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Photophysical properties of luminescent iridium and coinage metal complexes

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Photophysical properties of luminescent iridium and coinage metal complexes

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PHOTOPHYSICAL PROPERTIES OF LUMINESCENT IRIDIUM AND COINAGE METAL
COMPLEXES

by

Savannah C. Kapper

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

December 2021

Copyright 2021 Savannah C. Kapper
ii

Dedication

I would like to dedicate this thesis to the little family I built during my time in L.A.
iii

Acknowledgements
I would, first and foremost, like to thank my advisor, Prof. Mark Thompson, for not only
giving me the opportunity to be a part of his lab but for being an exemplary model of what it means
to be a mentor. His compassion and understanding are truly unmatched and something every
mentor should strive to emulate. I would particularly like to thank Prof. Thompson for fostering a
lab environment where labmates came to feel more like family than colleagues.
I would like to thank Judy Fong for all the help she has provided to me over the years. She
is such an instrumental part of our lab and to say we would all be lost without her assistance and
guidance is nothing short of the truth. If that wasn’t enough, Judy became a rock for many of us
during the coronavirus pandemic. She made sure to attend many of the virtual events our lab held
during the quarantine and brought some normalcy to such an abnormal time in our lives. She
always managed to take care of us even if that meant sending us virtual fruit to further our progress
in a video game.
I would like to thank Peter Djurovich who was a great source of help during my Ph.D.
program. His love of science is apparent and inspiring. Whenever I had an exciting result, Peter
was always the first person I told as I could always count on him to match my level of excitement.
I also appreciated him telling me when I was being too hard on myself.
I would like to thank my screening and qualifying members, Dr. Ralf Haiges, Prof. Sri
Narayan, Prof. Travis Williams, and Prof. Ravichandran for not only their time but their
suggestions with how to move forward with my projects. A special thanks to Prof. Ravichandron
and Prof. Marinescu who served on my defense committee. I would also like to thank Smaranda
iv

Marinescu who was my mentor for the Burg Fellowship where I had the opportunity to teach
CHEM 453 Inorganic Chemistry as a lecturer.
My Ph.D. would not have been possible without the support I received from both past and
present group members. Firstly, I would like to thank the senior students who not only trained me
on various techniques and instruments but offered me guidance throughout my program. These
colleagues include Dr. Muazzam Idris, Prof. Denise Femia, Dr. Rasha Hamze, Dr. Rebecca
Wilson, Dr. Thilini Batagoda, Dr. Patrick Saris, Dr. Shuyang Shi, Dr. John Facendola, Dr. John
Chen, Prof. Tian-yi Li, and Dr. Jessica Golden. I would also like to thank current group members
who have been a great source of support and friendship during my time at USC, including Jie Ma,
Moon Chul Jung, Austin Mencke, Jonas Schaab, Yang Goh, Megan Cassingham, and James
Fortwengler. Additionally, I would like to thank Dr. Abegail Tadle and Dr. Daniel Sylvinson
Muthiah Ravinson who joined the lab at the same as me. I couldn’t have asked for better people to
have gone on this journey with and I am thankful to call you both my friends. A special thanks to
my incredible hoodmates, Dr. Narcisse Ukwitegetse and Konstantin Mallon who were always
understanding, kind, and willing to help.
I have had the privilege of working with several amazing collaborators over the years.
These collaborators include Dr. JoAnna Milam-Guerrero, Dr. Laura Estergreen, Dr. Po Ling
Cheung (UCSD-Kubiak), Dr. Maria Naumova (DESY), and Dr. Jessie Peltier (UCSD-Bertrand).
My Ph.D. experience would not have been the same without my fiancé, Martin Torres, who
has been a part of this journey from the beginning. He not only encouraged me to go to graduate
school but uprooted his entire life to move halfway across the country in sake of that pursuit. His
outside perspective kept me grounded and helped shaped some of the best decisions I made in
v

graduate school. I would also like to thank our dog, Luna, and our two cats, Olive and Milo, who
kept me sane during my Ph.D. program.
A special thanks to my immediate family, Daniel, Laura, and Bailey Kapper, who always
supported my ambitions. I would also like to thank my extended family, Michelle, Lance, and
Alexandra Yelton, who welcomed Martin and I into their home with open arms. When we couldn’t
make it home for the holidays, they always made sure that we knew we were welcome to spend
the holidays with them. I would like to thank my Grandma and Grandpa Covey for their
unwavering support and belief that I could do anything I set my mind to. I would also like to thank
Martin’s family who have come to feel like my own.
Last but not least, I would like to thank my friends. I want to thank Caroline Lamb and
Sarah Banister who I met during my undergraduate studies. I know I can always count on them to
be there when I need moral support or to destress with a video game. I would also like to thank
those who I met along my Ph.D. journey, such as Dr. Caroline Black and Sanket Samal who I am
so lucky to call my friends.

vi

Table of Contents
Dedication ....................................................................................................................................... ii

Acknowledgements ........................................................................................................................ iii

List of Tables ................................................................................................................................. ix

List of Figures ................................................................................................................................. x

List of Schemes ............................................................................................................................. xv

Abstract ........................................................................................................................................ xvi

Chapter 1. Introduction ................................................................................................................... 1
1.1. Organic Light-Emitting Diodes ........................................................................................ 1
1.2. Jablonski diagram ............................................................................................................. 1
1.3. Iridium emitters ................................................................................................................ 2
1.4. Copper Emitters.............................................................................................................. 10
1.5. Boltzmann models .......................................................................................................... 16
1.6. Use of dopant materials as visible light photocatalysts.................................................. 17
1.7. References ...................................................................................................................... 21

Chapter 2. Phosphorescent Bis-cyclometalated Iridium Complexes Containing Bis-oxazoline
Derived Ancillary Ligands ............................................................................................................ 25
2.1. Introduction .................................................................................................................... 25
2.2. Results and Discussion ................................................................................................... 27
2.3. Experimental .................................................................................................................. 38
2.3.1. Synthesis ................................................................................................................. 38
2.3.2. NMR spectra ........................................................................................................... 44
2.3.3. X-ray Crystallography Studies ................................................................................ 54
2.3.4. Laser desorption/ionization time of flight (LDI-TOF) ........................................... 56
2.3.5. Thermal Gravimetric Analysis (TGA) .................................................................... 60
vii

2.3.6. Theoretical Calculations ......................................................................................... 60
2.3.7. Electrochemistry ..................................................................................................... 65
2.3.8. Photophysics ........................................................................................................... 68
2.4. Conclusion ...................................................................................................................... 74
2.5. References-Chapter 2 ..................................................................................................... 74

Chapter 3. Reducing nonradiative decay pathways in thiazole copper (I) complexes ................. 77
3.1. Introduction .................................................................................................................... 77
3.2. Results and Discussion ................................................................................................... 80
3.3. Experimental .................................................................................................................. 94
3.3.1. NMR spectra ........................................................................................................... 99
3.3.2. Photophysical characterization ............................................................................. 104
3.3.3. Electrochemistry ................................................................................................... 105
3.4. Conclusion .................................................................................................................... 107
3.5. Acknowledgements ...................................................................................................... 108
3.6. References-Chapter 3 ................................................................................................... 108

Chapter 4. Temperature and Magnetic Field Dependence on the Lifetime and Emission Spectra
using an Optical Probe ................................................................................................................ 110
4.1. Introduction .................................................................................................................. 110
4.2. Results and Discussion ................................................................................................. 111
4.2.1. 2 wt% fac-Ir(ppy)3 in polystyrene film ................................................................. 121
4.2.2. 2 wt% MACAuCz in polystyrene film ................................................................. 122
4.3. Future modifications to the probe ................................................................................ 118
4.4. Future work .................................................................................................................. 119
4.5. References-Chapter 4 ................................................................................................... 119

Chapter 5. Using Stern-Volmer quenching studies to screen novel photoredox catalysts ......... 120
5.1. Introduction .................................................................................................................. 120
5.2. Results and Discussion ................................................................................................. 121
5.2.1. Stern-Volmer quenching studies ........................................................................... 121
5.2.2. Oxidative electron transfer quenching of CAACCuCz ........................................ 122
viii

5.2.3. Reductive electron transfer quenching of CAACCuCz ........................................ 125
5.2.4. Stern-Volmer quenching studies of fac-Ir(tpz)3 .................................................... 128
5.3. Experimental ................................................................................................................ 130
5.4. References-Chapter 5 ................................................................................................... 133

Appendix A. Phenyl bis-oxazoline as an ancillary ligand for bis-cyclometalated iridium
complexes ................................................................................................................................... 135
A.1. Introduction .................................................................................................................. 135
A.2. Results and Discussion ................................................................................................. 135
A.2.1. Photophysics .......................................................................................................... 135
A.2.2. Electrochemistry .................................................................................................... 138
A.2.3. Calculations ........................................................................................................... 138
A.3. Experimental ................................................................................................................ 139
Synthesis .............................................................................................................................. 139
A.4. Conclusion .................................................................................................................... 142
A.5. References- Appendix A .............................................................................................. 143

Appendix B. Design and use of the Physical Properties Measurement System (PPMS) .......... 144
B.1. Introduction .................................................................................................................. 144
B.2. Probe design ................................................................................................................. 144
B.3. First iterations ............................................................................................................... 135
B.4. Current interation of the optical probe ......................................................................... 138
B.5. Set ups........................................................................................................................... 138
B.5.1. Experimental ............................................................................................................ 139
B.5.2. Lifetime Collection .................................................................................................. 139
B.6. Data collected outside PPMS ....................................................................................... 142

ix

List of Tables
Table 1. Commonly used visible light photocatalysts compiled by MacMillan et. al.
36
This table
was modified to fit the page. ......................................................................................................... 18
Table 2. Bond lengths for 3
Δ
(left) and 3
Λ
.................................................................................... 29
Table 3. Electrochemistry of complexes 1-4
Δ,Λ
in DMF. ............................................................. 33
Table 4. Photophysical properties of complexes 1-4 in 2Me-THF. ............................................. 36
Table 5. Photophysics of 2
Δ,Λ
in various solvents. ....................................................................... 68
Table 6. Photophysics of 3
Δ
in various solvents. ......................................................................... 69
Table 7. Photophysics of 3
Λ
in various solvents. ......................................................................... 70
Table 8. Photophysics of 3RR
Δ
in various solvents. ...................................................................... 71
Table 9. Photophysics of 3RR
Λ
in various solvents. ...................................................................... 72
Table 10. Photophysics of 4
Δ,Λ
in various solvents. ..................................................................... 73
Table 11. Crystallographic structure information for 1................................................................ 82
Table 12. Calculated HOMO and LUMO values. The thiazole-copper-carbazole bond angle for
the geometry optimized ground state is also shown. .................................................................... 84
Table 13. Electrochemical measurements for complexes (Thia)Cu(XCz) complexes in DMF vs
Fc................................................................................................................................................... 88
Table 14. Photophysical characterization of (Thia)Cu(XCz) complexes in 2Me-THF, MeCy, and
1 wt% in PS. .................................................................................................................................. 92
Table 15. Photophysical data of 1-Ph in 2Me-THF, MeCy, and 1 wt% in PS film. ................... 94
Table 16. Two- and three-level fits of the variable temperature lifetime data for a 2 wt%
MACAuCz in PS film. ................................................................................................................ 117
Table 17. Quenching constants of various oxidative quenchers for CAACCuCz in THF......... 124
Table 18. Quenching constants of various reductive quenchers for CAACCuCz in THF......... 127
Table 19. Quenching constants of various reductive quenchers for fac-Ir(tpz)3 in toluene. ...... 129
Table 20. Quenching constants of various reductive quenchers for CAACCuCz in THF......... 130
Table 21. Quenching rate constants (kq) for MACCuCz and CAACCuCz using 1,2,4,5-
tetracyanobenzene as a quencher. ............................................................................................... 131
Table 22. Quenching rate constants (kq) for MACCuCz and CAACCuCz using BIH as a
quencher. ..................................................................................................................................... 132
Table 23. Photophysics of (ppy)2Ir(BOX) complexes in 2Me-THF. ......................................... 136
Table 24. Photophysics of (C^N)Ir(BOX-Ph) complexes in 2Me-THF. ................................... 137
Table 25. Oxidation and reduction potentials for (ppy)2Ir(BOX) complexes. ........................... 138

x

List of Figures
Figure 1. Simplified device structure of an OLED. ....................................................................... 1
Figure 2. A Jablonski diagram. ...................................................................................................... 2
Figure 3. The HOMO (a), LUMO (b), and triplet spin-density (c) calculations for a well-known
green emitter, fac-Ir(ppy)3 using B3LP/LACVP**. The various substitution positions are shown
in the HOMO picture. ..................................................................................................................... 4
Figure 4. Blue-shifting of homoleptic iridium complexes. ............................................................ 5
Figure 5. NHC Iridium Carbene Complexes synthesized in our group. ........................................ 6
Figure 6. Jablonski diagram of fac-Ir(ppz)3 versus fac-Ir(C^C:)3 complexes.
3
............................. 7
Figure 7. Red-shifting of homoleptic iridium complexes.
28
.......................................................... 8
Figure 8. Jahn-Teller distortion brought about by the excitation of a 4-coordinate copper
complex. ........................................................................................................................................ 11
Figure 9. Jablonski diagram depicting TADF.
31
.......................................................................... 12
Figure 10. DFT calculations of HOMO (solid) and LUMO (opaque) for CAACCuCz obtained
using B3LYP/LACVP**.
31
........................................................................................................... 13
Figure 11. Types of distortions that can occur in coinage metal complexes.
32
............................ 14
Figure 12. DFT calculations of HOMO (left) and LUMO (right) for MACCuCz obtained using
B3LYP/LACVP*. ......................................................................................................................... 14
Figure 13. Blue-shifting of 2-coordinate coinage metal complexes. ........................................... 15
Figure 14. A Jablonksi diagram showing the splitting of the singlet and triplet sublevels with
weak and strong SOC.................................................................................................................... 17
Figure 15. A Jablonski diagram of a Ir visible light photocatalyst explaining how the material
can act as both an oxidant and a reductant in the excited state. .................................................... 19
Figure 16. Oxidative (left) and reductive (right) quenching of the photocatalyst by a quencher. 20
Figure 17. The impact of static and dynamic quenching as a function of quencher
concentration.
36
............................................................................................................................. 21
Figure 18. Crystal structure of 3
Δ
(left) and 3
Λ
(right). Hydrogens were omitted for clarity. ..... 28
Figure 19. LDI-TOF of 3
Δ
. ........................................................................................................... 30
Figure 20.
1
H-NMRs for acid-induced degradation of (ppy)2Ir(acac) using 0.2 M HCl in ether. 31
Figure 21.
1
H-NMRs for acid-induced degradation of 3
Δ,Λ
using 0.2 M HCl in ether. ............... 31
Figure 22. TGA of 3
Δ
versus (ppy)2Ir(acac). ................................................................................ 32
Figure 23: Molar absorptivity of complexes 1-4
Δ,Λ
in 2Me-THF. ............................................... 34
Figure 24. Emission of complexes 1a-5b in 2Me-THF at (left) RT and (right) 77 K. ................. 37
Figure 25. Circular dichroism of 3SS
Δ
,3SS
Λ
, 3RR
Δ
, and 3RR
Λ
in CH2Cl2. ...................................... 37
Figure 26. Synthesis of BOXSS-CN.
26-27
...................................................................................... 39
Figure 27. NMRs of BOXSS-H, BOXSS-CN, BOXRR-CN, and the BOXSS-CN purchased from
Sigma Aldrich. .............................................................................................................................. 44
Figure 28.
1
H-NMR of 1
Δ,Λ
in d6-acetone with minor impurity of one diastereomer. ................. 45
Figure 29.
13
C-NMR of 1
Δ,Λ
in d6-acetone. .................................................................................. 45
Figure 30.
1
H-NMR of 2
Δ,Λ
in d6-acetone. ................................................................................... 46
Figure 31.
13
C-NMR of 2
Δ,Λ
in d6-acetone. .................................................................................. 46
Figure 32.
1
H-NMR of 3
Δ
in d6-acetone. ..................................................................................... 47
xi

Figure 33.
13
C-NMR of 3
Δ
in d6-acetone ..................................................................................... 47
Figure 34. COSY NMR of 3
Δ
in d6-acetone. ............................................................................... 48
Figure 35.
1
H-NMR of 3
Λ
in d6-acetone. ..................................................................................... 48
Figure 36.
13
C-NMR of 3
Λ
in d6-acetone. .................................................................................... 49
Figure 37. COSY-NMR of 3
Λ
in d6-acetone (from 3.6 ppm to 9.0 ppm). ................................... 49
Figure 38.
1
H-NMR of 4
Λ, Λ
in d6-acetone. .................................................................................. 50
Figure 39.
13
C-NMR of 4
Λ, Λ
in d6-acetone. ................................................................................. 50
Figure 40. COSY-NMR of 4
Λ, Λ
in d6-acetone. ............................................................................ 51
Figure 41.
1
H-NMR of 3RR
Δ
in d6-acetone. .................................................................................. 51
Figure 42.
13
C-NMR of 3RR
Δ
in d6-acetone. ................................................................................. 52
Figure 43.
1
H-NMR of 3RR
Λ
in d6-acetone. .................................................................................. 52
Figure 44.
13
C-NMR of 3RR
Λ
in d6-acetone. ................................................................................. 53
Figure 45. Crystal structures of 3
Δ
and 3
Λ
. .................................................................................. 54
Figure 46. LDI-TOF of 1
Δ,Λ
. ........................................................................................................ 56
Figure 47. LDI-TOF of FIrpic. ..................................................................................................... 56
Figure 48. LDI-TOF of 2
Δ,Λ
. ........................................................................................................ 57
Figure 49. LDI-TOF of fac-Ir(ppy)3. ........................................................................................... 57
Figure 50. LDI-TOF of (ppy)2Ir(acac). ........................................................................................ 58
Figure 51. LDI-TOF of 3
Λ
. .......................................................................................................... 58
Figure 52. LDI-TOF of 3RR
Δ
. ....................................................................................................... 59
Figure 53. LDI-TOF of 3RR
Λ
. ....................................................................................................... 59
Figure 54. LDI-TOF of 4
Δ,Λ
. ........................................................................................................ 60
Figure 55. TGA of 3RR
Δ
and 3RR
Λ
. ............................................................................................... 60
Figure 56. HOMO (left) and LUMO (right) of complex 1
Δ
. B3LYP/LACVP*. ......................... 61
Figure 57. HOMO (left) and LUMO (right) of complex 1
Λ
. B3LYP/LACVP*. ......................... 61
Figure 58. HOMO (left) and LUMO (right) of complex 2
Δ
. B3LYP/LACVP*. ......................... 62
Figure 59. HOMO (left) and LUMO (right) of complex 2
Λ
. B3LYP/LACVP*. ......................... 62
Figure 60. HOMO (left) and LUMO (right) of complex 3
Δ
. B3LYP/LACVP*. ......................... 63
Figure 61. HOMO (left) and LUMO (right) of complex 3
Λ
. B3LYP/LACVP*. ......................... 63
Figure 62. HOMO (left) and LUMO (right) of complex 4
Δ
. B3LYP/LACVP*. ......................... 64
Figure 63. HOMO (left) and LUMO (right) of complex 4
Λ
. B3LYP/LACVP*. ......................... 64
Figure 64. CV (left) and DPV (right) of 1
Δ,Λ
in DMF (vs Fc). .................................................... 65
Figure 65. CV (left) and DPV (right) of 2
Δ,Λ
in DMF (vs Fc). .................................................... 65
Figure 66. CV of 3
Δ
in DMF (vs Fc). ........................................................................................... 66
Figure 67. CV of 3
Λ
in DMF (vs Fc). .......................................................................................... 66
Figure 68. DPV of 3RR
Δ
in DMF (vs Fc). ..................................................................................... 66
Figure 69. CV (left) and DPV (right) of 3RR
Λ
in DMF (vs Fc). .................................................. 67
Figure 70. CV (left) and DPV (right) of 4
Δ,Λ
in DMF (vs Fc). .................................................... 67
Figure 71. Absorbance (a), Emission RT (b), and Emission 77 K of 2
Δ,Λ
in various solvents. ... 68
Figure 72. Absorbance (a), Emission RT (b), and Emission 77 K of 3
Δ
in various solvents. ..... 69
Figure 73. Absorbance (a), Emission RT (b), and Emission 77 K of 3
Λ
in various solvents. 3
Λ

doesn’t absorb well in MeCy. ....................................................................................................... 70
xii

Figure 74. Absorbance (a), Emission RT (b), and Emission 77 K of 3RR
Δ
in various solvents.
3RR
Δ
didn’t absorb well in MeCy. ................................................................................................. 71
Figure 75. Absorbance (a), Emission RT (b), and Emission 77 K of 3RR
Λ
in various solvents. .. 72
Figure 76. Absorbance (a), Emission RT (b), and Emission 77 K of 4
Δ,Λ
in various solvents. ... 73
Figure 77. Absorbance spectra of the BOXSS-CN and BOXRR-CN ligands in CH2Cl2. .............. 74
Figure 78. Recently reported (carbene)Cu
I
(Cz) emitters.
7, 9-11
.................................................... 79
Figure 79. (Thiazole)Cu(XCz) studied where X = H, Me, IPr, or Ph. ......................................... 80
Figure 80. Single crystal X-ray structure of 1. Hydrogens were omitted for clarity. .................. 81
Figure 81. HOMO (shaded) and LUMO (dashed) orbitals of the 1. ............................................ 83
Figure 82. Geometry optimized ground state for 1-Me (left) and 1-Ph (right). .......................... 84
Figure 83. Potential energy surface scan of (Thia)Cu(XCz) complexes. .................................... 85
Figure 84.
1
H-NMR of 1-Me in acetone at RT versus -70 ℃. .................................................... 86
Figure 85.
1
H-NMR of 1-IPr in acetone at RT versus -70 ℃. .................................................... 87
Figure 86. Calculated NMRs using Spartan of the anti and syn isomers of 1-IPr. ..................... 87
Figure 87. Molar absorptivity of (Thia)Cu(XCz) complexes in toluene. .................................... 89
Figure 88. Emission spectra of (Thia)Cu(XCz) complexes in 2Me-THF, MeCy, Tol, and 1% wt
in PS films. .................................................................................................................................... 91
Figure 89. Emission spectra of 1-Ph in 2Me-THF, MeCy, and 1 wt% PS. ................................. 93
Figure 90.
1
H-NMR of 1-methylcarbazole in acetone. ................................................................ 99
Figure 91.
1
H-NMR of 1-isopropylcarbazole in acetone. ............................................................ 99
Figure 92.
1
H-NMR of (Thia)CuCl in acetone. ......................................................................... 100
Figure 93.
1
H-NMR of (Thia)Cu(Cz) in acetone. ...................................................................... 100
Figure 94.
13
C-NMR of (Thia)Cu(Cz) in acetone. ..................................................................... 101
Figure 95.
1
H-NMR of (Thia)Cu(MeCz) in acetone. ................................................................. 101
Figure 96.
13
C-NMR of (Thia)Cu(MeCz) in acetone. ................................................................ 102
Figure 97.
1
H-NMR of (Thia)Cu(IPrCz) in acetone. ................................................................. 102
Figure 98.
13
C-NMR of (Thia)Cu(IPrCz) in acetone. ................................................................ 103
Figure 99.
1
H-NMR of (Thia)Cu(PhCz) in acetone. .................................................................. 103
Figure 100. Normalized absorbance of (Thia)Cu(XCz) complexes in 2Me-THF. .................... 104
Figure 101. Normalized absorbance of 2 wt% (Thia)Cu(XCz) complexes in PS film. ............. 104
Figure 102. CV (left) and DPV (right) of (Thia)Cu(Cz) in DMF versus Fc. ............................. 105
Figure 103. CV (left) and DPV (right) of (Thia)Cu(MeCz) in DMF versus Fc. ....................... 105
Figure 104. CV (left) and DPV (right) of (Thia)Cu(IPrCz) in DMF versus Fc. ........................ 106
Figure 105. HOMO (shaded) and LUMO (dashed) orbitals of the 1-Me. ................................. 106
Figure 106. HOMO (shaded) and LUMO (dashed) orbitals of the 1-IPr. ................................. 106
Figure 107. HOMO (shaded) and LUMO (dashed) orbitals of the 1-Ph. .................................. 107
Figure 108. HOMO (shaded) and LUMO (dashed) orbitals of the 1-Xylyl. ............................. 107
Figure 109. Lifetime data of fac-Ir(ppy)3. The red data was experimental data collected by drop
casting a film of 2 wt% fac-Ir(ppy)3 in PS film. The black data is previous literature data taken in
CH2Cl2......................................................................................................................................... 112
Figure 110. Emission spectra of 2 wt% fac-Ir(ppy)3 in PS film with a 435 nm filter. Spectra were
taken every ~10 K from 300 to 25 K. The left plot shows how the intensity changed as a function
xiii

of temperature. The right graph shows the normalized emission spectra at 300, 100, and 25 K.
..................................................................................................................................................... 113
Figure 111. Lifetime data of fac-Ir(ppy)3. The black data is previous literature data taken of 2
wt% of fac-Ir(ppy)3 in PMMA film. All other data were films of 2 wt% fac-Ir(ppy)3 in PS film.
..................................................................................................................................................... 114
Figure 112. Lifetime data of MACAuCz. The red data was experimental data collected by drop
casting a film of 2 wt% MACAuCz in PS film. The black data is previous literature data taken in
as a 1 wt% PS film.
2
.................................................................................................................... 115
Figure 113. Variable temperature lifetime data of a 2 wt% MACAuCz in PS film. The two-
(dashed) and three-level (solid) fits are shown. .......................................................................... 116
Figure 114. Emission spectra of 2 wt% MACAuCz in PS film with a 435 nm filter. Spectra were
taken every ~10 K from 300 to 40 K. The left plot shows how the intensity changed as a function
of temperature. The right graph shows the normalized emission spectra. .................................. 118
Figure 115. Stern-Volmer quenching studies of CAACCuCz in THF using 1,10-phenanthroline
(left) and o-dinitrobenzene (right) as oxidative quenchers. ........................................................ 123
Figure 116. Quenching of CAACCuCz using two different oxidative quenchers. The excited
state oxidation and reduction potentials are shown for CAACCuCz*. The ground state reduction
potential is shown for the oxidative quenchers, 1,10-phenanthroline (red) and o-dinitrobenzene
(blue). .......................................................................................................................................... 123
Figure 117. Oxidative electron transfer quenching of CAACCuCz in THF. ............................ 125
Figure 118. Stern-Volmer quenching studies of CAACCuCz in THF using para-tetramethyl-
phenylenediamine and tetramethyl-benzidine as reductive quenchers. ...................................... 126
Figure 119. Quenching of CAACCuCz using two different reductive quenchers. The excited
state oxidation and reduction potentials are shown for CAACCuCz*. The ground state oxidation
potentials are shown for the oxidative quenchers, para-tetramethyl-phenylenediamine (red) and
tetramethylbenzidine (blue). ....................................................................................................... 126
Figure 120. Reductive electron transfer quenching of CAACCuCz in THF. ............................ 127
Figure 121. Stern-Volmer quenching studies of fac-Ir(tpz)3 in toluene using 1,4-
diazabicyclo[2.2.2]ocatane (left) and N,N-dimethyl-p-toluidine (right) as reductive quenchers.
..................................................................................................................................................... 128
Figure 122. Stern-Volmer quenching studies of fac-Ir(tpz)3 in toluene using energy transfer
quenchers. ................................................................................................................................... 129
Figure 123. Quenching of MACCuCz in MeCN with BIH using fluorimeter. ......................... 131
Figure 124. Stern-Volmer quenching studies of MACCuCz with 1,2,4,5-tetracyanobenzene. . 131
Figure 125. Stern-Volmer quenching studies of MACCuCz (left) and CAACCuCz(right) with
BIH. ............................................................................................................................................. 132
Figure 126. Stern-Volmer quenching studies of CAACCuCz in THF using various reductive
quenchers. ................................................................................................................................... 132
Figure 127. Stern-Volmer plots for CAACCuCz using various oxidative quenchers. ............. 133
Figure 128. Emission spectra of (ppy)2Ir(BOX) complexes in 2Me-THF at RT and 77 K. ...... 136
Figure 129. Emission spectra of (ppy)2Ir(BOXss-Ph) (left) and (ppy)2Ir(BOXRR-Ph) (right) at RT
and 77 K. ..................................................................................................................................... 137
Figure 130. Emission spectra of (C^N)Ir(BOX-Ph) complexes in 2 Me-THF. ......................... 138
xiv

