis of BPEP. .................................................40
Figure 2.8. The structure of BPI platinum complexes with varying degrees of
benzannulation. ..................................................................................................................40
Figure 2.9. 250 MHz
1
H NMR spectra of complex 5.1 (CDCl
3
). Inset: expansion
of the region from 6.8 to 11 ppm. ......................................................................................41
Figure 3.1. Schematic representation of an ESIPT process with a generalized
oxygen donor and a nitrogen acceptor motif. ....................................................................68
Figure 3.2. Room temperature absorption (in CH
2
Cl
2
) and 77K emission (in 2-
MeTHF) of BPI. ................................................................................................................71
Figure 3.3. Absorption spectra of 3.3 in methanol, CH
2
Cl
2
and toluene. .........................72
Figure 3.4. Emission spectra of 3.3 in methanol, CH
2
Cl
2
and toluene. ............................73
Figure 3.5. Absorption (in MeOH, open symbol) and emission (in toluene, filled
symbol) spectra of 3.3 (square), 3.6 (circle), and 3.7 (triangle) at room
temperature. .......................................................................................................................75
Figure 3.6. Emission spectra of BPI, 3.3, 3.6 and 3.7 in 2-MeTHF at 77K. ....................76
Figure 3.7. Enol and keto forms of 3.3. ............................................................................76
Figure 3.8. HOMO and LUMO of 3.3. The HOMO (transparent) and LUMO
(mesh) surfaces are displayed as viewed above the π-symmetric orbitals, with
opposite phases above and below the plane of the molecule. ............................................77
Figure 3.9. Room-temperature absorption spectra of a) 3.1, b) 3.2, c) 3.4 and d)
3.5 in toluene, CH
2
Cl
2
and methanol. ................................................................................79
Figure 3.10. Test tube samples of 3.4 in toluene, THF, DCM, methanol and DMF.
............................................................................................................................................81
Figure 3.11. Room-temperature emission spectra of a) 3.1, b) 3.2, c) 3.4 and d)
3.5 in toluene, CH
2
Cl
2
and methanol. ................................................................................82
Figure 3.12. Absorption, excitation and emission spectra of 3.1 in methanol. .................83
Figure 3.13. Emission spectra of 3.1, 3.2, 3.4 and 3.5 in 2-MeTHF at 77K. ....................84
Figure 3.14. The room temperature absorption (black, empty) and emission (red,
filled) spectra of 3.4 in methanol. ......................................................................................85
xiii
Figure 4.1. Structure of substituted 2,5-bis(2-pyridylimino)isoindolate platinum
X complexes.......................................................................................................................91
Figure 4.2. HOMO and LUMO orbitals and energies for complexes 4.1-12. The
HOMO (solid) and LUMO (transparent) surfaces are displayed as viewed above
the π-symmetric orbitals, with opposite phases above and below the plane of the
molecule. The gray lines are a reference to the parent complex 4.1. .................................95
Figure 4.3. HOMO (bottom) and LUMO orbitals and the lowest energy transition
for BPI and 4.1. ..................................................................................................................98
Figure 4.4. Room-temperature absorption spectra of complexes 4.1-6 in CH
2
Cl
2
. ..........99
Figure 4.5. Room-temperature absorption spectra of complex 6. The calculated
transitions are shown as vertical bars with heights equal to the oscillator strength. .......100
Figure 4.6. The relative intensities and the orbitals involved in the two lowest
energy transitions of 4.6 found by TDDFT. ....................................................................102
Figure 4.7. Room-temperature absorption spectra of complexes 4.1 and 4.7-12 in
CH
2
Cl
2
..............................................................................................................................102
Figure 4.8. Room-temperature absorption spectra of complex 4.7 in various
solvents. ...........................................................................................................................103
Figure 4.9. Room-temperature emission spectra of complexes a) 4.1-5 and b) 4.7-
12 in toluene. ....................................................................................................................105
Figure 4.10. Energy vs ln(k
nr
) for 4.1-12. Linear fit (red line) was for complexes
4.1 and 4.7-12. .................................................................................................................107
Figure 4.11. Room-temperature emission spectra of complex 4.7 in various
solvents. ...........................................................................................................................108
Figure 4.12. Emission spectra of complexes a) 4.1-6 and b) 4.7-14 in 2-MeTHF
at 77K. ..............................................................................................................................109
Figure 4.13. The plot of lifetime (τ) versus temperature (K) for complex 4.1 in 2-
MeTHF. Inset: The data from 120 to 290 K plotted as the ln(1/ τ) versus (1/T). ............112
Figure 5.1. The structure of BPI platinum complexes with varying degrees of
benzannulation. ................................................................................................................119
xiv
Figure 5.2. CV of complexes 5.2 and 5.5 (150 mV/s). The insets (a and b) show
the DPV traces of complexes 5.2 and 5.5, respectively (top, oxidative scan;
bottom, reductive scan). The peaks at 0 V are due to the internal ferrocene
reference. ..........................................................................................................................123
Figure 5.3. a) Normalized absorption spectra of BPEP, BPI, benz(f)BPI,
benz(e)BPI and BIQI in CH
2
Cl
2
at room temperature. b) Room-temperature
absorption spectra of 5.1–5 in CH
2
Cl
2
. ............................................................................125
Figure 5.4. Emission spectra of 5.1–5 in a) toluene at room temeprature and b) 2-
MeTHF at 77K. ................................................................................................................126
Figure 5.5. Calculated structure of 5.2. With atoms carbon and nitrogen indicated
by black and blue spheres respectively. Hydrogen atoms were omitted for clarity. .......129
Figure 5.6. Qualitative orbital diagram of the valence orbitals for complexes 5.1’,
5.2 and 5.3. The HOMO (bottom, solid) and LUMO (top, transparent) surfaces
are displayed as viewed above the π-symmetric orbitals, with opposite phases
above and below the plane of the molecule. ....................................................................133
Figure 5.7. Qualitative orbital diagram of the valence orbitals for complexes 5.2,
5.4 and 5.5. .......................................................................................................................135
Figure 5.8. Qualitative orbital diagram for benzanulation at the 2,3-position (5.6)
and the 1,2-position (5.7) of 5.2. ......................................................................................136
Figure 5.9. Molecules other than 5.2 that exhibit a blue-shift in absorption upon
benzannulation. ................................................................................................................137
Figure 5.10. Qualitative orbital diagram for PTCAI and CTCAI. ..................................139
Figure 5.11. Qualitative orbital diagram for benzannulated
dibenzotetrathiafulvalene complexes. ..............................................................................141
Figure A1.1. Structure of (C^N)
2
Ir(5-R-dipy) complexes A1.1–7. See Figure
A1.3 for the isomers of A1.5. ..........................................................................................156
Figure A1.2. HPLC: Absorption/Mass Spectrum for A1.5.............................................166
Figure A1.3. Proton assignments for the 3 regio isomers of A1.5. .................................167
Figure A1.4. ORTEP drawings of compounds A1.3, A1.4 and A1.5(6’,6’).
(carbon (black), nitrogen (blue), oxygen (red), iridium (purple)). A second unique
structure for A1.4 found in the unit cell is not shown. ....................................................168
xv
Figure A1.5. The planes of the pyrrole rings (light and dark grey planes) of A1.3
define by the nitrogen, α and β carbon atoms adjacent to the methene linker. ................169
Figure A1.6. The out of plane (defined by Ir, N
pyr
and N
pyr
) distortion of the
dipyrrin (defined by N
pyr
, N
pyr
and C
meso
) in A1.3. ..........................................................170
Figure A1.7. (a) Qualitative orbital energy diagram illustrating the HOMO
(transparent) and LUMO (mesh) orbitals of A1.3 and A1.5(2’,2’), A1.5(2’,6’) and
A1.5(6’,6’). All values reported in eV. (b) Triplet spin-density surface of A1.3. ...........171
Figure A1.8. CV of A1.3 and A1.5. The CV of A1.3 has been offset vertically for
clarity. ..............................................................................................................................174
Figure A1.9. a) Room-temperature absorption spectra of A1.1-4 and b) A1.4-7 in
CH
2
Cl
2
..............................................................................................................................176
Figure A1.10. Room-temperature (a) and 77K (b) emission spectra of A1.1-4 in
2-MeTHF. Room-temperature (c) and 77K (d) emission spectra of A1.4-7 in 2-
MeTHF. ............................................................................................................................177
Figure A1.11. Absorption (in CH
2
Cl
2
, filled symbol) and emission (in 2-MeTHF,
open symbol) spectra of A1.6 (square) and A1.7 (circle) at room temperature. ............178
Figure A1.12. Energy level diagram and device architecture for OLEDs using
dopants A1.3 and A1.5.....................................................................................................183
Figure A1.13. Luminance (red, cd/m
2
) and current density (black, mA/cm
2
) as a
function of voltage (V) for OLEDs using compound A1.3 (filled squares) and
A1.5 (open triangles). ......................................................................................................183
Figure A1.14. EL spectra of OLEDs using dopants A1.3 and A1.5. ..............................184
Figure A1.15. Quantum efficiency as a function of current density (mA/cm
2
) for
OLEDs using dopants A1.3 and A1.5. .............................................................................185
Figure A2.1. Absorption spectrum of sodium dodecyl sulfate isolated HiPCO-
grown CNTs with chirality assignments from Weisman and Bachillo............................191
Figure A2.2. Device architecture (a) and detectivity (b) for CNT MEH-PPV
device. ..............................................................................................................................192
Figure A2.3. Synthesis of A2.6. a) n-butyllithium, I
2
; b) PCC; c) Cu; d) N
2
H
4
,
KOH; e) KOH, 2-ethylhexyl bromide, NaI; f) n-butyllithium, trimethyltin chloride.
..........................................................................................................................................194
xvi
Figure A2.4. Synthesis of molecules A2.6-10. a) X = O: Fe, Br
2
; X = S: Br
2
, HBr;
b) SeO
2
, EtOH; c) Ag
2
SO
4
, H
2
SO
4
; d) Br
2
, HBr; e) SOCl
2
, pyridine f) NaBH
4
; g)
TeCl
4
, NEt
3
. .....................................................................................................................196
Figure A2.5. Synthesis of polymers A2.P1-4. (R = 2-ethylhexyl) .................................197
Figure A2.6. Absorption spectra of polymers A2.P1-4 in CH
2
Cl
2
. ................................198
Figure A2.7. Responsivity (a, c) and detectivity (b, d) of CNT devices produced
with polymers A2.P3 (a,b) and A2.P4 (c,d). ...................................................................200
Figure A3.1. 8,16-diphenyl-s-indaceno[1,2,3-cd:5,6,7-c’d’]diphenalene (THc). ..........211
Figure A3.2. Absorption spectra of THc in CH
2
Cl
2
. ......................................................212
Figure A3.3. Synthesis of THc. a) KOH; b) xylene, KMnO
4
; c) Cl
2
CHOCH
3
,
TiCl
4
; d) NaBH
4
; e) PBr
3
; f) CH
3
COOtBu; g) p-toluenesulfonic acid; h) (COCl)
2
,
AlCl
3
; i) NaBH
4
; j) p-toluenesulfonic acid; k) p-chloranil. .............................................213
Figure A3.4. The
1
H NMR (250 MHz) spectra of A3.3 in CDCl
3
. Inset:
expansion of the 8.75 to 8.90 ppm region of the spectra. ................................................214
Figure A3.5. The
1
H NMR (250 MHz) spectra of THc in CDCl
3
with peak
assignments from reference 2. .........................................................................................215
Figure A3.6. Thin film absorption spectra of THc produced by (a) spin casting
and (b) organic vapor phase deposition. ..........................................................................217
Figure A4.1. General synthesis of PbS quantum dots.....................................................226
Figure 4A.2. PbS quantum dot absorption spectra of reaction products (a)
maintained at 120°C with various reaction times and (b) with various reaction
temperatures at a consistent 30 second reaction time. .....................................................228
Figure 4A.3. PbS quantum dot absorption spectra of reaction run at 225°C for 20
sec. ...................................................................................................................................230
xvii
Abstract
The light emitting and absorbing small molecules are interesting for many
applications ranging from solar energy conversion to photodynamic therapy. There are
many variables that contribute to the intensity, energy and efficiency of absorption and
emission including the HOMO/LUMO energy levels, molar absorptivities, excited state
lifetimes, geometry changes in the excited state, radiative and nonradiative rates, and
others. One of the fundamental goals of photophysical chemists is to understand how
molecular structure correlates with these properties. Once structure-property relationships
are understood, new molecules can be designed with particular applications in mind. In
this thesis, the synthesis, electrochemical and photophysical properties 1,3-bis(2-
pyridylimino)isoindoline (BPI) derivatives will be reported and structure property
relationships discussed.
In chapter one general concepts and nomenclature associated with the
photophysics of small molecules are introduced. The discussion begins with the simplest
of light absorbing materials, hydrogen, and then expands to many electron, molecular
systems.
Prior to discussing the photophysical properties of BPI derivatives, the synthesis
of both the BPI based molecules and platinum BPI complexes will be described in
chapter two. To confirm the identity of the compounds all products were characterized by
mass spectrometry, x-ray crystallography, elemental analysis and NMR spectroscopy.
Although the parent BPI is non-emissive at room temperature, fluorescence from
the dihydroxy substituted BPI derivatives is discussed in chapter 3. The unusual emission
from these compounds is attributed to an excited state proton transfer as supported by the
xviii
large apparent Stokes shift (6600 cm
-1
) between absorption and emission, the lack of
emission from the alkoxy substituted BPI and the large changes in lifetime/efficiency in
deauterated methanol (MeOD).
In chapter four, the photophysical and electrochemical characterization of a series
of platinum(II) complexes of the form (N^N^N)PtX where N^N^N is an assortment of
substituted 1,3-bis(2-pyridylimino)isoindolate ligands and X represents various anionic
monodentate ligands is discussed. It has been found that the quantum efficiency of
emission for all of the complexes is dictated by the nonradiative rates of deactivation
from the excited state. The nonradiative rates of the platinum chloride complexes are
found to correlate with the energy gap law. For other PtX complexes the graph of the
natural log of the nonradiative rates versus energy of emission was found to be nonlinear.
The nature of these nonradiative processes is investigated from temperature dependent
studies on the excited state lifetime.
Finally, in chapter five a series of five platinum(II) chloride BPI based complexes
with varying degrees of benzanulation are characterized. For this series of molecules,
either a blue shift or a red shift in absorption and emission maxima, relative to their
respective parent compounds, was observed that depended on the site of benzannulation.
Experimental data and first principles calculations suggest that a similar HOMO energy
level and a destabilized or stabilized LUMO with benzannulation is responsible for the
observed trends. An explanation for LUMO stabilization/destabilization is presented
using simple molecular orbital theory. This explanation is expanded to describe other
molecules with this unusual behavior.
1
CHAPTER 1. Introduction
1.1 Photochemistry vs. Photophysics
The interaction between light (photons) and matter is one of the most fundamental
processes in the universe.
1
This interaction can be broken down into two basic
categories: photochemistry and photophysics. In a photochemical process some material
(R) interacts with a photon (hν) to give the electronically excited material (R*) which
undergoes a net physical change to give product (P) and can be summarized by the
equation R + hν → R* → P. Although photochemical reactions are important for many
processes (e.g. photosynthesis,
2
bioluminescence
3
and photo-initiated polymerizations
4
)
the discussion herein will be focused on the photophysical properties of matter.
In a photophysical process, as opposed to a photochemical one, no net physical
change of the material that is excited is observed. In general, this process can described
by the equation R + hν
1
→ R* → R + hν
2
. As with the initial steps of a photochemical
reaction some material (R) interacts with a photon (hν
1
) to give the electronically excited
material (R*). The electronically excited material then relaxes to the ground state (R) by
either radiative or a nonradiative process. If the relaxation occurs via a radiative process,
the return to R from R* is accompanied by a release of light (hν
2
).
1.2 Photophysics of Hydrogen
The simplest example of a photophysical process is the excitation and emission of
hydrogen. A simple system like hydrogen (a single electron bound to a single proton)
which lacks complex electron-electron interactions can be depicted using the Bohr model
2
of the atom (Figure 1.1). In the Bohr model of hydrogen, a single electron orbits around a
central proton in a circular motion at a discrete set of distances and energies.
A consequence of the attractive electrostatic forces between the positive proton
and the negative electron is that the lowest energy configuration (ground state) of
hydrogen occurs when the distance of separation between the two point charges is the
smallest allowable distance (lowest energy orbital). When the hydrogen atom absorbs
energy equal to the energy difference between two orbitals (ΔE), the electron jumps to a
higher energy orbital (excited state). Although Figure 1.1a depicts excitation from the
ground state (n = 1) to the lowest energy excited states (n = 2), it is possible to excite the
electron to any of the orbitals up to the point before complete electron dissociation. Each
transition from the ground state (n = 1) to the excited state (n →∞) will have an energy
400 450 500 550 600 650 700
0.0
0.2
0.4
Wavelength (nm)
Figure 1.1. a) Bohr model representation of the
photoexcitation of a hydrogen atom. b) The absorption lines of
hydrogen in the visible region of the electromagnetic spectrum.
3
(ΔE) associated with the transition. When the source of energy for excitation is in the
form of electromagnetic radiation, the wavelength of light absorbed (λ) is related to the
change in energy (ΔE) by the equation ΔE = hc/λ where h is Planck’s constant (6.63 x 10-
37 joule seconds) and c is the speed of light (3.0 x 10
8
cm/s). The implication of having
many well defined absorption transitions is that when white light is passed through a
hydrogen sample, several wavelengths of visible light are absorbed (Figure 1.1b). The
single electron nature of a hydrogen atoms makes prediction of the wavelength of
absorption possible using the empirically derived Rydberg formula: 1/ λ = R(1/(n
l
)
2
-
1/(n
h
)
2
) where R is the Rydberg constant (1.0974 x 10
7
/m), n
l
and n
h
are the lower and
higher orbital number respectively.
A hydrogen atom that is in the excited state has potential energy equal to the
difference between the ground and excited state. The amount of time the atom spends in
the excited state (lifetime, τ) is not indefinite due to a thermodynamic drive to return to
the ground state. Upon returning to the ground state, light is given off that is equal in
energy to the difference between the two states, also described by the Rydberg formula.
What is now known as the Rydberg formula was originally proposed by Swedish
physicist Johannes Rydberg on November 5, 1888.
5
Since this time, the predictions of
hydrogen emission and absorption increased in accuracy and utility due to the inclusion
of properties such as the spins of the electrons and protons in the calculations. This
fundamental understanding of the photophysics of hydrogen is used in numerous
applications ranging from atomic spectroscopy to astronomy.
6-8
The strong understanding
of hydrogen’s photophysical properties is directly related to the simplicity of the
system(1H
+
, 1e
-
). For molecular systems (>1 atom, >1e
-
), predictions relating to the
4
photophysical properties is much more difficult. However, understanding the
photophysical properties of light absorbing/emitting small molecules is the first step in
the development of new materials for a large number of potential applications ranging
from solar energy conversion to photodynamic therapy.
9, 10
1.3 Molecular Photophysics
Molecules and their photophysical properties cannot be described by the Bohr
model or Rydberg formula; many additional variables must be taken into account because
of the multi-electron, multi-atom nature of molecules. For example, Heisenberg
uncertainty principle requires that atoms cannot be static but instead are always in motion,
vibrating in space relative to each other. Changes in molecular structure and energy are
the direct result of these atomic motions. The implications of these inherent and constant
geometry changes is that the ground state cannot be readily described by a single
geometry or energy but instead must be approximated by a potential energy surface
(Figure 2.1.). In these potential energy surface diagrams the x axis represents changes in
the molecules geometry and the y axis is the potential energy of the system. As the
geometry of the molecule changes so too will the potential energy associated with that
structure. The lowest energy ground state geometry (most probable geometry) is at the
lowest point on the potential energy surface.
5
Rather than addressing individual electrons in a molecule, they can first be
conceptualized as an electron density cloud composed of the summation of individual
electrons. According to the Born-Oppenheimer approximation, the movement of
electrons is much faster (10
-15
-10
-16
s) than the movement of atoms (10
-13
-10
-14
s). From
this approximation, the absorption of a photon by a molecule can be thought of as an
electromagnetic wave causing a very fast shift in electron density (charge transfer)
without changes in nuclear geometry. This step wise process can be summarized as a
vertical jump from the ground state to the excited state potential energy surface (Figure
1.2, abs) followed by a nuclear rearrangement to the most stable excited state geometry
(minimum of the excited state surface). The energy difference between the initial and
final excited state geometries is dissipated in the form of molecular vibrations (heat). As
was mentioned with hydrogen, excitation from the ground state to any of the higher lying
excited states is possible. However, unlike hydrogen, emission is not likely to be
observed from higher lying excited states in accordance with Kasha’s rule. Kasha’s rule
states that deactivation from higher lying excited states to the lowest energy excited state
abs
Ground State
First Excited State
Potential
Energy
em
nr
Figure 1.2. Potential energy surface of the ground
and first excited states with absorption(abs),
emission(em) and nonradiative(nr) transitions between
states labeled accordingly.
6
(internal conversion) via vibrational relaxation occurs faster than emission from these
states and as a result only emission from the lowest energy excited state is expected.
Once a molecule is in the lowest energy excited state there are two possible means
of returning to the ground state: radiative or nonradiative relaxation. During either of
these processes the total energy of the system must be conserved. For radiative relaxation,
a vertical jump from the first excited state to the ground state potential energy surface
(Figure 1.2, em) occurs simultaneously with the release of a photon at a wavelength equal
to the energy difference between the two states. In a one photon process the energy of the
incident radiation (hν
1
) must be greater than or equal to the energy of the radiated light
(hν
2
) due to thermodynamic limitations dictated by atomic motions of the material. The
energy difference between the two (hν
1
and hν
2
) is commonly referred to as the Stokes
shift and is directly the result of the structural differences between the ground and the
excited state. During a nonradiative deactivation processes light is not released but
instead the energy is dissipated through vibration. There are several pathways for
molecules to nonradiatively decay and they are to be discussed later.
1.4 Electron-Electron Interactions
Up until this point atoms/molecules have either been described as having a single
electron (hydrogen) or an electron density cloud (molecules). However, electron-electron
interactions become extremely important when discussing the photophysics of molecules.
The interactions of electrons in a system (atomic or molecular) are dictated by several
fundamental “rules”.
7
In classical mechanics, electrons are described as single point negative charges
that repel each other. According to Coulomb’s Law (F =q
1
q
2
/4πε
0
r
2
), the force of the
repulsion between two point charges (q
1
and q
2
) is inversely proportional to 4π multiplied
by the permittivity of space (ε
0
) and square of the distance between them (r
2
). More
simply put, like charges repel and the closer they are the higher the energy of the
interaction. In addition to the point charge of electrons, they also have a quantum
mechanical property known as “spin”. Although spin has no classical analog, it can
roughly be thought of as the angular momentum of an electron. Unlike the angular
momentum of a classically described object where there are many possible values; there
are only two allowed values of spin for an electron, either up (α) or down (β). In a single
electron system like hydrogen the spin of that electron has minimal importance. However,
the addition of more electrons to hydrogen requires the spin be taken into account. There
are two important rules to follow when filling the orbitals of an atom/molecule (for the
sake of simplicity Hund’s rule will be neglected). First, each orbital can contain two
electrons of the opposite spin (α and β) in accord with the Pauli exclusion principle.
Second, the Aufbau principle states that electrons will stepwise fill the orbitals in the
lowest energy configuration. According to these rules the first orbital (n = 1) of a
hydrogen anion will be filled with two electron of opposite spins (α and β). The third and
fourth electron will occupy the second orbital (n = 2) in the same manner and so on with
each additional electron. The rules that guide the filling of electrons in hydrogen also
apply to the orbitals of molecules.
8
The orbitals of a molecule (MOs) are constructed from the orbitals of the atoms
(AOs) that compose the molecule. There are two possible outcomes when evaluating the
interaction between AOs: bonding/antibonding or nonbonding. If the orbitals are similar
enough in energy and have the same symmetry as to physically interact with each other
then bonding (inphase) and antibonding (out-of-phase) MOs are produced (Figure 1.3a).
On the other hand, if the AOs of interest are extremely unequal in energy (Figure 1.3b) or
lack the correct symmetry (Figure 1.3c) then no interaction occurs which are described as
nonbonding orbitals. Regardless of the types of interaction the number of MOs in a
molecule will be equal to the total number of AOs from the atoms in the molecule. As
was seen with hydrogen the molecular orbitals will also be filled by pairs of electrons (α
and β) starting with the lowest energy orbitals and expanding from there.
Molecules with many atoms, for example 1,3-bis(2-pyridylimino)isoindolate
platinum(II) chloride ((BPI)PtCl; 37 atoms and 250 electrons) to be discussed in Chapter
Figure 1.3. Pictorial representation of the interaction between atomic
orbitals (AOs) of a) similar energies/symmetries, b) unequal energies and
c) dissimilar symmetries.
9
4 (Figure 1.4b), will have a large number of molecular orbitals that are either filled by
pairs of electrons (occupied orbitals) or empty (unoccupied orbitals) as can be seen in
Figure 1.4a. Much like with hydrogen, each electron has the possibility to be excited
from its ground state orbital to an unoccupied orbital. The energy of each transition is
equal to the energy difference between the occupied and the unoccupied orbital. As with
hydrogen, when white light is passed through a sample of (BPI)PtCl several wavelengths
of light will be absorbed that are equal in energy to these transitions.
The intensity of each peak (amount of light absorbed) or the probability of the transition
occurring is dependent on the nature of the unoccupied and occupied orbitals involved in
the transition. Experimentally, the intensity of absorption at a given wavelength is
quantified by molar absorptivity (ε). In this experiment incident light (I
0
) is passed
300 400 500 600 700
0.0
0.5
1.0
1.5
2.0
2.5
3.0
W avelength (nm)
ε ε ε ε (x10
4
M
-1
cm
-1
)
Lower E Higher E
Ground
State
Excited State
a) b)
c)
300 400 500 600 700
0.0
0.5
1.0
1.5
2.0
2.5
3.0
W avelength (nm)
ε ε ε ε (x10
4
M
-1
cm
-1
)
Lower E Higher E
Ground
State
Excited State
a) b)
c)
Figure 1.4. a) the ground state and three possible excited state electron
configurations of a molecule, b) 1,3-bis(2-pyridylimino)isoindolate platinum(II)
chloride ((BPI)PtCl), c) the absorption spectrum of (BPI)PtCl in dichloromethane.
10
through a solution of the molecule at a known concentration ([R]) and path length (l) and
the amount of light transmitted through the sample (I
t
) is measured. From these
known/measured quantities ε can be found using Beer’s Law: ε = [log (I
0
/I
t
)]l[R]. The
molar absorptivity of a molecule is a fundamental property that is independent of both
path length and concentration.
From the absorption spectrum of (BPI)PtCl it can be seen that there are several
transitions (Figure 1.4c, red lines) ranging from 250 to 550 nm with molar absortivities
greater than 1 x 10
4
M
-1
cm
-1
. Rather than having well defined, narrow absorption bands
like in hydrogen, molecules have broadened peaks due to vibrations of the molecule.
Molecular vibrations are represented as a movement along the ground state potential
energy surface. At any given moment, a molecule that is slightly distorted from its lowest
energy geometry can be excited from that point on the ground state potential energy
surface to the excited state surface. The energy of the transition from the distorted
molecule will be slightly lower or higher than that of a molecule in the lowest energy
ground state geometry. The broad peaks in the absorption spectra of (BPI)PtCl are the
summation of many transitions associated with any of the ground state geometries of the
molecule present in solution. If the molecular vibrations are inhibited by cooling the
sample significant peak sharpening is observed.
Although many orbitals and electrons are involved in the light absorption and
emission processes, the lowest energy transition is of considerable interest for
photophysical chemists. The lowest energy absorption transition possible for a molecule
with an even number of paired electrons is from the highest occupied molecular orbital
(HOMO) to the lowest unoccupied molecular orbital (LUMO). In the ground state of
11
such a molecule the LUMO is unoccupied and the HOMO is filled with two electrons of
opposite spin (α and β) in accord with the Pauli exclusion principle. During excitation an
electron will jump from the HOMO to the LUMO of the molecule followed by molecular
relaxation to the lowest energy excited state geometry. In the lowest energy excited state
a single electron occupies what was previously referred to as the HOMO and LUMO of
the molecule.
Simple descriptions of the nature of a transition can be helpful when
characterizing and comparing HOMO to LUMO transition. In general the nature of a
transition can be summarized by the location of the orbitals involved. For formaldehyde,
the HOMO is located on the lone pair of the oxygen (n) and the LUMO is on the double
bond between the carbon and oxygen (π*). The lowest energy transition for
formaldehyde can roughly be described as an n to π* charge transfer.
1
A molecule like
ethene, that has no lone pair, has a π to π* transition where an electron moves from the
bonding orbital (π) to an antibonding orbital (π*) associated with the double bonds
between carbons.
1
Molecules with metal centers and multiple independent π ligands are
often more complex due to the addition of both ligand centered (LCCT) and ligand to
ligand (LLCT) charge transfers are possible. The addition of metal centered orbitals can
also produce metal centered (MC) and metal to ligand charge transfer (MLCT) transitions.
Since these labels are only approximate descriptions a combination of two may be
necessary for a more accurate description of a transition.
12
1.5 Electron “Spin”
In Figure 1.4a the electron that jumps from the occupied orbitals to the empty
orbitals maintains the same down spin that it had in the ground state. However, since the
electrons in the excited state are in different orbitals the Pauli exclusion principles
restriction of and up (α) and a down (β) spin to a single orbital does not apply.
Electrons randomly paired by the quantum mechanical rules that govern their
interactions will result in four possible outcomes (Figure 1.5): up-down out-of-phase
(αβ−βα), up-up in phase (αα), down-down in phase (ββ) and up-down in phase (αβ+βα).
The up-up and down-down orientations are relatively straight forward in that both
electrons posses the same up or down spin. However, the two possible up-down pairings
are less intuitive and are the result of an additional rule embedded in the Pauli exclusion
principle which states that two electrons interacting in space cannot be distinguished from
one another. More simply, electron one and electron two cannot be described as up and
down respectively but instead as the additive (αβ+βα) and subtractive (αβ−βα)
Figure 1.5. Possible orientations of electrons in the ground and the excited state.
13
interaction between the two indistinguishable up-down electrons (αβ). Perhaps an easier
way to conceptualize this interaction is to visualize an electron as not having a vertical up
or down spin but instead an arrow precessing around the vertical axis (Figure 1.6).
In Figure 1.6, the spin of an electron is described by both a z component, up or
down, and a xy component. The difference between the two up-down interactions is in
the addition (αβ+βα) or cancellation (αβ−βα) of the horizontal (xy) component of the
electrons spin due to the in-phase and out-of-phase precession of the electrons. The up-
down out-of-phase (αβ−βα) interaction is described as the singlet excited state (S
0
) and
can be differentiated from the other three pairings because of the complete cancellation of
angular momentum in the z, x and y directions. The other three interactions, which do
have angular momentum in the xy directions, are collectively described as the triplet
excited state (T
0
). At room temperature and in the absence of a magnetic field, the three
triplet excited states are energetically equivalent and can thus be described as a single
Figure 1.6. Pictorial representation of the four possible two electron interactions.
Taken from Turro.
1
14
state. However, the singlet and triplet states are not equal in energy but instead have a
difference in energy (ΔE
st
) as the direct result of the different types of electron-electron
interactions.
The energy of the singlet (E
S
) and triplet (E
T
) excited states are defined by
equations 1.1 and 1.2.
E
S
= E
0
+ K + J (1.1)
E
T
= E
0
+ K - J (1.2)
The starting point for E
S
and E
T
calculations is the energy of an excited state where
electron-electron interactions are ignored (E
0
) which can be found from the electron
affinity and ionization potential of a molecule.
11
E
0
will then be altered by both classical
(K) and quantum mechanical (J) electron correlations. For both E
S
and E
T
the total energy
of each state will be increased, relative to E
0
, due to the classical electron-electron
repulsion (K). The J term (exchange energy) in equations 1.1 and 1.2 is a correction term
applied to the classical electron repulsion term K. For a singlet excited state, where the
electrons remain in the same orientation as the ground state, the electrons have a
propensity to pair in accord with the Pauli exclusion principle. The pairing of electrons
(increased proximity) of opposite spin will increase the energy of the singlet excited state
by J due to the increased charge-charge repulsion. On the other hand, the Pauli exclusion
principle reduces the interaction between electrons of similar spin and as a result the
energy of E
T
is reduced by J. From equations 1.1 and 1.2 it can be seen that the total
energy of E
T
will be lower in energy than E
S
by 2J. The exchange energy J and thus the
singlet-triplet energy separation (ΔE
ST
) are strongly dependent on the spatial separation
15
of the two unpaired electrons in the excited state. In general, larger separation of the
unpaired electrons (smaller overlap of the singly occupied orbitals) leads to a smaller
ΔE
ST
and vise versa.
1.6 Jablonski Diagram
1.6.1 Introduction. Based on the previous discussion, a qualitative energy diagram of
ground and the first excited states can be constructed (Figure 1.7). In this diagram, known
as a Jablonski diagram, the energy of the states increases from bottom to top with S
0
being the arbitrary zero energy level of the diagram.
In addition to displaying the relative energies of ground/excited states of a
molecule, the Jablonski diagram is also a convenient means of describing time dependent
Figure 1.7. A Jablonski diagram representing the ground (S
0
), singlet
excited (S
1
) and triplet excited (T
1
) states of a molecule and the
transitions between them. 1) Singlet to singlet absorption (S
0
+ hν →
S
1
); 2) fluorescence (S
1
→ S
0
+ hν); 3) internal conversion (S
1
→ S
0
+
heat); 4) intersystem crossing (S
1
→ T
1
+ heat); 5) Singlet to triplet
absorption (S
0
+ hν → T
1
); 6) phosphorescence (T
1
→ S
0
+ hν); 7)
intersystem crossing (T
1
→ S
0
+ heat).
16
transitions between the states (Figure 1.7, arrows 1-7). Starting from the ground state (S
0
),
absorption transitions to the singlet and triplet excited state, arrows 1 and 5 respectively,
are possible. For triplet absorption (S
0
+ hν → T
1
; 5) to occur, the spin of one of the
electrons must flip during the transition. In most small molecules, an electron flip is
“forbidden” because angular momentum in the system must be conserved. Although there
are situations where this transition becomes “allowed” (to be discussed later), it can
generally be assumed that the dominant means of molecular excitation is by a S
0
to S
1
excitation. As was mentioned above, a molecule in the excited state can return to the
ground state through radiative or nonradiative relaxation. In Figure 1.7 there are three
means by which energy can be dissipated from S
1
: fluorescence (2; S
1
→ S
0
+ hν),
internal conversion (3; S
1
→ S
0
+ heat) and intersystem crossing (4; S
1
→ T
1
+ heat).
1.6.2 Radiative Processes. Fluorescence (Figure 1.7; 2) is a relaxation from the singlet
excited state (S
n
) to the ground state of a molecule (S
0
) that is accompanied by the release
of light. The lifetime of the excited state, before fluorescence, is typically on the order of
nanoseconds and the energy difference between excitation and emission (Stokes shift) is
typically less than 2000 cm
-1
. In addition to the radiative S
1
to S
0
transition included in
Figure 1.7, there are several other radiative relaxation processes from S
1
that involve
fluorescence. These processes typically are the result of structural changes that occur
after excitation. Three common examples of excited state structural changes are the
formation of excimer/exciplexes, twisted intramolecular charge-transfer states (TICT)
and excited state intramolecular proton transfer (ESIPT) states. For molecules that
have excimer/exiplex, TICT and ESIPT states an “apparent Stokes shift” greater than
17
2000cm
-1
is common because large amounts of the excitation energy is lost through
vibration during structural changes. The phrase “apparent Stokes shift” is sometimes used
to describe the energy difference between excitation and emission because the absorption
and emission processes do not occur from the same molecule.
Formation and emission from an excimer or exciplex can be described by a
stepwise process in equations 1.3 and 1.4 respectively. A molecule is excited from S
0
to
S
1
through the absorption of light. For certain molecules in the excited state (R*), it is
energetically more favorable to combine with another ground state version of the
molecule (R) or solvent (Solv) in a bimolecular process to produce a supramolecular
excimer (R-R*) or exciplex (R-Solv*) respectively.
Excimer: R + hν → R* + R → R-R* → R-R + hν → R + R (1.3)
Exciplex: R + hν → R* + Solv → R-Solv* → R-Solv + hν → R + Solv (1.4)
The supramolecular structure then relaxes to the ground state (R-R or R-Solv) through
fluorescence. Because the supramolecular structure is no longer favorable in the ground
state it dissociates into R and Solv. Alternatively TICT and ESIPT molecules undergo a
unimolecular structural change in the excited state. For TICT molecules (Figure 1.8), it
is energetically favorable for the excited state (R*), which exhibits a partial charge
transfer, to undergo a rotation about a single bond coupled with electron transfer, to
produce a new TICT state (P*). The TICT state then relaxes to the ground state (P)
through fluorescence. In the ground state the twisted structure P is no longer favorable so
it vibrationally relaxes to the original structure R.
18
For ESIPT molecules (Figure 3.1), the electron density shift that occurs upon
excitation (R*) makes a proton transfer from a donor to an acceptor site favorable and a
new molecular structure P* is formed. Emission from P* then occurs giving P and the
proton is then transferred back to its original site to give structure R. In chapter 3, a
previously unreported class of ESIPT molecules that undergo an excited state proton
transfer process will be reported.
1.6.3 Nonadiative Processes. In addition to the radiative relaxation process in Figure 1.7,
there are two nonradiative deactivations from S
1
: internal conversion (S
1
→ S
0
+ heat; 3)
and intersystem crossing (S
1
→ T
1
+ heat; 4). As was stated for emission, the total energy
of the system must be conserved during nonradiative transition between states. For
nonradiative process, this energy is not lost through the release of light but instead
through vibrations (heat). Intersystem crossing from S
1
to T
1
, much like the previously
mentioned triplet absorption (S
0
+ hν → T
1
; 5) requires the spin flip of one of the
Figure 1.8. A pictorial representation of the absorption and emission
process for a TICT molecule.
19
unpaired electrons, a process that is “forbidden” due to conservation of momentum and
can be considered a negligible nonradiative process in most organic molecules. Internal
conversion, on the other hand, is a spin allowed transition that can be broken down into
temperature-dependent and temperature-independent pathways. An example of a
temperature dependent process is bond breaking. The intrinsic atomic vibrations of a
molecule due to the Heisenberg uncertainty principle are usually not strong enough to
break a bond. However, intrinsic atomic vibrations combined with ambient energy
provided by the surrounding environment can overcome the activation barrier necessary
to break a bond. A large amount of the excited state energy is then dissipated through the
bond breaking process. Once the excited state energy is lost it is again favorable to
reform the broken bond. The activation barrier of a temperature dependent process can be
probed by measuring the excited state lifetime at various temperatures. During this type
of measurement it can be expected that reducing the environmental temperature below
that which is required to reach one of these nonradiative states will significantly increase
both the lifetime and the intensity of emission because the rate of deactivation (k
nr
)
through this process will be significantly reduced. An example of this type of experiment
will be discussed in chapter 4 for (BPI)PtCl.
Temperature-independent nonradiative decay can occur through two possible
pathways: direct potential energy surface crossing and/or vibrational coupling to the
ground state. Direct potential energy surface crossing between the excited and ground
states must occur when the geometry and energy of the molecule is the same on both
surfaces. This criteria is met at the site of intersection between the two potential energy
surfaces (Figure 1.2). At this intersection, a jump can occur from the excited state to the
20
ground state potential energy surface through a common geometry which is then followed
by vibrational relaxation to the ground state (Figure 1.2, nr). This type of nonradiative
deactivation is more common when the ground and excited state structures are
significantly different. On the other hand, vibrational coupling is not dependent on
structural changes of the entire molecule but only the bond vibrations of the molecule. In
a quantum mechanical explanation, the ground state bond vibrations are described by a
vibrational wave function Ψ
1
which summarizes both the energy and the spatial
arrangement of the bond. In the excited state the same bond vibrations are described by a
different vibrational wave function Ψ
2
. While a molecule is in the excited state,
momentary changes in the wavefunction Ψ
2
can occur to where it briefly “looks like” Ψ
1
.
The similarity between the perturbed Ψ
2
and Ψ
1
results in mixing of the wavefunctions
and deactivation from the excited state to the ground state through vibrational coupling
occurs. The rate at which this process occurs is dependent on the energy difference
between the excited and ground states as governed by the energy gap law (EGL).
According to the EGL, the rate of nonradiative deactivation through vibronic coupling
will decrease exponentially as the energy difference between states increases. For
molecules that have similar vibrational deactivation modes, the plot of the natural log of
the nontadiative rates versus energy of emission (E
em
) will be linear. In chapter 3, the
photophysical properties of several (BPI)PtCl derivatives will be reported and their
possible correlation using the EGL will be examined.
21
1.6.4 Spin-Orbit Coupling. Up to this point several transitions in Figure 1.7 (4-7) have
been ignored because they require a “forbidden” electron spin-flip during the transition.
The spin-flip of a single electron is not allowed because it would require the total angular
momentum of the system to change. However, much like electrons, the atoms that
compose a molecule also have an angular momentum component. The angular
momentum of an atom and an electron can mix by a process known as spin-orbital
coupling. Through spin-orbital coupling, the angular momentum of an electron during a
spin flip is compensated for by the change in angular momentum of the nuclei and the S
n
→ T
n
or T
n
→ S
n
transitions in Figure 1.7 (4-7) are no longer “forbidden”. A transition
that is not forbidden does not necessarily mean that it is always allowed but instead the
allowedness is dependent on the angular momentum of the atoms and electrons involved.
The angular momentum of electrons is always the same regardless of the atom it
surrounds. However, the angular momentum for atoms varies greatly, with the total
angular momentum of the nuclei increasing as the number of protons and neutrons
increases. In general, the greater the atomic angular momentum, the greater the spin-
orbital coupling in the molecule and as a result an increased allowedness of S
n
→ T
n
or
T
n
→ S
n
transitions. For small molecules composed entirely of nitrogen, carbon,
hydrogen and oxygen, singlet-triplet transitions are usually considered to be “forbidden”.
Alternatively, for small molecules that incorporate heavy atoms such as platinum and
iridium the singlet-triplet transitions become strongly allowed.
For complexes that contain heavy atoms the number of transitions between states
becomes significantly more complicated (Figure 1.7, 1-7). There are now two possible
means of creating an excited state through light absorption: singlet absorption (S
0
+ hν →
22
S
1
; 1) and triplet absorption (S
0
+ hν → T
1
; 5). Although the triplet absorption is strongly
allowed in heavy atom complexes it is not completely allowed as with singlet absorption.
For this reason the singlet to singlet transition has a much higher molar absorptivity than
the singlet to triplet transition by several orders of magnitude. Thus triplet absorption, if
present at all, is often negligible relative to singlet absorption.
In the singlet excited state of heavy atom complexes, three possible modes of
deactivation are competing: fluorescence, internal conversion and intersystem crossing.
The dominant process will be the one that occurs faster than the others. For complexes
that incorporate a heavy atom, the rate of intersystem crossing (k
isc
) is typically much
faster than both the rate of fluorescence (k
F
) and internal conversion (k
IC
). For iridium
complexes it has been demonstrated that up to 100% of the singlet excited state will
undergo intersystem crossing to produce the triplet excited state.
12, 13
Both the radiative and nonradiative deactivation process from the triplet excited
state are similar to those of the singlet excited state. However, the partially forbidden
triplet to singlet nature of these transitions reduces the rate of deactivation and thus a
longer lived excited state lifetime (τ > μs) is observed. Emission from the triplet state is
called phosphorescence (T
1
→ S
0
+ hν; 6) and due to the inherent energy difference
between S
1
and T
1
described above, the energy difference between singlet absorption and
triplet emission is larger than 2000 cm
-1
. Both temperature dependent and temperature
independent deactivation pathways are active from the triplet state. Additionally, both
temperature independent pathways, direct potential energy surface crossing and/or
vibrational coupling, between T
1
and S
0
are observed.
23
1.7 Quantum Yield
In addition to the energy of absorption/emission energy, the excited state lifetime,
and radiative/nonradiative rates, one photophysical property that is of importance for
many potential applications is how efficiently a molecule emits the light it has absorbed.
