University of Southern California Dissertations and Theses

Synthesis and photophysical characterization of phosphorescent cyclometalated iridium (III) complexes and their use in OLEDs

(USC Thesis Other)

Synthesis and photophysical characterization of phosphorescent cyclometalated iridium (III) complexes and their use in OLEDs

PDF

Download a page range

Download transcript

Copy asset link

Request this asset

Transcript (if available)

Content SYNTHESIS AND PHOTOPHYSICAL CHARACTERIZATION OF
PHOSPHORESCENT CYCLOMETALATED IRIDIUM (III) COMPLEXES
AND THEIR USE IN ORGANIC LIGHT EMITTING DEVICES

by

Tissa Sajoto

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

May 2008

Copyright 2008 Tissa Sajoto

ii
Dedication

Dedicated to my parents and all my siblings:
Tobey Sajoto, Ratna Agustina Sajoto, Ingawati Sajoto, Talex Sajoto,
Jenny Sajoto, and Daan Sajoto

iii
Acknowledgements

First and foremost, I would like to thank my mentor and advisor,
Professor Mark Edward Thompson, for giving me the opportunity to be a part
of his research group and for guiding me throughout my graduate study.
Professor Thompson has been an inspiration to me. He is a positive
motivator and truly the best advisor I could have been placed with. Working
with him has been the most rewarding experience for me.
I would also like to thank Professor Robert Bau, Professor Surya
Prakash, Professor James Haw, Professor William Weber, and Professor
Edward Goo for their time and attendance at my screening and qualifying
exams as well as my thesis defense.
Additional thanks must be extended to my former and present
colleagues for the time that we spent together at USC. There are so many
people to thank, and everyone’s support has been appreciated. The
contributions of a few individuals particularly stand out. I would like to
express my great appreciation to Dr. Arnold Tamayo and Dr. Peter Djurovich
for sharing ideas and being very helpful with my research projects; Chao Wu,
Dr. Simona Garon, and Dr. Xiaofan Ren for training in device fabrication;
Jaime Avila and Frank Niertit for their help in fixing my computers as well as
recovering my hard drives; Dr. James Ly, Yun Tao, Wei Wei, Dr. CJ Jones,
Kenneth Hanson, Colin Hanson, Dr. Paulin Wahjudi, Siyi Wang, Rui Zhang,
Eugene Polikarpov, Slawa Diev, Dr. Biwu Ma, Dr. Jian Li, Dr. Laurent Griffe,

iv
Dr. Jasim Uddin, Jin Ho Oh, Carsten Borek, Marco Curreli, Valentina
Krylova, Kristin Martinez, Dolores Perez, Cody Schlenker, Dr. Seogshin
Kang, Dr. Vadim Ziatdinov, and Alex Alexander for their assistance and
friendship; Dr. Muhammed Yousufuddin, Timothy Stewart, and Kristen
Aznavour for help with X-ray crystallography; Judy Hom, Michele Dea, and
Heather Connor for tactical support; and special thanks to James Merritt and
Phil J. Sliwoski whose skillful hands created numerous pieces of special
glassware for some experiments.
I would also like to mention our collaborators who I have had a chance
to work with. Special thanks to Dr. Russell J. Holmes, Yiru Sun and
Professor Stephen R. Forrest from the Department of Electrical Engineering
at Princeton University, (and now at the University of Michigan).
I would like to thank my parents for raising me up to be disciplined and
passionate about learning. They have loved me strongly and taken such
good care of me—no amount of written thanks could even begin to express
my appreciation for my mom and dad. Along with my parents, I would also
like to thank my siblings for their support and love. I would never have come
to the United States to study without the help from my brothers, Talex and
Daan, and my sister, Jenny. Without their support, I would not be who I am or
where I am today. Rain or shine, they have always looked out for me, and
they are always available to help me tackle the difficulties I face and
celebrate the triumphs I experience.

v
Finally, I would like to thank my best friend, Erica Zuber-Hardbarger
and the Garvey Family for always being there when I have needed help. Last
but not least, I would like to thank Mark Garvey for bringing love and laughter
into my life and for being a thoughtful listener as I discussed my plans and
vented my frustrations.

"If A equals success, then the formula is A equals X plus Y plus Z. X is work.
Y is play. Z is keeping your mouth shut." Albert Einstein

vi
Table of Contents

Dedication ...................................................................................................... ii

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

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

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

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

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

Chapter 1. Phosphorescent Cyclometalated Iridium (III) Complexes:
Their Photophysics and Applications in Organic Light Emitting
Devices (OLEDs) ........................................................................................... 1
1.1. Photophysics of Cyclometalated Ir(III) Complexes .................................. 1
1.2. Applications of Cyclometalated Ir(III) Complexes .................................... 4
Chapter 1 References .................................................................................. 19

Chapter 2. Synthesis and Photophysical Characterization of
High Energy Phosphorescent Iridium (III) Complexes with
Cyclometalated Pyrazolyl or N-Heterocyclic Carbene (NHC) Ligands ......... 22
2.1. Introduction ........................................................................................... 22
2.2. Experimental ......................................................................................... 27
2.3. Results and Discussion ......................................................................... 47
2.3.1. Cyclometalated ppz-based ligands .................................................. 47
2.3.1.1 Synthesis .................................................................................... 50
2.3.1.2. X-ray Crystallography ................................................................ 50
2.3.1.3. Electrochemical Properties ........................................................ 51
2.3.1.4. Photophysical Properties ........................................................... 52
2.3.1.5. OLED Performance .................................................................... 56
2.3.2. Cyclometalated carbene ligands ...................................................... 58
2.3.2.1. Synthesis ................................................................................... 59
2.3.2.2. X-ray Crystallography ................................................................ 60
2.3.2.3. Electrochemical Properties ........................................................ 63
2.3.2.4. Photophysical Properties ........................................................... 65
2.3.2.5. OLED Performance .................................................................... 70
2.4. Conclusion ............................................................................................ 71
Chapter 2 References .................................................................................. 74

vii
Chapter 3. Heteroleptic Iridium (III) Complexes with Two
Chromophoric Cyclometalated Ligands and One High Energy
Ancillary Ligand: Synthesis, Characterization and Their Applications
in OLEDs ...................................................................................................... 77
3.1. Introduction ........................................................................................... 77
3.2. Experimental ......................................................................................... 82
3.3. Results and Discussions ....................................................................... 91
3.3.1. Synthesis ......................................................................................... 91
3.3.2. Photophysical Properties ................................................................. 93
3.3.3. Electrochemical Properties ............................................................ 100
3.3.4. OLED Studies ................................................................................ 102
3.4. Conclusion .......................................................................................... 110
Chapter 3 References ................................................................................ 113

Chapter 4. Broad Band Phosphorescent Tris-cyclometalated
Iridium (III) Benzoquinoline Complex: Synthesis, Characterization
and Their Applications in White OLEDs ..................................................... 114
4.1. Introduction ......................................................................................... 114
4.2. Experimental ....................................................................................... 115
4.3. Results and Discussion ....................................................................... 122
4.3.1. Synthesis of Ir(bzq)
3
complex ........................................................ 122
4.3.2. Photophysical Properties ............................................................... 124
4.3.2.1. Emission Spectra ..................................................................... 124
4.3.2.2. Absorption Spectra .................................................................. 125
4.3.3. Electrochemical Properties ............................................................ 126
4.3.4. X-ray Crystallography .................................................................... 127
4.3.5. OLED Studies ................................................................................ 129
4.4. Conclusion .......................................................................................... 138
Chapter 4 References ................................................................................ 139

Chapter 5. Temperature Dependent Study of Radiative and
Nonradiative States in Neutral Phosphorescent Cyclometalated
Iridium (III) Complexes ............................................................................... 140
5.1. Introduction ......................................................................................... 140
5.2. Experimental ....................................................................................... 146
5.3. Results and Discussion ....................................................................... 148
5.3.1. Photophysical Properties ............................................................... 148
5.3.1.1. Emission Properties ................................................................. 148
5.3.1.2. Absolute Quantum Yields ......................................................... 151
5.3.1.3. Lifetimes Measurements .......................................................... 152
5.3.2. Radiative State .............................................................................. 156
5.3.2.1. Temperature Dependence: Zero Field Splitting ....................... 156
5.3.3. Nonradiative State ......................................................................... 157
5.3.3.1. Temperature Independence: Energy Gap Law ........................ 157
5.3.3.2. Temperature Dependence: Ligand Field State ........................ 158

viii
5.3.4. Kinetic Parameters for the Luminescent Excited State Decay ....... 159
5.4. Conclusion .......................................................................................... 168
Chapter 5 References ................................................................................ 171

Bibliography ............................................................................................... 174

ix
List of Tables

Table 2.1: Crystallographic Data for fac-Ir(flim)
3
........................................... 44

Table 2.2: Selected Bond Distances ( Ǻ) and Angles (°) for fac- and
mer-Ir(ppz)
3
,
16
fac-Ir(flz)
3
, and fac- and mer-Ir(pmb)
3
24
................................ 73

Table 2.3: Photophysical Properties of Ir(III) Complexes (2-MeTHF) ........... 73

Table 3.1: Electrochemical Properties and Quantum Yields of flz-based
Ir(III) Complexes ......................................................................................... 111

Table 4.1: Selected Bond Distances and Bond Angles for mer-Ir(bzq)
3
..... 128

Table 4.2: Crystallographic Data for mer-Ir(bzq)
3
....................................... 128

Table 4.3: Crystallographic Data for fac-Ir(bzq)
3
........................................ 129

Table 5.1: Photophysical Properties of Ir(III) Complexes in 2-MeTHF........ 151

Table 5.2: Kinetic Parameters for the Luminescent Excited State Decay
in 2-MeTHF solution. .................................................................................. 160

Table 5.3: Crystallographic Data for fac-Ir(F
2
ppz)
3
, 4 ................................. 170

x
List of Figures

Figure 1.1: 40 inch Full Color OLED Display by Samsung at CES 2007 ........ 5

Figure 1.2: Typical OLED Structure ............................................................... 6

Figure 1.3: (a) Double Layer OLED; (b) Doped-double Layer OLED ............. 8

Figure 1.4: Exciton Formation by Hole-Electron Recombination .................... 9

Figure 1.5: Green to Red Emission Ir Phosphors ......................................... 11

Figure 1.6: Structures of Typical HTL and ETL Materials Used in OLEDs ... 12

Figure 1.7: Blue/ Near-UV Iridium Complexes in Chapter 2 ......................... 13

Figure 1.8: Schematic Energy Level Diagram .............................................. 15

Figure 2.1: Emission Spectra of Ir Phosphors (RT, in 2-MeTHF Solution) ... 24

Figure 2.2: Various Ancillary Ligands for (C^N)
2
Ir(L^L') Complexes ............ 25

Figure 2.3: Blue Cyclometalated Phosphorescent Ir(III) Complexes ............ 26

Figure 2.4: Emission Spectra of Ir(ppz)
3
Derivatives (77K, 2-MeTHF) ......... 48

Figure 2.5: Energy Level Scheme of the Emission and NR State ................ 49

Figure 2.6: CV Traces of fac-Ir(flz)
3
, fac-Ir(ppz)
3
, and fac-Ir(ppy)
3
................ 52

Figure 2.7: Absorption Spectra of fac-Ir(flz)
3
, fac-Ir(ppz)
3
, and fac-Ir(ppy)
3
.. 53

Figure 2.8: Emission Spectra of fac-Ir(flz)
3
, fac-Ir(ppz)
3
, and fac-Ir(ppy)
3
..... 54

Figure 2.9: (a) fac-flzIr:UGH2 Device; (b) fac-flzIr:mCP Device ................... 57

Figure 2.10: ORTEP Plots of (a) fac-Ir(ppz)
3
, (b) mer-Ir(ppz)
3
,
(c) fac-Ir(pmb)
3
, (d) mer-Ir(pmb)
3
, (e) fac-flzIr, (f) fac-flimIr; the
hydrogen atoms have been omitted for clarity .............................................. 62

Figure 2.11: CV Traces of fac-Ir(pmi)
3
and mer-Ir(pmi)
3
in DMF .................. 63

Figure 2.12: CV Traces of fac-Ir(pmb)
3
and mer-Ir(pmb)
3
in DMF ................ 64

Figure 2.13: CV Traces of fac-flzIr and fac-flimIr in DMF ............................. 64

xi
Figure 2.14: 77K Emission Spectra of fac-Ir(pmi)
3
and mer-Ir(pmi)
3
............ 67

Figure 2.15: Absorption and Emission Spectra of Ir(pmi)
3
and Ir(pmb)
3
....... 67

Figure 2.16: Emission Spectra of fac-flzIr vs. fac-flimIr ................................ 69

Figure 2.17: Absorption Spectra of fac-flzIr vs. fac-flimIr .............................. 70

Figure 2.18: flimIr-doped and flzIr-doped mCP Devices ............................... 71

Figure 3.1: Heteroleptic Iridium (III) Complexes with pmi as High
Energy Ancillary Ligand ................................................................................ 79

Figure 3.2: Structures of Chromophoric Cyclometalating Ligands (C^N)
Used in the First Part of Chapter 3 ............................................................... 79

Figure 3.3: More Reducible Heteroleptics Iridium (III) Complexes ............... 81

Figure 3.4: Structures of More Reducible Heteroleptic Iridium (III)
Complexes ................................................................................................... 82

Figure 3.5:
1
H NMR Spectra of mer-(czpz)
2
Ir(pmi) ....................................... 84

Figure 3.6:
1
H NMR of flz
2
Ir(pypz) ................................................................ 86

Figure 3.7:
1
H NMR of flz
2
IrpypzCF
3
............................................................ 87

Figure 3.8:
1
H NMR of flz
2
Irpic1 ................................................................... 88

Figure 3.9: 77K and RT Emission Spectra of (a) fac- and mer-(ppz)
2
Irpmi;
(b) Photophysical Properties of fac- and mer-Ir(ppz)
3
.................................. 94

Figure 3.10: 77K Emission Spectra of Heteroleptic mer-Ir(III) Complexes ... 94

Figure 3.11: RT Emission Spectra of Heteroleptic mer-Ir(III) Complexes ..... 95

Figure 3.12: 77K Photophysics of Heteroleptic Carbazolyl Ir Complexes
in 2-MeTHF .................................................................................................. 96

Figure 3.13: Absorption and Emission Spectra of mer-(czpz)
2
Ir(pmi) ........... 97

Figure 3.14: CIE Coordinates of mer-(czpz)
2
Ir(pmi) ..................................... 97

Figure 3.15: The Photophysical Properties of flz
2
Ir(pypz) ............................ 98

Figure 3.16: The Photophysical Properties of flz
2
Ir(pypzCF
3
) ...................... 99

xii
Figure 3.17: The Emission Properties of flz
2
Ir(pypzCF
3
) vs. Ir(flz)
3
.............. 99

Figure 3.18: The Photophysical Properties of flz
2
Ir(pic1) ........................... 100

Figure 3.19: Electrochemical Properties of flz-based Ir(III) Complexes ...... 101

Figure 3.20: Electrochemical Properties of More Reducible flz-based
Ir(III) Complexes ......................................................................................... 102

Figure 3.21: The Performance of flz
2
Ir(pypz)-doped mCP Device .............. 103

Figure 3.22: The EL Spectra of flz
2
Ir(pypz)-doped mCP Device at
Various Voltages (7-12V) ........................................................................... 103

Figure 3.23: The Performance of flz
2
Ir(pypz)-doped mCP Device with
fac-Ir(ppz)
3
as an Electron Blocking Layer ................................................. 104

Figure 3.24: The EL Spectra of flz
2
Ir(pypz)-doped mCP Device with
fac-Ir(ppz)
3
as an Electron Blocking Layer at Various Voltages (7-12V) .... 105

Figure 3.25: The Performance of flz
2
Ir(pypz)-doped mCP Device with
mCP as an Electron Blocking Layer ........................................................... 105

Figure 3.26: The Performance of flz
2
Ir(pypzCF
3
)-doped mCP Device ....... 106

Figure 3.27: The Performance of flz
2
Ir(pypzCF
3
)-doped mCP Device
with fac-Ir(ppz)
3
as an Electron Blocking Layer .......................................... 107

Figure 3.28: The EL Spectra of flz
2
Ir(pypzCF
3
)-doped mCP Device with
fac-Ir(ppz)
3
as an Electron Blocking Layer ................................................. 107

Figure 3.29: The Performance of flz
2
Ir(pypzCF
3
)-doped CBP Device ........ 108

Figure 3.30: The Performance of flz
2
Ir(pypzCF
3
)-doped CBP Device
with mCP as an Electron Blocking Layer .................................................... 109

Figure 3.31: The Performance of flz
2
Ir(pypzCF
3
)-doped CBP Device
with Ir(ppz)
2
acac as an Electron Blocking Layer ........................................ 109

Figure 3.32: The EL Spectra of (flz)
2
Ir(pypzCF
3
)-doped CBP Device
with Ir(ppz)
2
acac as an Electron Blocking Layer ........................................ 110

Figure 3.33: The Low Ф
RT
Hypothesis for More Reducible flz-based
Ir(III) Complexes ......................................................................................... 112

Figure 4.1: Chemical Structure of Ir(bzq)
3
; mer- and fac- isomers ............. 115

xiii
Figure 4.2:
1
H NMR of (a) (bzq)
2
Ir(μ-Cl)Ir(bzq)
2
in CDCl
3
;
(b) mer-Ir(bzq)
3
in CD
2
Cl
2
........................................................................... 119

Figure 4.3: Excitation and Emission Spectra of fac-Ir(bzq)
3
and
mer-Ir(bzq)
3
, in dilute 2-MeTHF solution (77K and RT) .............................. 125

Figure 4.4: Absorption Spectra of fac-Ir(bzq)
3
and mer-Ir(bzq)
3
................. 125

Figure 4.5: CV and DPV Trace of mer-Ir(bzq)
3
in DMF .............................. 126

Figure 4.6: ORTEP Plot of mer-Ir(bzq)
3
; The hydrogen atoms have
been omitted for clarity ............................................................................... 127

Figure 4.7: The Monochrome mer-Ir(bzq)
3
Device Performances in CBP .. 130

Figure 4.8: flzIr-mer-Ir(bzq)
3
-doped Devices Performance in Two
Different Hosts, mCP and CBP .................................................................. 131

Figure 4.9: Devices with mer-Ir(bzq)
3
Sandwiched Between flzIr ............... 132

Figure 4.10: mer-Ir(bzq)
3
-flzIr Doped Devices Performance in Two
Different Hosts, CBP and mCP .................................................................. 133

Figure 4.11: DTIC: mer-Ir(bzq)
3
Doped Devices Performance Using
the Same Hosts, CBP ................................................................................ 134

Figure 4.12: Devices with mer-Ir(bzq)
3
Sandwiched Between DTIC .......... 135

Figure 4.13: Monochrome Device for flimIr vs. flzIr in mCP ....................... 136

Figure 4.14: White OLEDs from fac-flimIr : mer-Ir(bzq)
3
in different
hosts, mCP and CBP along with their CIE coordinates .............................. 137

Figure 5.1: Structures of Compounds 1-10 ................................................ 145

Figure 5.2: 77K Excitation and Emission Spectra of 1-8 (in 2-MeTHF) ...... 149

Figure 5.3: 77K and RT Emission Spectra of 5 and 7 in 2-MeTHF ............ 150

Figure 5.4: Emission Intensity Measurements of fac-Ir(ppy)
3
, 1 ................. 152

Figure 5.5: Temperature Dependent Luminescent Lifetimes of flzIr, 9 ....... 153

Figure 5.6: Schematic Energy Diagram with Different Decay Rates .......... 155

xiv
Figure 5.7: Temperature Dependent Luminescent Lifetimes of
fac-Ir(ppy)
3
, 1 (Inset: Arrhenius Plot) .......................................................... 157

Figure 5.8: Temperature Dependent Luminescent Lifetimes of
fac-Ir(ppz)
3
, 3 and fac-Ir(F
2
ppz)
3
, 4 (inset: Arrhenius Plot) ......................... 163

Figure 5.9: Ligand Field State of fac-Ir(ppz)
3
, 3 .......................................... 164

Figure 5.10: Temperature Dependent Lifetimes of fac-Ir(F
2
ppy)
3
, 2 ........... 164

Figure 5.11: Temperature Dependent Luminescent Lifetimes of
(A) fac-(ppz)
2
Ir(ppy), 5 and fac-(ppz)
2
Ir(F
2
ppy), 6;
(B) fac-(F
2
ppz)
2
Ir(ppy), 7 and fac-(F
2
ppz)
2
Ir(F
2
ppy), 8 ............................... 165

Figure 5.12: Temperature Dependent Luminescent Lifetimes of
fac-Ir(pmb)
3
, 10 .......................................................................................... 166

Figure 5.13: Temperature Dependent Lifetimes of fac-Ir(ppz)
3
, 3,
in Various Matrices: Polystyrene, 2-MeTHF, and Poly-THF ....................... 167

Figure 5.14: Temperature Dependent Lifetimes of fac-Ir(pmb)
3
, 10, in
dilute 2-MeTHF solution vs. doped thin film in polystyrene matrix .............. 167

Figure 5.15: Temperature Dependent Kinetic Parameters for 2-8, 10 ........ 168

xv
List of Schemes

Scheme 2.1: Synthesis of ppz Type Ligands ............................................... 28

Scheme 2.2: Synthesis of flz Ligand ............................................................ 28

Scheme 2.3: Synthesis of Carbene Type Ligands ....................................... 35

Scheme 2.4: The First Ir-(C^C:)
3
Reported by Lappert ................................ 59

Scheme 2.5: (a) The Synthesis of Ir Carbene Dimers; (b) Complexes ......... 59

Scheme 3.1: Synthesis of Heteroleptic mer-Ir(III) Complexes ...................... 92

Scheme 3.2: Synthesis of More Reducible flz-based Ir(III) Complexes ........ 93

Scheme 4.1: Synthesis of mer-Ir(bzq)
3
....................................................... 123

Scheme 4.2: Synthesis of fac-Ir(bzq)
3
........................................................ 123

xvi
Abstract

Organic light emitting devices (OLEDs) are a new type of display
technology based on organic thin films. The materials that comprise these
films must be able to meet certain criteria in order to be considered for these
devices. The work presented here describes the development of novel
phosphorescent materials along with their photophysical characterization and
applications in OLEDs. Chapter 1 illustrates how these devices work, the
materials used in these devices, and how the properties of these materials
affect device performance. Chapter 2 describes the synthesis and
characterization of high energy phosphorescent materials from Ir(III)
complexes with cyclometalated pyrazolyl-based and N-heterocyclic carbene
(NHC)-based ligands. Chapter 3 portrays the synthesis and characterization
of heteroleptic Ir(III) complexes consisting of two chromophoric
cyclometalating (C^N) ligands and a single high energy ancillary ligand (L^X).
The incorporation of high energy ancillary ligands such as pmi on bis-
cyclometalated Ir(ppz)
2
does not lead to emission at room temperature.
However, the replacement of the ppz chromophoric ligands with carbazolyl,
diphenylamino, or fluorenylpyrazolyl-based chromophoric ligands leads to
emission at room temperature. In Chapter 3, more reducible flz-based Ir(III)
complexes have also been synthesized by incorporation of a high triplet
energy, more reducible ancillary ligand. Their electrochemical, spectroscopic,
and electroluminescent properties are discussed. Chapter 4 discusses the

xvii
synthesis and photophysics of triscyclometalated Ir(III) benzoquinoline
complexes, Ir(bzq)
3
. White phosphorescent OLEDs with mer-Ir(bzq)
3
as the
broad band emitter have been fabricated with a maximum external quantum
efficiency of ~12%. In Chapter 5, we utilize extensive temperature dependent
lifetime studies to estimate the zero-field splitting (ZSF) and ligand-field (LF)
state energies for blue and near-UV phosphorescent cyclometalated Ir(III)
complexes. This is the first time we can identify where the LF state is for blue
cyclometalated Ir(III) complexes. The thermal population of the LF state is
most likely one of the deactivation processes that blue cyclometalated Ir(III)
complexes exhibit. From the temperature dependent study, we learn that the
activation energies (E
a
) needed to thermally populate LF state and the
nonradiative decay rate constant (k
nr
(T)) are important factors that affect the
quantum efficiencies of high energy phosphorescent cyclometalated Ir(III)
complexes.