Figure 131. Triplet spin density calculations of (ppy)2Ir(BOXSS-Ph) (left) and (ppy)2Ir(BOXSS-
CN) (right). ................................................................................................................................. 139
Figure 132. Synthesis of BOXSS-Ph following a modified prep.
3
............................................. 140
Figure 133.
1
H-NMR of (ppy)2Ir(BOXSS-Ph). ........................................................................... 142
Figure 134.
1
H-NMR of (ppy)2Ir(BOXRR-Ph). .......................................................................... 142
Figure 135. Original optical probe design. ................................................................................ 145
Figure 136. The hat of the copper cage. ..................................................................................... 147
Figure 137. Current iteration of the optical probe. .................................................................... 148
Figure 138. The top (left) and side view (right) of the top hat for the optical probe. ................ 149
Figure 139. Picture of fiber optic cables after being pulled into the copper cage. .................... 150
Figure 140. Set up for emission collection. ............................................................................... 151
Figure 141. Set up for lifetime collection. ................................................................................ 152
Figure 142. Emission set up outside the PPMS. The picture in the upper right-hand corner shows
the sample (2 wt% Alq3 in PS film) while being excited with a 375 nm light source. ............... 153
Figure 143. Emission spectra of 2 wt% Alq3 in PS film at RT. ................................................. 153
Figure 144. Lifetime spectra of 2 wt% Alq3 in PS film at RT. .................................................. 154

xv

List of Schemes
Scheme 1. Synthesis of (C^N)2Ir(BOX-CN) complexes. ............................................................. 27
Scheme 2. Synthesis of (Thia)Cu(XCz) complexes. .................................................................... 81
Scheme 3. Synthesis of substituted carbazoles using modified prep
12
. ........................................ 96
Scheme 4. Synthesis of ThiaCuCl. ............................................................................................... 96
Scheme 5. Synthesis of (Thia)Cu(XCz) complexes. .................................................................... 97
Scheme 6. Synthesis of (C^N)2Ir(BOXSS-Ph) and (C^N)2Ir(BOXRR-Ph) complexes. ............... 140

xvi

Abstract
Luminescent organometallic complexes have shown great promise for their application in
organic light emitting diodes, photoredox catalysis, and as sensors in biological applications.
Chapter 1 gives an introduction into the photophysical properties and potential applications of
iridium and coinage metal complexes.
Organometallic iridium complexes with two cyclometalated ligands (C^N) and one bis-
oxazoline derived ancillary ligand (L^X), i.e. (C^N)2Ir(L^X), are reported in Chapter 2. The C^N
ligands are 1-phenylpyrazoline (ppz), 2-(4,6-difluorophenyl)pyridin (F2ppy), 2-phenylpyridine
(ppy), 1-phenylisoquinoline (piq). The box ligand is (4S)-(+)-phenyl-α-[(4S)-phenyloxazolidin-2-
ylidene]-2-oxazoline-2-acetonitrile with acronym BOXSS-CN. The emission of these complexes
span across the visible and into the near-ultraviolet region of the electromagnetic spectrum with
moderate to high photoluminescence quantum yields (ΦPL = 0.45-1.0). These complexes were
found to emit from a metal-ligand to ligand charge transfer (ML’LCT) state and have lifetimes
(1.3-2.1 μs), radiative rates (10
5
s
-1
), and nonradiative rates (10
4
-10
5
s
-1
) comparable to state-of-
the-art iridium emitters. The (ppy)2Ir(BOX-CN) complexes were resolved into the − and
- diastereomers using differences in their solubility and additionally characterized by x-ray
crystallography, stability, and circular dichroism studies.
Copper complexes have been investigated as possible alternatives to currently used noble
metal emitters like iridium. In particular, 2-coordinate copper (I) complexes have shown promising
photophysical properties that make them competitive with state-of-the-art phosphorescent
emitters. Chapter 3 looks at a series of 2-coordinate thiazole copper (I) carbazole complexes.
Substitution at the 1-position of carbazole (XCz where x = H, Me, IPr, Ph) was used to prevent
nonradiative decay pathways such as bending and rotating in the excited state. With few
xvii

exceptions, previous (carbene)Cu(Cz) complexes have focused on using sterically bulky carbenes
while only modifying the carbazole moiety to manipulate the energy of the HOMO. This chapter
looks at the use of both the carbene and carbazole to prevent rotation about the carbene-copper-
carbazole bond.
The use of an optical probe designed for the physical properties management system
(PPMS) is discussed in Chapter 4. The design and collection set ups for the probe can be found
in Appendix B. While emitters in our lab have been mainly synthesized for use in organic light-
emitting diodes (OLEDs), these complexes have properties that make them suitable for other
applications. Chapter 5 looks at the use of previously synthesized iridium and copper complexes
as visible light photocatalysts.

1

Chapter 1. Introduction
1.1. Organic Light-Emitting Diodes
Organic light-emitting diodes (OLEDs) are devices composed of organic, organometallic,
and/or polymer layers sandwiched between a cathode and an anode. A simplified device structure
of an OLED is shown in Figure 1. When a potential is applied across the device, negatively
charged electrons and positively charged holes are generated at the cathode and the anode
respectively. Holes are injected from the anode into the hole transport layer while electrons are
injected into electron transport layer from the anode. These electrons and holes make their way
through the device and into the emissive layer where they recombine to form excitons that
radiatively decay to produce light. The development of more efficient luminescent materials is
essential to advancing OLED technology.

Figure 1. Simplified device structure of an OLED.
1.2. Jablonski diagram
Designing efficient emitters requires a detailed understanding of how these materials
behave in the excited state. A general Jablonksi diagram is shown in Figure 2. When a photon of
light is absorbed by a chromophore, an electron is promoted from the ground state, S0, to a higher
2

lying singlet state, Sn. The electron rapidly undergoes internal conversion (IC) from the Sn state to
the lowest lying singlet state, S1. From here, there are a few relaxation paths the complex can take
to the ground state. The compound can either nonradiative decay to the ground state through IC or
it can radiatively decay through fluorescence. Alternatively, the compound can nonradiatively
decay to a triplet state, Tn, through a process known as intersystem crossing (ISC). Tn rapidly
decays nonradiatively to the lowest energy triplet state, T1, through IC. From the T1 state the
electron can give off light through phosphorescence or decay nonradiatively to the ground state.
Chromophores emit out of their lowest excited state (S1 or T1) as dictated by Kasha’s rule.

Figure 2. A Jablonski diagram.
1.3. Iridium emitters
Organometallic complexes containing heavy metals such as Pt and Ir have received
considerable attention as emitters. The heavy metals in these complexes induce spin-orbit coupling
which allows for harvesting of singlets and triplets leading to a theoretical efficiency limit of 100%
and typically emit on the μs timescale. The most common phosphorescent emitters in OLEDs are
cyclometalated iridium complexes. The first such emitters reported were tris-cyclometalated
3

complexes, Ir(C^N)3 where C is a covalently bound arene or other organic moiety and N is a
datively bound nitrogen of a heterocyclic ring.
1-2
The 2-phenylpyridine complex, fac-Ir(ppy)3, is
exemplary of this type of emitter. In these cyclometalated complexes the highest occupied
molecular orbital (HOMO) is composed of iridium d-orbitals and π-orbitals of the arene, while the
lowest occupied molecular orbital (LUMO) is primarily composed of π-orbitals of the heterocyclic
ring.
3
Thus, the excited state can be thought of as arising from a metal-ligand to ligand charge
transfer.
The ability to color-tune chromophores is important for applications in displays and
solid-state lighting. Varying the emission energy for homoleptic cyclometalated iridium
complexes, Ir(C^N:)3, has been successfully accomplished by strategic substitution on the phenyl
and pyridine rings of the cyclometalating (C^N:) ligands. The HOMO, LUMO, and triplet spin
density calculations for fac-Ir(ppy)3 are shown in Figure 3 below. The HOMO of fac-Ir(ppy)3 is
composed mainly of iridium metal character and a small contribution from the phenyl ring of the
(C^N:) ppy ligand. The LUMO, on the other hand, mainly resides on the pyridine. Therefore,
strategic substitution on the phenyl and pyridine rings of the ppy ligand can either stabilize or
destabilize the HOMO and LUMO.
4

Figure 3. The HOMO (a), LUMO (b), and triplet spin-density (c) calculations for a well-known
green emitter, fac-Ir(ppy)3 using B3LP/LACVP**. The various substitution positions are shown
in the HOMO picture.
Two common methods for blue-shifting Ir(C^N:)3 complexes are shown in Figure 4. The
first method (left) is stabilization of the HOMO by strategic substitution of electron-withdrawing
groups (EWGs) on the phenyl ring of the ppy ligand.
4
The HOMO, as shown previously in Figure
3, has two nodes at 4’ and 6’ on the phenyl ring. Addition of electron withdrawing groups to these
positions subsequently pulls electron density from the phenyl ring resulting in an overall
stabilization of the HOMO. Due to the electron density at the 5’ position, substitution with EWGs
at this position leads to a destabilization of the HOMO resulting from π- donation. The second
method (right of Figure 4) for blue-shifting homoleptic complexes is through destabilization of
the LUMO by decreasing the ring size of the nitrogen substituted ring.
5

Figure 4. Blue-shifting of homoleptic iridium complexes.
While both methods yield blue-emitting complexes, each strategy has its own drawbacks
that limit their overall efficiency in a device. For example, FIrpic, a well-known sky-blue emitter
containing fluorine EWGs, has been shown to undergo major decomposition pathways leading to
low operational lifetimes in devices.
5-8
One such decomposition pathway is the cleavage of the C-
F bonds upon sublimation and deposition, severely limiting the use of this material as an emitter
in OLEDs. Deep blue complexes that employ the later method suffer stability and efficiency issues
that are a direct result of their higher T1 energies, such as is the case with Ir(ppz)3
9
. These
complexes have high nonradiative rates at room temperature due to thermal deactivation through
higher lying triplet metal-centered (
3
MC)

states resulting in overall lower efficiencies.
10

Additionally, accessing these higher lying states can result in bond rupture of the weak Ir-N bond.
Up to this stage, the development of Ir-based blue phosphorescent materials with superior
efficiency and stability remains a challenge.
11
Recently cyclometalated N-heterocyclic carbenes (NHC)-Ir based chromophores,
Ir(C^C:)3, have attracted attention due to their promising properties as blue emitters.
3-4, 12-17
These
6

C^C: based emitters have an aryl group as do C^N: ligands, but utilize a carbene in place of the
nitrogen basic moiety. Our group reported one of the first blue-emitting Ir-carbene complexes for
OLEDs, using N-phenyl, N-methyl-imidazol-2-yl (pmi) and N-phenyl,
N-methyl-benzimidazol-2-yl (pmb) ligands (Figure 5).
3
Since then, several homoleptic
18-21
and
heteroleptic
16
derivatives of these complexes have also been reported. These Ir(C^C:)3 complexes
have advantages over blue emissive Ir(C^N:)3 complexes as they do not suffer from deactivation
of the excited state via thermal population of triplet metal-centered (
3
MC)

states, which can
severely diminish their ΦPL. Replacing the nitrogen basic moiety in the C^N: ligand with a strong
field carbene ligand, largely mitigates this problem by destabilizing the
3
MC states, which makes
them thermally inaccessible (Figure 6). Interestingly, it was found that even when the
3
MC states
are thermally populated, the carbene iridium complexes were able to undergo reversible population
of the radiative state leaving the Ir-carbene bond intact.
22
Since the Ir–N bond dissociation in the
excited state has been shown to be problematic in Ir(C^N:)3 complexes,
23
computational results
have suggested that replacement with the stronger Ir–C carbene bond will result in a more robust
emitter.
22, 24

Figure 5. NHC Iridium Carbene Complexes synthesized in our group.
7

Figure 6. Jablonski diagram of fac-Ir(ppz)3 versus fac-Ir(C^C:)3 complexes.
3

Further work on Ir(C^C:)3 complexes led to the use of the electrophilic N-phenyl,
N-methyl-pyridylimidazol-2-yl ligand (pmp) to create highly efficient deep blue facial (fac) and
meridianal (mer) Ir complexes [Ir(pmp)3] (Figure 5).
25
Since this report, several analogues of these
compounds have been reported.
4, 13
OLEDs implementing these dopants were able to reach
external quantum efficiencies (EQEs) of 15%.
25
While these results are promising and show the
potential of fac- and mer-Ir(pmp)3 as deep blue dopants, these complexes have inherent properties
that severely limit their widespread application in OLEDs. One such problem is that these emitters
have shallow LUMO energies, which hinders charge mobility. Additionally, the high emission
energy of these materials also makes it a challenge to find hosts that can efficiently nest these
emitters. In fact, the hosts used in these first devices were phosphine oxides that are innately
unstable and severely limit the overall lifetime of these devices. To mitigate these problems, our
group designed Ir complexes employing N-aryl, N-methyl-pyrazinoimidazol-2-yl carbene ligands,
i.e. fac- and mer-Ir(pmpz)3, that have more stabilized LUMO energy levels and lower triplet state
energies than their pyridyl analogs (Figure 5).
26
However, since poor synthetic yields made these
materials impractical for large scale implementation into OLEDs, an isoelectronic Ir complex was
synthesized using N-aryl, N-aryl-pyrazinoimidazol-2-yl carbene ligands, i.e. fac-Ir(tpz)3. The
8

symmetric nature of this ligand made this emitter easily scalable and led to efficient sky-blue
OLEDs with EQEs of 18%.
While a lot of recent focus has been spent on developing efficient blue Ir emitters, there is
also a need to develop more efficient red to near-infrared emitters. Red-shifting of homoleptic Ir
complexes can be obtained by decreasing the HOMO/LUMO gap by either stabilizing the LUMO
or destabilizing the HOMO. The most common strategies for red-shifting homoleptic complexes
is through extending the conjugation,
27
using a thiophene in place of phenyl, or a combination of
both of these methods (Figure 7).

Figure 7. Red-shifting of homoleptic iridium complexes.
28

While a wide variety of lower energy Ir emitters have been synthesized, these complexes
tend to suffer from lower-than-optimal ΦPL efficiencies. For example, red emitters have ΦPL values
that top out at around 0.50, while deep-red and near-IR emitters tend to have ΦPL efficiencies less
9

than 0.1.
28
These lower efficiencies are the result of these materials having lower radiative (kr) and
higher nonradiative decay rates (knr) than other luminescent Ir complexes, both of which negatively
impact the ΦPL of a material (Equation 1). The lower knr values are the result of a phenomenon
known as energy gap law, which states that the nonradiative decay rate (knr) increases with a
decrease in the energy gap between the ground and excited states due to easier vibronic coupling
between these two states.
29
Some methods for decreasing knr include making improving the rigidity
of the complex to prevent vibronic coupling to the ground state. The lower kr values for red emitters
are also the result of this energy gap. The energy difference between the excited and ground states
is directionally proportional to kr, resulting in red-emitters having overall lower kr than other color
emitters. The most efficient way to increase kr in red emitters is through the use of ancillary
ligands
28
and will discussed later on.
(1) 𝜙 𝑃𝐿
=
𝑘 𝑟 + 𝑘 𝑛𝑟
𝑘 𝑛𝑟

Ancillary ligands provide yet another method for energy-tuning of Ir complexes. For tris-
cyclometalated iridium complexes, tuning of emission energy is accomplished by varying the
cyclometalating ligand, which simultaneously impacts the both the energy of the
1
MLCT and the
3
LC states. Jian et. al. reported that the use of bis-cyclometalated iridium complexes, composed
of two cyclometalated ligands and one ancillary ligand, can vary the energy of the
1
MLCT without
changing the overall energy of the
3
LC state.
30
Although DFT calculations showed no noticeable
participation by the ancillary ligand in either the HOMO or LUMO of the complex, it was found
that these ligands can affect the overall energy of the HOMO through manipulation of the Ir
d-orbitals. In addition, a stabilization of the HOMO results in the destabilization of the
1
MLCT,
which results in less overall
1
MLCT character mixed in to the primarily
3
LC state. Less
1
MLCT
10

character in the excited state of the Ir complex had substantial effects on the photophysical
properties of these complexes including a decrease in both the kr and knr, longer lifetimes and more
vibronic character in the emission profiles. In a similar manner, ancillary ligands can be used to
increase the amount of MLCT character mixed into the excited state. This is particularly important
for red emitters as increasing the MLCT contribution improves spin orbit coupling (SOC) and
results in higher kr values.
1.4. Copper Emitters
While heavy metal complexes have had great success as dopants, there has been a recent
drive to replace these metals with more naturally occurring elements. Reasons for this push is both
due to potential supply issues as well as material cost. Iridium, for instance, is the least abundant
element on earth. Copper is one such element that has been looked at as a replacement for these
heavy metals. The first reported luminescent Cu (I) complexes were 3- and 4-coordinate
complexes. While these materials were found to be strongly luminescent in the solid state, they
were either weakly or completely non-emissive in solution. The diminished luminescence in
solution is the direct result of geometrical distortions between the ground and excited states
(Figure 8).
Take for example, the case of 4-coordinate copper (I) complexes, which typically have a
tetrahedral (Td) geometry in the ground state. These complexes are d
10
, meaning both the t2 and e
d-orbitals are completely filled. Excitation of this complex leads to an electron being promoted
from the t2 orbital of the metal to the π
*
orbital of the ligand. This metal to ligand charge transfer
(MLCT) results in a partially unfilled t2 orbital. Since the t2 are no longer completely filled, these
orbitals are no longer degenerate. To compensate for this change in degeneracy, the complex
undergoes a geometric distortion to lower the overall energy of the complex. In this case, the
11

complexes distorts to the lower symmetry square planar geometry (D4h). This change in the
geometry of the complex is known as a Jahn-Teller distortion. Similarly, when the molecule
relaxes to the ground state, the electron refills the half-filled d-orbital resulting in another structural
distortion back to the Td geometry. 3-coordinate copper complexes undergo a similar structural
distortion between its ground state (trigonal planar) and excited state (T-shaped). Overall, this
molecular distortion between the ground and excited states leads to high nonradiative rates and,
subsequently, low photoluminescence quantum yields (PLQYs) in solution. Although attempts
have been made to reduce these large structural distortions using bulky ligands, it was found that
2-coordinate copper (I) complexes do not have undergo these large distortions in geometry.

Figure 8. Jahn-Teller distortion brought about by the excitation of a 4-coordinate copper complex.
2-coordinate copper (I) complexes have shown great promise as highly emissive materials.
In contrast to the previously mentioned 3- and 4-coordinate copper (I) complexes, these complexes
have been shown to be highly emissive in both solid state and solution. There are several
characteristics of these 2-coordinate copper (I) complexes that allow for these complexes to
compete with start of the art iridium complexes. While the 3- and 4-coordinate copper (I)
12

complexes emit through phosphorescence, the 2-coordinate copper complexes undergo thermally
activated delayed fluorescence (TADF). A Jablonski diagram is shown for this process in Figure
9.
31
A key characteristic of TADF materials is that the energy gap between the S1 and T1 states be
as small as possible (ΔES1-T1). This small gap between the S1 and T1 states allows for ISC between
the two manifolds. Minimizing the S1/T1 gap requires that the HOMO and LUMO overlap as little
as possible. However, there must be enough overlap for the transition between the HOMO and
LUMO to allow the electronic transition to occur.

Figure 9. Jablonski diagram depicting TADF.
31

The 2-coordinate copper (I) complexes balance these two criteria using the copper metal
as an electronic bridge. Figure 10 shows the HOMO and LUMO orbitals for CAACCuCz. The
HOMO and LUMO reside mostly on the carbazole and carbene respectively. However, there is a
minor contribution of both the HOMO and LUMO from the copper metal. This small contribution
of copper allows it to act as conduit to pass electrons between the carbazole and carbene. For this
reason, it is also important the carbene and carbazole be coplanar. When the carbene and carbazole
were made to be perpendicular, it was found that the oscillator strength of complexes substantially
decreases, indicating a weaker interaction between the carbene and amide ligands. Finally, while
these materials do not undergo Jahn-Teller distortions, these materials are still susceptible to
13

bending and rotation in the excited state. Sterically bulky ligands can be used to minimize these
nonradiative decay paths.

Figure 10. DFT calculations of HOMO (solid) and LUMO (opaque) for CAACCuCz obtained
using B3LYP/LACVP**.
31

As previously mentioned, 3- and 4-coordinate coinage metal complexes can readily
undergo a structural distortion known as a Jahn-Teller distortion due to the MLCT character of the
excited state. All previously discussed 2-coordinate coinage metal complexes were able to avoid
similar types of distortions due to the ICT character of their excited state. However, when the
lowest energy excited state is a MLCT state, 2-coordinate complexes undergo another type of
distortion known as a Renner-Teller distortion (Figure 11). In this case, the complex can
nonradiatively decay to the ground state through bending. To avoid this type of distortions in 2-
coordinate coinage metal complexes, it is essential to ensure that the lowest energy excited state
be an ICT state.
14

Figure 11. Types of distortions that can occur in coinage metal complexes.
32

Energy-tuning of 2-coordinate copper complexes can be accomplished by similar means to
that of iridium complexes. The HOMO and LUMO for MACCuCz is shown in Figure 12. The
HOMO is located primarily on the carbazole unit with a minor contribution from the copper atom.
The LUMO is primarily localized on the carbene unit with a small amount of contribution from
the copper atom. Since the HOMO and LUMO are isolated on different parts of the molecule, it is
possible to independently tune the HOMO and LUMO levels.

Figure 12. DFT calculations of HOMO (left) and LUMO (right) for MACCuCz obtained using
B3LYP/LACVP*.
15

The most common method for blue- or red-shifting the emission of these complexes is
through substitution of the carbazole unit as shown in Figure 13. The addition of EWGs to the 3
and/or 6 positions of the carbazole ligand result in a stabilization of the HOMO for both the
CAAC
31
and MAC/DAC
33
derivatives. The addition of EDGs to the same positions would result
in a red-shift in the emission. Additionally, the use of a different carbene ligands is also one such
way of shifting the emission. By changing the carbene ligand, you can directly change the energy
of the LUMO. As an example, going from MAC with one amide to DAC with two amide groups
leads to a red-shift in the emission.