Quantum yield (Φ) is the numerical representation of the efficiency of this process and
can be calculated by dividing the number of photons emitted by the number of photons
absorbed. Quantum yield is also related to the rates of radiative (k
r
) and nonradiative (k
nr
)
processes by the equation Φ = k
r
/(k
r
+ k
nr
), where k
nr
is the sum off all possible
nonradiative processes mentioned above. For a molecule to exhibit high quantum yield
the radiative rates must be considerably higher than the nonradiative rates (k
r
>> k
nr
). If
the excited state lifetime (τ) is found experimentally (by measuring the time between
photon absorption and emission), k
r
and k
nr
can be calculated using k
r
= Φ/τ and
k
nr
= (1−Φ)/τ. A current goal of photophysical chemists it to understand what molecular
properties dictate k
r
and k
nr
so molecules can be modified to emit more efficiently.
1.8 1,3-bis(2-pyridylimino)isoindole
As we have seen above, there are many variables to be considered when
discussing a light absorbing/emitting molecule: HOMO/LUMO levels, molar absorptivity,
excited state lifetime, geometry changes in the excited state, radiative and nonradiative
rates, and so on. One of the fundamental goals of photophysical chemistry is to
understand how molecular structure correlates with these properties. Once structure
property relationships are understood, new molecules can be designed with particular
applications in mind. There are many molecules reported in the literature that have been
24
synthesized but minimal data regarding their photophysical properties have been reported.
One example of this type of molecules is (1,3-bis(2-pyridylimino)isoindole (Figure 2.1;
BPI). BPI ligands are used for a variety different applications
14-18
because they are
thermally stable, readily synthesized
19
and easily modified. Reports involving BPI
ligands or complexes have focused primarily on catalytic properties, and only minimal
data has appeared regarding the photophysical characteristics of these compounds.
20
In the chapters that follow, the synthesis, electrochemical and photophysical
properties 1,3-bis(2-pyridylimino)isoindoline derivatives will be discussed. First, in
chapter two, the synthesis of both the BPI based molecules and platinum BPI complexes
will be described. In chapter three the photophysics of a series of dihydroxy substituted
BPI compounds that exhibit ESIPT emission will be introduced. Chapter 4 will include
the photophysical and electrochemical characterization of a series of platinum(II)
complexes of the form (N^N^N)PtX where N^N^N is an assortment of substituted 1,3-
bis(2-pyridylimino)isoindolate ligands and X represents various anionic monodentate
ligands. Finally, in chapter five a paradigm to explain the blue- or red-shift in absorption
of small molecules depending on the site of π-extension is given based on both
experimental and theoretical results from a series of (BPI)PtCl derivatives with varying
degrees of benzannulation.
25
Chapter 1 References
(1) Turro, N. J.; Ramamurthy, V.; Scaiano, J. C., Principles of Molecular
Photochemistry: An Introduction. ed.; University Science Books: Sausalito, CA,
2009; p.
(2) Blankenship, R. E., Molecular Mechanisms of Photosynthesis. ed.; Blackwell
Publishing: Williston, 2002; p.
(3) Shimomura, O., Bioluminescence: Chemical Principles and Methods. ed.; World
Scientific Publishing Company: Singapore, 2006; p.
(4) Scranton, A. B.; Bowman, C. N.; Peiffer, R. W., Photopolymerization:
Fundamentals and Applications. 1 ed.; An American Chemical Society
Publication: New York, 1997; p.
(5) Mitchell, S.; Tootill, E.; Gjertsen, D.; Daintith, J., Biographical Encyclopedia of
Scientists, Second Edition. ed.; Taylor and Francis: New York, 1994; p.
(6) Muller, C. A.; Oort, J. H. Nature 1951, 168, 357-358.
(7) Ewen, H. I.; Purcell, E. M. Nature 1951, 168, 356-358.
(8) Cohen, J. M.; Kazaks, P. A.; Kuharetz, B.; Struble, M.; Azbell, M. International
Journal of Theoretical Physics 1987, 27, (1), 33-36.
(9) Acc. Chem. Res. 2009, 42, 1859 (special issues).
(10) Celli, J. P.; Spring, B. Q.; Rizvi, I.; Evans, C. L.; Samkoe, K. S.; Verma, S.;
Pogue, B. W.; Hasan, T. Chem. Rev. 2010, ASAP.
(11) Michl, J.; Thulstrup, E. W. Tetrahedron 1976, 32, 205-209.
(12) Tang, K.-C.; Liu, K. L.; Chen, I.-C. Chem. Phys. Lett. 2004, 386, 437-441.
(13) Hedley, G. J.; Ruseckas, A.; Samuel, D. W. Chem. Phys. Lett. 2008, 450, 292-296.
(14) Kaizer, J.; Csay, T.; Kovari, P.; Speier, G.; Parkanyi, L. Journal of Molecular
Catalysis A: Chemical 2008, 280, 203-209.
(15) Kaizer, J.; Barath, G.; Csonka, R.; Speier, G.; Korecz, L.; Rockenbauer, A.;
Parkanyi, L. Journal of Inorganic Biochemistry 2008, 102, 773-780.
(16) Langlotz, B. K.; Wadepohl, H.; Gade, L. H. Angewandte Chemie International
Edition 2008, 47, 4670-4674.
26
(17) Saussine, L.; Brazi, E.; Robine, A.; Mimoun, H.; Fischer, J.; Weiss, R. Journal of
the American Chemical Society 1985, 107, 3534-3540.
(18) Tolman, C. A.; Druliner, J. D.; Krusic, P. J.; Nappa, M. J.; Seidel, W. C.;
Williams, I. D.; Ittel, S. D. Journal of Molecular Catalysis 1988, 48, 129-148.
(19) Siegl, W. O. J. Org. Chem. 1977, 42, (11), 1872-1878.
(20) Selvi, P. T.; Stoeckli-Evans, H.; Palaniandavar, M. Journal of Inorganic
Biochemistry 2005, 99, 2110-2118.
27
CHAPTER 2. Synthesis
2.1 Introduction
All of the molecules that are discussed below are closely related derivatives of
1,3-bis(2-pyridylimino)isoindoline (Figure 2.1, BPI). BPI was originally synthesized in
1952 by Elvidge and Linstead in a two step process.
1
In the first step, ammonia and
phthalonitrile were heated in a stainless-steal autoclave to give 1,3-diiminoisoindoline.
Second, 2-aminopyridine was added to 1,3-diiminoisoindoline to give BPI. This process
was later simplified to a one step reaction,
2
however the harsh reaction conditions
resulted in many undesirable side products including formation of phthalocyanine and
related chromophoric by-products.
Through a systematic variation of both solvent and catalyst Siegl found relatively
mild reaction condition under which BPI could be produced in gram scale quantities.
3
In
these reactions, alkaline earth salts facilitated the neucleophilic addition of 2-
aminopyridine to phthalonitrile to produce BPI which then could be isolated by
precipitation and recrystalization. The highest yield synthesis for BPI (76%) was found
Figure 2.1. Structure of 1,3-bis(2-
pyridylimino)isoindoline (BPI).
28
for the reaction preformed in refluxing n-butanol with 10 mol percent anhydrous calcium
chloride as the catalyst (Figure 2.2).
The ease of synthesis, high stability and readily modifiable structure of BPI
makes derivatives of this structure viable as candidates for many potential applications.
In this chapter the synthesis of BPI derivatives, based on the procedure developed by
Siegl, will be discussed. The compounds described below can be broken down into 4
primary categories: 1) alcohol/ethoxy substituted 1,3-bis(aryl or alkyl) isoindoline dyes,
2) substituted BPI platinum complex ligand precursors, 3) platinum complexes with BPI
substituted ligands, and finally 4) BPI platinum chloride complexes with varying degrees
of benzannulation. The molecules were characterized by mass spectrometry, elemental
analysis and NMR spectroscopy.
2.2 Synthesis of alcohol/ethoxy substituted 1,3-bis(aryl or alkyl)isoindoline
Molecules 3.1-7 (Table 2.1) were synthesized by a procedure similar to the one
shown in Figure 2.2. For complexes 3.1-3 and 3.5, 1,2-dicyanohydroquinone was reacted
with their respective aryl or alkylamine. After the reaction was discontinued the solvent
was either removed by distillation or the reaction mixture poured into water and the
Figure 2.2. Standard reaction conditions for the synthesis of
BPI and related compounds.
29
precipitate was collected by filtration. The solubility of 1,2-dicyanohydroquinone in
water and the lack of water solubility of the desired compounds made removal of 1,2-
dicyanohydroquinone possible by simply washing the residue with copious amounts of
water. The gradual decrease of blue fluorescence in the filtrate was indicative of the
removal of starting material. After washing with water, the products were then isolated
by either column chromatography or precipitation from boiling solvent followed by
recrystalization to give the desired products in 6-34% yield.
Table 2.1. The structure of alcohol/ethoxy substituted 1,3-bis(aryl or alkyl)isoindoline
dyes 3.1-7.
Complex R1 R2 R3 R4
3.1 -C
12
H
25
H H H
3.2 (4-tBu-Ph) H H H
3.3 2-Pyridyl H H H
3.4 2-Pyridyl Cl H H
3.5 1-isoquinolyl H H H
3.6 2-Pyridyl H Et H
3.7 2-Pyridyl H Et Et
The relatively insoluble dichloro substituted compound 3.4 was synthesized by a
reaction between aminopyridine and 2,3-dichloro-5,6-dicyano-1,4-hydroquinone and
isolated by precipitation. The 2,3-dichloro-5,6-dicyano-1,4-hydroquinone starting
30
material for this reaction was synthesized by reducing 2,3-dichloro-5,6-dicyano-1,4-
benzoquinone with Na
2
SO
3
according to literature procedure.
4
The 3,6-diethoxyphthalonitrile precursor for both compounds 3.6 and 3.7 was
synthesized by the alkylation of 1,2-dicyanohydroquinone with iodoethane in the
presence of base.
5
By monitoring the reaction between 3,6-diethoxyphthalonitrile and
amino pyridine with MALDI-TOF MS it was found that only the diethoxy compound 3.7
was produced in the reaction mixture. However, 3.7 can decompose on silica gel (EMD,
Grade 62, 60-200 Mesh) to give 3.6. Both compounds could be isolated from a wet
loaded column as a non-emissive orange colored fraction (3.7) and an orange/red colored
fraction with orange emission under UV radiation (3.6). Rotary evaporating of the crude
reaction mixture onto silica gel for a dry packed column resulted in predominantly the
decomposed product 3.6.
Two additional compounds, where R1 was an unsubstituted phenyl or a 4-pyridyl
group, were synthesized as indicated by MALDI-TOF MS. However, the low solubility
of these complexes made further isolation and characterization difficult so the workup
procedures were discontinued.
Crystals of 3.3 and 3.7 suitable for x-ray diffraction were grown from cooling a
saturated solution of CH
2
Cl
2
and slow diffusion of hexane into a concentrated solution of
CH
2
Cl
2
respectively. ORTEP drawings of these compounds can be seen in Figure 2.3.
Select bond angles and distances can be seen in Table 2.2 with a comparison to the
previously published structure of the parent BPI molecule.
31
Table 2.2. Select bond angles (°) and distances (Å) for BPI,
6
3.3 and 3.7.
Bonds (Å) BPI 3.3 3.7
O-C3 - 1.359(2) 1.3651(12)
N1-C1 1.2925(14) 1.286(2) 1.2929(12)
N2-C1 1.3832(13) 1.384(2) 1.3838(12)
C1-C2 1.4801(15) 1.466(3) 1.4787(13)
C2-C3 1.3882(15) 1.372(3) 1.3986(13)
C2-C5 1.398(2) 1.383(4) 1.4010(19)
C3-C4 1.3972(17) 1.399(3) 1.389(10)
C4-C6 1.400(3) 1.399(3) 1.3957(19)
Angles (°)
O-C3-C4 - 120.61(19) 124.32(10)
O-C3-C2 - 122.33(19) 118.42(10)
C1-C2-C3 130.92(10) 129.99(19) 130.05(10)
C1-N1-R1 120.98(10) 121.37(18) 121.49(9)
By comparing the bond lengths and angles of the previously published BPI
6
and
3.3 it can be seen that hydroxyl substitution has a minimal effect parent structure. All
bonds and angles of 3.3 are within 0.02 Å and 1° of the parent BPI. Interestingly, the
diethoxy substituted compound 3.7 exhibits a closer structural resemblance to BPI than
Figure 2.3. ORTEP drawings of compounds 3.3 and 3.7. (carbon
(black), nitrogen (blue), oxygen (red))
32
that of 3.3 with the bond lengths and angles of 3.7 deviated from BPI by less than 0.01 Å
and 0.5°. On the other hand the differences between 3.7 and 3.3 are more pronounce with
bond length and angle variations up to 0.03 Å and 4°. The most pronounced structural
difference between 3.3 and 3.7 is the bond angle defined by the O-C3-C2. The oxygen
atom of 3.3 (O-C3-C2 = 122.33(19)°) is tilted away from the N1 atom by 3.91(15)°
relative to 3.7 (O-C3-C2 = 118.42(10)°). Despite this tilt, the O and N1 separation for 3.3
(2.914(2) Å) is smaller than that of 3.7 (2.943(1) Å). The smaller O-N1 separation is
presumably due to the hydrogen bonding between O and N1.
2.3 Substituted BPI platinum complex ligand precursors
The ligand precursors (3.1-7) for platinum complexes 4.1-12 can be seen in Table
2.3. The compounds were synthesized by reacting 2-aminopyridine with various
substituted phthalonitrile precursors similar to the reaction shown in Figure 2.2.
Table 2.3. The structure of substituted BPI platinum complex ligand precursors.
Complex R3 R4 R5 R6
BPI H H H H
4-t-BuBPI H t-Bu H H
3-NO
2
BPI -NO
2
H H H
4-NO
2
BPI H -NO
2
H H
4-OC
5
H
11
BPI H -OC
5
H
11
H H
4-IBPI H -I H H
4,5-diClBPI H -Cl -Cl H
The progress of the reactions was monitored by thin layer chromatography
(eluting with CH
2
Cl
2
) for disappearance of fluorescent blue dicyanobenzene starting
material. The reaction time is affected by both steric and electronic effects of the
33
dicyanobenzene substituent. The addition of electron withdrawing (NO
2
, I, Cl) or electron
donating groups (t-Bu, OC
5
H
11
) at the R
4
and R
5
positions results in shorter (< 2 days)
and longer reaction times (5-10 days) respectively. The shorter and longer reaction times
are presumably due to the decreased and increased electron density at the site of 2-
aminopyridine addition. Although electronically similar, a nitro substituent at the R
3
position (3-NO
2
BPI), as opposed to R
4
(4-NO
2
BPI), increases reaction time with starting
material still present after 4 days presumably due to steric hinderance at the R
3
position.
Upon cooling the reaction mixture to room temperature precipitate was either formed
immediately or after pouring the reaction solution into a large amount of water. After
collecting precipitate by filtration and washing with a large excess of water, products
were either used for the next reaction without further purification or flashed through a
plug of silica gel to separate product from substituted dicyanobenzene starting material
(4-t-BuBPI, 3-NO
2
BPI).
Several attempts to produce the tetrofluoro substituted BPI (R
3-6
= F) under the
same reaction conditions described above were unsuccessful in that a molecular ion peak
was not observed by MALDI-TOF MS.
34
2.4 BPI platinum complexes
The synthesis of the (BPI)PtCl complex (4.1 or 5.2) was first reported by Meder
et al. In their report, dichloro[(1,2,5,6-η)-1,5-cyclooctadiene]platinum(II) ((COD)PtCl
2
)
was used as the platinum precursor, rather than the more commonly used (PhCN)
2
PtCl
2
which was ineffective in metallating BPI under the reaction conditions they examined.
7
In accord with this result, the platinum complexes below (Table 2.4) were synthesized
using (1,2,5,6-η)-1,5-cyclooctadiene platinum precursors.
Table 2.4. The structure of BPI platinum complexes 4.1-12.
N
N
N
N
N
Pt X
R
3
R
4
R
5
R
6
Complex X R3 R4 R5 R6
4.1 -Cl H H H H
4.2 -F H H H H
4.3 -CN H H H H
4.4 -OOCCH
3
H H H H
4.5 -Ph H H H H
4.6 -PhNMe
2
H H H H
4.7 -Cl H t-Bu H H
4.8 -Cl -NO
2
H H H
4.9 -Cl H -NO
2
H H
4.10 -Cl H -OC
5
H
11
H H
4.11 -Cl H -I H H
4.12 -Cl H -Cl -Cl H
(COD)PtCl
2
was synthesized in 92% yield by mixing 1,5-cyclooctadiene and
K
2
PtCl
4
in the presence of acid.
8
The addition of aryl-magnesium bromide Grignard
reagents to (COD)PtCl
2
gave (COD)PtPh
2
9
and (COD)Pt(Ph-4-NMe
2
)
2
10
in 89% and
78% respectively. Several attempts to produce the sterically hindered [(1,2,5,6-η)-1,5-
cyclooctadiene]bis(2,4,6-trimethylphenyl)platinum(II) complex ((COD)Pt(Mes)
2
) by a
35
similar reaction scheme resulted in a mixture of several platinum products with no
dominant product clearly present. This result is not surprising considering the previously
published reports that give (COD)Pt(Mes)
2
,
11
(COD)PtBr(Mes)
12
and (COD)PtCl(Mes)
13
as the dominate product (30-90% yield) of the reaction between (COD)PtCl
2
and (2,4,6-
trimethylphenyl)magnesium bromide. Due to the complexity of the reaction mixture,
isolation of (COD)Pt(Mes)
2
was discontinued.
Following the procedure developed by Meder et al. (BPI)PtCl (4.1 or 5.2) was
synthesized in 73% yield. In this general reaction (Figure 2.4), BPI and (COD)PtCl
2
are
first suspended in methanol followed by the addition of triethylamine. Upon heating to
reflux the reaction mixture turned from a pale yellow color to bright orange. After
cooling to room temperature, precipitate began to form that was collected by filtration
and washed with water and a small amount of methanol. The substituted ligands,
discussed in section 2.3, were metalated using the same reaction as the parent to give
complexes 4.7-12 in 52-81% yield. Similar workup procedures to 4.1 were followed to
isolate 4.7-11 however the low solubility of 4.12 required that the molecule be purified
by sublimation at 315˚C at reduced pressure (~10
-4
torr).
Figure 2.4. Reaction scheme for the platination of BPI with
(COD)PtCl
2
.
36
Unlike the synthesis of [Pt(trpy)X]
+
complexes from the parent [Pt(trpy)Cl]
+
,
14
attempts to synthesize (BPI)PtX complexes 4.2-6 by nucleophilic substitution of 4.1 were
found to be unsuccessful. However, chlorine substituted complexes 4.2-4 were
synthesized in 43-84% yield by the addition of AgF, KAg(CN)
2
and AgOAc to the parent
complex 4.1. In this reaction, a mixture silver salt and 4.1 in CH
2
Cl
2
were stirred at room
temperature for 24 hours. Complexes 4.2 and 4.4 were isolated by first passing the
reaction mixture through a plug of celite followed by recrystallization. Due to the low
solubility of 4.3, filtration through a plug of silica was not possible. However, Soxhlet
extraction using CH
2
Cl
2
as the solvent followed by cooling of the extracted mixture was
found to be an effective means of isolating 4.3 in 43% yield. Several attempts to isolate
the trifluoroacetate substituted platinum BPI complex from the reaction of 4.1 and silver
trifluoroacteate were unsuccessful due to the low solubility of the produt.
The (BPI)Pt(Ph-R) complexes 4.5 (R = H) and 4.6 (R = NMe
2
) were synthesized
in 37 and 49% yield from the phenyl substituted platinum precursor (COD)Pt(Ph-R)
2
similar to other (N^N^N)PtPh complexes.
15, 16
Complexes 4.1-6 are soluble in common
organic solvents, with solubility decreasing along the trend 4.6 > 4.5 ~ 4.4 > 4.2 ~ 4.1 >>
4.3. All complexes were air stable yellow to red solids except complex 4.6 which
would range from a red powder to a black crystalline solid.
In addition to the Pt-X complexes reported above (4.1-6) Pt-Me was chosen as an
additional target molecule to investigate the effects of the monoanionic ligand and the
photophysical properties of (BPI)PtX. Preliminary attempts to synthesize (BPI)PtMe
from commercially available (COD)PtMe
2
were unsuccessful even at elevated
temperatures (reflux in toluene). However, the desired molecule could be obtained using
37
(COD)PtMeCl as the platinum precursor, which was synthesized by the addition of 1
equivalent of acetyl chloride to (COD)PtMe
2
(Figure 2.5).
17
The formation of (BPI)PtMe was supported by both 1H NMR and MALDI-TOF
MS (m/z = 509.53). In the proton NMR spectrum of the product there are two strong
indicating peaks that the product of this reaction is in fact (BPI)PtMe (Figure 2.6, Day 1).
First, the triplet at 1.04 ppm is indicative of a methyl group bound directly to platinum(II)
(J
Pt-H
= 36 Hz) which was not observed in the other Pt BPI complexes. Second is the peak
at 9.17 ppm corresponding to the pyridyl proton on the BPI ligand adjacent to the
platinum center (J
Pt-H
= 26.75 Hz). Over the course of one day at room temperature, under
atmospheric conditions, the UV-Vis absorption spectra of the product showed a
significant blue-shift in the lowest energy transition. Such shifts in absorption are usually
associated decomposition of the molecule. To further investigate the decomposition of
(BPI)PtMe, sample was dissolved in CDCl
3
and left at room temperature exposed to light
in a nitrogen glove bag for 3 days with
1
H NMR measurements preformed every 24 hours.
The results of these measurements can be seen in Figure 2.6.
The gradual decomposition of terpyridine (terpy) platinum (II) methyl complexes
have been reported. By careful ligand design Taylor et al. were able to isolate the
Figure 2.5. Reaction scheme for the synthesis of (BPI)PtMe.
38
intermediate in this decomposition pathway.
18
In their proposed mechanism, photo-
excited (terpy)PtMe acts as a sensitizer to produce singlet oxygen. The reactive singlet
oxygen then inserts into the platinum methyl bond to produce the platinum methylperoxo
complex. The methylperoxo species then decomposes to (terpy)PtOH in concurrence
with the production of formaldehyde.
This proposed decomposition mechanism coincides closely with the changes in
1
H NMR found with (BPI)PtMe. After 24 hours, the triplet peak associated with a methyl
group bound directly to platinum (1.04 ppm) is no longer present. In addition, the peak at
9.17 ppm associated with the pyridyl proton adjacent to the methyl group has disappeared
and two new peaks with similar splitting patterns are observed at 10.4 and 10.3 ppm. The
p p m ( f 1 )
5 . 0 1 0 . 0
0
5 0 0
1 0 0 0
1 5 0 0
p p m ( f 1 )
5 . 0 1 0 . 0
0
1 0 0
2 0 0
3 0 0
4 0 0
5 0 0
p p m ( f 1 )
5 . 0 1 0 . 0
0
1 0 0
2 0 0
3 0 0
4 0 0
Day 1
Day 2
Day 3
N
N
N
Pt O
H
O Me
N
N
N
Pt OH
H
p p m ( f 1 )
5 . 0 1 0 . 0
0
5 0 0
1 0 0 0
1 5 0 0
p p m ( f 1 )
5 . 0 1 0 . 0
0
1 0 0
2 0 0
3 0 0
4 0 0
5 0 0
p p m ( f 1 )
5 . 0 1 0 . 0
0
1 0 0
2 0 0
3 0 0
4 0 0
Day 1
Day 2
Day 3
N
N
N
Pt O
H
O Me
N
N
N
Pt OH
H
Figure 2.6. Monitored decomposition of (BPI)PtMe
1
H NMR (CDCl
3
).
39
growth of singlet peaks at 3.95 ppm and 9.74 ppm are also observed. Based on the report
by Taylor et al. the peaks are tentatively assigned as the methyl (3.95 ppm) and pyridyl
(10.4 ppm) protons of (BPI)PtOOMe, the pyridyl proton (10.3 ppm) of (BPI)PtOH and
formaldehyde (9.74 ppm). After an additional 24 hours the peaks associated with
(BPI)PtOOMe decrease and only the pyridyl proton (10.3 ppm) of (BPI)PtOH is
observed in this region. An oxygen and light mediated decomposition is supported by the
reduced decomposition rates found when the sample was kept under nitrogen or shielded
from light. Attempts to isolate (BPI)PtOH were unsuccessful.
The relatively rare occurrence of an oxygen insertion in a Pt(II) methyl bond
18, 19
and the possibilities for light mediated methane activation suggest that further
investigation into the decomposition of (BPI)PtMe is beneficial.
2.5 Benzannulated BPI platinum chloride complexes
The ligand precursors for complexes 5.2-5 (BPI, benz(f)BPI, benz(e)BPI and
BIQI, respectively) were synthesized in 15–83% yield using the procedure by Siegl
3
mentioned in sections 2.1 and 2.2. The relatively low yield of benz(e)BPI (15%), even
after 20 days at reflux, compared to the other compounds (67-83%) is likely due to steric
hindrance similar to what was previously mentioned for 3-NO
2
BPI versus 4-NO
2
BPI.
The precursor for complex 5.1 (BPEP) was synthesized by bromination of 3-
hexyne,
20
followed by substitution with cyanide, photoisomerization
21
and the
nucleophilic addition procedure mentioned above (Figure 2.7). Photoisomerization of
(E)-3,4-dicyano-3-hexene was required since all attempts to produce BPEP from the (E)-
isomer were unsuccessful. The significantly lower yield of BPEP, 4%, may be due to
40
thermal isomerization from (Z)-3,4-dicyano-3-hexene to the unreactive (E)-
isomer.
21
The complexes 5.1–5 (Figure 2.8) were synthesized in 44–90% yield using the
procedure developed by Meder et al.
7
The complexes were characterized by mass
spectrometry, elemental analysis and NMR spectroscopy.
Complexes 5.1-5 are soluble in common organic solvents, although increased
benzannulation decreases solubility. Differences in solubility can most clearly be
Figure 2.7. Reaction scheme for the synthesis of BPEP.
Figure 2.8. The structure of BPI platinum
complexes with varying degrees of
benzannulation.
41
observed by the quality of the
1
H NMR spectra. Well resolved
195
Pt satellites (J
Pt-H
= 20.5
Hz) for the pyridyl hydrogens in the meta-position (10.3 ppm), similar to those reported
for [(2,2’;6’,2”-terpyridine)PtCl]
+
,
22
can be identified in the highly soluble, diethyl
substituted complex 5.1 (Figure 2.9).
However, due to the low solubility of 5.5, we were unable to obtain an acceptable
1
H
NMR spectrum for this complex. Therefore, the identity and purity of 5.5 was confirmed
by mass spectrometry and elemental analysis.
Figure 2.9. 250 MHz
1
H NMR spectra of complex 5.1 (CDCl
3
). Inset: expansion of
the region from 6.8 to 11 ppm.
42
2.6 Experimental Section
2.6.1 General. 3-hexyne, 2-aminopyridine, 1,2-dicyanobenzene, 1-aminoisoquinoline,
bromine, copper (I) cyanide, 1,5-cyclooctadiene, 4-tert-butylphthalonitrile, 4-
iodophthalonitrile, 4-(N,N-Dimethyl)aniline magnesium bromide, phenylmagnesium
bromide, silver(I) fluoride, potassium silver(I) cyanide, silver acetate, ethlyl iodide,
dodecylamine, p-tert-butyl-aniline, 2,3-dichloro-5,6-dicyanobenzoquinone (Aldrich), 1,2-
dicyanonaphthalene, 2,3-dicyanonaphthalene, 4,5-dichlorophthalonitrile, 3-
nitrophthalonitrile, 4-nitrophthalonitrile, 4-pentoxyphthalonitrile, 4-iodophthalonitrile,
2,3-dicyanohydroquinone (TCI America), calcium chloride (J.T.Baker) and K
2
PtCl
4
(Pressure Chemical Company) were purchased from the corresponding supplier (in
parentheses) and used without further purification. All reported NMR spectra were
obtained on a Bruker AC-250 MHz FT NMR, a Varian Mercury 400 or a Varian 400
MHz NMR with all shifts relative to residual solvent signals. Solid probe mass
spectrometer (MS) spectra were taken with Hewlett-Packard MS instrument with electron
impact ionization and model 5973 mass selective detector. MALDI-TOF mass spectra
were recorded on a Voyager-DE STR Mass Spectrometer using a positive-MALDI-TOF
method without matrix. Elemental analyses (CHN) were performed at the Microanalysis
Laboratory at the University of Illinois, Urbana-Champaign, IL.
1,3-bis(dodecylimino)-4,7-dihydroxyisoindole (3.1). A solution of 1.00g 1,2-
dicyanohydroquinone (6.24 mmol), 2.43 g dodecylamine (13.11 mmol) and 0.14g CaCl
2
(1.3 mmol) in 30ml 1-butanol was refluxed under N
2
for 5 days. The reaction mixture
was poured into 500 mL of H
2
O. The precipitate was collected by filtration and was
43
washed with water until no blue fluorescents was observed from the filtrate. The
precipitate was then dissolved in boiling methanol and then cooled to 0°C for 3 days.
Precipitate was then collected by filtration and washed with MeOH. 1.1 g (34%), orange
solid. Product was further purified by dissolving in CH
2
Cl
2
and layering with MeOH. MS
(Maldi-TOF): m/z = 513.91. HRMS-FAB (m/z): [M + H]
+
calcd for C
32
H
56
N
3
O
2
,
514.4367; found, 514.4376.
1
H NMR (400 MHz, CDCl
3
, δ) 6.70 (s, 2H), 3.69 (t, J = 6.4
Hz, 4H), 1.76-1.64 (m, 4H), 1.49-1.05 (m, 36H), 0.86 (t, J = 6.4 Hz, 6H).
13
C NMR (100
MHz, CDCl
3,
δ) 173.5, 155.2, 128.5, 113.3, 50.8, 43.3, 31.9, 29.64, 29.62, 29.60, 29.5,
29.3, 29.2, 26.7, 22.7, 14.1.
1,3-bis(p-tert-butyl-phenylimino)-4,7-dihydroxyisoindole (3.2). A solution of 1.00g
1,2-dicyanohydroquinone (6.24 mmol), 2.09 ml p-tert-butyl-analine (13.11 mmol) and 66
mg CaCl
2
(0.62 mmol) in 10ml 1-hexanol was refluxed under N
2
for 2 days. The solvent
was removed under reduced pressure and the residue was washed with water. The
remaining solid dissolved in methanol and loaded onto silica gel by rotary evaporation.
The product was then dry loaded onto a silica gel column and product separated by first
eluting with CH
2
Cl
2
then a 100:1 mixture of CH
2
Cl
2
and Methanol. The emissive orange
fraction was collected and rotary evaporated to dryness. The residue was then dissolved
in hot methanol and cooled to -40°C for two days. The precipitate was collected by
filtration. 152 mg (6%), purple powder. MS (Maldi-TOF): m/z = 441.75. HRMS-FAB
(m/z): [M + H]
+
calcd for C
28
H
32
N
3
O
2
, 442.2489; found, 442.2483.
1
H NMR (500 MHz,
CDCl
3
, δ) 7.32 (d, J = 7.5 Hz, 4H), 6.95 (d, J = 7.5 Hz, 4H), 6.93 (s, 2H), 1.24 (s, 18H).
44
13
C NMR (125 MHz, CDCl
3,
δ) 151.4, 148.3, 148.1, 143.9, 126.5, 121.4, 121.0, 116.0,
34.5, 31.3.
1,3-bis(2-pyridylimino)-4,7-dihydroxyisoindole (3.3). A solution of 1.0 g (6.24 mmol)
2,3-dicyanohydroquinone, 1.23 g (13.11 mmol) 2-aminopyridine and 0.14 g (1.3 mmol)
CaCl
2
in 20 ml 1-butanol was refluxed under N
2
. Despite the presents of fluorescent blue
2,3-dicyanohydroquinone starting material, as observed by TLC (CH
2
Cl
2
), the reaction
was discontinued after 20 days. The reaction mixture was poured into 500 mL of H
2
O.
The precipitate was collected by filtration and was washed with water until no blue
fluorescents was observed from the filtrate. The precipitate was then dissolved in boiling
CH
2
Cl
2
and then cooled to -40°C overnight. Precipitate was then collected by filtration
and washed with MeOH. 0.485 g (24 %), yellow needles. MS (Maldi-TOF): m/z =
331.85. HRMS-FAB (m/z): [M + H]
+
calcd for C
18
H
14
N
5
O
2
, 332.1142; found, 332.1136.
1
H NMR (400 MHz, CDCl
3
), δ 13.3 (s, 1H), 8.57 (ddd, J = 4.8, 2.0, 0.8 Hz, 2H), 7.75
(ddd, J = 8.0, 7.6, 2.0 Hz, 2H), 7.35 (d, J = 8.0 Hz, 2H), 7.11 (ddd, J = 7.6, 4.8, 0.8 Hz,
2H), 7.00 (s, 2H).
13
C NMR (100 MHz, CDCl
3
) δ 159.3, 154.9, 149.0, 147.9, 147.9, 138.1,
122.4, 121.4, 120.4, 116.2.
2,3-dichloro-5,6-dicyano-1,4-hydroquinone. 4.16 g (33 mmol) of Na
2
SO
3
in 75 ml of
H
2
O was added in one portion to 5g (22 mmol) of 2,3-dichloro-5,6-dicyano-1,4-
benzoquinone and the mixture was rigorously shaken for 5 minutes followed by stirring
for 15 minutes. During this time the solution changed from red to yellow in color and a
white precipitate began to form. The precipitate was collected by filtration and washed
45
with water and a small amount of hexane. The remaining solid was then dried under
vacuum. 1.64 g (33 %), white powder. The product was used for the next reaction
without further purification or characterization.
5,6-dichloro-1,3-bis(2-pyridylimino)-4,7-dihydroxyisoindole (3.4). A solution of 800
mg (3.5 mmol) 2,3-dichloro-5,6-dicyano-1,4-hydroquinone, 690 mg (7.34 mmol) 2-
aminopyridine and 78 mg (0.73 mmol) CaCl
2
in 15 ml of 1-hexanol was refluxed under
N
2
for 2 days. The solvent was removed under reduced pressure. The residue was washed
with water until no blue fluorescents was observed from the filtrate. The remaining solid
was dissolved in refluxing CH
2
Cl
2
and filtered while hot. The filtrate was then cooled to
0°C for 2 days. 254 mg (18 %), black needles. MS (Maldi-TOF): m/z = 400.06. HRMS-
FAB (m/z): [M + H]
+
calcd for C
18
H
12
Cl
2
N
5
O
2
, 400.0363; found, 400.0354.
1
H NMR
(400 MHz, CDCl
3
), δ 8.55 (d, J = 4.8 Hz, 2H), 7.81 (t, J = 7.6 Hz, 2H), 7.32 (d, J = 7.6
Hz, 2H), 7.18 (t, J = 5.6 Hz, 2H).
1,3-bis(1-isoquinolylimino)-4,7-dihydroxyisoindole (3.5). A solution of 160 mg (1.0
mmol) 2,3-dicyanohydroquinone, 300 mg (2.08 mmol) 1-aminopyridine and 78 mg (0.73
mmol) CaCl
2
in 15 ml of 1-hexanol was refluxed under N
2
for 2 days. The solvent was
removed under reduced pressure. The residue was washed with water until no blue
fluorescents was observed from the filtrate. The remaining solid was dissolved in
refluxing CH
2
Cl
2
and filtered while hot. The filtrate was then cooled to -40°C for 2 days.
64 mg (15 %), green crystalline powder.
MS (Maldi-TOF): m/z = 431.63. HRMS-FAB
(m/z): [M + H]
+
calcd for C
26
H
18
N
5
O
2
, 432.1455; found, 432.1446.
1
H NMR (400 MHz,
46
CDCl
3
), δ 8.62 (d, J = 8.4, 2H), 8.53 (d, J = 6.0, 2H), 7.84 (d, J = 8.4, 2H), 7.75 (t, J =
6.8, 2H), 7.68 (t, J = 6.8, 2H), 7.53 (d, J = 6.0, 2H), 7.10 (s, 2H).
3,6-Diethoxyphthalonitrile. 5.20 g (32.5 mmol) 2,3-dicyanohydroquinone was dissolved
in 125 mL acetone, bubbled with nitrogen for five minutes followed by the addition of 5
g (63.2 mmol) K
2
CO
3
and 13 ml (163 mmol) ethyl iodide. The mixture was refluxed
under nitrogen for 60 hours. Upon cooling to room temperature precipitate began to form.
The precipitate was collected by filtration and washed with H
2
O and OEt
2
. 5.37 g (77%),
white powder.
1
H NMR (250 MHz, CDCl
3
), δ 7.15 (s, 2H), 4.13 (q, J = 7.0 Hz, 4H), 1.47
(t, J = 7.0 Hz, 6H).
1,3-bis(2-pyridylimino)-4-ethoxy-7-hydroxyisoindole (3.6). A solution of 1.17 g (5.43
mmol) 3,6-diethoxyphthalonitrile, 1.28 g (13.6 mmol) 2-aminopyridine and 0.117 g
(1.03 mmol) CaCl
2
in 17 ml 1-hexanol was refluxed under N
2
and monitored for the
disappearance of 3,6-diethoxyphthalonitrile by TLC. Upon cooling to room temperature,
the solution was poured into 1 L of water and the product was extracted using CH
2
Cl
2
.
The organic layer was reduced in volume (50 ml) and the solution was then rotary
evaporated onto a silica gel. A silica gel column was then dry loaded with the residue
coated silica gel. Fluorescent blue 3,6-diethoxyphthalonitrile starting material was
obtained by first eluting with CH
2
Cl
2
. The desired poduct (fluorescent orange band) was
then collected by eluting with CH
2
Cl
2
:MeOH (100:1). Solvent was removed by rotary
evaporation and the residue was then dissolved in hot methanol and cooled to 0°C. The
precipitate was then collected by filtration. 0.140 g (7 %), yellow needles. MS (Maldi-
47
TOF): m/z = 360.20. HRMS-FAB (m/z): [M + H]
+
calcd for C
20
H
18
N
5
O
2
, 360.1455;
found, 360.1452.
1
H NMR (400 MHz, CDCl
3
), δ 13.8 (s, 1H), 8.60-8.55 (m, 2H), 7.77-
7.70 (m, 2H), 7.48 (d, J = 8.0, 1H), 7.33 (d, J = 8.0, 1H), 7.13-7.06 (m, 2H), 7.05 (s, 1H),
7.04 (s, 1H), 4.28 (q, J = 6.8, 2H), 1.55 (t, J = 6.8, 3H).
13
C NMR (100 MHz, CDCl
3
) δ
160.4, 159.3, 155.4, 153.0, 150.4, 149.5, 148.0, 147.5, 138.0, 137.9, 124.1, 122.1, 121.0,
120.6, 120.3, 120.1, 118.8, 66.1, 14.9. Elemental analysis for C
20
H
18
N
5
O
2
: calcd: C 66.84,
H 4.77, N 19.49; found: C 67.16, H 4.65, N 19.08.
1,3-bis(2-pyridylimino)-4,7-diethoxyisoindole (3.7). A solution of 1.17 g (5.43 mmol)
3,6-diethoxyphthalonitrile, 1.28 g (13.6 mmol) 2-aminopyridine and 0.117 g (1.03
mmol) CaCl
2
in 17 ml 1-butanol was refluxed under N
2
and monitored for the
disappearance of 3,6-diethoxyphthalonitrile by TLC. After 20 days of reflux the reaction
was discontinued even though starting material was still observed. Upon cooling to room
temperature, the solution was poured into 1 L of water and the product was extracted
using CH
2
Cl
2
. The organic layer was reduced in volume (50 ml) and the solution was
then wet loaded onto a silica gel column. Fluorescent blue 3,6-diethoxyphthalonitrile
starting material was obtained by first eluting with CH
2
Cl
2
. The desired poduct (non
fluorescent orange band) was then collected by eluting with CH
2
Cl
2
:MeOH (9:1). Solvent
was removed by rotary evaporation and the residue was recrystalized by first dissolving it
in CH
2
Cl
2
and then layering with hexanes. 0.241 g (12 %), orange crystals. MS (Maldi-
TOF): m/z = 388.20. HRMS-FAB (m/z): [M + H]
+
calcd for C
22
H
21
N
5
O
2
, 388.1768;
found, 388.1768.
1
H NMR (400 MHz, CDCl
3
), δ 8.60 (d, J = 5.0, 2H), 7.73 (t, J = 8.0 Hz,
2H), 7.44 (d, J = 8.0 Hz, 2H), 7.10 (s, 2H), 7.07 (t, J = 5.0 Hz, 2H), 4.28 (q, J = 6.8 Hz,
48
4H), 1.59 (t, J = 6.8 Hz, 6H),.
13
C NMR (100 MHz, CDCl
3
) δ 160.9, 153.1, 150.6, 147.5,
137.7, 124.0, 123.8, 119.8, 119.1, 65.9, 14.9. Elemental analysis for C
22
H
21
N
5
O
2
: calcd:
C 68.20, H 5.46, N 18.08; found: C 68.48, H 5.34, N 17.58.
1,3-bis(2-pyridylimino)isoindole (BPI). A solution of 1.28g 1,2-dicyanobenzene
(10mmol), 1.97g 2-aminopyridine (21mmol) and 0.11g CaCl
2
(1mmol) in 20ml 1-butanol
was refluxed under N
2
for 48 hours. Upon cooling to room temperature, product began to
precipitate. The precipitate was collected by filtration, washed with water and
recrystalized with ethanol/water. 2.02 g (67.5%), pale yellow needles.
1
H NMR (250
MHz, CDCl
3
, δ) 8.62 (ddd, J = 4.75, 2, 0.75 Hz, 2H), 8.21 (s, 2H), 7.79 (td, J = 8, 2 Hz,
2H), 7.64-7.72 (m, 2H), 7.59 (d, J = 8 Hz, 2H), 7.16 (ddd, J = 7.25, 4.75, 0.75 Hz, 2H).
Elemental analysis for C
18
H
13
N
5
: calcd: C 73.23, H 4.38, N 23.40; found: C 72.59, H
4.24, N 22.95.
4-t-BuBPI. A solution of 1 g (5.43 mmol) 4-tert-butylphthalonitrile, 1.28 g (13.6 mmol)
2-aminopyridine and 0.12 g (1.0 mmol) CaCl
2
in 20 ml 1-butanol was refluxed under N
2
for 5 days. Upon cooling to room temperature, the solution was poured into 50 mL of
water and precipitate began to form. The precipitate was collected by filtration. Product
was then isolated by column chromatography on silica gel eluting with CH
2
Cl
2
. First a
fluorescent blue fraction of 4-tert-butylphthalonitrile starting material was collected
followed by a yellow fraction containing product. The yellow fraction was evaporated to
dryness and used without further purification. 0.439 g (23%), yellow solid.
1
H NMR
(250 MHz, CDCl
3
, δ) 8.61 (d, J = 5 Hz, 2H), 8.1 (d, J = 1 Hz, 1H), 8.0 (d, J = 8 Hz, 1H),
7.82-7.67 (m, 3H), 7.46 (dd, J = 8, 5 Hz, 2H), 7.11 (t, J = 8.0 Hz, 2H), 1.64 (s, 9H).
49
3-NO
2
BPI. A solution of 0.86 g (4.79 mmol) 3-nitrophthalonitrile, 0.98 g (10.4 mmol) 2-
aminopyridine and 0.10 g (0.89 mmol) CaCl
2
in 15 ml 1-butanol was refluxed under N
2
for 4 days. Upon cooling to room temperature, precipitate began to form. The precipitate
was collected by filtration. The crude product as then dissolved in ethylacetate and passed
through a plug of silica. The yellow fraction was evaporated to dryness and used without
further purification. 0.703 g (41%), yellow solid.
1
H NMR (250 MHz, CDCl
3
, δ) 8.92 (d,
J = 2 Hz, 2H), 8.29 (d, J = 7 Hz, 1H), 7.85-7.72 (m, 4H), 7.45 (t, J = 8 Hz, 2H), 7.20-7.10
(m, 2H).
4-NO
2
BPI. A solution of 1 g (5.78 mmol) 4-nitrophthalonitrile, 1.14 g (12.1 mmol) 2-
aminopyridine and 0.12 g (1.1 mmol) CaCl
2
in 20 ml 1-butanol was refluxed under N
2
for 48 hours. Upon cooling to room temperature, product began to precipitate. The
precipitate was collected by filtration, washed with water and used without further
purification. 1.69 g (85%), bright yellow powder.