1
Chapter 1. Phosphorescent Cyclometalated Iridium (III)
Complexes: Their Photophysics and Applications in Organic
Light Emitting Devices (OLEDs).

1.1. Photophysics of Cyclometalated Ir(III) Complexes

The photophysical characterization of octahedral 4d
6
and 5d
6
metal
complexes have been studied extensively.
1
The majority of these studies
have been focused on the photophysical properties of metal-diimine
complexes of Ru(II) and Os(II) with diimine ligands such as bipyridine and
phenanthroline.
2
These metal-diimine complexes have been widely used in
photocatalysis and photoelectrochemistry.
3
These complexes are attractive
for photochemical applications due to their long-lived excited-states and high
luminescent efficiencies. These properties increase the likelihood of either an
energy or an electron-transfer process occurring prior to a radiative or
nonradiative relaxation. The photophysics of the related Rh(III) and Ir(III)
complexes have also been investigated.
4
Tris-chelate complexes of Rh and Ir
have been prepared with diimine ligands as well as cyclometalated ligands,
such as 2-phenylpyridinato-C
2
,N (ppy).
5-6
The cyclometalated ligands are
monoanionic, thus forming neutral metal tris-chelate complexes. Ir(III)
complexes with the monoanionic cyclometalating ligands are isoelectronic
with the cationic trisdiimine complexes of Ru(II) and Os(II).
Cyclometalated Ir(III) complexes have many attractive properties that
make them very useful for various applications. Those beneficial properties
consist of high luminescent efficiency, microsecond lifetimes, tunable ground

2
and excited states, chemical stability, reversible electrochemistry, and
thermal stability. Most Ir(III) complexes exhibit intense phosphorescent
emission at both low temperatures and room temperature, while their Rh(III)
analogues only show some measurable emission at low temperatures.
5-6
The
stronger spin-orbit coupling expected for Ir relative to Rh significantly mixes
the singlet and triplet states of Ir, largely removing the spin-forbidden nature
of the phosphorescent transitions, leading to efficient phosphorescence for
these Ir(III) complexes i.e. Ф of fac-Ir(ppy)
3
in fluid solution = 1.0.
7
However,
both tri-chelate complexes of Rh and Ir show excited state lifetimes in the
microsecond regime (μs), as expected for a high-spin excited state.
5-6

Cyclometalated Ir(III) complexes exhibit much longer lifetimes
4-5
than
fluorescent lifetimes, which are typically in the order of nanoseconds (ns).
8

However, the lifetimes of these Ir complexes are still significantly shorter than
the phosphorescent lifetimes based on organic luminophores.
8
The
phosphorescent lifetimes for organic luminophores range from milliseconds
to minutes (common for a spin-forbidden transition). The significant decrease
in the lifetime of the triplet excited state for the Ir complexes relative to the
triplet excited state of an organic molecule is a direct consequence of the
strong spin-orbit coupling of the heavy Ir(III) metal ion. The electronic
transitions responsible for luminescence in these cyclometalated Ir
complexes have been assigned to a mixture of MLCT and ligand-centered
(LC) transitions.
6a, 9-10

3
Since the optical properties and related uses of the cyclometalated Ir
complexes strongly depend on the characteristics of their ground and excited
states, it becomes desirable to understand the interactions between these
states and thus determine how to systematically alter the photophysical
properties by appropriate ligand or complex design. Emission energies of
luminescent cyclometalated Ir complexes are principally determined by the
triplet energy of the cyclometalating ligand (C^N). Two approaches for tuning
the triplet energy of the cyclometalating ligand include fluorination
11
of the
cyclometalated ligands or variation of the heterocyclic portion of the
cyclometalated ligands, i.e. changing from pyridyls to pyrazoles
11
to
imidazoles.
12

Additionally, due to their chemical and thermal stability,
cyclometalated Ir(III) complexes are effective starting materials to make other
active materials. Ease of synthesis and functionalization of cyclometalated
Ir(III) make them very attractive to researchers in various fields.

4
1.2. Applications of Cyclometalated Ir(III) Complexes

There are many reported applications of cyclometalated Ir(III)
complexes in the area of photonic applications. These compounds can be
employed as sensitizers for outer-sphere electron-transfer reactions,
13-14

photocatalysts for CO
2
reduction,
15
biological labeling reagents,
16

photoreductants,
17
and singlet oxygen sensitizers.
18
In particular, we are
mostly interested in employing these luminescent cyclometalated Ir(III) as
emissive dopants in multicolor electroluminescent displays based on organic
light emitting devices (OLEDs). Electroluminescent devices incorporating
these iridium-based phosphors are the most efficient devices reported to
date.
19

It is now accepted in the electroluminescent display industry that
phosphorescence-based OLEDs offer many advantages over existing display
technologies. The most common display technology used for portable
applications to flat panel display (FPD) TVs is liquid crystal displays (LCDs).
A non-organic LCD display does not emit light; a white fluorescent backlight
sitting behind the LCD panel is filtered by switchable polarizers in order to
generate the pixel colors and to create the image you see on screen.
Individual liquid crystals allow light to pass or block it. Since the polarizer
filter is employed in LCD, this leads to a loss in efficiency since most of the
light is absorbed by the color filters, and creates viewing angle problems due
to the polarized emission. On the other hand, OLED displays do not require a

5
backlight since the organic material self-generates light, so they require very
little external power. Since the red, green and blue pixels of OLEDs are
emissive, then OLEDs in general can be more efficient than LCDs.
Additionally, OLEDs do not suffer from viewing angle problems thus they
always display sharp quality images independent of viewing angles (Figure
1.1). In contrast to conventional inorganic LEDs, OLEDs can be made
flexible, transparent, and lightweight.

Figure 1.1. 40 inch Full Color OLED Display by Samsung at CES 2007.
20

OLEDs have attracted a great deal of attention due to their potential
use in lighting as well as future panel display applications. The basic
structure of an OLED consists of a stack of two or more thin organic layers
with a total thickness of about 1000 Ǻ sandwiched between a transparent

6
anode and a metallic cathode (Figure 1.2). The organic layers consist of a
hole transporting layer (HTL), an emissive layer containing a dopant and a
host material, and an electron transporting layer (ETL). When an external
driving voltage is applied, the introduced positive and negative charges are
injected into the organic materials. The positive (holes) and negative
(electrons) charges migrate through the device and recombine to form
excitons in the emissive layer. The device lights up (produces
electroluminescence) as excitons decay radiatively. The emission color
depends on the energy of the exciton. Particular structures of the organic
layers and the choice of anode and cathode should be considered to highly
maximize the recombination process in the emissive layer, thus maximizing
the light output from the OLED device.

Figure 1.2. Typical OLED Structure

The earliest OLEDs work was demonstrated in 1987 at Eastman
Kodak labs by Ching Wan Tang and Steven Van Slyke. They made the first
double heterostructure device in which its structure comprised of ITO/

+
(-)
(+)
glass substrate
transparent conductor as anode (ITO)
Organic layers
~ 1000 Å
metal cathode
+
(-)
(+)
glass substrate
transparent conductor as anode (ITO)
+
(-)
(+)
glass substrate
transparent conductor as anode (ITO)
Organic layers
~ 1000 Å
metal cathode

7
diamine HTL/ Alq
3
/ Mg:Ag.
21
A glass substrate was coated with a transparent
indium tin oxide (ITO) acting as the anode. A diamine was used as the hole
transporting material. Alq
3
(tris(8-hydroxyquinoline) aluminum (III)) served as
both an electron transporting layer (ETL) and an emissive layer. Electrons
were injected from a Mg:Ag alloy cathode with an additional layer of Ag to
protect the Mg from oxidation. In this double layer device, electrons and
holes combined at the diamine/Alq
3
interface (Figure 1.3 (a)). This double
layer device utilized HTL and ETL to confine excitons and prevent leakage.
The utilization of HTL and ETL could lead to efficient charge carrier
injections. Nevertheless, this double layer device gave a fluorescent
emission with poor external quantum efficiency (~1%).
21
The significant
problem with this double layer device could be that the excitons emitting from
a dense, pure matrix typically go through significant self-quenching that leads
to poor external quantum efficiency.
21

In 1989, Tang, Van Slyke, and Chen showed that it was possible to
add small quantities of a highly fluorescent dye (green Coumarin 540 or red
DCM fluorescent dyes) to a charge transporting material (Alq
3
) in the double
layer device to easily tune the OLED emission color. By introducing the
fluorescent dopant they were able to improve the device efficiency up to
2.5%.
22
Inside the emissive layer, energy will transfer readily from the host
(Alq
3
) to a dopant with a smaller optical gap resulting in efficient emission
from the dopant (Figure 1.3 (b)). The self-quenching of excitons is also
suppressed by lowering the concentration of excitons and the device

8
efficiency is improved. An additional benefit of doping is to control emission
colors of OLEDs by doping different emissive dyes.

Figure 1.3. (a) Double Layer OLED; (b) Doped-double Layer OLED

Excitons in an OLEDs are believed to be created in a ratio of about
3:1 (Figure 1.4), i.e., approximately 75% triplets (spin parallel) and 25%
singlets (spin antiparallel).
23
A fluorescence device only utilizes singlet
excitons while the energy of triplet excitons is generally lost to non-radiative
decay processes that heat up the device. This inefficient utilization of triplet
excitons limits the internal quantum efficiency of fluorescence-based devices
to only 25%. In contrary to fluorescence-based devices, phosphorescence-
based OLEDs utilizing highly luminescent cyclometalated Ir(III) complexes as
dopants can achieve 100% internal quantum efficiency. Such efficiencies can
be achieved because all the triplet and singlet excitons are harvested. A
carefully designed device utilizing the cyclometalated Ir complex such as fac-
Ir(ppy)
3
has been demonstrated to emit with nearly 100% internal efficiency.
Alq
3
HTL
2.6 eV
5.5 eV
2.7 eV
5.7 eV
(-)
(+)
Alq
3
HTL
2.6 eV
5.5 eV
2.7 eV
5.7 eV
(-)
(+)
Alq
3
HTL
2.6 eV
5.5 eV
2.7 eV
5.7 eV
(-)
(+)

9
OLEDs utilizing phosphorescent materials that emit from triplet excited states
are expected to result in higher internal quantum efficiency.

Figure 1.4. Exciton Formation by Hole-Electron Recombination

In the initial stage of OLED development, fluorescent materials were
typically used to produce fluorescence (emission from singlets), while most
researchers avoided the use of phosphorescence (emission from triplets).
The reason for this is a general assumption that phosphorescent materials
would not emit efficiently at room temperature, and that the very long lifetime
typically exhibited for phosphorescence would limit the utility of the devices.
Phosphorescence generally occurs in the order of μs. Phosphorescence is
referred to as a "forbidden" transition because the transition requires a
change in spin states. However, our research group has demonstrated that
phosphorescent emission could be achieved efficiently. In 1998, our research
group in collaborations with Professor Stephen Forrest’s research group at
Princeton University found that one way to bypass the efficiency and lifetime
problems associated with triplet emission was by utilizing heavy metal
+
hole electron
or
triplet (75%) singlet (25%)
excitons
+
hole electron
or
+
hole electron
or
triplet (75%) singlet (25%)
excitons excitons

10
complexes, especially those containing iridium and platinum. Heavy atoms
such as Ir and Pt can promote intersystem crossing by a mechanism known
as spin-orbit coupling. Strong spin-orbit-coupling mixes singlet and triplet
metal-to-ligand charge transfer (MLCT) states. Mixing of
1
MLCT and
3
MLCT
states with the
3
LC (triplet ligand-centered) state creates a hybrid
3
(LC-
MLCT). This mixing removes the spin-forbidden nature of the radiative
relaxation of the triplet state thus leading to high phosphorescence
efficiencies.
24
Our group has found that highly emissive Ir complexes can be formed
with two cyclometalated ligands (abbreviated as C^N) and a single
monoanionic, bidentate ancillary ligand (L^L). The emission colors from
those Ir complexes are strongly dependent on the choice of cyclometalating
ligand, ranging from green to red, with room temperature lifetimes on the
order of μs. OLEDs have been made with (C^N)
2
Ir(L^L) phosphor dopants,
giving efficient green, yellow or red emission (Figure 1.5).
25

11

Figure 1.5. Green to Red Emission Ir Phosphors

OLED displays can be fabricated on different types of substrates
ranging from rigid glass to flexible polymers are usually coated with a
transparent conductive anode material, indium tin oxide (ITO). Most organic
molecules have low charge transport mobilities (<10
-2
cm
2
/Vs).
26
Thus, the
films are required to be very thin (~1000 Å) in order to pass enough currents
at low operating voltages. Organic films comprised of small molecules are
usually grown by vapor deposition (sublimation) onto the substrate under
high vacuum conditions (< 10
-6
torr). On the other hand, high molecular
weight polymers that are not volatile enough for vapor deposition are typically
spin-coated or printed onto the substrate. A low work function metal (e.g. Ca,
Al, or Mg) is vapor deposited on top of the organics to serve as the cathode.
N
Ir
N
O C
C
O
N
Ir
N
Ir
N
Ir
SN
Ir
ON
Ir
NN
Ir
SN
Ir
N
Ir
S
ON
Ir
ON
Ir
SN
O
Ir
O
NMe
2
2
2
2
2 2
ppy tpy bzq
bo αbsn
2
bin
2
bt
2
thp
2
op
2
ppo
2
C6
N
Ir
2
S
N
Ir
2
btp
pq
SN
Ir
2
βbsn
R
Ir
2
pbz
N

12
To improve the device performance, multi-layered materials are used,
each of which serves different functions, i.e. hole carrier, emissive layer, or
electron carrier. The most commonly used hole-transporters consist of an
organic triarylamine-based compound. A series of metal quinolates are
utilized widely as electron transporting materials. The chemical structure of
several typical HTL and ETL molecules, i.e. diamine, N,N’-bis-(1-naphthyl)-
N,N’-diphenylbenzidine ( α-NPD), aluminum tris(8-hydroqunilonate)(Alq
3
), are
shown in Figure 1.6.

Figure 1.6. Structures of Typical HTL and ETL Materials Used in OLEDs

In general, multi-color display applications require efficient and stable
blue, green and red OLEDs. Iridium cyclometalates, as mentioned earlier,
exhibit favorable photophysical properties for OLEDs including short
phosphorescent lifetimes, high quantum efficiencies, and good stability. The
emission color can be readily tuned from blue to red by judicious modification
of the cyclometalating ligands and/or ancillary ligands. Work on
phosphorescence-based organic light emitting devices (PHOLEDs) has
N N
NPD
Alq
3
3
N
O
Al
Alq
3
3
N
O
Al
N N
Diamine

13
employed the green emitting tris-cyclometalated complex, fac-Ir(ppy)
3
. Much
effort has been devoted to synthesizing analogous triscyclometalated
complexes that emit in the blue and red part of the visible spectrum. The
work presented here mostly describes the development of novel blue
phosphorescent materials with interesting photophysical properties as well as
their application in organic light emitting devices (OLEDs). Note that red and
green iridium complexes have been well developed to be used in OLEDs
while blue iridium complexes are still less common.
Chapter 2 focuses on the synthesis and the photophysics of new blue
and near-UV phosphorescent materials from iridium complexes with
cyclometalated pyrazolyl-based and N-heterocyclic carbene (NHC)-based
ligands. (Figure 1.7).

Figure 1.7. Blue/ Near-UV Iridium Complexes in Chapter 2

There are many different approaches in achieving high energy (blue)
phosphorescent materials. Two approaches have been performed by former
group members. One approach is fluorination of fac-Ir(ppy)
3
that emits at 510
nm at room temperature. The fluorination of fac-Ir(ppy)
3
results in the
N
N
Ir
3
N
N
3
CH
3
Ir
N
N
3
Ir
N
N
Ir
3
fac-Ir(pmi)
3
fac-Ir(pmb)
3 fac-flzIr fac-flimIr
N
N
Ir
3
fac-Ir(ppz)
3

14
synthesis of fac-Ir-(4,6 difluoroppy)
3
; the fluorination caused 50 nm blue-shift
emission from that of fac-Ir(ppy)
3
at room temperature. The second approach
is exchanging the heterocyclic portion of the cyclometalating ligand with the
one that has a higher triplet energy, i.e. replacing pyridyl groups with
pyrazolyl groups.
11
fac- Ir(ppz)
3
[ppz= 1-phenylpyrazole] displays intense
blue phosphorescent emission (410 nm at 77K)
11
but it gives very weak
emission at room temperature. ( Ф < 0.01).
7
In chapter 2, we began to
investigate the effects of phenyl substitution on fac-Ir(ppz)
3
and also to see if
the emission efficiency can be improved by phenyl substitutions. The phenyl
substitutions can cause minor-shifts and red-shifts in the emission but the
emission is still not efficient in fluid solution at room temperature. There are
two dominant possible deactivations that may occur in fac-Ir(ppz)
3

derivatives. While Ir complexes are in their triplet excited states form, they
may thermally populate a higher state known as the nonradiative (NR) state.
From this NR state, they go through a non-radiative decay pathway and
return to their ground state at a rate constant equal to k
nr
(T) (refer to Figure
1.8).

15

Figure 1.8. Schematic Energy Level Diagram

Tris biphenyl-pyrazolyl Ir complex emits intensely at 77K but it is only
weakly emissive at room temperature. We then have assumptions that the
rotation of the phenyl group may also play some roles in the resulting weak
emission at room temperature. The excited state properties of
cyclometalated iridium complexes, as mentioned earlier, are mainly
determined by the C^N ligand and thus their photophysical properties can be
tuned by using different C^N ligands. It has been shown in Chapter 2 that
increasing the π-conjugation of the cyclometalating ligand lowers its triplet
energy thereby decreasing the triplet energy of the resulting iridium
complex.
12
We proposed locking these biphenyl groups by having fluorenyl
groups as the part of the ligands in this tris-cyclometalated Ir(III) complex.
fac-flzIr was synthesized and characterized. fac-flzIr emits at room
temperature with a high quantum yield in fluid solution ( Ф
298K
= 0.81). fac-flzIr
S
1
T
1
ISC
hν
abs
k
r
(T)
NR
E
a
k
nr
k
nr
(T)
S
1
T
1
ISC
hν
abs
k
r
(T)
NR
E
a
k
nr
k
nr
(T)
(Nonradiative)

16
is a little too green (480 nm at 298K) for a blue device but it is so far the only
fac-tris-homoleptic (ppz derivatives) iridium complex that emits efficiently at
room temperature. In chapter 2, we also proposed on having carbene
systems as photoactive ligands instead of pyrazoles. Tris-carbene Ir
complexes have stronger ligand field state compared to tris-pyrazolyl Ir
complexes. As a result, we can expect the nonradiative state energy for tris-Ir
carbene complexes is somewhat higher than that of tris-Ir-pyrazolyl
complexes thus the possibility of d-d transition deactivation can decrease in
the case of tris-Ir-carbene complexes. In summary, in chapter 2, it is
demonstrated that there are two approaches to achieve efficient blue to near-
UV emission from triscyclometalated iridium (III) materials related to fac-
lr(ppz)
3
. The first involves replacement of the phenyl group of the ppz ligand
with a 9,9-dimethyl-2-fluorenyl group, i.e., fac-tris(1-[(9,9-dimethyl-2-
fluorenyl)]pyrazolyl-N,C
2
')iridium(III), abbreviated as flzIr. The second
approach utilizes NHC ligands to form triscyclometalated Ir complexes.
Complexes with two different NHC ligands, i.e., iridium tris(1-phenyl-3-
methylimidazolin-2-ylidene-C,C
2
'), abbreviated as Ir-(pmi)
3
, and iridium tris(1-
phenyl-3-methylbenzimidazolin-2-ylidene-C,C
2
'), abbreviated as Ir(pmb)
3
.
Both fac-Ir(pmi)
3
and fac-Ir(pmb)
3
complexes phosphoresce in the near-UV
region (E
0-0
= 380 nm) at room temperature. In addition, the carbene analog
of flzIr (fac-flimIr) has also been synthesized and characterized. fac-flimIr
displays efficient room temperature emission with a λ
max
of 466 nm. OLED
devices have been fabricated with fac-flzIr or fac-flimIr as the emissive

17
dopant. Both emit blue light from the Ir based dopant. OLED performances of
these devices are also shown in chapter 2.
All synthesized Ir complexes in chapter 2 are easily oxidized but
difficult to reduce. In chapter 3, however, a series of more reducible flz-based
iridium complexes have been synthesized by the incorporation of high triplet
energy, more reducible ancillary ligand i.e. pyridyl-pyrazolate, pyridyl
pyrazolate trifluoromethyl, and picolinic acid and their electrochemical and
photophysical properties examined. The electrochemical properties of the
iridium complexes could be easily tuned by various high triplet energy, more
reducible ancillary ligand. The HOMO and LUMO energies in the complexes
can be independently altered by simple ligand design. (flz)
2
Ir(pypz) could be
easier to reduce with a difference of 0.5V from reduction of flzIr, while make
the HOMO level 0.27V deeper. The electrochemistry, UV-Vis absorption and
photoluminescence of the flz-based more reducible heteroleptic iridium
complexes were investigated. OLED devices have also been fabricated with
the synthesized flz-based more reducible heteroleptic iridium complexes as
the emissive dopants.
In chapter 4, triscyclometalated iridium (III) complexes with broad
band luminescence, mer-Ir(bzq)
3
, have been synthesized and characterized.
Their photophysical properties have been thoroughly investigated. This
chapter also show how useful the broad band luminescent materials for white
OLEDs applications. White phosphorescent OLEDs have been fabricated
with mer-Ir(bzq)
3
as the broad band emitter and fac-flzIr or fac-flimIr as blue-

18
green phosphorescent emitter. These devices emit white light with maximum
quantum efficiency of ~12%.
In Chapter 5 of this thesis, temperature dependence of various blue
phosphorescent cyclometalated Ir(III) complexes has been investigated in
solution and in some cases, also in rigid matrices. These temperature
dependent studies offer very useful information regarding the deactivation
pathways of these complexes. There is a good correlation between Ф and E
a
for all these cyclometalated Ir complexes examined in chapter 5. In general,
the larger the E
a
value is (the more energy barrier it requires to go NR state
from triplet states), the higher the efficiency ( Ф) is. The kinetic parameters of
the nonradiative (NR) deactivating state extracted from the temperature
dependent study is very useful to evaluate various blue phosphors for
OLEDs or other purposes. It turns out that almost all NR states of blue
phosphorescent cyclometalated iridium complexes can be thermally
populated at around 3-4 eV; these voltages are within the turn-on voltage
range where OLEDs devices usually operate. This would set a limit in finding
good blue phosphorescent iridium complexes to be employed as dopants in
OLEDs.