Figure 13. Blue-shifting of 2-coordinate coinage metal complexes.
While a lot of the initial focus was on 2-coordinate copper complexes, recent attention has
focused on the incorporation of other coinage metals into these 2-coordinate motifs. Our group
recently explored two sets of isostructural and isoelectronic two-coordinate coinage metal
complexes, CAAC(M)Cz and MAC(M)Cz (M = Cu, Ag, Au).
34
While these materials showed
similar photophysical properties across a series, the lifetime of the Ag complexes was found to be
substantially shorter than their isostructural Cu and Au complexes. To understand why the Ag
complexes had significantly faster lifetimes, the lifetime was varied as a function of temperature
and fitted to a Boltzmann model to extract out the singlet-triplet gap (ΔES1-T1), the zero-field
splitting (ZFS) and the lifetimes of the S1 and T1.
16

1.5. Boltzmann models
The temperature dependent lifetime data can be fit to a two- or three-fit Boltzmann model.
A Jablonski diagram depicting the splitting of the S1 and T1 for the two fits are depicted in Figure
14. The major difference between the two models is in how they treat the splitting of the T1 states,
which consists of three substates (T1
I
, T1
II
, and T1
III
). The degree to which these levels split is the
direct result of SOC. The two-fit model assumes that the SOC of the molecule isn’t large enough
two split the T1 substates. In this case, the three T1 substates are considered degenerate. Since the
T1 states are degenerate in the two-fit model, ΔES1-T1 can be thought of as the energy difference
between the S1 and T1 states. The lifetimes of the S1 and T1 states can be calculated from the two-
fit model. The three-fit model, on the other hand, takes SOC, and hence, the splitting of T1 states
into consideration. The splitting between the lowest and highest substates, T1
I
and T1
III

respectively, is known as the zero-field splitting (ZFS) and can be obtained by the three-fit model.
The ΔES1-T1 is the energy difference between the S1 and T1
I
states. The lifetimes of S1, as well as
the individual T1 states, can be readily calculated from the three-fit model.
The best fit for a particular set of data depends on the type of chromophore being excited.
Organic compounds which typically have small SOC factors would be expected to follow the two-
fit model. In fact, thermal equilibration of the triplet substates for organic compounds is observed
even at cryogenic temperatures. In contrast, heavy metals containing complexes would be expected
to follow the three-model fit.
17

Figure 14. A Jablonksi diagram showing the splitting of the singlet and triplet sublevels with
weak and strong SOC.
1.6. Use of dopant materials as visible light photocatalysts
While our group has mainly focused on the use of emissive organometallic complexes in
OLEDs, traits that makes these materials efficient dopants also make them advantageous for other
applications. One potential use of these emitters are as visible light photocatalysts in photoredox
catalysis. In photoredox catalysis, a photocatalyst is promoted into its excited where it is able to
either reduce or oxidize a substrate or another catalyst that can then go on to react with a substrate.
One of the major advantages of photoredox catalysis is its ability to produce unique
transformations at relatively mild conditions.
35
For an emitter to be a good visible light
photocatalyst, there are several characteristics it must possess. The first, and most obvious feature,
is that they should absorb somewhere in the visible light part of the spectrum.
36-38
Another obvious
trait is that these materials must have good stability in both the ground and excited state.
Additionally, these emitters should have moderately long lifetimes to give the photocatalyst time
to diffuse through the solution and find a substrate to reduce or oxidize. While these materials do
not necessarily need to be oxidants and reductants in the ground state, they must be potent excited
18

state oxidants and reductants. A modified table of commonly used visible light sensitizers by
MacMillan et. al.
36
is shown in Table 1.
Table 1. Commonly used visible light photocatalysts compiled by MacMillan et. al.
36
This table
was modified to fit the page.

A Jablonski diagram describing how an Ir based visible light photocatalyst can act as both
an oxidant and a reductant is shown in Figure 15. This description holds true for most octahedral
d
6
metal complexes. Absorption of a photon of light by the photocatalyst results in the promotion
of an electron from the filled t2g set of the Ir metal d-orbitals to the π
*
orbital of the ligand, leading
to a hole in the t2g. The strong SOC character of the Ir metal allows the excited electron to readily
undergo ISC from the S1 to the T1 state. Since decaying from the T1 state to the ground state is a
spin forbidden process, as it requires the electron to undergo a spin flip, the lifetime of this state is
longer (on the order of μs) than for purely fluorescent compounds. The longer lifetime of these
complexes gives them time to react with a substrate. The Ir photocatalyst can act as an oxidant by
receiving an electron to fill its t2g set, resulting in a completely filled t2g set with one electron in
the π
*
orbital of the ligand. Likewise, the photocatalyst can act as a reductant by giving up the
electron from the π
*
orbital of the ligand, leading to a completely empty π
*
orbital and a hole in the
19

t2g set of orbitals. The potential for a photocatalyst to either give up or receive an electron depends
on its excited state redox properties.

Figure 15. A Jablonski diagram of a Ir visible light photocatalyst explaining how the material can
act as both an oxidant and a reductant in the excited state.
Prior to the implementation of a potential visible light photocatalyst into a reaction,
preliminary studies are often run to determine the excited state oxidative and reductive capabilities
of the photocatalyst. Stern-Volmer quenching studies are one such way probe the potential of an
emitter for photocatalytic applications. These studies allow us to quickly look at two competing
processes: radiative decay out of the emitting state (emission) and electron transfer between the
photocatalyst and a substrate.
36
In Stern-Volmer quenching studies a photocatalysts is excited in
the presence of a quencher. Depending on the excited state of the photocatalyst and on the ground
state of the quencher used, the photocatalysts can either undergo an oxidative or reductive
20

quenching mechanism (Figure 16). In the oxidative quenching case, the photocatalyst in its excited
state reduces the quencher. For this to happen, the photocatalyst must be a more potent reductant
in its excited state than the quencher it needs to reduce. In the reductive quenching mechanism,
the photocatalyst is reduced by the quencher. For this to occur, the photocatalyst must be a more
potent oxidant in it excited state than the quencher in its ground state. Additionally, to rule out any
other processes going on, it is necessary for the triplet of the quencher to be higher in energy than
the photocatalyst to ensure that electron transfer is the only mechanism occurring during these
studies. If the triplet of the quencher falls below that of the photocatalyst, energy transfer becomes
a competitive process.

Figure 16. Oxidative (left) and reductive (right) quenching of the photocatalyst by a quencher.
Stern-Volmer quenching rates can be determined by plotting how emission intensity or
lifetime of the photocatalyst varies as a function of quencher concentration. The photocatalyst, at
a certain concentration, has a set emission intensity. When quencher is added to a solution of the
photocatalyst, an electron transfer pathway between the photocatalyst and quencher can occur that
is competitive with phosphorescence. This results in an observable drop in the emission intensity
as a function of quencher concentration. A similar phenomenon is observed with the lifetime of
the photocatalyst. As concentration of quencher increases, the lifetime becomes faster. While both
21

methods are effective at determining Stern-Volmer quenching rates, one major advantage to using
lifetime over emission intensity is changes in lifetime are only observed for dynamic quenching
(Figure 17). Dynamic quenching is quenching that occurs when the photocatalyst is in its excited
state, while static quenching occurs when two molecules form a complex prior to excitation. Since
we are looking at electron transfer between the excited photocatalyst and the quencher in the
ground state, we are looking specifically at dynamic quenching. As emission intensity cannot
differentiate between static and dynamic quenching, plotting lifetime as a function of quencher is
the preferred method.

Figure 17. The impact of static and dynamic quenching as a function of quencher
concentration.
36

1.7. References
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17. Schildknecht, C.; Ginev, G.; Kammoun, A.; Riedl, T.; Kowalsky, W.; Johannes, H.-
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Tris(phenylbenzimidazolinato) IrIII Carbene Complexes as a Blue Phosphorescent Material.
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Iridium(III) Complexes. Inorganic Chemistry 2018, 57 (15), 8881-8889.
23. Sajoto, T.; Djurovich, P. I.; Tamayo, A. B.; Oxgaard, J.; Goddard, W. A.; Thompson,
M. E., Temperature Dependence of Blue Phosphorescent Cyclometalated Ir(III) Complexes.
Journal of the American Chemical Society 2009, 131 (28), 9813-9822.
24. Arroliga-Rocha, S.; Escudero, D., Facial and Meridional Isomers of Tris(bidentate) Ir(III)
Complexes: Unravelling Their Different Excited State Reactivity. Inorganic Chemistry 2018, 57
(19), 12106-12112.
25. Lee, J.; Chen, H.-F.; Batagoda, T.; Coburn, C.; Djurovich, P. I.; Thompson, M. E.;
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Emissive fac/mer-Iridium (III) NHC Carbene Complexes and their Application in OLEDs.
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in Deep-Red Luminescent Iridium(III) Complexes. Inorganic Chemistry 2020, 59 (4), 2266-
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Containing Conjugated Polymers and Monomers. Journal of the American Chemical Society
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Coordinate Cu(I) Complexes Featuring Nonconventional N-Heterocyclic Carbenes. Journal of
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25

Chapter 2. Phosphorescent Bis-cyclometalated Iridium Complexes Containing Bis-oxazoline
Derived Ancillary Ligands
2.1. Introduction
Luminescent iridium (III) complexes have recently garnered attention for their application
in biosensors
1
, photoredox catalysis
2-3
and organic light-emitting diodes
4
. Interest in these heavy
metal emitters stems from their demonstrated ability to harvest both singlet and triplet excitons
and give photoluminescent efficiencies up to 100%. Spin orbit coupling (SOC) of the heavy
iridium ion leads to ultrafast intersystem crossing to the triplet excited state. Next, the strong SOC
of the heavy iridium atom of these emitters impart substantial singlet character to the nominally
triplet states leading to emission on the μs timescale and near unity efficiencies for
phosphorescence.
Some of the most common and successful phosphorescent emitters are bis-cyclometalated
iridium complexes, (C^N)2Ir(L^X),
5
where the cyclometalating (C^N) ligand is composed of a C
that is a covalently bound arene or other organic moiety and N is datively bound nitrogen of a
heterocyclic ring
6-7
and the ancillary ligand (L^X) is monoanionic bidentate ligand. Some benefits
of these (C^N)2Ir(L^X) over their tris-cyclometated iridium complex counterparts, Ir(C^N)3,
include easier synthesis and tuning of the emission properties for the heteroleptic complexes.
8

While a wide variety of ancillary ligands have been incorporated into bis-cyclometalated iridium
complexes,
9-16
few work well across the entire visible spectral range. Of these ancillary ligands,
very few are chiral.
17-20

C2-symmetric bis(oxazoline) units, commonly referred to as BOX, have been widely
implemented as ligands for chiral catalysis
21-22
and coordination chemistry
23
. These compounds
26

are considered “privileged ligands” for their ability to perform a wide variety of chemical
transformations with a high degree of selectivity.
24
The wide use of BOX is owed in part to its
ease of synthesis. Enantiomerically pure chiral BOX ligands can be readily synthesized from chiral
precursors. While BOX had been broadly implemented as ligands, their use in bis-cyclometalated
iridium complexes is severely limited.
To the best of our knowledge, the first and only use of BOX in bis-cyclometalated iridium
complexes was reported by Marchi et. al.
25
The C^N ligand used in these complexes was F2ppy
whose Ir(C^N)3 is a sky-blue emitter. In comparison to the L^X = acac counterpart, both the chiral
and achiral BOX ligands resulted in a significant red-shift in the emission (58 and 100 nm,
respectively). In this case the BOX ligand is not truly ancillary as the HOMO and excited state
are largely composed of BOX π-orbitals. The authors reported that upon cycling electrochemically
a new iridium (IV) species was formed, presumably stabilized by the strongly electron donating
BOX ligand.
Building on this work, we looked at strategically modifying the meso-position of the BOX
ligand to stabilize the HOMO, resulting in a blue-shift in the λmax of emission. This stabilization
was accomplished through the use of an electron withdrawing cyano (CN) group. The BOX-CN
complexes highlighted in this study include racemic mixtures of the Δ- and Λ- diastereomers of
(ppz)2Ir(BOX-CN) (1
Δ,Λ
), (F2ppy)2Ir(BOX-CN) (2
Δ,Λ
) and (piq)2Ir(BOX-CN) (4
Δ,Λ
) as well as
diastereotopically pure Δ- and Λ- isomers of (ppy)2Ir(BOX-CN) (3
Δ
and 3
Λ
). All complexes were
photophysically and electrochemically characterized. 3
Δ
and 3
Λ
were additionally characterized
through X-ray crystallography, circular dichroism, and stability studies.
27

2.2. Results and Discussion
2.2.1. Synthesis.
BOX-CN was synthesized in two steps following literature procedures.
26-27
The
(C^N)2Ir(BOX-CN) complexes were synthesized by deprotonation of the BOX-CN ligand using
K2CO3 and reaction with [(C^N)2Ir(μ-Cl)]2 (Scheme 1). Complexes 1-4
Δ,Λ
were isolated in yields
of 65-83% and were obtained in roughly 1:1 ratios of the Δ- and Λ- diastereomers based on NMR.
The microcrystalline powders of the complexes ranged in color from white (1
Δ,Λ
) to red (4
Δ,Λ
)
based on the C^N ligand used. All complexes are air- and moisture-stable. No special handling
was required. We took advantage of the differences in solubility to separate the diastereomers of
3, 3
Δ
and 3
Λ
. 3
Δ
dissolves easily in ethyl acetate while 3
Λ
is not as soluble. The major fraction of
3
Δ
was purified by washing this fraction with cold ethyl acetate. The material dissolved in the cold
ethyl acetate was pure 3
Δ
. 3
Λ
was purified by heating the major fraction containing mostly 3
Λ
in
ethyl acetate. The mixture was filtered hot.

Scheme 1. Synthesis of (C^N)2Ir(BOX-CN) complexes.
28

2.2.2. X-ray Crystallography
Single crystal x-ray crystallography was used examine the two diastereomers of
(ppy)2Ir(BOX-CN). These crystals were grown by dissolving the complex in a minimum amount
of CH2Cl2, running this solution through a microfilter and layering MeOH on top of this solution.
This sample was allowed to slowly evaporate to produce crystals suitable for x-ray
crystallography. The structures of the Δ- and Λ- diastereomers of (ppy)2Ir(BOX), 3
Δ
and 3
Λ

respectively, are shown in Figure 18. The determined bond lengths and angles are shown in Table
2. The structure about the iridium ion is pseudo-octahedral for both 3
Δ
and 3
Λ
. 3
Δ
has bond lengths
for the Ir-N(pyridine) and Ir-C(phenyl) bonds of 2.033-2.053 (2) Å and 2.013-2.014 (2) Å respectively.
The Ir-N(BOX) bond lengths are significantly longer at 2.171-2.199 (2) Å. The bond lengths for 3
Λ

are within the same range as those for 3
Δ.
3
Λ
has bond lengths for Ir-N(pyridine), Ir-C(phenyl), and Ir-
N(BOX) of 2.046-2.069 (2) Å, 2.022-2.037 (2) Å, and 2.176-2.183 (2) Å respectively. Overall, the
Ir-N(pyridine) and Ir-C(phenyl) have similar bond lengths. One noticeable difference between the two
structures has to do with the overlap between the pyridyl ppy and the phenyl on the BOX ligand
for 3
Λ
. This overlap forms a compact structure and is likely the reason for why this material has
poor solubility in several solvents.

Figure 18. Crystal structure of 3
Δ
(left) and 3
Λ
(right). Hydrogens were omitted for clarity.
29

Table 2. Bond lengths for 3
Δ
(left) and 3
Λ
.
Bond lengths 3
Δ
3
Λ

Ir-N(pyridine) 2.033 (2) 2.069 (2)
Ir-N(pyridine) 2.053 (2) 2.046 (2)
Ir-C(phenyl) 2.013 (2) 2.022 (2)
Ir-C(phenyl) 2.014 (2) 2.037 (2)
Ir-N(BOX) 2.199 (2) 2.183 (2)
Ir-N(BOX) 2.171 (2) 2.176 (2)

2.2.3. Reactivity Studies
Laser desorption/ionization time of flight (LDI-TOF) spectra were taken of all
(C^N)2Ir(BOX-CN) complexes. The LDI for 3
Δ
is shown in Figure 19. LDI-TOF of 3Δ. Similar
to what was observed for Ir(ppy)2(acac), the parent ion was not observed for most complexes,
suggesting that these complexes have similar stabilities to Ir(ppy)2(acac).
28
Interestingly, 2
Δ,Λ
is
the only derivative where the parent ion can still be detected. Instead of the parent ion peak, these
complexes have a major peak with a molecular weight indicative of loss of the BOX-CN ligand.
Similar observations in the LDI-TOF spectra of Ir(ppy)2(acac) prompted Nazeerudin et. al. to look
at the acid-induced degradation of this complex.
28
Addition of HCl to Ir(ppy)2(acac) dissolved in
CDCl3 resulted in the formation of the chloride bridge Ir dimer via cleavage of the Ir-O bonds of
the acac ancillary ligand.
30

Figure 19. LDI-TOF of 3
Δ
.
Similar acid-induced degradation reactions were performed on 3
Δ,Λ
to see if these
complexes also underwent the same degradation parthway as the acac analogue. Ir(ppy)2(acac)
was ran alongside 3
Δ,Λ
as a control. 0.2 M HCl was added to NMR tubes of the iridium complexes
dissolved in CDCl3.

The resulting
1
H-NMR spectras are shown for Ir(ppy)2(acac) and 3
Δ,Λ
in
Figure 20 and Figure 21 respectively. Addition of HCl readily converts Ir(ppy)2(acac) into the
chloride bridged dimer. Surprisingly, 3
Δ,Λ
does not appear to follow the same degradation pathway
as Ir(ppy)2(acac). In fact, very little decomposition is observed for 3
Δ,Λ
, implying that the BOX-
CN ligand is more stable to acid than its acac counterpart.

31

Figure 20.
1
H-NMRs for acid-induced degradation of (ppy)2Ir(acac) using 0.2 M HCl in ether.

Figure 21.
1
H-NMRs for acid-induced degradation of 3
Δ,Λ
using 0.2 M HCl in ether.
32

To further probe the overall stability of these complexes, thermal gravimetric analysis
(TGA) was performed on 3
Δ
and 3
Λ
. TGA was also taken of (ppy)2Ir(acac) as a reference. These
materials show remarkable stability with sublimation observed above 400 ℃. In comparison, the
acac derivative had sublimation temperature below 400 ℃. The TGA data suggests that the BOX
complexes are more stable.

Figure 22. TGA of 3
Δ
versus (ppy)2Ir(acac).
2.2.4. Computation
Density functional theory (DFT) was performed using QChem and IQmol at the
B3LYP/LACVP* level. For all five complexes, the highest occupied molecular orbital (HOMO)
is localized on the iridium and BOX ligand while the lowest occupied molecular orbital (LUMO)
is mostly localized on the pyridine ring with small contributions from the iridium and phenyl ring
of the ppy moiety. These calculations indicate that these complexes undergo a metal-ligand to
ligand charge transfer (ML’LCT), analogous to the tris-cyclometalated complexes. However, the
ligand contribution of the HOMO is from the BOX-CN and not the arene of the C^N ligand. The
HOMO of the (C^N)2Ir(BOX-CN) complexes is stabilized in comparison to the tris complexes as
a result of the electronegativity of the cyano group at the meso position of the BOX-CN ligand.
33

2.2.5. Electrochemistry
Cyclic voltammetry and differential pulse voltammetry (DPV) electrochemical
measurements were carried out on complexes 1-4
Δ,Λ
in dimethylformamide. Cyclic voltammetry
was used to determine the reversibility of oxidation and reduction features, while DPV was used
to assign the oxidation and reduction potentials. The electrochemical potentials are summarized in
Table 3. The tris, acac and picolinate analogues of 2
Δ,Λ
, 3
Δ
and 3
Λ
are also listed for reference.
All complexes show up to one reversable oxidation and up to 3 quasi-reversible/reversible
reduction waves. The reduction potentials vary depending on the C^N ligand used. With the
exception of 2
Δ,Λ
, the oxidation potentials are similar, regardless of C^N ligand used. 3
Δ
and 3
Λ

show the same oxidation and reduction potentials within experimental error.

Table 3. Electrochemistry of complexes 1-4
Δ,Λ
in DMF.

E
ox
a
E
red
a

1
Δ,Λ
0.44 -3.31
2
Δ,Λ
0.58 -2.51, -2.86, -3.23 (q)
fac-Ir(F2ppy)3
b
0.78 -2.51, -2.81
(F2ppy)2Ir(acac)
b
0.74 -2.45, -2.79 (q), -3.02 (q)
FIrpic
b
0.90 -2.29, -2.63 (q), -3.01
3
Δ
0.36 -2.69
3
Λ
0.44 -2.69
Ir(ppy)3
b
0.31 -2.70, -3.00
(ppy)
2
Ir(acac)
b
0.40 -2.61 (q), -2.92 (q)
(ppy)2Ir(pic)
b
0.55 -2.39, -2.78, -3.11 (q)
4
Δ,Λ
0.41 -2.22, -2.49, -3.24
a
Potentials are quoted relative to the ferrocene/ferrocenium couple.
b
Literature.
34

2.2.6. Photophysical Properties
3
Δ
and 3
Λ
show similar absorbance spectra (Figure 23). However, there are noticeable
differences at ~350 and ~400 nm that are likely the result of the slight structural differences
between the two diastereomers. 3
Λ
has better π-orbital overlap between the pyridine in the ppy
ligand and the phenyls on the bis-oxazoline ligand. Features above 350 nm (ε ≈ 1 x 10
4
M
-1
cm
-
1
)

are assigned to a ligand centered (LC) transition, which is spin-allowed. Absorption bands at
360-440 nm (ε ≈ 4 x 10
3
M
-1
cm
-1
) are assigned to
1
ML’LCT spin allowed transitions based on
calculations. The weakest absorption bands are assigned to
3
ML’LCT transitions, which are spin-
forbidden. Overall, absorption bands shift with respect to the C^N ligand used, with 1
Δ,Λ
and 4
Δ,Λ

being the most blue- and red-shifted spectra respectively.
300 400 500 600
0
5
10
15
20
25
e (10
3
M
-1
cm
-1
)
Wavelength (nm)
1
,
2
,
3

3

4
,

Figure 23: Molar absorptivity of complexes 1-4
Δ,Λ
in 2Me-THF.
2.2.7. Luminescence
The emission spectra of the (C^N)Ir(BOX-CN) complexes at RT and 77 K are shown in
Figure 24. The photophysical properties are summarized in Table 4. The emission of these
materials ranges from the near UV to red depending on the C^N ligand used. Aside from 2
Δ,Λ
, all
complexes are blue-shifted from their respective tris complex. As mentioned previously, the
35

HOMO of these (C^N)Ir(BOX-CN) is partially localized on the BOX-CN ligand. The electron
withdrawing nature of the cyano group pulls electron density off the BOX and Ir metal center,
resulting in a stabilization of the HOMO and subsequent blue-shift in the emission. For all
complexes, the photophysical properties do not vary with increasing solvent polarity. This
indicates less charge transfer character of the excited state. Overall, these complexes have fast
lifetimes (1.2-2.1 μs) and moderate to high ΦPL values (0.45-0.99) in 2Me-THF. The high radiative
(10
5
s
-1
) and lower nonradiative rates (10
4
-10
5
s
-1
). The emission maxima increase upon cooling to
77 K is indicative of the complex not being able to nonradiatively relax to lower energy states. The
lifetime also increases upon cooling due to subduing these nonradiative pathways.
1
Δ,Λ
is non-emissive at RT due to thermally population of metal center states (
3
MC), which
are nonemissive. Upon cooling, these states are no longer thermally accessible, resulting in these
materials being emissive at 77 K. The emission maximum and lifetimes are comparable to that of
Ir(ppz)3
29
. As mentioned previously, 2
Δ,Λ
is the only complex that is red-shifted in emission from
both its tris and bis-cyclometalated complexes. This red-shift in emission is the result of 2
Δ,Λ

having a HOMO shifted away from a C^N ligand with a deeper HOMO. 3
Δ
and 3
Λ
are the Δ- and
Λ- isomers of (ppy)2Ir(BOX-CN), respectively. The photophysical properties of 3
Δ
and 3
Λ
are
similar to that of Ir(ppy)3 and the acac derivative, (ppy)2Ir(acac). However, one major difference
between these analogues is the emission maxima. 3
Δ
and 3
Λ
are blue-shifted by ~6 and ~20 nm at
RT from the Ir(ppy)3 and (ppy)2Ir(acac) respectively. This blue-shift in the emission is the result
of the BOX-CN ligand stabilizing the HOMO. Additionally, the increased LC character in 3
Δ
and
3
Λ
leads to a decrease in the spin-orbital coupling, resulting in a slightly lower kr for these
complexes to that of the acac derivative. The vibronic character of the emission for 3
Δ
and 3
Λ
becomes more pronounced at 77 K. In addition, the lifetimes at RT and 77 K for these complexes
36

are slightly longer than those of (ppy)2Ir(acac), which is likely a result of less MLCT character
mixing in excited states of 3
Δ
and 3
Λ
. Finally, 4
Δ,Λ
is the most red-shifted of the (C^N)2Ir(BOX-
CN) complexes. 4
Δ,Λ
has a significantly lower PLQY to that of the other BOX-CN complexes.
However, the PLQY of 4
Δ,Λ
is comparable to that of the tris complex Ir(piq)3, indicating that the
drop in the PLQY is not the result of the BOX-CN ligand but has to do with the C^N ligand used.
A drop in PLQY with an increase in the nonradiative rate is the result of energy gap law.

Table 4. Photophysical properties of complexes 1-4 in 2Me-THF.