1
H NMR (250 MHz, CDCl
3
, δ) 8.92 (d,
J = 2 Hz, 1H), 8.65 (d, J = 4.5 Hz, 2H), 8.52 (dd, J = 8.25, 2 Hz, 1H), 8.23 (d, J = 8.25
Hz, 1H), 7.81 (td, J = 7.5, 2 Hz, 2H), 7.50 (dd, J = 7.5, 2.75 Hz, 2H), 7.18 (dd, J = 7.5,
4.5 Hz, 2H).
4-OC
5
H
11
BPI. A solution of 1 g (4.67 mmol) 4-pentoxyphthalonitrile, 1.10 g (11.68
mmol) 2-aminopyridine and 0.10 g (0.89 mmol) CaCl
2
in 10 ml 1-butanol was refluxed
under N
2
for 11 days. Upon cooling to room temperature, the solution was poured into
50 mL of water and precipitate began to form. The precipitate was collected by filtration,
50
washed with water and used without further purification. 1.56 g (87%), yellow powder.
1
H NMR (250 MHz, CDCl
3
, δ) 8.59 (t, J = 4.75 Hz, 2H), 7.94 (d, J = 8.5 Hz, 1H), 7.80-
7.70 (m, 2H), 8.23 (d, J = 2.25 Hz, 1H), 7.42 (dd, J = 8, 4.75 Hz, 2H), 7.20-7.05 (m, 3H),
4.12 (t, J = 10.8 Hz, 2H), 1.94-1.77 (m, 4H), 1.58-1.32 (m, 2H), 0.95 (t, J = 10.8 Hz, 3H).
4-IBPI. A solution of 1 g (3.94 mmol) 4-Iodophthalonitrile, 0.927 g (9.85 mmol) 2-
aminopyridine and 0.085 g (0.75 mmol) CaCl
2
in 12 ml 1-butanol was refluxed under
N
2
for 2 days. Upon cooling to room temperature precipitate began to form. The
precipitate was collected by filtration, washed with water and used without further
purification. 1.42 g (85%), green powder.
1
H NMR (250 MHz, CDCl
3
, δ) 8.63 (dd, J =
3.2, 1.2 Hz, 1H), 8.61 (dd, J = 3.2, 1.2 Hz, 1H), 8.44 (dd, J = 2.4, 1.2 Hz, 1H), 7.98 (dd, J
= 12.8, 2.4 Hz, 1H), 7.84-7.73 (m, 3H), 7.45 (d, J = 12.8 Hz, 2H), 7.17-7.10 (m, 2H).
4,5-diClBPI. A solution of 1.0 g (5.1 mmol) 4,5-dichlorophthalonitrile, 1.2 g (12.75
mmol) 2-aminopyridine and 0.12 g (1 mmol) CaCl
2
in 15 ml 1-butanol was refluxed
under N
2
for 2 days. Upon cooling to room temperature, precipitate began to form. The
precipitate was collected by filtration and washed with water. 1.80 g (96 %), light green
solid.
1
H NMR (250 MHz, CDCl
3
, δ) 8.60 (d, J = 5.0, 2H), 8.17 (s, 1H), 7.78 (td, J = 8.0,
1.5 Hz, 2H), 7.46 (d, J = 8.0 Hz, 2H), 7.14 (t, J= 5.0 Hz, 2H).
Dichloro[(1,2,5,6-η)-1,5-cyclooctadiene]platinum(II) ((COD)PtCl
2
). 2.5 g (6 mmol)
K
2
PtCl
4
was dissolved in 40 ml H
2
O and filtered. To the red filtrate, 60 ml glacial acetic
acid and 2.5 ml (20mmol) of 1,5-cyclooctadiene was added. The solution was then heated
51
to 90˚C for 1 hour. The solution turned from deep red to yellow with a light yellow
precipitate. The volume was then reduced to 30 ml and filtered. The precipitate was then
washed with water, ethanol and ether. 2.05g (92%).
(1,5-cyclooctadiene) Diphenyl platinum(II) ((COD)PtPh
2
). 0.503 g (1.34 mmol) of
(COD)PtCl
2
was places in a flame dried 100 ml three neck round-bottom flask and
purged with nitrogen. 25 ml of freshly distilled ether (from sodium, benzophenone) was
added via syringe and the suspension was cooled to -78˚C. 3.1 ml (3.1mmol) of 1 M
phenylmagnesium bromide in THF was added dropwise. The solution was then allowed
to slowly warm to room temperature. Once at room temperature, 1 ml methanol was
added followed by 10 ml CH
2
Cl
2
. The solution was then filtered and rotary evaporated.
540 mg (88.2 %), white powder.
Bis[4-(dimethylamino)phenyl](1,5-cyclooctadiene) platinum(II) ((COD)Pt(Ph-4-
NMe
2
)
2
)
.
0.3 g (0.804 mmol) of (COD)PtCl
2
was places in a flame dried 100 ml three
neck round-bottom flask and purged with nitrogen. 25 ml of freshly distilled ether (from
sodium, benzophenone) was added via syringe and the suspension was cooled to 0˚C.
3.23 ml (1.616 mmol) of 0.5 M 4-dimethylaniline magnesium bromide in THF was added
dropwise. The solution was then warmed to room temperature and allowed to stir for 12
hours. A saturated NH
4
Cl solution was added to quench any remaining Grignard reagent.
The organic layer was then separated and the remaining aqueous layer was extracted with
ether. The combined organic extracts were washed with water, dried with MgSO
4
,
filtered through a plug of silica and rotary evaporated. 0.340 g (78%), white powder.
52
(BPI)PtCl (4.1 or 5.2 for chapters 4 and 5 respectively).
0.50g (1.34mmol) (COD)PtCl
2
and 0.37g (1.24mmol) BPI were suspended in 25ml of methanol. To this solution
0.186ml (1.34mmol) triethylamine was added and the solution was heated to 50˚C under
nitrogen for 24 hours. Precipitate began to form upon cooling to room temperature. The
precipitate was collected by filtration and washed with water. The product was then
recrystalized with dichloromethane/hexane (1:1). 0.454 g (70%), bright orange solid. MS
m/z (relative intensity): 529.10 (100%), 528.10 (97.4%), 527.10 (79.6%), 530.05 (45.6%),
531.00 (42.9%).
1
H NMR (400 MHz, d
6
-DMSO, δ) 10.15 (dd, J = 6.4, 1.6 Hz, 2H), 8.19
(ddd, J = 8.8, 7.2, 1.6 Hz, 2H), 8.09 (dd, J = 5.6, 3.2 Hz, 2H), 7.77 (dd, J = 5.6, 3.2 Hz,
2H), 7.70 (dd, J = 8.8, 1.6 Hz, 2H), 7.31 (td, J = 6.4 and 1.6 Hz, 2H).Elemental analysis
for C
18
H
12
N
5
PtCl: calcd: C 40.88, H 2.29, N 13.24; found: C 40.77, H 2.21, N 12.68.
(BPI)PtF (4.2). 400 mg (0.76 mmol) 4.1 and 491 mg (3.79 mmol) AgF were rigorously
stirred in 100 mL CH
2
Cl
2
for 24 hours. Solution was then passed through a plug of silica
eluting with CH
2
Cl
2
. The solution was then rotary evaporated to dryness. The solid was
then dissolved in a minimal amount of CH
2
Cl
2
followed by layered addition of MeOH.
After gradual diffusion, precipitate began to form. The precipitate was collected by
filtration, washed with MeOH and dried under vacuum. 0.325 g (84 %), orange solid. MS
m/z (relative intensity): 511.10 (83.16%), 512.05 (100%), 513.00 (78.45%), 514.10
(15.67%), 515.00 (18.28%).
1
H NMR (400 MHz, CDCl
3
, δ) 9.91 (dd, J
HH
= 6.4 Hz, J
HF
= 10.8 Hz, 2H), 8.08 (dd, J = 5.6 and 3.2 Hz, 2H), 8.0 (t, J = 7.2 Hz, 2H), 7.68 (d, J = 8
Hz, 2H), 7.61 (dd, J = 5.2 and 2.8 Hz, 2H), 7.2 (t, J = 6.0 Hz, 2H).
13
C-NMR (100 MHz,
53
CDCl
3
, δ)148.8, 145.9, 145.6, 137.6, 131.1, 127.7, 122.0, 119.62, 119.58. Elemental
analysis for C
18
H
12
N
5
PtF•CH
2
Cl
2
: calcd: C 38.20, H 2.36, N 11.72; found: C 38.82, H
2.09, N 11.87.
(BPI)PtCN (4.3). 500 mg (0.95 mmol) 4.1 and 995 mg (5 mmol) KAg(CN)
2
were
rigorously stirred in 250 mL CH
2
Cl
2
for 24 hours. Solution was then rotory evaporated to
dryness. Product was then extracted using a soxhlet apparatus with 250 mL refluxing
CH
2
Cl
2
. When extracting solution was no longer yellow, the solution was cooled to rt and
then -40˚C. After one day of cooling, precipitate was collected and the volume reduced
and cooled again. This process was repeated several times. 0.210 g (43%), yellow needles.
MS m/z (relative intensity): 518.25 (85.76%), 519.20 (100%), 520.20 (72.19%), 521.21
(17.13%), 522.25 (17.19%).
1
H NMR (400 MHz, CDCl
3
, δ) 10.17 (d, J
HH
= 6.4 Hz, J
PtH
= 26 Hz, 2H), 8.02 (dd, J = 5.2 and 3.2 Hz, 2H), 7.93 (t, J = 7.6 Hz, 2H), 7.66 (d, J = 8
Hz, 2H), 7.59 (dd, J = 5.6 and 3.2 Hz, 2H), 6.98 (t, J = 6.8 Hz, 2H).
13
C-NMR (100 MHz,
CDCl
3
, δ) 157.6, 152.4, 150.8, 138.5, 137.6, 131.7, 128.8, 122.6, 120.8. Elemental
analysis for C
19
H
12
N
6
Pt: calcd: C 43.93, H 2.33, N 16.18; found: C 43.97, H 2.05, N
15.33.
(BPI)PtOOCCH
3
(4.4). 300 mg (0.57 mmol) 4.1 and 440 mg (3 mmol) AgOAc were
rigorously stirred in 50 mL CH
2
Cl
2
for 24 hours. The solution was then passed through a
plug of celite eluting with CH
2
Cl
2.
The volume was reduce to 15 mL under reduced
pressure followed by slow evaporation at room temperature. Precipitate was collected by
filtration and washed with MeOH. 0.155 g (49%), orange plates. MS m/z (relative
54
intensity): 551.10 (83.66%), 552.10 (100%), 553.10 (78.57%), 554.10 (17.36%), 555.45
(18.56%). NMR (400 MHz, CDCl
3
, δ) 9.36 (dd, J
HH
= 6.8 and 1.6 Hz, J
PtH
= 11.6 Hz,
2H), 8.08 (dd, J = 5.6 and 3.2 Hz, 2H), 7.95 (ddd, J = 8.4, 6.8 and 1.6 Hz, 2H), 7.66 (dd,
J = 7.2 and 1.6 Hz, 2H), 7.62 (dd, J = 5.2 and 2.8 Hz, 2H), 7.09 (td, J = 5.2 and 1.6 Hz,
2H), 2.3 (s, 3H).
13
C-NMR (100 MHz, CDCl
3
, δ) 177.6, 151.2, 150.0, 147.1, 137.7,
137.6, 131.3, 128.1, 122.2, 119.8, 24.7. Elemental analysis for C
19
H
12
N
6
Pt: calcd: C
43.48, H 2.74, N 12.68; found: C 43.44, H 2.52, N 12.17.
(BPI)PtPh (4.5). 0.095 g (0.208 mmol) (COD)PtPh
2
and 0.072 g (0.192 mmol) BPI
were suspended in 20 ml of methanol. To this solution 0.038 ml (0.208 mmol)
triethylamine was added and the solution was heated to 50˚C under nitrogen overnight.
Precipitate began to form upon cooling to room temperature. The precipitate was
collected by filtration and washed with methanol. The product was then recrystalized by
dissolving in a minimal amount of CH
2
Cl
2
followed by layered addition of methanol.
0.044 g (37%), orange needles. MS m/z (relative intensity): 568.15 (75.44%), 569.10
(100%), 570.15 (95.29%), 571.20 (48.40%), 572.15 (39.80%).
1
H NMR (400 MHz,
CDCl
3
, δ) 8.57 (d, J
HH
= 6.4 Hz, J
PtH
= 28 Hz, 2H), 8.08-8.05 (m, 2H), 7.76 (td, J = 7.6
and 2 Hz, 2H), 7.65-7.55 (m, 6H), 7.13 (t, J = 7.6 Hz, 2H), 7.03 (t, J = 7.2 Hz, 1H), 6.49
(td, J = 6.8 and 2 Hz, 2H).
13
C-NMR (100 MHz, CDCl
3
, δ) 156.9, 154.0, 153.6, 152.2,
139.0, 136.9, 136.8, 130.9, 129.3, 128.7, 123.5, 122.2, 118.7. Elemental analysis for
C
24
H
17
N
5
Pt: calcd: C 50.53, H 3.00, N 12.28; found: C 50.83, H 2.81, N 11.98.
55
(BPI)PtPhNMe
2
(4.6). 0.100 g (0.18 mmol) (COD)Pt(Ph-4-NMe
2
)
2
and 0.049 g (0.165
mmol) BPI were suspended in 5 ml of methanol. To this solution 0.030 ml (0.18 mmol)
triethylamine was added and the solution was heated to 60˚C under nitrogen for 4 days.
Precipitate began to form upon cooling to room temperature. The precipitate was
collected by filtration and washed with methanol. The product was then recrystalized by
dissolving in a minimal amount of CH
2
Cl
2
followed by layered addition of methanol.
0.054 g (49%), black crystals. MS m/z (relative intensity): 612.15 (99.94%), 613.15
(100%), 614.15 (84.14%), 615.15 (22.34%), 616.15 (13.26%).
1
H NMR (400 MHz,
CDCl
3
, δ ppm) 8.81 (dd, J = 6.8 and 1.6 Hz, J
PtH
= 26.8 Hz, 2H), 8.12 (dd, J = 5.2 and
2.8 Hz, 2H), 7.82 (ddd, J = 6.8, 5.6 and 1.6 Hz, 2H), 7.68-7.62 (m, 4H), 7.48 (d, J = 8.8
Hz, 2H), 6.79 (d, J = 8.8 Hz, 2H), 6.59 (td, J = 6.8 and 1.6 Hz, 2H), 2.98 (s, 6H).
13
C-
NMR (100 MHz, CDCl
3
, δ ppm) 154.2, 153.5, 152.2, 147.6, 139.1, 136.6, 136.4, 130.8,
128.6, 122.1, 118.6, 115.3, 110.0. Elemental analysis for C
26
H
22
N
6
Pt: calcd: C 50.90, H
3.61, N 13.70; found: C 51.09, H 3.40, N 13.36.
(4-t-BuBPI)PtCl (4.7). 0.2 g (0.54 mmol) (COD)PtCl
2
and 0.173 g (0.486 mmol) 4-t-
BuBPI were suspended in 15 ml of methanol. To this solution 0.074 ml (0.54 mmol)
triethylamine was added and the solution was heated to 50˚C under nitrogen overnight.
Precipitate began to form upon cooling to room temperature. The precipitate was
collected by filtration and washed with MeOH. The bright orange solid was then
recrystallized by dissolving it in a minimal amount of CH
2
Cl
2
followed by layered
addition of hexane. 0.171 g (70%), orange plates. MS m/z (relative intensity): 583.15
(86.21%), 584.15 (100%), 585.10 (96.98%), 586.15 (48.63%), 587.10 (41.17%).
1
H
56
NMR (400 MHz, CDCl
3
, δ) 10.4-10.2 (m, 2H), 8.13 (dd, J = 1.6, 0.4 Hz, 1H), 7.99 (dd, J
= 8.0, 0.4 Hz, 1H), 7.97-7.90 (m, 2H), 7.69 (dd, J = 8.0, 1.6 Hz, 1H), 7.68-7.61 (m, 2H),
7.07-7.01 (m, 2H), 1.46 (s, 9H).
13
C NMR (100 MHz, CDCl
3
, δ) 155.7, 152.4, 151.5,
151.3, 150.1, 150.0, 138.1, 137.5, 134.8, 128.8, 127.5, 127.4, 122.1, 119.7, 119.6, 119.3,
35.6, 31.4. Elemental analysis for C
22
H
20
N
5
PtCl: calcd: C 45.17, H 3.45, N 11.97; found:
C 45.16, H 3.27, N 11.65.
(3-NO
2
BPI)PtCl (4.8). 0.1 g (0.268 mmol) (COD)PtCl
2
and 0.084 g (0.243 mmol) 3-
NO
2
BPI were suspended in 15 ml of methanol. To this solution 0.037 ml (0.268 mmol)
triethylamine was added and the solution was heated to 50˚C under nitrogen overnight.
Upon cooling to room temperature, precipitate began to form. The precipitate was
collected by filtration and washed with H
2
O and MeOH. The orange solid was then
recrystallized by dissolving hot CH
2
Cl
2
and cooling the solution to -40˚C overnight. The
precipitate was collected by filtration and washed with MeOH. 0.097 g (64%), maroon
powder. MS (Maldi-TOF): m/z = 574.11.
1
H NMR (400 MHz, CDCl
3
, δ) 10.33 (t, J =
6.4 Hz, 2H), 8.31 (d, J = 6.8 Hz, 1H), 7.99-7.93 (m, 2H), 7.81-7.74 (m, 2H), 7.64 (d, J =
8 Hz, 1H), 7.58 (d, J = 8 Hz, 1H), 7.13-7.06 (m, 2H). Elemental analysis for
C
18
H
11
N
6
O
2
PtCl: calcd: C 37.67, H 1.93, N 14.64; found: C 37.44, H 1.78, N 13.70.
(4-NO
2
BPI)PtCl (4.9). 0.1 g (0.268 mmol) (COD)PtCl
2
and 0.084 g (0.243 mmol) 4-
NO
2
BPI were suspended in 20 ml of methanol. To this solution 0.037 ml (0.268 mmol)
triethylamine was added and the solution was heated to 50˚C under nitrogen overnight.
Upon cooling to room temperature, precipitate began to form. The precipitate was
57
collected by filtration and washed with MeOH. The orange solid was then recrystallized
by dissolving hot CH
2
Cl
2
and cooling the solution to -40˚C overnight. The precipitate
was collected by filtration and washed with MeOH. 0.092 g (60%), maroon powder. MS
(Maldi-TOF): m/z = 574.01.
1
H NMR (400 MHz, CDCl
3
, δ) 10.5-10.3 (m, 2H), 8.92 (d, J
= 2.0 Hz, 1H), 8.53 (dd, J = 8.0, 2.0 Hz, 1H), 8.26 (d, J = 8.0 Hz, 1H), 8.04-7.98 (m, 2H),
7.70 (t, J = 6.8 Hz, 2H). Elemental analysis for C
18
H
11
N
6
O
2
PtCl: calcd: C 37.67, H 1.93,
N 14.64; found: C 37.58, H 1.74, N 14.04.
(4-OC
5
H
11
BPI)PtCl (4.10). 0.1 g (0.268 mmol) (COD)PtCl
2
and 0.094 g (0.243 mmol)
4-OC
5
H
11
BPI were suspended in 10 ml of methanol. To this solution 0.037 ml (0.268
mmol) triethylamine was added and the solution was heated to 50˚C under nitrogen
overnight. Upon cooling to room temperature, precipitate began to form. The precipitate
was collected by filtration and washed with H
2
O and MeOH. The orange solid was then
recrystallized by dissolving it in a minimal amount of CH
2
Cl
2
followed by layered
addition of hexane. 0.078 g (52%), red powder. MS m/z (relative intensity): 613.15
(81.44%), 614.10 (100%), 615.05 (95.62%), 616.10 (47.02%), 617.10 (41.05%).
1
H
NMR (400 MHz, CDCl
3
, δ) 10.3 (dd, J = 6.4, 2 Hz, 1H), 10.27 (dd, J = 6.4, 2 Hz, 1H),
7.95-7.86 (m, 3H), 7.61-7.55 (m, 2H), 7.54 (d, J = 2.4 Hz, 1H), 7.12 (dd, J = 8.0, 2.4 Hz,
1H), 7.04-6.98 (m, 2H), 4.13 (t, J = 6.4 Hz, 2H), 1.91-1.82 (m, 2H), 1.55-1.37 (m, 4H),
0.96 (t, J = 7.2 Hz, 3H).
13
C NMR (100 MHz, CDCl
3
, δ) 162.7, 152.4, 151.1, 151.0,
150.1, 150.0, 139.6, 138.0, 129.2, 127.4, 127.3, 123.7, 119.6, 119.4, 118.7, 107.0, 68.7,
28.9, 28.2, 22.4, 14.0.
Elemental analysis for C
23
H
22
N
5
OPtCl: calcd: C 44.92, H 3.61, N
11.39; found: C 45.06, H 3.49, N 10.82.
58
(4-IBPI)PtCl (4.11). 0.1 g (0.268 mmol) (COD)PtCl
2
and 0.103 g (0.243 mmol) 4-IBPI
were suspended in 10 ml of methanol. To this solution 0.037 ml (0.268 mmol)
triethylamine was added and the solution was heated to 50˚C under nitrogen overnight.
Upon cooling to room temperature, precipitate began to form. The precipitate was
collected by filtration and washed with H
2
O and MeOH. The orange solid was then
recrystallized by dissolving hot CH
2
Cl
2
and cooling the solution to -40˚C overnight. The
precipitate was collected by filtration and washed with MeOH. 0.085 g (53%), orange
powder. MS m/z (relative intensity): 653.00 (79.09%), 653.95 (100%), 654.95 (94.33%),
655.95 (45.88%), 657.00 (31.88%).
1
H NMR (400 MHz, CDCl
3
, δ) 10.33 (d, J = 6.8 Hz,
2H), 8.64 (dd, J = 1.6, 0.8 Hz, 1H), 8.00 (dd, J = 8.0, 1.6 Hz, 1H), 7.98-7.93 (m, 2H),
7.83 (dd, J = 8.0, 0.8 Hz, 1H), 7.64 (d, J = 8.0 Hz, 2H), 7.07 (t, J = 6.8 Hz, 2H).
Elemental analysis for C
18
H
11
N
5
IPtCl: calcd: C 33.02, H 1.69, N 10.70; found: C 32.79,
H 1.54, N 10.06.
(4,5-diClBPI)PtCl (4.12). 0.1 g (0.268 mmol) (COD)PtCl
2
and 0.106 g (0.29 mmol) 4,5-
diClBPI were suspended in 10 ml of methanol. To this solution 0.043 ml (0.29 mmol)
triethylamine was added and the solution was heated to 50˚C under nitrogen overnight.
Upon cooling to room temperature, precipitate began to form. The precipitate was
collected by filtration and washed with H
2
O and MeOH. 129 mg crude product was
obtained (81%). 40 mg of crude product was sublimed at 315˚C (~10
-4
torr). 26 mg
(sublimation yield: 65%), dark orange needles. MS m/z (relative intensity): 594.95
(53.66%), 595.95 (72.475%), 596.95 (100%), 597.95 (69.59%), 598.95 (71.85%), 599.90
59
(30.89%), 600.95 (26.56%).
1
H NMR (400 MHz, CDCl
3
, δ) 10.35 (dd, J = 6.4, 1.6 Hz,
2H), 8.20 (s, 2H), 7.97 (td, J = 7.2, 1.6 Hz, 2H), 7.64 (dd, J = 8.4, 2.0 Hz, 2H), 7.09 (td, J
= 6.4, 1.6 Hz, 2H). Elemental analysis for C
18
H
10
N
5
PtCl
3
: calcd: C 36.17, H 1.69, N
11.72; found: C 36.12, H 1.50, N 11.42.
(E)-3,4-dibromo-3-hexene. 5.06 g (0.061 mol) of 3-hexyne was dissolved in 20 ml
acetic acid. 10 g (0.061 mol) of Br
2
in 20 ml acetic acid was added dropwise to the
hexyne solution. The reaction was stirred at room temperature under nitrogen overnight.
The solution was then poured into 100 ml H
2
O, extracted with hexane, washed with 5%
sodium bicarbonate solution and dried with MgSO
4
. The solvent was then evaporated
and the product used for the next step without further purification. 13.1g (90%).
1
H NMR
(250 MHz, CDCl
3
, δ) 2.68 (q, J = 7.5 Hz, 4H), 1.11 (t, J = 7.5 Hz, 6H).
(E)-3,4-dicyano-3-hexene. 12 g (0.136 mol) of CuCN in 70 ml dry DMF was refluxed
under N
2
for 1 hour. The mixture was then cooled to room temperature. 13.1 g (0.0549
mol) of (E)-3,4-dibromo-3-hexene was added via cannula. This solution was then
carefully maintained at 130˚C for 18 hrs. The mixture was then cooled to room
temperature, poured into 500 ml of 6 M NH
4
OH and stirred for 1 hour. The precipitate
was then filtered off and washed with Et
2
O (3 x 25 ml). The filtrate was then extracted
three times with 50 ml Et
2
O. The combined ether fractions were then washed with H
2
O,
sat. aq NaCl, dried with MgSO
4
and rotary evaporated to a yellow liquid. 4.5 g (62%).
1
H
NMR (250 MHz, CDCl
3
, δ) 2.59 (q, J = 7.5 Hz, 4H), 1.24 (t, J = 7.5 Hz, 6H).
60
(Z)-3,4-dicyano-3-hexene. In a 200 ml quartz reaction flask 10 g (74.6 mmol) of (E)-
3,4-dicyano-3-hexene was dissolved in 170 ml acetonitrile. The solution was bubble
degassed with N
2
for 10 min. The sealed flask was then irradiated with 254 nm light for
90 hours. After removal of acetonitrile by rotary evaporation the E isomer was distilled
off at 70˚C. The remaining solution was used for the next step without further
purification. 6.27 g (63%).
1
H NMR (250 MHz, CDCl
3
, δ) 2.40 (q, J = 7.5 Hz, 4H), 1.22
(t, J = 7.5 Hz, 6H).
2,5-bis(2-pyridylimino)3,4-diethylpyrrole (BPEP). A solution of 2 g (14.92 mmol) (Z)-
3,4-dicyano-3-hexene, 2.8 g (29.8 mmol) 2-aminopyridine and 0.4 g (4 mmol) CaCl
2
in
80 ml 1-butanol was refluxed under N
2
for 10 days. After distillation of 1-butanol the
remaining residue was separated on a column of silica gel, eluting first with CH
2
Cl
2
then
a mixture of CH
2
Cl
2
:ethyl acetate (9:1). The orange fraction was collected and rotary
evaporated to dryness. 187 mg (4%), red needles.
1
H NMR (250 MHz, CDCl
3
, δ) 8.52
(ddd, J = 5, 2, 0.75 Hz, 2H), 7.74 (dd, J = 7.5, 2 Hz, 2H), 7.38 (ddd, J = 7.75, 1.25, 0.75
Hz, 2H), 7.09 (ddd, J = 7.5, 5, 1.25 Hz, 2H), 2.6 (q, J = 7.25 Hz, 4H), 1.24 (t, J = 7.25
Hz, 6H).
2,5-bis(2-pyridylimino)3,4-diethylpyrrolate platinum (II) chloride (5.1). 132 mg
(0.354 mmol) (COD)PtCl
2
and 100 mg (0.328 mmol) BPEP were suspended in 7 ml
methanol. After the addition of 0.05 ml (0.354 mmol) NEt
3
the mixture was heated to
60˚C under nitrogen overnight. The mixture was then rotary evaporated to dryness and
run through a plug of silica eluting with CH
2
Cl
2
. The product was then recrystallized by
61
dissolving the residue in a minimum amount of CH
2
Cl
2
and layering with methanol. 85
mg (50%), thin red needles. MS m/z (relative intensity): 535.05 (100%), 534.10 (97.5%),
533.10 (82.2%), 536.10 (46.4%), 537.05 (42.5%).
1
H NMR (400 MHz, CDCl
3
, δ) 10.33
(dd, J = 6.4, 1.6 Hz, 2H), 7.90 (td, J = 7.2, 2.0 Hz, 2H), 7.58 (dd, J = 8.0, 1.6 Hz, 2H),
7.02 (td, J = 6.8, 1.6 Hz, 2H), 2.71 (q, J = 7.6 Hz, 4H), 1.27 (t, J = 7.6 Hz, 6H).
13
C-NMR
(100 MHz, CDCl
3
, δ) 154.3, 152.4, 150.3, 145.3, 137.8, 127.8, 119.7, 18.0, 14.5.
Elemental analysis for C
18
H
18
N
5
PtCl: calcd: C 40.42, H 3.39, N 13.09; found: C 40.70, H
3.40, N 12.33.
1,3-bis(2-pyridylimino)benz(f)isoindole (benz(f)BPI). A solution of 2 g (11.2 mmol)
2,3-dicyanonaphthylene, 2.21 g (23.5 mmol) 2-aminopyridine and 0.124 g (1.12 mmol)
CaCl
2
in 30 ml 1-butanol was refluxed under N
2
for 20 days. Upon cooling to room
temperature, product began to precipitate out of solution. The precipitate was collected
by filtration, washed with water and recrystallized with 100 ml ethanol/water (1:1). 3.07
g (78.5%), pale yellow solid.
1
H NMR (250 MHz, CDCl
3
, δ) 8.64 (dd, J = 5, 2 Hz, 2H),
8.61 (s, 2H), 8.07 (dd, J = 6.25, 3.5 Hz, 2H), 7.79 (td, J = 7.5, 2 Hz, 2H), 7.62 (dd, J =
6.25, 3.5 Hz, 2H), 7.5 (d, J = 7.5 Hz, 2H) 7.14 (ddd, J = 7.5, 5, 2 Hz, 2H).
1,3-bis(2-pyridylimino)benz(f)isoindolate platinum (II) chloride (5.3). 0.50 g (1.34
mmol) (COD)PtCl
2
and 0.433 g (1.24 mmol) benz(f)BPI were suspended in 25 ml of
methanol. To this solution 0.186 ml (1.34 mmol) triethylamine was added and the
solution was heated to 50˚C under nitrogen for 24 hours. Precipitate began to form upon
cooling to room temperature. The precipitate was collected by filtration and washed with
62
water. 0.554g (78%), pale orange solid. Sample was further purified by sublimation
(300˚C, ~10
-4
torr). MS m/z (relative intensity): 579.05 (100%), 578.10 (97.4%), 577.10
(79.3%), 580.10 (48.3%), 581.05 (40.0%).
1
H NMR (400 MHz, CDCl
3,
δ) 10.3 (dd, J =
6.8, 1.6 Hz, 2H), 8.59 (s, 2H), 8.09 (dd, J = 6.0, 3.6 Hz, 2H), 7.95 (td, J = 7.2, 1.6 Hz,
2H), 7.69-7.62 (m, 4H), 7.05 (td, J = 6.8, 1.6 Hz, 2H). Elemental analysis for
C
22
H
14
N
5
PtCl: calcd: C 45.64, H 2.44, N 12.10; found: C 45.50, H 2.31, N 11.69.
1,3-bis(2-pyridylimino)benz(e)isoindole (benz(e)BPI). A solution of 1.0 g (5.6 mmol)
1,2-dicyanonaphthalene, 1.09 g (11.7 mmol) 2-aminopyridine and 0.124 g (1.12 mmol)
CaCl
2
in 20 ml 1-butanol was refluxed under N
2
and monitored for the disappearance of
1,2-dicyanonaphthalene by TLC. After 20 days of reflux the reaction was discontinued
even though starting material was still observed. Upon cooling to room temperature,
precipitate began to form. The precipitate was collected by filtration and washed with
water. Product was then isolated by column chromatography on silica gel eluting first
with CH
2
Cl
2
then slow addition of ethylacetate to the eluting solvent. Three fractions
were isolated: first 1,2-dicyanonaphthalene (R
f
= 0.6, CH
2
Cl
2
), second was 1-(2-
pyridylimino) isoindol-3-amine (R
f
= 0.3, CH
2
Cl
2
), and finally a yellow fraction
containing 1,3-bis(2-pyridylimino)benz(e)isoindole (R
f
= 0.1, CH
2
Cl
2
). 0.320 g (15%),
yellow solid.
1
H NMR (250 MHz, CDCl
3
, δ) 9.65 (d, J = 8.25, 1H), 8.64 (s, 2H), 8.18-
8.04 (m, 2H), 7.97 (d, J = 8.25 Hz, 1H), 7.89-7.45 (m, 6H), 7.20-7.08 (m, 2H).
1,3-bis(2-pyridylimino)benz(e)isoindolate platinum (II) chloride (5.4). 0.1 g (0.268
mmol) (COD)PtCl
2
and 0.085 g (0.243 mmol) benz(e)BPI were suspended in 10 ml of
63
methanol. To this solution 0.037 ml (0.268 mmol) triethylamine was added and the
solution was heated to 50˚C under nitrogen for 24 hours. Precipitate began to form upon
cooling to room temperature. The precipitate was collected by filtration and washed with
methanol. The red solid was then dissolved in boiling toluene and then cooled to -40°C
overnight. The red powder was then collected by filtration and washed with MeOH.
0.062 g (44%), red solid. MS m/z (relative intensity): 579.05 (100%), 578.10 (99.8%),
577.10 (82.5%), 580.10 (49.3%), 581.05 (41.9%).
1
H NMR (400 MHz, CDCl
3
, δ) 10.37
(s, 2H), 9.67 (d, J = 8 Hz, 1H), 8.17 (d, J = 8.4 Hz, 1H), 8.09 (d, J = 8.4 Hz, 1H), 7.86-
7.60 (m, 7H), 7.08 (d, J = 6.8 Hz, 2H). Elemental analysis for C
22
H
14
N
5
PtCl: calcd: C
45.64, H 2.44, N 12.10; found: C 45.43, H 2.18, N 11.67.
1,3-bis(1-isoquinolylimino)isoindole (BIQI). A solution of 0.421 g (3.29 mmol)1,2-
dicyanobenzene, 1 g (6.9 mmol) 1-aminoisoquinoline and 0.11 g (1 mmol) CaCl
2
in 20
ml 1-butanol was refluxed under N
2
for 5 days. Upon cooling to room temperature,
product began to precipitate out of solution. The precipitate was collected by filtration,
washed with water. 1.091 g (83%), green needles.
1
H NMR (250 MHz, CDCl
3
, δ) 9.03
(d, J = 8 Hz, 2H), 8.57 (d, J = 5.75 Hz, 2H), 8.28 (dd, J = 5.5, 3 Hz, 2H), 7.88-7.63 (m,
8H), 7.53 (d, J = 5.75 Hz, 2H).
1,3-bis(1-isoquinolylimino)isoindolate platinum (II) chloride (5.5). 0.360 g (0.965
mmol) (COD)PtCl
2
and 0.356 g (0.893 mmol) BIQI were suspended in 20 ml of
methanol. To this solution 0.134 ml (0.965 mmol) triethylamine was added and the
solution was heated to 50˚C under nitrogen for 24 hours. Precipitate began to form upon
64
cooling to room temperature. The precipitate was collected by filtration and washed with
water. 0.505 g (90%), dark purple solid. Sample was further purified by sublimation
(350˚C, ~10
-4
torr). Due to low solubility, no NMR data was obtained. MS m/z (relative
intensity): 628.10 (100%), 629.05 (82.4%), 627.00 (61.2%), 630.00 (47.7%), 631.10
(37.9%). Elemental analysis for C
26
H
16
N
5
PtCl: calcd: C 49.65, H 2.56, N 11.13; found: C
49.59, H 2.41, N 10.72.
2.6.2 X-ray Crystallography Diffraction data for compounds 3.3 and 3.7 were collected
on a Bruker SMART APEX CCD diffractometer with graphite monochromated Mo Kα
radiation (λ = 0.71073 Å). The cell parameters for the complexes were obtained from a
least-squares refinement of the spots (from 60 collected frames) using the SMART
program. One hemisphere of crystal data for each compound was collected up to a
resolution of 0.80 Å, and the intensity data were processed using the Saint Plus program.
All of the calculations for the structure determination were carried out using the
SHELXTL package (Version 5.1).
23
Absorption corrections were applied by using
SADABS.
24
In most cases, hydrogen positions were input and refined in a riding manner
along with the attached carbons. A summary of the refinement details and the resulting
factors are given in Table 2.5.
65
Table 2.5. Crystallographic data for compounds 3.3 and 3.7.
3.3 3.7
Empirical formula C
18
H
13
N
5
O
2
C
22
H
21
N
5
O
2
Formula weight 331.33 387.44
Temperature, K 293(2) 138(2)
Wavelength (Å) 0.71073 0.71073
Crystal system Orthorhombic Monoclinic
Space group Pnma P2(1)/c
a (Å)
16.050(3)
13.616(2)
b (Å)
20.222(4)
11.0329(16)
c (Å)
4.5470(9)
14.632(2)
α (deg) 90 90
β (deg) 90 116.918(10)
γ (deg) 90 90
V (Å
3
) 1475.8(5) 1959.9(5)
Z 4 4
D
calcd
(g/cm
3
) 1.491 1.313
µ (mm
-1
) 0.102 0.088
F(000) 688 816
θ range 2.01 to 27.54 1.68 to 27.47
Reflections collected 11676 11793
Independent
reflections
1733 [R(int) =
0.0869]
4410 [R(int) =
0.0543]
Refinement method
Full-matrix least-
squares on F
2
Full-matrix least-
squares on F
2
Data/restraints /
parameters
1773/0/116 4410/0/268
GOF on F
2
1.028 1.259
Final R indices[I>2σ(I)] 0.0587 0.0450
R indices (all data) 0.1108 0.0711
66
Chapter 2 References
(1) Elvidge, J. A.; Linstead, R. P. J. Chem. Soc. 1952, 5000-5007.
(2) Clark, P. F.; Elvidge, J. A.; Linstead, R. P. J. Chem. Soc. 1953, 3593-3601.
(3) Siegl, W. O. Journal of Organic Chemistry 1977, 42, (11), 1872-1878.
(4) Matsunami, M.; Takaki, A.; Maekawa, H.; Nishiguchi, I. Sci. Technol.Adv. Mater.
2005, 6, 172-180.
(5) Broring, M.; Kleeberg, C. Inorg. Chim. Acta. 2007, 360, 3281-3286.
(6) Schilf, W. J. Mol. Struct. 2004, 691, 141-148.
(7) Meder, M.; Galka, C. H.; Gade, L. H. Monatshefte fur Chemie 2005, 136, 1693-
1706.
(8) McDermott, J. X.; White, J. F.; Whitesides, G. M. J. Am. Chem. Soc. 1976, 98,
(21), 6521-6528.
(9) Brainard, R. L.; Nutt, W. R.; Lee, T. R.; Whitesides, G. M. Organometallics 1988,
7, 2379-2386.
(10) Shekhar, S.; Hartwig, J. F. J. Am. Chem. Soc. 2004, 126, 13016-13027.
(11) Palkovits, H.; Ziegler, U.; Schmidtberg, G.; Brune, u. H. A. J. Organomet. Chem.
1988, 338, 119-137.
(12) Fallis, K. A.; Anderson, G. K.; Rath, N. P. Organometallics 1993, 12, 2435-2439.
(13) Hackett, M.; Whitesides, G. M. J. Am. Chem. Soc. 1988, 110, 1449-1462.
(14) Aldridge, T. K.; Stacy, E. M.; McMillin, D. R. Inorgnic Chemistry 1994, 33, 722-
727.
(15) Arena, G.; Calogero, G.; Campagna, S.; Scolaro, L. M.; Ricevuto, V.; Romeo, R.
Inorg. Chem. 1998, 37, 2763-2769.
(16) Harkins, S. B.; Peters, J. C. Organometallics 2002, 21, 1753-1755.
(17) Clark, H. C.; Manzer, L. E. J. Organomet. Chem. 1973, 59, 411-428.
(18) Taylor, R. A.; Law, D. J.; Sunley, G. J.; White, A. J. P.; Britovsek, G. J. P. Angew.
Chem. Int. Ed. 2009, 48, 5900-5903.
67
(19) Grice, K. A.; Goldberg, K. I. Organometallics 2009, 28, 953-955.
(20) Pincock, J. A.; Yates, K. Canadian Journal of Chemistry 1970, 48, 3332-3348.
(21) Fitzgerald, J.; Taylor, W.; Owen, H. Synthesis 1991, 9, 686-688.
(22) Cummings, S. D. Coordination Chemistry Reviews 2009, 253, 449-478.
(23) Sheldrick, G. M. SHELXTL, 5.1; Bruker Analytical X-ray System, Inc: Madison,
WI, 1997.
(24) Blessing, R. H. Acta Crystallographica Section A 1995, 51, 33-38.
68
CHAPTER 3. The Photophysics of Dihydroxy Substituted BPI
Derivatives
3.1 Introduction
Emission from organic molecules, that do not contain heavy atoms, typically
occurs from the singlet excited state with an energy difference between absorption and
emission less than 2000 cm
-1
. In chapter one, several processes that result in an “apparent
Stokes shift” greater than 2000 cm
-1
were introduced. One such example was excited
state intramolecular charge transfer (ESIPT). In the ground state of an ESIPT molecule a
proton donor atom and a proton acceptor atom are in close proximity and are connected
by an intramolecular hydrogen bond. A schematic representation of an ESIPT process
with a generalized oxygen donor and a nitrogen acceptor motif can be seen in Figure 3.1.
h
S
0
S
1
S
1
'
S
0
'
h
N
OH
N
OH
*
HN
O
*
HN
O
ESIPT
Figure 3.1. Schematic representation of an
ESIPT process with a generalized oxygen donor
and a nitrogen acceptor motif.
69
In the ground state (S
0
) of the representative motif (Figure 3.1), the hydrogen
atom resides predominantly on the oxygen atom. A hydroxyl group attached to an alkene
is labeled an enol and thus this form of the phototautomer is typically described as the
enol form of the molecule. The redistribution of electron density that occurs upon
excitation increases the acidity of the proton donor (O) and/or the basicity of the proton
acceptor (N) in the excited enol form (S
1
). The changes in acidity/basicity makes a proton
transfer from the oxygen to the nitrogen favorable resulting in the excited keto form of
the molecule (S
1
’). The proton transfer process typically occurs on the scale of
picoseconds after excitation.
1
The excited keto form then either radiatively or
nonradiatively relaxes down to the ground state keto form of the molecule (S
0
’) followed
by a proton transfer to give the ground state keto form (S
0
). Because the absorbing and
emitting species are different tautamers, the energy difference between absorption and
emission are much larger (>2000 cm
-1
) than typical fluorescent molecules. The unique
properties of ESIPT molecules makes them ideal candidates as material for laser dyes,
2
fluorescent probes,
3
photostabilizers
4
and high energy radiation detectors.
5
During the synthesis of various BPI derivatives (Chapter 2) we have found that
the dihydroxy substituted BPI exhibits several of the characteristics common to ESIPT
molecules. What follows is the systematic investigation into this new class of proton
transfer dyes (Table 3.1).
70
Table 3.1. The structure of alcohol/ethoxy substituted 1,3-bis(aryl or alkyl)isoindoline
dyes 3.1-7.
HN
N
N
R
3
R
2
R
2
R
4
R
1
R
1
Complex R1 R2 R3 R4
BPI 2-Pyridyl H H H
3.1 -C
12
H
25
H OH OH
3.2 (4-tBu-Ph) H OH OH
3.3 2-Pyridyl H OH OH
3.4 2-Pyridyl Cl OH OH
3.5 1-isoquinolyl H OH OH
3.6 2-Pyridyl H OEt OH
3.7 2-Pyridyl H OEt OEt
3.2 Experimental Section
3.2.1 Photophysical Characterization. The UV-visible spectra were recorded on a
Hewlett-Packard 4853 diode array spectrophotometer. Steady state emission experiments
at room temperature and 77K were performed on a Photon Technology International
QuantaMaster Model C-60SE spectrofluorimeter. Quantum efficiency measurements
were carried out using a Hamamatsu C9920 system equipped with a xenon lamp,
calibrated integrating sphere and model C10027 photonic multichannel analyzer.
3.2.2 Computational Method. All calculations were performed using the Titan software
package (Wavefunction, Inc.). The gas phase geometry optimizations were calculated
using B3LYP functional with the 6-31G* basis set as implemented in Titan. The energy
71
levels and orbital diagrams of the highest occupied molecular orbital (HOMO) and lowest
unoccupied molecular orbital (LUMO) were obtained from the optimized geometry of the
singlet state.
3.3 Results and Discussion
3.3.1 Photophysics of BPI and hydroxyl/alkoxy substituted BPI. The parent (1,3-
bis(2-pyridylimino)isoindole (Figure 2.1; BPI) molecule exhibits highly structured
absorption bands between 300–425 nm (Figure 3.2). Although BPI was found to be
nonemissive at room temperature, highly structured emission from 400-550 nm was
observed upon cooling the solution to 77K in 2-MeTHF. The 3.4 ns lifetime and small
Stokes shift (~410 cm
-1
) are indicative of typical fluorescent emission (S
1
→ S
0
+ hν).
300 400 500 600
0.0
0.5
1.0
1.5
2.0
0.0
0.2
0.4
0.6
0.8
1.0
Normalized PL (a.u.)