19
Chapter 1 References

1. (a) Balzani, V.; Scandola, F. Supramolecular Photochemistry; Ellis
Horwood: Chichester, U.K., 1991. (b) Balzani, V.; Credi, A.; Scandola, F.
Transition Metals in Supramolecular Chemistry; Fabbrizzi, L., Poggi, A., Eds.;
Kluwer: Dordrecht, The Netherlands, 1994; p1. (c) Lehn, J-M.
Supramolecular Chemistry-Concepts and Properties; VCH: Weinheim,
Germany, 1995. (d) Bignozzi, C.A.; Schoonover, J.R.; Scandola, F. Prog.
Inorg. Chem. 1997, 44, 1.

2. (a) Anderson, P.A.; Anderson, R.F.; Furue, M.; Junk, P.C.; Keene, F.R.;
Patterson, B.T.; Yeomans, B.D. Inorg. Chem. 2000, 39, 2721-2728. (b) Li, C.;
Hoffman, M.Z. Inorg. Chem. 1998, 37, 830-832. (c) Berg-Brennan, C.;
Subramanian, P.; Absi, M.; Stern, C.; Hupp, J. T. Inorg. Chem. 1996, 35,
3719-3722. (d) Kawanishi, Y.; Kitamura, N.; Tazuke, S. Inorg. Chem. 1989,
28, 2968-2975.

3. (a) Kalyanasundaran, K. Coord. Chem. Rev. 1982, 46, 159. (b) Chin, K.-
F.; Cheung, K.-K.; Yip, H.-K.; Mak, T.C.W.; Che, C.M. J.Chem.Soc., Dalton
Trans. 1995, 4, 657-665. (c) Sonoyama, N.; Karasawa, O.; Kaizu, Y. J.
Chem.Soc., Faraday Trans. 1995, 91, 437. (d) Tan-Sien-Hee, L.;
Mesmaeker, A.K.-D. J.Chem.Soc., Dalton Trans. 1994, 24, 3651-3658. (e)
Kalyanasundaram, K.; Gratzel, M. Coord. Chem. Rev. 1998, 177, 347-414.

4. (a) Balzani, V.; Juris, A.; Venturi, M.; Campagna, S.; Serroni, S. Chem.
Rev. 1996, 96, 759. (b) Shaw, J.R.; Sadler, G.S.; Wacholtz, W.F.; Ryu, C.K.;
Schmehl, R.H. New. J. Chem. 1996, 20, 749.

5. (a) Sprouse, S.; King, K.A.; Spellane, P.J.; Watts, R.J. J. Am.Chem. Soc.
1984, 106, 6647. (b) King, K.A.; Spellane, P.J.; Watts, R.J. J.Am.Chem.Soc.
1985, 107, 1432. (c) Ohsawa, Y.; Sprouse, S.; King, K.A.; DeArmond, M.K.;
Hanck, K.W.; Watts, R.J. J.Phys. Chem. 1987, 91, 1047. (d) Ichimura, K.;
Kobayashi, T.; King, K.A.; Watts, R.J. J. Phys. Chem. 1987, 91, 6104. (e)
Garces, F.O.; King, K.A.; Watts, R.J. Inorg. Chem. 1988, 27, 3464. (f)
Garces, F.O.; Watts, R.J. Inorg. Chem. 1990, 29, 582. (g) Wilde, A.P.; King,
K.A.; Watts, R.J. J. Phys.Chem. 1991, 95, 629. (h) Dedeian, K.; Djurovich,
P.I.; Garces, F.O.; Carlson, G.; Watts, R.J. Inorg. Chem. 1991, 30, 1685-
1687.
6. (a) Colombo, M.G.; Hauser, A; Güdel, H.U. Inorg. Chem. 1993, 32, 3088.
(b) Colombo, M.G.; Brunold, T.C.; Riedener, T.; Güdel, H.U. Inorg. Chem.
1994, 33, 545.

20
7. Sajoto, T.; Djurovich, P.I.; Tamayo, A.; Thompson, M.E.; Temperature
Dependence of Blue Phosphorescent Cyclometalated Iridium(III) Complexes;
manuscript in preparation, 2008.

8. Turro, N.J. Modern Molecular Photochemistry; The Benjamin/Cummings
Publishings Co., Inc.; Menlo Park, California, 1978. Murov, S.L.; Carmichael,
I.; Hug, G.L. Handbook of Photochemistry; Marcel Dekker: New York, 1993.

9. (a) Strouse, G.F.; Güdel, H.U.; Bertolasi, V.; Ferretti, V. Inorg. Chem.
1995, 34, 5578. (b) Lever, A.P.B. Inorganic Electronic Spectroscopy, 2
nd
Ed.:
Elsevier; New York, 1984, pp. 174-178.

10. (a) Wiedenhofer, H.; Schutzenmeier S.; Von Zelewsky, A.; Yersin, H. J.
Phys. Chem. 1995, 99, 13385. (b) Schmidt, J.; Wiedenhofer, H.; Von
Zelewsky, A.; Yersin, H. J. Phys. Chem. 1995, 99, 226.

11. Tamayo, Arnold B.; Alleyne, Bert D.; Djurovich, Peter I.; Lamansky,
Sergey; Tsyba, Irina; Ho, Nam N.; Bau, Robert; Thompson, Mark E J. Am.
Chem. Soc. 2003, 125(24), 7377-7387.

12. Sajoto, T.; Djurovich, P.I.; Tamayo, A.; Yousufudddin, M.; Bau, R.;
Thompson, M.E. Inorg. Chem. 2005, 44, 7992-8003.

13. (a) Sutin, N. Acc. Chem Res. 1968, 1, 225. (b) Meyer, T.J. Acc. Chem.
Res. 1978, 11, 94.

14. Schmid, B.; Garces, F.O.; Watts, R.J. Inorg. Chem. 1994, 32, 9.

15. (a) Belmore, K.A.; Vanderpool, R.A.; Tsai, J.C.; Khan, M.A.; Nicholas,
K.M. J. Am.Chem.Soc. 1988, 110, 2004. (b) Silavwe, N.D.; Goldman, A.S.;
Ritter, R.; Tyler, D.R. Inorg. Chem. 1989, 28, 1231.

16. Lo, K. K. –W.; Chung, C, -K.; Lee, T. K. –M.; Lui, L. –K.; Tsang, K. H. –
K.; Zhu, N. Inorg. Chem. 2003, 42, 6886.

17. King, K.A.; Spellane, P.J.; Watts, R.J. J. Am. Chem. Soc. 1985, 107,
1431.

18. (a) Demas, J. N.; Harris, E.W.; McBride, R.P. J. Am. Chem. Soc. 1977,
99, 3547. (b) Demas, J. N.; Harris, E.W.; Flynn, C.M.; Diemente, J.D. J. Am.
Chem. Soc. 1975, 97, 3838. (c) Gao, R.; Ho, D.G.; Hernandez, B.; Selke, M.;
Murphy, D.; Djurovich, P.I.; Thompson, M.E. J. Am. Chem. Soc. 2002, 124,
14828.

21
19. (a) Baldo, M.A.; O’Brien, D.F.; You, Y.; Shoustikov, A.; Sibley, S.;
Thompson, M.E.; Forrest, S.R. Nature, 1998, 395, 151. (b) Baldo, M.A.;
Lamansky, S.; Burrows, P.E.; Thompson, M.E.; Forrest, S.R. Appl. Phys.
Lett. 1999, 75, 4. (c) Thompson, M.E.; Burrows, P.E.; Forrest, S.R. Curr.
Opin. Solid State Mater.Sci. 1999, 4, 369. (d) Baldo, M.A.; Thompson, M.E.;
Forrest, S.R. Nature 2000, 403, 750. (e) Lamansky, S.; Djurovich, P.I. ;
Abdel-Razzaq, F.; Garon, S.; Murphy, D.L.; Thompson, M.E. J. Appl. Phys.
2002, 92, 1570. (f) Chen, F.C.; Yang, Y.; Thompson, M.E.; Kido, J. Appl.
Phys. Lett. 2002, 80, 2308. (g) Markham, J.P.J,; Lo, S.-C.; Magennis, S.W.;
Burn, P.L.; Samuel, I.D.W. Appl. Phys. Lett. 2002, 80, 2645. (h) Zhu, W.; Mo,
Y.; Yuan, M.; Yang, W.; Cao, Y. Appl. Phys. Lett. 2002, 80, 2045.

20. http://www.engadget.com/2005/05/20/samsungs-40-inch-oled-tv-pics/

21. Tang, C. W.; Van Slyke, S. A. Appl. Phys. Lett. 1987, 51, 913.

22. Tang, C. W.; Van Slyke, S. A.; Chen, C. H. Chen J. Appl. Phys. 1989, 65,
3610.

23. Baldo, M. A.; O'Brien, D. F.; Thompson, M. E.; Forrest, S. R. Physical
Review B, 1999, 60, 14422.

24. (a) Sprouse, S.; King, K.A.; Spellane, P.J.; Watts, R.J. J. Am. Chem. Soc.
1984, 106, 6647-6653. (b) Crosby, G. A. J. Chem. Phys. 1967, 64, 160.

25. Lamansky, S.; Djurovich, P.; Murphy, D.; Abdel-Razzaq, F.; Lee, H.-E.;
Adachi, C.; Burrows, P. E.; Forrest, S. R.; Thompson, M. E. J. Am. Chem.
Soc. 2001, 123, 4304-4312.

26. (a) Tang, C. W. Inf. Disp. 1996, 10, 16. (b) Sibley, S.; Thompson, M. E.;
Burrows, P. E.; Forrest, S. R. In “Optoelectronic Properties of Inorganic
Complexes”, Roundhill, D. M., Fakler, J. Eds.; Plenum Press: New York. (c)
Burrows, P. E. Gu, G.; Bulovic, V.; Forrest, S. R.; Thompson, M. E. IEEE
Trans. Electron. Dev. 1997, 44, 1188. (d) Forrest, S. R.; Burrows, P. E.;
Thompson, M. E. In Organic Electroluminescent Materials and Devices;
Miyata, S., Nalwa, H. S., Eds.; Grodon and Breach: Langhorne, PA, 1996. (e)
Rothberg, L. J.; Lovinger, A. J. J. Mater. Res. 1996, 11, 3174.

22
Chapter 2. Synthesis and Photophysical Characterization of
High Energy Phosphorescent Iridium (III) Complexes with
Cyclometalated Pyrazolyl or N-Heterocyclic Carbene (NHC)
Ligands.

2.1. Introduction

Cyclometalated iridium (III) complexes have attracted a great deal of
attention due to their use in photonic applications. For example, these Ir
complexes can be employed as singlet oxygen sensitizers,
1
photoreductants,
2
sensitizers for outer-sphere electron transfer reactions,
3
photocatalysts for CO
2
reduction
4
as well as biological labeling reagents.
5

These Ir(III) complexes exhibit emission colors ranging from blue to red
depending on the triplet energy of the cyclometalating ligands (C^N). Ligand
and metal-based orbitals are both involved in the excited states of these
complexes. While the emission spectrum often resembles simple ligand
phosphorescence suggesting a ligand localized excited state, the radiative
lifetimes for the complexes are in the microsecond regime, clearly indicating
strong metal participation (and spin-orbit coupling). Thus, the excited state is
best treated as an admixture of triplet ligand centered (
3
LC, π-π*) and singlet
metal-to-ligand-charge-transfer (
1
MLCT) states. Different emission colors
from these cyclometalated Ir(III) complexes make them very useful in the
field of organic light-emitting devices (OLEDs), where they have been used
as phosphorescent dopants in the emissive layer.
6

23
Since the optical properties and related uses of cyclometalated Ir
complexes are strongly dependent on the characteristics of their ground and
lowest excited states, it becomes desirable to better understand the
interactions between these states and thus determine how to systematically
alter the photophysical properties by appropriate ligand or complex design.
Moreover, high energy emitting species are currently still in demand because
the availability of highly efficient blue phosphorescent OLEDs are still limited
and they have not been well understood. In this chapter, the synthesis and
photophysical characterization of new blue and near-UV phosphorescent
materials based on iridium complexes with cyclometalated pyrazolyl and
carbene based ligands are reported.
Color tuning in the Ir-based phosphors has been accomplished by
alteration of the cyclometalating ligand (C^N).
7
To understand the strategies
used to alter the color by C^N ligand modification, fac-Ir(ppy)
3
will be used as
a prototypical phosphors, and variation in the emission energies will be
discussed relative to changes in the C^N ligands. The cyclometalated ligand
can be conceptually broken into two fragments. The N of C^N, i.e. pyridine of
ppy, is formally neutral and the principal contributor to the lowest unoccupied
molecular orbital (LUMO). The C of C^N, i.e. the phenyl group of ppy, carries
a formal negative charge and the highest occupied molecular orbital (HOMO)
is principally composed of π orbitals of the C ring and the metal d orbitals.
ppy-based Ir complexes emit green light, λ
max
= 510 nm for both fac-Ir(ppy)
3

and (ppy)
2
Ir(acac) (acac = 2,4-pentadionato-O,O, Figure 2.1). If the phenyl

24
and pyridyl groups are bridged by a vinyl group, i.e. (bzq)
2
Ir(acac), the C^N
π-system is expanded and a bathochromic shift is observed. If the π-system
of the pyridyl fragment is enlarged to a 2-quinolyl moiety, (pq)
2
Ir(acac) in
Figure 2.1, the emission color red shifts further.
7
A similar red shift occurs
when the phenyl fragment of ppy is replaced with a benzothiophene
((btp)
2
Ir(acac), or naphthyl group. Interestingly, attempts to blue shift the
emission spectrum by replacing the phenyl with a vinyl group, thereby
decreasing the size of the C^N π-system, lead to a red shifted emission.
8

Therefore, alternative methods are required to increase the triplet energies of
Ir complexes with cyclometalated aromatic ligands.

450 500 550 600 650 700
0.0
0.2
0.4
0.6
0.8
1.0
1.2
1.4
N
Ir
2
(btp)
2
Ir(acac)
O
O
S
N
Ir
2
(pq)
2
Ir(acac)
O
O
N
Ir
2
(bzq)
2
Ir(acac)
O
O
N
Ir
2
(ppy)
2
Ir(acac)
O
O
N
Ir
3
Ir(ppy)
3
N
Ir
F
F 3
Ir(F
2
ppy)
3
Photoluminscent Int. (arb. units)
Wavelength (nm)

Figure 2.1. Emission Spectra of Ir Phosphors (RT, in 2-MeTHF Solution)

25
A number of approaches to increase the emission energy of ppy-
based Ir complexes have focused on methods to decrease the HOMO
energy while keeping the LUMO energy relatively unchanged. The addition of
electron withdrawing groups to the phenyl ring has been used as one way to
achieve this goal.
9
The most common electron withdrawing group used for
this purpose is fluoride, and a typical example of this blue shifting is seen for
fac-Ir(F
2
ppy)
3
in Figure 2.1. An alternate approach to lower the HOMO
energy involves the use of ancillary ligands to tune the HOMO energies. We
have recently reported a detailed study of ancillary ligand effects on the
emission energies of (C^N)
2
Ir(L^L
I
) complexes.
10
The emission energy of
ppy-based Ir complexes can be significantly increased by judicious choice of
the ancillary ligand (Figure 2.2.); however, shifting the green emission
ppy
2
Ir(L^L
I
) complexes to a saturated blue color leads to a significant
decrease in luminance efficiency.
10

Figure 2.2. Various Ancillary Ligands for (C^N)2Ir(L^L') Complexes.
10

26
In contrast to the approaches that rely on altering the HOMO energy
to blue shift the phosphorescence of cyclometalated Ir complexes, the
strategy described in this chapter involves replacing the heterocyclic
fragment of the C^N ligands in Ir(C^N)
3
complexes such that the LUMO is
destabilized relative to a cyclometalated ppy ligand. The replacement of the
pyridyl ring with either an N-pyrazolyl- or carbene-based group leads to a
significant increase in the LUMO energy,
9
consistent with the higher
reduction potentials for these moieties relative to pyridine. By careful
selection of aromatic and heterocyclic groups in tris-cyclometalated Ir
complexes, it has been shown in this chapter that it is possible to achieve
efficient blue and near-UV phosphorescence at room temperature with either
pyrazolyl- or carbene-based materials. The chemical structures of all Iridium
complexes synthesized and characterized in this chapter are shown in
Figure 2.3 below.

Figure 2.3. Blue Cyclometalated Phosphorescent Ir(III) Complexes

N
N
Ir
3
N
N
3
CH
3
Ir
N
N
3
Ir
N
N
Ir
3
fac-Ir(pmi)
3
fac-Ir(pmb)
3 fac-flzIr fac-flimIr
N
N
Ir
3
fac-Ir(ppz)
3

27
2.2. Experimental

Reagents and Synthesis of Ligands. Solvents and reagents were
purchased from Aldrich, Matrix Scientific, and EM Science, and were used
without further purification. N,N-dimethylformamide (EM Science, anhydrous
– 99.8%) and tetra-n-butylammonium hexafluorophosphate – (TBAH) (Fluka,
electrochemistry grade) were used for spectroscopic and electrochemical
measurements. IrCl
3
·nH
2
O was purchased from Next Chimica. 1-
phenylpyrazole and 1-phenylimidazole were purchased from Aldrich
Chemical Co. and used as received. Other ppz-based ligands are
synthesized by methods shown in Scheme 2.1. The flzIr ligand was
synthesized by Buchwald coupling reaction of pyrazoles and dimethyl iodo
fluorenyl (Scheme 2.2). The Buchwald reaction was done in DMF or dioxane
with 10 mol% CuI, 20 mol% 1,10-phenanthroline, 2.1 equiv. of cesium
carbonate as a base by heating it at 110°C for 24 hours under nitrogen
atmosphere.
11
The PMI ligand was synthesized simply by methylation of 1-
phenylimidazole using iodomethane at room temperature in toluene. The
PMB ligand was synthesized by a two step reaction: Buchwald coupling
reaction of benzimidazole and iodobenzene followed by methylation using
methyl-iodide in toluene. The flimIr ligand was synthesized by Buchwald
coupling reaction of imidazole and dimethyl-iodofluorenyl followed by
methylation using iodomethane in toluene.

28

Scheme 2.1. Synthesis of ppz Type Ligands

Scheme 2.2. Synthesis of flz Ligand

N
N
R R
R
X
+
B
OH HO
N
N
R R
R
PPh
3
, Pd(II)OAc, 2M K
2
CO
3
DME, reflux under N
2
overnight
HN
NH
2
.HCl
X
+
RR
OO
RO OR
OR OR
R
or
N
N
R R
R
X
reflux, 3 hours
EtOH

I
1. I
2
,H
5
IO
6
, 80% HOAc (aq)
@ 80 degrees, under N
2
4 hours
2. CH
3
I, BzEt
3
NCl, 50% NaOH(aq)
@ RT in DMSO, under N
2
overnight
3. Pyrazole, CuI, K
2
CO
3
,
dodecane, 1,2-trans-CDA
@ 110 degrees in dioxane
under N
2
, in the dark, overnight
3
N
N
I
12

29
Synthesis of Ir Complexes. All experiments involving IrCl
3
·xH
2
O or any
other Ir (III) species were carried out in an inert atmosphere despite the
stability of the compounds in air, the main concern being their oxidative and
thermal stability of intermediate complexes at the high temperatures used in
the reactions. Cyclometalated Ir (III) µ-chloro-bridged dimers of general
formula (C^N)
2
Ir(µ-Cl)
2
Ir(C^N)
2
(where C^N represents a cyclometalating
ligand) were synthesized first before the synthesis of tris-cyclometalated
Ir(III) complexes. Cyclometalated Ir(III) µ-chloro-bridged dimers of general
formula (C^N)
2
Ir(µ-Cl)
2
Ir(C^N)
2
(where C^N represents a cyclometalating
ligand) for pyrazole-based ligands were synthesized by a method similar to
the one reported by Nonoyama,
12
which involves heating to 110
°
C IrCl
3
·H
2
O
with 2-2.5 equivalents of cyclometalating ligand in a 3:1 mixture of 2-
ethoxyethanol and deionized water. Bis-cyclometalated iridium
acetylacetonate complexes with general formula (C^N)
2
Ir(acac) were
synthesized by the method reported by Lamansky.
7
For imidazolate-based
ligands, the dimers were synthesized in 2-ethoxyethanol which involves
heating to 120
°
C IrCl
3
·H
2
O with 2-2.1 equiv. of cyclometalating ligand and
excess of silver oxide. Synthesis and characterization of fac-Ir(ppz)
3
has
been previously reported.
9
Detailed synthesis and characterization of fac-
Ir(flz)
3
(aka. fac-flzIr),

fac- and mer-Ir(pmi)
3
, and fac- and mer-Ir(pmb)
3
, and
fac-flimIr are given below.

30
Synthesis of 2-Iodofluorene. A 250mL round-bottomed flask was charged
with 20.0g (120mmol) fluorene, 16.0g (60mmol) iodine and 4.0g (17mmol)
periodic acid. 150mL (80%) acetic acid was added to the reaction mixture.
The mixture was stirred under nitrogen at 80ºC for 4 hours. The mixture was
then allowed to cool to ambient temperature. The solid residue was vacuum-
filtered, dissolved in toluene and then washed with 5% sodium hydrogen
sulphite (to remove excess iodine). The toluene solution was concentrated
under vacuo and then passed through a flash column using toluene as the
eluent to give 32.0g (91%yield) of the product (off white solid).
Synthesis of 2-iodo-9,9-dimethyl-fluorene. A 500 mL round bottomed flask
was charged with 21.8 g (70 mmol) 2-Iodofluorene and 1.18 g (5 mmol)
benzyltriethylammonium chloride. 200 mL of dimethylsulfoxide (DMSO) was
then added followed by 28 mL (50%) NaOH. The mixture was allowed to stir
under nitrogen for 1 hour, before 29 g (210 mmol) methyl iodide was added
through the septum. The mixture was allowed to stir at room temperature for
18 hours. After cooling to ambient temperature the mixture was transferred to
a 1 L separatory funnel. 100 mL of water and 100 mL of diethylether were
added to the mixture. The organic layer was collected and the aqueous layer
was extracted with diethyl ether (4 x 100 mL). The organic fractions were
combined, dried over anhydrous magnesium sulfate, and the solvent
evaporated under vacuo. A flash column was then performed using hexanes
as the eluent to give 21.0 g (88% yield) of the product (yellow oil).