λmax
(nm)
τ
(µs)
ΦPL
kr
(10
5
s
-1
)
knr
(10
5
s
-1
)
λmax.77K
(nm)
τ77K (µs)
1
Δ,Λ
- - - - - 410 18 (43), 28 (57)
Ir(ppz)3
29
- - - - - 412 14
2
Δ,Λ
480 2.1 0.99 4.7 <0.05 466 2.8
Ir(F2ppy)3
29
466 1.7 0.98 5.8 0.12 454 2.6
FIrpic 470 1.7 0.99 5.8
a
<0.06
a
460 2.9
3
Δ
503 1.9 0.92 4.8 0.42 489 3.2
3
Λ
501 2.0 0.91 4.6 0.45 488 3.1
Ir(ppy)3
29
508 1.6 0.97 6.1 0.19 491 4.0
(ppy)2Ir(acac) 522 1.5 0.92 6.1
a
0.53
a
506 5.2
4
Δ,Λ
614 1.7 0.45 2.7 3.2 602 2.2
Ir(piq)3
30
624 1.3 0.45 3.5
a
4.2
a
- -
a
Calculated from literature values.
37

450 500 550 600 650 700 750 800 850
0
0.2
0.4
0.6
0.8
1
Normalized Intensity (a.u.)
Wavelength (nm)
2
,
3

3

4
,
RT

400 450 500 550 600 650 700 750 800
0
0.2
0.4
0.6
0.8
1
Normalized Intensity (a.u.)
Wavelength (nm)
1
,
2
,
3

3

4

77 K

Figure 24. Emission of complexes 1a-5b in 2Me-THF at (left) RT and (right) 77 K.
2.2.8. Chiroptic properties
Circular dichroism spectra were taken of the (ppy)2Ir(BOX-CN) complexes (Figure 25).
Mirror images with similar intensity are observed for the enantiomer pairs, 3SS
Δ
/3RR
Λ
and
3RR
Δ
/3SS
Λ
. Transitions above 300 are ascribed to LC transitions while transitions between 300-375
nm are from MLCT transitions. Interestingly, 3RR
Δ
and 3SS
Λ
have intense CD transitions in this
region.
250 300 350 400 450 500 550 600
-80
-60
-40
-20
0
20
40
60
80
I
CPL
Wavelength (nm)
-SS
-SS
-RR
-RR

Figure 25. Circular dichroism of 3SS
Δ
,3SS
Λ
, 3RR
Δ
, and 3RR
Λ
in CH2Cl2.
38

2.3. Experimental
2.3.1. Synthesis
General
All reactions were carried out under nitrogen using standard Schlenk line techniques unless
otherwise noted. Diethyl malonimidate dihydrochloride, 2-Methyl tetrahydrofuran (2Me-THF)
and methylcyclohexane (MeCy) were purchased from Sigma-Aldrich and used without and further
purification. Tetrahydrofuran (THF), dichloromethane (CH2Cl2), and toluene were dried using a
dry solvent system from Glass Contour. Dimethylformamide (DMF) was purchased from
Milipore. The chloride-bridged C^N iridium dimer precursors, [(C^N)2Ir(μ-Cl)]2, were
synthesized following standard Nonoyama conditions. All NMRs were performed on a Varian
400 NMR spectrometer and referenced to the deuterated acetone’s residual proton signal.
Elemental analysis was performed at the University of Southern California. Absorbance and molar
absorptivity data were measured using a UV-VIS Hewlett-Packard 4853 diode array spectrometer.
Photoluminescence quantum yields were recorded using a Hamatsu C9920 integrating sphere
equipped with a xenon lamp. Lifetimes were measured using a Time-Correlated Single Photon
Counting (TCSPC). Steady state excitation and emission spectra were obtained using a Photon
Technology International QuantaMaster phosphorescence/fluorescence spectrofluorimeter. Both
Cyclic Voltammetry (CV) and Differential pulse voltammetry (DPV) were performed through use
of an EG&G potentiostat/galvanostat model 283. The electrolyte was composed of 0.1 M tetra-n-
butylammonium hexafluorophosphate (TBAF) in anhydrous DriSolv acetonitrile and
dimethylformamide. The measurements were taken under an inert atmosphere. The working,
counter, and pseudoreference electrodes were composed of glassy carbon, platinum wire, and
silver wire respectively. All complexes were referenced to an internal ferrocene/ferrocenium
39

(Fc/Fc
+
) redox couple. A Bruker Autoflex Speed MALDI-TOF spectrometer was used to obtain
mass spectroscopy data. Neat films of the materials were deposited on the Maldi plate by
dissolving the complex in CH2Cl2 and spotting the plate with this solution. QCHEM 5.1 and iQmol
were used to run ground-state geometry optimized and triplet spin density calculations on all
complexes at the B3LYP/LACVP* level.

Individual Syntheses
General synthesis of BOXSS-CN/ BOXRR-CN ((4S)-(+)-phenyl-α-[(4S)-phenyloxazolidin-2-
ylidene]-2-oxazoline-2-acetonitrile) and ((4R)-(+)-phenyl-α-[(4R)-phenyloxazolidin-2-
ylidene]-2-oxazoline-2-acetonitrile), respectively. BOXSS-CN was either purchased from Sigma
Aldrich and used without purification or synthesized in two steps from diethylmalonimidate
dihydrochloride. Bis((S)-4-phenyl-4,5-dihydrooxazol-2-yl)methane (BOXSS-H) was first
synthesized following a prep by Guan et. al.
26
using (S)- and (R)-phenylglycinol, respectively.
BOX-H was converted to BOXSS-CN following a prep by Nolin et. al.
27
BOXRR-CN was
synthesized in a similar manner.

Figure 26. Synthesis of BOXSS-CN.
26-27

General synthesis of all complexes with BOXSS-CN/ BOXRR-CN. 1-4 were synthesized
following a two-step procedure. The chloride-bridged dimers of the respective cyclometalating
ligand were synthesized following standard Nonoyama reaction conditions. To an oven-dried
40

flask, the BOX ligand (2.2 equiv.), K2CO3 (10 equiv.) and THF (40 mL) were added and allowed
to stir at RT for ~1h. [(ppy)2Ir(μ-Cl)]2 (250 mg) was added to the flask and the reaction was
brought to reflux and stirred overnight. The reaction mixture was cooled to room temperature,
reduced to half the volume, filtered to remove excess potassium carbonate, and the solvent was
removed in vacuo. Excess BOX ligand was removed from the reaction mixture by a silica column
using 50:50 hexanes: ethyl acetate.
General Synthesis for (ppz)2Ir(BOXss-CN) BOXSS-CN (117 mg, 535 μmol), K2CO3 (336 mg,
2.43 mmol), ppy iridium dimer (250 mg, 243 μmol). White microcrystalline powder. (326 mg,
83% yield of isomer mixture).
(ppz)2Ir(BOXSS-CN) (1
Δ,Λ
).
1
H NMR (400 MHz, Acetone-d6) δ 8.49 (d, J = 2.9 Hz, 2H), 7.38 (d,
J = 7.9 Hz, 2H), 7.27 (d, J = 2.2 Hz, 2H), 7.14 (dd, J = 5.0, 1.9 Hz, 6H), 6.81 – 6.66 (m, 6H), 6.56
(t, J = 2.6 Hz, 2H), 6.23 (td, J = 7.4, 1.2 Hz, 2H), 5.47 (dd, J = 7.5, 1.4 Hz, 2H), 4.11 (t, J = 8.7
Hz, 2H), 4.04 (dd, J = 8.6, 3.6 Hz, 2H), 3.90 (dd, J = 8.9, 3.6 Hz, 2H). 13C NMR (101 MHz,
acetone) δ 143.48, 143.37, 139.78, 135.51, 134.13, 128.08, 127.17, 126.69, 126.38, 124.75,
121.06, 110.66, 107.00, 75.25, 69.39.

Elemental Analysis: Anal. Calcd. for C38H30IrN7O2: C, 56.4;
H, 3.74; N, 12.1. Found: C, 56.1; H, 3.75; N 11.8.

General Synthesis for (F2ppy)2Ir(BOXSS-CN) BOXSS-CN (300 mg, 905 mmol), K2CO3 (568 mg,
4.11 mol), ppy iridium dimer (500 mg, 411 mmol). Light yellow microcrystalline powder. (482
mg, 65% yield of isomer mixture).
NMR is a mixture of diastereomers. I was able to determine which peaks belonged to which
diastereomer by overlaying NMRs that contained 1:1 of the isomers with an NMR of 3:4 of the
diastereomers.
41

Diastereomer starting at 8.82 ppm
1
H NMR (400 MHz, Acetone-d6) δ 8.82 (ddd, J = 5.8, 1.6, 0.8
Hz, 2H), 7.57 (dddd, J = 8.4, 2.4, 1.5, 0.8 Hz, 2H), 7.48 (ddd, J = 7.4, 5.8, 1.5 Hz, 2H), 7.32 (ddd,
J = 7.3, 5.8, 1.4 Hz, 2H), 6.91 (tt, J = 7.4, 1.3 Hz, 2H), 6.73 (dd, J = 8.5, 7.1 Hz, 4H), 6.26 (ddd, J
= 12.8, 9.4, 2.4 Hz, 2H), 6.17 – 6.11 (m, 4H), 5.37 (dd, J = 8.9, 2.4 Hz, 2H), 4.83 (dd, J = 8.7, 2.7
Hz, 2H), 4.72 (d, J = 8.6 Hz, 2H), 4.00 – 3.97 (m, 2H).
Diastereomer starting at 8.79 ppm
1
H NMR (400 MHz, Acetone-d6) δ 8.79 (ddd, J = 5.8, 1.7, 0.8
Hz, 2H), 8.26 – 8.18 (m, 2H), 7.99 (dddd, J = 8.2, 7.5, 1.7, 0.8 Hz, 2H), 7.13 – 7.07 (m, 6H), 6.81
– 6.76 (m, 4H), 6.34 (ddd, J = 12.8, 9.3, 2.4 Hz, 2H), 4.80 – 4.74 (m, 2H), 4.20 (dd, J = 8.9, 8.2
Hz, 2H), 4.07 – 4.00 (m, 4H).
13
C NMR (101 MHz, Acetone-d6) δ 157.01, 151.88, 148.55, 142.20, 142.15, 138.37, 137.66,
127.95, 127.69, 127.36, 127.04, 126.54, 123.17, 122.97, 122.92, 122.28, 122.07, 114.76, 112.40,
96.75, 96.48, 75.96, 75.50, 69.77, 69.19, 13.57, -5.66. Elemental Analysis: Anal. Calcd. for
C38H30IrN7O2: C, 55.8; H, 3.13; N, 7.76. Found: C, 55.5; H, 3.10; N 7.76.
General Synthesis for (ppy)2Ir(BOXSS-CN) BOXSS-CN (340 mg, 1.03 mol), K2CO3 (645 mg,
4.66 mol), ppy iridium dimer (500 mg, 466 mmol). Bright yellow powder. (636 mg, 82% yield of
isomer mixture).
Column chromatography was ran using 50:50 hexanes: ethyl acetate. The first major fraction to
come off the column was primarily 3
Δ
came as 3
Λ
doesn’t dissolve well in either hexanes or ethyl
acetate. After most of 3
Δ
came off the column, CH2Cl2 was used to flush 3
Λ
resulting in a second
major fraction that was primarily 3
Λ
. 3
Δ
dissolves easily in ethyl acetate while 3
Λ
is not as soluble.
The major fraction of 3
Δ
was purified by washing this fraction with cold ethyl acetate. The material
dissolved in the cold ethyl acetate was pure 3
Δ
. 3
Λ
was purified by heating the major fraction
42

containing mostly 3
Λ
in ethyl acetate. The mixture was filtered hot. The solid collected in the filter
was pure 3
Λ
.
Δ-(ppy)2Ir(BOXss-CN) (3
Δ
).
1
H NMR (400 MHz, Acetone-d6) δ 8.50 (d, J = 5.4 Hz, 2H), 8.01 (d,
J = 8.1 Hz, 2H), 7.88 – 7.79 (m, 2H), 7.65 (d, J = 7.5 Hz, 2H), 7.18 – 7.02 (m, 8H), 6.77 – 6.70
(m, 2H), 6.63 (dd, J = 7.4, 2.2 Hz, 4H), 6.28 (td, J = 7.4, 1.3 Hz, 2H), 5.50 (d, J = 7.7 Hz, 2H),
4.10 – 3.99 (m, 4H), 3.93 (dd, J = 8.5, 4.2 Hz, 2H).
13
C NMR (101 MHz, acetone) δ 168.01,
166.58, 152.47, 151.31, 144.08, 142.70, 137.08, 133.66, 128.47, 127.91, 127.18, 127.13, 123.84,
121.64, 120.51, 118.21, 75.46, 68.55. Elemental Analysis: Anal. Calcd. for C42H32IrN5O2: C, 60.7;
H, 3.88; N, 8.43. Found: C, 60.5; H, 3.80; N 8.34.
Λ-(ppy)2Ir(BOXss-CN) (3
Λ
):
1
H NMR (400 MHz, Acetone-d6) δ 8.74 (d, J = 5.3 Hz, 2H), 7.65 –
7.57 (m, 2H), 7.34 (ddd, J = 7.3, 5.8, 1.5 Hz, 2H), 7.26 (d, J = 8.3 Hz, 2H), 6.92 – 6.86 (m, 2H),
6.82 (t, J = 7.4 Hz, 2H), 6.62 (t, J = 7.7 Hz, 4H), 6.58 – 6.50 (m, 4H), 6.00 (d, J = 7.1 Hz, 4H),
5.96 – 5.89 (m, 2H), 4.73 (dd, J = 8.6, 2.4 Hz, 2H), 4.62 (t, J = 8.4 Hz, 2H), 3.92 (dd, J = 8.2, 2.5
Hz, 2H).
13
C NMR (101 MHz, Acetone-d6) δ 168.51, 148.01, 145.42, 142.42, 136.39, 130.42,
128.76, 127.46, 126.03, 124.73, 123.71, 122.25, 120.22, 119.06, 75.77, 69.82. Elemental Analysis:
Anal. Calcd. for C42H32IrN5O2: C, 60.7; H, 3.88; N, 8.43. Found: C, 60.4; H, 3.83; N 8.34.
General Synthesis for (ppy)2Ir(BOXRR-CN) BOXRR-CN (340 mg, 1.03 mol), K2CO3 (645 mg,
4.66 mol), ppy iridium dimer (500 mg, 4.66 mmol). Bright yellow powder. (612 mg, 79% yield of
isomer mixture). The Δ- and Λ- isomers of the (ppy)2Ir(BOXRR-CN) complexes were separated
similarly to the (ppy)2Ir(BOXSS-CN). 3
Δ
and 3RR
Λ
are enantiomers. As such, 3RR
Λ
comes off the
column first and dissolves readily in ethyl acetate as was the case with 3
Δ
. 3
Λ
and 3RR
Δ
are also
43

enantiomers. 3RR
Δ
doesn’t dissolve well in ethyl acetate and its major fraction comes off the
column after switching from ethyl acetate to CH2Cl2 similarly to 3
Λ
.
Δ-(ppy)2Ir(BOXRR-CN) (3RR
Δ
):
1
H NMR (400 MHz, Acetone-d6) δ 8.78 (ddd, J = 5.8, 1.6, 0.8 Hz,
2H), 7.65 (ddd, J = 8.1, 7.4, 1.6 Hz, 2H), 7.37 (ddd, J = 7.3, 5.7, 1.5 Hz, 2H), 7.33 – 7.26 (m, 2H),
6.95 – 6.90 (m, 2H), 6.90 – 6.83 (m, 2H), 6.66 (t, J = 7.8 Hz, 4H), 6.64 – 6.55 (m, 4H), 6.08 – 6.00
(m, 4H), 6.00 – 5.92 (m, 2H), 4.76 (dd, J = 8.5, 2.4 Hz, 2H), 4.66 (t, J = 8.4 Hz, 2H), 3.95 (dd, J
= 8.2, 2.4 Hz, 2H).
13
C NMR (101 MHz, Acetone-d6) δ 168.51, 148.01, 142.42, 136.40, 130.42,
128.76, 127.46, 126.02, 124.72, 123.71, 122.25, 120.22, 119.06, 75.77, 69.82.
Λ-(ppy)2Ir(BOXRR-CN) (3RR
Λ
):
1
H NMR (400 MHz, Acetone-d6) δ 8.50 (ddd, J = 5.8, 1.6, 0.8 Hz,
2H), 8.02 (ddd, J = 8.2, 1.4, 0.7 Hz, 2H), 7.84 (ddd, J = 8.1, 7.4, 1.6 Hz, 2H), 7.65 (dd, J = 7.7,
1.3 Hz, 2H), 7.17 – 7.02 (m, 8H), 6.73 (ddd, J = 7.7, 7.2, 1.2 Hz, 2H), 6.67 – 6.59 (m, 4H), 6.28
(ddd, J = 7.6, 7.2, 1.3 Hz, 2H), 5.50 (ddd, J = 7.7, 1.3, 0.5 Hz, 2H), 4.07 (dd, J = 8.5, 4.2 Hz, 2H),
4.02 (t, J = 8.5 Hz, 2H), 3.93 (dd, J = 8.5, 4.2 Hz, 2H).
13
C NMR (101 MHz, Acetone-d6) δ 168.01,
152.47, 151.31, 144.08, 142.70, 137.08, 133.66, 128.47, 127.91, 127.18, 127.13, 123.84, 121.64,
120.51, 118.21, 75.46, 68.55.
General Synthesis for (piq)2Ir(BOXss-CN) BOXSS-CN (143 mg, 432 μmol), K2CO3 (272 mg,
1,96 mmol), ppy iridium dimer (250 mg, 196 μmol). Bright yellow powder. (636 mg, 82% yield
of isomer mixture). Dark red microcrystalline powder. (289 mg, 79% yield of isomer mixture).
(piq)2Ir(BOXSS-CN) (4
Δ,Λ
).
1
H NMR (400 MHz, Acetone-d6) δ 8.49 (d, J = 2.9 Hz, 2H), 7.38 (d, J
= 7.9 Hz, 2H), 7.27 (d, J = 2.2 Hz, 2H), 7.14 (dd, J = 5.0, 1.9 Hz, 6H), 6.81 – 6.66 (m, 6H), 6.56
(t, J = 2.6 Hz, 2H), 6.23 (td, J = 7.4, 1.2 Hz, 2H), 5.47 (dd, J = 7.5, 1.4 Hz, 2H), 4.11 (t, J = 8.7
Hz, 2H), 4.04 (dd, J = 8.6, 3.6 Hz, 2H), 3.90 (dd, J = 8.9, 3.6 Hz, 2H). 13C NMR (101 MHz,
44

Acetone-d6) δ 156.19, 143.75, 142.06, 140.69, 136.94, 136.76, 133.61, 131.03, 130.87, 130.63,
130.04, 129.58, 128.93, 128.60, 128.07, 127.87, 127.53, 127.44, 127.15, 127.08, 127.06, 126.67,
126.41, 126.26, 126.25, 125.82, 125.64, 124.91, 120.72, 120.27, 120.10, 119.62, 75.75, 75.51,
69.43, 68.61.

Elemental Analysis: Anal. Calcd. for C38H30IrN7O2: C, 64.5; H, 3.90; N, 7.52. Found:
C, 64.0; H, 3.82; N 7.44.
2.3.2. NMR spectra

Figure 27. NMRs of BOXSS-H, BOXSS-CN, BOXRR-CN, and the BOXSS-CN purchased from
Sigma Aldrich.
45

Figure 28.
1
H-NMR of 1
Δ,Λ
in d6-acetone with minor impurity of one diastereomer.

Figure 29.
13
C-NMR of 1
Δ,Λ
in d6-acetone.
46

Figure 30.
1
H-NMR of 2
Δ,Λ
in d6-acetone.

Figure 31.
13
C-NMR of 2
Δ,Λ
in d6-acetone.
47

Figure 32.
1
H-NMR of 3
Δ
in d6-acetone.

Figure 33.
13
C-NMR of 3
Δ
in d6-acetone
48

Figure 34. COSY NMR of 3
Δ
in d6-acetone.

Figure 35.
1
H-NMR of 3
Λ
in d6-acetone.

49

Figure 36.
13
C-NMR of 3
Λ
in d6-acetone.

Figure 37. COSY-NMR of 3
Λ
in d6-acetone (from 3.6 ppm to 9.0 ppm).
50

Figure 38.
1
H-NMR of 4
Λ, Λ
in d6-acetone.

Figure 39.
13
C-NMR of 4
Λ, Λ
in d6-acetone.
51

Figure 40. COSY-NMR of 4
Λ, Λ
in d6-acetone.

Figure 41.
1
H-NMR of 3RR
Δ
in d6-acetone.
52

Figure 42.
13
C-NMR of 3RR
Δ
in d6-acetone.

Figure 43.
1
H-NMR of 3RR
Λ
in d6-acetone.
53

Figure 44.
13
C-NMR of 3RR
Λ
in d6-acetone.
2.3.3. X-ray Crystallography Studies

Figure 45. Crystal structures of 3
Δ
and 3
Λ
.
Single x-ray crystallography was used to structurally characterize the Δ- and Λ-(ppy)2Ir(SS BOX-
CN) (3
Δ
and 3
Λ
respectively). The sample, crystal, data collection, and refinement are provided.

Δ-(ppy)2Ir(SS-BOX-CN) (3
Δ
) Λ-(ppy)2Ir(SS-BOX-CN) (3
Λ
)
54

Cifs are also provided. Thermal ellipsoids are shown at 50% probability. Hydrogens were omitted
for clarity. Atom colors are: Ir (blue), N (purple) C (gray), O (red).
Sample and crystal data for Δ-(ppy)2Ir(BOXSS-CN) (3
Δ
) and Λ-(ppy)2Ir(BOXSS-CN) (3
Λ
)
Complex 3
Δ
3
Λ

Chemical formula 3 (C42H32IrN5O2) C42H32IrN5O2
Formula weight 2492.77 g/mol 830.92
Temperature 100 K 100 K
Wavelength 0.71073 Å 0.71073 Å
Crystal system Monoclinic Orthorhombic
Space group P 1 21 1 P 21 21 21
a (Å) 17.121 (10) 10.021 (3)
b (Å) 14.689 (9) 14.262 (5)
c (Å) 24.264 (14) 23.831 (8)
α (deg) 90 90
β (deg) 109.717 (9) 90
γ (deg) 90 90
Volume (Å
3
) 5813 (6) 3406 (2)
Z 4 4
F(000) 2472.0 1648.0
Theta range for data collection 2.45 to 29.92 2.65 to 31.40
Index ranges -20<=h<=20
-17<=k<=17
-28<=l<=28
-5<=h<=13
-19<=k<=4
-10<=l<=33
Reflections Collected 99844 7011
Unique (Rint) 20386 6622
data/restraints/parameters 20386/1246/1633 6622/0/451
Goodness of Fit 1.054 0.923
Final R indices R1 = 0.0295 R1 =0.0327
55

[I>2σ(I)] wR2 = 0.0738 wR2 =0.0680
R indices (all data) R1 = 0.0310
wR2 =0.0748
R1 =0.0350
wR2 =0.0685
CCDC number

2.3.4. Laser desorption/ionization time of flight (LDI-TOF)

Figure 46. LDI-TOF of 1
Δ,Λ
.
56

Figure 47. LDI-TOF of FIrpic.

Figure 48. LDI-TOF of 2
Δ,Λ
.
57

Figure 49. LDI-TOF of fac-Ir(ppy)3.

Figure 50. LDI-TOF of (ppy)2Ir(acac).
58

Figure 51. LDI-TOF of 3
Λ
.

Figure 52. LDI-TOF of 3RR
Δ
.
59

Figure 53. LDI-TOF of 3RR
Λ
.

Figure 54. LDI-TOF of 4
Δ,Λ
.
60

2.3.5. Thermal Gravimetric Analysis (TGA)
0 100 200 300 400 500 600 700 800
50
60
70
80
90
100
Weight %
Temperature (°C)
-RR
-RR

Figure 55. TGA of 3RR
Δ
and 3RR
Λ
.

2.3.6. Theoretical Calculations
Ground state geometries of all complexes reported were optimized at the B3LYP/LACVP** level.

Calculations
HOMO
(eV calc)
LUMO
(eV calc)
1
Δ
-4.95 -1.03

Figure 56. HOMO (left) and LUMO (right) of complex 1
Δ
. B3LYP/LACVP*.
61

Calculations
HOMO
(eV calc)
LUMO
(eV calc)
1
Λ
-4.95 -1.03

Figure 57. HOMO (left) and LUMO (right) of complex 1
Λ
. B3LYP/LACVP*.

Calculations
HOMO
d

(eV calc)
LUMO
d
(eV
calc)
2
Δ
-5.25 -1.93

Figure 58. HOMO (left) and LUMO (right) of complex 2
Δ
. B3LYP/LACVP*.

62

Calculations
HOMO
(eV calc)
LUMO
(eV calc)
2
Λ
-5.28 -1.93

Figure 59. HOMO (left) and LUMO (right) of complex 2
Λ
. B3LYP/LACVP*.

Calculations
HOMO
(eV calc)
LUMO
(eV calc)
Δ -4.92 -1.58

Figure 60. HOMO (left) and LUMO (right) of complex 3
Δ
. B3LYP/LACVP*.

63

Calculations
HOMO
(eV calc)
LUMO
(eV calc)
Λ -4.95 -1.58

Figure 61. HOMO (left) and LUMO (right) of complex 3
Λ
. B3LYP/LACVP*.

Calculations
HOMO
(eV calc)
LUMO
(eV calc)
4
Δ
-4.90 -2.10

Figure 62. HOMO (left) and LUMO (right) of complex 4
Δ
. B3LYP/LACVP*.

64

Calculations
HOMO
(eV calc)
LUMO
(eV calc)
4
Λ
-4.90 -2.04

Figure 63. HOMO (left) and LUMO (right) of complex 4
Λ
. B3LYP/LACVP*.
2.3.7. Electrochemistry
-3 -2 -1 0 1 2
Current (a.u.)
Potential (V vs Fc/Fc+)
-3 -2 -1 0 1
Current (a.u.)
Potential (V vs Fc/Fc+)
Fc/Fc+

Figure 64. CV (left) and DPV (right) of 1
Δ,Λ
in DMF (vs Fc).
65

Figure 65. CV (left) and DPV (right) of 2
Δ,Λ
in DMF (vs Fc).

Figure 66. CV of 3
Δ
in DMF (vs Fc).

Figure 67. CV of 3
Λ
in DMF (vs Fc).
-4 -3 -2 -1 0 1
-40
-30
-20
-10
0
10
20

I ()
I (A)
Volts vs Fc
+
/Fc
-3 -2 -1 0 1 2
-50
-40
-30
-20
-10
0
10
20
I ( A)
Volts vs Fc
+
/Fc
66

Figure 68. DPV of 3RR
Δ
in DMF (vs Fc).
-4 -3 -2 -1 0 1
Current (arb. units)
Potential (vs Fc/Fc+)
Fc/Fc+

-3 -2 -1 0 1
Current (arb. units)
Potential (Fc vs Fc+)
Fc/Fc+

Figure 69. CV (left) and DPV (right) of 3RR
Λ
in DMF (vs Fc).

67

-3 -2 -1 0 1 2
Current (a.u.)
Potential (V vs Fc/Fc+)
-3 -2 -1 0 1
Current (a.u.)
Potential (V vs Fc/Fc+)

Figure 70. CV (left) and DPV (right) of 4
Δ,Λ
in DMF (vs Fc).