Wavelength (nm)
ε ε ε ε (x10
4
M
-1
cm
-1
)
Figure 3.2. Room temperature absorption (in CH
2
Cl
2
) and 77K
emission (in 2-MeTHF) of BPI.
72
In both toluene and CH
2
Cl
2
the R
3
and R
4
hydroxyl substituted BPI (Table 3.1;
3.3), was found to exhibit similar absorption characteristics to the parent BPI compound
(Figure 3.3). However, in methanol several weak transitions (ε ≈ 1000 M
-1
cm
-1
) from 500
to 600 nm were observed (inset: Figure 3.3).
The photoluminescent properties of 3.3 in various solvents can be seen in Table
3.2. Regardless of solvent, structured emission at approximately 600 nm was observed
upon excitation into the higher energy absorption band (360 nm). Representative
emission spectra of 3.3 in a polar-aprotic (CH
2
Cl
2
), nonpolar (toluene) and a protic
(MeOH) solvent can be seen in Figure 3.4.
300 350 400 450 500 550 600 650
0.0
0.5
1.0
1.5
2.0
2.5
500 550 600
0.00
0.05
0.10
W avelength (nm )
Wavelength (nm)
ε ε ε ε (x10
4
M
-1
cm
-1
)
Methanol
CH
2
Cl
2
Toluene
Figure 3.3. Absorption spectra of 3.3 in methanol,
CH
2
Cl
2
and toluene.
73
Table 3.2. Photoluminescent properties of 3.3 in various solvents at room temperature.
Solvent λ λ λ λmax(nm) Φ Φ Φ ΦPL τ τ τ τ (ns)
Isopropanol 600 0.448 5.31
CH
2
Cl
2
597 0.401 3.95
CHCl
3
597 0.395 4.36
n-butanol 602 0.378 4.58
Toluene 602 0.366 3.29
Chlorobenzene 602 0.347 3.35
Cyclohexane 597 0.309 3.14
Acetonitrile 597 0.309 3.66
MeOH 592 0.305 3.67
Ethyl Acetate 597 0.3 3.42
DMSO 612 0.299 3.05
Acetone 597 0.291 3.35
2-MeTHF 600 0.286 3.05
DMF 607 0.28 2.94
Ethanol 593 0.278 3.86
Despite the similarities in emission wavelength, the quantum efficiency of 3.3
varied greatly depending on the solvent ranging from 27.8% in ethanol to 44.8% in
isopropanol. The excited state lifetimes varied between 5.31 and 2.94 ns with decreased
lifetimes generally correlating with decreased quantum yields. How the polarity and
aprotic/protic nature of the solvent is correlated with emission efficiency is unclear as no
500 550 600 650 700 750
0.0
0.2
0.4
0.6
0.8
1.0
Normalized PL (a.u.)
Wavelength (nm)
MeOH
CH
2
Cl
2
Toluene
Figure 3.4. Emission spectra of 3.3 in methanol,
CH
2
Cl
2
and toluene.
74
obvious trends in Table 3.2 were found. For thin films composed of 2% (w/w) of 3.3 in
poly(methyl methacrylate) (PMMA) the emission lifetime (3.56 nm) and quantum yield
(0.25) are similar to that of the methanol solution (Table 3.4).
Although the excited state lifetime of 3.3 is indicative of fluorescent emission, the
large apparent Stokes shift (6600 cm
-1
) is relatively unique. As stated in chapter 1, there
are three common examples of excited state structural changes typically associated with
large apparent Stokes shift: excimer/exciplex formation, twisted intramolecular charge-
transfer (TICT) and excited state intramolecular proton transfer (ESIPT). The ridged
nature of the BPI ligand makes a TICT process unlikely and although the large π-system
of 3.3 is generally favorable for dimer formation, structured emission in Figure 3.4 is not
common for dimer emission. The close proximity of an alcohol and an amine makes an
ESIPT process a likely explanation for the large apparent Stokes shift observed for 3.3.
A common test for ESIPT is to replace the alcohol groups with alkoxy substituent
as a means of turning off proton transfer.
6
Because there are two possible sites for proton
transfer, both the monoalkoxy (3.6) and the dialkoxy (3.7) substituted derivatives of 3.3
were examined for their photophysical properties. As can be seen in Figure 3.5 the molar
absorptivities (ε ~ 2 x 10
4
M
-1
cm
-1
) and absorption profiles (300-475 nm) for 3.3, 3.6 and
3.7 are similar.
75
The monohydroxy substituted compound 3.6 exhibits similar excited state
lifetimes and photoluminescent efficiencies to 3.3 (Table 3.4). On the other hand, the
diethoxy substituted derivative (3.7) was found to be nonemissive at room temperature.
Upon cooling to 77K, 3.7 exhibited emission at energies (452 nm) more similar to the
parent BPI than that of 3.3 (Figure 3.6). The absence of emission at ~600 nm in the
dialkoxy substituted species (Table 3.4) is strong support for an ESIPT process being
active in 3.3 and 3.6. Additionally, the involvement of a proton in excited state processes
is implied by an increase in lifetime and quantum yield of 3.3 from 3.67 ns and 0.305 in
methanol to 6.69 ns and 0.690 in deuterated methanol (Table 3.4; MeOD). Whether one
or two protons are involved in the ESIPT process is unclear, however the similarities in
emission properties of 3.3 and 3.6 suggest that only a single proton is likely active in 3.3.
300 400 500 600 700 800
0.0
0.5
1.0
1.5
2.0
0.0
0.2
0.4
0.6
0.8
1.0
Normalized PL (a.u.)
3.3
3.6
3.7
Wavelength (nm)
ε ε ε ε (x10
4
M
-1
cm
-1
)
Figure 3.5. Absorption (in MeOH, open symbol) and
emission (in toluene, filled symbol) spectra of 3.3
(square), 3.6 (circle), and 3.7 (triangle) at room
temperature.
76
From the electron density map of the in the crystal structure and the ground state
geometry calculations of 3.3 the high energy absorption (300-450 nm) and emission are
tentatively attributed to the enol and the keto form of the molecule respectively (Figure
3.7). It is interesting to note that the low energy absorption (500-600nm) observed from
3.3 in methanol (inset: Figure 3.3) suggests the presents of the keto form even in the
ground state. The absence of the keto form in toluene and CH
2
Cl
2
also indicates that there
is an equilibrium between the two form that is influenced by solvent.
400 500 600 700 800
0.0
0.2
0.4
0.6
0.8
1.0
Normalized Emission (a.u.)
Wavelength (nm)
BPI
3.3
3.6
3.7
Figure 3.6. Emission spectra of BPI, 3.3, 3.6 and
3.7 in 2-MeTHF at 77K.
NH
N
N
N
N
OH
OH
NH
N
HN
N
N
OH
O
Enol form Keto form
Figure 3.7. Enol and keto forms of 3.3.
77
The spatial distribution of the HOMO and LUMO obtained from the ground state
geometry of 3.3 (enol form) also offer support to an ESIPT process (Figure 3.8). The
HOMO and LUMO of 3.3 are delocalized on the hydroquinone moiety and BPI portion
of the molecule respectively. During lowest energy excitation (HOMOLUMO) an
electron density shift from the hydroquinone to the (pyridylimino)3,4-pyrrole portion of
the molecule is expected, increasing the acidity of the oxygen and the basicity of nitrogen.
This shift in electron density and changes in acidity/basicity is likely responsible for the
excited state proton transfer.
3.3.2 Absorption properties of dihydroxy bisiminoisoindole derivatives. The ESIPT
nature of 3.3 is not surprising considering that hydroxyphthalimide is known to exhibit
emission from an ESIPT state and there is a large amount of structural similarity between
phthalimide and BPI. However, the dihydroxy substituted 1,3-bisiminoisoindole motif in
Figure 3.8. HOMO and LUMO of 3.3. The HOMO (transparent) and
LUMO (mesh) surfaces are displayed as viewed above the π-symmetric
orbitals, with opposite phases above and below the plane of the molecule.
78
3.3 offers one important advantage over hydroxyphthalimide based ESIPT dyes, two
readily modifiable substitutents (Table 3.1, R1) not present in phthalimide. Modification
of the substituents of 3.3 is a possible means of investigating the structure-property
relationships that control excited state proton transfer process with the long term goal of
developing guiding principles for ESIPT-luminophore design.
In an effort to elucidate the effects of substitution on BPI based proton transfer
dyes, several molecules based on the 1,3-bisiminoisoindole motif have been synthesized
and characterized (Table 3.1). The photophysical properties of compounds 3.1-7 are
summarized in Table 3.3 and 3.4.
Table 3.3. Absorption maxima and molar absorptivity of compounds 3.1-7.in toluene,
CH
2
Cl
2
and methanol.
Molecule
absorbance λ λ λ λ (nm) (ε, ε, ε, ε, x10
4
M
-1
cm
-1
) ) ) )
Toluene CH
2
Cl
2
MeOH
3.1 336(0.24), 499(0.84) 347(0.36), 492(0.97) 345(0.34), 472(0.85)
3.2 379(1.71) 375(1.76)
384(1.05), 549(0.74),
574(0.56), 593(0.43)
3.3
370(1.70), 388(2.00),
413(1.59), 437(1.09)
369(2.06), 387(2.40),
413(1.84), 431(1.22)
366(1.68), 384(1.92),
408(1.56), 543(0.07),
587(0.07)
3.4
401(1.56), 423(2.01),
448(1.54), 436(1.31),
516(0.07), 555(0.11),
603(0.09)
363(1.29), 478(0.31),
514(0.97), 554(2.18),
599(2.87)
372(2.32), 392(2.63),
417(1.96), 517(0.56),
555(1.04), 601(1.04)
3.5
330(0.86), 344(0.65),
413(2.97), 436(3.31),
464(2.09)
329(0.77), 343(0.62),
412(2.93), 434(3.14),
462(1.92)
-
3.6
371(2.36), 391(2.89),
414(2.20)
371(2.82), 390(3.34),
411(2.55)
367(1.83), 386(2.11),
410(1.62)
3.7
376(3.76), 394(4.11),
419(2.43)
375(2.88), 394(3.21),
420(1.95)
371(1.83), 393(2.22),
416(1.82), 451(0.64)
79
The absorption spectra of 3.1, 3.2, 3.4 and 3.5 in toluene, CH
2
Cl
2
and methanol
can be seen in Figure 3.9. The molar absorptivity of 3.5 was not measured in methanol
due to its low solubility.
In all three solvents (MeOH, CH
2
Cl
2
and toluene; Figure 3.8a) 3.1 has two broad
featureless absorption peaks from 300-400nm (ε ~ 0.4 x 10
4
M
-1
cm
-1
) and 400-550 nm (ε
~ 0.9 x 10
4
M
-1
cm
-1
). Despite the decreased conjugation upon substitution of the pyridyl
groups with alkyl chains, the low energy peak of 3.1 is red-shifted relative to 3.3. This
unexpected red-shift in absorption combined with the presence of a lower intensity,
300 400 500 600
0.0
0.2
0.4
0.6
0.8
1.0
Wavelength (nm)
ε ε ε ε (x10
4
M
-1
cm
-1
)
MeOH
CH
2
Cl
2
Toluene
a)
300 400 500 600
0.0
0.5
1.0
1.5
MeOH
CH
2
Cl
2
Toluene
Wavelength (nm)
ε ε ε ε (x10
4
M
-1
cm
-1
)
b)
300 400 500 600
0
1
2
3
MeOH
CH
2
Cl
2
Toluene
Wavelength (nm)
ε ε ε ε (x10
4
M
-1
cm
-1
)
c)
300 400 500 600
0
1
2
3
CH
2
Cl
2
Toluene
Wavelength (nm)
ε ε ε ε (x10
4
M
-1
cm
-1
)
d)
Figure 3.9. Room-temperature absorption spectra of a) 3.1, b) 3.2, c) 3.4 and d) 3.5 in
toluene, CH
2
Cl
2
and methanol.
80
higher energy peak at 350 nm suggests that the equilibrium of 3.1 is shifted from the enol
form, as was seen with 3.3, to the keto form of 3.1 in all three solvents.
In both methanol and CH
2
Cl
2
compound 3.2 has a broad featureless absorption
(Figure 3.9b) at similar energies (300-400 nm) and molar absorptivities (ε ~ 1.8 x 10
4
M
-
1
cm
-1
) to that of 3.3. Also similar to but more pronounced than in 3.3 are the changes in
absorption specta of 3.2 in methanol. The appearance of a relatively strong (ε ~ 0.7 x 10
4
M
-1
cm
-1
) broad absorption peak from 500-600 nm is accompanied by the decrease in
intensity of the peak at ~375 nm. Again the high energy and the low energy absorption
peaks are tentatively assigned as being due to the enol and the keto form of 3.2
respectively.
Like compounds 3.1 and 3.2, the equilibrium between enol and keto forms of 3.4
is perturbed by the solvent as can be seen in Figure 3.9c. In toluene the absorption profile
of 3.4 is dominated by the high energy, enol form of the molecule. In CH
2
Cl
2
, a structure
low energy peak due to the keto form of 3.4 appears which is the dominant species in
methanol. Because the low energy and high energy absorption peaks are at opposite ends
of the visible spectrum (blue and red respectively) large changes in solution color are
expected. In Figure 3.10 is a photograph of compound 3.4 in toluene, THF, DCM,
methanol and DMF.
81
In solutions where the enol form is dominant, blue portion of the visible spectrum
is absorbed and thus a yellow color is seen (Figure 3.10; toluene). Alternatively, if the
keto form is dominant, almost all of the visible spectrum, except for the blue region, will
be absorbed and a blue color can be expected (Figure 3.10; MeOH). Since both species
can be present in solution (Figure 3.9c; CH
2
Cl
2
) in varying ratios, the solution colors will
vary between the two extremes. The tentative conclusion to be reached from Figure 3.10
is that increases in solvent polarity increases the favorability of the keto form.
While the absorption profile remains similar, extending the conjugation of 3.3 by
replacing the pyridyl groups at R1 with isoquinolyl groups (3.5) resulted in a ~30 nm red-
shift in absorption. The shift in the low energy transition is presumable due LUMO
stabilization that occurs upon benzanulation of 3.3. This type of LUMO stabilization with
benzanulation of BPI compounds is expanded upon in chapter 5.
It is interesting to note that the absorption spectra of complexes where R1 is a
pyridyl or isoquinolyl group (3.3-7) are more structured than those containing a phenyl or
Figure 3.10. Test tube samples of 3.4 in toluene, THF,
DCM, methanol and DMF.
82
alkyl group (3.1-2). It is likely that hydrogen bond between the nitrogen of the pyridyl or
isoquinolyl group and the isoindole proton imparts additional ridgidity to the molecules
and thus greater vibrational character is observed.
3.3.3 Emissive properties of dihydroxy bisiminoisoindole derivatives. The emissive
properties of compounds 3.1, 3.2, 3.4 and 3.5 in methanol, CH
2
Cl
2
, toluene and PMMA
are summarized in Table 3.4. Due to their low solubility, thin film measurements of 3.4
and 3.5 in PMMA was not obtained. The room temperature and 77K emission spectra of
3.1, 3.2, 3.4 and 3.5 are shown in Figure 3.11 and 3.13 respectively.
400 500 600 700
0.0
0.2
0.4
0.6
0.8
1.0
Normalized Emission (a.u.)
Wavelength (nm)
MeOH
CH
2
Cl
2
Toluene
a)
500 550 600 650 700 750
0.0
0.2
0.4
0.6
0.8
1.0
Normalized Emission (a.u.)
Wavelength (nm)
MeOH
CH
2
Cl
2
Toluene
b)
500 550 600 650 700 750
0.0
0.2
0.4
0.6
0.8
1.0
Normalized Emission (a.u.)
Wavelength (nm)
MeOH
CH
2
Cl
2
Toluene
c)
550 600 650 700 750
0.0
0.2
0.4
0.6
0.8
1.0
Normalized Emission (a.u.)
Wavelength (nm)
MeOH
CH
2
Cl
2
Toluene
d)
Figure 3.11. Room-temperature emission spectra of a) 3.1, b) 3.2, c) 3.4 and d)
3.5 in toluene, CH
2
Cl
2
and methanol.
83
Both the efficiency and energy of emission from the dialkyl substituted compound
(3.1) varied greatly depending on the environment. Upon excitation into the high energy
absorption peak (350nm) the emission in CH
2
Cl
2
, toluene and PMMA (Figure 3.11a) is
dominated by a low energy transition (>500 nm) with efficiencies ranging from 0.061 (in
CH
2
Cl
2
) to 0.007 (in PMMA). In methanol a relatively strong high energy peak (400-500
nm) is present which becomes the dominant emissive species at 77K in 2-MeTHF (Figure
3.13).
The excitation spectra of 3.1 in methanol, monitoring the low energy emission
(600 nm), closely resembles the absorption spectra in methanol (Figure 3.12). The
excitation spectra of the high energy peak (473 nm) is dominated by a higher energy peak
at approximately 400 nm. As with absorption, the low and high energy components are
tentatively assigned to be from the keto and enol forms of the molecule.
300 400 500 600 700
0.0
0.5
1.0
1.5
2.0
Absorption
Excitation (Em: 473 nm)
Excitation (Em: 600 nm)
Emission (Ex: 350 nm)
Intensity (a.u.)
Wavelength (nm)
Figure 3.12. Absorption, excitation and emission spectra
of 3.1 in methanol.
84
Emission energy of 3.2 was considerably less variable (Figure 3.11b) than 3.1,
ranging from 590nm (in toluene) to 624 nm (in PMMA). However, like compound 3.1,
the highest and lowest efficiency emissions were in methanol (0.121) and PMMA (0.010).
It is interesting to note that although the lifetime and energies of 3.2 are similar to 3.3, the
efficiencies are lower by more than a factor of three. For example, in methanol the
lifetime of 3.2 and 3.3 are 4.14 ns and 3.67 nm and the efficiencies are 0.121 and 0.305
respectively. From the equation k
r
= Φ/τ it can be seen that a reduced radiative rate in 3.2
(k
r
= 2.8 x 10
7
s
-1
) relative to 3.3 (k
r
= 8.3 x 10
7
s
-1
) is likely responsible for the lower
efficiency. Despite there differences is efficiency, the similarity in excited state lifetimes
(3-4 ns) and emission energies compared to compound 3.3 indicates that the emission is
likely to come from the keto form of the molecule.
500 600 700
0.0
0.2
0.4
0.6
0.8
1.0
Normalized Emission (a.u.)
Wavelength (nm)
3.1
3.2
3.4
3.5
Figure 3.13. Emission spectra of 3.1, 3.2, 3.4 and 3.5 in
2-MeTHF at 77K.
85
The dichloro substituted compound 3.4 is red-shifted by 10 to 20 nm relative to
3.3 (Figure 3.11c) with comparable lifetimes and efficiencies to the parent molecule.
From the absorption and emission spectra of 3.4 in methanol it can be seen that the
Stokes shift between the absorption and emission peaks attributed to the keto form of the
molecule is 382 cm
-1
(Figure 3.14) with a similar vibrational progression.
The lowest energy emission of the benzannulated compound 3.5 (Figure 3.11d) is
red-shifted by ~20 nm relative to 3.3, similar to what was observed with absorption. In all
three solvents in Figure 3.11d, significant variation in the low energy 650-750 nm portion
of the spectrum can be seen. Although most of the molecules reported here exhibit
vibrational structure in this region the variability in the position and intensity of this low
energy peak are suggestive of a secondary emissive process. The measured excited state
lifetime measured at both the low and high energy peak of 3.5 can be accurately fit to a
double exponential decay giving lifetimes of 0.844 and 3.97 ns in methanol, further
300 400 500 600 700 800
0.0
0.5
1.0
1.5
2.0
2.5
0.0
0.2
0.4
0.6
0.8
1.0
Normalized Em (a.u.)
Wavelength (nm)
ε ε ε ε (x10
4
M
-1
cm
-1
)
Figure 3.14. The room temperature absorption (black,
empty) and emission (red, filled) spectra of 3.4 in
methanol.
86
supporting the presents of two emissive processes. The double exponential decay is also
observed (3.15, 5.78) upon cooling 3.5 to 77K in 2-MeTHF. Although one of the
emissive processes is assumed to be similar to the parent 3.3, the nature of the second
emissive process is currently unknown.
Table 3.4. Photophysical properties of BPI and 3.1-7 in various solvents and PMMA.
Complex
emission at rt emission at 77K
a
Solvent λ
max
(nm) τ (ns) Φ
PL
λ
max
(nm) τ (ns)
BPI
MeOH
416 3.4 CH
2
Cl
2
- - -
Toluene
3.1
MeOH 471, 549 6.99, 8.39 0.482
474 8.84
CH
2
Cl
2
469, 567 6.84, 7.89 0.061
Toluene 575 7.34 0.049
PMMA 554 7.46 0.007
3.2
MeOH 600 4.14 0.121
625
4.7
CH
2
Cl
2
604 3.71 0.023
Toluene 590 3.05 0.040
PMMA 624 3.39 0.010
3.3
MeOH 592 3.67 0.305
598
5.11
MeOD 593 6.69 0.690
CH
2
Cl
2
597 3.95 0.401
Toluene 602 3.29 0.366
PMMA 593 3.56 0.25
3.4
MeOH 613 4.15 0.254
622
5.99
CH
2
Cl
2
612 4.64 0.392
Toluene 614 3.64 0.346
3.5
MeOH 612, 662 0.844, 3.97 0.036
624
5.78, 3.15 CH
2
Cl
2
612, 676 0.907, 3.30 0.029
Toluene 620, 670 0.882, 2.67 0.044
3.6
MeOH 600 3.8 0.293
620
5.27
CH
2
Cl
2
615 4.64 0.387
Toluene 622 4.06 0.344
PMMA 616 4.36 0.292
3.7
MeOH
452 3.72 CH
2
Cl
2
- - -
Toluene
(a) In 2-MeTHF. All samples recorded in PMMA were at 2% (w/w).
87
3.4 Conclusion
In this chapter, the photophysics of a new class of emitters based on the
dihydroxy substituted 1,3-bisiminoisoindole motif was reported. For the parent dihydroxy
substituted BPI compound a large apparent Stokes shift (6600 cm
-1
) between absorption
and emission was observed. This unusual behavior is attributed to an excited state proton
transfer as supported by both the lack of emission from the alkoxy substituted BPI and
the large changes in lifetime/efficiency in deauterated methanol (MeOD). It was found
that substitution of the parent compound could be used to change the equilibrium
between the keto and enol forms of the molecule. For both the dichloro and the phenyl
substituted compounds the equilibrium could be shifted from the enol form in toluene to
the keto form in methanol. Similarly, emission from both species could be observed from
the dialkyl substituted compound. The simplicity of synthesis, readily variable structure,
relatively high efficiencies (>0.20) and molar absorptivities (ε > 1 x 10
4
M
-1
cm
-1
) makes
dihydroxy substituted BPI based ESIPT dyes an ideal candidate for many potential
applications.
88
Chapter 3 References
(1) Gelabert, R.; Moreno, M.; Lluch, J. M. ChemPhysChem 2004, 5, 1372-1378.
(2) Chou, P.; McMorrow, D.; Aartsma, T. J.; Kasha, M. J. Phys. Chem. 1984, 88,
4596-4599.
(3) Sytnik, A.; Del Valle, J. C. J. Phys. Chem. 1995, 99, 13028-13032.
(4) Chou, P.-T.; Martinez, M. L. Radiat. Phys. Chem. 1993, 41, 373-378.
(5) Stein, M.; Keck, J.; Waiblinger, F.; Fluegge, A. P.; Kramer, H. E. A.; Hartschuh,
A.; Port, H.; Leppard, D.; Rytz, G. J. Phys. Chem. A 2002, 106, 2055-2066.
(6) Mutai, T.; Tomoda, H.; Ohkawa, T.; Yabe, Y.; Araki, K. Angew. Chem. 2008, 120,
9664-9666.
89
CHAPTER 4. Systematic Investigation of the Photophysical and
Electrochemical Properties of 1,3-bis(2-pyridylimino)isoindolate
Platinum(II) Derivatives
4.1 Introduction
In the previous chapter it was shown that without diol substitution, BPI was
nonemissive at room temperature and only weekly emissive at 77K. The addition of a
heavy metal to organic compounds is well known to cause strong perturbations of its
photophysical properties. Spin-orbital coupling between the heavy atom and the electrons
allows for efficient intersystem crossing to the triplet excited and thus phosphorescent
emission is possible as discussed in chapter 1. The planar nature of BPI combined with
three adjacent coordinating nitrogen atoms makes it a good candidate as a ligand for
square planar platinum complexes.
Square planar platinum(II) complexes are known to exhibit a rich array of
photophysical properties and many potential applications have been suggested to exploit
their luminescent characteristics.
1-4
Chelating ligands that have been used to produce
these square planar complexes include bidentate, tridentate and tetradentate ligands.
5
Of
these, the tridentate ligands possess two notable advantages. First, they can inhibit square
planar to tetrahedral (D
2d
) distortions
6
that promote nonradiative decay. Second, unlike
tetradentate ligands, tridentate ligands provide an available coordination site that permits
further modification of the complex. This feature enables one to use either anionic (e.g.,
Cl, NCS, OH, OMe, or alkyne) or neutral (e.g., amines, pyridines) ligands to alter the
charge and/or spectroscopic properties of the parent structure.
7-10
A variety of tridentate ligands have been used to prepare luminescent Pt(II)
complexes. Perhaps the most studied of these is 2,2’:6’,2”-terpyridine (abbreviated
90
N^N^N) and related ligands that coordinate to platinum through three imine nitrogen
atoms.
4, 11
Analogs of 2,2’:6’,2”-terpyridine, in which a phenyl group is substituted for
one or two of the imine moieties to produce mono- and dianionic ligands of the type
(C^N^N)
-
or (N^C^N)
-
or (C^N^C)
2-
have also been investigated.
2-5
However, there are
few examples of Pt(II) complexes with monoanionic (N^N^N)
-
ligands,
12-15
and even
fewer reports of luminescence from complexes with these kinds of ligands.
15-18
Upon deprotonation of the central amine BPI falls into the category of a
monoanionic (N^N^N)
-
ligand. Recently, a series of (BPI)PtCl derivatives were
synthesized and their photophysical properties investigated.
18
The parent (BPI)PtCl was
found to have phosphorescent emission at 631 nm with a quantum efficiency of 0.54 % in
CH
2
Cl
2
. Unlike the significant changes in photophysical properties of ((2,2’:6’,2”-
terpyridine)PtCl)
+1
when the chlorine atom is substituted with an acetylene group,
19
the
(BPI)Pt acteylene complex has similar absorption/emission spectra to the parent
(BPI)PtCl with the emission efficiency decreasing to 0.36%. This result is contrary to the
expectation that the addition of a strong field ligand will increase the platinum d-d energy
separation and thus reduce non-radiative deactivation through this pathway.
20-22
On the
other hand, the platinum chloride complexes with (1,3-bis(2-pyridylimino)isoindolate
ligand derivatives display significant variations in electrochemical properties, emission
wavelength and efficiency relative to (BPI)PtCl.
To better understand this new class of emitter it is important to expand the
investigation into how perturbations from both the BPI and the monoanionic
monodentate ligand affect its properties. Herein we report the synthesis, photophysical
and electrochemical characterization of a series of platinum(II) complexes of the form
91
(N^N^N)PtX where N^N^N is an assortment of substituted 1,3-bis(2-
pyridylimino)isoindolate ligands and X represents various anionic monodentate ligands
(Figure 4.1).
Complex X R3 R4 R5 R6
4.1 -Cl H H H H
4.2 -F H H H H
4.3 -CN H H H H
4.4 -OOCCH
3
H H H H
4.5 -Ph H H H H
4.6 -PhNMe
2
H H H H
4.7 -Cl H t-Bu H H
4.8 -Cl -NO
2
H H H
4.9 -Cl H -NO
2
H H
4.10 -Cl H -OC
5
H
11
H H
4.11 -Cl H -I H H
4.12 -Cl H -Cl -Cl H
Figure 4.1. Structure of substituted 2,5-bis(2-pyridylimino)isoindolate platinum X
complexes.
4.2 Experimental Section
4.2.1 Electrochemical and Photophysical Characterization. All cyclic voltammetry
(CV) and differential pulse voltammetry (DPV) were preformed using an EG&G
Potentiostat/Galvanostat model 283. DMF (purchased from VWR) was used as the
solvent under inert atmosphere with 0.1 M tetra(n-butyl)ammonium hexafluorophosphate
(Aldrich) as the supporting electrolyte or a solution of anhydrous 0.1 M NBu
4
ClO
4
in
CH
2
Cl
2
(VWR) as indicated. A glassy carbon rod, a platinum wire and a silver wire were
used as the working electrode, the counter electrode and the pseudo reference electrode
respectively. CV was used to determine electrochemical reversibility, while all redox
92
potentials were found using DPV and reported relative to a ferrocenium/ferrocene
(Fc
+
/Fc) redox couple used as an internal standard.
23
The UV-visible spectra were recorded on a Hewlett-Packard 4853 diode array
spectrophotometer. Steady state emission experiments at room temperature and 77K were
performed on a Photon Technology International QuantaMaster Model C-60SE
spectrofluorimeter. Quantum efficiency measurements were carried out using a
Hamamatsu C9920 system equipped with a xenon lamp, calibrated integrating sphere and
model C10027 photonic multichannel analyzer.
Samples for transient luminescent decay measurements were prepared in 2-
MeTHF solution. The samples were deaerated by bubbling with N
2
and flame-sealed
under vacuum. Measurements in the range of 77-290 K were performed using an Oxford
OptistatDN-V cryostat instrument equipped with an intelligent temperature controller. All
phosphorescent lifetimes were measured time-correlated single-photon counting using an
IBH Fluorocube instrument equipped with a 405 nm LED excitation source.
4.2.2 Computational Methods. All properties reported here are determined with first
principles electronic structure calculations using the GAMESS electronic structure
code.
24
Geometry optimizations for 4.1-12 (see Figure 4.1) are calculated with density
functional theory (DFT), employing the hybrid B3LYP functional.
25-29
Platinum is
described using the small-core model core potential MCPtzp (triple zeta + polarization
basis set) while chlorine and iodine use MCPdzp (double zeta + polarization basis set).
30
All remaining atoms are treated with the all-electron cc-pVDZ basis set.
31
All stationary
points are confirmed as minima on the ground state potential energy surface by
93
calculating and diagonalizing the Hessian (matrix of energy second derivatives). Vertical
excitation energies are calculated with time dependent density functional theory
(TDDFT) using the B3LYP functional. The effects of solvent on the geometry and
vertical excitation energies are studied using the Conductor-like Polarizable Continuum
Model (CPCM).
32
4.3 Results and Discussion
4.3.1 Computational Results. Through investigation of various computational methods,
to be discussed in chapter 5 section 5.3.3, it has been found that density functional theory
(DFT) reliably predicts X-ray crystallographic, electrochemical and photophysical
properties of 4.1. As a result, a similar theoretical treatment was applied to complexes
4.2-12. It has also been found that CPCM calculations exhibit better quantitative
agreement with experiment than gas phase predictions and thus only CPCM results are
presented.
From the optimized structures of 4.1-12, vertical excitation energies are
determined using time dependent DFT (TDDFT) for the lowest energy transitions (Table
4.1). The platinum chloride complexes, 4.1 and 4.7-12, have relatively small
perturbations (489-537 nm) in the lowest energy transitions compared to the chloride
substituted complexes 4.2-6 (444-661 nm). The nature of these excitations can further be
understood through the TDDFT excitation amplitudes. Since the sum of the squares of all
such amplitudes is unity, it is indicated that the HOMOLUMO contribution dominates
these transitions (84-99%). Consequently the HOMO and LUMO are largely responsible
for the absorption wavelength.
94
Table 4.1. TDDFT vertical excitation energies for the CPCM solvated complexes.
Complex
TDDFT Vertical
Excitation Energy eV
nm (error)
Square of HOMO-
LUMO TDDFT
Amplitude
4.1 489 (2) 0.84
4.2 492 (5) 0.91
4.3 444 (21) 0.91
4.4 471 (17) 0.91
4.5 475 (22) 0.91
4.6 661 (191) 0.99
4.7 491 (5) 0.92
4.8 515 (10) 0.94
4.9 537 (26) 0.95
4.10 490 (2) 0.91
4.11 498 (1) 0.92
4.12 494 (4) 0.92
The Kohn-Sham HOMO and LUMO energies for the ground state structures are
given in Table 4.2. It can be seen that the HOMO of 4.1 is largely localized on the [(2-
pyridylimino)3,4-pyrrolate]PtCl portion of the molecule and the LUMO is localized over
the entire BPI ligand with decreased orbital character on the platinum center and chlorine
atom (Figure 4.2). Similar HOMO and LUMO characteristics are seen for all complexes
reported with the exception of 4.6. For Structure 4.6, the substitution of the chlorine atom
with a dimethyl aniline group results in a shift of the HOMO from the BPI ligand onto
the dimethyl aniline moiety.
Table 4.2. HOMO/LUMO energies for the CPCM solvated complexes.
Complex
HOMO Orbital
Energy (eV)
LUMO Orbital
Energy (eV)
Kohn-Sham Orbital
Energy Shift (eV)
4.1 -5.77 -2.64 3.13
4.2 -5.76 -2.63 3.13
4.3 -6.00 -2.70 3.30
4.4 -5.84 -2.64 3.20
4.5 -5.68 -2.52 3.16
4.6 -4.83 -2.48 2.35
4.7 -5.75 -2.61 3.14
4.8 -5.86 -2.89 2.97
4.9 -5.89 -3.07 2.82
4.10 -5.72 -2.54 3.18
4.11 -5.81 -2.73 3.08
4.12 -5.90 -2.81 3.09
95
4.3.2 Electrochemistry. The electrochemical properties of 4.1-12 were investigated
using cyclic voltammetry (CV) and differential pulsed voltammetry (DPV). The results of
these measurements are shown in Table 4.3, with all values reported relative to ferrocene.
All of the complexes reported here display at least one irreversible oxidation from 0.58 to
0.97 V and at least two reversible reduction peaks from -1.15 to -2.39 V. In good
agreement with values reported by Wen et al.,
18
the parent complex 4.1 displays an
irreversible oxidation (0.79 V) and two reversible reduction waves (-1.44 V, -1.87 V).
4.1 4.2 4.3 4.4 4.5 4.6
4.7 4.8 4.9 4.10 4.11 4.12
4.1 4.2 4.3 4.4 4.5 4.6
4.7 4.8 4.9 4.10 4.11 4.12
Figure 4.2. HOMO and LUMO orbitals and energies for complexes 4.1-12. The
HOMO (solid) and LUMO (transparent) surfaces are displayed as viewed above the π-
symmetric orbitals, with opposite phases above and below the plane of the molecule.
The gray lines are a reference to the parent complex 4.1.
96
With respect to the spatial features of the HOMO and LUMO of 4.1, substitution of the
chlorine atom would be expected to have a larger effect on the oxidation potentials
(HOMO) then that of the reduction potentials (LUMO). Conversely, substitutions of 4.1
at the R
3-5
positions be expected to have a larger effect on the reduction potentials
(LUMO) then that of the oxidation potentials (HOMO).
Table 4.3. Electrochemical potentials for 4.1–4 reported in volts (V) relative to Fc
+
/Fc.
a
Unless otherwise noted, electrochemical reductions are reversible and oxidations are
irreversible.
Complex E
1/2
red
(V) E
1/2
red1
(V) E
peak
ox1
(V) Δ Δ Δ ΔE
1/2
(V)
b
4.1 -1.87 -1.44 0.79 2.23
4.2 -2.01 -1.51 0.73 2.24
4.3 -1.86 -1.42 0.97 2.39
4.4 -1.96 -1.51 0.88 2.39
4.5 -2.09 -1.62 0.69 2.31
4.6
c
-2.12 -1.67 0.08
d
, 0.58 1.75
4.7 -1.90 -1.47 0.83 2.30
4.8 -1.93, -1.81, -1.60 -1.24 0.95 2.19
4.9 -2.39, -1.42 -1.15 0.93 2.08
4.10 -1.92 -1.48 0.84 2.32
4.11 -1.89, -1.75
e
-1.36 0.84 2.20
4.12 -1.69 -1.30 0.84 2.14
(a) Measurements were performed in an anhydrous solution of 0.1 M NBu
4
PF
6
in DMF.
(b) ΔE
1/2
= E
ox
- E
1/2
red1
. (c) measured with decamethylferrocene as the internal standard
and corrected for -0.57 V vs Fc
+
/Fc. (d) reversible oxidation
(e) irreversible reduction.
Like the parent complex 4.1, the monodentate monoanionic ligand substituted
complexes 4.2-6 all display a single irreversible oxidation wave (0.58-0.97 V), with the
exception of 4.6 which also has a reversible oxidation wave (0.08 V). Excluding 4.6, the
most pronounced changes in oxidation potential were found with cyano substituted 4.3
(0.97 V) and phenyl substituted 4.5 (0.69 V). It is likely that the electron donating (Ph)
97
and withdrawing (CN) nature of the substituent is responsible for the shift in oxidation
potential. The addition of a dimethylamine donor group in the para position of the phenyl
group in 4.5 (4.6) shifts the irreversible oxidation peak by -0.11 V (relative to 4.5). The
additional reversible oxidation wave (0.08 V) in 4.6 is likely a dimethylaniline centered
process (Figure 4.2; HOMO of 4.6). The first reduction potential of 4.2-6 are between -
1.42 to -1.67 V. Again the most pronounced changes in reduction potential are found
with the cyano substituted 4.3 (-1.42 V) and the dimethylaniline substituted 4.6 (-1.67 V).
The tridentate ligand substituted complexes 4.7-12 all display a single irreversible
oxidation and at least two reversible reduction waves. As can be seen in Table 4.3, the
irreversible oxidation potentials of 4.7-12 range from 0.83 to 0.95 V. The first reduction
on the other hand has greater variability ranging from -1.15 to -1.48 V. The addition of
electron-donating (OC
5
H
11
, t-Bu) or electron withdrawing (NO
2
, Cl, I) groups to 4.1
results in a negative (4.7 and 4.10) or a positive shift (4.8, 4.9, 4.11 and 4.12) in the first
reduction potential (Table 2) similar to what was observed with (4-R-trpy)PtCl
derivatives.
33
Although 4.8 and 4.9 both have a NO
2
substitution on the BPI ligand,
substitution at R
4
results in a ~0.1 V more negative reduction potential than that of the R
3
substitution. If one was to consider only inductive effects, it might be expected that
substitution at both R
3
and R
4
with NO
2
would have similar reduction potentials.
However, comparing the calculated geometries of 4.8 and 4.9 it can be seen that steric
hinderance forces a 45° out of plane rotation of the nitro group at R
3
. This out of plane
rotation in 4.8 reduces the electron withdrawing due to resonance and as a result 4.8 is
more difficult to reduce than 4.9.
98
Additional reduction waves, not present in 4.1, were observed for complexes 4.8, 4.9
and 4.11. These additional reduction waves are presumably due to reversible reduction of
the nitro groups in 4.8, 4.9 and the irreversible reductive elimination of the iodo
substituent of 4.11 at -1.75 V.
34
4.3.3 Electronic Spectroscopy. The unsubstituted, unmeatallated BPI ligand displays
several absorption bands between 300–425 nm that are assigned to π-π* transitions. From
TDDFT calculations the lowest energy transition (calculated: 391 nm) is dominated by a
HOMO to LUMO transition (0.84). The LUMO is delocalized over the entire molecule.
The HOMO orbital of BPI is on the (2-pyridylimino)3,4-pyrrole portion of the molecule,
with minimal character on the benzene ring (Figure 4.3). The transition between these
orbitals is assigned as a π-π* transition.
-2.37
-5.90
-2.64
-5.77
489 (0.84) 391 (0.84)
-2.37
-5.90
-2.64
-5.77
489 (0.84) 391 (0.84)
Figure 4.3. HOMO (bottom) and LUMO
orbitals and the lowest energy transition
for BPI and 4.1.
99
Upon platination of BPI, the ligand-centered (LC) π-π* transitions (ε ≈ 2 x 10
4
M
-
1
cm
-1
) undergo a red-shift, while a new, low energy transitions appear between 425-550
nm (ε ≈ 1.4 x 10
4
M
-1
cm
-1
). From DFT calculations it can be seen that the low energy
absorption (calculated: 489 nm) is also dominated by a HOMO to LUMO transition
(0.84). With platination the LUMO is stabilized and remains on the ligand with minimal
character on the metal center. The HOMO on the other hand is destabilized and shifted
onto the platinum and chlorine portions of the molecule. The nature of these orbitals
suggests that this low energy absorption band is a combination of metal to ligand (ML)
and ligand to ligand (LL) charge transfer (CT) transition.
The absorption spectra for complexes 4.1–12 were recorded in CH
2
Cl
2
and are
shown in Figure 4.4 and 4.7. With the exception of 4.1, to be discussed later, the lowest
energy absorption transitions were found to be in good correlation with the values found
by TDDFT (Table 4.1) with deviations of less than 30 nm from experiment.
320 360 400 440 480 520 560 600
0.0
0.5
1.0
1.5
2.0
2.5
Wavelength (nm)
ε ε ε ε (x10
4
M
-1
cm
-1
)
4.1
4.2
4.3
4.4
4.5
4.6
Figure 4.4. Room-temperature absorption spectra of
complexes 4.1-6 in CH
2
Cl
2
.
100
Similar to the parent 4.1, Pt-X complexes 4.2-6 have ligand centered transition at
~350 nm with similar molar absorptivities (ε = 1.79-2.24 x 10
4
M
-1
/cm
-1
) (Figure 4.4).
For 4.2, 4.4 and 4.5, two low energy transition from 400-525 nm (ε = 0.9-1.2 x 10
4
M
-
1
/cm
-1
) are distinguishable. The greatest perturbation in the charge transfer transition was
observed with the cyano substituted 4.3. The highly structured CT band is blue-shifted by
~50 nm with an increased molar absorptivity (ε = 1.96 x 10
4
M
-1
/cm
-1
) relative to 4.1. The
blue-shift in absorption is due to a HOMO stabilization of 0.23 eV upon substitution.
In contrast to the other complexes, the charge transfer transition of the
dimethylaniline substituted complex 4.6 is broadened and featureless. The absorption
spectra of 4.6 in CH
2
Cl
2
and the 20 lowest energy transitions, indicated by vertical bars
with heights equal to the oscillator strength, found by TDDFT can be seen in Figure 4.5.
300 400 500 600 700
0.0
0.5
1.0
1.5
2.0
0.00
0.05
0.10
0.15
0.20
0.25
0.30
0.35
0.40
Oscillator Strength
Wavelength (nm)
ε ε ε ε (x10
4
M
-1
cm
-1
)
Figure 4.5. Room-temperature absorption spectra of complex 6. The
calculated transitions are shown as vertical bars with heights equal to the
oscillator strength.
101
Table 4.4. The relative intensities and the orbitals involved in the 20 lowest energy
transitions of 4.6 found by TDDFT.
Transition Energy (nm)
Dominent Contributor
(square of the amplitude)
Relative
intensity
1 661 HOMO -> LUMO (1.00) 7.31E-04
2 476 HOMO-1 → LUMO (0.81) 0.23364
3 431 HOMO-2 → LUMO (0.99) 2.10E-05
4 419 HOMO → LUMO+1 (0.99) 4.50E-04
5 374
HOMO → LUMO+2 (0.53)
HOMO-4 → LUMO (0.39)
0.10901
6 372
HOMO-4 → LUMO (0.45)
HOMO → LUMO+2 (0.45)
0.17091
7 371 HOMO-3 → LUMO (0.74) 0.124
8 352 HOMO-5 → LUMO (0.82) 0.00487
9 351 HOMO-7 → LUMO (0.79) 0.00137
10 350 HOMO → LUMO+3 (0.95) 0.00458
11 335 HOMO-1 → LUMO+1 (0.89) 0.05926
12 329 HOMO-6 → LUMO (0.87) 0.29268
13 315 HOMO → LUMO+6 (0.82) 0.00791
14 311 HOMO-8 → LUMO (0.67) 7.22E-04
15 308 HOMO-2 → LUMO+1 (0.98) 9.61E-04
16 306 HOMO-1 → LUMO+2 (0.83) 0.01336
17 305 HOMO-9 → LUMO (0.64) 0.00284
18 300 HOMO → LUMO+4 (0.96) 1.60E-05
19 297 HOMO-10 → LUMO (0.87) 7.68E-04
20 295 HOMO → LUMO+5 (0.77) 0.02447
From calculation (Table 4.4), a low energy transition at 661 nm that is dominated
by a HOMO to LUMO transition is expected. However the oscillator strength of this
transition (7.3 x 10
-4
) is more than three orders of magnitude lower than the transition at
476 nm (0.23). The orbitals that dominate the transition at 476 nm (HOMO-1LUMO;
0.81) more closely resemble the HOMO and LUMO of the parent complex and thus a
similar molar absorptivity is expected (Figure 4.6). The low oscillator strength of the
transition at 661 nm is likely due to the minimal orbital overlap between the HOMO and
LUMO of 4.6.