31
Synthesis of 1-[2-(9,9-dimethylfluorenyl)]pyrazole. In the dark, an oven-
dried 100 ml round-bottomed flask containing a stir bar was charged with CuI
(0.410 g, 2.153 mmol), pyrazole (3.550 g, 52.14 mmol.), and potassium
carbonate (12.60 g, 91.17 mmol) respectively. The round-bottomed flask with
the contents was sealed with septa and degassed with argon for 15 minutes.
Dodecane (2 ml, 8.81 mmol), 2-iodo-9,9-dimethylfluorenyl (13.9 g, 43.41
mmol), trans-1,2-cyclohexanediamine (0.52 ml, 0.433 mmol.), and 1,4-
dioxane (60 ml) were then successively added into the round-bottomed flask
under a continuous flow of argon. The reaction mixture was degassed with
argon for 30 minutes. The reaction was stirred with heating via an oil bath at
110ºC for 24 hours in the dark under nitrogen. The reaction mixture was
cooled to ambient temperature and concentrated in vacuo. 50 ml of ethyl
acetate was added into the concentrated reaction mixture. It was then filtered
and washed with 40 ml of ethyl acetate. The filtrate was concentrated under
vacuo to give the crude product. The crude product was purified by column
chromatography on silica gel (10% ethyl acetate: 90% hexane as the eluent)
providing 8.200 g (67% yield) of 1-[2-(9,9-dimethylfluorenyl)pyrazole as
yellow liquid, in which then solidified over time.
Synthesis of (flz)
2
Ir(μ-Cl)Ir(flz)
2
. The fluorenylpyrazole-based Ir(III)
dichloro-bridged dimer was synthesized by the following procedure. A 100 ml
round-bottomed flask was charged with iridium trichloride hydrate (0.250 g,
0.837 mmol), 2-fluorenylpyrazole (0.500 g, 1.92 mmol), and 60 ml of 2-
ethoxyethanol-water mixture (3:1). The reaction mixture was then stirred and

32
heated with an oil bath at 110ºC for 16 hours under nitrogen and then
allowed to cool to ambient temperature. Addition of water gave a 0.415 g
(yield = 66%) of a yellowish-white solid which was found to be dimer. This
product was used without further purification to prepare the acac complex.
Synthesis of fac-Ir(flz)
2
(acac). In a 100 ml round-bottomed flask, the
fluorenylpyrazole-based Ir(III) dichloro-bridged dimer (0.250 g, 0.168 mmol),
2,4-acetylacetone ( 0.036 ml, 0.352 mmol), excess K
2
CO
3
, and 60 ml of
1,2-dichloroethane were combined. The reaction mixture was stirred and
heated with an oil bath at 90ºC for 16 hours under nitrogen. The reaction
mixture was then cooled to ambient temperature, vacuum filtered to remove
the insoluble salts, and the filtrate was collected. The solvent was removed
under reduced pressure. Addition of methanol gave 0.248 g of light yellow
solid which was found to be (flz)
2
Ir(acac) (yield = 91%).
1
H NMR (360 MHz,
CDCl
3
), ppm: 8.16 (dd, J = 2.9 Hz, 1.0 Hz, 2H), 7.69 (dd, J = 2.2 Hz, 0.73 Hz,
2H), 7.25-7.29 (m, 2H), 7.31-7.35 (m, 2H), 7.19 (s, 2H), 7.09-7.18 (m, 4H),
6.71 (dd, J = 2.9 Hz, 2.2 Hz, 2H), 6.54 (s, 2H), 5.23 (s, 1H), 1.40 (s, 6H),
1.38 (s, 12H).
Synthesis of fac-Ir(flz)
3
. A 50 ml round-bottomed flask was charged with
(flz)
2
Ir(acac) complex (0.100 g, 0.125 mmol), the 2-fluorenylpyrazole ligand
(0.036 g, 0.138 mmol) and 25 ml of glycerol. The reaction mixture was stirred
and heated in an oil bath at 210-220°C for 24 hours under nitrogen
atmosphere. After cooling to ambient temperature, distilled water was added
to the reaction mixture and the precipitate was vacuum filtered and dried.

33
The crude product was purified by flash column chromatography on silica gel
using dichloromethane as the eluent to give the pure facial tris-
cyclometallated fluorenylpyrazole-based Ir(III) complex (0.0895 g, 75%).
1
H
NMR (360 MHz, CDCl
3
), ppm: 8.1 (dd, J = 2.8 Hz, 0.5 Hz, 3H), 7.36 (dd, J =
6.7 Hz, 1.3 Hz, 3H), 7.29 (s, 3H), 7.28 (s, 3H), 7.26 (dd, J = 6.3 Hz, 1.5 Hz,
3H), 7.14 (ddd, J = 7.5 Hz, 7.4 Hz, 1.5 Hz, 3H), 7.10 (ddd, J = 7.4 Hz, 7.2 Hz,
1.3 Hz, 3H), 7.03 (dd, J = 2.1 Hz, 0.4 Hz, 3H), 6.41 (dd, 2.8 Hz, 2.2 Hz, 3H),
1.56 (s, 9H), 1.46 (s, 9H); 13C (360 MHz, CDCl
3
), ppm: 153.74, 146.77,
143.75, 140.02, 138.47, 136.74, 136.55, 128.86, 126.54, 125.73, 124.87,
121.98, 119.88, 106.53, 105.55, 46.23, 28.03, 27.19. CHN Analysis (%) -
calc’d: C, 66.85; H, 4.68; N, 8.66; observed: C, 66.22; H, 4.52; N, 8.55
Synthesis of imidazolium ligand precursors. 1-Phenylimidazole was
purchased from Aldrich. 1-Phenyl-benzimidazole was prepared by a modified
Ullmann coupling reaction between benzimidazole and the phenyl iodide in
anhydrous N,N-dimethylformamide using a CuI/1,10-phenanthroline catalyst
and Cs
2
CO
3
base as previously reported.
17
The carbene precursor
imidazolium salts were prepared by methylating the corresponding
imidazoles with excess methyl iodide in toluene.
Synthesis of 1-Phenyl-3-methyl-imidazolium iodide. 1-Phenylimidazole
was purchased from Aldrich and used without further purification. Methyl
iodide (1.90 ml, 30.52 mmol) was syringed into a 25 ml round-bottomed flask
charged with 1-phenyl-imidazole (2.00 g, 13.87 mmol) and toluene (15 ml).
The reaction was stirred and heated at 30ºC for 24 hours. The white

34
precipitate was filtered and washed with 20 ml of toluene. The white
precipitate was air-dried and weighed to give 2.580 g of 1-phenyl-3-methyl-
imidizolate iodide (65% yield).
1
H NMR (250 MHz, CDCl
3
), ppm: 10.28 (s,
1H), 7.77-7.70 (m, 4H), 7.56-7.46 (m, 3H), 4.21 (s, 3H).
Synthesis of 1-Phenyl-3-methyl-benzimidazolium iodide. (Scheme 2.3)
In the dark, an oven-dried 50 ml round-bottomed flask containing a stir bar
was charged with CuI (0.171 g, 0.897 mmol), benzimidazole (1.273 g, 10.77
mmol.), and cesium carbonate (6.138 g, 18.84 mmol) respectively. The
round-bottomed flask with the contents was sealed with septa and degassed
with argon for 15 minutes. Iodobenzene (1ml, 8.97 mmol), 1,10-
phenanthroline (0.323 g, 1.79 mmol.), and anhydrous N,N-
dimethylformamide (25 ml) were then successively added into the round-
bottomed flask under a continuous flow of argon. The reaction mixture was
degassed with argon for 30 minutes. The reaction was stirred with heating
via an oil bath at 110ºC for 24 hours in the dark under nitrogen. The reaction
mixture was cooled to ambient temperature and concentrated in vacuo. 10 ml
of ethyl acetate was added into the concentrated reaction mixture. It was
then filtered and washed with 30 ml of ethyl acetate. The filtrate was
concentrated under vacuo to give the crude product. The crude product was
purified by column chromatography on silica gel (40% ethyl acetate: 60%
hexane as the eluent) providing 0.780 g of 1-phenyl benzimidazole (45%
yield) as yellow liquid. Methyl iodide (0.550 ml, 8.84 mmol) was syringed into
a 25 ml round-bottomed flask charged with 1-phenyl benzimidazole (0.780 g,

35
4.02 mmol) and toluene (15 ml). The reaction was stirred and heated at 30ºC
for 24 hours. The white precipitate was filtered and washed with 20 ml of
toluene. The white precipitate was air-dried and weighed to give 0.725 g of 1-
phenyl-3-methyl-benzimidizolate iodide (54% yield).
1
H NMR (250 MHz,
CDCl3), ppm: 9.30 (s, 1H), 7.90-7.80 (m, 4H), 7.75-7.60 (m,5H), 4.50 (s, 3H).

Scheme 2.3. Synthesis of Carbene Type Ligands

Synthesis of (pmi)
2
Ir(μ-Cl)Ir(pmi)
2
. A 100 ml round-bottomed flask was
charged with silver(I) oxide (0.428 g, 1.85 mmol), 1-phenyl-3-methyl-
imidazolate iodide (0.946 g, 3.31 mmol), iridium trichloride hydrate (0.301 g,
1.01 mmol), and 60 ml of 2-ethoxyethanol. The reaction was stirred and
heated with an oil bath at 120ºC for 15 hours under nitrogen while protected

N
N
CH
3
I
-
+
N
N
N
N
H
CuI
Cs
2
CO
3
1, 10 Phen
DMF, 110 deg. C, 24 h.
+
I
CH
3
I
Toluene
RT
24 h.
2. Synthesis of pmb ligand
N
N
CH
3
+
I
-
I
2
, H
5
IO
6
,
80% HOAc (aq)
@ 80 degrees
under N
2
4 hours
CH
3
I, BzEt
3
NCl, 50% NaOH(aq)
@ RT in DMSO, under N
2
overnight
CuI
Cs
2
CO
3
1, 10 Phen
DMF, 110 deg. C, 24 h.
CH
3
I
in Toluene
RT
24 h.
1. Synthesis of flim ligand
I
I
N
H
N
N
N

36
from light with aluminum foil. The reaction mixture was cooled to ambient
temperature and the solvent was removed under reduced pressure. The
black mixture was extracted with ca. 20 ml dichloromethane and the extract
was reduced to ca. 2 ml volume. Addition of methanol gave an off-white solid
which was found to be the dimer and some unreacted ligand. This product
was as is in the synthesis of the tris-cyclometallates without further
purification.
1
H NMR (250 MHz, CDCl
3
): 7.50 (d, J = 2.0 Hz, 4H), 7.07 (d, J =
2.0 Hz, 4H), 6.09 (dd, J = 7.8 Hz, 1.0 Hz, 4H), 6.63 (ddd, J = 7.5 Hz, 7.5 Hz,
1.4 Hz, 4H), 6.15 (ddd, J = 7.5 Hz, 7.5 Hz, 1.4 Hz, 4H), 3.87 (s, 12H).
Synthesis of fac-Ir(pmi)
3.
(from (pmi)
2
Ir(μ-Cl)Ir(pmi)
2
): A 50 ml round-
bottomed flask was charged with silver(I) oxide (0.278 g, 1.20 mmol), 1-
phenyl-3-methyl-imidazolate iodide (0.080 g, 0.280 mmol),
(pmi)
2
Ir(μ-Cl)Ir(pmi)
2
(0.108 g, 0.091 mmol) and 25 ml of 1,2-dichloroethane.
The reaction was stirred and heated with an oil bath at 77ºC for 15 hours
under nitrogen, while protected from light with aluminum foil. The reaction
mixture was cooled to ambient temperature and concentrated under reduced
pressure. Filtration through celite, using dichloromethane as the eluent, was
performed to remove the silver(I) salts. A light brown solution was obtained
and further purified by flash column chromatography on silica gel using
dichloromethane as the eluent and was then reduced in volume to ca. 2 ml.
Addition of methanol gave 0.010 g (8% yield) of iridium complex as a
colorless solid.
1
H NMR (360 MHz, CD
2
Cl
2
), ppm: 7.43 (d, J = 2.0 Hz, 3H),
7.16 (dd, J= 7.7 Hz, 1.0 Hz, 3H), 6.89 (ddd, J= 8.0 Hz, 7.3 Hz, 1.5 Hz, 3H),

37
6.78 (d, J= 2.0 Hz, 3H), 6.71 (ddd, J= 8.0 Hz, 7.3 Hz, 1.5 Hz, 3H), 6.60 (dd;
J= 7.2 Hz, 1.4 Hz, 3H);
13
C (360 MHz, CD
2
Cl
2
), ppm: 176.77, 150.12, 148.05,
137.80, 125.02, 120.73, 120.56, 114.71, 110.42, 36.95.; CHN (%) analysis -
calc’d: C, 54.28; H, 4.10; N, 12.66; observed: C, 54.09; H, 3.83; N, 12.47.
Synthesis of fac-Ir(pmi)
3.
(from IrCl
3
): A 25 ml round-bottomed flask was
charged with silver(I) oxide (0.165 g, 0.712 mmol), 1-phenyl-3-methyl-
imidazolate iodide (0.200 g, 0.699 mmol), iridium trichloride hydrate (0.0592
g, 0.198 mmol), and 15 ml of 2-ethoxyethanol. The reaction was stirred and
heated with an oil bath at 120ºC for 24 hours under nitrogen, while protected
from light with aluminum foil. The reaction mixture was cooled to ambient
temperature and concentrated under reduced pressure. Flash column
chromatography on celite, using dichloromethane as the eluent, was
performed to remove the silver(I) salts. A brown oil was obtained and further
purified by flash column chromatography on silica gel, using dichloromethane
as the eluent, to give 0.050 g of facial tris-iridium complex (33% yield) as an
off-white solid. The analytical data for this material matched those given
above for the same complex.
Synthesis of mer-Ir(pmi)
3
. A 50 ml round-bottomed flask was charged with
silver(I) oxide (0.076 g, 0.328 mmol), 1-phenyl-3-methyl-imidazolate iodide
(0.109 g, 0.381 mmol), iridium trichloride hydrate (0.029 g, 0.097 mmol), and
20 ml of 2-ethoxyethanol. The reaction was stirred and heated with an oil
bath at 120ºC for 15 hours under nitrogen while protected from light with
aluminum foil. The reaction mixture was cooled to ambient temperature and

38
concentrated under reduced pressure. Filtration through celite, using
dichloromethane as the eluent, was performed to remove the silver(I) salts. A
white solid was obtained after removing the solvent in vacuo and was
washed with methanol to give 0.016 g (24% yield) of meridional tris-iridium
complex as a white solid.
1
H NMR (360 MHz, CDCl
3
), ppm: 7.42 (d, J = 2.0
Hz, 1H), 7.37 (d, J = 2.0 Hz, 1H), 7.28 (d, J = 2.0 Hz, 1H), 6.9-7.2 (m, 3H),
6.78-6.85 (m, 3H), 6.5-6.75 (m, 3H), 3.04 (s, 1H), 3.02 (s, 1H), 2.95 (s, 1H);
13
C (360 MHz, CDCl
3
), ppm: 175.08, 173.62, 172.46, 151.43, 150.09, 148.87,
148.07, 147.44, 146.69, 139.76, 139.54, 137.27, 124.76, 124.71, 124.50,
124.33, 120.57, 120.40, 119.98, 119.66, 119.44, 119.39, 114.13, 114.11,
114.08, 110.07, 109.48, 36.99, 36.93, 35.87; CHN (%) analysis - calc’d: C,
54.28; H, 4.10; N, 12.66; observed: C, 54.25; H, 3.77; N, 12.44.
Synthesis of [(pmb)
2
Ir(μ-Cl)]
2
. A 50 ml round-bottomed flask was charged
with silver(I) oxide (2.787g, 12.0 mmol), 1-phenyl-3-methyl-benzimidazolate
iodide (3.378 g, 10.0 mmol), iridium trichloride hydrate (1.00 g, 3.35 mmol),
and 25 ml of 2-ethoxyethanol. The reaction was stirred and heated with an oil
bath at 120ºC for 24 hours under nitrogen while protected from light with
aluminum foil. The reaction mixture was cooled to ambient temperature and
concentrated under reduced pressure. Flash column chromatography on
celite using dichloromethane as the eluent was performed to remove the
silver(I) salts. A brown oil was obtained and addition of ethanol gave a light
brown solid. The brownish solid was filtered and washed with ethanol. It was
further purified by flash column chromatography on silica gel using

39
dichloromethane as the eluent to give 0.100 g of [(pmb)
2
IrCl]
2
(5% yield) as a
yellowish solid.
1
H NMR (360 MHz, CDCl
3
): 8.184 (m, 4H), 7.617 (dd, J = 7.9
Hz, 1.2 Hz, 4H), 7.515 (m, 4H), 7.300 (m, 4H), 6.780 (ddd, J = 8.3 Hz, 7.8
Hz, 1.3 Hz, 4H), 6.377 (ddd, J = 8.2 Hz, 7.6 Hz, 1.1 Hz, 4H), 6.239 (dd, J =
7.6 Hz, 1.3 Hz, 4H), 3.78 (s, 12H).
Synthesis of Ir(pmb)
3
. A 50 ml round-bottomed flask was charged with
silver(I) oxide (0.0886 g, 0.382 mmol), 1-phenyl-3-methyl-benzimidazolate
iodide (0.225 g, 0.669 mmol), [(pmb)
2
Ir(μ-Cl)]
2
(0.412 g, 0.319 mmol) and 25
ml of 1,2-dichloroethane. The reaction was stirred and heated with an oil bath
at 95ºC for 24 hours under nitrogen while protected from light with aluminum
foil. The reaction mixture was cooled to ambient temperature and
concentrated under reduced pressure. Flash column chromatography on
50:50 celite and silica gel using dichloromethane as the eluent was
performed to give 0.514 g of a mixture of meridianal and facial Ir(pmb)
3
(3:1)
as an-off white solid. Column chromatography using ethyl acetate/hexanes
(20:80) as the eluent was performed to give 0.400 g predominantly mer-
Ir(pmb)
3
with facial impurity (77% yield). The remaining fac-Ir(pmb)
3
was
eluted using ethyl acetate/hexanes (40:60) to give 0.110g (21% yield) of pure
fac-Ir(pmb)
3
. Repeated column chromatography was required to obtain mer-
Ir(pmb)
3
free of the fac impurity.
fac-Ir(pmb)
3
.
1
H NMR (360 MHz, CDCl
3
), ppm: 8.08 (d, J = 8.2 Hz, 3H), 7.86
(d, J = 7.8 Hz, 3H), 7.24 (ddd, J = 8.8 Hz, 6.9 Hz, 1.3 Hz, 3H), 7.15 (ddd, J =
7.7 Hz, 8.06 Hz, 0.85 Hz, 3H), 7.12 (d, J = 1.1 Hz, 2H), 7.09 (d, J = 1.1 Hz,

40
1H), 7.05 (ddd, J = 8.2 Hz, 7.0 Hz, 1.6 Hz, 3H), 6.72 (ddd, J = 7.7 Hz, 7.1 Hz,
1.1 Hz, 3H), 6.65 (dd, J = 7.3 Hz, 3H) 3.22 (s, 9H);
13
C (360 MHz, CDCl
3
),
ppm: 189.58, 148.75, 148.65, 137.02, 136.31, 132.63, 124.64, 122.59,
121.68, 120.86, 111.98, 111.125, 109.49, 33.42; CHN (%) analysis - calc’d:
C, 61.97; H, 4.09; N, 10.32; observed: C, 62.16, H, 3.77; N, 10.31.
mer-Ir(pmb)
3
.
1
H NMR (360 MHz, CDCl
3
), ppm; 8.16 (d, J = 8.7 Hz, 1H),
8.14 (d, J = 8.2 Hz, 1H), 8.05 (d, J = 7.8 Hz, 1H), 7.85 (d, J = 7.5 Hz, 1H),
7.82 (d, J = 7.8 Hz, 1H), 7.75 (d, J = 7.3 Hz, 1H), 6.46-7.47 (m, 18H), 3.25 (s,
3H), 3.18 (s, 3H), 3.17 (s, 3H);
13
C (360 MHz, CDCl
3
), ppm:. 188.22, 185.95,
184.89, 150.84, 149.64, 149.27, 148.79, 147.86, 147.84, 139.10, 138.93,
136.67, 136.60, 136.22, 132.49, 132.52, 132.48, 124.75, 124.53, 124.34,
122.69, 122.61, 121.86, 121.75, 121.43, 120.61, 120.21, 120.23, 112.35,
111.77, 111.13, 111.09, 111.05, 109.64, 109.56, 109.39, 33.40, 33.39, 33.33,
32.73 CHN (%) analysis - calc’d: C, 61.97; H, 4.09; N, 10.32; observed: C,
61.88; H, 3.69; N, 10.21
Synthesis of 1,(9,9-dimethylfluorenyl)imidazole. A three neck 250 mL
round bottomed flask was charged with 5.10g (1.2 molar equivalent)
imidazole, 2.13 g (20 mol%) 1,10-phenanthroline and 40.6 g (2.1 molar
equivalent) cesium carbonate. Argon was then allowed to flow over the
material for about 10 min. While Argon was still flowing, 1.12 g (10 mol%)
copper iodide was added to the mixture in the dark. The three-neck flask was
covered with aluminum foil to protect the reaction mixture from light. 20.0 g
(62 mmol) 2-iodo-9,9-dimethyl-fluorene, was dissolved in 20 mL of

41
anhydrous dimethylformamide (DMF) and added to the mixture via a syringe
through the septum. 20 mL of DMF was then further added to allow the
mixture to stir. The reaction mixture was heated to 110ºC for 48 hours. After
cooling, the mixture was filtered using vacuum filtration. The residue was
washed with ethyl acetate and the filtrate concentrated under vacuo. A flash
column was performed using hexanes (to get rid of any unreacted 2-iodo-9,9-
dimethyl-fluorene, the product stayed in the column). Following the hexanes,
a new receiving flask was placed under the column and the eluent was
changed to ethylacetate to give the product 10.0 g (62% yield) of product.
Synthesis of [1,(9,9-dimethylfluorenyl)-3-methyl-imidazolate]iodide. 2.3
mL (34 mmol) methyl iodide was syringed into a 250 mL round-bottomed
flask charged with 5 g (16 mmol) 1,(9,9-dimethylfluorenyl)imidazole and 50
mL toluene. The reaction was stirred and heated to 30°C for 24 hours. The
white precipitate was filtered and washed with toluene to give 7.0 g (99%
yield) of product.
Synthesis of 3:1 mixture of mer:fac-flimIr. A 250 mL round-bottomed flask
was charged with 1.53 g (11 mmol) silver(I) oxide, 5.0 g (11 mmol) [1,(9,9-
dimethylfluorenyl)-3-methyl-imidazolate]iodide and 0.66 g (3.6 mmol)
iridium(III)trichloride hydrate and 100 mL of 2-ethoxyethanol. The reaction
was stirred and heated at 80ºC for 24 hours under nitrogen while protected
from light with aluminum foil. The reaction mixture was cooled to ambient
temperature and concentrated under reduced pressure. Flash column
chromatography on silica gel using dichloromethane as the eluent was done

42
to give a 1.7 g (42%yield) of a 3:1 ratio of the mer/fac isomers of the tris Ir(III)
product.
fac-flimIr -
1
H NMR (360 MHz, CDCl
3
), ppm: 8.88 (d, J = 8.8 Hz, 2H), 8.72
(d, J = 8.8 Hz, 2H), 8.06 (d, J = 2.9 Hz, 2H), 7.98 (d, J = 8.8 Hz, 2H), 7.91 (d,
J = 8.3 Hz, 2H), 7.50 (t, J = 8.8 Hz, 7.3 Hz, 2H), 7.16 (ddd, J = 9.3 Hz, 6.8
Hz, 1.2 Hz, 2H), 7.09 (d, J = 8.6 Hz, 2H), 6.93 (dd, 8.3 Hz, 2.0 Hz, 2H), 6.75
(d, 2.4 Hz, 2H), 6.52 (dd, J = 2.9 Hz, 2.4 Hz, 2H), 5.92 (d, J = 1.7 Hz, 2H),
1.03 (s, 18H) ;
13
C (360 MHz, CDCl
3
), ppm: 176.61, 153.60, 148.20, 147.19,
146.65, 140.96, 135.34, 129.14, 126.25, 124.77, 121.61, 119.63, 119.56,
114.24, 104.28, 46.05, 36.48, 28.63, 26.99. CHN (%) analysis - calc’d: C,
67.43; H, 5.36; N, 8.28; observed: C, 67.64; H, 5.00; N, 8.30.