68

2.3.8. Photophysics
300 350 400 450 500 550
0
0.2
0.4
0.6
0.8
1
Normalized Intensity (a.u.)
Wavelength (nm)
2Me-THF
CH
2
Cl
2
Toluene
MeCy

450 500 550 600 650 700
0
0.2
0.4
0.6
0.8
1
Normalized Intensity (a.u.)
Wavelength (nm)
2Me-THF
DCM
Toluene
MeCy
450 500 550 600 650 700
0
0.2
0.4
0.6
0.8
1
Normalized Intensity (a.u.)
Wavelength (nm)
2Me-THF 77 K
MeCy 77 K

Figure 71. Absorbance (a), Emission RT (b), and Emission 77 K of 2
Δ,Λ
in various solvents.
Table 5. Photophysics of 2
Δ,Λ
in various solvents.
Complex 2
Δ,Λ

λ
max

(nm)
τ
(µs)
F
PL

k
r

(10
5
s
-1
)
k
nr

(10
4
s
-1
)
λ
max.77K

(nm)
τ
77K
(µs)
FIrpic in 2Me-THF 470 1.7 0.99 5.8 0.058 460 2.9
2Me-THF 480 2.1 0.99 4.7 0.48 466 2.8
CH
2
Cl
2

474 2.1 1.0 4.8 - - -
Toluene 476 1.7 1.0 5.9 - - -
MeCy 476 1.6 0.65 4.1 22 476 2.7
69

300 400 500
0
0.2
0.4
0.6
0.8
1
Normalized Intensity (a.u.)
Wavelength (nm)
2Me-THF
CH
2
Cl
2
Toluene
MeCy

450 500 550 600 650 700
0
0.2
0.4
0.6
0.8
1
Normalized Intensity (a.u.)
Wavelength (nm)
2Me-THF
CH
2
Cl
2
Toluene
MeCy
450 500 550 600 650 700
0
0.2
0.4
0.6
0.8
1
Normalized Intensity (a.u.)
Wavelength (nm)
2Me-THF
MeCy

Figure 72. Absorbance (a), Emission RT (b), and Emission 77 K of 3
Δ
in various solvents.
Table 6. Photophysics of 3
Δ
in various solvents.
Complex 3a
λ
max

(nm)
τ
(µs)
F
PL

k
r

(10
5
s
-1
)
k
nr

(10
4
s
-1
)
λ
max.77K

(nm)
τ
77K
(µs)
2Me-THF 503 2.5 0.92 4.8 0.49 489 3.2
CH
2
Cl
2

501 1.9 0.96 5.1 2.1 - -
Toluene 503 1.6 0.93 1.6 4.3 - -
MeCy 501 1.7 0.86 5.1 8.2 501 3.1
70

350 400 450 500 550
0
0.5
1
1.5
Normalized Intensity (arb. units)
Wavelength (nm)
2Me-THF
CH
2
Cl
2
Toluene

450 500 550 600 650 700
0
0.2
0.4
0.6
0.8
1
Normalized Intensity (a.u.)
Wavelength (nm)
2Me-THF RT
DCM RT
Toluene RT
MeCy RT
500 550 600 650 700
0
0.2
0.4
0.6
0.8
1
Normalized Intensity (a.u.)
Wavelength (nm)
2Me-THF 77 K
MeCy 77 K

Figure 73. Absorbance (a), Emission RT (b), and Emission 77 K of 3
Λ
in various solvents. 3
Λ

doesn’t absorb well in MeCy.
Table 7. Photophysics of 3
Λ
in various solvents.
Complex 3
Λ
λ
max

(nm)
τ
(µs)
F
PL

k
r

(10
5
s
-1
)
k
nr

(10
4
s
-1
)
λ
max.77K

(nm)
τ
77K
(µs)
2Me-THF 501 2.0 0.92 4.8 4.9 488 3.2
CH
2
Cl
2

499 2.0 0.99 5.0 5.0 - -
Toluene 501 1.6 0.97 6.1 1.9 - -
MeCy 501 1.6 1.0 6.3 - 493 2.9
71

350 400 450 500 550
0
1
Normalized Absorbance (arb. units)
Wavelength (nm)
2Me-THF
CH
2
Cl
2
Toluene

450 500 550 600 650 700
0
0.2
0.4
0.6
0.8
1
Normalized Intensity (arb. units)
Wavelength (nm)
2Me-THF
CH
2
Cl
2
Toluene

450 500 550 600 650 700
0
0.2
0.4
0.6
0.8
1
Normalized Intensity (arb. units)
Wavelength (nm)
2Me-THF 77 K

Figure 74. Absorbance (a), Emission RT (b), and Emission 77 K of 3RR
Δ
in various solvents.
3RR
Δ
didn’t absorb well in MeCy.
Table 8. Photophysics of 3RR
Δ
in various solvents.
Complex 3RR
Δ

λ
max

(nm)
τ
(µs)

PL

k
r

(10
5
s
-1
)
k
nr

(10
4
s
-1
)
λ
max.77K

(nm)
τ
77K
(µs)
2Me-THF 502 2.0 1.0 5.0 - 488 3.3
CH
2
Cl
2

500 1.9 0.93 4.9 3.7 - -
Toluene 502 1.6 1.0 6.3 - - -

72

450 500 550 600 650 700
0
0.2
0.4
0.6
0.8
1
Normalized Intensity (a.u.)
Wavelength (nm)
2Me-THF
CH
2
Cl
2
Toluene
MeCy

450 500 550 600 650 700
0
0.2
0.4
0.6
0.8
1
Normalized Intensity (arb. units)
Wavelength (nm)
2Me-THF 77 K
MeCy 77 K

Figure 75. Absorbance (a), Emission RT (b), and Emission 77 K of 3RR
Λ
in various solvents.

Table 9. Photophysics of 3RR
Λ
in various solvents.
Complex 3RR
Λ

λ
max

(nm)
τ
(µs)

PL

k
r

(10
5
s
-1
)
k
nr

(10
4
s
-1
)
λ
max.77K

(nm)
τ
77K
(µs)
2Me-THF 505 1.9 0.98 5.2 1.1 488 3.5
CH
2
Cl
2

501 1.9 0.99 5.2 0.53 - -
Toluene 503 1.6 1.0 6.3 - - -
73

300 350 400 450 500 550 600 650
0
0.5
1
1.5
2
2.5
3
3.5
Normalized Intensity (a.u.)
Wavelength (nm)
2Me-THF
DCM
Toluene
MeCy

550 600 650 700 750 800 850
0
0.2
0.4
0.6
0.8
1
Normalized Intensity (a.u.)
Wavelength (nm)
2Me-THF
CH
2
Cl
2
Toluene
MeCy
RT
550 600 650 700 750 800 850
0
0.2
0.4
0.6
0.8
1
Normalized Intensity (a.u.)
Wavelength (nm)
2Me-THF
MeCy
77 K

Figure 76. Absorbance (a), Emission RT (b), and Emission 77 K of 4
Δ,Λ
in various solvents.

Table 10. Photophysics of 4
Δ,Λ
in various solvents.
Complex 4
Δ,Λ

λ
max

(nm)
τ
(µs)
F
PL

k
r

(10
5
s
-1
)
k
nr

(10
5
s
-1
)
λ
max.77K

(nm)
τ
77K
(µs)
2Me-THF 614 1.7 0.45 2.7 3.2 602 2.2
CH
2
Cl
2

612 1.8 0.45 2.5 3.1 - -
Toluene 616 1.6 0.47 2.9 3.3 - -
MeCy 614 1.7 0.42 2.5 3.4 616 2.2

74

250 300 350 400
0
0.2
0.4
0.6
0.8
1
Normalized Absorbance (arb. units)
Wavelength (nm)
BOX
ss
-CN
BOX
RR
-CN
DCM

Figure 77. Absorbance spectra of the BOXSS-CN and BOXRR-CN ligands in CH2Cl2.

2.4. Conclusion
A series of bis-cyclometalated iridium complexes containing bis-oxazoline derived
ancillary ligands were synthesized. Strategic substitution at the meso-position of the BOX ligand
with a cyano group was used to stabilize the HOMO of these materials, leading to a significant
blue-shifted in the emission from the parent BOX complex. All complexes were analyzed for
unique electrochemical, photophysical, and computational properties. The emission of these
complexes varied across the visible spectra with moderate to high photoluminescence quantum
yields. The − and - isomers of (ppy)2Ir(BOX-CN) were separated using differences in solubility
and additionally characterized through x-ray crystallography, stability, and circular dichroism
studies.
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75

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77

Chapter 3. Reducing nonradiative decay pathways in thiazole copper (I) complexes
3.1. Introduction
There has been a recent push to replace noble metal emitters such as Ir and Pt with more
earth abundant compounds.
1-4
Copper complexes have been widely investigated as possible
alternatives to these state-of-the-art emitters. However, while previously examined 3- and 4-
coordinate copper complexes were highly emissive in the solid state, these complexes were either
non-emissive or weakly emissive in fluid solution. The low luminescence efficiencies were the
direct result of their metal to ligand charge transfer (MLCT) excited state. When these complexes
are excited, an electron from the t2 set of the copper metal d-orbitals is excited into the π* orbital
of the ligand, resulting in an unequal filling of the t2. To compensate, the complexes undergo a
structural distortion that results in high nonradiative decay rates. This distortion is suppressed in
the solid state, which is why these complexes can be highly emissive in a rigid matrix.
Recent work has turned to two-coordinate copper complexes with the structure
(carbene)Cu
I
(amide). These complexes are among the most promising contenders to noble metal
emitters as they do not suffer from the same issues as their 3- and 4-coordinate counterparts. In
fact, these complexes have been shown to have high photoluminescence quantum yields (PLQYs)
in both fluid and rigid media.
5-8
Additionally, these materials have fast lifetimes and high radiative
decay rates, which are necessary to make these competitive with existing materials for applications
such as OLEDs.
9
These 2-coordinate systems are more efficient than their 3- and 4-coordinate
analogues because of the process by which they emit.
Two-coordinate copper complexes undergo a different type of emission process known as
thermally activated delayed fluorescence (TADF). In TADF, the singlet and triplet levels are
78

brought close enough in energy that electrons can thermally populate between the two states. Due
to the small spin orbit coupling (SOC) of the copper atom, the decay rates out of the triplet are
slow. Instead, these triplets can thermal population to the S1 state, where they can radiatively decay
to the ground state through delayed fluorescence. Several characteristics must be met for a material
to be a highly efficient TADF emitter. The first, and most obvious trait, is that these complexes
need to have a small singlet triplet gap (ΔES1-T1). A small ΔES1-T1 can be accomplished by having
as little overlap between the HOMO and LUMO as possible. However, too little overlap prevents
efficient charge transfer. Balance between these two criteria is met through use of the copper atom.
A small contribution of the HOMO and LUMO is localized on the copper atom, which allows the
copper atom to act as an electronic bridge shuttling electrons from the donor to the acceptor. Other
qualities of TADF emitters can be met through ligand choice. Sterically bulky ligands, for
example, can be used to prevent rotation and bending in the excited state, hindering a nonradiative
decay pathway. Not only that but bulky ligands can be used to keep the carbene and carbazoles
coplanar, allowing for efficient charge transfer between the two moieties. Overall, the strategic
design of 2-coordinate copper complexes can result in highly efficient emitters.
Since the first reports of these highly luminescent (carbene)Cu
I
(amide) complexes, much
work has been done on modifying both sides of these complexes. Several different carbenes have
been utilized in the (carbene)copper(carbazole) structure and are shown in Figure 78. As the
LUMO of these complexes is typically on the carbene, changing the carbene can alter the energy
of the LUMO, significantly impacting the λmax of emission. While there are various reasons for
employing different carbenes, one common characteristics of these ligands is that they are
routinely used to provide the steric bulk needed to prevent nonradiative decay pathways mentioned
previously. Different amide groups have also been employed in these two-coordinate copper
79

systems. Yet, carbazole is the most commonly used. Modification of the carbazole leads to changes
in the HOMO energy of the 2-coordinate copper complex. Since carbazoles can be easy to modify,
addition of electron donating and withdrawing groups can lead to easy tuning across the visible
spectrum.
7
With few exceptions, modification of the carbazole only focuses on color tuning.
9
In
contrast to previously published work, This chapter looks at using both the carbene and carbazole
to limit nonradiative decay pathways through use of substituted carbazole and a thiazole carbene
unit.

Figure 78. Recently reported (carbene)Cu
I
(Cz) emitters.
7, 9-11

This study looks at a series of (Thia)Cu(XCz) complexes (where X = H, Me, IPr, and Ph)
with substitutions at the 1-position of carbazole (Figure 79). These carbazoles were strategically
designed to decrease the nonradiative rate of the parent complex by limiting rotation about the
carbene-copper-carbazole bond. Preliminary computational studies were used to determine which
substitutions would be the most promising. Potential energy surface (PES) scans were performed
80

to determine the barrier to rotation between the syn- and anti-conformations of a given molecule.
Electrochemical studies found 1, 1-Me, and 1-IPr to have similar electrochemical properties.
Photophysical characterization was performed to determine how substitution at the 1-position of
carbazole affects the optical properties. To the best of our knowledge, this is the first use of thiazole
as a carbene for luminescent two-coordinate copper complexes.

Figure 79. (Thiazole)Cu(XCz) studied where X = H, Me, IPr, or Ph.
3.2. Results and Discussion
3.2.1. Synthesis
Substituted carbazoles were synthesized using a modified procedure.
12
In place of using a
microwave reactor for 3.5 h, the reaction was done in a pressure flask heated to 110 °C overnight.
ThiaBF4 was synthesized following literature procedure.
13
ThiaCuCl was synthesized following a
modified procedure by Shi et. al.
7
where 2 equivalents of CuCl (rather than 1 equivalent) was used
to prevent dimerization of the thiazole carbene. Finally, the (Thia)Cu(XCz) complexes were
synthesized following a similar prep to that by Shi et. al.
7
(Scheme 2). XCz (X = H, Me, IPr, Ph)
was deprotonated using NaOtBu and then reacted with (Thia)CuCl to form the respective
(Thia)Cu(XCz) complex. 1, 1-Me, and 1-IPr were white microcrystalline powders. 1-Ph was an
81

off-white powder. Complexes were synthesized in yields of 72-82%. 1, 1-Me, and 1-IPr are air
stable while 1-Ph is air and moisture-sensitive.

Scheme 2. Synthesis of (Thia)Cu(XCz) complexes.
3.2.2. Crystal Structure
A single crystal of 1 suitable for X-ray diffraction was obtained through sublimation. The
bond angles and lengths are comparable to that of previously reported 2-coordinate copper amide
complexes.
8
The Cu-C(thiazole) and Cu-N(carbazole) bond lengths are comparable at 1.872 and 1.860
Å respectively. The bond length of 3.730 Å for the C(thiazole)-Cu-C(carbazole) is also consistent with
previously published complexes of 3.74 Å. The C(thiazole)-Cu-C(carbazole) has a bond angle
approaching 180° (176.84°).

Figure 80. Single crystal X-ray structure of 1. Hydrogens were omitted for clarity.

82

Table 11. Crystallographic structure information for 1.
Bond Length (Å)
Cu-C(thiazole) 1.872
Cu-N(carbazole) 1.860
C(thiazole)-Cu-C(carbazole) 3.730
Bond Angle (°)
C(thiazole)-Cu-C(carbazole) 176.84
Ratio
C(thiazole)-Cu/Cu-C(carbazole) 1.006

3.2.3. Computational Studies
QCHEM 5.1 and iQmol were used to perform ground-state geometry optimized and triplet
spin density calculations on the (Thia)Cu(XCz) complexes at the B3LYP/LACVP* level. The
calculated HOMO and LUMO surfaces for 1 are shown in Figure 81. Overall, the ground state
optimization calculations give similar results across the (Thia)Cu(XCz) series. In all complexes,
the HOMO is shown to principally localized on carbazole moiety while the LUMO is primarily
localized on carbene. As was seen with previously published two-coordinate Cu complexes, a
minor, but not insignificant, contribution from the Cu d-orbitals was also found in both the
calculated HOMO and LUMO. This small overlap is what allows the copper to shuttle electrons
between the carbazole and carbene units.
83

Figure 81. HOMO (shaded) and LUMO (dashed) orbitals of the 1.
The calculated HOMO and LUMO values obtained from the geometry optimized
calculations are shown in Table 12. Overall, the values for the HOMO and LUMO do not
significantly change across the series. The calculated HOMO values indicate that the substitutions
at the 1-position of carbazole does not significantly impact the HOMO energies of the complexes.
As would be expected, the LUMO is similar for all complexes since no changes were made to the
carbene across the series. Table 12 also includes the calculated thiazole-copper-carbazole bond
angle. As was previously observed, the closer the carbene-copper-carbazole bond is to 180°, the
better overlap between the carbene and carbazole. This better overlap leads to improved charge
transfer. Complexes 1, 1-Me, and 1-IPr show nearly a nearly coplanar structure with a thiazole-
copper-carbazole bond angle of ~180°. In contrast, 1-Ph has a distorted thiazole-cu-carbazole
bond angle of 172°. When the structure of 1-Ph is compared to other complexes, such as 1-Me
(Figure 82), the distortion of its ground state structure is evident. Deformation of the linear
geometry can not only hinder overlap between the HOMO and LUMO orbitals, but it can lead to
even further distortions in the excited state, considerably affecting the photophysical properties of
the complex.

84

Table 12. Calculated HOMO and LUMO values. The thiazole-copper-carbazole bond angle for
the geometry optimized ground state is also shown.
Complex HOMO (eV) LUMO (eV) Thiazole-copper-carbazole
bond angle (°)
1 -4.14 -1.80 179
1-Me -4.14 -1.77 179
1-IPr -4.11 -1.77 176
1-Ph -4.16 -1.66 172

Figure 82. Geometry optimized ground state for 1-Me (left) and 1-Ph (right).
To better understand the barrier to rotation about the thiazole-copper-carbazole bond,
potential energy surface (PES) scan calculations were performed on 1, 1-Me, and 1-IPr at the
B3LYP/LACVP* level with a dispersion DFT-D3(BJ) correction. The results for these
calculations are shown in Figure 83. BZICuCz was used as a reference compound to better
comprehend how the substitutions on the carbazole affect the barrier to rotation,. It should be noted
that values between 150 and 180° for BZICuCz were artificially plotted (labeled with asterisks).
Since this complex is symmetric, the values between 150 and 180° should match with values
between 0 and 30°. The energy barrier between the anti- and syn-isomers of 1-Me was found to
be 2 kcal/mol. The equilibrium constant between these two conformations was calculated to be
85

~0.034 indicating that ~3.4% of the molecules will be in the syn conformation at a given time. 1-
IPr has a significantly higher energy barrier of 4 kcal/mol between the conformations. This value
is twice as high as the barrier calculated for 1-Me, implying that the IPr group significantly hinders
rotation about the thiazole-copper-carbazole bond. The equilibrium constant between the two
conformers for 1-IPr was found to be ~0.001, signifying that only ~0.1% of the conformers at a
given time will be in the syn conformation. Overall, these calculations show that substitution at
the 1-position of carbazole can hinder the rotation about the thiazole-copper-carbazole bond. 1-
IPr especially impedes this nonradiative decay pathway.
0 30 60 90 120 150 180
0
2
4
6
8
Energy Barrier (kcal/mol)
Dehedral Angle
BZICuCz
1-H
1-Me
1-iPr
*
*
*

Figure 83. Potential energy surface scan of (Thia)Cu(XCz) complexes.
3.2.4. NMR studies
1
H-NMRs were taken of 1-Me at -70 °C and RT (Figure 84) to see if we could
experimentally observe changes in the spectra that would suggest a barrier to rotation.
Interestingly, we were able to observe a significant upfield shift of both the H on the 1-position of
carbazole and the septet-split hydrogen of the isopropyl group on Dipp. The shielding of these two
protons shows that these two protons are spending more time near each other at -70 °C than at RT.
86

Not only that but this data shows that 1-Me is spending more time in the anti-conformation at -70
°C since the complex can as easily rotate between the two confirmations.
1
H-NMRs at -70°C and RT were also taken of 1-IPr (Figure 85). As was seen in 1-Me,
the hydrogen at the 1-position of carbazole and the septet hydrogen of the Dipp isopropyl groups
shift upfield at -70 ℃, suggesting that at lower temperatures, these protons are being shielded by
each other for a longer time than at room temperature. Even more surprising is, at low
temperatures, we can see the protons from the syn-isomer appear. These peaks match those of the
Spartan calculated NMR spectras (Figure 86), suggesting that at low temperatures, 1-IPr is not
able to freely rotate between the syn and anti-isomers on the NMR timescale. Overall, these NMRs
show experimentally that there is a barrier to rotation that exists within the substituted complexes.

Figure 84.
1
H-NMR of 1-Me in acetone at RT versus -70 ℃.
87

Figure 85.
1
H-NMR of 1-IPr in acetone at RT versus -70 ℃.

Figure 86. Calculated NMRs using Spartan of the anti and syn isomers of 1-IPr.

88

3.2.5. Electrochemistry
Cyclic voltammetry (CV) and differential pulse voltammetry (DPV) were performed on all
complexes in DMF vs Fc. CV was used to determine the reversibility of redox waves while DPV
was used to determine oxidation and reduction potentials for the series of (Thia)Cu(XCz)
complexes. All complexes have irreversible oxidation and quasi-reversible to irreversible
reduction potentials and are similar across the series. Minor changes in the oxidation potential are
due to the slight electron donating potential of the substituents. The electron donating potential
increases from H to Me to IPr and results in the complexes being overall easier to oxidize with
increasing electron donation.
Table 13. Electrochemical measurements for complexes (Thia)Cu(XCz) complexes in DMF vs
Fc.
Eox [V] Ered [V] ΔEredox [V]
1 - -2.73, -3.27 -
1-Me 0.71 -2.81 (q), -3.26 (ir) 3.52
1-IPr 0.61 -2.76 (q), -3.22 (ir) 3.37
3.2.6. Photophysical properties
Molar absorptivity measurements were taken for all (Thia)Cu(XCz) complexes in toluene
(Figure 87). The extinction coefficients of these complexes are comparable to previously reported
2-coordinate copper complexes.
7, 9
Vibronic features between 300-380 nm can be ascribed to
localized transitions on the carbazole moiety. A lower energy CT band appears between ~375-425
nm. Interestingly, the extinction coefficient of the ICT band increases in the order of 1 < 1-Me <
1-IPr and indicating better overlap and, hence, charge transfer between the carbene and carbazole
89

moieties. The increase in the CT band insinuates that the addition of these bulky groups leads to
better coplanarity between the carbene and carbazole across the series from 1 < 1-Me < 1-IPr.
300 350 400 450 500
0
5
10
15
e (10
3
M
-1
cm
-1
)
Wavelength(nm)
1-H
1-Me
1-iPr
Toluene

Figure 87. Molar absorptivity of (Thia)Cu(XCz) complexes in toluene.
Emission spectra (Figure 88) were taken of the (Thia)Cu(XCz) complexes in 2Me-THF,
MeCy, Tol, and 2 wt% PS. The luminescent properties are summarized in Table 14. Similar trends
for 1, 1-Me, and 1-IPr are observed in both the solution and in a rigid matrix at RT. These
complexes have broad and featureless ICT based emission at RT. The PLQY values range from
moderate to near unity (PLQY = 0.4-1.0). An increase in the PLQY is observed from 1 < 1-Me <
1-IPr and is the direct result of a decrease in the nonradiative rate. Increasing the steric bulk on
the carbazole moiety, decreases the nonradiative rate by preventing rotation about the carbene-Cu-
Cz bond upon excitation. The radiative rates are on par with state-of-the art iridium emitters (10
5

s
-1
) and are mostly constant across the series. The lifetime values at RT range from 0.9 to 2.1 μs
and are comparable to other two-coordinate copper complexes.
7-9
Addition of these electron
donating groups (EDGs) on the carbazole leads to a slight destabilization of the HOMO, resulting
90

in a slight red-shift of the λmax of emission that increases in the order of electron donating ability
(1 < 1-Me < 1-IPr).
Emission and lifetime data were also obtained at 77 K. The low temperature data confirms
that 1, 1-Me, and 1-IPr emit through TADF as indicated by the significant increase in the lifetime
observed upon cooling. This increase in the lifetime is also accompanied by a significant blue shift
in the λmax of emission due to destabilization of the ICT state, resulting in a triplet carbazole (
3
Cz)
excited state at 77 K in solution. Excimers were observed in MeCy for 1 and 1-Me due to poor
solubility in nonpolar solvents. In PS film, the broad and featureless emission at 77 K is indicative
of an ICT based emission, similar to what was observed at RT. The rigidity of the P.S. prevents
destabilization of the ICT state, keeping it the lowest energy excited state. The slight blue-shift in
emission upon cooling is due to the complexes not being able to structurally reorganize, as they
could at RT. Multiexponential lifetimes were observed for all compounds in various media and
are likely the result of the complexes being frozen in multiple conformers at 77 K.

91

400 450 500 550 600 650 700
0
0.5
1
400 450 500 550 600 650 700
0
0.5
1

1-H
1-Me
1-iPr
RT
2Me-THF

Normalized PL Intensity (a.u.)
Wavelength (nm)
77 K

400 450 500 550 600 650 700
0
0.5
1
400 450 500 550 600 650 700
0
0.5
1

Normalized PL Intensity (a.u.)
RT
MeCy

Wavelength (nm)
77K
*
*

400 450 500 550 600 650 700
0
0.2
0.4
0.6
0.8
1
Normalized PL
Wavelength (nm)
1-H
1-Me
1-iPr
Toluene

400 450 500 550 600 650 700
0
0.5
1
400 450 500 550 600 650 700
0
0.5
1

PS Film
RT

Normalized PL Intensity (a.u.)
Wavelength (nm)
77 K

Figure 88. Emission spectra of (Thia)Cu(XCz) complexes in 2Me-THF, MeCy, Tol, and 1% wt
in PS films.
92

Table 14. Photophysical characterization of (Thia)Cu(XCz) complexes in 2Me-THF, MeCy, and
1 wt% in PS.