102
For the BPI substituted complexes 4.7-12, the ligand centered transitions are
similar to 4.1 (~350 nm, ε = 1.5-2.5 x 10
4
M
-1
/cm
-1
) with the exception of 4.10 which
exhibit a red shifted absorption (Figure 4.7). The absorptivity of the charge transfer
transition remains similar (ε = 0.57-1.35 x 10
4
M
-1
/cm
-1
) however the wavelength varies
depending on the nature and position of BPI ligand substitution.
-5.63
-4.83
-2.48
661 nm
(7.31x10
-4
)
476 nm
(0.234)
HOMO
HOMO-1
LUMO
Figure 4.6. The relative intensities and the orbitals involved
in the two lowest energy transitions of 4.6 found by TDDFT.
300 350 400 450 500 550 600
0.0
0.5
1.0
1.5
2.0
2.5
ε ε ε ε (10
4
M
-1
cm
-1
)
Wavelength (nm)
4.1
4.7
4.8
4.9
4.10
4.11
4.12
Figure 4.7. Room-temperature absorption spectra of
complexes 4.1 and 4.7-12 in CH
2
Cl
2
.
103
The addition of electron donating groups (tert-butyl and pentoxy) at R
4
has
minimal effect on the absorption onset and peak positions of 4.7 and 4.10 relative to 4.1.
Electron withdrawing groups, on the other hand, result in a red-shift in absorption onset
with the magnitude of the shift decreasing along the trend 4.9(R
4
= NO
2
) > 4.8(R
3
= NO
2
)
> 4.12(R
4,5
= Cl) > 4.11(R
4
= I). As already noted from TD-DFT calculations, the lowest
energy vertical excitation of these complexes is dominated by a HOMO to LUMO
transition (Table 4.1). Because the variability in the HOMO of 4.8, 4.9, 4.11 and 4.12 is
relatively small (< 0.1 eV), the stabilization of the LUMO in the order of 4.9(-3.07 eV) >
4.8(-2.89 eV) > 4.12(-2.81 eV) > 4.11(-2.73 eV) is primarily responsible for the observed
absorption trends.
From the results listed in Table 4.6 it is apparent that tert-butyl substitution (4.7)
has minimal affect on the photophysical properties compared to the parent compound 4.1.
In order to study environmental effects on absorption properties of (BPI)PtCl, the highly
soluble (4-tert-butylBPI)PtCl complex (4.7) was examined in various solvents and ridged
350 400 450 500 550 600
0.0
0.1
0.2
0.3
0.4
0.5
0.6
0.7
0.8
0.9
1.0
Wavelength (nm)
Absorption (a.u.)
Acetonitrile
DMSO
OEt2
Hexanes
Figure 4.8. Room-temperature absorption
spectra of complex 4.7 in various solvents.
104
matrix. The absorption spectra of 4.7 in various solvents can be seen in Figure 4.8. While
the ligand centered transtion at ~350 nm remains constant regardless of solvent polarity,
the low energy transition exhibits a negative solvatochromic effect, shifting the lowest
energy absorption transition from 505 nm in hexane to 485 nm in acetonitrile (Figure 4.8).
Negative solvatochromic shifts of this type are attributed to a decrease in the molecules
dipole moment upon excitation.
35
This shift in absorption also supports a charge transfer
nature of this transition.
Complexes 4.1-12 were luminescent in glassy solvent (2-MeTHF) at 77K (Figure 4.12)
and all complexes reported here, with the exception of 4.6, displayed broad room
temperature emission in toluene (Figure 4.9).The emissive properties of substituted
complexes 4.1-12 are listed in Table 4.6.
The broad room temperature emission spectra of 4.1-5 can be seen in Figure 4.9a.
Variations in the monodentate anionic ligand results in emission with λ
max
ranging from
594 to 656 nm for 4.1-5. Complexes 4.2 and 4.4 display similar emission maxima (620
nm), lifetime (0.6-0.84 μs) and photoluminescent efficiency (0.011) as the parent
complex 4.1. As was observed with electrochemistry, the most pronounced variations in
emissive properties are found for 4.3 and 4.5. Of 4.1-5, the phenyl substituted complex
4.5, exhibits the most red shifted emission (656 nm), shortest lifetime (0.1 μs) and lowest
efficiency (0.004). Although the radiative rate of 4.5 (4.0 x 10
4
s
-1
) is approximately three
times larger than that of the parent complex 4.1 (1.4 x 10
4
s
-1
), the lower efficiency can be
attributed to an order of magnitude increase in the nonradiatve rate (k
nr(4.5)
= 99.6 x 10
5
s
-1
,
k
nr(4.1)
= 9.96 x 10
5
s
-1
). Complex 4.3, on the other hand, exhibits the most blue shifted
emission (594 nm), longest lifetime (8.4 μs) and highest efficiency (0.048).
105
Unlike the other molecules, 4.3 exhibits a structured emission with a vibronic
progression of ~1,200 cm
-1
. The increase in efficiency of 4.3 relative to 4.1 is attributed
to an order of magnitude decrease in the nonradiative rates (1.13 x 10
5
s
-1
). The non-
emissive nature of 4.6 at room temperature may be due to photo-induced electron transfer
500 550 600 650 700 750 800
0.0
0.1
0.2
0.3
0.4
0.5
0.6
0.7
0.8
0.9
1.0
Normalized Intensity (a.u.)
Wavelength (nm)
4.1
4.2
4.3
4.4
4.5
a)
500 550 600 650 700 750 800
0.0
0.1
0.2
0.3
0.4
0.5
0.6
0.7
0.8
0.9
1.0
b)
4.7
4.8
4.9
4.10
4.11
4.12
Normalized Intensity (a.u.)
Wavelength (nm)
Figure 4.9. Room-temperature emission spectra of
complexes a) 4.1-5 and b) 4.7-12 in toluene.
106
from the electron rich dimethylaniline to the electron deficient BPI Pt portion of the
molecule.
The BPI substituted complexes 4.7-12 also exhibit broad room temperature
emission with λ
max
ranging from 635 to 680 nm (Figure 4.9b). The addition of electron
donating tert-butyl and pentoxy groups at R
4
results in a small blue shift of 4.7 (638 nm)
and 4.10 (635 nm) in the emission maxima relative to the parent complex 4.1 (641 nm).
The magnitude of the red-shift in emission observed for complexes substituted with
electron withdrawing groups follows the trend 4.9(680 nm) > 4.8(678 nm) > 4.12(657
nm) > 4.11(650 nm), similar to what was observed with ΔE
1/2
. The variations in
photoluminescent efficiency (0.003-0.018) and the lifetimes (0.3-1.1 μs) of 4.7-12 can
best be explained by their radiative and nonradiative rates. While the radiative rates
remain approximately constant (0.9 to 1.6 x 10
4
s
-1
), the variation in non-radiative rates
(8.9 to 33.2 x 10
5
s
-1
) dictates the efficiency of emission.
The “energy gap law” states that the nonradiative decay rate (k
nr
) will decrease
exponentially with increasing energy of emission for molecules with similar vibrational
coupling between the excited and ground states.
36
The plot of the natural log of the
nontadiative rates versus energy of emission (E
em
) for 4.1-12 can be seen in Figure 4.10.
The platinum chloride complexes 4.1 and 4.7-12 exhibit a linear relationship with the
slope of -1.24 and a y-intercept of 33.168. The chlorine substituted complexes 4.2-5, on
the other hand, do not have a linear relationship. The nonlinearity of these complexes
implies that substitution of the monodentate anionic ligands results in different
vibrational coupling paths from the excited state to the ground state.
107
To better understand the room temperature emissive properties of the parent
(BPI)PtCl, the photophysics of the highly soluble tert-butyl substituted complex 4.7 was
investigated with respect to both concentration and environment. The quantum yield of
4.7 in toluene was found to be constant (Φ = 0.018) over concentrations ranging from 3
to 80 μM indicating that no quenching due to intermolecular interactions was present.
Variations in solvent have minimal effect on the emission maxima (Figure 4.11),
however the solvent does significantly effect the quantum efficiency. The highest
quantum yields were observed in non-polar solvents (hexane, cyclohexane), gradually
decreasing with increased solvent polarity (2-MeTHF, Acetone, acetonitrile) and finally
no emission was observed in the most polar solvent DMSO (Table 4.5).
14.5 15.0 15.5 16.0 16.5 17.0
11.5
12.0
12.5
13.0
13.5
14.0
14.5
15.0
15.5
16.0
16.5
R
2
= 0.9703
10
7
1
11
12
8
9
2
3
4
ln (k
nr
)
E
em
(cm
-1
x 10
-3
)
5
y = -1.2367x + 33.168
Figure 4.10. Energy vs ln(k
nr
) for 4.1-12. Linear fit (red line)
was for complexes 4.1 and 4.7-12.
108
Table 4.5. Photophysical properties of 4.7 in various solvents at room temperature.
Solvent λ λ λ λ
max
(nm) Φ Φ Φ Φ
PL
τ τ τ τ (μ μ μ μs) k
r
(10
4
s
-1
) k
nr
(10
5
s
-1
)
Hexane 632 0.022 1.07 2.06 9.1
Cyclohexane 635 0.018 0.98 1.84 10
Toluene 638 0.018 1.1 1.64 8.9
Benzene 639 0.017 1.1 1.55 8.9
heptane 630 0.017 1.1 1.55 8.9
CH
2
Cl
2
636 0.015 1.1 1.36 9
OEt
2
634 0.014 1.05 1.33 9.4
2-MeTHF 637 0.011 0.77 1.43 12.8
Acetone 639 0.01 0.92 1.09 10.8
Acetonitrile 638 0.006 0.64 0.94 15.5
DMSO - - - - -
Room temperature emission of 4.7 doped in PMMA and polystyrene (2%, w/w)
more than double the PL efficiency (Φ = 0.029, 0.030) and the excited state lifetime (τ =
2.39, 2.43 μs) relative to solution. Because the radiative rate of 4.7 remains
550 600 650 700 750 800
0.0
0.1
0.2
0.3
0.4
0.5
0.6
0.7
0.8
0.9
1.0
1.1
Hexanes
Cyclohexane
Toluene
Benzene
Heptane
CH2Cl2
OEt2
2-MeTHF
Acetone
Acetonitrile
Normalized Intensity (a.u.)
Wavelength (nm)
Figure 4.11. Room-temperature emission spectra of complex
4.7 in various solvents.
109
approximately constant in solution (k
r(toluene)
= 1.6 x 10
4
s
-1
) and solid matrix (k
r(PMMA,
polystyrene)
= 1.2 x 10
4
s
-1
) the increased efficiency is due to a decrease in the rate of non-
radiative deactivation processes (k
nr(toluene)
= 8.9 x 10
5
s
-1
, k
nr(PMMA)
= 4.1 x 10
5
s
-1
, k
nr
(polystyrene)
= 4.0 x 10
5
s
-1
).
550 600 650 700 750 800
0.0
0.1
0.2
0.3
0.4
0.5
0.6
0.7
0.8
0.9
1.0
Normalized Intensity (a.u.)
Wavelength (nm)
4.1
4.2
4.3
4.4
4.5
4.6
a)
550 600 650 700 750 800
0.0
0.1
0.2
0.3
0.4
0.5
0.6
0.7
0.8
0.9
1.0
b)
4.7
4.8
4.9
4.10
4.11
4.12
Normalized Intensity (a.u.)
Wavelength (nm)
Figure 4.12. Emission spectra of complexes a) 4.1-6
and b) 4.7-14 in 2-MeTHF at 77K.
110
The emission spectra of 4.1-12 at 77K in 2-MeTHF can be seen in Figure 4.12.
Upon cooling to 77K the complexes exhibit a rigidochromic blue shift ranging from 23 to
57 nm with a structured vibrational progression ranging from 1340 to 1560 cm
-1
. The
trends in emission wavelength in Figure 4.12 reflect those observed at room temperature.
Table 4.6. Photophysical properties of complexes 4.1-14.
X =
absorbance λ (nm)
(ε, x10
4
M
-1
cm
-1
)
a
emission at rt
b
k
r
(10
4
s
-1
)
d
k
nr
(10
5
s
-1
)
e
emission at 77K
c
λ
max
(nm)
τ (μs) Φ
PL
λ
max
(nm)
τ (μs)
4.1
250(5.37), 277(3.51),
348(2.24), 473(1.36),
487(1.35)
641 0.99 0.014 1.4 9.96 595 6.8
4.2
250(4.20), 277(2.61),
349(1.88), 387(0.87),
476(1.00), 497(0.91)
620 0.84 0.011 1.3 11.8 592 6.6
4.3
245(4.46), 268(2.21),
342(2.24), 437(1.69),
465(1.96)
594 8.4 0.048 0.57 1.13 567 35
4.4
249(4.86), 278(2.93),
349(2.21), 464(1.34),
488(1.31)
620 0.6 0.011 1.83 16.5 584 11.5
4.5
249(4.35), 289(2.37),
352(1.99), 472(1.17),
497(1.13)
656
(615)
0.1
(2.62)
0.004
(0.018)
4
(0.69)
99.6
(3.75)
603 3.5
4.6
252(4.91), 287(2.87),
342(1.78), 470(0.94)
- - - - - 594 7.6
4.7
250(5.36), 278(3.86),
352(2.49), 472(1.33),
486(1.32)
638
(610)
[615]
1.1
(2.39)
[2.42]
0.018
(0.029)
[0.030]
1.6
(1.2)
[1.2]
8.9
(4.1)
[4.0]
593
(608)
7.3
(7.3)
4.8
235(3.23), 278(2.75),
338(1.53), 483(1.05),
505(1.05)
678 0.32 0.003 0.9 31.2 625 2.9
4.9
232(3.23), 277(3.41),
346(2.14), 492(1.09),
511(1.08)
680 0.3 0.004 1.3 33.2 632 2.4
4.10
261(4.13), 280(3.69),
351(1.74), 386(1.63),
472(0.90), 492(0.83)
635 0.93 0.014 1.5 10.6 592 6.9
4.11
257(3.80), 279(3.57),
353(2.04), 478(1.00),
497(0.97)
650 0.73 0.01 1.4 13.6 607 5.2
4.12
257(4.60), 279(3.62),
351(1.90), 479(1.06),
498(1.05)
657 0.63 0.007 1.1 15.8 615 3.5
(a) In CH
2
Cl
2
. (b) In toluene deaerated with N
2
. (c) In 2-MeTHF. (d) k
r
= Φ/τ. (e) k
nr
= (1-Φ)/τ. 2% complex by weight doped in (PMMA) and [polystyrene].
111
4.3.4 Temperature Dependence. As mentioned above, the radiative rates of 4.1-12 at
room temperature are relatively constant (0.57 to 1.6 x 10
4
s
-1
), therefore the variations in
efficiency (Φ = 0.004 to 0.048) can be attributed to the non-radiative rates (1.3 to 99.6 x
10
5
s
-1
) of excited state deactivation. A commonly proposed nonradiative deactivation
pathway in emissive platinum chloride complexes is through thermally accessible, low
lying
3
d-d, metal centered excited states.
10
The increased efficiency observed when the
chlorine atom is substituted with strong-field ligands such as CN, acetylene and ketonyl
groups is attributed to the destabilization of the empty Pt(II) d(x
2
-y
2
) orbital.
Destabilization of the empty Pt(II) d orbital results in an increased activation energy (E
a
)
to these short lived
3
d-d metal centered excited states
22, 37
and a reduced likelihood of
nonradiative deactivation by this metal centered pathway.
38
As can be seen in Table 4.6,
substitution of the chlorine atom of 4.1 with the strong-ligand field CN group (4.3) results
in an 8 fold increase in excited state lifetime (from 0.99 to 8.4 μs) and an order of
magnitude decrease in the nonradiative rate (from 9.96 to 1.13 x 10
5
s
-1
) suggesting that a
thermally accessible
3
d-d metal centered deactivation may be responsible for the lower
quantum efficiency of 4.1 relative to 4.3. The thermal accessibility of nonradiative
excited states in numerous transition-metal complexes has been investigated through
temperature dependence studies of their luminescenent lifetimes.
38-45
To gain insight into
excited state deactivation pathways in this new class of emitter, the changes in lifetime
with respect to temperature was evaluated for the parent complex 4.1.
The luminescent lifetimes (τ) of 4.1 was measured at 10 degree intervals between
80 and 290K in 2-MeTHF and the graph of τ versus temperature (T) can be seen in
Figure 8. Minimal changes in lifetime (from 0.77 to 1.1 us) are observed from 290K to
112
120K. At the glass transition temperature of 2-MeTHF, a sharp increase in lifetime can be
seen presumably due to the change in rigidity of the matrix.
The temperature dependent data plotted as the ln(1/ τ) versus (1/T) above 120 K
can be seen in the inset of Figure 4.13. Using a similar method as those reported by
Allsopp et al.
39
the data can be fit with a single exponential Arrhenius type equation (1/τ
= kr + knr + Aexp(-E
a
/RT)) where τ is the lifetime at temperature T, R is the gas constant,
k
r
and k
nr
are the temperature independent radiative and nonradiative rates, E
a
is the
activation energy and A is the preexponential factor of the thermal excited state. From the
fit of the data we find that the E
a
is 245 cm
-1
for 4.1. Although the nature of this thermally
accessible deactivation state is unknown, the energy barrier is well below those attributed
100 150 200 250 300
0
1
2
3
4
5
6
7
3 4 5 6 7 8
-0.1
0.0
0.1
0.2
0.3
ln(1/ τ τ τ τ)
1000/T (K
-1
)
Lifetime (μ μ μ μs)
Temperature (K)
Figure 4.13. The plot of lifetime (τ) versus temperature (K) for
complex 4.1 in 2-MeTHF. Inset: The data from 120 to 290 K plotted
as the ln(1/ τ) versus (1/T).
113
to metal centered excited states of previously studied platinum complexes (3700 cm
-1
).
38
It appears that the relatively large k
nr
(>10
5
s
-1
) for BPIPtCl complexes are largely due to
temperature independent nonradiative processes. The result coincides with the conclusion
reached by Tong and Che from their theoretical analysis of cyclometalated platinum(II)
complexes that the energy splitting between the two highest lying d orbitals may not be
an adequate predictor of phosphorescence efficiency.
21
There are two types of
temperature independent nonradiative decay processes: direct surface crossing from T
1
to
S
0
and vibrational coupling to the ground state. The lack of vibrational structure of the
room temperature emission is suggestive of large structural distortions of the excited state
relative to the ground state indicating the former as a possible mode of temperature
independent nonradiative decay.
4.4 Conclusion. In this chapter the synthesis, photophysical and electrochemical
characterization of a series of platinum(II) complexes of the form (N^N^N)PtX where
N^N^N is an assortment of substituted 1,3-bis(2-pyridylimino)isoindolate ligands and X
represents various anionic monodentate ligands. Relative to the parent (BPI)PtCl,
substitutions of the BPI ligand and the chlorine atom are found to have the most
pronounced effect on the reduction and oxidation potentials respectively. The positive or
negative shift in potential is dependent on the electron donating or withdrawing nature of
the substituent. The photophysical properties of the complexes are also dictated by the
nature of the substituent. The most blue- and red-shifted absorption/emission spectra are
found for the (BPI)PtCN and the (4-NO
2
BPI)PtCl complexes respectively. The quantum
efficiency of emission for all of the complexes is dictated by the nonradiative rates of
114
deactivation from the excited state. The nonradiative rates of the platinum chloride
complexes are found to correlate with the energy gap law. The nonlinearity of the natural
log of the nontadiative rates versus energy of emission (E
em
) for PtX complexes implies
that substitution of the monodentate anionic ligands results in different vibrational
coupling paths from the excited state to the ground state. A commonly proposed
nonradiative deactivation pathway in emissive platinum chloride complexes is through
thermally accessible, low lying
3
d-d, metal centered excited states. From the temperature
dependent data plotted as the ln(1/ τ) versus (1/T) for (BPI)PtCl it was found that
nonradiative deactivation through thermally accessible metal centered excited states is
unlikely to be responsible for the high nonradiative rates.
115
Chapter 4 References
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Chemistry Reviews 2008, 252, 2596-2611.
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(7) Wong, K. M.-C.; Yam, V. W.-W. Coordination Chemistry Reviews 2007, 251,
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(9) Kip, H.-K.; Cheng, L.-K.; Cheung, K.-K.; Che, C.-M. Journal of the Chemical
Society, Dalton Transactions 1993, (1), 2933-2938.
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727.
(11) Garner, K. L.; Parkes, L. F.; Piper, J. D.; Williams, J. A. G. Inorg. Chem. 2010,
ASAP.
(12) Patra, D.; Pattanayak, P.; Paratihar, J. L.; Chattopadhyay, S. Polyhedron 2007, 26,
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1706.
(15) Zhang, H.; Zhang, B.; Li, Y.; Sun, W. Inorganic Chemistry 2009, 48, 3617-3627.
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H.; Chou, P.-T.; Wu, C.-H.; Shih, P.-I.; Shu, C.-F. Chem. Asian J. 2008, 3, 2112-
2123.
(17) Wang, K.-W.; Chen, J.-L.; Cheng, Y.-M.; Chung, M.-W.; Hsieh, C.-C.; Lee, G.-
H.; Chou, P.-T.; Chen, K.; Chi, Y. Inorg. Chem. 2010, ASAP.
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Chem. 2010, 49, (5), 2210-2221.
(19) Yam, V. W.-W.; Tang, R. P.-L.; Wong, K. M.-C.; Cheung, K.-K.
Organometallics 2001, 20, 4476-4482.
(20) Yip, H.-K.; Cheng, L.-K.; Cheung, K.-K.; Che, C.-M. J. Chem. Soc. Dalton Trans.
1993, 2933.
(21) Tong, G. S.-M.; Che, C.-M. Chem. Eur. J. 2009, 15, (29), 7225-7237.
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(23) Gagne, R. R.; Koval, C. A.; Lisensky, G. C. Inorg. Chem. 1980, 19, 2854-2855.
(24) Schmidt, M. W.; Baldridge, K. K.; Boatz, J. A.; Elbert, S. T.; Gordon, M. S.;
Jensen, J. H.; Koseki, S.; Matsunaga, N.; Nguyen, K. A.; Su, S.; Windus, T. L.;
Dupuis, M.; Montgomery, J. A. J. Journal of Computational Chemistry 1993, 14,
(11), 1347-1363.
(25) Hohenberg, P. Physical Review 1964, 136, (3B), B864-871.
(26) Kohn, W.; Sham, L. J. Physical Review 1965, 140, (4A), A1133-1138.
(27) Stephens, P. J.; Devlin, F. J.; Chabalowski, C. F.; Frisch, M. J. The Journal of
Physical Chemistry 1994, 98, (45), 11623-11627.
(28) Hertwig, R. H.; Koch, W. Chemical Physics Letters 1997, 268, 345-351.
(29) Becke, A. D. Journal of Chemical Physics 1993, 98, (7), 5648-5652.
(30) Mori, H.; Ueno-Noto, K.; Osanai, Y.; Noro, T.; Fujiwara, M.; Klobukowski, M.;
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(31) Dunning Jr., T. H. Journal of Chemical Physics 1989, 90, (2), 1007-1023.
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(33) McMillin, D. R.; Moore, J. J. Coordination Chemistry Reviews 2002, 229, 113-
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(34) Jaworski, J. S.; Kacperczyk, A.; Kalinowski, M. K. Journal of Physical Organic
Chemistry 1992, 5, 119-122.
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L.; Jolliet, P.; Maeder, U. Inorg. Chem. 1988, 27, 3644-3647.
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118
CHAPTER 5. A Paradigm for Blue- or Red-Shifted Absorption
Depending on the Site of π π π π-Extension as Exemplified in the
Photophysics of 1,3-Bis(2-pyridylimino)isoindolate Platinum(II)
Chloride and Others
5.1 Introduction
In the previous chapter, it was shown that the addition of electron donating and/or
electron withdrawing groups to (BPI)PtCl can be used to induce either hypsochromic
(blue) or bathochromic (red) shifts in the absorption/emission spectra. On the other hand,
extending conjugation, particularly through benzannulation of aromatic rings, is
commonly assumed to destabilize the highest occupied molecular orbital (HOMO) and
stabilize the lowest unoccupied molecular orbital (LUMO). This decrease in separation
between the HOMO and the LUMO energies will inevitably lead to red-shifted spectra.
1, 2
The most common example of this is the red-shift observed when going from benzene to
naphthalene to anthracene.
3
However there are several examples of small molecules that
undergo a blue-shift in absorption upon benzannulation.
4-7
This phenomena was most
recently reported for benzannulation of the square planar 1,3-bis(2-
pyridylimino)isoindolate platinum chloride, (BPI)PtCl, complex (2 in Chart 1).
8
Although
rationalizations for the unexpected blue-shifts have accompanied these reports, a
generalized description with predictive capacity to explain the effect of benzannulation
on absorption is currently unavailable.
In this chapter the synthesis and characterization of a family of (BPI)PtCl derivatives
(Figure 5.1) for which both red- and blue-shifts are observed when the π-system is
extended. The direction of the shift is dependent on the site of benzannulation. An
explanation for this phenomenon, based on the experimental and theoretical results, will
119
be given using molecular orbital diagrams. This explanation is expanded to describe other
molecules with this unusual behavior.
5.2 Experimental Section
5.2.1 Electrochemical and Photophysical Characterization. All cyclic voltammetry
(CV) and differential pulse voltammetry (DPV) were performed using a EG&G
Potentiostat/Galvanostat model 283. DMF (VWR), distilled from Type 4A 1/16”
molecular sieves (Alfa Aesar), was used as the solvent under inert atmosphere with 0.1 M
tetra(n-butyl)ammonium hexafluorophosphate (Aldrich) as the supporting electrolyte. A
glassy carbon rod, a platinum wire and a silver wire were used as the working electrode,
the counter electrode and the pseudo reference electrode respectively. Electrochemical
reversibility was determined using CV, while all redox potentials were found using DPV
Figure 5.1. The structure of BPI platinum
complexes with varying degrees of
benzannulation.
120
and reported relative to a ferrocenium/ferocene (Fc
+
/Fc) redox couple used as an internal
standard.
9
The UV-visible spectra were recorded using a Hewlett-Packard 4853 diode array
spectrophotometer. Steady-state emission experiments were performed on a Photon
Technology International QuantaMaster model C-60 spectrofluorimeter. All lifetime
measurements were performed on an IBH Fluorocube lifetime instrument by a time-
correlated single-photon counting method using a 405-nm LED excitation source.
Quantum efficiency measurements were carried out using a Hamamatsu C9920 system
equipped with a xenon lamp, calibrated integrating sphere and model C10027 photonic
multichannel analyzer.
5.2.2 Computational Methods. All properties reported here are determined with first
principles electronic structure calculations using the GAMESS electronic structure
code.
10
To clearly demonstrate a possible origin of the observed hypsochromic behavior,
properties are predicted and analyzed for 2,5-bis(2-pyridylimino)pyrrolate platinum (II)
chloride (5.1’) rather than the diethyl substituted 2,5-bis(2-pyridylimino)3,4-
diethylpyrrolate platinum (II) chloride structure (5.1). Geometry optimizations for 5.1’
and 2-5.5 (see Figure 1) are calculated with density functional theory (DFT), employing
the hybrid B3LYP functional.
11-15
Platinum and chlorine are described using small-core
model core potentials MCPtzp (triple zeta + polarization basis set) and MCPdzp (double
zeta + polarization basis set), respectively,
16
whereas all remaining atoms are treated with
the all-electron cc-pVDZ basis set.
17
All stationary points are confirmed as minima on the
ground state potential energy surface by calculating and diagonalizing the Hessian
121
(matrix of energy second derivatives). Vertical excitation energies are calculated with
time dependent DFT (TDDFT) using the B3LYP functional. The effects of solvent on the
geometry and vertical excitation energies are studied using the Conductor-like
Polarizable Continuum Model (CPCM).
18
The TDDFT Tamm-Dancoff approximation (TDA)
19-22
is used here for the
purposes of conveniently analyzing the TDDFT excitation energies and validating an
orbital analysis. Application of the TDA to the random-phase approximation (RPA)
results in the simple configuration interaction with single excitations (CIS) method. As
noted by Dreuw and Head-Gordon, application of the TDA to the DFT linear response
equations (TDDFT TDA) is formally analogous to applying the TDA to the RPA.
Therefore TDDFT TDA provides an analog to the simple configuration interaction with
single excitations (CIS) method. This is a crucial feature since an excited state dominated
by a single CIS configuration can be approximately characterized using simple orbital
arguments. Similar use of an orbital argument is applied here if the TDDFT TDA method
predicts an excited state dominated by a single excitation (i.e. HOMOLUMO).
5.3 Results and Discussion
5.3.1 Electrochemistry. The electrochemical properties of the complexes 5.1–5 were
examined using cyclic voltammetry (CV) and differential pulsed voltammetry (DPV).
The results of these measurements are listed in Table 5.1, representative scans for
complexes 5.2 and 5.5 are shown in Figure 5.2. All five complexes display irreversible
oxidation waves at ~0.8 V. A small return wave near 0.80 V can also be observed for
122
complexes 5.1–4; however, full reversibility was not apparent at any of the tested scan
rates (50–500 mV/s).
Table 5.1. Electrochemical potentials for 5.1–5 reported in volts (V) relative to Fc
+
/Fc.
a
complex E
1/2
red2
E
1/2
red1
E
ox
ΔE
1/2
b
5.1 -1.89 -1.41 0.79 2.20
5.2 -1.87 -1.44 0.79 2.22
5.3 -1.95 -1.53 0.80 2.33
5.4 -1.73 -1.32 0.77 2.09
5.5
c
-1.58 -1.23 0.79 2.07
(a) Measurements were performed in an anhydrous solution of 0.1 M NBu
4
PF
6
in DMF.
(b) ΔE
1/2
= E
ox
- E
1/2
red1
. (c) Two additional reversible reduction waves were observed at
-1.62 and -1.93 V.
Multiple reversible reduction waves were observed in all five complexes. The
complexes with pyridyl groups (5.1–4) display two reversible waves. For complexes
5.1-3 the first reduction peak shifts to more negative values with each successive
benzannulation. The trend is counter to the common expectation that the species with the
larger π-orbital system will provide a greater stabilization to the negative charge.
23
It is
worth noting that butadiene addition at the 6,7- and the 5,6-positions of 5.2 results in a
negative shift (5.3; -1.53 V) and a positive shift (5.4; -1.32 V) in reduction potential
relative to 5.2 (-1.44 V).
123
For complex 5.5, a total of four reversible reduction peaks were observed (E
1/2
red
= -1.23, -1.58, -1.62, -1.93 V). The two new reduction waves are likely due to additional
reduction sites on the isoquinolyl moieties. Like 5.4, complex 5.5 displays a positive shift
in reduction potential relative to 5.2, as opposed to the negative shift observed for 5.3.
This shift in potential leads to a decrease in ΔE
1/2
for 5.5 and 5.4, relative to the trend of
increasing ΔE
1/2
observed in the series 5.1–3 (Table 5.1).
-2.0 -1.5 -1.0 -0.5 0.0 0.5 1.0
-150
-125
-100
-75
-50
-25
0
25
50
75
100
125
150
175
-2.0 -1.5 -1.0 -0.5 0.0 0.5 1.0
-40
-20
0
20
40
I (μ μ μ μA)
Potential (V vs Fc
+
/Fc)
-2.0 -1.5 -1.0 -0.5 0.0 0.5 1.0
-40
-30
-20
-10
0
10
20
30
I (μ μ μ μA)
Potential (V vs Fc
+
/Fc)
b a
5.2
5.5
I (μ μ μ μA)
Potential (V vs Fc
+
/Fc)
= 25 μA
Figure 5.2. CV of complexes 5.2 and 5.5 (150 mV/s). The insets (a and b) show
the DPV traces of complexes 5.2 and 5.5, respectively (top, oxidative scan;
bottom, reductive scan). The peaks at 0 V are due to the internal ferrocene
reference.
124
5.3.2 Electronic Spectroscopy. The absorption spectra for complexes 5.1–5 and their
ligand precursors were recorded in CH
2
Cl
2
. The spectra for the ligand precursors and
5.1–5 are shown in Figure 5.3. The BPI ligand (Figure 5.3a) displays several absorption
bands between 300–425 nm that are assigned to π-π* transitions. The spectra for the other
four ligands display π-π* transitions with a similar vibrational progression (Figure 5.3a).
Upon platination of BPI, the ligand-centered (LC) π-π* transitions (ε ≈ 2 x 10
4
M
-1
cm
-1
)
undergo a red-shift, while new, low energy transitions appear between 425-550 nm (ε ≈
1.4 x 10
4
M
-1
cm
-1
). The low energy absorption bands are assigned to nominal (vide infra)
metal-to-ligand charge transfer (MLCT) transitions. Similarly distinct LC and MLCT
absorption transitions are also observed in the spectra of 5.1 and 5.3–5 (Figure 5.3b).
Both the absorption onset and overall peak position of the MLCT transitions in
5.1–3 display a clear trend: a blue-shift with each successive benzannulation of the
pyrrolate group. This trend is in agreement with the observations of increasing ΔE
1/2
in
the series, but is counter to the intuitive expectation that expansion of the aromatic π-
system will lead to red-shifted absorption.
1, 2
It is also noteworthy that benzannulation of
the isoindole ring of 5.2 results in either a blue-shift (in 5.3) or a red-shift (in 5.4)
depending on the site of attachment. These observed trends in absorption are in
agreement with the change in ΔE
1/2
values.
125
300 350 400 450 500
0.0
0.2
0.4
0.6
0.8
1.0
1.2
1.4
a)
Wavelength (nm)
Normalized Absorption (a.u.)
BPEP
BPI
benz(f)BPI
benz(e)BPI
BIQI
300 350 400 450 500 550 600 650
0.0
0.5
1.0
1.5
2.0
2.5
Wavelength (nm)
ε ε ε ε (10
4
M
-1
cm
-1
)
5.1
5.2
5.3
5.4
5.5
b)
Figure 5.3. a) Normalized absorption spectra of BPEP, BPI,
benz(f)BPI, benz(e)BPI and BIQI in CH
2
Cl
2
at room temperature.
b) Room-temperature absorption spectra of 5.1–5 in CH
2
Cl
2
.
126
500 550 600 650 700 750 800
0.0
0.1
0.2
0.3
0.4
0.5
0.6
0.7
0.8
0.9
1.0
1.1
5.2
5.3
5.4
5.5
Normalized Intensity (a.u.)
Wavelength (nm)
a)
560 600 640 680 720 760
0.0
0.1
0.2
0.3
0.4
0.5
0.6
0.7
0.8
0.9
1.0
b)
Normalized Intensity (a.u.)
Wavelength (nm)
5.1
5.2
5.3
5.4
5.5
Figure 5.4. Emission spectra of 5.1–5 in a) toluene at room
temeprature and b) 2-MeTHF at 77K.
127
All of the complexes were luminescent in glassy solvent (2-MeTHF) at 77K
(Figure 5.4b) and complexes 5.2–5 were also emissive at room temperature (Figure 5.4a).
Emission data for 5.1–5 is summarized in Table 5.2. The spectra recorded at 77K display
vibronic structure and exhibit long lifetimes (τ = 0.081–20.8 μsec), both features
consistent with phosphorescence from a ligand-centered triplet state that is strongly
perturbed by the heavy Pt atom. The quantum yields at room temperature for complexes
5.2–5 varied between 0.3 and 11.5%, whereas 5.1 was non-emissive and only weakly
luminescent even at 77K. The emission properties of 5.2 and 5.3 are in accord with data
reported by Wen et al.,
8
although we observe a somewhat higher value for the quantum
yield of 5.2 (Φ = 0.015 vs 0.0054) and 5.3 (Φ = 0.098 vs 0.0379) in CH
2
Cl
2
(Table 5.2)
presumably due to differences in measurement techniques. The emission energies of
5.1-5 parallel the shifts observed in the absorption spectra that occur with each successive
benzannulation. Interestingly, the complexes that show the most red-shifted emission
(λ
max
≈ 650 nm) have both the smallest (5.1) and the largest (5.5) π-systems.
128
Table 5.2. Photophysical properties of complexes 5.1-5.
complex
absorbance λ (nm)
(ε, x10
4
M
-1
cm
-1
)
a
emission at rt
b
k
r
(10
4
s
-1
)
d
k
nr
(10
5
s
-1
)
e
emission at
77K
c
λ
max
(nm)
τ (μs)
Φ
PL
λ
max
(nm)
τ (μs)
5.1
234(2.32),
278(2.14),
385(1.26),
500(0.73)
- - - - - 650 0.081
5.2
250(5.37),
277(3.51),
348(2.24),
473(1.36),
487(1.35)
641
0.99
(0.97)
0.014
(0.015)
1.4 9.96 595 6.8
5.3
229(4.16),
300(5.03),
387(1.78),
409(1.89),
467(1.20),
477(1.21)
611
4.5
(3.2)
0.115
(0.098)
2.6 1.97 566 20.8
5.4
243(2.93),
280(2.95),
376(1.40),
402(1.37),
502(0.57),
529(0.46)
682 0.15 0.003 2 66.5 638 1.04
5.5
245(5.51),
262(5.48),
382(1.61),
403(1.55),
426(1.29),
511(1.75),
536 (1.62)
711 0.051 0.003 5.9 195.5 648 2.0
(a) In CH
2
Cl
2
. (b) In toluene deaerated with N
2
. Data in parentheses recorded in CH
2
Cl
2
.
(c) In 2-MeTHF. (d) k
r
= Φ/τ. (e) k
nr
= (1-Φ)/τ.
129
5.3.3 Computational Results. The geometry optimized structure of 5.2 (Figure 5.5) is in
good agreement with the x-ray crystal structure obtained by Meder et al. for the alkyl
substituted analog (6-Me-3-tBuBPI)PtCl (Table 5.3).
24
The calculated metal-ligand bond lengths differ by less than 0.05 Å while the
chelate bond angles differ by less than 0.5°. The calculations accurately describe an out
of the plane distortion (~10°) of the chlorine atom caused by steric conflict with the
ortho-hydrogens (at position 1) of the pyridyl rings (Cl···H = 2.24 Å). Similar bond
lengths and angles in the coordination sphere were found in the calculated structures of
complexes 5.1’ and 5.3–5 (Table 5.3).
Figure 5.5. Calculated structure of 5.2. With
atoms carbon and nitrogen indicated by black
and blue spheres respectively. Hydrogen atoms
were omitted for clarity.
130
Table 5.3. Selected bond lengths (Å) and angles (degrees) for 5.1-5 from DFT
calculations and reported x-ray data of 5.2.
Complex Method r[Pt-Cl] (Å) r[Pt-N
pyr
] (Å) r[Pt-N
ind
] (Å) ∠(Cl-Pt-N
ind
) (°)
5.1’ B3LYP 2.36 2.08 1.99 172.4
5.2 B3LYP 2.36 2.09 2.00 171.6
5.3 B3LYP 2.36 2.09 2.00 171.4
5.4 B3LYP 2.36 2.08 2.00 171.4
5.5 B3LYP 2.36 2.08 1.99 169.9
5.1’ CPCM/ B3LYP 2.37 2.09 1.99 171.4
5.2 CPCM/ B3LYP 2.37 2.09 2.00 170.5
5.3 CPCM/ B3LYP 2.37 2.09 2.00 170.2
5.4 CPCM/B3LYP 2.37 2.08 2.00 170.6
5.5 CPCM/ B3LYP 2.37 2.08 1.99 169.0
5.2 Exp: X-ray
a
2.335(2) 2.049(4) 1.966(3) 170.14(12)
(a) From Meder et al. (pyr = pyridine, ind = indolate)
From the optimized structures, vertical excitation energies can be determined
using time-dependent density functional theory (TDDFT). The lowest energy vertical
transition for both gas phase and solution (CPCM) calculations (Table 5.4) show
qualitative agreement with the experimental absorption trends (Table 5.2). The CPCM
calculations are in better quantitative agreement with the experimental data than are the
gas phase predictions. As is observed in the experiments for complexes 5.1-3, a blue-shift
in absorption predicted with each successive benzannulation at the pyrrole position.
Although complexes 5.4 and 5.5 are also benzannulated versions of 5.2, they display a
red-shift in absorption relative to 5.2, as opposed to the blue-shift observed for 5.3. Also
listed in Table 5.4 are the contributions of the HOMO-LUMO amplitudes to the TDDFT
excitation energies. Since the sum of the squares of all such amplitudes is unity, it is clear
that the HOMOLUMO contribution dominates these transitions (82-92%). Note also
131
that the TDA vertical excitation energies are in excellent qualitative (e.g., trends) and
quantitative agreement with the TDDFT predictions. This is important as the TDA is
essentially equivalent to the CIS wave function approach, the large amplitudes in Table
5.4 provide credence to the use of a HOMO-LUMO argument for qualitatively
understanding the observed and predicted trends. Since the HOMOLUMO transition
dominates the excitations that are of interest here, interpretations of the predictions and
observations are likely to employ the frontier orbitals.
Table 5.4. TDDFT and TDA vertical excitation energies for gas phase and CPCM
solvated complexes.
Complex
TDDFT
Vertical Excitation
Energy nm (error)
TDDFT TDA
Vertical Excitation
Energy nm (error)
Square of
HOMOLUMO
TDDFT Amplitude
5. 1’ 541 (-) 566 (-) 0.83
5.2 519 (32) 508 (21) 0.85
5.3 498 (21) 488 (11) 0.85
5.4 564 (35) 553 (24) 0.87
5.5 575 (39) 564 (28) 0.83
CPCM-5.1’ 541 (-) 525 (-) 0.82
CPCM-5.2 489 (2) 478 (9) 0.84
CPCM-5.3 472 (5) 462 (15) 0.86
CPCM-5.4 533 (4) 522 (7) 0.92
CPCM-5.5 540 (4) 527 (11) 0.82
The Kohn-Sham HOMO and LUMO energies for the ground state geometries are
given in Table 5.5. The trends in Table 5.5 correspond closely with those observed in the
electrochemistry experiments (Table 5.1). The calculated HOMO energy levels vary by
no more than 0.03 eV, qualitatively agreeing with the near equivalent oxidation potentials
for 5.1–5. The HOMOs of 5.1’ and 5.2–5 are predominantly localized on the
[(pyridylimino)3,4-pyrrolate]PtCl portion of the molecules (Figure 5.6 and 5.7) and thus
the HOMO energies appear to be dictated by this moiety. In contrast to the invariance in
132
HOMO energies, the energy of the LUMO increases in going from 5.1’ to 5.2 to 5.3. This
trend corresponds to a more negative reduction potential with each successive
benzannulation, as is documented in Table 5.1. On the other hand, the LUMO energies
decrease from 5.2 to 5.4 to 5.5 and reflect the values observed for the reduction potentials
of each respective complex.
Table 5.5. HOMO/LUMO energies and the Kohn-Sham Shifts (HOMO-LUMO gap) for
the gas phase and CPCM solvated complexes.
Complex
HOMO Orbital
Energy (eV)
LUMO Orbital
Energy (eV)
Kohn-Sham Orbital
Energy Shift (eV)
5.1’ -5.55 -2.78 2.78
5.2 -5.55 -2.56 2.99
5.3 -5.52 -2.45 3.07
5.4 -5.52 -2.69 2.83
5.5 -5.52 -2.78 2.75
CPCM-5.1’ -5.74 -2.83 2.91
CPCM-5.2 -5.77 -2.64 3.13
CPCM-5.3 -5.77 -2.56 3.21
CPCM-5.4 -5.74 -2.78 2.96
CPCM-5.5 -5.74 -2.86 2.88
Both the theoretical and experimental results suggest that the uncharacteristic
blue-shift in absorption going from 5.1 to 5.2 to 5.3 is due to the destabilization of the
LUMO with successive expansion of the π-system of the pyrrolate moieties. In a recent
report, the destabilization of the LUMO of 5.3 relative to 5.2 was rationalized using
energetic considerations and bonding/antibonding interactions between the (2-
pyridylimino)3,4-pyrrolate and naphthyl portions of the molecules. However, we find
that combining a naphthyl fragment with a (2-pyridylimino)3,4-pyrrolate moiety leads to
either a destabilization (in 5.3) or stabilization (in 5.4) of the LUMO for the two isomers.
Clearly the energy of the LUMO in 5.3 and 5.4 is not dictated solely by the LUMO
133
energy of naphthalene, and thus the model proffered by Wen et al. does not fully explain
the observed phenomena.