X-ray Crystallography. Diffraction data for fac-flzIr, fac-Ir(pmb)
3
, mer-
Ir(pmb)
3
and fac-flimIr were collected at T = 153(2)K, 143(2)K, and 143(2)K,
respectively. The data set were collected on a Bruker SMART APEX CCD
diffractometer with graphite monochromated Mo Kα radiation (λ = 0.71073 Å).
The cell parameters for the iridium complexes were obtained from the least-
squares refinement of the spots (from 60 collected frames) using the SMART
program. One hemisphere of crystal data for each of the three compounds
were collected up to a resolution of 0.86 Å, and the intensity data were
processed using the Saint Plus program. All the calculations for the structure
determination were carried out using the SHELXTL package (version 5.1).
13
Initial atomic positions were located by Patterson methods using XS and the

43
structures of the compounds were refined by least squares method using
SHELX93 with <9000 independent reflections within the range of θ = 1.35-
27.49°. Absorption corrections were applied by using SADABS.
14
In most
cases, hydrogen positions were input and refined in a riding manner along
with the attached carbons. Crystallographic data for fac-Ir(flz)
3
, fac- and mer-
isomers of Ir(pmb)
3
(i.e. tables of bond lengths and angles, crystal data,
atomic coordinates, bond distances, bond angles, and anisotropic
displacement parameters) have been reported in the Supporting Materials of
reference 24. Crystal data and structure refinement for fac-Ir(flim)
3
is given in
Table 2.1.

44
Table 2.1. Crystallographic Data for fac-Ir(flim)
3

Empirical formula C
57
H
51
IrN
6

Formula weight 1012.24
Temperature 296(2) K
Wavelength 0.71073 Å
Crystal system Monoclinic
Space group P2(1)/n
Unit cell dimensions a = 13.933(3) Å; α = 90°.
b = 19.836(4) Å; β = 107.992(4)°.
c = 18.229(4) Å; γ = 90°.
Volume
4791.7(18) Å
3

Z 4
Density (calculated)
1.403 Mg/m
3

Absorption coefficient
2.830 mm
-1

F(000) 2048
Crystal size
0.13 x 0.10 x 0.07 mm
3

Theta range for data collection 1.56 to 27.54°.
Index ranges -18<=h<=17, -25<=k<=24, -23<=l<=18
Reflections collected 29467
Independent reflections 10841 [R(int) = 0.1007]
Completeness to theta = 27.54° 98.1 %
Transmission factors min/max ratio: 0.439
Refinement method
Full-matrix least-squares on F
2

Data / restraints / parameters 10841 / 0 / 581
Goodness-of-fit on F
2

1.313
Final R indices [I>2sigma(I)] R1 = 0.0627, wR2 = 0.1095
R indices (all data) R1 = 0.1318, wR2 = 0.1625
Largest diff. peak and hole
1.216 and -0.899 e.Å
-3

Electrochemistry. Cyclic voltammetry and differential pulsed voltammetry
were performed using an EG&G potentiostat/galvanostat model 283.
Anhydrous DMF was used as solvent under an inert atmosphere and 0.1 M
tetra-n-butylammonium hexafluorophosphate was used as supporting
electrolyte. A glassy carbon rod was used as the working electrode, a
platinum wire used as the counter electrode, and a silver wire was used as a

45
pseudo-reference electrode. The redox potentials are based on values
measured from differential pulsed voltammetry and are reported relative to
either a ferrocenium/ferrocene (Cp
2
Fe
+
/Cp
2
Fe) redox couple or a
decamethylferrocenium/decamethylferrocene (Me
5
Cp
2
Fe
+
/Me
5
Cp
2
Fe) redox
couple used as an internal reference,
15
while electrochemical reversibility
was determined using cyclic voltammetry.

Photophysics. The UV-visible spectra were recorded on a Hewlett-Packard
4853 diode array spectrophotometer. Steady state emission at room
temperature and 77K were determined using a Photon Technology
International QuantaMaster Model C-60SE spectrofluorimeter.
Phosphorescence lifetime measurements (>2μs) were performed on the
same fluorimeter equipped with a microsecond xenon flashlamp or on an IBH
Fluorocube lifetime instrument by a time correlated single photon counting
method using either a 331 or a 405 nm LED excitation source. The absolute
quantum yields in fluid solution have been measured using a more reliant
method compared to those of previously reported.
16
The quantum yield
measurement experiments were carried out in dilute 2-MeTHF solution. The
sample was placed in a 1 cm
2
quartz cell and degassed with N
2
. The
quantum yields and the lifetimes of 1wt% doped thin films for fac-Ir(flz)
3
and
fac-Ir(pmb)
3
in poly-(methylmetacrylate) have also been measured. 2 mg of
the sample along with 180 mg of poly-(methylmetacrylate) were dissolved in
1 ml of toluene; the dissolved sample was spincoated on a 0.5x0.5cm
2
quartz

46
substrate at 3000 rpm for 40 seconds. The quantum efficiencies were
measured using a calibrated Hamamatsu integrating sphere equipped with a
xenon lamp (with either a 330 nm (for fac-Ir(pmb)
3
) or 380 nm (fac-flzIr)
excitation wavelengths) and photonic multi-channel analyzer C10027. The
accuracy of the quantum efficiency measurements is + 5-10% error of
measurements. The quantum efficiencies data have been processed with
PLQY measurement software U6039-05.

NMR.
1
H and
13
C NMR spectra were recorded on a Bruker AM 360 MHz
instrument and chemical shifts were referenced to residual protiated solvent.
Elemental analyses (CHN) were performed at the Microanalysis Laboratory
at the University of Illinois, Urbana-Champaign.

OLED Fabrication. p-Bis(triphenylsilyl)benzene (UGH2), N,N’-diphenyl-N,N’-
bis(1-naphthyl)benzidine (NPD), N,N’-dicarbazolyl-3,5-benzene (mCP) were
provided by Universal Display Corporation and used without further
purifications. 2, 9-dimethyl-4,7-diphenyl-1,10-phenanthroline (BCP) was
purchased from the Aldrich Chemical Company and was purified by
temperature gradient vacuum sublimation. Other materials such fac-flzIr and
fac-flimIr was also purified by sublimation before used in the chamber. Prior
to device fabrication, purchased 2mm wide striped pre-patterned ITO
substrates were cleaned by sonication in soap solution, rinsed with deionized
water and dried with N
2
. Then, photoresists were spincoated onto each

47
substrate. The substrates were then placed in the vacuum-oven for 45
minutes. The photoresists were washed off by acetone and N
2
-dried. They
were then treated with UV ozone for 10 min. Organic layers were deposited
sequentially by thermal evaporation from resistively heated tantalum boats at
a rate of 2-2.5 Å s
-1
. After organic film deposition, the chamber was vented
and a shadow mask with a 2mm wide stripe was put on the substrate
perpendicular to the ITO stripes. Cathodes consisted of a 10 Å thick layer of
LiF followed by a 1000 Å thick of Al. The devices were tested in air within 2
hours of fabrication. Device current-voltage and light-intensity characteristics
were measured using LabVIEW program by National Instruments with a
Keithley 2400 SourceMeter/2000 Multimeter coupled to a Newport 1835-C
Optical Meter, equipped with a UV-818 Si photocathode. Only light emitting
from the front face of the devices was collected and used in subsequent
calculation. The electroluminescence spectra were measured on a PTI
QuantaMasterTM Model C-60SE spectrofluorimeter, equipped with a 928
PMT detector and corrected for detector response.

2.3. Results and Discussion

2.3.1. Cyclometalated ppz-based ligands

There are many different approaches in achieving high energy (blue)
phosphorescent materials. Two approaches have been done by former group
members. One approach is fluorination of fac-Ir(ppy)
3
that emits at 510 nm at

48
room temperature. The fluorination of fac-Ir(ppy)
3
results in the synthesis of
fac-Ir-(4,6 difluoroppy)
3
; the fluorination caused 50 nm blue-shift emission
from that of fac-Ir(ppy)
3
at room temperature. The second approach is
exchanging the heterocyclic fragment of the cyclometalating ligand with the
one that has a higher triplet energy, i.e. replacing pyridyl groups with
pyrazolyl groups.
16
fac- Ir(ppz)
3
[ppz= 1-phenylpyrazole] displays intense
blue phosphorescent emission (410 nm at 77K)
9
but it gives very weak
emission at room temperature. ( Ф < 0.01).
17

In this chapter, we began with investigating the effects of phenyl
substitution on fac-Ir(ppz)
3
and also to see if the emission efficiency can be
improved by phenyl substitutions. The phenyl substitutions can cause minor-
shifts and red-shifts in the emission (see Figure 2.4) but the emission is still
not efficient in fluid solution at room temperature.

Figure 2.4. Emission Spectra of Ir(ppz)
3
Derivatives (77K, 2-MeTHF)

400 500 600 700
0.0
0.2
0.4
0.6
0.8
1.0

Normalized Intensity
Wavelength (nm)
λ
max
(emission)
414 nm at 77K
416 nm at 77K
422 nm at 77K
467 nm at 77K
472 nm at 77K
N
N
Ir
3
N
N
Ir
3
N
N
Ir
3
N
N
Ir
3
N
N
Ir
3

49
There are two dominant possible deactivations that may occur in fac-
Ir(ppz)
3
derivatives. While Ir complexes are in their triplet excited states form,
they may thermally populate a higher state known as the nonradiative (NR)
state. From this NR state, they go through a non-radiative decay pathway
and return to their ground state at a rate constant equal to k
nr
(T) (refer to
Figure 2.5). To achieve efficient luminescence from cyclometalated ppz-
based Ir complexes, it is necessary to retard or eliminate non-radiative
processes that deactivate the excited state at room temperature. A more
likely deactivation process for fac-Ir(ppz)
3
is a thermal population to a NR
state, such as a ligand field (d-d) or ppz ligand centered (e.g. n-π*) state. A
schematic representation of the emission and deactivating (NR) processes is
given in Figure 2.5. For complete deactivation at room temperature, the NR
deactivating rate (k
nr
(T)) must be significantly greater than the radiative rate
(k
r
), and the energy difference (E
a
) between the emissive triplet (T
1
) and the
NR state must be small enough that the higher energy NR state is thermally
accessible.

Figure 2.5. Energy Level Scheme of the Emission and NR State
S
1
T
1
ISC
hν
abs
k
r
(T)
NR
E
a
k
nr
k
nr
(T)
S
1
T
1
ISC
hν
abs
k
r
(T)
NR
E
a
k
nr
k
nr
(T)
(Nonradiative)

50

One approach to increase the luminescent efficiency of cyclometalated ppz-
based Ir complexes is to lower the triplet energy to a value such that the NR
state is no longer thermally accessible at room temperature. This concept
was used in the design of an analog of fac-Ir(ppz)
3
in which the phenyl group
of ppz is replaced with a fluorenyl group, fac-Ir(flz)
3
.
2.3.1.1. Synthesis

Cyclometalated Ir(III) µ-chloro-bridged dimers of general formula (C^N)
2
Ir(µ-
Cl)
2
Ir(C^N)
2
(where C^N represents a cyclometalating ligand) for pyrazole-
based ligands were synthesized by a method similar to the one reported by
Nonoyama,
12
which involves heating to 110
°
C IrCl
3
·H
2
O with 2-2.5
equivalents of cyclometalating ligand in a 3:1 mixture of 2-ethoxyethanol and
deionized water. Bis-cyclometallated iridium acetylacetonate complexes with
general formula (C^N)
2
Ir(acac) were synthesized by the method reported by
Lamansky.
12
(C^N)
2
Ir(acac) complex was then reacted with 1.2 equivalents of
C^N ligand in a glycerol refluxed at 210-220ºC under N
2
to form fac-Ir(C^N)
3

complexes.
2.3.1.2. X.-Ray Crystallography

The fac-Ir(ppz)
3
and fac-Ir(flz)
3
complexes are expected to have very
similar electronic configurations at the iridium center. Crystallographic
analysis of both compounds support a high degree of structural similarity for
the two compounds. Both fac-Ir(ppz)
3
and fac-Ir(flz)
3
show a pseudo-

51
octahedral coordination of three pyrazole nitrogens and three phenylene
carbons in a facial arrangement. The Ir-N and Ir-C bond lengths for the two
structures are statistically equivalent. The average Ir-N (2.110(6) Å) and Ir-C
(2.022(7) Å) bond lengths of fac-Ir(flz)
3
are within one sigma of the
corresponding averages for fac-Ir(ppz)
3
(average Ir-N = 2.124(5) Å, average
Ir-C = 2.021(6) Å). The structural data suggest a nearly identical environment
around the Ir center for the two complexes, and thus are expected to have
ligand field states of very similar energies.
2.3.1.3. Electrochemical Properties

The cyclic voltammogram for fac-Ir(flz)
3
closely resembles that of fac-Ir(ppz)
3

with a reversible oxidation at 0.31 V and no measurable reduction is
observed. Iridium complexes with the cyclometalated ppz ligand have HOMO
energies similar to their ppy analogs, but the LUMO energies are shifted to
significantly higher energies. This is reflected in the cyclic voltammograms of
these complexes, which show nearly identical oxidation potentials of 0.41 V
for fac-Ir(ppz)
3
and 0.31 V for fac-Ir(ppy)
3
(Figure 2.6.). In contrast, the two
complexes have markedly different reduction potentials, i.e. reduction for
fac-Ir(ppz)
3
is not observed prior to solvent reduction. The higher LUMO
energy of fac-Ir(ppz)
3
relative to fac-Ir(ppy)
3
is reflected in the photophysical
properties as well.

52

Figure 2.6. CV Traces of fac-Ir(flz)
3
, fac-Ir(ppz)
3
, and fac-Ir(ppy)
3

2.3.1.4. Photophysical Properties

The emission and absorption spectra for fac-Ir(ppz)
3
are blue shifted
by nearly 100 nm (0.57 eV) from those of fac-Ir(ppy)
3
. The room temperature
photoluminescent (PL) efficiency of the fac-Ir(ppz)
3
complex is very low. The
fac-Ir(ppz)
3
complex gives very weak emission ( Ф <0.01) at room
temperature, but emits strongly at 77K.
The absorption spectrum of fac-Ir(flz)
3
is red shifted by roughly 65 nm
(0.40 eV) from that of fac-Ir(ppz)
3
(Figure 2.7), and shows significantly higher
absorptivity than the ppz analog. The bands below 325 nm in the Ir(flz)
3

spectrum are most likely due to intraligand transitions of the flz ligand and
those at longer wavelengths due to MLCT transitions. The extinction
coefficients for the Ir(flz)
3
bands below 325 nm are roughly a factor of three
in DMF

53
greater than the same bands in the flz ligand, as expected for a metal
complex with three flz ligands. The MLCT transitions for fac-Ir(flz)
3
are more
intense than their counterparts in either the Ir(ppz)
3
or Ir(ppy)
3
spectra. This
is most likely due to fact that the ligand flz absorptions have markedly higher
oscillator strengths than those of either ppz or ppy.

Figure 2.7.Absorption Spectra of fac-Ir(flz)
3
, fac-Ir(ppz)
3
, and fac-Ir(ppy)
3

fac-Ir(flz)
3
gives efficient PL at room temperature, Ф = 0.81,
17
which is
red shifted from the Ir(ppz)
3
emission spectrum. The red shift originates from
the lower triplet energy for the flzH ligand (445 nm, 2.79 eV) versus that for
ppzH (380 nm, 3.26 eV).
18
Interestingly, the flz complex shows a negligible
rigidochromic effect. In contrast, comparison of the room temperature and
77K PL spectra for fac-Ir(ppy)
3
(Figure 2.8) illustrates a significant
rigidochromic effect for that complex. The magnitude of the rigidochromic
effect has been related to the degree of MLCT character in the excited state.
250 300 350 400 450 500 550
0
15k
30k
45k
60k
75k
90k

Absorbance (M
-1
cm
-1
)
Wavelength (nm)
fac-Ir(ppz)
3
fac-Ir(flz)
3
fac-Ir(ppy)
3

54
An excited complex reaches its fully relaxed geometry upon solvent
reorientation at room temperature, whereas the geometry of the complex is
held fixed in the rigid matrix, at low temperature. Since forming MLCT excited
states involve substantial charge redistribution, such transitions display
hypsochromic shifts upon going from room temperature fluid solution to 77K
glass. In contrast, largely ligand based excited states, e.g. π-π* states,
generally have low levels of charge redistribution and thus give very small
rigidochromic effects. Greater MLCT character in the excited state of the Ir
complexes is expected to lead to larger rigidochromic shifts.
25
A clear
correlation was demonstrated for (C^N)
2
Ir(L^L
I
) complexes between the
degree of MLCT character in the excited state and the magnitude of the
rigidochromic shift. The absence of a rigidochromic shift for fac-Ir(flz)
3

suggests that the excited state is largely ligand based, as expected for the
addition of a low triplet energy moiety, i.e. the fluorene.

Figure 2.8. Emission Spectra of fac-Ir(flz)
3
, fac-Ir(ppz)
3
, and fac-Ir(ppy)
3

400 450 500 550 600 650
0.0
0.2
0.4
0.6
0.8
1.0

Emission (arb. units)
Wavelength (nm)
fac-Ir(ppz)
3

fac-Ir(flz)
3

fac-Ir(ppy)
3

55
The replacement of a phenyl moiety with a fluorene in a
cyclometallated Ir complex has been reported previously.
25
In this work, it
was demonstrated that the emission of Ir(ppy)
3
could be markedly red shifted
by incorporation of a fluorene moiety. In these cases, however, both Ir(ppy)
3

and the fluorenyl analog are highly emissive at room temperature, so the red
shift had very little impact on the efficiency of luminescence. The observed
decrease in the emission energy for the fac-Ir(flz)
3
complex is due to the
predominant fluorenyl character in the excited state. The measured lifetime
at room temperature is 48 μs. The radiative and non-radiative decay rates (k
r

and k
nr
, respectively) for fac-Ir(flz)
3
estimated from the lifetime and quantum
efficiency, are 1.7 x 10
4
s
-1
and 3.2 x 10
3
s
-1
. These rates are an order of
magnitude lower than those reported for both blue and green emissive
cyclometalated Ir complexes, such as those illustrated in Figure 2.1. The
decreased radiative rate is consistent with a low level of MLCT character in
the fac-Ir(flz)
3
excited state, as indicated by the well defined vibronic fine
structure in the PL spectrum, the low oscillator strength for the MLCT
absorbance and the absence of a rigidochromic shift in emission energy.
Relatively little MLCT character in the lowest energy excited state of
fac-Ir(flz)
3
is expected, since the fluorene substitution lowers the
3
LC energy,
without significantly shifting the MLCT level relative to fac-Ir(ppz)
3
. A similar
correlation between the radiation rate and the degree of MLCT character in
the excited state was observed for related (C^N)
2
Ir(L^L
I
) complexes.

56
Considerable work has been done to understand the deactivation
processes in luminescent Ru(II) and Os(III) tris-dimmine complexes.
19
The
Ir(III) complexes reported here are isoelectronic with those materials, and are
expected to mimic the photophysics of their Os(II) counterparts. While Ru(II)
dimmine complexes typically show significant deactivation through ligand
field (dissociative) states, the Os(II) analogs show less efficient deactivation,
with kinetic parameters consistent with deactivation only through MLCT
states. The difference between the Ru and Os complexes is due to the larger
ligand field splitting observed for 5d over 4d elements, which destabilizes the
ligand field states in the Os analogs, to energies that are too high to be
thermally accessible from the emissive triplet state. Luminescent Ir
complexes are generally expected to behave similarly to their Os
counterparts, being quenched nearly exclusively by MLCT states.
20
However,
the complexes reported here have very high emission energies, approaching
that of the ligand field states. For example, the triplet energy of fac-Ir(ppz)
3
is
3.0 eV (70 kcal/mol), a value comparable to the Ir-phenyl bond strength.
21

2.3.1.5. OLED Performance

Some OLEDs were fabricated with fac-flzIr as an emissive dopant.
Two different hosts were used, UGH2 and mCP. mCP serves as a better
host for fac-flzIr; it gives a max. Q.E. of 6.35%. (Figure 2.9 (b)

57

Figure 2.9. (a) fac-flzIr:UGH2 Device; (b) fac-flzIr:mCP Device

110
1E-6
1E-5
1E-4
1E-3
0.01
0.1
1
10
100

Current Density (Cd/m
2
)
Voltage (V)
300 400 500 600 700 800
0.0
0.2
0.4
0.6
0.8
1.0
Normalized Intensity
Wavelength (nm)
0.01 0.1 1 10 100 1000
1
2
3

Q.E. (%)
Current Density (mA/cm
2
)
110
0.01
0.1
1
10
100
1000

Brightness (Cd/m
2
)
Voltage (V)
Turn-On 3.5 V
Q.E. max= 2.7%
110
1E-6
1E-5
1E-4
1E-3
0.01
0.1
1
10
100

Current Density (Cd/m
2
)
Voltage (V)
300 400 500 600 700 800
0.0
0.2
0.4
0.6
0.8
1.0
Normalized Intensity
Wavelength (nm)
0.01 0.1 1 10 100 1000
1
2
3

Q.E. (%)
Current Density (mA/cm
2
)
110
0.01
0.1
1
10
100
1000

Brightness (Cd/m
2
)
Voltage (V)
Turn-On 3.5 V
300 400 500 600 700 800
0.0
0.2
0.4
0.6
0.8
1.0
Normalized Intensity
Wavelength (nm)
0.01 0.1 1 10 100 1000
1
2
3

Q.E. (%)
Current Density (mA/cm
2
)
110
0.01
0.1
1
10
100
1000

Brightness (Cd/m
2
)
Voltage (V)
Turn-On 3.5 V
110
0.01
0.1
1
10
100
1000

Brightness (Cd/m
2
)
Voltage (V)
Turn-On 3.5 V
Q.E. max= 2.7%
400 500 600 700 800
0.0
0.2
0.4
0.6
0.8
1.0
1E-3 0.01 0.1 1 10 100 1000
0.01
0.1
1
10
110
1E-3
0.01
0.1
1
10
100
1000
10000
110
1E-7
1E-6
1E-5
1E-4
1E-3
0.01
0.1
1
10
100
1000

Normalized Intensity
Wavelength (nm)

Q.E. (%)
Current Density (mA/cm
2
)
Q.E. max = 6.35 %

Brightness (Cd/m
2
)
Voltage (V)
Turn-On 3.6 V

Current Density (mA/cm
2
)
Voltage (V)
(a)
(b)

58
2.3.2. Cyclometalated carbene ligands

An alternate approach to achieve efficient blue phosphorescence from
cyclometalated Ir complexes at room temperature involves increasing the
energy of the nonradiative (NR) state, such that even at a high triplet energy,
the NR state is not thermally populated. (Figure 2.5) The key is to design
cyclometalating ligands that destabilize the NR state. A logical candidate for
the NR state is a ligand field, metal-localized state. If the ligand-metal bonds
are strengthened (stronger ligand field), the ligand field deactivating NR
states will be destabilized since they involve antibonding counterparts to the
metal-ligand bonding orbitals. Of the number of potential ligand choices that
could have stronger ligand fields than pyrazolyl, the ligand type used here is
a carbene. The syntheses of the carbene ligand precursors are well known,
making access to the complexes very straightforward. Carbene ligands form
very strong bonds to transition metals, which shift the metal-carbene
antibonding orbitals to high energy, decreasing or eliminating quenching
through the ligand field state. The two carbene based complexes studied in
this chapter contain imidazole- and benzimidazole-based carbene ligands
(pmi and pmb, respectively, Figure 2.3). The carbene moieties were used in
conjunction with a phenyl group to form the cyclometalating ligands. The
carbene moiety is a neutral, two electron donor ligand (Scheme 2.4), making
the cyclometalated ligand a bidentate monoanionic ligand, similar to the C^N
ligands that have been used to make stable iridium tris-chelates. The first

59
cyclometalated Ir carbene complexes were reported by Lappert, et. al., in
1980 (see Ir-Lappert in Scheme 2.4).
22

N
N
Ir
3
Ir(pmi)
3
N
N
Ir
3
Ir(pmb)
3
N
N
N
N
N
N
:
N
N
Ir
3
C
7
H
7
Ir-Lappert
N
N
Ir
3
Ir(pmi)
3
N
N
Ir
3
Ir(pmb)
3
N
N
N
N
N
N
:
N
N
Ir
3
C
7
H
7
Ir-Lappert

Scheme 2.4. The First Ir-(C^C:)
3
Reported by Lappert

2.3.2.1.Synthesis

The Ir(C^C:)
3
complexes were prepared by a modification of the method
used to prepare the Ir(C^N)
3
analogues. A stoichiometric amount of
imidazolium (pmiH
+
) or benzadolium (pmbH
+
) iodide salts, silver (I) oxide,
and iridium (III) chloride hydrate were refluxed in a 2-ethoxyethanol solution
to give a mixture of fac- and mer-Ir(C^C:)
3
complexes in low yield (<10%)
along with a product formulated as [(C^C:)
2
IrCl]
2
(Scheme 2.5 (a)).