1-Ph does not follow the same trend observed for the other complexes. Emission spectra
of 1-Ph in 2Me-THF, MeCy, and 1 wt% PS film are shown in Figure 89. Photophysical data for
this complex is summarized in Table 15. The PLQY solution data is significantly lower for 1-Ph
than the other synthesized complexes. The geometry optimized ground state structure of 1-Ph
93

shows the compound to be in a bent geometry as opposed to the linear geometry observed for the
other complexes. Excited state calculations show that the bending becomes much more apparent
in the excited state. This particular bending is known as a Renner Teller distortion and leads to
weak emission in fluid solution. However, when the complex is dispersed in a rigid matrix like
PS, the PLQY of the complex increases significantly as the molecule can’t freely bend like it could
it solution. Multi-exponential lifetimes were observed at both RT and 77 K for the 1 wt% PS film
as well as at 77 K in fluid solution. Conformers of 1-Ph are the reason for these multi-exponential
lifetimes.
400 500 600 700
0
0.5
1
400 500 600 700
0
0.5
1

2Me-THF
MeCy
PS
RT

Normalized PL Intensity (a.u.)
Wavelength (nm)
77 K

Figure 89. Emission spectra of 1-Ph in 2Me-THF, MeCy, and 1 wt% PS.

94

Table 15. Photophysical data of 1-Ph in 2Me-THF, MeCy, and 1 wt% in PS film.

3.3. Experimental
3.3.1. Synthesis
General: Sodium tert-butoxide, palladium acetate, 2-bromotoluene, 2-methyltetrahydrofuran,
methylcyclohexane, and polystyrene standard were purchased from Sigma-Aldrich. 2-
chloroaniline was purchased from Acros Organics. Tri-tert-butylphosphonium tetrafluoroborate
was purchased from Strem Chemicals. All used without further purification and all reaction were
performed under a N2 atmosphere unless otherwise noted. 2-Methyl tetrahydrofuran (2Me-THF)
and methylcyclohexane (MeCy) were purchased from Sigma-Aldrich and used without and further
purification. Tetrahydrofuran (THF) and toluene (Tol) were purified using a Pure Process
Technology solvent dispensing system. Dimethylformamide (DMF) was purchased from Milipore.
All NMRs were performed on a Varian 400, Varian 500, or Varian 600 NMR spectrometer and
referenced to the deuterated acetone’s residual proton signal unless otherwise noted. Elemental
analysis was performed at the University of Southern California. Absorbance and molar
1-Ph λmax
(nm)
Φ τ
(μs)
kr
(10
5
s
-1
)
knr
(10
5
s
-1
)
λmax, 77 K
(nm)
τ77 K
(ms)
2Me-THF 530 0.16 198 0.008 0.042 436
500
at 436 nm
4.26 (3%)
32.2 (58%)
54.9 (40%)
at 500 nm
19 (2%)
1.29 (28%)
3.89 (70%)

MeCy 516 0.014 3.0 4.7 330 504 2.3 (38%)
0.72 (62%)
1 wt% PS 500 0.62 7.7
(7%)
38
(39%)
130
(54%)
7 4.6 520 0.29 (29%)
0.93 (44%)
3.2 (26%)

95

absorptivity data were measured using a UV-VIS Hewlett-Packard 4853 diode array spectrometer.
Photoluminescence quantum yields were recorded using a Hamatsu C9920 integrating sphere
equipped with a xenon lamp. Lifetimes were measured using a Time-Correlated Single Photon
Counting (TCSPC). Steady state excitation and emission spectra were obtained using a Photon
Technology International QuantaMaster phosphorescence/fluorescence spectrofluorimeter. Both
Cyclic Voltammetry (CV) and Differential pulse voltammetry (DPV) were performed through use
of an EG&G potentiostat/galvanostat model 283. The electrolyte was composed of 0.1 M tetra-n-
butylammonium hexafluorophosphate (TBAF) in anhydrous DriSolv acetonitrile and
dimethylformamide. The measurements were taken under an inert atmosphere. The working,
counter, and pseudoreference electrodes were composed of glassy carbon, platinum wire, and
silver wire respectively. All complexes were referenced to an internal ferrocene/ferrocenium
(Fc/Fc
+
) redox couple. QCHEM 5.1 and iQmol were used to run ground-state geometry optimized
and triplet spin density calculations on all complexes at the B3LYP/LACVP* level.
Individual syntheses
General procedure for synthesizing substituted carbazoles: Substituted carbazoles were
synthesized using a modified prep by Bedford et. al.
12
Pd(OAc)2, NaOtBu, and [(t-Bu)3PH]BF4
were added to a pressure flask with a nitrogen side arm. The flask was pumped and purged with
N2 gas three times. Under positive N2 pressure, 2-chloroaniline and the corresponding substituted
aryl bromine were added. The flask was heated to 110 ℃ overnight. The reaction was allowed to
cool to room temperature and 2 M HCl was added to quench the reaction. An extraction was
performed using H2O and DCM and the corresponding organic phase was dried with MgSO4. The
solvent was removed in vacuo and the crude product was purified by a silica column using 70:30
hexanes:DCM. The NMRs of these substituted carbazoles matched those of the literature for the
96

methyl
12
, isopropyl
14
, and phenyl
15
derivatives respectively. The thiazole ligand was synthesized
following a literature prep.
13

Scheme 3. Synthesis of substituted carbazoles using modified prep
12
.
Synthesis of ThiaCuCl: ThiaBF4 (500 mg, 1.38 mmol, 1 eq) and CuCl (274 mg, 2.77 mmol, 2 eq)
were added to a Schlenk flask. The flask was pumped and purged with N 2 gas three times. THF
(100 mL) was added to the flask and the mixture was allowed to stir for ~15 minutes. KHMDS
(1.98 mL, 0.7 M, 1 eq) was added dropwise to the flask and the mixture was allowed to stir at RT
overnight. The crude mixture was filtered through celite and the filtrate was rotavaped to dryness.
The resulting solid was dissolved in minimal acetone and precipitated using hexanes/pentanes.

Scheme 4. Synthesis of ThiaCuCl.
General Procedure for (Thia)Cu(XCz) complexes: (Thia)Cu(xCz) was synthesized following a
modified prep by Shi et. al.
7
The synthetic scheme is shown in Scheme 5. XCz (1.05 eq) was added
to an oved dried flask. The flask was pumped and purged with N2 gas three times. THF (~30 mL)
was added to the flask followed by NaOtBu (2.0 M, 1.05 eq). This solution was stirred for ~30
97

minutes. ThiaCuCl (1.00 eq) was added to the reaction flask in stirred overnight. The solution was
filtered through celite and the solvent was removed in vacuo. The solid was dissolved in minimum
DCM and precipitated with pentane. The resulting solid was washed with ether to get pure product.

Scheme 5. Synthesis of (Thia)Cu(XCz) complexes.
ThiaCuCl:
1
H NMR (400 MHz, Acetone-d6) δ 7.59 (t, J = 7.8 Hz, 1H), 7.45 (d, J = 7.8 Hz, 2H),
2.50 (s, 3H), 2.18 (h, J = 6.9 Hz, 2H), 1.24 (d, J = 6.8 Hz, 6H), 1.19 (d, J = 6.9 Hz, 6H).
ThiaCuCz (1):
1
H NMR (400 MHz, acetone) δ 7.88 (ddd, J = 7.7, 1.3, 0.8 Hz, 2H), 7.78 (t, J =
7.8 Hz, 1H), 7.59 (d, J = 7.8 Hz, 2H), 7.03 (ddd, J = 8.2, 6.9, 1.3 Hz, 2H), 6.87 – 6.80 (m, 4H),
2.60 – 2.56 (m, 3H), 2.35 (p, J = 6.8 Hz, 2H), 2.17 (s, 3H), 1.24 (dd, J = 6.8, 2.5 Hz, 12H).
13
C
NMR (126 MHz, Acetone-d6) δ 150.08, 145.15, 142.07, 130.92, 125.08, 124.25, 123.17, 118.92,
115.16, 114.46.
ThiaCuMeCz (1-Me):
1
H NMR (400 MHz, acetone) δ 7.86 (ddd, J = 7.7, 1.4, 0.7 Hz, 1H), 7.78
(t, J = 7.3 Hz, 2H), 7.59 (d, J = 7.8 Hz, 2H), 7.01 – 6.91 (m, 2H), 6.86 – 6.77 (m, 2H), 6.56 (dd,
J = 8.1, 0.9 Hz, 1H), 2.65 (s, 3H), 2.58 (s, 3H), 2.36 (p, J = 6.8 Hz, 2H), 2.18 (s, 3H), 1.25 (d, J =
3.7 Hz, 6H), 1.23 (d, J = 3.7 Hz, 6H).
13
C NMR (101 MHz, Acetone-d6) δ 145.03, 130.91,
125.10, 124.22, 122.91, 118.84, 117.06, 115.33, 115.23, 115.03.
98

ThiaCuIPrCz (1-IPr): (Thia)CuCl (100 mg, 1.00 eq), NaOtBu (2.0 M, 0.14 mL, 1.05 eq), IPrCz
(59 mg, 1.05 eq).
1
H NMR (400 MHz, Acetone-d6) δ 7.79 (d, J = 7.9 Hz, 2H), 7.76 – 7.71 (m, 1H),
7.57 (d, J = 7.8 Hz, 2H), 7.07 (d, J = 7.2 Hz, 1H), 6.84 (t, J = 7.5 Hz, 2H), 6.74 (t, J = 7.3 Hz, 1H),
6.20 (d, J = 8.0 Hz, 1H), 4.35 (hept, J = 7.0 Hz, 1H), 2.55 (s, 3H), 2.31 (hept, J = 7.5 Hz, 2H), 2.14
(s, 3H), 1.42 (d, J = 6.9 Hz, 6H), 1.19 (dd, J = 8.8, 6.8 Hz, 12H).
13
C NMR (101 MHz, Acetone-
d6) δ 150.04, 145.15, 132.04, 130.90, 125.12, 124.63, 124.51, 122.86, 118.60, 118.59, 116.85,
115.48, 115.10, 114.97.
ThiaCuPhCz (1-Ph):
1
H NMR (400 MHz, acetone) δ 7.87 (dd, J = 7.6, 1.3 Hz, 1H), 7.83 (ddd, J =
7.2, 1.7, 0.7 Hz, 1H), 7.77 (d, J = 7.9 Hz, 1H), 7.75 – 7.71 (m, 2H), 7.58 – 7.51 (m, 4H), 7.49 –
7.44 (m, 1H), 7.03 (dd, J = 7.1, 1.3 Hz, 1H), 6.91 (dd, J = 7.6, 7.1 Hz, 1H), 6.83 – 6.72 (m, 2H),
5.75 (ddd, J = 8.0, 1.4, 0.8 Hz, 1H), 2.42 (q, J = 0.8 Hz, 3H), 2.16 (hept, J = 6.8 Hz, 2H), 2.01 (s,
3H), 1.15 (d, J = 6.9 Hz, 6H), 1.11 (d, J = 6.8 Hz, 6H).
99

3.3.1. NMR spectra

Figure 90.
1
H-NMR of 1-methylcarbazole in acetone.

Figure 91.
1
H-NMR of 1-isopropylcarbazole in acetone.
100

Figure 92.
1
H-NMR of (Thia)CuCl in acetone.

Figure 93.
1
H-NMR of (Thia)Cu(Cz) in acetone.
101

Figure 94.
13
C-NMR of (Thia)Cu(Cz) in acetone.

Figure 95.
1
H-NMR of (Thia)Cu(MeCz) in acetone.
102

Figure 96.
13
C-NMR of (Thia)Cu(MeCz) in acetone.

Figure 97.
1
H-NMR of (Thia)Cu(IPrCz) in acetone.
103

Figure 98.
13
C-NMR of (Thia)Cu(IPrCz) in acetone.

Figure 99.
1
H-NMR of (Thia)Cu(PhCz) in acetone.
104

3.3.2. Photophysical characterization
300 350 400 450
0
0.5
1
1.5
Normalized Absorbance (arb. units)
Wavelength (nm)
1
1-Me
1-IPr
1-Ph

Figure 100. Normalized absorbance of (Thia)Cu(XCz) complexes in 2Me-THF.
300 350 400 450 500
0
0.5
1
1.5
2
2.5
Normalized Absorbance (arb. units)
Wavelength (nm)
1
1-Me
1-IPr

Figure 101. Normalized absorbance of 2 wt% (Thia)Cu(XCz) complexes in PS film.
105

3.3.3. Electrochemistry
-3 -2 -1 0 1
Current (arb. units)
Potential (V vs Fc/Fc+)
Fc/Fc+

-3 -2 -1 0
Current (arb. units)
Potential (V vs Fc/Fc+)

Figure 102. CV (left) and DPV (right) of (Thia)Cu(Cz) in DMF versus Fc.
-3 -2 -1 0 1
Current (a.u.)
Potential (V vs Fc/Fc+)
-3 -2 -1 0 1
Current (a.u.)
Potential (V vs Fc/Fc+)

Figure 103. CV (left) and DPV (right) of (Thia)Cu(MeCz) in DMF versus Fc.
106

-3 -2 -1 0 1
Current (a.u.)
Potential (V vs Fc/Fc+)
-3 -2 -1 0 1
Current (a.u.)
Potential (V vs Fc/Fc+)

Figure 104. CV (left) and DPV (right) of (Thia)Cu(IPrCz) in DMF versus Fc.
3.3.4. DFT Calculations

Figure 105. HOMO (shaded) and LUMO (dashed) orbitals of the 1-Me.

Figure 106. HOMO (shaded) and LUMO (dashed) orbitals of the 1-IPr.
107

Figure 107. HOMO (shaded) and LUMO (dashed) orbitals of the 1-Ph.

Figure 108. HOMO (shaded) and LUMO (dashed) orbitals of the 1-Xylyl.
3.4. Conclusion
A series of 2-coordinate thiazole copper carbazole complexes with substituted carbazoles
(XCz where X = H, Me, IPr, and Ph) were synthesized. These carbazoles were strategically
designed to prevent rotation about the thiazole-copper-carbazole bond, subsequently deterring this
nonradiative decay pathway. Potential energy surface (PES) scans showed that the barrier to
rotation increase significantly from 1 < 1-Me < 1-IPr showing that the bulkiness of the substituent
considerably impacts the ability of the complex to freely rotate. Electrochemical characterization
demonstrated that these complexes have similar redox potentials. 1, 1-Me, and 1-IPr showed ICT
based emission at RT and
3
Cz based emission at 77 K, a known characteristic of TADF emitters.
The PLQY of these emitters increased across the series from 1 < 1-Me < 1-IPr and is accompanied
by a substantial decrease in the nonradiative rate, showing that these bulky substitutions do in fact
108

prevent these complexes from nonradiatively decaying through bending and rotation in the excited
state. The 1-Ph derivative has very different properties from the other complexes. Calculations
showed that this complex is bent in its ground state and becomes even more distorted in its excited
state. 1-Ph undergoes a Renner-Teller distortion in its excited state leading to low PLQY in
solution. The work provided in this chapter shows that nonradiative rates can be impeded by
strategic substitution of the carbazole ligand.
3.5. Acknowledgements
This project was done in collaboration with Jie Ma. Jie synthesized and characterized
(Thia)CuCl, (Thia)Cu(Cz), and (Thia)Cu(PhCz). My work focused on the synthesis of the
substituted carbazoles (1-methyl carbazole, 1-isopropyl carbazole, and 1-phenyl carbazole) as well
as the synthesis and characterization of ThiaCuMeCz and ThiaCuIPrCz. All calculations were
performed by Jie, while I completed all low temperature NMR studies.
3.6. References-Chapter 3
1. Hamze, R.; Kapper, S. C.; Sylvinson Muthiah Ravinson, D.; Haiges, R.; Djurovich, P.
I.; Thompson, M. E., Molecular dynamics of four-coordinate carbene-Cu(I) complexes
employing tris(pyrazolyl)borate ligands. Polyhedron 2020, 180, 114381.
2. Liu, Y.; Yiu, S.-C.; Ho, C.-L.; Wong, W.-Y., Recent advances in copper complexes for
electrical/light energy conversion. Coord. Chem. Rev. 2018, 375, 514-557.
3. Tsuge, K.; Chishina, Y.; Hashiguchi, H.; Sasaki, Y.; Kato, M.; Ishizaka, S.; Kitamura,
N., Luminescent copper(I) complexes with halogenido-bridged dimeric core. Coord. Chem. Rev.
2016, 306, 636-651.
4. Barbieri, A.; Accorsi, G.; Armaroli, N., Luminescent complexes beyond the platinum
group: the d10 avenue. Chemical Communications 2008, (19), 2185-2193.
5. Di, D.; Romanov, A. S.; Yang, L.; Richter, J. M.; Rivett, J. P. H.; Jones, S.; Thomas,
T. H.; Abdi Jalebi, M.; Friend, R. H.; Linnolahti, M.; Bochmann, M.; Credgington, D., High-
performance light-emitting diodes based on carbene-metal-amides. Science 2017, 356 (6334),
159-163.
6. Romanov, A. S.; Becker, C. R.; James, C. E.; Di, D.; Credgington, D.; Linnolahti, M.;
Bochmann, M., Copper and Gold Cyclic (Alkyl)(amino)carbene Complexes with Sub-
Microsecond Photoemissions: Structure and Substituent Effects on Redox and Luminescent
Properties. Chemistry – A European Journal 2017, 23 (19), 4625-4637.
109

7. Shi, S.; Jung, M. C.; Coburn, C.; Tadle, A.; Sylvinson M. R, D.; Djurovich, P. I.;
Forrest, S. R.; Thompson, M. E., Highly Efficient Photo- and Electroluminescence from Two-
Coordinate Cu(I) Complexes Featuring Nonconventional N-Heterocyclic Carbenes. Journal of
the American Chemical Society 2019, 141 (8), 3576-3588.
8. Hamze, R.; Shi, S.; Kapper, S. C.; Muthiah Ravinson, D. S.; Estergreen, L.; Jung, M.
C.; Tadle, A. C.; Haiges, R.; Djurovich, P. I.; Peltier, J. L.; Jazzar, R.; Bertrand, G.;
Bradforth, S. E.; Thompson, M. E., "Quick-Silver" from a Systematic Study of Highly
Luminescent, Two-Coordinate, d(10) Coinage Metal Complexes. J Am Chem Soc 2019, 141
(21), 8616-8626.
9. Hamze, R.; Peltier, J. L.; Sylvinson, D.; Jung, M.; Cardenas, J.; Haiges, R.;
Soleilhavoup, M.; Jazzar, R.; Djurovich, P. I.; Bertrand, G.; Thompson, M. E., Eliminating
nonradiative decay in Cu(I) emitters: > 99% quantum efficiency and microsecond lifetime.
Science 2019, 363 (6427), 601-606.
10. Hamze, R.; Idris, M.; Muthiah Ravinson, D. S.; Jung, M. C.; Haiges, R.; Djurovich, P.
I.; Thompson, M. E., Highly Efficient Deep Blue Luminescence of 2-Coordinate Coinage Metal
Complexes Bearing Bulky NHC Benzimidazolyl Carbene. Frontiers in Chemistry 2020, 8 (401).
11. Li, J.; Wang, L.; Zhao, Z.; Li, X.; Yu, X.; Huo, P.; Jin, Q.; Liu, Z.; Bian, Z.; Huang,
C., Two-Coordinate Copper(I)/NHC Complexes: Dual Emission Properties and Ultralong Room-
Temperature Phosphorescence. Angewandte Chemie International Edition 2020, 59 (21), 8210-
8217.
12. Bedford, R. B.; Betham, M., N-H Carbazole Synthesis from 2-Chloroanilines via
Consecutive Amination and C−H Activation. The Journal of Organic Chemistry 2006, 71 (25),
9403-9410.
13. Piel, I.; Pawelczyk, M. D.; Hirano, K.; Fröhlich, R.; Glorius, F., A Family of
Thiazolium Salt Derived N-Heterocyclic Carbenes (NHCs) for Organocatalysis: Synthesis,
Investigation and Application in Cross-Benzoin Condensation. Eur. J. Org. Chem. 2011, 2011
(28), 5475-5484.
14. Chianese, A. R.; Rogers, S. L.; Al-Gattas, H., Palladium-catalyzed synthesis of
carbazoles from N-(2-halophenyl)-2,6-diisopropylanilines via C–C cleavage. Tetrahedron
Letters 2010, 51 (17), 2241-2243.
15. Budén, M. E.; Vaillard, V. A.; Martin, S. E.; Rossi, R. A., Synthesis of Carbazoles by
Intramolecular Arylation of Diarylamide Anions. The Journal of Organic Chemistry 2009, 74
(12), 4490-4498.
110

Chapter 4. Temperature and Magnetic Field Dependence on the Lifetime and Emission
Spectra using an Optical Probe
4.1. Introduction
As the name implies, the physical properties management system (PPMS) is an instrument
designed to probe the physical properties of a given material. In particular, this instrument can be
used to study how a material responds to changes in temperature and/or magnetic field. Recently,
our lab has been looking at lifetime changes as a function of temperature to glean more information
about the excited state of a given molecule.
1-3
While these initial findings were instrumental in
helping us to understand the excited state of several two-coordinate coinage metal complexes,
there were significant drawbacks to the cryostat that was used for data collection. For example,
one major disadvantage of the cryostat was that it required the use of large amounts of liquid
helium. Additionally, the temperature of the sample being analyzed was not well-controlled, which
lead to a significant degree of error within the measurements. This chapter looks at the use of an
optical probe constructed for the PPMS designed to specifically combat these issues. The optical
probe design and experimental set ups are discussed later in Appendix B.
As mentioned previously, the PPMS is designed to have great control over the temperature.
In addition, this instrument has a compressor that recycles the liquid helium it uses to cool down,
significantly reducing the amount being used. While these advantages, in and of themselves, are a
compelling enough reason to design an apparatus for the PPMS that can be used to collect lifetime
data at various temperatures, codes can also be written to automate this process that initially took
~12 hours to perform by hand. Moreover, new experiments previously unavailable to us could
become viable. For example, one benefit of the PPMS is that you can study how materials respond
to a change in the magnetic field. Being able to see how the lifetime of a material changes as a
111

function of magnetic field could allow us to better understand why a material behaves the way it
does. In fact, preliminary magnetic data taken by Rasha and JoAnna surprisingly showed that the
lifetime of some of the two-coordinate copper complexes varied drastically as a function of
magnetic field.
4.2. Results and Discussion
4.2.1. 2 wt% fac-Ir(ppy)3 in polystyrene film
An optical probe for the physical properties measurement system (PPMS) was built to
investigate the effects of temperature and magnetic field on the photophysical properties of
luminescent complexes. The design of the probe as well as the experimental set ups are outlined
in Appendix B. Prior to testing new materials, the optical probe was benchmarked against
previously collected data by Yersin et. al. for fac-Ir(ppy)3.
4
Lifetime data of a 2 wt% fac-Ir(ppy)3
in polystyrene (PS) film was collected from 300 K to 10 K and plotted versus the literature (Figure
109). It should be noted that the literature data was collected in CH2Cl2 and that a direct comparison
with this data was not possible as the optical probe is only set up for films.
The lifetime data collected using the optical probe showed a similar trend to that of the
literature. However, the lifetime values obtained were slightly shorter at lower temperatures,
suggesting that more preliminary testing and/or modifying of the probe is needed before new
complexes can be analyzed. There are several possible reasons as to why the data collected deviates
from the literature. As is typically the case the liquid helium cryostats we have used in the past,
shorter than reported lifetimes could be indicative of the film not being cooled properly. While
improper cooling of the sample is within the realm of possibilities, one of the major advantages of
PPMS is that it has a high degree of control over the temperature. This suggests that there is another
112

reason for the discrepancies. For instance, a far more likely reason for variations between the two
data sets is that different matrices were used. These matrices, not only have different degrees of
rigidity, but different polarities that can significantly impact the photophysical properties of a
material. Alternatively, the differences in the lifetime could be the result of a light leak during
collection. Near the end of the lifetime data collection, it was noticed that there was a decent
amount of light leaking into the detector that affected the background of the lifetime measurement.
This small amount of light could be the reason for these small deviations in the lifetime. Overall,
the data obtained from the 2 wt% fac-Ir(ppy)3 shows promise for the optical probe as a data
collection method for variable temperature lifetime data.

Figure 109. Lifetime data of fac-Ir(ppy)3. The red data was experimental data collected by drop
casting a film of 2 wt% fac-Ir(ppy)3 in PS film. The black data is previous literature data taken in
CH2Cl2.
Variable temperature emission data was taken of a 2 wt % fac-Ir(ppy)3 in PS film (Figure
110). Emission spectra were taken in increments of 10 K, from 300 K to 30 K. An additional
spectrum was taken at 25 K as the PPMS would not go lower than 25 K under high vacuum (10
-6

Torr). Upon cooling the film, a significant drop in the emission intensity was observed. This is the
113

opposite of what we would expect as cooling the samples down freezes out nonradiative decay
pathways meaning that the emission intensity should increase. The emission intensity does not
return upon warming, suggesting that the change is irreversible. Based on this information, the
decline in intensity is the result of the film shrinking and/or peeling off the quartz substrate upon
cooling. While this unexpected decrease in the emission intensity limits the amount of information
that can be gathered from this experiment, normalizing the emission spectra allows us to see how
the overall emission profile changes as a function of temperature. For example, as the temperature
goes from 300 to 25 K, we can see the emission become more vibronic in character, characteristic
of less MLCT character in the excited state at lower temperatures.
500 600 700
1400
1600
1800
2000
2200
Intensity (arb. units)
Wavelength (nm)
Decrease in
Temperature

450 500 550 600 650 700 750
0
0.5
1
Normalized Intensity (arb. units)
Wavelength (nm)
300 K
100 K
25 K

Figure 110. Emission spectra of 2 wt% fac-Ir(ppy)3 in PS film with a 435 nm filter. Spectra were
taken every ~10 K from 300 to 25 K. The left plot shows how the intensity changed as a function
of temperature. The right graph shows the normalized emission spectra at 300, 100, and 25 K.
As mentioned earlier, preliminary lifetime data for a 2 wt% fac-Ir(ppy)3 in PS film was
collected from RT to 10 K. However, data recently obtained with the new cryostat was acquired
by first cooling the system down and then collecting from 4 K to RT. For a direct comparison
between the cryostat and the optical probe, lifetime data was collected on a 2 wt% fac-Ir(ppy)3 in
114

PS film from 10 K to RT. The lifetime data of these films as well data collected by Yersin of fac-
Ir(ppy)3 in a PMMA film are shown in Figure 111.
4
The lifetime data collected using the probe
showed monoexponential fits from 10 to 20 K and above 75 K while biexponential fits were
observed from 20 to 75 K. The cryostat saw similar fit trends. Surprisingly, the optical probe
reported longer lifetimes at lower temperatures from both the cryostat and the literature data in this
biexponential regime. One reason for the longer lifetime values could be due to the probe not
having enough time to equilibrate between lifetime runs. However, when the sample was allowed
to equilibrate at 30 K for 10 minutes, there was not an observed change in the lifetime obtained
suggesting that the sample was at the correct temperature prior to the lifetime being taken. In the
future, another run should be taken from RT to 10 K to see if there is an observable hysteresis from
collecting data in both directions.
0 50 100 150 200 250 300
0
20
40
60
80
100
120
Yersin
10 K to RT
10 K to RT (bi exp fit)
New Cryostat
t (s)
T (K)
Waited 10 minutes.
Still the same lifetime.