8
Here, a more quantitative analysis of the LUMO
destabilization is presented, using simple molecular orbital theory that relies on both
energetic and symmetry considerations of the benzannulation process.
One can visualize the formation of the frontier molecular orbitals of 5.2 by
combining the valence orbitals of 5.1’ with those of 1,3-butadiene as illustrated in Figure
5.6. The HOMO of 5.1’ consists of contributions from the respective p- and d-orbitals of
the chloride and platinum atoms, as well as from the π-system of the pyridyl and imino-
5.1’ 5.2 5.3 5.1’ 5.2 5.3
Figure 5.6. Qualitative orbital diagram of the valence orbitals for complexes 5.1’, 5.2
and 5.3. The HOMO (bottom, solid) and LUMO (top, transparent) surfaces are
displayed as viewed above the π-symmetric orbitals, with opposite phases above and
below the plane of the molecule.
134
pyrrolate portions of the ligand. There is minimal HOMO density at the site of
benzannulation of 5.1’ by 1,3-butadiene, thus no orbital mixing is observed and the
HOMO energy remains unchanged in 5.2. The LUMO of 5.1’ is localized primarily on
the π-system of the ligand with only a small contribution from the d-orbital on the Pt
atom. If one ignores the out of plane distortion of the chloride atom, 5.1’ can be idealized
as having C
2v
symmetry. In this point group, the LUMO of 5.1’ can be considered to have
b
2
symmetry. The frontier orbitals of cis-1,3-butadiene also fall under the C
2v
point group
with the HOMO and LUMO designated as b
2
and a
2
, respectively. The a
2
symmetry of
the LUMO of 1,3-butadiene is not the appropriate symmetry (b
2
) to mix with the LUMO
of 5.1’. However, both the HOMO of 1,3-butadiene and the LUMO of 5.1’ have the same
b
2
symmetry, so they can combine to create an occupied bonding MO (not shown) and an
unoccupied antibonding orbital (LUMO of 5.2) with the addition of a new nodal plane at
the site of attachment. The favorable orbital symmetry enables the HOMO of 1,3-
butadiene to act as an effective electron donating group to the LUMO of 5.1’. The net
effect of these interactions is an unaltered HOMO and a destabilized LUMO, resulting in
the blue-shifted absorption upon benzannulation of 5.1’. Likewise, a similar combination
between the frontier orbitals of 5.2 and 1,3-butadiene leads to an unaltered HOMO and a
destabilized LUMO as seen in 5.3 (Figure 5.6). Even when the geometry distorts
somewhat from the idealized C
2v
symmetry, the nodal behavior of the orbitals at the site
of butadiene addition can be used to make the same qualitative arguments. This is
expanded upon in the following paragraphs.
135
The arguments regarding the symmetry of interacting orbitals can also be used to
interpret the effects of benzannulation at other positions of 5.2. The stabilizing effect on
the LUMO when 5.2 is benzannulated at either the 5,6- or 3,4-positions (to form 5.4 and
5.5, respectively) is illustrated in Figure 5.7. The orbitals of 5.2 can be characterized by
the presence or absence of a bisecting nodal plane at the site of benzannulation. The
absence of a perpendicular bisecting nodal plane at either of the relevant positions of the
LUMO of 5.2 favors a cooperative interaction with the LUMO of 1,3-butadiene that leads
to a bonding/antibonding pair of MOs, whereas interactions with the HOMO of 1,3-
butadiene are disfavored. The end result is a stabilized LUMO in both 5.4 and 5.5.
5.4 5.2 5.5 5.4 5.2 5.5
Figure 5.7. Qualitative orbital diagram of the valence orbitals for complexes 5.2, 5.4
and 5.5.
136
Analogous symmetry considerations predict that benzannulation at either the 1,2- (5.7) or
the 2,3- (5.6) position of 5.2 should stabilize and destabilize the LUMO, respectively, an
outcome that is supported by calculation (Figure 5.8).
The molecular orbital diagram in Figure 5.6 is similar to that used by Uno et. al.
to explain increased reduction potentials of p-quinones caused by benzannulation.
25
Moreover, a destabilizing effect on the LUMO, and thus an increase in reduction
potentials, has been observed in other molecules that have their π-systems extended with
either 1,3-butadiene or ethene. These examples include tetracyanoquinones (TCNQ),
26
indoanilines,
4
anhydrides,
5
Ru(polypyridyl)
3
6
complexes and phthalocyanines,
27
as well
5.7 5.2 5.6 5.7 5.2 5.6
Figure 5.8. Qualitative orbital diagram for benzanulation at the 2,3-position (5.6) and
the 1,2-position (5.7) of 5.2.
137
as in simple polycyclic aromatic hydrocarbons.
28
The destabilization of the LUMO has
been attributed to either molecular distortions (in TCNQ),
26
an increase in the total
antibonding character of the orbital (in indoanilines and anhydrides),
4, 5
or an increased
localization of the π* orbital (in Ru(polypyridyl) complexes).
6
The molecular orbital
model presented here can be successfully applied to all of these molecular systems as
well.
As with complexes 5.1–3, benzannulation in several of these systems leads to
destabilization of the LUMO, which manifests itself in both increased reduction
potentials and blue-shifts in the lowest energy absorption transitions. A necessary
requirement to observe the blue-shift is for the HOMO energy to be either stabilized or
N
O
NEt
2
N
N
O O
O O
S S
S S
dibenzotetrathiafulvalene PTCAI
1
12
6
7
Indoaniline
1
2
N
N
Ru
3
(Ru(2,2'-bipyridine)
3
)
2+
2+
1
2
1
2
3
4
1 2
3
Figure 5.9. Molecules other than 5.2 that exhibit
a blue-shift in absorption upon benzannulation.
138
remain relatively unchanged upon benzannulation. This condition is met when the
HOMO is electronically isolated from the site of benzannulation. For example,
indoaniline dyes (Figure 5.9) have a HOMO localized on the p-diamino-phenyl fragment
and a LUMO localized on the p-quinoaniline moiety.
4
The low energy charge transfer
absorption bands in these molecules undergo a progressive shift from 596 nm to 589 nm
to 558 nm when the 1,2- and 3,4-positions of the quinoaniline fragment are successively
benzannulated. The shift to higher energy is attributed to an increase in LUMO energy
that accompanies each benzannulation, while the HOMO energy remains relatively
unchanged. Likewise, benzannulation at the 1,2-positions of (Ru(2,2’-bipyridine)
3
leads
to a 60 nm blue-shift in the lowest energy absorption band.
6
This shift is the result of
LUMO destabilization as the reduction potential is shifted by 0.16 V (E
1/2
= -1.51 V vs
SCE in Ru(2,2’-biisoquinoline)
3
vs -1.35 V in Ru(bpy)
3
). While the HOMO energy is
stabilized by 0.14 V, the change relative to the LUMO is smaller, and thus a blue-shift is
observed.
Althought the discussion so far has focused on molecules that exhibit a blue-
shifted absorption upon benzannulation, there are several examples where LUMO
destabilization occurs and red-shifted absorption is observed. For example, theoretical
investigations of porphyrins have shown that these molecules exhibit a destabilized
LUMO upon addition of butadiene.
2, 27
The amount of LUMO destabilization is small
relative to the HOMO destabilization, thus an overall red shift is observed. Similarly,
DFT calculations by Nguyen and Pachter show that the LUMO of tetra-azaporphyrins are
destabilized when benzannulated to form phthalocyanines.
27
139
Thus far, the orbital symmetry analysis used to explain the destabilization of the
LUMO has been limited to benzannulation with 1,3-butadiene, however, the same
principles can also be applied to molecules whose π-systems are expanded by the
addition of ethene. For example, Adachi, et. al. found that benzannulation with ethene at
the 1,12- and 6,7-positions of 3,4,9,10-perylenetetracarboxylic dianhydride diimide
(PTCAI, Chart 2) to give coronenetetracarboxylic dianhydride diimide (CTCAI) resulted
in an increase in the LUMO energy.
5
The LUMO of PTCAI (b
2g
symmetry) has an in-
phase pair of orbitals at the 1,12- and 6,7-positions that can combine with the π-
symmetric HOMO, but not the π-antisymmetric LUMO, of ethene in a fashion similar to
that shown in Figure 5.6 for 5.2 (Figure 5.10). The favorable interaction between the
Figure 5.10. Qualitative orbital diagram for PTCAI and CTCAI.
140
LUMO of PTCAI and the HOMO of ethene will consequently destabilize the LUMO of
PTCAI. The upward shift in the LUMO energy that occurs upon ethene addition to
PTCAI has a parallel in the change in the reduction potentials found for perylene (E
1/2
= -
1.64 V vs SCE) versus corannulene (E
1/2
= -2.03 V vs SCE).
28
A slightly more complex situation alters the HOMO of PTCAI when the π-system
is expanded to form CTCAI. The HOMO of PTCAI is stabilized by a
bonding/antibonding interaction between the π-antisymmetric LUMO of ethene and the
out-of-phase pair of orbitals at the 1,12- and 6,7-positions in the HOMO (a
u
) of PTCAI
(Figure 5.10). On the other hand, the HOMO-4 (b
1u
) of PTCAI has an in-phase pair of
orbitals at the same positions and as a result, this orbital is strongly destabilized by an
antibonding interaction with the π-symmetric HOMO of ethene. The energy of the
HOMO-4 of PTCAI is destabilized to the point where it becomes the HOMO of CTCAI.
The result of these interactions is that both the HOMO and LUMO of CTCAI are
stabilized and destabilized, respectively, relative to the parent PTCAI. Thus, a net blue-
shift in the lowest energy transition from 526 nm in PTCAI
29
to 511 nm in CTCAI is
observed.
30
The arguments given above to explain the stabilization/destabilization of the
LUMO energies upon benzannulation can also be used to rationalize related shifts in
HOMO energies in molecules that serve as electron donors. For example,
tetrathiafulvalene (TTF, E
1/2
= 0.35 V vs SCE) becomes more difficult to oxidize upon
benzannulation to form dibenzotetrathiafulvalene (E
1/2
= 0.60 V vs SCE).
7
Benzannulation of dibenzotetrathiafulvalene results in either an increase (1,2-position;
E
1/2
= 0.72 V vs SCE )
7
or decrease (2,3-position; E
1/2
= 0.52 V vs SCE)
31
in oxidation
141
potential depending on the orbital symmetry at the site of butadiene addition (Figure
5.11). The atypical HOMO stabilization upon benzannulation again results in a blue-
shifted absorption from 516 nm in dibenzotetrathiafulvalene to 502 nm in the linear
dinaphthotetrathiafulvalene.
5.4 Conclusion
A series of (BPI)PtCl derivatives with varying degrees of benzannulation have
been prepared and their properties have been characterized. It is observed that the
absorption/emission wavelength undergoes a red- or blue-shift depending on the site of
Figure 5.11. Qualitative orbital diagram for benzannulated dibenzotetrathiafulvalene
complexes.
142
benzannulation. Experimental data and first principles calculations suggest that the
observed trends are caused by an unvaried HOMO energy level and a destabilized or
stabilized LUMO with benzannulation. An explanation for the
stabilization/destabilization of the LUMO is presented using simple molecular orbital
theory. The molecular orbital model presented here can also be successfully applied to
indoaniline dyes, (Ru(2,2’-bipyridine)
3
)
2+
, 3,4,9,10-perylenetetracarboxylic dianhydride
diimide and dibenzotetrathiafulvalene to explain unusual blue-shifts in absorption with
benzannulation.
Although the focus in this report has been to describe blue-shifts in absorption upon
benzannulation, the ability to selectively tune HOMO and LUMO energy levels while
extending conjugation may be particularly useful in organic electronics. This concept is
exemplified in TTF systems mentioned above where the increased field-effect transistor
performance of dinaphthotetrathiafulvalene over dibenzotetrathiafulvalene has been
attributed to the more extended π-system and its effects on film morphology.
7
This orbital
analysis can also readily be applied to design new solar cell and charge transfer materials
where molecular organization and the ability to tune the energy of the frontier orbitals of
donor and acceptor molecules is of the utmost importance.
143
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APPENDIX 1: Efficient Dipyrrin-Centered Phosphorescence at Room
Temperature from Bis-Cyclometalated Iridium(III) Dipyrrinato
Complexes
A1.1 Introduction
Since their initial synthesis by Hans Fischer in 1934,
1
complexes with dipyrrinato
(dipy) ligands have been widely studied because of their synthetic utility as porphyrin
precursors and their rich photophysical properties.
2
Interest in the photophysics of these
complexes continues to grow predominantly thanks to the discovery of the highly
absorptive, strongly emissive boron difluoride dipyrrinato complex (BODIPY)
3
and its
more recent applications as a biological label, tunable laser dye and dopant in
electroluminescent devices.
4
In addition to BODIPY, the monoanionic dipyrrinato ligand
has been used as a bidentate chelate for numerous metal cations including Cr(III), Mn(II
+ III), Fe(II + III), Pd(II), Rh(II)
2
and more recently Ru(II),
5
Rh(III) and Ir(III).
6
While a vast number of emissive BODIPY dyes have been prepared, there are
very few reports of luminescent dipyrrinato compounds where the ligand is coordinated
to a metal cation. Prior examples include complexes with Zn(II)
7,8
or group 13 ions
(Al(III),
9
Ga(III) or In(III)
10
). The majority of the metal dipyrrinato complexes are non-
emissive and little is known about the triplet excited state of these species. In fact, one of
the attractive features noted for efficient fluorescence from BODIPY dyes is the
negligible intersystem crossing into the triplet state.
4
Phosphorescence from the
dipyrrinato dyes has been observed at 77 K through formation of the triplet excited state
either by charge separation and then recombination,
11
triplet energy transfer
12
or
sensitization by a heavy atom solvent.
13
To facilitate the investigation of the triplet
156
properties of the dipyrrinato ligand it is important to efficiently produce a triplet excited
state so that room temperature phosphorescence can be observed.
Recently, room temperature phosphorescence from dipy (Φ = 0.013) has been
observed by coordinating the ligand directly to a platinum (II) cyclometalate (C^N)
complex.
14
Much like platinum (II) cyclometalates, tris- and bis-cyclometalated
iridium(III) complexes are known to have long-lived excited state lifetimes and highly
efficient phosphorescent emission. The high efficiency emission is attributed to
intersystem crossing from the singlet to the triplet excited state facilitated by strong spin-
orbit coupling of the iridium heavy atom.
15
Although a series of (η
5
-C
5
Me
5
)IrL(5-(4-R-
Ph)dipy) (L = Cl, phosphino, 2,2’-bipyridyl; R = CN, NO
2
) complexes have been recently
prepared,
6
these derivative were reported to be non-emissive. In this report we describe
the synthesis and characterization of a series of bis-cyclometalated Ir(III) compounds
containing dipyrrinato ligands (Figure A1.1) that exhibit phosphorescence at room
temperature. Through systematic variation of the cyclometalating ligand and the meso
subsistent of the dipyrrin moiety, it was found that the photochemical and
electrochemical properties were dictated by the dipyrrinato ligand.
Figure A1.1. Structure of (C^N)
2
Ir(5-R-dipy) complexes
A1.1–7. See Figure A1.3 for the isomers of A1.5.
157
A1.2 Experimental Section
A1.2.1 Synthesis. Mesitylaldehyde, benzaldehyde, acetaldehyde, pyrrole, pyrazole,
trifluoroacetic acid, indium(III) chloride, 1-phenylpyrazole, 2-phenylpyridine, 2-
phenylquinoline, (Aldrich), paraformaldehyde (Fisher), 5-iodo-1,3-benzodioxole (Matrix
Scientific) and IrCl
3
·nH
2
O (Next Chimica) were purchased from the corresponding
supplier (in parentheses) and used without further purification. NMR spectra were
recorded on Bruker AM 360 MHz or Varian 400 MHz NMR instrument as indicated and
chemical shifts were referenced to residual protonated solvent. Elemental analyses
(CHN) were performed at the Microanalysis Laboratory at the University of Illinois,
Urbana-Champaign.
Dipyrromethane,
16
5-methyl-dipyrromethane,
16
5-phenyl-dipyrromethane
17
and 5-
mesityl-dipyrromethane
17
were prepared following procedures developed by Lindsey et
al. 1-(4,5-methylenedioxopheny)pyrazole was prepared by Ullmann-type coupling of 5-
Iodo-1,3-benzodioxole with pyrazole.
18
Cyclometalated Ir(III) dichloro-bridged dimers
of general formula [(C^N)
2
Ir(μ-Cl)]
2
were synthesized by heating IrCl
3
·H
2
O to 110 ºC
with 2-2.5 equiv of cyclometalating ligand in a 3:1 mixture of 2-ethoxyethanol and
deionized water as previously reported by Nonoyama.
19
Synthesis of (C^N)
2
Ir(dipyrrinato) Complexes. To a solution of dipyrromethane (0.5
mmol) in 20 ml of dry THF, 2,3-dicloro-5,6-dicyano-1,4-benzoquinone (DDQ) was
added (0.5 mmol) and allowed to stir at room temperature for 1 hour. A large excess of
potassium carbonate (1 g) was then added and the mixture was stirred for 15 minutes
followed by the addition of [(C^N)
2
Ir(μ-Cl)]
2
(0.25 mmol). The solution was then
158
refluxed under N
2
overnight. After cooling to room temperature, solids were removed by
vacuum filtration and washed with dichloromethane (3 x 50 ml). The collected filtrate
was then evaporated to dryness under reduced pressure. The crude product was then
passed through a silica gel column using dichloromethane:hexane (9:1) as eluent. Solvent
from the first orange fraction was then evaporated to dryness under reduced pressure. The
pure product was precipitated with methanol (CH
3
OH), collected by filtration, washed
with CH
3
OH and air-dried.
Iridium(III) bis(1’-phenylpyrazolato-N,C
2’
)(dipyrrinato) (A1.1) - Yield: 7%
1
H NMR
(400 MHz, CDCl
3
), δ 6.29 (dd, J = 4.0, 1.0 Hz, 2H), 6.39-6.41 (m, 4H), 6.78 ( td, J = 7.5,
1.0 Hz, 2H), 6.86 (d, J = 1.0 Hz, 2H), 6.91 (dd, J = 7.5, 1.0 Hz, 2H), 6.94 (d, J = 2.0 Hz,
2H), 6.97 (dd, J= 4.0 Hz, 2H), 7.17 (d, J= 8.0 Hz, 2H), 7.31 (s, 1H), 7.96 (d, J= 2.0 Hz,
2H).
13
C NMR (100 MHz, CDCl
3
) δ 106.9, 110.4, 116.8, 121.4, 125.1, 125.7, 130.5,
133.8, 134.2, 134.4, 137.7, 144.0, 151.8. Elemental analysis for C
27
H
21
N
6
Ir: calcd: C
52.16, H 3.40, N 13.52; found: C 51.47, H 3.40, N 12.72.
Iridium(III) bis(1’-phenylpyrazolato-N,C
2’
)(5-methyldipyrrinato) (A1.2) - Yield:
13%
1
H NMR (400 MHz, CDCl
3
), δ 2.76 (s, 3H), 6.30 (dd, J = 4.0, 1.0 Hz, 2H), 6.36
(dd, J = 7.5, 1.0 Hz, 2H), 6.39 (t, J = 3.0 Hz, 2H), 6.77 ( td, J = 7.5, 1.0 Hz, 2H), 6.89-
6.93 (m, 6H), 7.18 (d, J = 8.0 Hz, 2H), 7.29 (dd, J = 4.0, 1.0 Hz, 2H), 7.94 (d, J = 3.0 Hz,
2H).
13
C NMR (100 MHz, CDCl
3
) δ 19.4, 106.8, 110.4, 116.2, 121.2, 125.0, 125.7, 126.7,
134.1, 135.1, 137.6, 138.3, 143.8, 145.0, 151.1. Elemental analysis for C
28
H
23
N
6
Ir: calcd:
C 52.90, H 3.65, N 13.22; found: C 52.75, H 3.54, N 12.93.
159
Iridium(III) bis(1’-phenylpyrazolato-N,C
2’
)(5-phenyldipyrrinato) (A1.3) - Yield:
70%
1
H NMR (400 MHz, CDCl
3
), δ 6.23 (dd, J = 2.5, 1.5 Hz, 2H), 6.39 (dd, J = 7.5, 1.0
Hz, 2H), 6.46 (t, J = 2.5 Hz, 2H), 6.49 (dd, J = 4.5, 1.5 Hz, 2H), 6.78 (td, J = 7.5, 1.0 Hz,
2H), 6.93 (td, J = 7.5, 1.5 Hz, 2H), 6.99 (t, J = 1.5 Hz, 2H), 7.00 (d, J = 1.5 Hz, 2H), 7.19
(dd, J = 8.0, 1.0 Hz, 2H), 7.37-7.47 (m, 5H), 7.99 (dd, J = 3.0, 1.0 Hz, 2H).
13
C NMR
(100 MHz, CDCl
3
) δ 106.9, 110.5, 116.5, 121.3, 125.1, 125.8, 126.9, 127.9, 130.5, 130.9,
134.2, 135.1, 137.6, 137.9, 139.7, 143.9, 148.3, 152.1. Elemental analysis for C
33
H
25
N
6
Ir:
calcd: C 56.80, H 3.61, N 12.04; found: C 56.69, H 3.22, N 11.93.
Iridium(III) bis(1’-phenylpyrazolato-N,C
2’
)(5-mesityldipyrrinato) (A1.4) - Yield:
73%
1
H NMR (400 MHz, CDCl
3
), δ 2.06 (s, 6H), 2.36 (s, 3H), 6.16 (dd, J = 4.0, 1.5 Hz,
2H), 6.38 (dd, J = 4.0, 1.5 Hz, 2H), 6.42-6.45 (m, 4H), 6.79 (td, J = 7.5, 1.0 Hz, 2H),
6.90-6.95 (m, 6H), 7.01 (d, J = 2.0 Hz, 2H), 7.19 (dd, J = 8.0, 1.0 Hz, 2H), 7.99 (d, J =
2.0 Hz, 2H).
13
C NMR (100 MHz, CDCl
3
) δ 19.8, 21.1, 106.9, 110.5, 116.5, 121.3, 125.1,
125.8, 127.4, 129.3, 134.26, 134,28, 136.1, 136.3, 136.7, 137.5, 138.1, 144.0, 147.2,
151.6. Elemental analysis for C
36
H
31
N
6
Ir: calcd: C 58.44, H 4.22, N 11.36; found: C
58.26, H 3.74, N 11.02.
Iridium(III) bis[1’-(4,5-methylenedioxophenyl)pyrazolato- N,C
2’
](5-
phenyldipyrrinato), iridium(III) [1’-(4,5-methylenedioxophenyl)pyrazolato-
N,C
2’
][1’-(4,5-methylenedioxophenyl)pyrazolato- N,C
6’
](5-phenyldipyrrinato),
iridium(III) bis[1’-(4,5-methylenedioxophenyl)pyrazolato- N,C
6’
](5-
phenyldipyrrinato) (A1.5(2’,2’), A1.5(2’,6’) and A1.5(6’,6’) respectively) – Yield: 58%
160
Product was further purified by sublimation under reduced pressure. All characterization
reported herin were preformed on sublimed sample.
1
H NMR (400 MHz, CDCl
3
), δ 7.90
(dd, J = 2.8, 0.8 Hz, 2H), δ 7.84 (dd, J = 2.8, 0.8 Hz, 2H), δ 7.83 (dd, J = 2.8, 0.8 Hz, 2H),
δ 7.76 (dd, J = 2.8, 0.8 Hz, 2H), 7.50-7.35 (m, 20H), 7.14 (t, J = 1.2 Hz, 2H), 7.12 (t, J =
1.2 Hz, 2H), 7.05 (t, J = 1.2 Hz, 2H), 7.03 (t, J = 1.2 Hz, 2H), 6.93 (dd, J = 2.8, 0.8 Hz,
2H), 6.91 (dd, J = 2.8, 0.8 Hz, 2H), 6.87 (dd, J = 2.8, 0.8 Hz, 2H), 6.85 (dd, J = 2.8, 0.8
Hz, 2H), 6.84 (s, 2H), 6.83 (s, 2H), 6.80 (d, J = 8 Hz, 2H), 6.78 (d, J = 8 Hz, 2H), 6.52-
6.48 (m, 8H), 6.46 (d, J = 8 Hz, 2H), 6.45 (d, J = 8 Hz, 2H), 6.41-6.38 (m, 4H), 6.31-6.28
(m, 4H), 6.28-6.23 (m, 8H), 5.88 (d, J = 1.6 Hz, 2H), 5.87 (d, J = 1.6 Hz, 2H), 5.81 (d, J
= 1.6 Hz, 2H), 5.80 (d, J = 1.6 Hz, 2H), 5.79 (s, 2H), 5.76 (s, 2H), 5.60 (d, J = 1.6 Hz,
2H), 5.58 (d, J = 1.6 Hz, 2H), 5.43 (d, J = 1.6 Hz, 2H), 5.40 (d, J = 1.6 Hz, 2H).
13
C
NMR (100 MHz, CDCl
3
) δ 153.3, 152.6, 152.2, 152.1, 151.7, 148.3, 145.27, 145.0, 143.5,
143.3, 142.9, 142.8, 141.0, 140.4, 139.6, 139.5, 139.4, 138.3, 138.1, 137.2, 137.0, 136.4,
135.0, 134.9, 134.5, 134.4, 130.9, 130.8, 130.5, 130.4, 130.0, 128.6, 128.0, 127.9, 127.8,
126.9, 124.9, 124.6, 124.0, 123.7, 116.8, 116.7, 116.4, 116.3, 116.1, 114.7, 113.3, 113.1,
106.9, 106.7, 106.0, 105.8, 104.2, 103.9, 101.5, 101.4, 100.4, 100.3, 99.6, 99.5, 93.9, 93.7.
Elemental analysis for C
35
H
25
N
6
O
4
Ir: calcd: C 53.49, H 3.21, N 10.69; found: C 53.16, H
2.84, N 10.42.
Iridium(III) bis(2-phenylpyridinato-N,C
2’
)(5-mesityldipyrrinato) (A1.6) - Yield: 66%
1
H NMR (360 MHz, CDCl
3
), δ 7.89 (ddd, J = 5.9, 1.5, 0.7 Hz, 2H), 7.80 (dd, J = 8.05,
5.9 Hz, 2H), 7.61-7.54 (m, 4H), 6.90 (ddd, J = 7.8, 7.3, 1.5 Hz, 2H), 6.88 (s, 2H), 6.85
(ddd, J = 7.6, 5.8, 1.5 Hz, 2H), 6.81 (ddd, J = 7.8, 7.3, 1.5 Hz, 2H), 6.71 (dd, J = 1.7, 1.2
161
Hz, 2H), 6.41 (dd, J = 7.6, 1.2 Hz, 2H), 6.37 (dd, J = 4.2, 1.5 Hz, 2H), 6.14 (dd, J = 4.4,
1.2 Hz, 2H), 2.34 (s, 3H), 2.02 (s, 6H);
13
C NMR (90 MHz, CDCl
3
) δ 168.8, 156.8, 151.8,
149.6 (2C), 147.3, 144.5, 136.7, 136.2, 135.9, 133.6, 132.3, 129.5 (2C), 127.4, 123.8,
121.6, 120.7, 118.6, 116.9. Elemental analysis for C
40
H
33
N
4
Ir: calcd: C 63.05, H 4.37, N
7.35; found: C 62.90, H 4.11, N 7.37.
Iridium(III) bis(2-phenylquinalato-N,C
2’
)(5-mesityldipyrrinato) (A1.7) – Yield:
71.5%
1
H NMR (360 MHz, CDCl
3
), δ 8.06 (dd, J = 10.3, 8.8 Hz, 2H), 8.03 (dd, J = 10.3,
8.8 Hz, 2H), 7.81 (d, J = 3.4 Hz, 2H), 7.79 (d, J = 4.6 Hz, 2H), 7.66 (dd, J = 8.1, 1.5 Hz,
2H), 7.31 (dd, J = 8.1, 7.3 Hz, 2H), 7.06 (ddd, J = 9.3, 7.8, 1.5 Hz, 2H), 6.96 (dd, J = 8.3,
7.3 Hz, 2H), 6.72 (s, 2H), 6.70 (dd, J = 8.3, 7.3 Hz, 2H), 6.61 (d, J = 1.9 Hz, 2H), 6.47 (d,
J = 7.6 Hz, 2H), 6.24 (dd, J = 4.4, 1.0 Hz, 2H), 6.11 (dd, J = 4.2, 1.0 Hz, 2H), 2.26 (s,
3H), 1.45 (s, 6H);
13
C NMR (90 MHz, CDCl
3
), δ 171.21, 164.84, 157.93, 150.06, 149.18,
147.30, 146.930, 138.22, 136.50, 136.44, 136.09, 134.49, 133.94, 130.26, 129.80, 129.65,
127.94, 127.70, 127.47, 127.14, 125.86, 125.71, 120.86, 117.06, 21.02, 19.23. Elemental
analysis for C
48
H
37
N
4
Ir•CH
2
Cl
2
: calcd: C 62.15, H 4.15, N 5.92; found: C 62.57, H 4.05,
N 6.08.
A1.2.2 X-ray Crystallography. Diffraction data for compounds A1.3, A1.4 and
A1.5(6’,6’) were collected on a Bruker SMART APEX CCD diffractometer with graphite
monochromated Mo Kα radiation (λ = 0.71073 Å). The cell parameters for the complexes
were obtained from a least-squares refinement of the spots (from 60 collected frames)
using the SMART program. One hemisphere of crystal data for each compound was
162
collected up to a resolution of 0.80 Å, and the intensity data were processed using the
Saint Plus program. All of the calculations for the structure determination were carried
out using the SHELXTL package (Version 5.1).
20
Absorption corrections were applied by
using SADABS.
21
In most cases, hydrogen positions were input and refined in a riding
manner along with the attached carbons. A summary of the refinement details and the
resulting factors are given in supporting information (Table A1.1).
Table A1.1. Crystallographic data for compounds A1.3, A1.4 and A1.5(6’,6’).
A1.3 A1.4 A1.5(6’,6’)
Empirical formula C
33
H
25
IrN
6
C
36
H
31
IrN
6
C
35
H
25
IrN
6
O
4
Formula weight 697.79 739.87 785.81
Temperature, K 133(2) 143(2) 143(2)
Wavelength (Å) 0.71073 0.71073 0.71073
Crystal system Orthorhombic Triclinic Monoclinic
Space group Pbca P-1 P2(1)/c
a (Å) 14.4741(17) 10.797(10) 10.5093(15)
b (Å) 15.3546(18) 12.0765(13) 26.688(4)
c (Å) 23.826(3) 13.2534(9) 10.6929(15)
α (deg) 90 96.441(2) 90
β (deg) 90 98.012(2) 107.259(2)
γ (deg) 90 93.279(2) 90
V (Å
3
) 5295.3(11) 3059.6(5) 2864.1(7)
Z 8 4 4
D
calcd
(g/cm
3
) 1.751 1.606 1.822
µ (mm
-1
) 5.078 4.399 4.716
F(000) 2736 1464 1544
θ range 1.71 to 27.53 1.62 to 27.51 1.53 to 27.55
Reflections collected 30830 18572 16868
Independent reflections
6062 [R(int) =
0.0325]
13091 [R(int) =
0.0520]
6418 [R(int) =
0.0578]
Refinement method
Full-matrix
least-squares
on F
2
Full-matrix
least-squares
on F
2
Full-matrix
least-squares
on F
2
Data/restraints/
parameters
6062/0/361 130391 /0/ 751 6418 / 12 / 415
GOF on F
2
1.036 1.031 1.231
Final R indices[I>2σ(I)] 0.0279 0.0674 0.0404
R indices (all data) 0.0359 0.1083 0.0632
163
A1.2.3 Electrochemical and Photophysical Characterization. Cyclic voltammetry
(CV) and differential pulse voltammetry (DPV) were preformed using an EG&G
Potentiostat/Galvanostat model 283. DMF (purchased from VWR) was used as the
solvent under inert atmosphere with 0.1 M tetra(n-butyl)ammonium hexafluorophosphate
(Aldrich) as the supporting electrolyte or a solution of anhydrous 0.1 M NBu
4
ClO
4
in
CH
2
Cl
2
(VWR) as indicated. A glassy carbon rod, a platinum wire and a silver wire were
used as the working electrode, the counter electrode and the pseudo reference electrode
respectively. Electrochemical reversibility was established using CV, while all redox
potentials were determined using DPV and reported relative to a ferrocenium/ferrocene
(Fc
+
/Fc) redox couple used as an internal standard.
22
The UV-visible spectra were recorded on a Hewlett-Packard 4853 diode array
spectrophotometer. Steady state emission experiments at room temperature and 77K were
performed using a Photon Technology International QuantaMaster Model C-60SE
spectrofluorimeter. Phosphorescence lifetime measurements were performed by a time-
correlated single-photon counting method using an IBH Fluorocube lifetime instrument
by equipped with a 405 nm LED excitation source. Quantum efficiency measurements
were carried out using a Hamamatsu C9920 system equipped with a xenon lamp,
calibrated integrating sphere and model C10027 photonic multichannel analyzer.
A1.2.4 Computational Method. All calculations were performed using the Titan
software package (Wavefunction, Inc.). The gas phase geometry optimizations were
calculated using B3LYP functional with the LACVP** basis set as implemented in Titan.
The energy levels and orbital diagrams of the highest occupied molecular orbital
164
(HOMO) and lowest unoccupied molecular orbital (LUMO) were obtained from the
optimized geometry of the singlet state. The spin-density of the triplet state was
calculated from the energy minimized triplet geometries.
A1.2.5 Device Fabrication. Prior to device fabrication, indium/tin oxide (ITO) on glass
was patterned as 2-mm-wide stripes with a resistivity of 20 Ω □
-1
. The substrates were
cleaned by sonication in a soap solution, rinsed with deionized water, boiled in
trichloroethylene, acetone, and ethanol for 5-6 min in each solvent, and dried with
nitrogen. Finally, the substrates were treated with UV ozone for 10 min. Layers of NPD
(400 Å), 10% A1.3 or A1.5 doped into Alq
3
(250 Å) and BCP (400 Å) were vapor-
deposited onto the substrates in a high-vacuum chamber. Lithium fluoride (10 Å) and
aluminum (1200 Å) were then vapor-deposited onto the substrates through a shadow
mask, that defined four devices per substrate with a 2-mm
2
active area each, in the same
high-vacuum chamber. The devices were tested within 3 h of fabrication. The electrical
and optical intensity characteristics of the devices were measured with a Keithly 2400
source/meter/2000 multimeter coupled to a Newport 1835-C optical meter, equipped with
a UV-818 Si photodetector. Only light emitting from the front face of the device was
collected and used in subsequent efficiency calculations. The electroluminescent (EL)
spectra were measured on a PTI QuantaMaster model C-60SE spectrofluorimeter,
equipped with a 928 PMT detector and corrected for detector response.
23
The EL
intensity was found to be uniform throughout the area of each device.
165
A1.3 Results and Discussion
A1.3.1 Synthesis and Structure The bis-cyclometalated Ir(III) dipyrrinato complexes
(Figure 1) were prepared by a modified “one-pot” procedure introduced by Lindsey for
bis(dipyrrinato)metal complexes.
24
In a stepwise manner, dipyrromethane was first
oxidized using DDQ followed by sequential addition of K
2
CO
3
and cyclometalated Ir(III)
dichloro-bridged dimers to give complexes A1.3–7 in 50–75% yield. Using the same
synthetic method, complexes A1.1 and A1.2 were obtained in 5–15% yield. The lower
yields for complexes A1.1 and A1.2 (comparable to those found for the boron difluoride
analogs
25,26
) are likely due to thermal instability
27
of the dipyrrin intermediate under the
given reaction conditions (refluxing THF).
All of the complexes were fully characterized by
1
H and
13
C NMR spectroscopy
and elemental analysis. The relatively simple NMR spectra of complexes A1.1–4, A1.6
and A1.7 are indicative of a C
2
-symmetric species having the same trans-N disposition
for the C^N chelate as the dimeric Ir starting material. However, the NMR spectra of
(ooppz)
2
Ir(5-Ph-dipy) (A1.5) was more complex. Analysis by HPLC-MS indicated the
presence of three species, in an approximate 1:2:1 ratio, which had identical mass and
similar absorption spectra (Figure A1.2).
166
Figure A1.2. HPLC: Absorption/Mass Spectrum for A1.5.
167
Using a combination of
1
H–
1
H COSY and
1
H–
1
H decoupled NMR, along with
comparison to
1
H NMR spectra of complexes A1.1–4, three regioisomeric forms of A1.5
were established: bis(2’-ooppz)Ir(5-Ph-dipy) A1.5(2’,2’), (2’-ooppz)(6’-ooppz)Ir(5-Ph-
dipy) A1.5(2’,6’) and bis(6’-ooppz)Ir(5-Ph-dipy) A1.5(6’,6’) (Figure A1.3). The
statistical ratio of the regioisomers indicates that there is no preference for either the 2’ or
6’ positions during cyclometalation of the ooppz ligand.
Crystals of complexes A1.3, A1.4 and A1.5(6’,6’) suitable for X-ray diffraction
analysis were obtained by zone sublimation. The structures show ligands arranged in a
pseudo-octahedral geometry around the metal center with the expected trans-
configuration of pyrazolyl groups (Figure A1.4).
Figure A1.3. Proton assignments for the 3 regio isomers of A1.5.
168
Bond lengths and angles for the C^N ligands are comparable to those found in
literature for similar heterolypic complexes (Table A1.2).
28
Likewise, the bond lengths
and angles of the dipyrrinato moiety are similar to those of other metal dipyrrinato-based
complexes. The iridium-pyrrolic nitrogen (M–N
pyr
) bond lengths (Ir–N
pyr
≈ 2.11 Å) are
comparable to those found in the (η
5
-C
5
Me
5
)Ir(Ph
3
P)(5-(4-NO
2
Ph)dipy) complex (Ir–N =
2.074(5) and 2.090(5)). Similar distances have also been observed in (ppy)Pt(5-
mesityldipy) complex where the Pt–N
pyr
bond lengths are 2.091(6) Å and 2.027(6) Å.
Table A1.2. Selected Bond Distances and Angles for A1.3, A1.4, A1.5(6’,6’),
(ppz)
2
Ir(bpy)
+
, and Zn(5-Ph-dpym)
2
.
Complex A1.3 A1.4 A1.5(6’,6’) (ppz)
2
Ir(bpy)
+
Zn(5-Ph-dipy)
2
Bond Distances (Å)
M-N
pyr
2.111(2) 2.118(8) 2.103(4)
-
1.980(5)
2.124(3) 2.130(8) 2.121(5) 1.972(5)
Ir-N
pz
2.010(3) 2.003(9) 2.015(4) 2.005(9)
-
2.016(2) 2.012(9) 2.026(5) 2.015(9)
Ir-C
pz
2.020(3) 2.015(11) 2.013(6) 2.017(11)
-
2.021(3) 2.025(12) 2.028(5) 2.022(10)
Bond Angles (˚)
N
pyr
-M-N
pyr
86.66(9) 86.7(3) 86.55(17) - 94.2(2)
N
pz
-Ir-N
pz
173.36(10) 175.5(4) 171.77(17) 173.4(4) -
C
pz
-Ir-N
pz
79.89(11) 80.2(5) 80.2(2) 80.1(4)
-
80.16(12) 80.7(4) 80.4(2) 81.3(4)
pz = pyrazole, pyr = pyrrole.
Figure A1.4. ORTEP drawings of compounds A1.3, A1.4 and A1.5(6’,6’). (carbon
(black), nitrogen (blue), oxygen (red), iridium (purple)). A second unique structure
for A1.4 found in the unit cell is not shown.
169
The two pyrrole rings in complexes A1.3, A1.4 and A1.5(6’,6’) are not coplanar,
unlike what is observed for dipyrrinato ligands in boron,
29
zinc
24
and iron
30
complexes.
Instead, the dipyrrinato ligand is bent and the pyrrole rings have a fold-angle, defined
here using planes formed by the nitrogen, α and β carbon atoms adjacent to the C5 carbon
(Figure A1.1 and Figure A1.5). Fold-angles of 17.9(2)° and 17.7(5)° are found in
complexes A1.3 and A1.5(6’,6’), respectively, while A1.4 contains two unique molecules
in the asymmetric unit cell, one with a bent dipyrrinato ligand (fold-angle = 11.1(9)°), the
other near planar (fold-angle = 1.0(8)°).
Figure A1.5. The planes of the pyrrole rings (light and dark grey
planes) of A1.3 define by the nitrogen, α and β carbon atoms
adjacent to the methene linker.
170
The folding distortion is accompanied by a tilt of the dipyrrinato ligand away
from a square plane comprised of the two coordinated carbons, iridium center and two
N
pyr
atoms. This tilt-angle can be quantified using two planes, one defined by the Ir and
two N
pyr
atoms versus the other that includes the two N
pyr
atoms and the C5 carbon (see
Figure S18). The tilt-angles were found to be 17.3(1)° in A1.3, 22.6(2)° in A1.5(6’,6’),
14.3(3)° in A1.4 (bent) and 0.3(3)° in A1.4 (planar). In addition to the buckling and
tilting distortions, a twist of the pendant aryl ring away from an orthogonal conformation
was observed. The aryl ring is canted at an angle of 67.5(3)° in A1.3 and 72.3(5)° in
A1.5(6’,6’), 74.0(7)° in A1.4 (bent) and 78.0(7)° in A1.4 (planar). These out-of-plane
distortions in the dipyrrinato ligand appear to require low energy and are likely caused by
crystal packing forces since both planar and non-planar forms of the ligand are present in
the structure of A1.4.
Figure A1.6. The out of plane (defined by Ir, N
pyr
and N
pyr
) distortion of the dipyrrin
(defined by N
pyr
, N
pyr
and C
meso
) in A1.3.
171
A1.3.2 DFT Calculations. Density functional theory (DFT) calculations of complex
A1.1–7 were performed using the B3LYP functional with the LACVP** basis set.
Theoretical investigation of cyclometalated iridium complexes using DFT calculations
has repeatedly demonstrated good correlation with experimental observations.
31-34
Metrical parameters for the geometry-optimized structures of A1.3, A1.4 and A1.5(6’,6’)
are well-correlated with equivalent bond lengths and angles obtained by X-ray
crystallography. For example, the calculated bond lengths (Ir–N
pyr
= 2.18 Å, Ir–N
pz
=
2.05 Å and Ir–C
Ph
= 2.05 Å) and bond angles (N
pyr
–Ir–N
pyr
= 86.1°, N
pz
–Ir–N
pz
= 174.4°
and C
Ph
–Ir–N
pz
= 79.5°) for complex A1.3 are within 0.06 Å and 1° of the X-ray structure
(Table A1.2). One notable difference is that the dipyrrinato ligand is planar (fold-angle =
0°) in the calculated geometries, as opposed to bent in the crystal structure.
For complexes A1.1–4, A1.6 and A1.7, the calculations show that both valence
orbitals are localized on the dipyrrinato ligand. A representative example of the HOMO
and LUMO is illustrated for complex A1.3 in Figure A1.7. Roughly similar HOMO
Figure A1.7. (a) Qualitative orbital energy diagram illustrating the HOMO
(transparent) and LUMO (mesh) orbitals of A1.3 and A1.5(2’,2’), A1.5(2’,6’) and
A1.5(6’,6’). All values reported in eV. (b) Triplet spin-density surface of A1.3.
172
(-4.96 to -5.01 eV) and LUMO (-1.71 to -1.79 eV) energies are also calculated for these
derivatives (Table A1.3). Likewise, the LUMOs for the three regioisomers of A1.5 have
similar energy and spatial distribution as the other complexes. However, the HOMOs
differ depending on the site of metalation. Cyclometalation at the 2’ position of the ooppz
ligand has minimal affect on the location/energy of the HOMO in A1.5(2’,2’), whereas
cyclometalation at the 6’ position in (A1.5(6’,6’) and A1.5(2’,6’) shifts the HOMO from
dipyrrinato to the 6’-ooppz ligand (Figure A1.7). The change in location of the HOMO
also shifts the orbital energy to more positive values (-4.73 eV). However, these
differences in the HOMO character are not reflected in the triplet state. A representative
example of the spin density distribution for the HOMO and LUMO is illustrated in Figure
Figure A1.7b for complex A1.3. All of the complexes have nearly identical spin density
contours that are localized on the dipyrrinato ligand, little-to-no spin density is observed
on either the C^N ligand or the iridium atom.
Table A1.3. Calculated HOMO/LUMO values and oxidation/reduction potentials for
complexes A1.1–7.