The[(C^C:)
2
IrCl]
2
complex can then be treated with additional pmiH
+
or
pmbH
+
and silver (I) oxide in 1,2-dichloroethane to form a mixture of fac- and
mer-Ir(C^C:)
3
complexes (Scheme 2.5. (b)).
3 pmiH
+
I
-
(or pmbH
+
I
-
) + 3 Ag
2
O + IrCl
3
.xH
2
O Ir(C^C:)
3
+[(C^C:)
2
IrCl]
2
(a)
pmiH
+
I
-
(or pmbH
+
I
-
) + Ag
2
O + [(C^C:)
2
IrCl]
2
Ir(C^C:)
3
(b)
Scheme 2.5. (a) The Synthesis of Ir Carbene Dimers; (b) Complexes

60
A given synthesis produces a mixture of the fac- or mer- isomers of
the Ir(C^C:)
3
complex (see experimental section). The fac- and mer- isomers
of the carbene complexes are neither thermally nor photochemically
interconverted, so isomerically pure samples were isolated by either selective
precipitation/crystallization or chromatography. We presume that the inability
to interconvert the fac- and mer-isomers is principally due to Ir-C(carbene)
bonds being stronger than their Ir-N counterparts, making the partial ligand
dissociation that is necessary for isomerization more difficult for the C^C:
complexes than their C^N counterparts.
2.3.2.2. X-Ray Crystallography

Single crystals of fac-Ir(pmb)
3
, mer-Ir(pmb)
3
and fac-flimIr grown from
methanol/dichloromethane solution were characterized using X-ray
crystallography. All of the complexes analyzed here have the three
cyclometalating ligands in a pseudo-octahedral coordination geometry
around the iridium metal center. In both fac- and mer-Ir(pmb)
3
the C^C:
ligands are twisted from planarity presumably due to steric repulsion between
adjacent ligands. The twisting around the bridging C
phenyl
-N
carbene
bond is
smaller in the fac-isomer (dihedral angles are between 1 to 10 degrees) than
in the mer-isomer (dihedral angles vary between 5 to 27 degrees). This
variation in ligand distortion is most likely due to crystal packing effects. It is
instructive to compare the Ir coordination environment of facial isomer of
Ir(pmb)
3
to the same isomer for Ir(ppz)
3
. In fac-Ir(pmb)
3
, the average Ir-

61
C
carbene
distance (2.026(7) Å) is significantly shorter than the average Ir-N
distance in fac-Ir(ppz)
3
(2.124(5) Å). The short distance in fac-Ir(pmb)
3

suggests that the carbene moiety is more strongly bound to the Ir than the
pyrazolyl ligand. Moreover, the average Ir-C
phenyl
distance (2.081(7) Å) in fac-
Ir(pmb)
3
is longer than the average Ir-C
phenyl
distance in fac-Ir(ppz)
3
(2.021(6)
Å), suggesting that the carbene is a stronger field ligand than pyrazole. The
bonding parameters found for the meridianal isomer of the complex support
this view as well. In mer-Ir(pmb)
3
, the bond length of Ir-C
aryl
trans to
benzimidazolyl (Ir-C2 = 2.078(4) Å) is greater than the bond length of Ir-C
aryl

trans to pyrazolyl group in mer-Ir(ppz)
3
(Ir-C3 = 1.993(2) Å), illustrating the
stronger trans influence of the carbene ligand over that of pyrazolyl. The
lengths of the mutually trans Ir-C
aryl
bond (Ir-C1 and Ir1-C3, ave. = 2.093(4)
Å) in mer-Ir(pmb)
3
are slightly longer than those of mer-Ir(ppz)
3
(ave.=
2.040(2) Å), indicating greater electron donation from the carbene ligand than
from the pyrazolyl moiety. The structures both isomers of Ir(pmb)
3
are
consistent with a strong trans influence of a formally neutral carbene ligand.
The bond length differences suggest that the cyclometalated carbenes are
stronger field ligands than their pyrazolyl or pyridyl counterparts, giving the
carbene complexes higher energy ligand field states than their pyrazolyl- or
pyridyl-based counterparts. Molecular structures of fac-Ir(ppz)
3
, mer-Ir(ppz)
3
,
fac-Ir(pmb)
3
, mer-Ir(pmb)
3,
fac-flzIr, and fac-flimIr are shown in Figure 2.10.

62

N3

C1

N1

C 3

N 2
C2

N2
N3
C3
N1
C1
C2

Ir1
C5
C2
C6
C3
C4
C1

Ir1
C6
C3
C2
C5
C1
C4

Ir1
C1
N1
C3
C2
N2
N3

Figure 2.10. ORTEP Plots of (a) fac-Ir(ppz)
3
, (b) mer-Ir(ppz)
3
, (c) fac-
Ir(pmb)
3
, (d) mer-Ir(pmb)
3
, (e) fac-flzIr, (f) fac-flimIr. The hydrogen atoms
have been omitted for clarity.
a b
c
d
e f

63
2.3.2.3. Electrochemical Properties

The Ir(pmi)
3
and Ir(pmb)
3
complexes show electrochemical and
absorption properties similar to those of fac-Ir(ppz)
3
. Both fac-Ir(pmi)
3
and
fac-Ir(pmb)
3
(Figure 2.11 and 2.12) exhibit reversible oxidation at 0.22 and
0.48 V, respectively, and no reduction is observed within the accessible
solvent window (-3.0 V vs Fc/Fc
+
), similar to the data shown for fac-Ir(ppz)
3
in
Figure 2.6. The mer-isomers are easier to oxidize than their fac counterparts
(mer-Ir(pmi)
3
E
1/2
ox
= 0.14 V, mer-Ir(pmb)
3
E
1/2
ox
= 0.31 V) and an irreversible
reduction was seen for mer-Ir(pmb)
3
at -3.2 V.

Figure 2.11. CV Traces of fac-Ir(pmi)
3
and mer-Ir(pmi)
3
in DMF

64

Figure 2.12. CV Traces of fac-Ir(pmb)
3
and mer-Ir(pmb)
3
in DMF

Both fac-flzIr and fac-flimIr can be easily oxidized but they are difficult
to reduce. (Figure 2.13.; Fc*/Fc*
+
was used as a reference)

Figure 2.13. CV Traces of fac-flzIr and fac-flimIr in DMF
-3.00 -2.50 -2.00 -1.50 -1.00 -0.50 0.00 0.50 1.00 1.50

Current (mA)
Voltage (V vs. Fc*)
fac-flzIr
fac-flimIr
CV in anhydrous DMF using Fc* as internal reference

65
2.3.2.4. Photophysical Properties

The Ir(pmi)
3
and Ir(pmb)
3
complexes display strong emission at
energies in the near UV at 77K and also give luminescence at room
temperature in fluid solution. The excited state properties of the carbene-
based complexes are related to the C^N based complexes as both emit from
perturbed
3
LC states; however, significant differences are observed. For
example, there is a negligible difference in the emission spectra of
fac-Ir(pmi)
3
and fac-Ir(pmb)
3
, even though the π-system of the pmb ligand is
significantly larger than that of pmi. The insensitivity of the triplet energy upon
extending of the π-system of the carbene moiety is most likely due to poor
conjugation of the phenyl and benzimidazole fragments, such that the phenyl
and carbene moieties behave as independent lumiphores. This behavior is in
contrast to what occurs when the ppy ligand is modified by adding a fused
phenyl ring (compare (ppy)
2
Ir(acac) to (pq)
2
Ir(acac) in Figure 2.1); the
emission energy of the (pq)
2
Ir(acac) complex with the expanded π-system is
lowered by 0.34 eV.
The PL efficiencies for the carbene-based materials are nevertheless
higher than their pyrazolyl counterparts. (i.e. Ф
RT
for fac-Ir(pmb)
3
is 0.37 in 2-
MeTHF solution). The small rigidochromic shifts for the carbene complexes
suggest that the Ir(C^C:)
3
complexes have excited states with more MLCT
character than Ir(flz)
3
, but less than Ir(ppy)
3
. The shifts for Ir(C^C:)
3

complexes are intermediate between the negligible shift observed for fac-

66
Ir(flz)
3
(largely LC based excited state) and the larger shift observed for fac-
Ir(ppy)
3
, which exhibits substantial MLCT character in its excited state. The
radiative rates for the carbene compounds are higher than that of fac-Ir(flz)
3
.
The fac-Ir(pmb)
3
complex has radiative and nonradiative decay rates of 3.4 x
10
5
and 2.1 x 10
5
s
-1
, respectively. The facial analogs of the Ir(C^C:)
3

complexes have higher radiative decay rates than fac-Ir(flz)
3
. This is
consistent with greater
1
MLCT character in the excited states of the Ir(C^C:)
3

complexes relative to fac-Ir(flz)
3
, and is presumably due to the
1
MLCT and
3
LC levels being closer in energy, and thus more effectively mixed, in the
Ir(C^C:)
3
than in the flz analog. The nonradiative deactivating rates for the
carbene-based complexes are also markedly higher than that of fac-Ir(flz)
3
,
consistent with a readily accessible NR state for the carbene complexes. The
meridional isomers of both Ir(C^C:)
3
complexes have lower PL efficiencies
and correspondingly higher nonradiative deactivating rates than their facial
analogs, which was similar to the related properties for the facial and
meridianal isomers of Ir(C^N)
3
complexes. The 77K emission spectra for fac-
Ir(pmi)
3
and mer-Ir(pmi)
3
is shown in Figure 2.14.
Strong absorptions bands at wavelengths <270 nm are assigned to
ligand π-π*  transitions of the cyclometalating ligands, weaker absorption
bands between 270 and 360 nm are ascribed to MLCT transitions for the two
Ir(C^C:)
3
complexes (Figure 2.15). The extinction coefficient of the MLCT
band for fac-Ir(pmb)
3
is appreciably greater than that for fac-Ir(pmi)
3
. A weak

67
(ε ~ 100 M
-1
cm
-1
) low energy band at 380 nm is present in both complexes
and assigned to perturbed
3
LC transition.

Figure 2.14. 77K Emission Spectra of fac-Ir(pmi)
3
and mer-Ir(pmi)
3

Figure 2.15. Absorption and Emission Spectra of Ir(pmi)
3
and Ir(pmb)
3

250 300 350 400 450 500 550 600
0
10k
20k
30k
40k
50k

Wavelength (nm)
Absorbance (M
-1
cm
-1
)
0.0
0.2
0.4
0.6
0.8
1.0
fac-Ir(pmi)
3
fac-Ir(pmb)
3
Photoluminescence (arb. units)

68
The mer-Ir(C^C:)
3
complexes do not convert to their facial isomers on
irradiation, instead they eventually decompose under long term UV exposure.
The facial isomers also decompose on extensive irradiation, without the
formation of the meridianal compound, hence it is not possible to determine
which isomer of the Ir(C^C:)
3
complexes is thermodynamically favored. The
meridianal isomers of Ir(C^N)
3
complexes, on the other hand, can be
photochemically converted to their facial analogs with minimal
decomposition.
The observation of room temperature emission in the near-UV from
the Ir(C^C:)
3
complexes suggests that the NR state has been significantly
destabilized relative to the fac-Ir(ppz)
3
ligand field state. While lowering the
T
1
energy in fac-Ir(flz)
3
markedly decreased the rate of deactivation through
the higher energy state, resulting in a relatively small nonradiative rate (k
nr
=
3.2 x 10
3
s
-1
), the carbene based complexes still show substantial
deactivation, as evidenced by the relatively high nonradiative rates, and
moderate PL efficiencies, relative to Ir(flz)
3
. Cooling a sample to low
temperature can largely eliminate nonradiative deactivation pathways, giving
a measured lifetime that is closer to the radiative lifetime. All of the carbene
complexes show a marked increase in lifetime on cooling to 77K.
Interestingly, suspending the complexes in a rigid polystyrene matrix
increases the measured lifetimes of these materials by nearly an order of
magnitude. The increased τ in the solid state is significant with regards to the
use of carbene based materials as emitters in OLEDs, since this suggests

69
that the luminance efficiencies in doped solids are notably higher than those
measured in fluid solution. The polystyrene lifetimes suggest that the
luminance efficiencies for the carbene complexes are > 0.3 in the solid state
at room temperature. OLED have been fabricated with Ir(C^C:)
3
complexes
and give external quantum efficiencies > 5%,
23
consistent with luminance
efficiencies for the Ir(C^C:)
3
> 0.3.
The emission spectra in Figure 2.16 show about 15 nm blue-shifts at
77K and RT as we go from fac-flzIr to fac-flimIr. Small blue-shift in lowest
energy absorption band is also observed as we go from fac-flzIr to fac-flimIr.
(Figure 2.17)

Figure 2.16. Emission Spectra of fac-flzIr vs. fac-flimIr

450 500 550 600 650 700
0.0
0.2
0.4
0.6
0.8
1.0
Normalized Intensity

Wavelength (nm)
fac-flzIr at 77K (477 nm)
fac-flimIr at 77K (462 nm)
450 500 550 600 650 700
0.0
0.2
0.4
0.6
0.8
1.0

Normalized Intensity
Wavelength (nm)
fac-flzIr at RT (480 nm)
fac-flimIr at RT (466 nm)

70

Figure 2.17. Absorption Spectra of fac-flzIr vs. fac-flimIr

2.3.2.5. OLED Perfomance

OLED device performance using fac-flimIr as an emissive dopant is reported
in this chapter. The devices with flimIr as a dopant gives lower external
quantum efficiency and lower brightness compared to flzIr-doped device.
However, the electroluminescence of the device still remains voltage
independent. (Figure 2.18)

250 300 350 400 450 500 550 600 650 700
0
1x10
4
2x10
4
3x10
4
4x10
4
5x10
4
6x10
4
7x10
4
8x10
4
9x10
4

Molar Absorptivity (M
-1
cm
-1
)
Wavelength (nm)
fac-flzIr
fac-flimIr

71

ITO/ NPD (400 Ǻ)/dopant: mCP (8%, 250 Ǻ)/ BCP(400 Ǻ)/ LiF/Al

Figure 2.18. flimIr-doped and flzIr-doped mCP Devices

2.4. Conclusion

The approach to tuning the photophysical properties of
cyclometallated Ir complexes investigated here involved the control of the
relative energies of emitting and nonradiative (NR) states. The starting point
for this work was a high triplet energy Ir complex, that gives very weak
emission at room temperature, i.e. fac-Ir(ppz)
3
. By increasing the energy
separation between emitting and NR states, nonradiative decay rates could
400 500 600 700
0.0
0.2
0.4
0.6
0.8
1.0
0.1 1 10 100
1
2
3
4
5
6
7
8
110
1E-7
1E-6
1E-5
1E-4
1E-3
0.01
0.1
1
10
100
0.1 1 10
1E-3
0.01
0.1
1
10
100
1000
10000

Normalized Intensity
Wavelength (nm)
7V
8V
9V
10V
11V
12V
10Vback
flzIr

Q.E. (%)
Current Density (mA/cm
2
)
flzIr in mCP
flimIr in mCP

Current Density (mA/cm
2
)
Voltage (V)
flzIr in mCP
flimIr in mCP

Brightness (Cd/m
2
)
Voltage (V)
flzIr in mCP
flimIr in mCP

72
be decreased, leading to distinctly improved luminescent quantum yields.
This was demonstrated by both lowering the energy of the emitting state (i.e.
fac-Ir(flz)
3
) and increasing the energies of the NR states, as in Ir(C^C:)
3
.
While the flz complex gave a marked decrease in the energy of the excited
state, the carbene complexes maintained the high triplet energy of the
starting ppz based complex, giving near-UV luminescence at room
temperature. The next step in this study is to examine the temperature
dependence of the photophysical properties of these materials. The
temperature dependence of the emission lifetime and efficiency can be used
to determine the relative energies and decay rates for both the emissive and
NR states of the carbene- and pyrazolyl-based materials. With this
information in hand, we will be able to evaluate the nature of the NR states
and design ligands and complexes that more effectively destabilize the NR
states, leading to higher luminance efficiencies. A detailed temperature
dependent study will be discussed in Chapter 5 of this thesis.
Selected bond distances and angles of fac-Ir(flz)
3
, fac-Ir(pmb)
3
, and
mer-Ir(pmb)
3
are provided in Table 2.2, along with those of fac-Ir(ppz)
3
and
mer-Ir(ppz)
3
, for which structural data were taken from the literature. The
quantum efficiencies and lifetimes for fac-Ir(flz)
3
, Ir(pmi)
3
, and Ir(pmb)
3
are
given in Table 2.3.

73
Table 2.2. Selected Bond Distances ( Ǻ) and Angles (°) for fac- and mer-
Ir(ppz)
3
,
16
fac-Ir(flz)
3
, and fac- and mer-Ir(pmb)
3
24

Table 2.3. Photophysical Properties of Ir(III) Complexes (2-MeTHF)

Complexes 77K Room Temperature
λ
max
(nm)
τ
(μs)
λ
max
(nm)
τ
(μs)
Φ
RT
k
r
( s
-1
)
k
nr
( s
-1
)
fac-Ir(flz)
3
478 50 480 48 0.81 1.7 x 10
4
4.0 x 10
3

fac-Ir(pmi)
3
380 6.8 400 2.8 0.40 1.4 X 10
5
2.1 X 10
5

mer-Ir(pmi)
3
380 2.4 400 2.9 0.37 1.3 X 10
5
2.2 X 10
5

fac-Ir(pmb)
3
380 3.1 400 1.1 0.37 3.4 x 10
5
2.1 x 10
5

mer-Ir(pmb)
3
380 2.4 400 0.015 0.02 1.3 X 10
6
6.4 x 10
7

74
Chapter 2 References

1. (a) Demas, J. N.; Harris, E.W.; McBride, R.P. J. Am. Chem. Soc. 1977, 99,
3547. (b) Demas, J. N.; Harris, E.W.; Flynn, C.M.; Diemente, J.D. J. Am.
Chem. Soc. 1975, 97, 3838. (c) Gao, R.; Ho, D.G.; Hernandez, B.; Selke, M.;
Murphy, D.; Djurovich, P.I.; Thompson, M.E. J. Am. Chem. Soc. 2002, 124,
14828.

2. King, K.A.; Spellane, P.J.; Watts, R.J. J. Am. Chem. Soc. 1985, 107, 1431.

3. (a) Sutin, N. Acc. Chem Res. 1968, 1, 225. (b) Meyer, T.J. Acc. Chem.
Res. 1978, 11, 94. (b) Schmid, B.; Garces, F.O.; Watts, R.J. Inorg. Chem.
1994, 32, 9.

4. (a) Belmore, K.A.; Vanderpool, R.A.; Tsai, J.C.; Khan, M.A.; Nicholas,
K.M. J. Am.Chem.Soc. 1988, 110, 2004. (b) Silavwe, N.D.; Goldman, A.S.;
Ritter, R.; Tyler, D.R. Inorg. Chem. 1989, 28, 1231.

5. Lo, K. K. –W.; Chung, C, -K.; Lee, T. K. –M.; Lui, L. –K.; Tsang, K. H. –K.;
Zhu, N. Inorg. Chem. 2003, 42, 6886.

6. (a) Baldo, M.A.; O’Brien, D.F.; You, Y.; Shoustikov, A.; Sibley, S.;
Thompson, M.E.; Forrest, S.R. Nature, 1998, 395, 151. (b) Baldo, M.A.;
Lamansky, S.; Burrows, P.E.; Thompson, M.E.; Forrest, S.R. Appl. Phys.
Lett. 1999, 75, 4. (c) Thompson, M.E.; Burrows, P.E.; Forrest, S.R. Curr.
Opin. Solid State Mater.Sci. 1999, 4, 369. (d) Baldo, M.A.; Thompson, M.E.;
Forrest, S.R. Nature 2000, 403, 750. (e) Lamansky, S.; Djurovich, P.I. ;
Abdel-Razzaq, F.; Garon, S.; Murphy, D.L.; Thompson, M.E. J. Appl. Phys.
2002, 92, 1570. (f) Chen, F.C.; Yang, Y.; Thompson, M.E.; Kido, J. Appl.
Phys. Lett. 2002, 80, 2308. (g) Markham, J.P.J,; Lo, S.-C.; Magennis, S.W.;
Burn, P.L.; Samuel, I.D.W. Appl. Phys. Lett. 2002, 80, 2645. (h) Zhu, W.; Mo,
Y.; Yuan, M.; Yang, W.; Cao, Y. Appl. Phys. Lett. 2002, 80, 2045.