Figure 111. Lifetime data of fac-Ir(ppy)3. The black data is previous literature data taken of 2
wt% of fac-Ir(ppy)3 in PMMA film. All other data were films of 2 wt% fac-Ir(ppy)3 in PS film.

115

4.2.2. 2 wt% MACAuCz in polystyrene film
Lifetime data as a function of temperature was taken of a 2 wt% MACAuCz in PS film and
compared to data previously acquired using the older cryostat.
2
While temperatures above ~175 K
matched recently published data by our lab, lifetimes at lower temperatures deviated substantially.
Moreover, the lifetime values obtained using the probe are much longer than what was reported,
suggesting that the previously tested samples may not have been effectively cooled by the old
cryostat. The data obtained using the optical probe was fit to both a two- and three-level Boltzmann
model (Figure 113). The two-level fit assumes that the SOC factor of the material is small and,
hence, that no splitting of the T1 is observed. From this fit, one can derive the splitting between
the S1 and T1 (ΔES1-T1) as well as the lifetimes for the S1 (τfl) and T1 (τph) states. In contrast, the
three-level fit works well for materials with a large SOC factor, which result split the T1 states.
The lifetimes of the T1 substates (τI/II and τIII) as well as the τfl can be determined from this fit. The
three-model fit also includes energy gap parameters such as the ΔES1-T1 and the splitting between
the T1
I/II
and T1
III
, otherwise known as the zero-field splitting (ZFS).
0 100 200 300
0
20
40
60
80
100
120
140
Lifetime (us)
Temperature (K)
Cryostat
PPMS probe

Figure 112. Lifetime data of MACAuCz. The red data was experimental data collected by drop
casting a film of 2 wt% MACAuCz in PS film. The black data is previous literature data taken in
as a 1 wt% PS film.
2

116

While the two-level model breaks down at lower temperatures, the three-level model fit
swell across the data points collected, suggesting that the SOC factor of MACAuCz is large enough
to split the T1 sublevels. The parameters derived using both fits are shown in Table 16. Previously
data collected on the same sample are shown for comparison.
2
Since the fit for the two-level model
was poor in comparison to the three-level model, only the parameters for the three level model will
be discussed. The ΔES1-T1 found using the probe was slightly larger than what was reported
previously. While this value is slightly bigger than what was reported, it is not an unreasonable
ΔES1-T1 for a TADF emitter. Moreover, the value of 12 cm
-1
obtained for the ZFS is more
reasonable than the previously reported data, further validating the use of the probe for these
measurements.

Figure 113. Variable temperature lifetime data of a 2 wt% MACAuCz in PS film. The two-
(dashed) and three-level (solid) fits are shown.

117

Table 16. Two- and three-level fits of the variable temperature lifetime data for a 2 wt%
MACAuCz in PS film.

two-level model
5–300 K
three-level model
5–300 K
Au
MAC

∆𝐸 𝑆 1−𝑇 1
(cm
-1
)
tph/tfl
(s/ns)
∆𝐸 𝑆 1−𝑇 1

(cm
-1
)
ZFS
(cm
-1
)
tt,
(s)
tfl
(ns)
Probe 460 98/86 640 12 33/210 16
Literature
2
260 68/330 470 91 9.1/73 70

Variable emission spectra were taken of the 2 wt% MACAuCz in PS film and is shown in
Figure 114. As was observed with fac-Ir(ppy)3, these films showed a substantial decrease in the
emission intensity with a decrease in the temperature, indicative of the film peeling off the
substrate. As would be expected for this 2-coordinate coinage metal complex dispersed in a rigid
matrix, the structure of the emission is still broad and featureless at lower temperatures. The spectra
are shifted to slightly higher energy since the molecules are unable to freely rotate in the rigid
matrix.
118

400 500 600 700
1400
1450
1500
1550
Intensity (arb. units)
Wavelength (nm)
Decrease in
Temperature
450 500 550 600 650 700 750
0
0.5
1
Normalized Intensity (arb. units)
Wavelength (nm)

Figure 114. Emission spectra of 2 wt% MACAuCz in PS film with a 435 nm filter. Spectra were
taken every ~10 K from 300 to 40 K. The left plot shows how the intensity changed as a function
of temperature. The right graph shows the normalized emission spectra.
4.3. Future modifications to the probe
There are a few changes that can be made to the probe to improve overall data collection.
In the next iteration of the probe, one of the first modifications that should be made is to reconstruct
the top hat. As mentioned in Appendix B, the top hat is connected to the copper cage via a metal
rod and sits outside of the PPMS. Due to a design flaw in the probe, the top hat can conduct enough
heat into the PPMS through the rod, making it hard for instrument to stabilize at lower temperatures
(approximately 10 to 30 K). In fact, when the PPMS is set to 10 K, the temperature fluctuates
anywhere between 10 K to 15.5 K. By minimizing the amount of the material metal sticking
outside of the probe, we can hopefully minimize the amount of heat being conducted into the
PPMS. Aside from reconstructing the top hat, another modification that can be done to help
regulate the temperature is remaking the guide rings on the rod. The purpose of these rings is to
press up against the inside of the PPMS to distribute the temperature evenly, preventing
119

fluctuations in the temperature. The rings that were cut by the machine shop appear to be slightly
too small and could be the reason for instabilities in the temperature.
4.4. Future work
Future work should also look at optimizing films for emission spectra collection. The use
of spin-coated films, which are thinner and adhere better to the substrate, will likely prevent the
film from peeling, likely mitigating the drop in emission intensity observed for the drop cast films.
4.5. References-Chapter 4
1. Hamze, R.; Peltier, J. L.; Sylvinson, D.; Jung, M.; Cardenas, J.; Haiges, R.;
Soleilhavoup, M.; Jazzar, R.; Djurovich, P. I.; Bertrand, G.; Thompson, M. E., Eliminating
nonradiative decay in Cu(I) emitters: > 99% quantum efficiency and microsecond lifetime.
Science 2019, 363 (6427), 601-606.
2. Hamze, R.; Shi, S.; Kapper, S. C.; Muthiah Ravinson, D. S.; Estergreen, L.; Jung, M.
C.; Tadle, A. C.; Haiges, R.; Djurovich, P. I.; Peltier, J. L.; Jazzar, R.; Bertrand, G.;
Bradforth, S. E.; Thompson, M. E., "Quick-Silver" from a Systematic Study of Highly
Luminescent, Two-Coordinate, d(10) Coinage Metal Complexes. J Am Chem Soc 2019, 141
(21), 8616-8626.
3. Shi, S.; Jung, M. C.; Coburn, C.; Tadle, A.; Sylvinson M. R, D.; Djurovich, P. I.;
Forrest, S. R.; Thompson, M. E., Highly Efficient Photo- and Electroluminescence from Two-
Coordinate Cu(I) Complexes Featuring Nonconventional N-Heterocyclic Carbenes. Journal of
the American Chemical Society 2019, 141 (8), 3576-3588.
4. Hofbeck, T.; Yersin, H., The Triplet State of fac-Ir(ppy)3. Inorganic Chemistry 2010, 49
(20), 9290-9299.
120

Chapter 5. Using Stern-Volmer quenching studies to screen novel photoredox catalysts
5.1. Introduction
Photoredox catalysis has gained momentum recently for its ability to perform novel
transformations under relatively mild reaction conditions.
1
While a number of reports have come
out of this field,
2-4
only a few different visible light photocatalysts have actually been utilized.
1

Moreover, the choice of photocatalyst is routinely determined through “trial and error” rather than
designing (or strategically choosing) a photocatalyst with optimized properties for a particular
system.
5
Although currently used photocatalysts have been shown to be quite effective, the
development of new photocatalysts will allow for optimization of reaction conditions by having
various photocatalysts with unique excited state properties to choose from. Additionally, the
development of tunable photocatalysts would be beneficial as it would allow the photocatalyst to
be tailored to fit a desired reaction.
5

While our lab has primarily worked on designing luminescent metal complexes for
applications in OLEDs, efficient dopants tend to have characteristics that also make them ideal for
applications in photoredox catalysis. This chapter looks at the excited state redox properties of
recently developed emitters to determine their viability as photocatalysts. Stern-Volmer quenching
studies will be used to probe the excited state properties of 2-coordinate copper complexes, which
can then be used to determine the overall reductive and oxidative electron transfer quenching of
these complexes. In particular, we will focus on (carbene)Cu
I
(carbazole) complexes, which have
been shown to have properties that are advantageous in a visible light photocatalyst.
Aside from the characteristics commonly associated with efficient photocatalysts, an added
appeal of these systems is that oxidation and reduction potentials can be separately tuned, allowing
121

for easy optimization of the redox properties of these materials. The ability to independently
modify these properties is the direct result of the oxidation and reduction occurring on different
parts of the molecule. For example, oxidation and reduction of these complexes routinely occur at
the carbazole and carbene respectively. Strategic substitution of electron withdrawing groups on
the carbazole can shift the oxidation to more positive potentials, while the use of electron donating
groups has the opposite effect. Furthermore, the use of different carbenes can be used to manipulate
the reduction potential of these materials. The second half of this chapter will look at the excited
state redox properties of a N-heterocyclic carbene (NHC) Ir complex, fac-Ir(tpz)3. This complex
was originally designed as a sky-blue emitter for OLEDs but has properties that would be valuable
for photoredox catalysis. In comparison to one of the most used Ir based visible light
photocatalysts, fac-Ir(ppy)3, fac-Ir(tpz)3 is a much more potent excited state reductant, signifying
its potential for use as a photocatalyst.
5.2.Results and Discussion
5.2.1. Stern-Volmer quenching studies
Stern-Volmer quenching studies are an effective way of probing the dynamic quenching
processes that can occur between a photocatalyst and a quencher. In these experiments, various
amounts of quencher are added to a solution of photocatalyst. When the photocatalyst absorbs a
photon of light, it is promoted into its excited state where it can undergo energy transfer or single
electron transfer (SET) with a quencher molecule. These bimolecular processes result in a decrease
in the emission intensity or lifetime of the photocatalyst as a function of quencher concentration.
While changes in both the emission intensity and lifetime values can be used to probe
dynamic quenching processes, emission intensity cannot differentiate between dynamic and static
quenching. Since the focus of our studies is specifically on how the photocatalyst reacts with a
122

quencher while in its excited state, all Stern-Volmer quenching studies will be performed using
lifetime measurements. When changes in lifetime are plotted as a function of quencher
concentration, a straight line is obtained that corresponds to Equation 2, where [Q] the
concentration of the quencher, kq is the Stern-Volmer quenching constant, and τ and τ0 are the
lifetimes of the photocatalyst with and without the addition of quencher respectively. The slope of
the line is equal to kqτ0. Since τ0 doesn’t change when the photocatalyst and solvent are held
constant, the slope of the lines can be directly compared.
(2)
𝜏 0
𝜏 = (𝑘 𝑞 )(𝜏 0
)[𝑄 ] + 1
5.2.2. Oxidative electron transfer quenching of CAACCuCz
Stern-Volmer quenching analyses were performed on CAACCuCz using eight different
oxidative quenchers. Plots for two of these quenchers, 1,10-phenanthroline and o-dinitrobenzene,
are shown for comparison in Figure 115. The steeper slope for the Stern-Volmer quenching plot
of o-dinitrobenzene indicates that this compound undergoes bimolecular quenching with
CAACCuCz more effectively than 1,10-phenanthroline. The large difference in the slopes of the
two Stern-Volmer plots shown can be readily explained using the molecular energy diagram shown
in Figure 116. In order for a photocatalyst to undergo efficient oxidative quenching, the quencher
selected should have a less negative reduction potential than the excited state oxidation potential
of the photocatalyst. If the reduction potential of the oxidative quencher is at a much more negative
potential, oxidative quenching of the photocatalyst will likely not occur. CAACCuCz has an
excited state oxidation potential of -1.95 V, meaning that the driving force required to reduce o-
dinitrobenzene with a reduction potential of -0.71 V is much better in comparison to 1,10-
phenanthroline with a reduction potential of -2.04 V. Overall, the higher the slope, the higher the
kq.
123

Figure 115. Stern-Volmer quenching studies of CAACCuCz in THF using 1,10-phenanthroline
(left) and o-dinitrobenzene (right) as oxidative quenchers.

Figure 116. Quenching of CAACCuCz using two different oxidative quenchers. The excited state
oxidation and reduction potentials are shown for CAACCuCz*. The ground state reduction
potential is shown for the oxidative quenchers, 1,10-phenanthroline (red) and o-dinitrobenzene
(blue).
The kq values for the various oxidative quenchers used are shown in Table 17. For
comparison, the reduction potentials for these quenchers as well as the slopes determined from
Stern-Volmer are also shown. As would be expected from the information gleaned from Figure
0.0 0.5 1.0 1.5 2.0
1.0
1.5
2.0
2.5
3.0
3.5
4.0
4.5
t
0
t
mM [1,10-phenanthroline]
y = 1.7x + 1
R
2
= 1.000
0 0.5 1 1.5 2
20
40
60
80
t
0
t
mM [o-dinitrobenzene]
y = 33.3x + 1
R
2
= 0.9976
124

116, oxidative quenchers that are easier to reduce have much higher kq values. These kq values
level off around a slope of 33, which likely indicates that the rate limiting step of quenching is
diffusion limited at these redox potentials. When the reduction potentials of various oxidative
quenchers are plotted vs kq, an oxidative electron transfer quenching plot can be obtained (Figure
117). The poor fit for this data is likely the result of energy transfer which can be competitive with
electron transfer when the triplet energy of the quencher is below that of the photocatalyst.
Table 17. Quenching constants of various oxidative quenchers for CAACCuCz in THF.
Oxidative quenchers used for
quenching CAACCuCz
Ered
vs. SCE
(V)
slope of SV
(mM
-1
)
kq
(M
-1
s
-1
)
2,2'-bipyridine -2.18 0.037 1.42E+07
pyrazine -2.08 0.12 4.62E+07
1,10 phenanthroline -2.04 1.7 6.54E+08
2,2-bipyrimidine -1.80 0.79 3.04E+08
phenazine -1.23 33 1.27E+10
o-dinotrobenzene -0.91 33.3 1.28E+10
1,2,4,5-tetracyanobenzene -0.71 31.9 1.23E+10

125

Figure 117. Oxidative electron transfer quenching of CAACCuCz in THF.
5.2.3. Reductive electron transfer quenching of CAACCuCz
Stern-Volmer quenching plots of CAACCuCz using two different reductive quenchers are
shown in Figure 118. The oxidative potentials of the two quenchers, para-tetramethyl-
phenylenediamine and tetramethyl-benzidine, are 0.13 and 0.43 V respectively. The difference in
the slopes of the two plots can be readily understood using Figure 119. For a photocatalyst to
undergo efficient reductive quenching, the quencher should have a less positive oxidation potential
than that of the excited state reduction potential of the photocatalyst. Due to the weak excited state
reduction potential (0.08 V) of CAACCuCz*, very few reductive quenchers can efficiently quench
this lumophore. In fact, all reductive quenchers used were harder oxidize than CAACCuCz*. With
respect to the two quenchers shown in Figure 118, the driving force required reduce CAACCuCz,
is lower for tetramethyl-benzidine than it is para-tetramethyl-phenylenediamine.
126

0 0.5 1 1.5 2
5
10
15
20
25
t
0
t
mM [para-tetramethyl-phenylenediamine]
y = 12.0x + 1
R
2
= 0.9997

Figure 118. Stern-Volmer quenching studies of CAACCuCz in THF using para-tetramethyl-
phenylenediamine and tetramethyl-benzidine as reductive quenchers.

Figure 119. Quenching of CAACCuCz using two different reductive quenchers. The excited state
oxidation and reduction potentials are shown for CAACCuCz*. The ground state oxidation
potentials are shown for the oxidative quenchers, para-tetramethyl-phenylenediamine (red) and
tetramethylbenzidine (blue).

127

Table 18. Quenching constants of various reductive quenchers for CAACCuCz in THF.
Reductive quenchers used for
quenching CAACCuCz
Eox
vs SCE
(V)
slope of SV
(mM
-1
)
kq
(M
-1
s
-1
)
para-tetramethyl-phenylenediamine 0.13 12 4.62E+09
phenothiazine 0.21 0.92 3.54E+08
10-methylphenothiazine 0.32 0.19 7.31E+08
tetramethyl-benzidine 0.43 0.52 7.69E+08

Due to the limited number of reductive quenchers that could be used to quench
CAACCuCz*, the reductive electron transfer quenching of CAACCuCz had to few points to
adequately fit the data (Figure 120). In fact, several points appeared to level off at higher oxidation
potentials, which could be the result of dexter triplet transfer. Further analysis is needed to support
this hypothesis.

Figure 120. Reductive electron transfer quenching of CAACCuCz in THF.
128

5.2.4. Stern-Volmer quenching studies of fac-Ir(tpz)3
Stern-Volmer quenching plots were obtained for fac-Ir(tpz)3 using two different reductive
quenchers, 1,4-diazabicyclo[2.2.2]octane and N,N-dimethyl-p-toluidine (Figure 121). As was the
case for CAACCuCz, effective quenching of fac-Ir(tpz)3 by a reductive quencher requires that the
oxidation potential of the quencher be at a less positive potential than the excited state reduction
potential of fac-Ir(tpz)3
*
. However, the reductive quenchers initially chosen had oxidation
potentials at more positive potentials, resulting in very little quenching observed for fac-Ir(tpz)3
*
.
This is evident by the small slopes and kq values observed. Future work should include study of
reductive quenchers that are less potent oxidizers than the ones already studied.
0 2 4 6 8
1
1.1
1.2
1.3
1.4
t
0
t
mM of 1,4-diazabicyclo[2.2.2]octane
y = 0.466x + 1
R
2
= 0.9999

0 2 4 6 8
1
1.1
1.2
1.3
1.4
t
0
t
mM of N,N-dimethyl-p-toluidine
y = 0.566x + 1
R
2
= 0.970

Figure 121. Stern-Volmer quenching studies of fac-Ir(tpz)3 in toluene using 1,4-
diazabicyclo[2.2.2]ocatane (left) and N,N-dimethyl-p-toluidine (right) as reductive quenchers.

129

Table 19. Quenching constants of various reductive quenchers for fac-Ir(tpz)3 in toluene.

While the majority of these Stern-Volmer quenching studies thus far have looked at the use
of quenchers that undergo SET with a photocatalyst, quenching by energy transfer can also occur
in these systems. To probe this type of bimolecular quenching, futher Stern-Volmer quenching
studies were performed on fac-Ir(tpz)3 using quenchers with low triplet energies. These quenchers
can readily undergo energy transfer reactions with the photocatalyst. Overall, the results show that
anthracene is able to undergo energy transfer more readily with fac-Ir(tpz)3 because it has a lower
triplet energy to that of naphthalene.
0 2 4 6 8
0
5
10
15
t
0
t
mM of Naphthalene
y = 1.854x +1
R
2
= 0.998

0 2 4 6 8
0
5
10
15
20
25
30
t
0
/t
mM of Anthracene
y = 3.601x + 1
R
2
= 0.9996

Figure 122. Stern-Volmer quenching studies of fac-Ir(tpz)3 in toluene using energy transfer
quenchers.
130

Table 20. Quenching constants of various reductive quenchers for CAACCuCz in THF.

a
Literature value.
6

5.3. Experimental
5.3.1. General
Tetrahydrofuran (THF) and toluene (tol) were dried using a dry solvent system from Glass
Contour. Stern-Volmer quenching studies were performed by taking 2 mL of a ~20 μM stock
solution of the corresponding photocatalyst (MACCuCz, CAACCuCz, and fac-Ir(tpz)3) and
diluting it with various concentrations of a quencher to a total volume of 4 mL. 8 mM stock
solutions of a quenchers were made and diluted to obtain a total concentration of 0.1, 0.2, 0.3, and
0.4 mM in the 4 mL solution. Lifetime measurements were obtained using an IBH Fluorocube
instrument with a time-correlated single photon counting (TCSPC) method. A 405 nm laser
excitation source was used for all lifetime measurements at room temperature. All samples were
bubble degassed using N2 gas for ~7 minutes prior to measurements. Steady state emission spectra
were obtained using a Photon Technology International QuantaMaster
phosphorescence/fluorescence spectrofluorimeter.
5.3.1. Stern-Volmer quenching plots for 2-coordinate copper (I) carbazole complexes
131

450 500 550 600 650 700
0
1
2
3
4
5
6
7
PL Intensity (10
5
)
MACCuCz in MeCN
Wavelength (nm)
0 mM BIH
0.5 mM BIH
1.0 mM BIH
1.5 mM BIH
2.0 mM BIH

Figure 123. Quenching of MACCuCz in MeCN with BIH using fluorimeter.
0.0 0.5 1.0 1.5 2.0
2
4
6
8
10
12
14
16
t
0
/t
[1,2,4,5-tetracyanobenzene]
y= 6.55x + 1
R
2
= 0.9999

Figure 124. Stern-Volmer quenching studies of MACCuCz with 1,2,4,5-tetracyanobenzene.
Table 21. Quenching rate constants (kq) for MACCuCz and CAACCuCz using 1,2,4,5-
tetracyanobenzene as a quencher.

132

0 0.5 1 1.5 2
1
2
3
4
5
t
0
/t
[BIH] (mM)
y = 1.94x + 1
R
2
= 0.988

0 1 2 3 4
1.0
1.5
2.0
2.5
3.0
t0t
mM [BIH]
y = 0.52x + 1
R
2
= 0.979

Figure 125. Stern-Volmer quenching studies of MACCuCz (left) and CAACCuCz(right) with
BIH.
Table 22. Quenching rate constants (kq) for MACCuCz and CAACCuCz using BIH as a quencher.

0.0 0.5 1.0 1.5 2.0
1.0
1.2
1.4
1.6
1.8
2.0
2.2
2.4
2.6
2.8
t
0
t
mM [phenothiazine]
y = 0.92x + 1
R
2
= 0.9989

0 0.5 1 1.5 2
1
1.05
1.1
1.15
1.2
1.25
1.3
1.35
1.4
t
0
/t
mM [10-methylphenothiazine]
y = 0.19x + 1
R
2
= 0.9997

Figure 126. Stern-Volmer quenching studies of CAACCuCz in THF using various reductive
quenchers.
133

0 0.5 1 1.5 2
1
1.5
2
2.5
t
0
t
mM [2,2'-bipyrimidine]
y = 0.79x + 1
R
2
= 0.9985

0 0.5 1 1.5 2
0
10
20
30
40
50
60
70
t
0
/t
mM [phenazine]
y = 33.0 x + 1
R
2
= 0.9999

Figure 127. Stern-Volmer plots for CAACCuCz using various oxidative quenchers.
5.4. References-Chapter 5
1. Prier, C. K.; Rankic, D. A.; MacMillan, D. W. C., Visible Light Photoredox Catalysis
with Transition Metal Complexes: Applications in Organic Synthesis. Chemical Reviews 2013,
113 (7), 5322-5363.
2. Shields, B. J.; Doyle, A. G., Direct C(sp3)–H Cross Coupling Enabled by Catalytic
Generation of Chlorine Radicals. Journal of the American Chemical Society 2016, 138 (39),
12719-12722.
3. Nielsen, M. K.; Shields, B. J.; Liu, J.; Williams, M. J.; Zacuto, M. J.; Doyle, A. G.,
Mild, Redox-Neutral Formylation of Aryl Chlorides through the Photocatalytic Generation of
Chlorine Radicals. Angewandte Chemie International Edition 2017, 56 (25), 7191-7194.
0 2 4 6 8
1.00
1.05
1.10
1.15
1.20
1.25
1.30
t0/t
mM [ 2,2'-bipyridine]
y = 0.037x + 1
R
2
= 0.9947
0.0 0.5 1.0 1.5 2.0
1.0
1.5
2.0
2.5
3.0
3.5
4.0
4.5
t
0
t
mM [1,10-phenanthroline]
y = 1.7x + 1
R
2
= 1.000
134

4. Ackerman, L. K. G.; Alvarado, J. I. M.; Doyle, A. G., Direct C-C Bond Formation from
Alkanes Using Ni-Photoredox Catalysis. Journal of the American Chemical Society 2018, 140
(43), 14059-14063.
5. Arias-Rotondo, D. M.; McCusker, J. K., The photophysics of photoredox catalysis: a
roadmap for catalyst design. Chemical Society Reviews 2016, 45 (21), 5803-5820.
6. Seixas de Melo, J. S.; Pina, J.; Dias, F. B.; Maçanita, A. L., Experimental Techniques
for Excited State Characterisation. In Applied Photochemistry, Evans, R. C.; Douglas, P.;
Burrow, H. D., Eds. Springer Netherlands: Dordrecht, 2013; pp 533-585.
135

Appendix A. Phenyl bis-oxazoline as an ancillary ligand for bis-cyclometalated iridium
complexes
A.1. Introduction
The use of BOX-CN as an ancillary ligand for bis-cyclometalated iridium complexes was
previously described in Chapter 2. This chapter focuses on BOX-Ph ancillary ligands, (4S)-(+)-
phenyl-α-[(4S)-phenyloxazolidin-2-ylidene]-2-oxazoline-2-benzene and (4R)-(+)-phenyl-α-
[(4R)-phenyloxazolidin-2-ylidene]-2-oxazoline-2-benzene, with acronyms BOXSS-Ph and
BOXRR-Ph that were not described in the earlier chapter. Unlike the (C^N)2Ir(BOX-CN)
complexes, these analogues suffer from stability issues. It was shown that these complexes
decompose in the presence of trace amounts of water. Additionally, these materials showed red-
shifted emission, lower PLQY, and higher nonradiative rates than their BOX-CN counterparts,
severely limiting their application as dopants.
A.2. Results and Discussion
A.2.1. Photophysics
The photophysics of the (ppy)2Ir(BOX-Ph) derivatives are shown in Table 23 and Figure
128. The BOX-CN, tris, acac derivatives are shown for comparison. Both the (ppy)2Ir(BOXRR-Ph)
and (ppy)2Ir(BOXSS-Ph) are red-shifted from the BOX-CN, tris, and acac derivatives by 44 nm,
38, and 24 nm respectively. The BOX-Ph complexes have slightly longer lifetimes (τ = 2.5 µs)
and lower PLQYs (Φ = 0.59-0.69). The knr values for these complexes are almost a magnitude
higher (knr = 1.2-1.6 x 10
5
s
-1
) than both the BOX-CN and acac derivatives, which is likely a result
of the freely rotating phenyl ring at the meso position of the BOX ligand. The red-shift in the
emission maxima indicates that the BOXSS-Ph /BOXRR-Ph ligand are participating more strongly
136

in the photophysics of the overall complex than the BOX-CN and acac ligands. In addition, this
participation by the BOXSS-Ph/BOXRR-Ph is likely the reason these complexes have longer
lifetimes. It should be noted that a higher energy shoulder appears at 77 K for the BOX-Ph
complexes in 2Me-THF. When the samples were taken in THF (Table 24, Figure 129) from the
solvent dispensing system (SDS), the shoulder went away, indicating that the complexes are likely
reacting with residual water to produce a higher energy compound.
Table 23. Photophysics of (ppy)2Ir(BOX) complexes in 2Me-THF.