Complex
Calculation
a
Electrochemistry
b
HOMO (eV) LUMO (eV) E
ox
(V) E
1/2
red
(V) ΔE (V)
A1.1 -4.99 -1.72 0.52 -1.95 2.47
A1.2 -4.97 -1.71 0.52 -1.98 2.5
A1.3 -4.98 -1.76 0.53 -1.96 2.49
A1.4 -4.98 -1.79 0.55 -1.89 2.44
A1.5(6’,6’) -4.73 -1.77
0.39, 0.56
c
-1.92
c
2.31 A1.5(2’,6’) -4.72 -1.75
A1.5(2’,2’) -5.01 -1.79
A1.6 -4.99 -1.8 0.51 -1.91 2.42
A1.7 -4.96 -1.79 0.56 -2.70, -2.46, -1.96 2.52
(a) B3LYP/LACVP**. (b) Redox measurements were performed in an anhydrous 0.1 M
NBu
4
PF
6
DMF solution and reported relative to internal Fc
+
/Fc. (c) Performed on a
mixture of regioisomers of A1.5 in an anhydrous 0.1 M NBu
4
ClO
4
CH
2
Cl
2
solution.
173
A1.3.3 Electrochemistry. The electrochemical properties of the complexes A1.1–7 were
investigated using cyclic voltammetry and differential pulsed voltammetry, results of
these measurements are listed in Table A1.3. The complexes all display a reversible
reduction wave between -1.89 V and -1.96 V. These potentials are much less cathodic
than what is found for related Ir(C^N)
2
(acetylacetonate) complexes (E
1/2
red
= -3.1 V to -
2.45 V)
35
and indicate a reduction process associated with the dipyrrinato ligand. The
assignment is consistent with the similarity in the reduction potentials for A1.1–7 (Table
A1.3) and supported by the results from DFT calculations which show closely related
LUMO energies for all of the complexes. Two additional reversible reduction peaks were
observed with complex A1.7 at higher potential (-2.46 V and -2.70 V). These processes
are assigned to the reduction of the two quinolinyl moieties since they occur at potentials
similar to values reported for the (pq)
2
Ir(acetylacetonate) complex.
36
Complexes A1.1–4, A1.6 and A1.7 display irreversible oxidation waves from
0.51 to 0.56 V. Irreversible or quasi-reversible oxidative processes have also been
observed in Fe(5-Ph-dipy)
3
,
30
Zn(5-Ph-dipy)
2
24
and (η
5
-C
5
Me
5
)IrCl(5-(4-cyanoPh)dipy)
6
at similar potentials. On the other hand, bis- and tris-(C^N) Ir(III) complexes typically
undergo a one-electron, reversible oxidation assigned to the metal-aryl ligand portion of
the molecules.
31,35,37
The irreversible response for A1.1–4, A1.6 and A1.7, and close
similarity in potential to other dipyrrinato containing materials, suggests that oxidation is
associated with the dipyrrinato ligand. The DFT calculations support this interpretation as
they show that the HOMO of A1.1–4, A1.6 and A1.7 is localized on the dipyrrinato
ligand (Figure A1.7). In contrast, a regioisomeric mixture of A1.5 displays a reversible
oxidation wave at a potential ~130 mV more negative than that of the other complexes
174
(Table A1.3). Further, a small, irreversible oxidation wave can be resolved at 0.56 V in
CH
2
Cl
2
(Figure A1.8).
The data correspond well with the HOMO energies obtained by DFT calculations.
Both A1.5(6’,6’) and A1.5(2’,6’) have HOMOs localized on the C^N, rather than the
dipyrrinato ligand (Figure A1.7) and HOMO energies (-4.73 eV) that are destabilized
compared to the other complexes (-4.96 eV to -5.01 eV). For these two isomers, the data
indicate that the initial oxidation process is localized on the C^N ligand. The second
smaller peak at 0.56 V is tentatively assigned to oxidation of the A1.5(2’,2’) regioisomer
since the calculations show the HOMO is located at a similar location (dipyrrinato) and
energy (-5.01 eV) as complexes A1.1–4, A1.6 and A1.7. The lower intensity of this
second oxidation wave can be attributed to the lower abundance of the A1.5(2’,2’) isomer
(~25%) relative to the other two isomers of 5.
0.2 0.3 0.4 0.5 0.6 0.7 0.8
0
20
40
60
80
100
120
A1.3
A1.5
I (μ μ μ μA)
Potential (V vs Fc
+
/Fc)
Figure A1.8. CV of A1.3 and A1.5. The CV of A1.3 has
been offset vertically for clarity.
175
A1.3.4 Electronic Spectroscopy. Absorption and emission data for complexes A1.1–
7 recorded at room temperature and 77K are summarized in Table A1.4. The absorption
spectra of the complexes in dichloromethane show intense bands (ε > 10
4
M
-1
cm
-1
)
between 200–400 nm that are assigned to both spin-allowed π-π
*
ligand-centered (LC)
and metal-to-ligand charge transfer (MLCT) transitions associated with the C^N ligand.
A distinct feature is a very intense absorption band (ε ~ 3.3–4.0 x 10
4
M
-1
cm
-1
) extending
from 400 to 540 nm (Figure A1.9). This band has similar absorption intensity and
wavelength to boron- and metal-dipyrrinato dyes
5,24,38-40
and is thus assigned to the
1
π-π
*
ligand-centered transition of the dipyrrinato ligand. The assignment is further supported
by comparing derivatives having either different C^N ligands (A1.4–7) or substituents at
the C5 position of the dipyrrinato chromophore (A1.1–4). Variation in the C^N ligand
has minimal affect on the absorption wavelength and intensity of the peak at ~480 nm in
complexes A1.4–7 (Figures A1.9b). However, a small red shift (~7 nm) in the peak is
observed when the parent dipyrrinato ligand in A1.1 (λ
max
= 474 nm) is substituted with
either a methyl or aryl group (A1.2–4). Another feature associated with the dipyrrinato
ligand can be observed near 310 nm in complex A1.3, where the absorptivity of this peak
is nearly double that of A1.4 (Table A1.4 and Figure A1.9a). A similar enhanced
absorbance found in analogous BF
2
-dipyrrinato compounds has been attributed to an in-
plane rotation of the phenyl group, which increases probability of this transition.
41
176
All complexes display vibronically structured luminescence in fluid solution at
room temperature and in glassy media at 77K (Figure A1.10). The emission peak
maxima fall in a narrow range at both room temperature (658–685 nm) and 77K (644–
670 nm), with microsecond lifetimes (room temperature, 5–13 μs; 77K, 12–23 μs) at 77K.
Lower energy vibrational modes extend out past 800 nm (Figures A1.10). For complexes
A1.1–7, large apparent Stokes shifts (5500–6200 cm
-1
) and long excited-state lifetimes
are indicative of phosphorescence. In contrast, metal- and boron-containing dipyrrinato
250 300 350 400 450 500 550 600
0.0
0.5
1.0
1.5
2.0
2.5
3.0
3.5
4.0
a)
Wavelength (nm)
ε ε ε ε (10
4
M
-1
cm
-1
)
A1.1
A1.2
A1.3
A1.4
250 300 350 400 450 500 550 600
0.0
0.5
1.0
1.5
2.0
2.5
3.0
3.5
b)
Wavelength (nm)
ε ε ε ε (10
4
M
-1
cm
-1
)
A1.4
A1.5
A1.6
A1.7
Figure A1.9. a) Room-temperature absorption
spectra of A1.1-4 and b) A1.4-7 in CH
2
Cl
2.
177
complexes typically display fluorescent emission centered around 510 nm with only
small Stokes shifts (<1000 cm
-1
) from the lowest energy absorption band.
24,38,41
The Ir complexes all emit at similar wavelength regardless of the cyclometalating
ligand. This is best exemplified by comparing the emission spectra of the (ppy)
2
Ir and
(pq)
2
Ir dipyrrinato complexes (A1.6 and A1.7) to analogous derivatives coordinated with
diketonate ligands. Bis-cyclometalated iridium acetylacetonate complexes emit from a
triplet state with
3
LC/MLCT character at energies that are strongly dependent on the
nature of the cyclometalating ligand. As a result, emission maxima of (ppy)
2
Ir(acac)
(λ
max
= 516 nm) and (pq)
2
Ir(acac) (λ
max
= 597 nm) differ considerably.
37
In contrast, the
600 640 680 720 760 800 840
0.0
0.1
0.2
0.3
0.4
0.5
0.6
0.7
0.8
0.9
1.0
A1.1
A1.2
A1.3
A1.4
a)
Normalized PL (a.u.)
Wavelength (nm)
600 640 680 720 760 800 840
0.0
0.1
0.2
0.3
0.4
0.5
0.6
0.7
0.8
0.9
1.0
A1.1
A1.2
A1.3
A1.4
b)
Normalized PL (a.u.)
Wavelength (nm)
600 640 680 720 760 800 840
0.0
0.1
0.2
0.3
0.4
0.5
0.6
0.7
0.8
0.9
1.0
A1.4
A1.5
A1.6
A1.7
c)
Normalized PL (a.u.)
Wavelength (nm)
640 720 800
0.0
0.1
0.2
0.3
0.4
0.5
0.6
0.7
0.8
0.9
1.0
A1.4
A1.5
A1.6
A1.7
d)
Normalized PL (a.u.)
Wavelength (nm)
Figure A1.10. Room-temperature (a) and 77K (b) emission spectra of A1.1-4 in 2-
MeTHF. Room-temperature (c) and 77K (d) emission spectra of A1.4-7 in 2-MeTHF.
178
emission maxima of A1.6 and A1.7 are similar (677 and 675 nm) as can be seen in Figure
A1.11.
Small variations in emission λ
max
are found with differing substituents on the
dipyrrinato ligand (Figure A1.10a and b). Both the parent complex A1.1 and mesitylene
derivatives A1.4, A1.6 and A1.7 emit at λ
em
= 672–677 nm, whereas a small blue-shift
(λ
em
= 658 nm) and red-shift (λ
em
= 683–685 nm) were observed for the methyl (A1.2)
and the phenyl substituted (A1.3 and A1.5) complexes, respectively. The absence of any
effect of the cyclometalating ligand, and the influence of the R substituent on λ
max
,
indicate that emission originates from the dipyrrinato ligand. Phosphorescence from the
dipyrrinato ligand is further supported by the fact that cyclometalation at the 2’- or 6’-
positions in A1.5 has minimal affect on the photophysical properties of the complexes.
The measured lifetime for a regioisomeric mixture of A1.5 can be accurately fit to a
single exponential decay, which implies identical decay constants for the excited state of
300 400 500 600 700 800
0
1
2
3
4
0.0
0.2
0.4
0.6
0.8
1.0
Normalized PL (a.u.)
Wavelength (nm)
ε ε ε ε (10
4
M
-1
cm
-1
)
A1.6
A1.7
Figure A1.11. Absorption (in CH
2
Cl
2
, filled
symbol) and emission (in 2-MeTHF, open
symbol) spectra of A1.6 (square) and A1.7
(circle) at room temperature.
179
each isomer. The assignment is consistent with DFT calculations that show the lowest
triplet state localized on the dipyrrinato ligand (Figure A1.7b).
Phosphorescence from compounds containing a dipyrrinato ligand has rarely been
directly observed. The phosphorescent spectra from BF
2
(dipy) compounds has been
reported at 77 K with the addition of iodoethane as a heavy atom solvent.
13
Triplet
emission at 77K has also been observed in a multicomponent BF
2
(dipy)–M(II)
terpyridine complexes due to charge-separation followed by recombination (M = Ru),
11
or by triplet energy transfer (M = Pt),
12
resulting in a
3
π-π* excited state localized on the
dipyrrinato moiety. Similarly, a boron dipyrrinato chromophore appended to a
(ppy)
2
Ir(bpy) complex has been shown to display phosphorescence at 77K through triplet
energy transfer from the excited state of the Ir fragment.
42
For the series of complexes
reported here, direct coordination of the dipyrrinato ligand to iridium, as in the previously
reported (C^N)Pt(dipy) complexes,
14
facilitates efficient intersystem crossing to the
triplet state and thus, phosphorescence from the dipyrrinato ligand is observed at room
temperature.
The luminescent quantum efficiencies (Φ) of complexes A1.1–7 range from 0.06
to 0.115 at room temperature in deaerated solution. A pronounced difference in efficiency
is seen between 5-phenyl substituted complexes A1.3 and A1.5 (Φ = 0.06) versus the 5-
mesityl derivatives A1.4, A1.6 and A1.7 (Φ = 0.09–0.115). A related, albeit much larger,
increase in quantum yield has also been observed in fluorescent zinc bis-dipyrrinato
complexes when the phenyl group (Φ = 0.006) is replaced with mesitylene (Φ = 0.36).
8
Detailed studies by Li, et. al. on related boron compounds concluded that the reduced
efficiency is due to rotation of the aryl ring, accompanied by a corresponding puckering
180
distortion of the dipyrrinato ligand. The distortion results in an excited-state conformer
that undergoes facile non-radiative deactivation to the ground state.
29,41
A similar
deactivation pathway, albeit less pronounced, is most likely active in the aryl substituted
complexes A1.3–7. This conclusion is supported by the lower efficiency and shorter
lifetimes in A1.3 and A1.5 as compared to A1.4, A1.6 and A1.7. The effects of aryl
rotation can also be observed when comparing the differing response of emission
behavior to solvent rigidity. While the excited state lifetimes of A1.4, A1.6 and A1.7
double upon cooling to 77 K, a three-fold increase in lifetime is found for A1.3 and A1.5,
presumably due to the rigid environment hindering rotation of the phenyl group. Similar
behavior is also observed at room temperature when the photophysical properties of
complexes A1.3 and A1.4 are examined in rigid media (polymethylmethacrylate, PMMA,
Figure S22). The radiative rates (k
r
) of both A1.3 and A1.4 remain constant upon doping
in PMMA (2%, w/w). However, while the non-radiative rate (k
nr
) of the mesityl
derivative (A1.4) is unchanged in PMMA, the k
nr
of the phenyl derivative (A1.3) is
lowered from 1.8 to 1.1 x 10
5
s
-1
(Table 2) resulting in an increased efficiency (Φ = 0.092).
Again, this behavior coincides with the rigid media inhibiting the rotation of the phenyl
ring and thus, decreasing the rate of nonradiative deactivation to the ground state.
Complexes A1.1–7 have relatively high nonradiative rates (k
r
~1 x 10
5
s
-1
) and
display only a minimal increase (x 2–3) in lifetime upon cooling from room temperature
to 77 K. Similar behavior has also been observed for the red phosphor, bis[2-(2’-
benzothienyl)pyridinato-N,C3’]iridium acetylacetonate, and is attributed to an intrinsic
temperature-independent nonradiative decay process.
43,44
Temperature-independent
181
nonradiative processes typically involve geometric distortions caused by low energy
molecular vibrations of the emissive ligand.
Dipyrrins can roughly be described as being half of a porphyrin ring and the
triplet emission energies for complexes A1.1–7 are comparable to those of Pt(porphyrins).
Despite this similarity, phosphorescent emission from Ir(5-Ph-dipy) A1.3 (Φ = 0.06) is
less than one third as efficient than from platinum tetraphenylporphyrin (PtTPP,
Φ = 0.19).
45
A comparison of radiative and nonradiative rates between A1.3 and PtTPP
shows higher values for both rates in A1.3 (k
r
= 1.1 x 10
4
s
-1
; k
nr
= 1.8 x 10
5
s
-1
) than in
PtTPP (k
r
= 3.5 x 10
3
s
-1
; k
nr
= 1.5 x 10
4
s
-1
).
45
The difference in quantum yields is
therefore caused by the ten-fold higher k
nr
values in A1.3. A likely origin of the high
nonradiative rates in A1.3 is the out-of-plane distortion of the pyrrole rings observed in
the crystal structures of A1.3, A1.4 and A1.5(6’,6’) (Figure A1.4). The presence of both a
planar and nonplanar form of the dipyrrinato ligand in the unit cell of A1.4 suggests a
low energy barrier for this type of distortion. For Pt(TPP), on the other hand, the ability
to traverse such a large amplitude distortion is limited by the structural rigidity of the
porphyrin ring system.
182
Table A1.4. Photophysical properties of complexes A1.1–7.
complex
absorbance
λ (nm)
(ε, x10
4
M
-
1
cm
-1
)
a
emission at rt
b,c,d
emission at 77K
b
λ
max
(nm) τ (μs) Φ
PL
k
r
(10
4
s
-1
) k
nr
(10
5
s
-1
)
λ
max
(nm) τ (μs)
A1.1
228 (3.13),
245 (2.94),
311 (0.74),
474 (3.31)
672 12.9 0.075 0.58 0.72 661 23.1
A1.2
229 (3.67),
243 (3.20),
310 (0.82),
480 (3.80)
658 9.9 0.094 0.95 0.92 644 22.3
A1.3
229 (3.67),
244 (3.48),
304 (1.36),
481 (3.52)
683
(675)
5.3
(8.1)
0.06
(0.092)
1.1
(1.1)
1.8
(1.1)
668 16.0
A1.4
228 (4.58),
245 (3.46),
310 (0.76),
483 (3.59)
676
(673)
12.7
(12.6)
0.115
(0.116)
0.91
(0.92)
0.70
(0.70)
664 22.4
A1.5
e
229 (4.37),
260 (2.88),
300 (2.17),
481 (3.53)
685 4.3 0.06 1.4 2.2 670 16.0
A1.6
246 (3.48),
342 (0.85),
404 (0.94),
483 (3.84)
677 6.3 0.099 1.6 1.4 665 12.9
A1.7
269 (5.03),
342 (1.81),
388 (0.97),
485 (3.60)
675 9.6 0.092 0.96 0.95 659 18.7
(a) In CH
2
Cl
2
. (b) In 2-MeTHF deaerated with N
2
. Data in parentheses recorded in
PMMA (2% w/w). (c) k
r
= Φ/τ. (d) k
nr
= (1 - Φ)/τ. (e) Mixture of regioisomers.
183
A1.3.5 OLED. Organic light emitting diodes (OLEDs) using complexes A1.3 and A1.5
as emissive dopants were fabricated by high-vacuum thermal evaporation. The device
architecture, shown in Figure A1.12, is identical to the one employed to make efficient
OLEDs doped with Pt(octaethylporphyrin).
46
The voltage-current density and voltage-luminance characteristics of the
fabricated OLEDs are shown in Figure A1.13. The turn-on voltages were 5.9 and 6 V for
devices with an aluminum tris(8-hydroxyquinoline) (Alq
3
) host doped with 10% A1.3
and A1.5, respectively, and both reached a luminance of 100 cd/m
2
at 12 volts.
Figure A1.12. Energy level diagram and device
architecture for OLEDs using dopants A1.3 and
A1.5.
0 2 4 6 8 10 12
0
100
200
300
400
500
A1.3
A1.5
Voltage (V)
Current Density (mA/cm
2
)
1E-3
0.01
0.1
1
10
100
Brightness (cd/m
2
)
Figure A1.13. Luminance (red, cd/m
2
) and current
density (black, mA/cm
2
) as a function of voltage (V) for
OLEDs using compound A1.3 (filled squares) and A1.5
(open triangles).
184
Both devices exhibited narrow, deep-red emission (λ
max
= 682 nm) when positive
bias was applied to the ITO electrode (Figure A1.14). The electroluminescent (EL)
spectra are coincident with the photoluminescent (PL) spectra of the corresponding
complexes at room temperature.
However, for the device employing compound A1.3, it was observed that, with
increasing driving voltage, the EL color slowly evolved from deep saturated red, to
orange to yellow. Examination of the EL spectra from this device shows that this
perceived color change at higher voltage is due to mixed emission from both the
phosphorescent dopant and Alq
3
host (Figure A1.14). In contrast, emission from Alq
3
is
reduced significantly when A1.5 is used as the dopant. The decreased contribution from
Alq
3
could be due to better hole trapping by the dopant since both the A1.5(2’,6’) and
A1.5(6’,6’) isomers are easier to oxidize than dopant A1.3. Improved charge trapping
could also be responsible for the lower conductivity of devices doped with A1.5
compared to those doped with A1.3 (Figure A1.13).
400 500 600 700 800
0.0
0.2
0.4
0.6
0.8
1.0
A1.3
A1.5
EL Intensity (a.u.)
Wavelength (nm)
x 300
Figure A1.14. EL spectra of OLEDs using
dopants A1.3 and A1.5.
185
The maximum external quantum efficiency was 0.6% and 1.0% for the device
using compound A1.3 and A1.5, respectively (Figure A1.15). The relatively poor device
performance, especially when compared relative to other cyclometalated Ir-based devices,
is likely due to the low solution photoluminescent efficiencies of the dopants.
A1.4 Conclusion
In summary, a series of dipyrrinato-based bis-cyclometalated Ir(III) complexes has been
synthesis and characterized. The electrochemical, spectroscopic and electroluminescent
properties were examined. The oxidation and reduction potentials of this series of
molecules, with one exception, were found to be centered on the dipyrrinato ligand.
Cyclometalation at the 6’-position of ooppz ligand results in a shift in the location of the
HOMO from dipyrrinato to the cyclometalating ligand, and thus the oxidation potential is
shifted to more negative potentials relative to the other molecules. All of the complexes
0.01 0.1 1 10 100 1000
0.01
0.1
1
A1.3
A1.5
Quantum Efficiency (%)
Current Density (mA/cm
2
)
Figure A1.15. Quantum efficiency as a function
of current density (mA/cm
2
) for OLEDs using
dopants A1.3 and A1.5.
186
have high molar absorptivity (10
4
M
-1
cm
-1
) at similar wavelengths (~480 nm) and exhibit
phosphorescent emission at room temperature in the deep red part of the visible spectrum
(658-685 nm) with quantum efficiencies ranging from 0.06 to 0.115. OLEDs made using
two of the complexes as dopants had external quantum efficiencies of 0.6 and 1.0%.
Despite the modest quantum efficiency, particularly with respect to other
cyclometalated iridium complexes, these derivatives provide efficient phosphorescence
from a dipyrrinato ligand at room temperature. The (C^N)
2
Ir(dipy) complexes have
several advantages not present in the fluorescent dipyrrinato analogues. 1) Selective
monitoring of emission with no absorption spectra overlap is possible due to the large
Stokes shift between absorption and emission maxima. 2) The red-shifted phosphorescent
emission (λ
max
≈ 680 nm) is in the biological tissue window (650–900 nm) making these
complexes possible candidates for biological labeling applications. 3) Efficient triplet
excited state formation upon photoexcitation is an important step in singlet oxygen
formation for both oxygen sensing and photodynamic therapy. 4) The high energy
absorption wavelength and oxidation potential of the complexes can easily be modified
by changing the cyclometalating ligand with minimal affect on the photophysical
properties of the dipyrrinato ligand.
187
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190
APPENDIX 2: The Synthesis of Near-infrared Absorbing
Donor/Acceptor Polymers and Their Application in Photodetectors
A2.1 Introduction
Near-infrared (NIR) absorbing molecules are interesting for many different
applications including optical sensors,
1
biological/medicinal sensors,
2
night vision
devices
3
and others. One particular area of interest is the development of NIR organic
photodetectors (PD)
4
in which NIR light is absorbed by a chromophore, the exciton is
dissociated in the device and the charge collected at the electrodes resulting in an
electrical signal that can be used to produce an image.
5
Organic PDs that absorb in the
visible spectrum (350-650 nm) are relatively common however the number of organic
NIR-PDs (650-2500 nm) is limited.
6-8
Carbon nanotubes are extensively investigated for there conductive properties and
tensile strength but are also known to exhibit absorption in the NIR. The absorption
maxima of CNTs are dependent on the diameters and chiralities of the tubes. Current
CNT synthetic methods result in heterogeneous population of CNT of various diameters
and chiralities. The resulting polydispersed mixture of CNT will exhibit a broad
absorption as can be seen in Figure A2.1.
9,10
191
Recently, Arnold et al. have used carbon nanotubes (CNT) as the NIR
chromophore in an organic NIR-PD.
11
The basic architecture of CNT PDs can be seen in
Figure A2.2a. The devices were produced by a combination of solution processing and
vapor phase deposition. A solution of suspend CNTs, poly[2-methoxy-5-(3’,7’-
dimthyloctyloxy)-1,4-phenylenevinylene] (MDMO-PPV) or poly[3-hexylthiophene]
(P3HT) and phenyl-C61-butyric acid methyl ester (PCBM) in chlorobenzene was doctor
bladed onto an indium tin oxide patterned glass substrate, followed by the vapor phase
deposition of C60, bathocuproine (BCP) and an aluminum anode. As can be seen in
Figure A2.2b the specific detectivity (D*), the figure of merit used to compare PDs of
different sizes and architecture, of this device is almost entirely above 10
10
cm Hz
1/2
W
-1
from 400 to 1400 nm. The D* from 750-1000 nm falls below 10
10
cm Hz
1/2
W
-1
presumably due to the limited CNT absorption between the E
11
and E
22
absorption
transitions (Figure A2.1).
Figure A2.1. Absorption spectrum of sodium dodecyl sulfate isolated
HiPCO-grown CNTs with chirality assignments from Weisman and
Bachillo.
10
192
One of the goals of a PD is to have uniform D* across the spectral range of
interest. In an effort to increase the spectral response 750-1000 nm gap, tin-
phthalocyanine (SnPc), which is known to exhibit thin film absorption from 600-1000 nm,
was co-depositied with C60 in the CNT NIR-PDs. Although the addition of SnPc does
raise the D* to more than 10
10
cm Hz
1/2
W
-1
from 400-1400 nm it also increases the
number of components in the device and thus increase the complexity of fabrication.
11
An
alternative approach is to modify current components of the device to give a photo
response from 750-1000 nm. Because CNTs and C60 cannot be readily modified to
change their absorption properties, the polymer component is a good candidate for
alteration.
In the NIR-PD described above the polymer serves two primary purposes. The
first is to act as a solublizing agent for the CNTs so that they can be solution processed.
The second is as a part of the charge separation event that transfers electrons from the
C 60
G lass
IT O
C NT s + polymer + P C B M
Ag Ag Ag
B C P
10
0
10
2
10
4
10
6
10
8
10
10
10
12
400 600 800 1000 1200 1400
D* A3_3
D* A4_3
D* B3_2
D* B3_4
D* B3_4-Biased
D* [cm-Hz
1/2
W
-1
]
Wavelength [nm]
Figure A2.2. Device architecture (a) and detectivity (b) for CNT MEH-PPV device.
b
a
193
CNT to the fullerene acceptors. In the report by Arnold et al they examined two
polymeric materials, MEH-PPV and P3HT, both of which have strong absorption in the
visible spectrum. It is likely that the absorption of these polymers contribute to the high
D* (~10
11
cm Hz
1/2
W
-1
) observed from 400-700 nm. Replacing MEH-PPV and P3HT
with a polymer that absorbs from 750-1000 nm may help to produce a uniform D* in
these NIR-PD.
A photovoltaic device containing a polymer that absorbs near the CNT PDs
region of lowest detectivity (750-1000 nm) was recently published by Bazan, et. al.
12
This polymer (A2.P2) is shown in figure Figure A2.5. The absorption in the NIR for this
molecule is attributed to charge transfer from the donor (dithiophene) to the acceptor
(thiadiazole) unit of the polymer. It has been demonstrated with various donor/acceptor
molecules/poymers that changes in the donor and/or acceptor can be used to tune the
absorption properties.
13-15
Here in we report the synthesis of a series of polymers
composed on the dithiophene donor and various diazole acceptor units and their use in
CNT based NIR-PD.
A2.2 Synthesis
Polymers A2.P1-4 (Figure A2.5) were synthesized by Stille coupling between the
4,4-bis(2-ethylhexyl)-2,6-bis(trimethylstannanyl)-4H-cyclopenta-[2,1-b:3,4-
b’]dithiophene (A2.6) donor molecule and the dibromo substituted acceptor molecules.
The synthesis of the donor molecule (A2.6) and acceptor molecules (A2.7-11) can be
seen in Figure A2.3 and Figure A2.4 respectively.
194
The trimethyl tin substituted donor molecule (A2.6), was synthesized in 6 steps at
25% overall yield (Figure A2.3). First, Bis(2-iodo-3-thienyl)methanol (A2.1) was
produced by a one-pot multi-step process developed by Brzezinski and Reynolds.
16
In the
second and third steps, the alcohol A2.1 was oxidized with pyridinium chlorochromate
followed by Ullmann coupling reaction using copper powder to give
cyclopentadithiophenone (A2.3).
16
Fine copper powder was found to be necessary in that
all attempts to make A2.3 using 40 mesh copper powder were unsuccessful. A2.3 was
then reduced by a modified Wolff-Kischner reduction using N
2
H
4
and KOH to give
cyclopentadithiophenone (A2.4).
17
Alkyl substitution of A2.4 was preformed in a mixture
of KOH, 2-ethylhexyl bromide and NaI to give dialkyl substituted complex A2.5. Finally,
the addition of n-butyllithium followed by trimethyltin chloride to A2.5 gave Stille
coupling reagent A2.6.
18
Figure A2.3. Synthesis of A2.6. a) n-butyllithium, I
2
; b) PCC; c)
Cu; d) N
2
H
4
, KOH; e) KOH, 2-ethylhexyl bromide, NaI; f) n-
butyllithium, trimethyltin chloride.
195
The synthesis of dibromo substituted acceptor molecules A2.7-A2.11 can be seen
in Figure A2.4. The dibromo substituted oxygen (A2.7), sulphur (A2.8) and selenium
(A2.9) benzodiazole complexes were synthesized by the addition of Br
2
to the
benzodiazole starting materials in the presents of Fe powder,
13
HBr
19,20
and AgSO
4
21,22
respectively. The 4,7-dibromo-2,1-3-azabenzothiadiazole (A2.10) on the other hand was
synthesized by bromination of 3,4-diaminopyridine
23
followed by the addition of thionyl
chloride.
24
Attempts to produce 4,7-dibromo-2,1-3-azabenzoselenadiazole by the
addition of SeO
2
to 3,4-diaminopyridine in ethanol were unsuccessful as no product was
observed by mass spectroscopy. The tellurium acceptor A2.11 was synthesized by first
reducing A2.7 with NaBH
4
to give 3,4-diamino-2,5-dibromobenzene
25
followed by the
addition of TeCl
4
.
26
The complexes were characterized by
1
H NMR,
13
C NMR, MS or
MALDI.
196
Stille coupling between the 4,4-bis(2-ethylhexyl)-2,6-bis(trimethylstannanyl)-4H-
cyclopenta-[2,1-b:3,4-b’]dithiophene (A2.6) donor molecule and the dibromo substituted
acceptor molecules (A2.7-10) using tris(dibenzylideneacetone)dipalladium(0) (Pd
2
(dba)
3
)
and triphenylphosphine
18
gave polymers A2.P1-4 in 40-75% yield (Figure A2.5).
Preliminary measurements indicate that the molecular weights of polymers A2.P1-4 were
between 7 and 20 kDa as determined by gel permeation chromatography (GPC) using
THF as the eluting solvent and polystyrene standards as a reference. The addition of
Pd
2
(dba)
3
to a mixture of A2.6 and tellurium acceptor A2.11 resulted in a brown
precipitate and no polymer formation was observed by UV-Vis spectroscopy. The brown
precipitate was not further characterized.
Figure A2.4. Synthesis of molecules A2.6-10.
a) X = O: Fe, Br
2
; X = S: Br
2
, HBr; b) SeO
2
,
EtOH; c) Ag
2
SO
4
, H
2
SO
4
; d) Br
2
, HBr; e)
SOCl
2
, pyridine f) NaBH
4
; g) TeCl
4
, NEt
3
.
197
The polymers were found to be soluble in common organic solvents and the
absorption spectra in CH
2
Cl
2
can be seen in Figure A2.6. All four polymers display
similar absorption characteristics with a high energy transition from 350 to 500 nm and a
broad structureless low energy transition from 500 to 900 nm. The absorption maxima are
640, 675, 730 and 735 nm for polymers containing oxygen (A2.P1), sulphur (A2.P2),
selenium (A2.P3) and sulphur pyridine (A2.P4) acceptor units. Changing the chalcogen
atom in the diazole acceptor unit results in a red shift with each step down the periodic
table from oxygen (A2.P1, 640 nm) to sulphur (A2.P2, 675 nm) to selenium (A2.P3, 730
nm). A 60 nm red shift is also observed when the benzene portion of the thiadiazole
acceptor unit (A2.P2) is replaced with a pyridine unit (A2.P4). This trend is similar to
those found with polymers composed of other donating units and diazole acceptor units.
13
Figure A2.5. Synthesis of polymers A2.P1-4. (R = 2-ethylhexyl)
198
The polymers (A2.P3, A2.P4) that most closely matched 750-1000 nm gap
between the CNTs E
11
and E
22
absorption transitions were chosen to be tested in organic
NIR-PDs. Similar to the fabrication mentioned above, a solution of 0.3 % of A2.P3 and
0.1% HiPCO CNTs in chlorobenzene was doctor bladed onto an indium tin oxide
patterned glass substrate, followed by the vapor phase deposition of 1000Å of C60 and an
aluminum anode. Likewise a solution of 0.3 % of A2.P4 and 0.05% arc-discharge CNTs
in chlorobenzene was doctor bladed onto an indium tin oxide patterned glass substrate,
followed by the vapor phase deposition of 1500Å of C60 and an aluminum anode. The
responsivity and detectivity of NIR-PDs produced with polymers A2.P3 and A2.P4 can
be seen in Figure A2.7.
For the NIR-PDs produced from A2.P3, a D* greater than 10
8
cm Hz
1/2
W
-1
was
observed from 400 to 1400 nm. Although the NIR-PD made with A2.P3 did increase the
uniformity of detection relative to the MEH-PPV and P3HT devices mentioned above, a
400 500 600 700 800 900 1000
0.0
0.1
0.2
0.3
0.4
0.5
0.6
0.7
0.8
0.9
1.0
A2.P1
A2.P2
A2.P3
A2.P4
Absorption (a.u.)
Wavelength (nm)
Figure A2.6. Absorption spectra of polymers A2.P1-4 in
CH
2
Cl
2
.
199
two order of magnitude decrease in D* was also observed. The apparent cause of the
decrease in D* is unclear however there are several possible explanations. The polymers
may not interact as well with the CNTs hindering the charge separation event that
transfers electrons from the CNT to the fullerene acceptors. The shorter length of the
polymers, relative to MEH-PPV and P3HT (>30 kDa), may reduce the CNT coverage
and increase the number of contact between CNTs resulting in less charge separation.
As can be seen in Figure A2.7d, the NIR-PD made with A2.P4 exhibits a varied
response with a D* of ~10
10
cm Hz
1/2
W
-1
from 400 to 900nm and ~10
7
cm Hz
1/2
W
-1
from
900 to 1600nm. This response is considerably lower than what was observed for the
devices mentioned above. The decreased performance may not be due to the polymer but
the type of CNTs used. As opposed to the previously mentioned devices using CNTs
produced by HiPCO methods, the NIR-PD with A2.P4 was made using CNTs produced
by arc-discharge. The arc-discharge method is known to produce CNTs with larger
diameters resulting in a bathochromic shift in absorption and also a narrowing of the band
gap. It is possible that the differences in orbital energies of A2.P4 and the arc discharge
CNTs are responsible for the poor device performance, however the differences in CNTs
makes direct comparisons difficult.
200
To further understand the structure/energy relationships of polymers A2.P1-4 in
NIR-PDs several additional studies are necessary. The first would be to test A2.P1-4 in
devices composed of both HiPCO and arc discharge CNTs to see the effect of different
orbital energy alignments on the D* of these devices. Second, devices with the same
polymer (one of A2.P1-4) but different molecular weights, which can be produced by
either differing reaction conditions or by using GPC to separate polymers of various sizes,
could be studied to understand the effect of polymer length on the device performance.
Additionally, substitutions of the 2-ethylhexyl moiety of the polymers may have a
significant effect on film morphology and thus alter the device performance.
Figure A2.7. Responsivity (a, c) and detectivity (b, d) of CNT devices produced with
polymers A2.P3 (a,b) and A2.P4 (c,d).
a
c
b
d
201
A2.3 Experimental Section
A2.3.1 General Information. All reported NMR spectra were obtained on a Bruker AC-
250 MHz FT NMR or a Varian 400 MHz NMR with all shifts relative to residual solvent
signals. The UV-visible spectra were recorded using a Hewlett-Packard 4853 diode array
spectrophotometer.
Bis(2-iodo-3-thienyl)methanol (A2.1). 12.5 g (0.077 mol) of 3-bromothiophene was
placed in a flame dried 1000 ml three neck flask. 100 ml of ether freshly distilled from
sodium and benzophenone was added via syringe. The solution was then cooled to -78°C.
Over 60 min, 50 ml (0.08 mol) of 1.6 M n-butyllithium was added dropwise and then
allowed to stir at -78°C for 2 hours. A second solution was prepared by first withdrawing
8.59g (0.077 mol) 3-aldehydethiophene in a 50 ml air tight syringe. The remainder of the
syringe (~50 ml) was filled with dry ether. The 3-aldehydethiophen solution was added
dropwise over 60 minutes to the 3-bromothiophene solution still cooled at -78°C. The
solution was then stirred at -78°C for 30 minutes, allowed to warm to room temperature
and stirred for an additional 30 minutes. The solution was then cooled to -20°C and 100
ml (0.16 mol) of 1.6 M n-butyllithium was added dropwise over 2 hours. The mixture
was allowed to react for 2 hours undisturbed. The solution was then warmed to room
temperature in a water bath and allowed to react for 30-60 min. The solution was again
cooled to -20°C and 60 g of I
2
dissolved in 600 ml of dry ether was added slowly via
cannula. The resulting solution was allowed to warm to room temperature overnight. 20
g of Na
2
SO
3
dissolved in 200 ml H
2
O was added and the resulting solution was
rigorously stirred for 1 hour. The ether layer was then collected and the aqueous layer
202
washed with ether. The combined organic layers were then rotary evaporated to dryness
and the solid washed with a small amount of hexane. 32.27 g (94%), pale yellow powder.
1
H NMR (250 MHz, CDCl
3
, δ) 7.44 (d, J = 5.5 Hz, 2H), 6.93 (d, J = 5.5 Hz, 2H), 5.77 (s,
1 H), 2.26 (s, 1H).
Bis(2-iodo-3-thienyl)ketone (A2.2). 23.3g (0.108 mol) of pyridinium chlorochromate
was added in one portion to a solution of 32.27 g (0.072 mol) of bis(2-iodo-3-
thienyl)methanol in 720 ml CH
2
Cl
2
and the solution stirred at room temperature
overnight. The mixture was passed through a plug of silica gel (l = 20 cm, d = 5 cm)
eluting with CH
2
Cl
2
. The solution was rotary evaporated to dryness. 30.88 g (96%), pale
yellow powder.
1
H NMR (250 MHz, CDCl
3
, δ) 7.47 (d, J = 5.5 Hz, 2H), 7.05 (d, J = 5.5
Hz, 2H).
4H-cyclopenta-[2,1-b:3,4-b’]dithiophen-4-one (A2.3). 12 g (0.189 mol) of copper
powder was added in one portion to a solution of 27.74 g (0.062 mol) bis(2-iodo-3-
thienyl)ketone in 200 ml of DMF and the solution was refluxed under nitrogen for 18
hours. Upon cooling to room temperature the precipitate was collected by filtration and
washed with ether. The filtrate was then washed with water. The organic layer was
collected and the aqueous layer was extracted with ether (2x). The combined organic
layers were washed with water and the rotary evaporated to dryness. The product (red
fraction) was isolated by column chromatography on silica gel eluting with
CH
2
Cl
2
:hexane (1:2). 5.9 g (49.6 %), orange powder. (
1
H NMR 250 MHz, CDCl
3
, δ) 7.04
(d, J = 4.75 Hz, 2H), 6.99 (d, J = 4.75 Hz, 2H).
203
4H-cyclopenta-[2,1-b:3,4-b’]dithiophene (A2.4). 5.9 g (30.7 mmol) 4H-cyclopenta-
[2,1-b:3,4-b’]dithiophen-4-one was suspended in 200 ml ethylene glycol. 7.5 ml
hydrazine hydrate was added followed by 6.2 g of ground KOH. The solution was then
slowly (over 8 hours) heated under N
2
to reflux. The reaction was then allowed to reflux
for 5 hours and then cooled to room temperature. 200 ml of water was added and the
organic layer was collected. The aqueous layer was extracted with ether (3x). The
combined organic layers were washed with water, brine and saturated NH4Cl. The
organic layer was rotary evaporated to give a brown oil which was further purified by
flash column chromatography (l = 15 cm, d = 5 cm) eluting with hexane. 4.4 g (80 %),
white powder. (
1
H NMR 250 MHz, CDCl
3
, δ) 7.19 (d, J = 4.75 Hz, 2H), 7.10 (d, J = 4.75
Hz, 2H), 3.55 (s, 2H).
4,4-bis(2-ethylhexyl)-4H-cyclopenta-[2,1-b:3,4-b’]dithiophene (A2.5). 4.7 g (26.4
mmol) of 4H-cyclopenta-[2,1-b:3,4-b’]dithiophene was dissolved in 120 ml DMSO and
bubbled with nitrogen for 5 min. 5.92 g (105.5 mmol) of KOH was added followed by
157 mg (1.05 mmol) of NaI and 9.86 ml (52.9 mmol) 95 % 2-ethylhexyl bromide. The
reaction was stirred under N
2
for two days. Water was added (200 ml) and the solution
extracted with ether (3 x 200 ml). The solution was then rotary evaporated onto silica gel.
The product was isolated by column chromatography on silica gel (l = 20 cm, d = 4 cm)
eluting with hexane. 8.56 g (81% %), colorless oil. (
1
H NMR 250 MHz, CDCl
3
, δ) 7.10
(d, J = 5.0 Hz, 2H), 6.92 (dt, J = 5.0, 1.25 Hz, 2H), 1.86 (dd, J = 4.75, 3.5 Hz, 2H), 1.05-
0.82 (m, 16H), 0.75 (d, J = 6.75 Hz, 2H), 0.58 (d, J = 7.25 Hz, 2H).
204
4,4-bis(2-ethylhexyl)-2,6-bis(trimethylstannanyl)-4H-cyclopenta-[2,1-b:3,4-
b’]dithiophene (A2.6). 1.5 g (3.72 mmol) of 4,4-bis(2-ethylhexyl)-4H-cyclopenta-[2,1-
b:3,4-b’]dithiophene was dissolved in 30 ml of THF freshly distilled from sodium
benzophenone and cooled to -78°C. To this solution, 9.3 ml (14.9 mmol) of 1.6 M n-
butyllithium in hexane was added dropwise and stirred at -78°C for 1 hour. The mixture
was then allowed to warm to room temperature over 3 hours. The reaction was then
cooled to -78°C, 18 ml (14.9 mmol) of 1.6 M n-butyllithium was added dropwise and
allowed to warm to room temperature overnight. Water was added and the solution
extracted with ether (3 x 200 ml). The combined organic layers were washed with water,
dried with sodium sulfate and then rotary evaporated to dryness. The residue was
dissolved in a small amount of toluene and passed through a plug of Celite pretreated
with triethylamine, eluting with toluene. Solvent was removed and the residue was dried
under vacuum at 80°C overnight. The residue was dissolved in hexane and passed
through a plug of densly packed celite. The solvent was removed and dried under vacuum
overnight. 2.36 g (87 %), brown oil. (
1
H NMR 250 MHz, CDCl
3
, δ) 6.97-6.93 (m, 2H),
1.92-1.76 (m, 4H), 1.06-0.80 (m, 16H), 0.74 (d, J = 6.25 Hz, 6H), 0.59 (d, J = 7.25 Hz,
6H), 0.35 (s, 18H).
4,7-dibromo-2,1-3-benzoxadiazole (A2.7). 0.465 g (8.33 mmol) of Fe powder and 5 g
(41.79 mmol) 2,1,3-benzoxadiazole were placed in a flame dried 50 ml round bottom
flask and heated to 90°C under nitrogen until melted. 6.25 mL (124.85 mmol) of Br
2
was
added slowly over 2 hours. The reaction was allowed to react for an additional 2 hours.
Upon cooling to room temperature the solution became a black solid. The black solid was
205
stirred in 200 ml H
2
O overnight. The precipitate was collected by filtration and stirred in
100 ml of NaHCO
3
for 1 hour. The precipitate was collected by filtration, dissolved in
ethyl acetate and rotary evaporated onto silica gel. The product was purified by column
chromatography (l = 10 cm, d = 5 cm) eluting with hexane:ethylacetate (90:10). The blue
emissive fraction was collected, rotary evaporated and recrystalized in ethanol. 8.5 g
(74 %), yellow needles. (
1
H NMR 250 MHz, CDCl
3
, δ) 7.51 (s, 2H).