7. Lamansky, S.; Djurovich, P.; Murphy, D.; Abdel-Razzaq, F.; Lee, H.-E.;
Adachi, C.; Burrows, P. E.; Forrest, S. R.; Thompson, M. E. J. Am. Chem.
Soc. 2001, 123, 4304-4312.

8. Paulose, B.M. J.S.; Rayabarapu, D.K.; Duan, J.-P. Cheng, C.-H. Adv.
Mater. 2004, 16, 2003.

9. Tamayo, Arnold B.; Alleyne, Bert D.; Djurovich, Peter I.; Lamansky,
Sergey; Tsyba, Irina; Ho, Nam N.; Bau, Robert; Thompson, Mark E J. Am.
Chem. Soc. 2003, 125(24), 7377-7387.

75
10. Li, J.; Djurovich, P.I.; Alleyne, B.D.; Yousufuddin, M.; Ho, N.N. ; Thomas,
J.C.; Peters, J.C.; Bau, R.; Thompson, M.E. Inorg. Chem. 2005, 44, 1713-
1727.

11. Klapars, A.; Antilla, J. C.; Huang, X.; Buchwald, S. L. J. Am. Chem. Soc.,
2001, 123; 7727-7729.

12. (a) Nonoyama, M., Bull. Chem. Soc. Jpn., 1974, 47, 767. (b) Lamansky,
S.; Djurovich, P.I.; Murphy, D.; Abdel-Razaq, F.; Kwong, R.; Tsyba, I.; Bortz,
M.; Mui, B.; Bau.R.; Thompson, M.E. Inorg. Chem. 2001, 40, 1704-1711.

13. Sheldrick, G.M. SHELXTL, version 5.1.; Bruker Analytical X-ray System,
Inc.; Madison, WI, 1997.

14. Blessing, R.H. Acta Crystallogr. 1995, A51, 33.

15. (a) Gagne, R.R.; Koval, C.A.; Lisensky, G.C. Inorg. Chem. 1980, 19,
2854. (b) Sawyer, D.T.; Sokkowiak, A.; Roberts, J.L., Jr. Electrochemistry for
Chemists, 2
nd
ed.: John Wiley and Sons: New York, 1995; p 467.

16. (a) Demas, J.N.; Crosby, G.A. J. Phys. Chem. 1978, 82, 991. (b)
DePriest, J.; Zheng, G.Y.; Goswami, N.; Eichhorn, D.M.; Woods, C.; Rillema,
D.P. Inorg. Chem. 2000, 39, 1955.

17. Sajoto, T.; Djurovich, P.I.; Tamayo, A.; Thompson, M.E.; Temperature
Dependence of Blue Phosphorescent Cyclometalated Iridium(III) Complexes ;
manuscript in preparation, 2008.

18. Pavlik, J.W.; Connors, R.E.; Burns, D.S.; Kurzwell, E.M. J.Am. Chem.
Soc. 1993, 115, 7465.

19. (a) Forster, L.S. Coord. Chem. Rev. 2002, 227, 59. (b) Brennaman, M.K.;
Meyer, T.J.; Papanikolas, J.M. J. Phys. Chem. A. 2004, 108, 9938. (c) Wang,
X.-Y.; Del Guerzo, A.; Schmehl, R.H. J. Photochem. Photobiol. C. 2004, 5,
55.

20. Lumpkin, R.S.; Kober, E.M.; Worl, L.A.; Murtaza, Z.; Meyer, T.J. J. Phys.
Chem. 1990, 94, 239.

21. Nolan, S.P.; Hoff, C.D.; Stoutland, P.O. ; Newman, L.J.; Buchanan, J.M.;
Bergman, R.G.; Yang, G.K.; Peters, K.S. J. Am. Chem. Soc. 1987, 109,
3143.

22. Hitchcock; P.B.; Lappert, M.F.; Terreros, P.J. Organomet. Chem. 1982,
239, C26.

76
23. Holmes, R.; Forrest, S.R.; Sajoto, T.; Tamayo, A.; Djurovich, P.I.;
Thompson, M.E.; Brooks, J.; Tung, Y.-J.; D’Andrade, B.W.; Weaver, M.S.;
Kwong, R.C.; Kwong, R.C.; Brown, J.J. Appl. Phys. Lett. 2005, 87, 243507.

24. Sajoto, T.; Djurovich, P.I.; Tamayo, A.; Yousufudddin, M.; Bau, R.;
Thompson, M.E. Inorg. Chem. 2005, 44, 7992-8003.

25. (a) Gong, X.; Robinson, M.R.; Ostrowski, J.C.; Moses, D.; Bazan, G.C.;
Heeger, A.J.; Adv. Mater. 2002, 14, 581. (b) Ostrowski, J.C.; Robinson, M.R.;
Heeger, A.J.; Bazan, G.C. Chem. Commun. 2002, 7, 784. (c) Gong, X.;
Robinson, M.R.; Ostrowski, J.C.; Moses, D.; Bazan, G.C.; Heeger, A.J.; Liu,
M.S.; Jen, A.K. Adv. Mater. 2003, 15, 45. (d) Gong, X.; Robinson, M.R.;
Ostrowski, J.C.; Moses, D.; Bazan, G.C.; Heeger, A.J. Appl. Phys. Lett.
2005, 86, 171108. (e) Wu, F.; Su, H.; Shu, C.; Luo, L.; Diau, W.; Cheng, C.;
Duan, J.; Lee, G. J. Mater. Chem. 2005, 15, 1035. (f) Tsuboyama, A.;
Iwawaki, H.; Furugori, M.; Mukaide, T.; Kamatani, J.; Igawa, S.; Moriyama,
T.; Miura, S.; Takiguchi, T.; Okada, S.; Hoshino, M.; Ueno, K. J. Am. Chem.
Soc. 2003, 125, 12971.

77
Chapter 3. Heteroleptic Iridium (III) Complexes with Two
Chromophoric Cyclometalated Ligands and One High Energy
Ancillary Ligand: Synthesis, Characterization and Their
Applications in OLEDs

3.1. Introduction

One of the most significant research efforts related to organic light-
emitting diodes (OLEDs) is the development of phosphorescent metal
complexes displaying all three primary colors (red, green and blue) for full
color displays. Cyclometalated iridium (III) complexes have attracted a great
deal of attention in display applications due to their high luminescent
efficiencies and microsecond lifetimes. These cyclometalated iridium (III)
complexes exhibit emission colors range from blue to red depending on the
triplet energy of the cyclometalating ligands (C^N).
1
Our group has previously
reported the use of (C^N)
2
Ir(O^O) complexes as phosphorescent dopants in
OLEDs. Some of these bis-cyclometalated iridium complexes exhibit similar
emission properties as their tris-cyclometalated analogues. In addition to
employing different C^N ligands, our group has also achieved color tuning of
cyclometalated iridium complexes using a number of approaches including
modification of the prototypical pyridyl-based cyclometalated iridium
complexes. To achieve blue phosphorescence, one method focuses on
increasing the HOMO energy while keeping the LUMO energy relatively
unchanged. To achieve this goal, the addition of electron withdrawing groups
such as F atoms to the phenyl ring has been used.
2
For example, fac-

78
Ir(F
2
ppy)
3
has an emission energy 50 nm blue-shifted from that of fac-
Ir(ppy)
3
. Recently, we also reported an alternate approach to lower the
HOMO energy by using ancillary ligands to tune the HOMO energies of bis-
cyclometalated derivatives.
3
The emission energy can be significantly
increased by judicious choice of the ancillary ligand.
A new approach of color tuning cyclometalated iridium complexes is to
design heteroleptic complexes modified by two distinct cyclometalating
ligands (C^N). It would be interesting to investigate how iridium complexes
containing two chromophoric C^N ligands and one high energy ancillary
ligand will behave. The synthesis and characterization of heteroleptic
cyclometalated iridium (III) complexes containing two chromophoric
cyclometalating ligands and one high energy ancillary ligand are discussed in
this chapter.
The first part of this chapter discusses heteroleptic iridium (III)
complexes consisting two chromophoric cyclometalated ligands i.e.
phenylpyrazoles (ppz), diphenylamines (NPh
2
), carbazoles (cbz), and
fluorenylpyrazoles (flz) and one high energy ancillary ligand such as
phenylimidazoles (pmi) as shown in Figure 3.1. It is revealed that in these
systems that the ground and excited state properties of such heteroleptic
systems can be easily controlled by simple modification of chromophoric
cyclometalating ligands. Structures of various chromophoric cyclometalating
ligands (C^N) explored in this chapter are shown in Figure 3.2.

79
Ir
C
C
N
C
2
(C^N)
2
Ir(C^C)
“ High Energy
Ancillary
Ligands”
C^N should have a
lower triplet
energy than the
“ancillary ligand”
N
N
C
C
≈
“Chromophoric
Ligands”
N
N
Z
Z= H, NPh
2
, cbz, flz

Figure 3.1. Heteroleptic Iridium (III) Complexes with pmi as High Energy
Ancillary Ligand

Figure 3.2. Structures of Chromophoric Cyclometalating Ligands (C^N)
Used in the First Part of Chapter 3
Tris-cyclometalated Ir(III) complexes have been given significant
attention in the past years due to their photochemical applications.
Previously, we reported that fac-Ir(ppz)
3
displays deep-blue/violet

Ir
C
N
2
N
N
N
N
N
Ir
2
(ppz-mNPh
2
)
2
N
N
Ir
2
N
N
Ir
2
(flz)
2

(ppz)
2
N
N
N
Ir
2
(czpz)
2
N
N
N
Ir
2
(ppz-pNPh
2
)
2

80
phosphorescence (414 nm) at 77K, but is very weakly emissive at RT (Φ
PL
<
0.01) in fluid solution.
2
We have recently reported that the nature of possible
deactivation states in fac-Ir(ppz)
3
could be eliminated in two different ways
(discussed in Chapter 2).
4
The first involves replacement of the phenyl group
of the ppz ligand with a 9,9-dimethyl-2-fluorenyl group, i.e., fac-Ir(flz)
3
. Fac-
Ir(flz)
3
gives high photoluminescence efficiency at RT (Φ
PL
= 0.81) with λ
max
=
480 nm. The second approach involves utilizing ligands with a strong ligand
field strength i.e., N-heterocyclic carbene (NHC) ligands as the replacement
of the ppz ligand. The fac-Ir(pmb)
3
phosphoresce with λ
max
= 380 nm at RT
(Φ
PL
= 0.37). Although possible deactivating nonradiative (NR) states in
Ir(ppz)
3
had been eliminated, fac-Ir(flz)
3
and fac-Ir(pmb)
3
still do not display
the right blue color purity of phosphors. Fac-Ir(flz)
3
is in the green region
(CIE, x= 0.16, y= 0.50) whereas fac-Ir(pmb)
3
(CIE, x= 0.17, y= 0.04) are in
the near-UV region. Achieving purely blue-emitting phosphors is quite
challenging. The goal is to get the right blue color purity of phosphors (CIE,
x= 0.14, y= 0.14) with high quantum yield and high radiative rates.
In this chapter, a series of heteroleptics tris-cyclometalated Ir(III)
complexes have been synthesized and their photophysical properties have
been investigated. These heteroleptic Ir complexes contain three ligands of
two different types: two ligands serve as the chromophoric ligands and the
other one only serves as an ancillary ligand. The chromophoric ligand
dictates the emission color of the Ir(III) phosphors therefore should have a
lower triplet energy than the ancillary ligand. In the first part of this chapter,

81
the ancillary ligand used in these heteroleptic Ir(III) complexes is one with a
higher triplet energy than ppz, NPh
2
, cbz and flz cyclometalating ligands. (i.e.
phenyl-methyl-imidazole (pmi)).
The second part of this chapter discusses the synthesis and
characterization of meridional (mer) heteroleptic more reducible tris-
cyclometalated iridium (III) complexes with two chromophoric
fluorenylpyrazolyl cyclometalating ligands and one high energy more
reducible ancillary ligand (Figure 3.3).

“chromophoric
ligands”
N
N
Ir
2
L
X
(C^N)
2
Ir(L^X)
L^X: “ high energy, more
reducible ancillary
ligands”
N
N
N
CF
3
N
O
O
L
X
=
(C^N)
N
N
N

Figure 3.3. More Reducible Heteroleptics Iridium (III) Complexes

Heteroleptic more reducible tris-cyclometalated Ir(III) complexes can be
achieved by the incorporation of high energy, more reducible ancillary
ligands such as pyridylpyrazole, CF
3
-substituted pyridylpyrazolate and
picolinate ligands. Structures of these more reducible heteroleptic iridium (III)
complexes are shown in Figure 3.4.

82

N
N
Ir
N
N
2
N

N
N
Ir
N
N
2
N
CF
3

N
N
Ir
N
O
2
O

Figure 3.4. Structures of More Reducible Heteroleptic Iridium (III)
Complexes

Some OLEDs that have been fabricated with flz
2
Ir(pypz) or flz
2
Ir(pypzCF
3
) as
the phosphorescent dopants will also be discussed in this chapter.

3.2. Experimental

Synthesis of ligands: 1-Phenylpyrazole and 1-Phenylimidazole were
purchased from Aldrich and used without further purification. 1-phenyl-3-
methylimidazolium iodide salt was prepared by methylating 1-
phenylimidazole with excess methyl iodide in toluene. 9-Methyl-3-pyrazol-1-
yl-9H-carbazole (czpz) ligand was prepared by a modified Ullmann coupling
reaction between pyrazole and the 3-iodo-9-methyl-9H-carbazole in
anhydrous N,N-dimethylformamide using a CuI/1,10-phenanthroline catalyst
and Cs
2
CO
3
base as previously described.
5
ppz-mNPh
2
ligand and ppz-
pNPh
2
ligands were also prepared by a modified Ullmann coupling reaction
between pyrazole and the 4-bromo triphenylamine or 3-bromo
triphenylamine. flz ligand was prepared as described in Chapter 2.

83
Synthesis of (czpz)
2
Ir(μ-Cl)Ir(czpz)
2
:

A carbazolylpyrazolyl-based-Ir(III)-μ-
dichloro-bridged dimer was synthesized in a 50 ml round-bottomed flask that
was charged with iridium trichloride hydrate (0.800 g, 2.68 mmol), 9-Methyl-
3-pyrazol-1-yl-9H-carbazole (1.33 g, 5.38 mmol) and 25 ml of a 2-
ethoxyethanol-water-mixture (3:1). The reaction mixture was stirred and
heated with an oil bath at 120ºC for 24 hours under nitrogen and then
allowed to cool to ambient temperature. The solid was filtered and washed
with cold methanol (2x20 ml). It gave 1.764 g of (czpz)
2
Ir(μ-Cl)Ir(czpz)
2
(46%
yield) as grayish-white solid, which was used without further purification in
the next step to prepare the heteroleptic-Ir(III) complex.
Note that (ppz)
2
Ir(μ-Cl)Ir(ppz)
2
, (ppz-mNPh
2
)
2
Ir(μ-Cl)Ir(ppz-mNPh
2
)
2,
(ppz-
pNPh
2
)
2
Ir(μ-Cl)Ir(ppz-pNPh
2
)
2
were also synthesized using the same
procedures as the synthesis of (czpz)
2
Ir(μ-Cl)Ir(czpz)
2
.
Synthesis of mer-(czpz)
2
Ir(pmi): A 50 ml round-bottomed flask was
charged with silver(I) oxide (0.041 g, 0.177 mmol), 1-phenyl-3-methyl-
imidazolate iodide (0.042g, 0.147 mmol), (czpz)
2
Ir(μ-Cl)Ir(czpz)
2
(0.100 g,
0.069 mmol) and 25 ml of 1,2-dichloroethane. The reaction was stirred and
heated with an oil bath at 95ºC for 24 hours under nitrogen, while protected
from light with aluminum foil. The reaction mixture was cooled to ambient
temperature and concentrated under reduced pressure. Filtration through
celite, using dichloromethane as the eluent, was performed to remove the
silver(I) salts. It was further purified by flash column chromatography on silica
gel using dichloromethane as the eluent. Methanol was added onto the solid

84
and the solid was vacuum-filtered. The solid was washed with more
methanol and air-dried. It gave 0.015 g (26% yield) of mer-(czpz)
2
Ir(pmi) as
characterized by
1
H NMR (Figure 3.5).

Figure 3.5.
1
H NMR Spectra of mer-(czpz)
2
Ir(pmi)
Note that mer-(ppz)
2
Ir(pmi), mer-(ppz-mNPh
2
)
2
Ir(pmi), mer-(ppz-
pNPh
2
)
2
Ir(pmi), and mer-(flz)
2
Ir(pmi) were synthesized following the same
procedures as the synthesis of mer-(czpz)
2
Ir(pmi) described above.
ppm (t1)
6.50 7.00 7.50 8.00 8.50
0
5
1
0.76
0.87
0.77
0.84
0.87
0.82
2.98
2.08
1.02
1.89
2.91
4.06
2.92
mer-(czpz)
2
Ir(pmi)- Aromatic Region (360 MHz, DMSO-d)
N
N
N
Ir N
N
2
ppm (t1)
3.0 4.0 5.0 6.0 7.0 8.0
0
5
1
1
2
0.76
0.87
0.77
0.84
0.87
0.82
2.98
2.08
1.02
1.89
2.91
6.00
2.90
4.06
2.92
mer-(czpz)
2
Ir(pmi)- Full Region (360 MHz, DMSO-d)
N
N
N
Ir N
N
2

85
Synthesis of mer-(flz)
2
Ir(pypz): A 50 ml round-bottomed flask was charged
with (flz)
2
Ir(μ-Cl)Ir(flz)
2
(1.0 g), pyridylpyrazolate (0.243 g), potassium
carbonate (0.927 g), , and 25 ml of 2-ethoxyethanol. The reaction was stirred
and heated to reflux with an oil bath at 120ºC for 24 hours under nitrogen.
The brownish reaction mixture turned to orange then it turned to yellow. The
reaction mixture was cooled to ambient temperature. The reaction mixture
was transferred into 400 ml beaker. 200 ml of deionized water was added
into the beaker to dissolve potassium carbonate. The yellowish precipitates
were vacuum-filtered and the solid was washed with deionized water (2x50
ml), hexanes (2x100ml), and air-dried. It gave 1.087 g of mer-(flz)
2
Ir(pypz) as
characterized by
1
H NMR in Figure 3.6.
Synthesis of mer-(flz)
2
Ir(pypzCF
3
): A 100 ml round-bottomed flask was
charged with (flz)
2
Ir(μ-Cl)Ir(flz)
2
(3.0 g), pyridylpyrazolateCF
3
(1.08 g),
potassium carbonate (2.78 g), and 50 ml of 2-ethoxyethanol. The reaction
was stirred and heated to reflux with an oil bath at 120ºC for 24 hours under
nitrogen. The brownish reaction mixture turned to yellowish solution with
some precipitates floating in the reaction mixture. The reaction mixture was
cooled to ambient temperature. The reaction mixture was transferred into
400 ml beaker. 200 ml of deionized water was added into the beaker to
dissolve potassium carbonate. The yellowish precipitates were vacuum-
filtered and the solid was washed with hexanes (2x100ml) and air-dried. It
gave 3.555 g of mer-(flz)
2
Ir(pypzCF
3
) as characterized by
1
H NMR in Figure

86
3.7. 2 grams of mer-(flz)
2
Ir(pypzCF
3
) was sublimed before being used in the
chamber.

ppm (f1)
6.50 7.00 7.50 8.00
0
5
1
1

ppm (f1)
1.10 1.20 1.30 1.40 1.50 1.60 1.70 1.80 1.90
0
5
1
1
2
2
3

Figure 3.6.
1
H NMR of flz
2
Ir(pypz):
(a) Aromatic Region; (b) Aliphatic Region

87

ppm (f1)
6.50 7.00 7.50 8.00

ppm (f1)
1.50

Figure 3.7.
1
H NMR of flz
2
IrpypzCF
3
:
(a) Aromatic Region; (b) Aliphatic Region

Synthesis of mer-(flz)
2
Ir(pic1): A 50 ml round-bottomed flask was charged
with (flz)
2
Ir(μ-Cl)Ir(flz)
2
(1.0 g), picolinic acid (0.206 g), potassium carbonate
(0.927 g), and 25 ml of 2-ethoxyethanol. The reaction was stirred and heated
to reflux with an oil bath at 120ºC for 24 hours under nitrogen. The brownish

88
reaction mixture turned yellow. The reaction mixture was cooled to room
temperature. The reaction mixture was transferred into 400 ml beaker. 200
ml of deionized water was added into the beaker to dissolve potassium
carbonate. The yellow precipitates were vacuum-filtered and the solid was
washed with deionized water (2x50 ml), hexanes (2x100ml) and air-dried. It
gave 1.020 g of mer-(flz)
2
Ir(pic1) as characterized by
1
H NMR in Figure 3.8.

ppm (f1)
6.50 7.00 7.50 8.00 8.50
0
5
1

ppm (t1)
1.10 1.20 1.30 1.40 1.50 1.60 1.70 1.80 1.90
0
5
1
1
2

Figure 3.8.
1
H NMR of flz
2
Irpic1:
(a) Aromatic Region; (b) Aliphatic Region

89
Photophysics. The UV-visible spectra were recorded on a Hewlett-Packard
4853 diode array spectrophotometer. Steady state emission at room
temperature and 77K were determined using a Photon Technology
International QuantaMaster Model C-60SE spectrofluorimeter.
Phosphorescence lifetime measurements (>2μs) were performed on the
same fluorimeter equipped with a microsecond xenon flashlamp or on an IBH
Fluorocube lifetime instrument by a time correlated single photon counting
method using a 405 nm LED excitation source. The absolute quantum yields
in fluid solution have been measured using a more reliant method compared
to those of previously reported.
6
The quantum yield measurement
experiments were carried out in dilute 2-MeTHF solution. The sample was
placed in a 1 cm
2
quartz cell and degassed with N
2
. The photoluminescence
of 10wt% doped thin films for mer-(czpz)
2
Ir(pmi), flz
2
Ir(pypz), flz
2
Ir(pypzCF
3
),
and flz
2
Ir(pic1) in polystyrene have also been measured. 2 mg of the sample
along with 18 mg of polystyrene were dissolved in 1 ml of toluene; the
dissolved sample was spincoated on a 0.5x0.5cm
2
quartz substrate at 3000
rpm for 40 seconds. The quantum efficiencies were measured using a
calibrated Hamamatsu integrating sphere equipped with a xenon lamp with a
380 nm excitation wavelength and photonic multi-channel analyzer C10027.
Electrochemistry. Cyclic voltammetry and differential pulsed voltammetry
were performed using an EG&G potentiostat/galvanostat model 283.
Anhydrous DMF was used as solvent under inert atmosphere and 0.1 M
tetra-n-butylammonium hexafluorophosphate was used as supporting

90
electrolyte. A glassy carbon rod was used as the working electrode, a
platinum wire used as the counter electrode, and a silver wire was used as a
pseudo-reference electrode. The redox potentials are based on values
measured from differential pulsed voltammetry and are reported relative to
either a ferrocenium/ferrocene (Cp
2
Fe
+
/Cp
2
Fe) redox couple or a
decamethylferrocenium/decamethylferrocene (Me
5
Cp
2
Fe
+
/Me
5
Cp
2
Fe) redox
couple used as an internal reference,
7
while electrochemical reversibility was
determined using cyclic voltammetry.
NMR.
1
H and
13
C NMR spectra were recorded on a Bruker AM 250 MHz
instrument and chemical shifts were referenced to residual protiated solvent.
OLED Fabrication. N,N’-diphenyl-N,N’-bis(1-naphthyl)benzidine (NPD),
N,N’-dicarbazolyl-3,5-benzene (mCP), and 4,4'-bis(carbazol-9-yl)biphenyl
(CBP) were provided by Universal Display Corporation and used without
further purifications. 2, 9-dimethyl-4,7-diphenyl-1,10-phenanthroline (BCP)
was purchased from the Aldrich Chemical Company and was purified by
temperature gradient vacuum sublimation. Other materials such as
flz
2
Ir(pypz) and flz
2
Ir(pypzCF
3
) were also purified by sublimation before used
in the chamber. Prior to device fabrication, purchased 2mm wide striped pre-
patterned ITO substrates were cleaned by sonication in soap solution, rinsed
with deionized water and dried with N
2
. Then, photoresists were spincoated
onto each substrate. The substrates were then placed in the vacuum-oven
for 45 minutes. The photoresists were washed off by acetone and N
2
-dried.
They were then treated with UV ozone for 10 min. Organic layers were

91
deposited sequentially by thermal evaporation from resistively heated
tantalum boats at a rate of 2-2.5 Å s
-1
. After organic film deposition, the
chamber was vented and a shadow mask with a 2mm wide stripe was put on
the substrate perpendicular to the ITO stripes. Cathodes consisted of a 10 Å
thick layer of LiF followed by a 1000 Å thick of Al. The devices were tested in
air within 2 hours of fabrication. Device current-voltage and light-intensity
characteristics were measured using LabVIEW program by National
Instruments with a Keithley 2400 SourceMeter/2000 Multimeter coupled to a
Newport 1835-C Optical Meter, equipped with a UV-818 Si photocathode.
Only light emitting from the front face of the devices was collected and used
in subsequent calculation. The electroluminescence spectra were measured
on a PTI QuantaMasterTM Model C-60SE spectrofluorimeter, equipped with
a 928 PMT detector and corrected for detector response.