λmax
(nm)
τ
(µs)
ΦPL
kr
(10
5
s
-1
)
knr
(10
5
s
-1
)
λmax.77K
(nm)
τ77K (µs)
Δ-BOXSS-CN 503 1.9 0.92 4.8 0.48 489 3.2
Λ-BOXRR-CN 501 2.0 0.91 4.6 0.45 488 3.1
mix BOXSS-Ph 546 2.5 0.59 2.4 1.6 522 3.3
mix BOXRR-Ph 546 2.5 0.69 2.8 1.2 522 3.1
Ir(ppy)3
1
508 1.6 0.97 6.1 0.19 491 4.0
(ppy)2Ir(acac) 522 1.5 0.92 6.1 0.53 506 5.2

500 600 700
0
0.2
0.4
0.6
0.8
1
Normalized Intensity (a.u.)
Wavelength (nm)
-BOX
SS
-CN
-BOX
SS
-CN
mix BOX
SS
-CN
mix BOX
SS
-CN
RT

450 500 550 600 650
0
0.2
0.4
0.6
0.8
1
Normalized Intensity (a.u.)
Wavelength (nm)
77 K

Figure 128. Emission spectra of (ppy)2Ir(BOX) complexes in 2Me-THF at RT and 77 K.
137

400 450 500 550 600 650 700
0
0.2
0.4
0.6
0.8
1
Normalized PL Intensity (arb.)
Wavelength (nm)
RT
77 K
THF
400 500 600 700
0
0.2
0.4
0.6
0.8
1
Normalized PL Intensity (arb.)
Wavelength (nm)
RT
77 K
THF

Figure 129. Emission spectra of (ppy)2Ir(BOXss-Ph) (left) and (ppy)2Ir(BOXRR-Ph) (right) at RT
and 77 K.
In addition to (C^N)2Ir(BOX-Ph) complexes where C^N = ppy, complexes were also
synthesized where using ppz, pq, and piq. Like the ppy derivatives, these complexes are
significantly red-shifted from their Ir(C^N)3 counterparts with lower PLQYs and higher
nonradiative rates.
Table 24. Photophysics of (C^N)Ir(BOX-Ph) complexes in 2Me-THF.

λmax
(nm)
τ
(µs)
ΦPL
kr
(10
5
s
-1
)
knr
(10
5
s
-1
)
λmax.77K
(nm)
τ77K (µs)
(ppz)2Ir(BOXSS-Ph) - - - - - 426
6.0 (1.6), 0.2
(84)
Ir(ppz)3
1
- - - - - 412 14
(ppy)2Ir(BOXSS-Ph) 546 2.5 0.59 2.4 1.6 522 3.3
(ppy)2Ir(BOXRR-Ph) 546 2.5 0.69 2.8 1.2 522 3.1
(pq)2Ir(BOXSS-Ph) 669 .37 0.09 2.4 25 638 -
(piq)2Ir(BOXSS-Ph) 664 654 - - - - -
Ir(piq)3
2
624 1.3 0.45 3.5 4.2 - -

138

400 500 600 700 800
0
0.2
0.4
0.6
0.8
1

Normalized PL Intensity (AU)
Wavelength (nm)
SS-ppz
SS-ppy
RR-ppy
SS-piq

Figure 130. Emission spectra of (C^N)Ir(BOX-Ph) complexes in 2 Me-THF.
A.2.2. Electrochemistry
Cyclic Voltammetry (CV) and differential pulse voltammetry (DPV) were performed on
the (ppy)2Ir(BOX-Ph) complexes. These derivatives are much easier to oxidize than other
analogues, which could be the reason for their stability issues.
Table 25. Oxidation and reduction potentials for (ppy)2Ir(BOX) complexes.
Eox
a
Ered
a
HOMO
b

(eV)
LUMO
c

(eV)
HOMO
d

(eV calc)
LUMO
d

(eV calc)
Δ-BOXSS-CN 0.36 -2.69 -5.20 -1.66 -4.92 -1.58
Λ-BOXSS-CN 0.44 -2.69 -5.30 -1.66 -4.95 -1.58
mix-BOXSS-Ph -0.17 -2.85 -4.60 -1.47 -4.22 -1.41
mix-BOXRR-Ph -0.08 - -4.70 - -4.29 -1.52
(ppy)2Ir(acac)
e
0.41 -2.60 -5.26 -1.76 -4.73 -1.28

A.2.3. Calculations
The triplet spin density calculations for (ppy)2Ir(BOXSS-Ph) and (ppy)2Ir(BOXSS-CN) are
shown in Figure 131 for a direct comparison between the BOX-CN and BOXSS-Ph/BOXRR-Ph
139

complexes. The lowest state for these complexes was found to be
3
ML’LCT. These calculations
show that there is more density on the BOXSS-Ph ancillary ligand than on the BOX-CN ligand.
The larger amount of density on the BOXSS-Ph ligand implies that this ligand plays a much more
significant role in the photophysics than the BOX-CN of similar cyclometalating ligands, which
is likely the reason for the significant red-shift in the emission.

Figure 131. Triplet spin density calculations of (ppy)2Ir(BOXSS-Ph) (left) and (ppy)2Ir(BOXSS-
CN) (right).
A.3. Experimental
Synthesis
General synthesis of BOXSS-Ph/BOXRR-Ph ((4S)-(+)-phenyl-α-[(4S)-phenyloxazolidin-2-
ylidene]-2-oxazoline-2-benzene and (4R)-(+)-phenyl-α-[(4R)-phenyloxazolidin-2-ylidene]-2-
oxazoline-2-benzene), respectively. The BOXSS-Ph/BOXRR-Ph ligands were synthesized
following a procedure similar to the one reported by Walli et. al.,
3
using (S)- and (R)-
phenylglycinol respectively. The
1
H- and
13
C-

NMR spectra collected for both BOXSS/BOXRR
match those obtained Takacs et. al.
4

140

Figure 132. Synthesis of BOXSS-Ph following a modified prep.
3

General synthesis of all complexes. Complexes containing BOXSS-Ph /BOXRR-Ph were found to
decompose when trace amounts of water were present preventing separation of the two
diastereomers through column chromatography. These complexes were purified by running
through a plug of dried silica. The complexes were analyzed as a mixture of Δ- and Λ-
diastereomers.

Scheme 6. Synthesis of (C^N)2Ir(BOXSS-Ph) and (C^N)2Ir(BOXRR-Ph) complexes.
(ppy)2Ir(BOXSS-Ph): BOXSS-Ph (196 mg, 0.513 mmol), K2CO3 (322 mg, 2.33 mmol), ppy iridium
dimer (250 mg, 0.233 mmol). Bright orange microcrystalline powder.
1
H NMR (400 MHz,
Acetone-d6) δ 8.89 (dd, J = 5.8, 1.6 Hz, 2H), 8.71 (dd, J = 5.8, 1.6 Hz, 2H), 7.98 (d, J = 8.1 Hz,
2H), 7.78 (td, J = 7.8, 1.6 Hz, 2H), 7.65 (dd, J = 7.8, 1.3 Hz, 2H), 7.58 (td, J = 7.8, 1.6 Hz, 2H),
141

7.49 – 7.44 (m, 2H), 7.41 – 7.35 (m, 3H), 7.31 (ddd, J = 7.3, 5.8, 1.5 Hz, 2H), 7.26 (d, J = 8.2 Hz,
2H), 7.20 (dt, J = 13.0, 7.7 Hz, 3H), 7.10 (p, J = 3.9, 3.3 Hz, 6H), 7.04 – 6.89 (m, 6H), 6.87 – 6.78
(m, 2H), 6.73 (ddd, J = 9.8, 6.0, 2.3 Hz, 6H), 6.65 (t, J = 7.6 Hz, 4H), 6.60 – 6.52 (m, 4H), 6.31
(td, J = 7.4, 1.3 Hz, 2H), 6.18 – 6.11 (m, 4H), 6.08 – 5.97 (m, 2H), 5.66 (dd, J = 7.6, 1.2 Hz, 2H),
4.71 (dd, J = 8.2, 2.0 Hz, 2H), 4.37 (t, J = 8.2 Hz, 2H), 3.86 (dq, J = 5.4, 2.9 Hz, 4H), 3.73 (dd, J
= 8.1, 2.1 Hz, 2H), 3.68 (t, J = 9.1 Hz, 2H).
13
C NMR (101 MHz, CDCl3 δ ppm): Elemental
Analysis: Anal. Calcd. for C47H37IrN4O2+ 0.5 H2O: C, 63.4; H, 4.30; N, 6.29. Found: C, 63.3; H,
4.20; N 6.27.
(ppy)2Ir(BOXRR-Ph):

BOXRR-Ph (196 mg, mmol), K2CO3 (322 mg, mmol), ppy iridium dimer
(250 mg, mmol). Bright orange microcrystalline powder.
1
H NMR (400 MHz, Acetone-d6) δ
8.89 (ddd, J = 5.7, 1.6, 0.8 Hz, 2H), 8.71 (ddd, J = 5.8, 1.6, 0.8 Hz, 2H), 8.01 – 7.95 (m, 2H),
7.78 (ddd, J = 8.1, 7.4, 1.6 Hz, 2H), 7.68 – 7.62 (m, 2H), 7.62 – 7.54 (m, 2H), 7.48 – 7.43 (m,
2H), 7.41 – 7.35 (m, 2H), 7.32 (ddd, J = 7.3, 5.8, 1.5 Hz, 2H), 7.26 (dt, J = 8.4, 1.1 Hz, 1H), 7.25
– 7.15 (m, 4H), 7.13 – 7.07 (m, 6H), 7.04 – 6.89 (m, 6H), 6.86 – 6.79 (m, 2H), 6.77 – 6.69 (m,
6H), 6.65 (dd, J = 8.2, 7.3 Hz, 3H), 6.59 – 6.53 (m, 3H), 6.31 (ddd, J = 7.6, 7.2, 1.3 Hz, 2H),
6.17 – 6.12 (m, 2H), 6.05 – 5.99 (m, 1H), 5.66 (ddd, J = 7.6, 1.2, 0.5 Hz, 2H), 4.71 (dd, J = 8.3,
2.0 Hz, 1H), 4.38 (t, J = 8.2 Hz, 2H), 3.89 – 3.82 (m, 4H), 3.73 (dd, J = 8.1, 2.1 Hz, 1H), 3.68
(dd, J = 8.9 Hz, 2H). Elemental Analysis: Anal. Calcd. for C47H37IrN4O2 + 0.5 H2O: C, 63.4; H,
4.30; N, 6.29. Found: C, 63.2; H, 4.37; N 6.28.

142

NMR Studies

Figure 133.
1
H-NMR of (ppy)2Ir(BOXSS-Ph).

Figure 134.
1
H-NMR of (ppy)2Ir(BOXRR-Ph).
A.4. Conclusion
Four bis-cyclometalated iridium complexes containing BOXSS-Ph/BOXRR-Ph were
synthesized. These complexes were photophysically, electrochemically, and computationally
characterized. In comparison to the BOX-CN derivatives discussed in Chapter 2, the BOXSS-Ph
143

and BOXRR-Ph complexes have several characteristics which make them overall less promising
ancillary ligands. These complexes are less stabile, red-shifted, and have lower PLQYs to their
BOX-CN analogues.
A.5. References- Appendix A
1. Sajoto, T.; Djurovich, P. I.; Tamayo, A. B.; Oxgaard, J.; Goddard, W. A.; Thompson,
M. E., Temperature Dependence of Blue Phosphorescent Cyclometalated Ir(III) Complexes.
Journal of the American Chemical Society 2009, 131 (28), 9813-9822.
2. Deaton, J.; Young, R. H.; Lenhard, J.; Rajeswaran, M.; Huo, S., Photophysical
properties of the series fac- and mer-(1-phenylisoquinolinato-N'C2')(x)(2-phenylpyridinato-
p'C2')(3-x)iridium(III) (x = 1-3). Inorganic chemistry 2010, 49 20, 9151-61.
3. Walli, A.; Dechert, S.; Meyer, F., Tautomerism in Bis(oxazoline)s. Eur. J. Org. Chem.
2013, 2013 (31), 7044-7049.
4. Atkins, J. M.; Moteki, S. A.; DiMagno, S. G.; Takacs, J. M., Single enantiomer, chiral
donor-acceptor metal complexes from bisoxazoline pseudoracemates. Organic Letters 2006, 8
(13), 2759-2762.
144

Appendix B. Design and use of the Physical Properties Measurement System (PPMS)
B.1. Introduction
This appendix goes into depth on the design of an optical probe constructed to measure
lifetime and emission spectra as a function of temperature and magnetic field. Preliminary
experiments that were conducted outside of the PPMS are discussed in this section. Experiments
performed inside the PPMS were discussed previously in Chapter 4.
B.2. Probe design
The optical probe can be broken into three major components: the top hat, the rod, and the
copper cage. Each of these components was designed with a purpose and have criteria that need to
be met for the probe to function properly.
The top hat is the component of the probe that sits outside of the PPMS. As previously
mentioned, one of the reasons we wanted to build an optical probe was to be able to measure
lifetime as a function of temperature. However, without being able to place the entire system under
vacuum, going to lower temperatures would lead to condensation of water inside the PPMS.
Therefore, one of the first major criteria for the top hat was that it needed to make an airtight seal
with the opening of PPMS, allowing the system to be placed under vacuum. Additionally, getting
lifetime data from inside the PPMS requires being able to get light in and out optical probe. This
means that we need to create an opening in the top hat that still allows for the system to be put
under vacuum. The rod attaches the top hat to the copper cage. The overall length of the optical
probe must be exact, to plug the copper cage into the bottom of the PPMS while maintaining the
seal at the top. The rod is used to both connect and properly space the top hat and copper cage.
Guide rings are also used throughout the rod to keep the temperature stable across the probe.
145

Finally, the copper cage is the part of the probe that plugs into the bottom PPMS. This cage is what
allows us to have good control over the temperature and magnetic field being applied to the sample.
As the cage is the place where we have the best control over the forces being applied to our
material, it is essential that this is where our sample being measured should be held.
B.3. First iterations
The original design of the optical probe is shown in Figure 135. Fiber optic cables were used
to direct light both in and out of the probe.

Figure 135. Original optical probe design.
The top hat was composed of two parts. The bottom part of the top hat was designed to
match the o-ring already in place on the PPMS, allowing for an air-tight seal at the base of the top
hat. In the original design, the top part of the top hat is designed to incorporate two feedthroughs.
These feedthroughs are air-tight and have SMA 905 adapters on both sides allowing us to use fiber
146

optic cables to bring light in and out of the top of the probe. Overall, these two halves of the top
hat were held together using screws, while an o-ring was used to create a good seal between these
two parts.
The rod was cut make get the overall length of the probe to fit perfectly within the PPMS.
Three guide rings were added to the rod to help direct the fiber optic cables down into the copper
cage. These rings have cut-out grooves where the fiber optic cables can sit.
The first iteration of the copper cage included two quartz rods, a mirror, and a sample
holder. A hat was added to the top of the copper cage as a place to screw in the fiber optic cables
so that the cables could line up well with the mirror and sample. Due to the size of the holes needed
to screw in the fiber optic cables, the rod could not be directly screwed into the top of the copper
cage. Therefore, the hat had to be designed to attach to the rod while still allowing room to screw
in the fiber optic cables. A picture of the resulting design is shown in Figure 136. The rod can be
screwed into the top of the hat, while cut outs on the sides allow for the fiber optic cables to pass
through and screw into the bottom of the hat. Quartz rods inside the copper cage were used to
focus light. One quartz rod was used to direct the excitation light onto the mirror while the other
quartz rod was used to direct light from the sample into a quartz rod leading to a detector. The
mirror is composed of polish steel and is used to excite the sample at a 45° angle. The sample
holder was built to hold substrates that are 1 cm x 2 cm.
147

Figure 136. The hat of the copper cage.
In this iteration of the probe, excitation light enters through the top of the probe by
connecting an excitation source to a fiber optic cable. This cable is then connected to the SMA 905
adapter that has been integrated into the top hat. The light makes its way through the SMA 905
adapter into another fiber optic cable. The light travels down this cable and enters a quartz rod
which is designed to direct light at the mirror. The light bounces off the mirror and hits the sample
at a 45° angle. A quartz rod sits at the top of the sample designed to direct light being emitted from
the sample into another fiber optic cable exiting the probe. The light then makes its way through
this fiber optic cable followed by the SMA 905 adapter. The resulting light can then be directed
into a detector for measuring. Although this was the overall intention of this design, it proved to
be problematic for light collection and required significant modifications.
B.4. Current iteration of the optical probe
The design of the current iteration is shown in Figure 137.
148

Figure 137. Current iteration of the optical probe.
As mentioned, there were several modifications made from the previous design.
1. Removed the throughputs- While troubleshooting the original design it was found that data
collection took 10x longer when the throughputs were incorporated into the design. Since this
appeared to be a significant loss of light, we decided to remove these pieces from the overall
design.
2. Changed out the fiber optic cables- We originally used fiber optic cables with smaller openings
because they were designed for under vacuum applications. We decided that using fiber optic
cables like those used in the preliminary studies by Rasha wouldn’t cause enough of a leak to be
149

detrimental to our new design and would significantly improve the amount of light coming out of
the optical probe.
3. Extended out the top hat- The new fiber optic cables that were bought were significantly longer
than those used in the previous first iteration of the probe. We had the machine shop make
extensions to fit the new fiber optic cables. The top and side view of this iteration of the top hat is
shown in Figure 138.

Figure 138. The top (left) and side view (right) of the top hat for the optical probe.
4. Remove quartz rods- The quartz rod that was being used to direct light at the mirror proved to
be unnecessary as the fiber optic cable was effective enough at directing light onto the mirror. The
other quartz rod that was a part of the original design and was intended to direct light out of the
film and towards a fiber optic cable exiting the optical probe was also removed. This quartz rod
was not efficiently transferring light between the film and the fiber optic cable. It was decided to
remove this quartz rod as well and try another design.
4. Pulled the fiber optic cables into the cage- Instead of using the quartz rod to direct light into the
fiber optic cable, we made a decision to bring both fiber optic cables into the copper cage (Figure
150

139). This change in the design allows us to butt the fiber optic cable directly against the sample
and improve overall light collection. This also allows us to use different size quartz slides as we
can adjust these cables as needed. The other fiber optic cable can also be adjusted as needed to
ensure that the light is hitting the mirror effectively. These cables are held in place by small screws.
Overall, these modifications to the optical probe significantly improved the amount of light
we were able to get out and into the detector, allowing us to start collecting data.

Figure 139. Picture of fiber optic cables after being pulled into the copper cage.
B.5. Setups
B.5.1. Emission Collection
The setup for emission collection is shown in Figure 140. An excitation source is
connected to the top of the probe using fiber optic cables. This excitation light travels down the
fiber optic cable and hits a mirror which directs the light at the sample at a 45° angle. A fiber optic
cable sitting on top of the sample directs the emitting light out of the probe. The top of the probe
151

is connected to a filter holder using another fiber optic cable. Filters can be placed in the filter
holder to remove any stray excitation light before it makes its way to the detector via another fiber
optic cable.

Figure 140. Set up for emission collection.
B.5.2. Lifetime Collection
The set up for lifetime collection is shown in Figure 141. In this set up, the IBH is
connected to a light source (such as the 394 nm MCS LED). An SMA 905 adapter was made to
screw into some of the light sources currently used in lab. A fiber optic cable is attached to the
other side of this adapter and plugged into the top of the probe. The light follows the same path
through the probe as outlined in the emission collection section. Once the light makes it way out
of the probe, it passes through a fiber optic cable that is situated such that the light can pass directly
into the detector. Similarly, to the emission collection, if stray light from the excitation source is
making it into the detector, a filter can be used to remove this light before it makes its way to the
detector.
152

Figure 141. Set up for lifetime collection.
B.6. Data collected outside PPMS
Prior to collecting data inside the PPMS, we took lifetime and emission data outside of the
instrument. There were two reasons for decision. The first reason was that it is easier to make
changes to the set up outside where we could see what was going on with the sample. The second
reason was, merely, that the PPMS was down for a while and had to wait until the PPMS was
fixed. The setup for testing emission outside the PPMS is shown in Figure 142. 2 wt% Alq3 in PS
was used to test lifetime and emission outside of the PPMS. Alq3 was chosen since it is fluorescent
and, therefore, doesn’t undergo oxygen quenching. The emission and lifetime spectra for this
sample are shown in Figure 143 and Figure 144. The emission data for 2 wt% Alq3 correlates
well with literature spectras of Alq3. It should be noted, that the signal to noise was a function of
parameters set in the code. These parameters were later modified and significantly improved the
overall signal to noise of the spectra. The lifetime value for this sample was also found to match
153

literature values for Alq3. This data showed the potential for the probe to work inside the PPMS.
These further studies are summarized in Chapter 3.

Figure 142. Emission set up outside the PPMS. The picture in the upper right-hand corner shows
the sample (2 wt% Alq3 in PS film) while being excited with a 375 nm light source.

Figure 143. Emission spectra of 2 wt% Alq3 in PS film at RT.
154

Figure 144. Lifetime spectra of 2 wt% Alq3 in PS film at RT.

Abstract (if available)

Abstract Luminescent organometallic complexes have shown great promise for their application in organic light emitting diodes, photoredox catalysis, and as sensors in biological applications. Chapter 1 gives an introduction into the photophysical properties and potential applications of iridium and coinage metal complexes. ❧ Organometallic iridium complexes with two cyclometalated ligands (C^N) and one bis-oxazoline derived ancillary ligand (L^X), i.e. (C^N)₂Ir(L^X), are reported in Chapter 2. The C^N ligands are 1-phenylpyrazoline (ppz), 2-(4,6-difluorophenyl)pyridin (F₂ppy), 2-phenylpyridine (ppy), 1-phenylisoquinoline (piq). The box ligand is (4S)-(+)-phenyl-α-[(4S)-phenyloxazolidin-2-ylidene]-2-oxazoline-2-acetonitrile with acronym BOXSS-CN. The emission of these complexes span across the visible and into the near-ultraviolet region of the electromagnetic spectrum with moderate to high photoluminescence quantum yields (ΦPL = 0.45–1.0). These complexes were found to emit from a metal-ligand to ligand charge transfer (ML’LCT) state and have lifetimes (1.3–2.1 μs), radiative rates (10⁵ s⁻¹), and nonradiative rates (10⁴–10⁵ s⁻¹) comparable to state-of-the-art iridium emitters. The (ppy)₂Ir(BOX-CN) complexes were resolved into the Δ― and Λ– diastereomers using differences in their solubility and additionally characterized by x-ray crystallography, stability, and circular dichroism studies. ❧ Copper complexes have been investigated as possible alternatives to currently used noble metal emitters like iridium. In particular, 2-coordinate copper (I) complexes have shown promising photophysical properties that make them competitive with state-of-the-art phosphorescent emitters. Chapter 3 looks at a series of 2-coordinate thiazole copper (I) carbazole complexes. Substitution at the 1-position of carbazole (XCz where x = H, Me, IPr, Ph) was used to prevent nonradiative decay pathways such as bending and rotating in the excited state. With few exceptions, previous (carbene)Cu(Cz) complexes have focused on using sterically bulky carbenes while only modifying the carbazole moiety to manipulate the energy of the HOMO. This chapter looks at the use of both the carbene and carbazole to prevent rotation about the carbene-copper-carbazole bond. ❧ The use of an optical probe designed for the physical properties management system (PPMS) is discussed in Chapter 4. The design and collection set ups for the probe can be found in Appendix B. While emitters in our lab have been mainly synthesized for use in organic light-emitting diodes (OLEDs), these complexes have properties that make them suitable for other applications. Chapter 5 looks at the use of previously synthesized iridium and copper complexes as visible light photocatalysts.

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Creator Kapper, Savannah Caroline (author)

Core Title Photophysical properties of luminescent iridium and coinage metal complexes

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Degree Doctor of Philosophy

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Degree Conferral Date 2021-12

Publication Date 04/04/2022

Defense Date 08/18/2021

Publisher University of Southern California (original), University of Southern California. Libraries (digital)

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