13
C-NMR (62.5
MHz, CDCl
3
, δ) 191.0, 149.3, 108-7. MS (Maldi-TOF): m/z = 279.2.
4,7-dibromo-2,1-3-benzothiadiazole (A2.8). 20 g (146.88 mmol) benzothiadiazole was
dissolved in 250 ml of 47% HBr. 22.7 ml (440.6 mmol) Br2 in 75 ml of 47% HBr was
then added dropwise. The solution was then refluxed under nitrogen for 6 hours. The
mixture was then cooled to room temperature and orange precipitate began to form. To
this solution 500 ml of saturated NaHCO
3
was added and allowed to stir for 1 hour. The
precipitate was collected by filtration, washed with saturated NaHCO
3
until the solid was
white and then washed extensively with water. The solid was then dried at 100°C. 40.2 g
(94 %), white solid. (
1
H NMR 250 MHz, CDCl
3
, δ) 7.73 (s, 2H).
2,1-3-benzoselenadiazole. 10.81 g (0.1 mol) o-phenylenediamine was dissolved in 25 ml
of ethanol and brought to reflux. To this solution 12.2 g (0.11 mol) of SeO
2
in 50 ml H
2
O
was added and the mixture refluxed for an additional 30 min. Upon cooling to room
temperature precipitate began to form. The precipitate was collected by filtration and
washed with water. 16.3 g (89 %), brown needles. (
1
H NMR 250 MHz, CDCl
3
, δ) 7.86-
7.78 (m, 2H), 7.48-7.39 (m, 2H).
206
4,7-dibromo-2,1-3-benzoselenadiazole (A2.9). 1.02 ml (0.02 mol) of Br2 was added to
a solution of 1.83 g (0.01 mol) 2,1-3-benzoselenadiazole and 3.12 g (0.01 mol) silver
sulfate in 20 ml H
2
SO
4
. The mixture was stirred at room temperature for 2 hours. The
precipitate (AgBr) was removed by filtration and washed with H
2
SO
4
. The filtrate was
poured into 400 ml of ice water. The precipitate was collected by filtration, washed with
water and recrystalized from hot ethyl acetate. 1.1 g (70 %), yellow needles. (
1
H NMR
250 MHz, CDCl
3
, δ) 7.64 (s, 2H).
3,4-diamino-2,5-dibromopyridine. 5.1 g (45.8 mmol) of 98 % diaminopyridine in 10 ml
of 48 % HBr was heated to reflux under nitrogen with stirring. 7.5 ml of Br
2
was added
dropwise and the mixture refluxed for 5 hours. The reaction was cooled to room
temperature, the precipitate was collected by filtration, washed with sodium sulfite,
sodium carbonate and water. The product was purified by column chromatography (l =
10 cm, d = 5 cm) eluting with hexane:ethylacetate (40:60) and recrystalized from hot
methanol. 4.04 g (33 %), yellow powder. MS m/z: 267.1.
4,7-dibromo-2,1-3-azabenzothiadiazole (A2.10). 1.5 g (5.6 mmol) of 3,4-diamino-2,5-
dibromopyridine in 12 ml dry pyridine was cooled to 0°C under N
2
. To this solution 0.56
ml (7.65 mmol) of SOCl
2
was added dropwise and the solution stirred at 0°C for 1 hour.
The mixture was poured into 150 ml H
2
O and the precipitate collected by filtration. The
precipitate was dissolved in CHCl
3
and rotary evaporated onto a small amount of silica
gel. The product was purified by dry loaded column chromatography (l = 12 cm, d = 5
207
cm) eluting with chloroform, collecting everything before the yellow fractions. 0.81 g
(49 %), yellow powder. MS m/z: 295.1.
3,4-diamino-2,5-dibromobenzene. 18.2 g (0.48 mmol) of NaBH
4
was added portion
wise at 0°C to 7.65 g (26 mmol) of 4,7-dibromo-2,1-3-benzothiadiazole (A2.8) in 250 ml
ethanol. The mixture was allowed to stir at room temperature for 24 hours. Bubbling was
observed presumably due to the evolution of H
2
S. The solution was then rotary
evaporated in a fume hood (strong sulfur smell present). 500 ml of water was added and
the product extracted with ether (x 2) and the combined organic layers with washed with
water, brine and dried with Na
2
SO
4
. The organic layer was rotary evaporated to dryness
and vacuum was pulled for 24 hours. 5.48 g (80 %), yellow needles. (
1
H NMR 250 MHz,
CDCl
3
, δ) 6.84 (s, 2H), 3.89 (s, 4H).
4,7-dibromo-2,1-3-benzotelluradiazole (A2.11). 4.88 g (18.56 mmol) of 3,4-diamino-
2,5-dibromobenzene was dissolved in 35 ml freshly distilled pyridine(from KOH). 1 g
(3.7 mmol) of TeCl
4
in 55 ml dry pyridine was added drop wise via cannula and the
mixture allowed to stir at room temperature for 10 min. 3 ml of freshly distilled NEt
3
(from P
2
O
5
) was added and the mixture stirred for an additional hour. The mixture was
rotary evaporated to dryness and held under vacuum for 2 hours. 1 L of ethanol was
added to the residue and stirred for 1 hour. The precipitate was collected by filtration and
washed thoroughly with ethanol. 1.1 g (69 %), grey powder. (
1
H NMR 250 MHz, DMSO,
δ) 7.56 (s, 2H). MS m/z: 390.1.
208
General synthesis of polymers A2.P1-4. 0.291 g (0.399 mmol) of 4,4-bis(2-ethylhexyl)-
2,6-bis(trimethylstannanyl)-4H-cyclopenta-[2,1-b:3,4-b’]dithiophene (A2.6) and 0.391
mmol of dibromo substituted acceptor molecules A2.7-11 were dissolved in 30 ml of
toluene. The solution was then bubbled with N
2
for 5 min, followed by the addition of 7.2
mg (0.0078 mmol) of Pd
2
(dba)
3
and 16.4 mg (0.0625 mmol) of triphenylphosphine. The
mixture was then bubbled with nitrogen for an additional 10 min and heated to reflux
under nitrogen for 48 hours. The solution was then rotary evaporated to dryness in a 500
ml round-bottom flask. The residue was dissolved in 150 ml of chlorobenzene and 6.3 g
sodium diethyldithiocarbamate trihydrate in 84 ml of water was added and the mixture
was rigorously stirred at 80°C under nitrogen overnight. The mixture was cooled to room
temperature, the organic layer separated and passed through a column (d = 4 cm) packed
with alumina (l = 3 cm), silica gel (l = 3 cm) and celite (l = 3 cm) eluting with
chlorobenzene. The solution was then evaporated to dryness, dissolved in 10-20 ml of
chlorobenzene and layered with 500 ml methanol. The precipitate was collected by
filtration and washed with methanol. A2.P1 140 mg (69% yield), A2.P2 130 mg (63%
yield), A2.P3 172 mg (75% yield), A2.P4 85 mg (40 % yield).
209
Appendix 2 References
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(2) Porumb, G. G.; Sterian W. P.; Spulber, O.; Piscureanu, M. C. Proc. SPIE-Int. Soc.
Opt. Eng. 2001, 4430, 674-679.
(3) Schanze, K. S.; Reynolds, J. R.; Boncella, J. M.; Harrison, B. S.; Foley, T. J.;
Bouguettaya, M.; Kang, T.-S. Synthetic Metals 2003, 137, 1013-1014.
(4) Rogalski, A. Infrared Physics & Technology 2002, 43, 187.
(5) http://www.darpa.mil/mto/programs/hardi/index.html
(6) Xia, Y. J.; Wang, L.; Deng, X. Y.; Li, D. Y.; Zhu, X. H.; Cao, Y. Applied Physics
Letters 2006, 89.
(7) Wen, L.; Duck, B. C.; Dastoor, P. C.; Rasmussen, S. C. Macromolecules 2008, 41,
4576.
(8) Perzon, E.; Zhang, F. L.; Andersson, M.; Mammo, W.; Inganas, O.; Andersson, M.
R. Advanced Materials 2007, 19, 3308-3311.
(9) Avouris, P.; Freitag, M.; Perebeinos, V. Nat. Photonics 2008,2 (6), 341-350.
(10) Weisman, R. B.; Bachilo, S. M. Nano Lett. 2003, 3 (9), 1235-1238.
(11) Arnold, M. S.; Zimmerman, J. D.; Renshaw, C. K.; Xu, X.; Lunt, R. R.; Austin, C.
M.; Forrest, S. R. Nano Letters 2009, 9 (9), 3354-3358.
(12) Peet, J.; Kim, J. Y.; Coates, N. E.; Ma, W. L.; Moses, D.; Heeger, A. J.; Bazan, G.
C. Nature Materials 2007, 6, 497-500.
(13) Blouin, N.; Michaud, A.; Gendron, D.; Wakim, S.; Blair, E.; Neagu-Plesu, R.;
Belletete, M.; Durocher, G.; Tao, Y.; Leclerc, M. J. Am. Chem. Soc. 2008, 130,
732-742.
(14) Qian, G.; Dai, B.; Luo, M.; Yu, D.; Zhan, J.; Zhang, Z.;Ma, D.; Wang, Z. Y.
Chem. Mater. 2008, 20, 6208-6216.
(15) Yang, R.; Tian, R.; Hou, Q.; Yang, W.; Cao, Y. Macromolecules 2003, 36, 7453-
7460.
(16) Brzezinski, J. Z.; Reynolds, J. R. Synthesis, 2002, 8, 1053-1056.
210
(17) Coppo, P.; Cupertino, D. C.; Yeates, S. G.; Turner, M. L. Macromolecules 2003,
36, 2705-2711.
(18) Zhu, Z.; Waller, D.; Gaudiana, R.; Morana, M.; Muhlbacher, D.; Scharber, M.
Brabec, C. Macromolecules, 2007, 40, 1981-1986.
(19) Neto, B. A. D.; Lopes, A. S.; Ebeling, G.; Goncalves, R. S.; Costa, V. E. U.;
Quina, F. H.; Dupont, J. Tetrahedron, 2005, 61, 10975-10982.
(20) Liu, B.; Bazan, G. C. Nature Protocols, 2006, 1, 1698-1702.
(21) Huang, F.; Hou, L; Shen, H.; Yang, R.; Huo, Q.; Cao, Y. Journal of Polymer
Science: Part A: Polymer Chemistry, 2006, 44, 2521-2532.
(22) Bird, C. W.; Cheeseman, G. W. H.; Sarsfield, A. A. J. Chem. Soc. 1963, 4767-
4770.
(23) Lee, B.; Yamamoto, T. Macromolecules, 1999, 1375-1382.
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Chemistry, 2008, 46, 2975-2982.
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6755.
(26) Cozzolino, A. F.; Britten, J. F.; Vargas-Baca, I. Crystal Growth and Design, 2006,
6, 181-186.
211
APPENDIX 3: The Synthesis of 8,16-diphenyl-s-indaceno[1,2,3-cd:5,6,7-
c’d’]diphenalene for Application in Organic Photodetectors
A3.1 Introduction
Phenalenyl radical complexes are known to be highly reactive and dimerize at
room temperature due to kinetic instability.
1
Recently Kubo et al. have reported the
synthesis and characterization of a thermodynamically stabilized phenalenyl molecule
with singlet biradical character, 8,16-diphenyl-s-indaceno[1,2,3-cd:5,6,7-
c’d’]diphenalene labeled herein as The Hydrocarbon (THc, Figure A3.1).
2
By bridging
two phenalenyl groups with a benzene ring, electrons with antiparallel spins are permitted
to correlate in separate spaces and thus stabilize the radical character.
3
The absorption spectra of THc in CH
2
Cl
2
can be seen in Figure A3.2. There are
two narrow (FWHM = <100 nm) absorption bands at 360 and 750 nm with molar
absorptivities of 1.48 and 1.62 x 10
5
M
-1
/cm
-1
respectively. It was shown with previous
calculations that the low energy absorption at 750 nm is associated with a HOMO to
LUMO transition.
3
Ph
Ph
Figure A3.1. 8,16-diphenyl-s-indaceno[1,2,3-cd:5,6,7-
c’d’]diphenalene (THc).
212
In single crystals of THc grown from chlorobenzene solution, an intermolecular
spacing of 3.137 Å was found. Such a small spacing is indicative of strong intermolecular
interactions between two phenalenyl moieties. Calculations predict that the close spacing
is the result of highly favorable radical pairing of the phenalenyl units and as a result non-
covalent dimerization is observed. The close intermolecular interactions have a strong
effect on the absorption properties with the lowest energy absorption transition shifting
from 750 nm in solution to 1470 nm in single crystals.
2
In vapor deposited thin films of
THc, Chikamatsu et al. also observed large spectral perturbations with a broadened
absorption from 400 to 1500 nm, indicative of strong intermolecular interaction which is
further supported by x-ray diffraction and atomic force microscopy mesurments.
4
Thin
films of THc were also found to display good charge transport properties in field effect
transistors with hole and electron motilities of 3.2 and 2.6 x 10
-3
cm
2
/Vs,
4
comparable to
those found in low band gap semiconductors.
5-7
300 400 500 600 700 800 900
0.0
0.2
0.4
0.6
0.8
1.0
1.2
1.4
1.6
ε ε ε ε (x10
5
M
-1
cm
-1
)
Wavelength (nm)
Figure A3.2. Absorption spectra of THc in CH
2
Cl
2
.
213
The properties listed above make the THc molecule a promising alternative, to the
materials described in Appendix 2, for NIR-PDs. It has high absorptivity from 400-1400
nm, good charge transport properties and thin films can be prepared by either solution
processing or vapor deposition. To produce this molecule on a larger scale we will be
utilizing a procedure slightly modified from those previously published by Kubo et
al.(Figure A3.3).
2
Figure A3.3. Synthesis of THc. a) KOH; b) xylene, KMnO
4
; c) Cl
2
CHOCH
3
, TiCl
4
;
d) NaBH
4
; e) PBr
3
; f) CH
3
COOtBu; g) p-toluenesulfonic acid; h) (COCl)
2
, AlCl
3
; i)
NaBH
4
; j) p-toluenesulfonic acid; k) p-chloranil.
214
A3.2 Synthesis
THc was synthesized in 6 steps at 25% overall yield (Figure A3.3). First, an aldol
type reaction between acenaphthenequinone and 1,3-diphenylpropane-2-one was used to
give compound A3.1 in 93% yield. Second, a Diels-Alder reaction between A3.1 and
acenaphthylene followed by oxidation with KMnO
4
gave polycyclic aromatic
hydrocarbon A3.2.
8
In a key carbon-carbon bond formation step, formylation of A3.2 was
accomplished with dichloromethyl methyl ether and TiCl
4
catalyst similar to the reaction
used to synthesized the naphthalene linked diphenalenyl molecule, 4,13-di-tert-butyl-
8,9,17,18-tetraphenyldicyclopenta[b;g]naphthaleno[1,2,3-cd;6,7,8-c’d’]diphenalene.
9
The
Figure A3.4. The
1
H NMR (250 MHz) spectra of A3.3 in CDCl
3
. Inset: expansion
of the 8.75 to 8.90 ppm region of the spectra.
215
NMR of complex A3.3 is shown in Figure A3.4. From the inset of Figure A3.4, it can be
seen that a mixture of the 3,11- and 3,12-isomers of A3.3 are present. The integrated area
under the peaks indicates that one of the two isomers is favored by approximately a 4 to 1
ratio. The nature of the dominant isomer was not determined and the two isomers were
not isolated because the final product will be the same regardless of the stating isomer.
The dialdehyde complex A3.3 was then reduced with NaBH
4
and brominated with
PBr
3
to give A3.5 in 72% yield (2 steps). Nucleophilic substitution of A3.3 with tert-
butyl acetate in a lithium diisopropylamine solution followed by ester deprotection with
p-toluenesulfonic acid gave bis(propionic acid) compound A3.7 in 74% yield (2 steps).
Figure A3.5. The
1
H NMR (250 MHz) spectra of THc in CDCl
3
with peak
assignments from reference 2.
216
Intramolecular Friedel-Crafts cyclization with an excess of AlCl
3
was utilized in another
carbon-carbon bond forming step to give A3.8 in 90% yield. The diketone species, A3.8
was then reduced with NaBH4, dehydrated with p-toluenesulfonic acid and finally
oxidized with p-chloranil to give THc in 87% yield (3 steps).
The
1
H NMR (250 MHz) spectra of THc in CDCl
3
can be seen in Figure A3.5.
The peak shape and positions correspond closely with those previously reported by Kubo
et al. and the proton assignments in Figure A3.5 are based on their reports.
2
Significant
peak broadening is found for the non phenyl group protons, consistent with previous
reports of thermally accessible triplet state.
2,3
Thin films of THc were produced by both spincasting a 1% (w/w) solution in
dichloroethane and organic vapor phase deposition (OVPD) at a sublimation temperature
of 310°C. As can be seen in Figure A3.6 both methods produce similar absorption spectra
with a large absorption peaks at ~400 nm and broad absorption from 600 to 1500 nm.
The absorption coefficient at 400 nm of the OVPD filim was found to be nearly double
(7.6 x 10
4
cm
-1
) that of the spin cast solution (3.2 x 10
4
cm
-1
). The variations in
absorption coefficient may be due to molecular organization/orientation produced by the
two different methods. Powder x-ray diffraction would be required to better understand
the difference in film morphology of THc films produced from solution and gas phase.
Also variations in solution concentration and solvent may alter thin film organization and
increase the absorption coefficient.
The larger absorption coefficient for the OVPD grown film makes this the more
promising method for device fabrication. Preliminary PD fabrication consisting of a
device grown by OVPD consisting of THc donor layer and PTCDA or NTCDA acceptor
217
200 400 600 800 1000 1200 1400 1600 1800
-0.02
0.00
0.02
0.04
0.06
0.08
1.5x10
4
cm
-1
Absorption
Wavelength (nm)
3.2x10
4
cm
-1
25 nm THC @ 2k rpm
1% wt ratio in DCE
200 400 600 800 1000 1200 1400 1600
0.05
0.10
0.15
0.20
0.25
4.7x10
4
cm
-1
Absorption
Wavelength (nm)
7.6x10
4
cm
-1
35 nm THC film grown on ITO/glass in OVPD (@ 310 C)
Figure A3.6. Thin film absorption spectra of THc
produced by (a) spin casting and (b) organic vapor
phase deposition.
layers gave an external quantum efficiency of 0.01% however the results were not
readily reproducible. The origin of the lack of reproducibility is currently known. Further
investigation into film morphology and variations in the acceptor material are necessary
to utilize the broad NIR absorption of THc in NIR-PDs.
218
A3.3 Experimental Section
A3.3.1 General Information. All reported NMR spectra were obtained on a Bruker AC-
250 MHz FT NMR with all shifts relative to residual solvent signals. Solid probe mass
spectrometer (MS) spectra were taken with Hewlett-Packard MS instrument with electron
impact ionization and model 5973 mass selective detector. The UV-visible spectra were
recorded using a Hewlett-Packard 4853 diode array spectrophotometer.
Diphenylcyclopenta[a]acenaphthaylen-8-one (A3.1). A solution of 17.3 g (10mmol)
acenaphthenequinone, 20 g (95.0 mmol) 1,3-diphenylpropane-2-one in 100 mL ethanol
and 10 mL toluene were refluxed with rigorous stirring. To this solution 30 mL of KOH
saturated ethanol was added. The mixture was then refluxed for an additional 10 minutes.
The solution was cooled to 0°C with ice water and the precipitate collected by filtration.
The precipitate was then washed with ethanol. 31.5 g (93%), purple powder.
1
H NMR
(250 MHz, CDCl
3
, δ) .8.06 (d, J = 7.25 Hz, 2H), 7.91-7.79 (m, 6H), 7.64-7.47 (m, 6H),
7.45-7.35 (m, 2H).
7,14-diphenylacenaphtho[1,2-k]fluoranthene (A3.2). A solution of 5.8 g (30.4 mmol)
of 80% acenaphthylene, 12.0 g (33.6 mmol) A3.1 in 40 mL xylenes were refluxed under
nitrogen for 24 hours. Upon colling to room temperature 400 mL of ethanol was added
and the precipitate collected by filtration and washed with ethanol. The precipitate was
then dissolved in 320 mL benzene and 80 mL of acetone and refluxed under nitrogen.
KMnO
4
was then added slowly until the solution stays a light purple color. Upon cooling
to room temperature the precipitate was collected by filtration. The precipitate was then
219
run through a plug of silica gel eluting with CH
2
Cl
2
. The volume of CH
2
Cl
2
was then
reduced to 500 mL and washed with 500 mL H
2
O. The organic layer was rotary
evaporated to dryness. 14.0 g (97%), yellow powder.
1
H NMR (250 MHz, CDCl
3
, δ)
7.80-7.64 (m, 14H), 7.34 (t, J = 7.0 Hz, 4H), 6.74 (d, J = 7.0 Hz, 4H).
3,10/3,11-diformyl-7,14-diphenylacenaphtho[1,2-k]fluoranthene (A3.3) 4.8 mL (44
mmol) TiCl
4
was added to a solution of 1.0 g (2.09 mmol) A3.2 in 100 mL dry CH
2
Cl
2
.
To this solution 3 mL (33 mmol) of dichloromethyl methyl ether was added slowly. The
reaction was stirred at room temperature under nitrogen and monitored with TLC. The
reaction was discontinued after two days. The reaction was diluted with 100 ml CH
2
Cl
2
,
poured into 300 mL ice water followed by the addition 250 mL of 2 N HCl. The organic
layer was collected and the aqueous layer was extracted with CH
2
Cl
2
. The combine
organic layers were washed with sodium bicarbonate, brine and then dried with Na
2
SO
4
.
The organic layer was then rotary evaporated to dryness. The product (R
f
= 0.71) was
separated from 3-formyl-7,14-diphenylacenaphtho[1,2-k]fluoranthene (R
f
= 0.83) by
column chromatography on silica gel eluting with CH
2
Cl
2
. 1.01 g (90%), orange powder.
1
H NMR (250 MHz, CDCl
3
, δ) 10.3 (s, 2H), 8.82 (d, J = 8.5 Hz, 2H), 7.89-7.62 (m, 12H),
7.44 (t, J = 7.25 Hz, 2H), 6.78 (d, J = 7.25 Hz, 2H), 6.71 (d, J = 7.25 Hz, 2H).
3,10/3,11-bis(hydroxymethyl)-7,14-diphenylacenaphtho[1,2-k]fluoranthene (A3.4)
215 mg (5.62 mmol) NaBH
4
was added to a solution of 1 g (1.87 mmol) A3.3 in 270 mL
CH
2
Cl
2
and 110 mL ethanol. The mixture was stirred at room temperature under
nitrogen for 2 hours and then poured into 500 mL H
2
O followed by the addition 250 mL
220
of 2 N HCl. The organic layer was collected and the aqueous layer was extracted with
CH
2
Cl
2
. The combine organic layers were washed with sodium bicarbonate, brine and
then dried with Na
2
SO
4
. The organic layer was then rotary evaporated to dryness. 0.86 g
(85%), yellow powder.
1
H NMR (250 MHz, CDCl
3
, δ) 7.97 (d, J = 8.25 Hz, 2H), 7.84-
7.58 (m, 10H), 7.41-7.31 (m, 4H), 6.73 (d, J = 7.25 Hz, 2H), 6.67 (d, J = 7.25 Hz, 2H),
5.15 (s, 2H), 5.13 (s, 2H).
3,10/3,11-bis(bromomethyl)-7,14-diphenylacenaphtho[1,2-k]fluoranthene (A3.5) 0.5
mL (5.31 mmol) PBr
3
was added to a solution of 1 g (1.86 mmol) A3.4 in 300 mL
benzene. The mixture was heated to 95°C under nitrogen for 1.5 hours. The reaction was
cooled to room temperature, 200 mL of saturated sodium bicarbonate was added and the
organic layer was separated. The aqueous layer was extracted with benzene and the
combined organic layers were washed with brine, dried over Na
2
SO
4
and rotary
evaporated to dryness. 1.05 g (85%), yellow powder.
1
H NMR (250 MHz, CDCl
3
, δ) 7.96
(d, J = 8.25 Hz, 2H), 7.76-7.60 (m, 10H), 7.40 (dd, J = 8.25, 7.25 Hz, 2H), 7.34 (d, J =
7.25 Hz, 2H), 6.70 (d, J = 7.0 Hz, 2H), 6.60 (d, J = 7.0 Hz, 2H), 4.94 (s, 4H).
3,10/3,11-bis(2-butoxycarbonylethyl)-7,14-diphenylacenaphtho[1,2-k]fluoranthene
(A3.6) 1.86 g (16.8 mmol) of 97 % LDA in 200 mL of dry THF was cooled to -78C. To
this solution 3.7 mL (28.2 mmol) tert-butyl acetate was added and the mixture stirred for
1 hour. 2.52 g (3.81 mmol) of A3.5 was added to the solution and the mixture was
allowed to warm to -30°C over 2 hours. During this period the solution turned from
yellow to green in color. To the solution 300 mL of saturated NH
4
Cl was added and the
221
organic layer was separated. The aqueous layer was extracted with benzene and the
combined organic layers were washed with brine, dried over Na
2
SO
4
and rotary
evaporated to dryness. The product (R
f
= 0.43) was isolated by column chromatography
on silica gel eluting with benzene. 2.1 g (75%), yellow powder.
1
H NMR (250 MHz,
CDCl
3
, δ) 7.87 (d, J = 8.25 Hz, 2H), 7.78-7.61 (m, 10H), 7.35 (dd, J = 8.25, 7.25 Hz, 2H),
7.15 (d, J = 7.25 Hz, 2H), 6.71 (d, J = 7.25 Hz, 2H), 6.62 (d, J = 7.25 Hz, 2H), 3.35 (d, J
= 8.25 Hz, 4H), 2.62 (d, J = 8.25 Hz, 4H), 1.42 (s, 18H).
3,10/3,11-bis(2-carbonylethyl)-7,14-diphenylacenaphtho[1,2-k]fluoranthene (A3.7)
4.1 g (5.58 mmol) of A3.6 was dissolved in 300 ml of benzene and refluxed under N
2
. A
catalytic amount (100 mg) of p-toluene sulfonic acid monohydrate was added and the
mixture was refluxed for 3 hours. The solution was rotary evaporated to dryness and the
powder washed with sodium bicarbonate, water, hexane and benzene. 3.47 g (99%),
yellow powder.
1
H NMR (250 MHz, DMSO, δ) 7.98 (d, J = 8.25 Hz, 2H), 7.86-7.61 (m,
10H), 7.43 (t, J = 7.25 Hz, 2H), 7.24 (d, J = 7.5 Hz, 2H), 6.62 (d, J = 7.25 Hz, 2H), 6.52
(d, J = 7.25 Hz, 2H), 2.59 (t, J = 7.5 Hz, 4H).
3,4,5,11,12,13-hexahydro-3,11-/-3,13-dioxo-8,16-diphenyl-s-indaceno[1,2,3-cd:5,6,7-
c’d’]diphenalene. (A3.8) 800 mg (1.29 mmol) of A3.7 was refluxed under N2 in 5 ml
oxalyl chloride. The solvent was then removed under reduced pressure. The residue was
dissolved in 120 ml of dry CH
2
Cl
2
and cooled to -78°C. 1.5 g (11.3 mmol) of AlCl
3
was
added to the solution and allowed to warm to -30°C over 2 hours. During this time the
solution turned from yellow to dark orange. The mixture was poured into ice water
222
followed by the addition of 1 N HCl. The organic layer was collected and the aqueous
layer was extracted with CH
2
Cl
2
. The combine organic layers were washed with sodium
bicarbonate, brine and then dried with Na
2
SO
4
. The product (R
f
= 0.71) was isolated by
column chromatography on silica gel eluting with benzene:THF (4:1). 0.700 g (90%),
orange powder.
1
H NMR (250 MHz, CDCl
3
, δ) 7.97 (d, J = 7.5 Hz, 2H), 7.84-7.62 (m,
10H), 7.23 (d, J = 7.25 Hz, 2H), 6.82 (d, J = 7.25 Hz, 2H), 6.69 (d, J = 7.25 Hz, 2H),
3.44 (t, J = 7.25 Hz, 4H), 3.0 (t, J = 7.25 Hz, 4H).
3,4,5,11,12,13-hexahydro-3,11-/-3,13-dihydroxy-8,16-diphenyl-s-indaceno[1,2,3-
cd:5,6,7-c’d’]diphenalene. (A3.9) 133 mg (3.57 mmol) NaBH
4
was added to a solution
of 700 mg (1.19 mmol) A3.8 in 90 mL CH
2
Cl
2
and 35 mL ethanol. The mixture was
stirred at room temperature under nitrogen for 2 hours and then poured into H
2
O followed
by the addition 1 N HCl. The organic layer was collected and the aqueous layer was
extracted with CH
2
Cl
2
. The combine organic layers were washed with brine and then
dried with Na
2
SO
4
. The product (R
f
= 0.4) was isolated by column chromatography on
silica gel eluting with hexane:ethylacetate (1:1). 0.650 g (93%), orange powder.
1
H NMR
250 MHz, CDCl
3
, δ) 7.76-7.64 (m, 10H), 7.38 (d, J = 7.25 Hz, 2H), 7.10 (d, J = 7.25 Hz,
2H), 6.73 (d, J = 7.25 Hz, 2H), 6.65 (d, J = 7.25 Hz, 2H), 5.15-5.05 (m, 2H), 3.51-2.74
(m, 4H), 2.41-2.07 (m, 4H), 1.74 (d, J = 6.0 Hz, 2H).
3,11-/-3,13-dihydro-8,16-diphenyl-s-indaceno[1,2,3-cd:5,6,7-c’d’]diphenalene.
(A3.10) 200 mg (0.34 mmol) of A3.9 was dissolved in 70 ml of benzene and refluxed
under N
2
. A catalytic amount (10 mg) of p-toluene sulfonic acid monohydrate was added
223
and the mixture was refluxed for 30 minutes. The product (R
f
= 0.46) was isolated by
column chromatography on silica gel eluting with hexane:benzene (2:1). 180 mg (95%),
yellow powder.
1
H NMR 250 MHz, CDCl
3
, δ) 7.74-7.64 (m, 10H), 7.17 (d, J = 7.0 Hz,
2H), 6.94 (d, J = 7.0 Hz, 2H), 6.81-6.66 (m, 6H), 6.31-6.16 (m, 2H), 3.91-3.80 (m, 4H).
8,16-diphenyl-s-indaceno[1,2,3-cd:5,6,7-c’d’]diphenalene. (THc) 180 mg (0.32 mmol)
of A3.10 was dissolved in 70 ml of benzene and refluxed under N
2
. 80 mg of p-chloranil
was added and the mixture was refluxed for 30 minutes. The reaction was cooled to room
temperature. The solution was then passed through a plug of silica gel eluting
hexane:CH
2
Cl
2
(1:4). The solution was then rotary evaporated and passed through a
second column eluting with the same solvent. 180 mg (99%), black powder. The product
was further purified by sublimation (T = 320-325°C).
1
H NMR 250 MHz, CDCl
3
, δ)
7.59-7.47 (m, 10H), 7.17-6.84 (m, 6H), 6.82-6.57 (m, 4H), 5.74-5.65 (m, 4H). MS m/z:
552.
224
Appendix 3 References
(1) Platz, M. S. Diradicals (Ed.: W. T. Borden), Wiley, New York, 1982.
(2) Kubo, T.; Shimizu, A.; Sakamoto, M.; Uruichi, M.; Yakushi, K.; Nakano, M.;
Shiomi, D.; Sato, K.; Takui, T.; Morita, Y.; Nakasuji, K. Angew. Chem. Int. Ed.
2005, 44, 6564-6568.
(3) Ohashi, K.; Kubo, T.; Masui, T.; Yamamoto, K.; Nakasuji, K.; Takui, T.; Kai, Y.;
Murata, I. J. Am. Chem. Soc. 1998, 120, 2018-2027.
(4) Chikamatsu, M.; Mikami, T.; Chisaka, J.; Yoshida, Y.; Azumi, R.; Yase, K.;
Shimizu, A.; Kubo, T.; Morita, Y.; Nakasuji, K. Applied Physics Letters 2007, 91,
043506.
(5) Meijer, E. J.; de Leeuw, D. M.; Setayesh, S.; van Veenendaal, E.; Huisman, B. H.;
Blom, P. W. M.; Hummelen, J. C.; Scherf, U.; Klapwijk, T. M. Nat. Mater. 2003,
2, 678.
(6) Anthopoulos, T. D.; Setayesh, S.; Smits, E.; Colle, M.; Cantatore, E.; de Boer, B.;
Blom, P. W. M.; de Leeuw, D. M.; Adv. Mater. 2006, 18, 1900.
(7) Yasuda, T.; Tsutsui, T.; Jpn. J. Appl. Phys. Part 2 2006, 45, L595.
(8) Wehmeier, M.; wagner, M.; Mullen, K. Chem. Eur. J. 2001, 7(10), 2197-2205.
(9) Kubo, T.; Shimizu, A.; Uruichi, M.; Yakushi, K.; Nakano, M.; Shiomi, D.; Sato,
K.; Takui, T.; Morita, Y.; Nakasuji, K. Organic Letters 2007, 9(1) 81-84.
225
APPENDIX 4: The Synthesis of PbS Quantum Dots
A4.1 Introduction
The near-infrared photodetectors (NIR-PDs) described in Appendix 2 and 3 are
composed of organic molecules that absorb light between 400-1400 nm with detectivities
(D*) greater than 10
10
cm Hz
1/2
W
-1
. For some applications, extending the spectral width
from 400-1400 nm to 400-1900 nm is of particular interest.
1
The efficiency of exciton
dissociation to yield an electrical signal in PDs is strongly dependent on the lifetime of
the photo generated excited state, which are dependent on the non-radiative decay
processes. High non-radiative rates decrease exciton lifetimes and thus reduce device
performance. The most common non-radiative relaxation process in organic molecules is
through covalent bond vibrations. The excited state energies at 1900 nm are close to the
overtones of the principle vibrations in C-C and C-H bonds.
2
Thus the excited state
energy is readily transferred into bond vibrations and is lost as heat rather than the
excition dissociation. Extending absorption from 1400 to 1900 nm in PDs may be
inherently difficult with organic molecules due to these fundamental non-radiative decay
processes.
An alternative approach to using organic molecules in PD devices is to use
inorganic materials, namely quantum dots (QDs). Several NIR-PDs have been produced
using PbS QDs as the chromophoric material. For example, by spin casting PbS QDs on
gold electrodes, detectivities greater than 1 x 10
13
cm Hz
1/2
W
-1
from 400 to 1400 nm have
been achieved with high operating voltages (40 V) and long carrier lifetimes (70 ms)
which are not optimum for imaging applications.
3
The operating voltage and carrier
lifetime can be reduced by the addition of polymer to the QDs or by post-processing film
226
treatments, however the most red-shifted absorption of these devices is only out to ~1700
nm.
4,5
The wavelength of absorption in the devices mentioned above is related to the
size of the PbS QDs used to prepare the thin films. PbS QDs of a diameter smaller than
the excition radius in bulk PbS (~50 nm) will have absorption blue shifted relative to that
of bulk PbS (3024 nm) with a shift proportional to the size of the particle.
6
This is a
phenomena observed with QDs known as the quantum confinement effect.
7
Since the
particles used above (d = 4-6 nm) have absorptions ranging from 1400-1700 nm this
effect can be used to produce larger particles (~8 nm) and as a result NIR-PDs that absorb
out to 1900 nm may be achieved.
9
A large range of synthetic methods are available to produce quantum dots
including but not limited to physical methods such as molecular-beam epitaxial growth
8
and sonication of bulk semiconductors,
10
or templating methods using zeolites,
11,12
clays
13
, glasses
14,15
or a polymer matrix.
16,17
as a medium for controlled growth.
However for the sake of synthetic simplicity, scale and surface functionalization, the PbS
quantum dots utilized for the devices mentioned above were synthesized in solution in
the presents of a surfactant. The general synthesis of PbS QDs can be seen in Figure A4.1.
In this reaction lead(II) oxide and bis(trimethylsilyl)sulfide ((TMS)
2
S) are used as
the lead and sulfur sources respectively. The choice of solvent and stabilizing agent is
important to control both the nucleation event and the subsequent particle growth. Oleic
Figure A4.1. General synthesis of PbS quantum dots.
227
acid and octadecene have been found to serve well in this capacity. In a standard reaction,
PbO readily dissolves in a heated solution of oleic acid and octadecene to give the lead
oleate precursor. Upon injection of (TMS)
2
S, rapid nucleation occurs as indicated by the
color change from a clear yellow to brown solution. The solution is then cooled and the
PbS QDs can be isolate by successive precipitation steps.
6
There are several methods for varying particle size and size distribution by
changing reaction conditions. For example, variations in olecic acid concentration have
been shown to alter monomer reactivity and thus can be used to control both QD size and
size distribution.
18
Herein we report the changes in absorption (particle size) of PbS QDs
with respect to variations in reaction time and temperature in the reaction shown in
Figure A4.1.
A4.2 Synthesis
The PbS QDs were synthesized following the general procedure outline by Hines
and Scholes.
6
In a standard reaction, 0.9g (4 mmol) of PbO, 3 ml (9.5 mmol) of oleic acid
and 6 ml octadecene were placed in a 15 ml three-neck flask fitted with a reflux
condenser. The solution was heated to 100°C under vacuum for 2 hours followed by
bubbling with nitrogen. The solution temperature was then varied between 100 and
225°C. A solution of (TMS)
2
S in octadecene was then prepared. In a 3 ml syringe, 2 ml
of octadecene was taken up followed by 0.419 ml (TMS)
2
S. When the PbO solution
temperature was stabilized, the (TMS)
2
S solution was added via syringe as quickly as
possible. Immediately after injection the solution changes from yellow to brown. The
mixture was then allowed to react at the given temperature and then quickly submerged
228
in an ice bath after the desired amount of reaction time. Upon cooling to room
temperature the reaction mixture was diluted with toluene (~50 ml) and transferred to two
50 ml centrifuge tubes. Acetone was then added until the solutions reached the total
volume in each vial was 50 ml, the tubes were shaken vigorously and centrifuged for 5-
15 min. The supernatant was poured off and the remaining precipitate dissolved in 25 ml
toluene followed by the addition of acetone, rigorous shaking and centrifugation. The
entire process of solvation and precipitation was repeated a total of three times. The final
precipitate was suspended in toluene and the absorbance from 700 to 2400 nm was
measured. The variations in the absorption spectra of PbS QDs with respect to changes in
time and temperature can be seen in Figure 4A.2.
The standard reaction described above was repeated several times, with
temperatures maintained as 120°C and the reaction discontinued after 0.17, 0.5 1, 2, 5
and 10 minutes. As can be seen in Figure 4A.2a the absorption maxima of the QDs
gradually shifts from 850 nm at 10 seconds to 1100 nm at five minutes, with no visible
800 900 1000 1100 1200 1300 1400 1500 1600
0.0
0.1
0.2
0.3
0.4
0.5
0.6
10m
5m
2m
1m
30s
Absorption (a.u.)
Wavelength (nm)
10s
700 800 900 1000 1100 1200 1300 1400 1500 1600
0.0
0.1
0.2
0.3
0.4
100 C
120 C
150 C
200 C
Absorption (a.u.)
Wavelength (nm)
Figure 4A.2. PbS quantum dot absorption spectra of reaction products (a) maintained
at 120°C with various reaction times and (b) with various reaction temperatures at a
consistent 30 second reaction time.
a b
229
peak present at 10 min. It is clear that longer reaction times results in red shifted
absorption and thus larger PbS QDs are formed.
19
In addition to an increased particle size,
a gradual peak sharpening followed by peak broadening with time can also be seen, with
the sharpest peak at approximately 2 minutes. The peak width of the absorption maxima
are directly associated with the size-distribution of the nanoparticles in solution.
20
Similar
behavior has been observed and extensively studied with CdSe QDs.
21
In the reaction
solution, nucleation takes place rapidly after injection and growth continues until a
critical size is reached where the monomer concentration and the solubility of the
nanocrystals is in equilibrium. Particles under the critical size grow faster than the larger
ones, thus an average particle size narrowing (focusing) is observed. After the monomer
is completely consumed, the distribution broadens (defocusing) in a process known as
Ostwald ripening where the small particles shrink, while the larger particles continue to
grow.
22
This behavior is consistent with the absorption spectra in Figure 4A.2a. First
focusing and red shifting absorption is observed up to 1 minute followed by defocusing
and broadening until no peak is observed after 10 minutes.
The standard reaction described above was also repeated several times at
temperatures of 100, 120, 150 and 200°C with reaction times held constant at 30 seconds.
The PbS QD absorption spectra with respect to reaction temperature can be seen in
Figure 4A.2b. Absorption maxima of 830, 880, 1160 and 1390 nm were found for
reaction temperatures of 100, 120, 150 and 200°C respectively. The QDs exhibit a clear
red shift in absorption and an increase in particle size with increasing reaction
temperatures.
230
To reach the absorption goal of ~1900 nm a combination of both increased
reaction temperature and time was employed. The absorption spectra of PbS QDs
produced by running the standard reaction described above at 225°C for 20 sec. The
absorption maxima for this solution is ~1500 nm with broad absorption out to more than
1900 nm. Approximately 500 mg of PbS QDs prepared by this method were sent to our
collaborators in the Forrest research group at the University of Michigan, Ann Arbor.
Future work on this material will include the production of NIR-PDs similar to those
devices previous published which employ a PbS QD spun cast film as the chromophoric
material.
4,5
A4.3 Experimental Section
General Information. UV/Vis - NIR spectra were recorded on a Olis CARY 14
spectrophotometer. All spectra were measured as solutions in toluene at room
temperature using a 1 cm cell.
900 1200 1500 1800 2100 2400
0.00
0.01
0.02
0.03
0.04
0.05
Absorption (a.u.)
Wavelength (nm)
Figure 4A.3. PbS quantum dot absorption spectra
of reaction run at 225°C for 20 sec.
231
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1995, 16, 1617-1618.
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1559-1564.
(15) Takada, T.; Li, C.; Tseng, J. Y.; Mackenzie, J. D. Journal of Sol-Gel Science and
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232
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Nedeljkovic, J. M. Chemical Physics Letters 2000, 329, 168-172.
(18) Yu, W. W.; Peng, X. Angew. Chem. Int. Ed. 2002, 41, 2368.
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Abstract (if available)
Abstract
The light emitting and absorbing small molecules are interesting for many applications ranging from solar energy conversion to photodynamic therapy. There are many variables that contribute to the intensity, energy and efficiency of absorption and emission including the HOMO/LUMO energy levels, molar absorptivities, excited state lifetimes, geometry changes in the excited state, radiative and nonradiative rates, and others. One of the fundamental goals of photophysical chemists is to understand how molecular structure correlates with these properties. Once structure-property relationships are understood, new molecules can be designed with particular applications in mind. In this thesis, the synthesis, electrochemical and photophysical properties 1,3-bis(2-pyridylimino)isoindoline (BPI) derivatives will be reported and structure property relationships discussed.
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University of Southern California Dissertations and Theses
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Asset Metadata
Creator
Hanson, Kenneth
(author)
Core Title
Synthesis, photophysical and electrochemical characterization of 1,3-bis(2-pyridylimino)isoindole derivatives
School
College of Letters, Arts and Sciences
Degree
Doctor of Philosophy
Degree Program
Chemistry
Publication Date
06/04/2012
Defense Date
06/03/2010
Publisher
University of Southern California
(original),
University of Southern California. Libraries
(digital)
Tag
(BPI)PtCl,1,3-bis(2-pyridylimino)isoindole,ESIPT,OAI-PMH Harvest,phosphorescence
Language
English
Contributor
Electronically uploaded by the author
(provenance)
Advisor
Thompson, Mark E. (
committee chair
), Brutchey, Richard L. (
committee member
), Willner, Alan E. (
committee member
)
Creator Email
kghanson@usc.edu,vastib21@usc.edu
Permanent Link (DOI)
https://doi.org/10.25549/usctheses-m3112
Unique identifier
UC159232
Identifier
etd-Hanson-3692 (filename),usctheses-m40 (legacy collection record id),usctheses-c127-347605 (legacy record id),usctheses-m3112 (legacy record id)
Legacy Identifier
etd-Hanson-3692.pdf
Dmrecord
347605
Document Type
Dissertation
Rights
Hanson, Kenneth
Type
texts
Source
University of Southern California
(contributing entity),
University of Southern California Dissertations and Theses
(collection)
Repository Name
Libraries, University of Southern California
Repository Location
Los Angeles, California
Repository Email
cisadmin@lib.usc.edu
Tags
(BPI)PtCl
1,3-bis(2-pyridylimino)isoindole
ESIPT
phosphorescence