3.3. Results and Discussions

3.3.1. Synthesis

The synthesis of a series of meridional (mer) heteroleptic tris-
cyclometalated Ir (III) complexes with two chromophoric cyclometalating
ligands and one high energy ancillary ligand are reported in this chapter.
The first part of this chapter, the complexes synthesized are
composed of two chromophoric 1-phenylpyrazole (ppz), 9-Methyl-3-pyrazol-
1-yl-9H-carbazole (czpz), ppz-mNPh
2
or ppz-pNPh
2
cyclometalating ligands

92
and a single high energy ancillary ligand i.e. phenyl-methyl-imidazole (pmi)
(Figure 3.2). Reaction of the C^N-based dichloro-bridged dimers [(C^N)
2
Ir( μ-
Cl)]
2
with 2.5 eq. of the high energy ancillary ligand (i.e. pmi) in
dichloroethane to reflux at 95 ºC in the presence of excess silver (I) oxide,
selectively forms the meridional isomers (Scheme 3.1).

(N^C)
2
Ir
Cl
Ir(C^N)
2
Cl
+
(N^C)
2
Ir
Ag
2
O
Dichloroethane
reflux
N
N
CH
3
+
I
-
N
N

Scheme 3.1. Synthesis of Heteroleptic mer-Ir(III) Complexes

The second part of this chapter involves the synthesis of meridional
(mer) heteroleptic tris-cyclometalated Ir (III) complexes with two
chromophoric fluorenylpyrazolyl cyclometalating ligands and one high energy
more reducible ancillary ligand. The more reducible heteroleptic tris-
cyclometalated Ir (III) complexes can be achieved by the incorporation of
high energy, more reducible ancillary ligands such as pyridylpyrazole, CF
3
-
substituted pyridylpyrazolate and picolinate ligands (Figure 3.3). Reaction of
the flz-based dichloro-bridged dimers [(flz)
2
Ir( μ-Cl)]
2
with 2.5 eq. of the high
energy more reducible ancillary ligand in 2-ethoxyethanol at 120ºC in the
presence of K
2
CO
3
, selectively forms the meridional isomers (Scheme 3.2).

93

(flz)
2
Ir
Cl
Ir(flz)
2
Cl
+
(flz)
2
Ir
K
2
CO
3
2-ethoxyethanol
reflux
L
X
L
X
L
X
N
N
N
CF
3
N
O
O
N
N
N
=

Scheme 3.2. Synthesis of More Reducible flz-based Ir(III) Complexes

3.3.2. Photophysical Properties

The photophysical properties of meridional (mer) heteroleptic tris-
cyclometalated Ir (III) complexes with two chromophoric cyclometalating
(C^N) ligands and one high energy ancillary ligand are reported in this
chapter. The first heteroleptic Ir complexes synthesized in this chapter was
mer-Ir(ppz)
2
pmi. The mer-Ir(ppz)
2
pmi could isomerize into the facial isomer
(fac-Ir(ppz)
2
pmi). The emission characteristics of fac- and mer- Ir(ppz)
2
pmi
are very similar to fac- and mer- Ir(ppz)
3
. (Figure 3.9) The incorporation of
high energy ancillary ligands i.e. pmi on bis-cyclometalated Ir(ppz)
2
still did
not lead to emission at room temperature.

94

Figure 3.9. 77K and RT Emission Spectra of (a) fac- and mer-
(ppz)
2
Irpmi; (b) Photophysical Properties of fac- and mer-Ir(ppz)
3

2

It has been demonstrated that by simple substitution or modification of the
ppz chromophoric ligands with carbazolyl, diphenylamino, or fluorenyl-based
chromophoric ligands could lead room temperature emission. 77K and RT
emission spectra of heteroleptic mer-Ir (III) complexes are shown in Figure
3.10 and Figure 3.11.

Figure 3.10. 77K Emission Spectra of Heteroleptic mer-Ir(III) Complexes

400 450 500 550 600 650
0.0
0.2
0.4
0.6
0.8
1.0

Normalized Intensity
Wavelength (nm)
fac-Ir(ppz)
2
pmi
mer-Ir(ppz)
2
pmi

400 450 500 550 600 650
0.0
0.2
0.4
0.6
0.8
1.0

Normalized Intensity
Wavelength (nm)
mer-(czpz
2
-Ir-pmi)
mer-[(ppz-mNPh
2
)
2
-Ir-pmi]
mer-[(ppz-pNPh
2
)
2
-Ir-pmi]
mer-(flz)
2
-Ir-pmi
N
N
Ir N
N
2
N
N
Ir
3
fac-Ir(ppz)
3
N
N
Ir
3
fac-Ir(ppz)
3

95

Figure 3.11. RT Emission Spectra of Heteroleptic mer-Ir(III) Complexes

9-Methyl-3-pyrazol-1-yl-9H-carbazole (czpz) is chosen as the chromophoric
ligand, one is because it has a high triplet energy and second is because
carbazole derived molecules are commonly used in OLED devices. The
ancillary ligands used in these heteroleptic Ir(III) complexes are those with
higher energy than the 9-Methyl-3-pyrazol-1-yl-9H-carbazole ligand, i.e.,
phenyl-pyrazole (ppz), phenyl-methyl-imidazole (pmi) and phenyl-methyl-
benzimidazole (pmb). The 77K photophysics of all three complexes indicate
that the emission comes from the carbazolylpyrazolyl moiety (Figure 3.12).
400 450 500 550 600
0.0
0.2
0.4
0.6
0.8
1.0
1.2

Normalized Intensity
Wavelength (nm)
(czpz)
2
-Ir-pmi
(ppz-mNPh
2
)
2
-Ir-pmi
(ppz-pNPh
2
)
2
-Ir-pmi
(flz)
2
-Ir-pmi

96

400 450 500 550 600
0.0
0.2
0.4
0.6
0.8
1.0

Normalized Intensity
Wavelength (nm)
mer-(czpz)
2
Ir(ppz) [ λ
max
= 439 nm]
mer-(czpz)
2
Ir(pmi) [ λ
max
= 443 nm]
mer-(czpz)
2
Ir(pmb)[ λ
max
= 447 nm]

Figure 3.12. 77K Photophysics of Heteroleptic Carbazolyl Ir Complexes
in 2-MeTHF

The lowest excited state property of the heteroleptic complexes are
governed by the nature of the carbazolylpyrazolyl-based ligand. Tuning the
energy gap of the heteroleptic Ir(III) metal complexes were systematically
achieved with incorporation of different high energy ancillary ligands. Higher
energy ancillary ligand slightly increases the emission energy achieving blue
phosphorescence.

N
N
N
Ir
N
N
2
N
N
N
Ir N
N
2
N
N
N
Ir N
N
2

97
The mer-(czpz)
2
Ir(pmi) displays luminescence both in fluid solution
and as a thin film at 298K. It emits blue at RT in fluid solution and in 10%
polystyrene film with λ
max
= 448 nm (Figure 3.13).

Figure 3.13. Absorption and Emission Spectra of mer-(czpz)
2
Ir(pmi)

The CIE coordinates of mer-(czpz)
2
Ir(pmi): x= 0.15, y= 0.13, shows a
big improvement in terms of blue color purity, compared to that of fac-Ir(flz)
3

(Figure 3.14).

Figure 3.14. CIE Coordinates of mer-(czpz)
2
Ir(pmi)
mer-(czpz)
2
Ir(pmi)
N
N
N
Ir N
N
2
CIE Coordinates of
mer-(czpz)
2
Ir(pmi)
0
0.1
0.2
0.3
0.4
0.5
0.6
0.7
0.8
0.9
0 0.2 0.4 0.6 0.8
X
Y
520
560
600
480
CIE: x= 0.15, y= 0.13
flzIr (0.16, 0.50)
(0.15, 0.13)
N
N
Ir
3
N
N
Ir
3
Ir(pmi)
3
Ir(pmb)
3
CIE coords
CRT coords.
white (r=g=b)
mer-(czpz)
2
Ir(pmi)
flzIr
CIE coords
CRT coords.
white (r=g=b)
mer-(czpz)
2
Ir(pmi)
flzIr
N
N
Ir
3
Ir(flz)
3
= flzIr
(0.17, 0.05) (0.17, 0.04) (0.16, 0.50)
250 300 350 400 450 500 550 600 650
0
10000
20000
30000
40000
50000
60000
70000
80000

Absorbance
Wavelength (nm)
Molar Absorptivities (M
-1
cm
-1
)
0.0
0.2
0.4
0.6
0.8
1.0
77K
RT
10% in PS
Normalized Intensity

98
Among the heteroleptic meridional Ir (III) complexes shown in Figure
3.2., (flz)
2
Ir(pmi) is the only one whose quantum efficiency at room
temperature is quite high ( Ф
RT
= 0.31), however there is still no reduction
observed in the range of solvent window. Following this observation, a series
of more reducible flz-based Ir (III) complexes have been synthesized by the
incorporation of high triplet energy, more reducible ancillary ligand i.e.
pyridyl-pyrazolate, pyridyl pyrazolate trifluoromethyl, and picolinic acid and
their electrochemical, spectroscopic and electroluminescent properties
examined. The photophysical properties of flz
2
Ir(pypz) and flz
2
Ir(pypzCF
3
)
are shown in Figure 3.15 and Figure 3.16. Their photophysical properties
are similar to the parent compound, Ir(flz)
3
.They have more ligand centered
characteristics; these shown in their structured emissions. However, they
both are not as efficient emitters as Ir(flz)
3
.The comparison of emission
properties of flz
2
Ir(pypzCF
3
) vs. Ir(flz)
3
are shown in Figure 3.17. The
photophysical properties of flz
2
Ir(pic1) are shown in Figure 3.18.

Figure 3.15. The Photophysical Properties of flz
2
Ir(pypz)
300 350 400 450 500 550 600 650 700
0.0
0.2
0.4
0.6
0.8
1.0

Normalized Intensity
Wavelength (nm)
Absorption
77K Emission
RT Emission
10% in PS

99

Figure 3.16. The Photophysical Properties of flz
2
Ir(pypzCF
3
)

Figure 3.17. The Emission Properties of flz
2
Ir(pypzCF
3
) vs. Ir(flz)
3

300 350 400 450 500 550 600 650 700
0.0
0.2
0.4
0.6
0.8
1.0

Normalized Intensity
Wavelength (nm)
Absorption
77K Emission
RT Emission
10% in PS

450 500 550 600 650
0.0
0.2
0.4
0.6
0.8
1.0

Normalized Intensity
Wavelength (nm)
flz
2
-Ir-pypzCF
3
at 77K
flz
2
-Ir-pypzCF
3
at RT
Ir(flz)
3
at 77K
Ir(flz)
3
at RT
Emission Spectra in 2-MeTHF

100

Figure 3.18. The Photophysical Properties of flz
2
Ir(pic1)

3.3.3. Electrochemical Properties

The electrochemistry of heteroleptic flz-based tris-cyclometalated Ir
(III) complexes was examined. The portion of the complexes that control the
reduction potentials is the non-chromophoric ancillary ligand. Since the high
energy ancillary ligand, such as pmi incorporated in the complexes, has high
reduction potentials, no reduction is observed for (flz)
2
Ir(pmi); it is more
difficult to reduce than (flz)
2
Ir(acac) and Ir(flz)
3
, but it is easier to oxidize.
Electrochemical properties of flz-based Ir (III) complexes such as flz
2
Ir(acac),
flz
2
Ir(pmi) and Ir(flz)
3
are shown in Figure 3.19. The next challenge is how
we can tune the reduction potentials of these flz-based Ir (III) complexes.

300 400 500 600 700
0
10000
20000
30000
40000
50000

Absorption
Wavelength (nm)
Molar Absorptivity (M
-1
cm
-1
)
0.0
0.2
0.4
0.6
0.8
1.0
77K Emission
RT Emission
10% in PS
Normalized Intensity

101

Figure 3.19. Electrochemical Properties of flz-based Ir(III) Complexes

The electrochemical properties of these Ir complexes could be easily
tuned by various high triplet energy, more reducible ancillary ligand. The
HOMO and LUMO energies in the complexes can be independently altered
by simple ligand design. (flz)
2
Ir(pypz) could be easier to reduce with a
difference of 0.5V from reduction of Ir(flz)
3
, while make the HOMO level
0.27V deeper. The electrochemical properties of more reducible flz-based
Ir(III) complexes are shown in Figure 3.20.

-5 -4 -3 -2 -1 0 1
-300
-200
-100
0
100
200
300

I (μA)
Volts (vs Fc
+
/Fc)
fac-Ir(flz)
3
fac-Ir(flz)
3
, DPV
(flz)
2
Ir(pmi)
(flz)
2
Ir(acac)
N
N
Ir
2
N
N
N
N
Ir
2
O
O
N
N
Ir
3

102

Figure 3.20. Electrochemical Properties of More Reducible flz-based
Ir(III) Complexes

3.3.4. OLED Studies

OLED devices have been made and characterized using the
synthesized more reducible heteroleptic flz-based Ir (III) complexes i.e.
(flz)
2
Ir(pypz) and flz
2
Ir(pypzCF
3
) as the emissive material.
The first monochrome (flz)
2
Ir(pypz)-doped mCP devices have been
fabricated with a device structure of ITO/ NPD(400Å)/ (flz)
2
Ir(pypz):mCP (8%,
250 Å)/ BCP(400 Å)/ LiF(10 Å)/ Al (1100 Å). This monochrome device turns
on at a low voltage of about 3V and the electroluminescence comes from
(flz)
2
Ir(pypz) and NPD with a maximum external quantum efficiency of 1.5 %
and a maximum brightness of about 4,000 Cd/m
2
(Figure 3.21). Although
-3.0 -2.5 -2.0 -1.5 -1.0 -0.5 0.0 0.5 1.0

Current (a.u.)
Volts vs. Fc/Fc
+
flz
2
IrpypzCF
3
flz
2
Irpypz
flz
2
Irpic1
N
N
Ir
2
N
N
N
CF
3
N
N
Ir
2
N
N
N
N
N
Ir
2
N
O
O

103
flz
2
Ir(pypz) is more reducible than Ir(flz)
3
, the electron is still not trapped in
the emissive layer. Some recombination also occurs on the NPD layer. A
blocking layer i.e. Ir(ppz)
3
may solve this problem.

Figure 3.21. The Performance of flz
2
Ir(pypz)-doped mCP Device
The electroluminescence (EL) of (flz)
2
Ir(pypz)-doped mCP device shows that
the device is voltage-dependent. The higher the voltage is, the more
recombination occurs on NPD (Figure 3.22).

Figure 3.22. The EL Spectra of flz2Ir(pypz)-doped mCP Device at
Various Voltages (7-12V)
400 500 600 700 800
0.0
0.2
0.4
0.6
0.8
1.0
1E-4 1E-3 0.01 0.1 1 10 100
1E-3
0.01
0.1
1
110
1E-3
0.01
0.1
1
10
100
1000
110
1E-7
1E-6
1E-5
1E-4
1E-3
0.01
0.1
1
10
100

Normalized Intensity
Wavelength (nm)
EL

Q.E. (%)
Current Density (mA/cm
2
)
Q.E. max= 1.5 %

Brightness (Cd/m
2
)
Voltage (V)

Current Density (mA/cm
2
)
Voltage (V)
400 500 600 700 800
0.0
0.2
0.4
0.6
0.8
1.0

Normalized Intensity
Wavelength (nm)
7V
8V
9V
10V
11V
12V

104
Adding 100 Å of a blocking layer i.e. fac-Irppz
3
between the NPD and
the emissive layer in a device structure of ITO/ NPD(400Å)/ Ir(ppz)
3
(100 Å)/
(flz)
2
Ir(pypz):mCP (8%, 250 Å)/ BCP(400 Å)/ LiF(10 Å)/ Al (1100 Å) avoided
the recombination from occurring on the NPD layer. However, the device
performance is worse in terms of external quantum efficiency and brightness
compared to the device structure without an electron blocking layer. The Q.E.
decreases from 1.5 % to 0.8%; the brightness decreases from 4000 to 2000
Cd/m
2
(Figure 3.23).

Figure 3.23. The Performance of flz
2
Ir(pypz)-doped mCP Device with
fac-Ir(ppz)
3
as an Electron Blocking Layer
400 500 600 700 800
0.0
0.2
0.4
0.6
0.8
1.0
0.1 1 10 100
1E-3
0.01
0.1
1
110
1E-3
0.01
0.1
1
10
100
1000
110
1E-7
1E-6
1E-5
1E-4
1E-3
0.01
0.1
1
10
100

Normalized Intensity
Wavelength (nm)
EL

Q.E. (%)
Current Density (mA/cm
2
)
Q.E. max= 0.8 %

Brightness (Cd/m
2
)
Voltage (V)

Current Density (mA/cm
2
)
Voltage (V)

105
From the EL spectra, we can see that there is no NPD emission. The
devices, however, are voltage-dependent. The higher the voltage is, the first
vibronic peak decreases (Figure 3.24).

Figure 3.24. The EL Spectra of flz
2
Ir(pypz)-doped mCP Device with fac-
Ir(ppz)
3
as an Electron Blocking Layer at Various Voltages (7-12V)

Analogous device structure, but with mCP as a blocking layer, has
also been fabricated. The device performance of (flz)
2
Ir(pypz)-doped mCP
device with mCP as an electron blocking layer resulted in poorer
performance. Although the Q.E. is about 1.3%, the electroluminescence
shows more NPD emission than the dopant emission (Figure 3.25).

Figure 3.25. The Performance of flz
2
Ir(pypz)-doped mCP Device with
mCP as an Electron Blocking Layer
400 500 600 700 800
0.0
0.2
0.4
0.6
0.8
1.0

Normalized Intensity
Wavelength (nm)
7V
8V
9V
10V
11V
12V
400 500 600 700 800
0.0
0.2
0.4
0.6
0.8
1.0
0.1 1 10 100
1E-3
0.01
0.1
1
110
1E-3
0.01
0.1
1
10
100
1000
110
1E-7
1E-6
1E-5
1E-4
1E-3
0.01
0.1
1
10
100

Normalized Intensity
Wavelength (nm)
EL

Q.E. (%)
Current Density (mA/cm
2
)
Q.E. max= 1.3 %

Brightness (Cd/m
2
)
Voltage (V)

Current Density (mA/cm
2
)
Voltage (V)

106
In addition, monochrome (flz)
2
Ir(pypzCF
3
)-doped mCP devices have
also been fabricated with a device structure of ITO/ NPD(400Å)/
(flz)
2
Ir(pypzCF
3
):mCP (8%, 250 Å)/ BCP(400 Å)/ LiF(10 Å)/ Al (1100 Å). This
monochrome device turns on at a low voltage of about 3V and the
electroluminescence comes from (flz)
2
Ir(pypzCF
3
) and NPD with a maximum
external quantum efficiency of 0.695 % and a maximum brightness of about
200 Cd/m
2
(Figure 3.26). Although flz
2
Ir(pypzCF
3
) is also more reducible
than Ir(flz)
3
, the electron is still not completely trapped in the emissive layer.
Some recombination also occurs on the NPD layer. A blocking layer i.e.
Ir(ppz)
3
may solve this problem.

Figure 3.26. The Performance of flz
2
Ir(pypzCF
3
)-doped mCP Device
By adding 100 Å of an electron blocking layer i.e. fac-Irppz
3
between
the NPD and the emissive layer in a device structure of ITO/ NPD(400Å)/
Ir(ppz)
3
(100 Å)/ (flz)
2
Ir(pypzCF
3
):mCP (8%, 250 Å)/ BCP(400 Å)/ LiF(10 Å)/
Al (1100 Å), the EL spectra does not show any NPD emission. However, the
400 450 500 550 600 650
0.0
0.2
0.4
0.6
0.8
1.0
110 100
1E-4
1E-3
0.01
0.1
1
0.1 1 10
1E-4
1E-3
0.01
0.1
1
10
100
0.1 1 10
1E-3
0.01
0.1
1
10
100
1000

Normalized Intensity
Wavelength (nm)

Q.E. (%)
Current Density (mA/cm
2
)
Q.E. max = 0.695%

Current Density (mA/ cm
2
)
Voltage (V)

Brightness (Cd/m
2
)
Voltage (V)

107
device performance in terms of Q.E., turn-on voltage, and brightness (Figure
3.27) is similar to the one with no electron blocking layer. In comparison to
Ir(flz)
3
-mCP device (Q.E.= 6.35%), Ir(flz)
2
Ir(pypzCF
3
)-mCP devices have a
relatively low Q.E.

Figure 3.27. The Performance of flz
2
Ir(pypzCF
3
)-doped mCP Device with
fac-Ir(ppz)
3
as an Electron Blocking Layer
The (flz)
2
Ir(pypzCF
3
)-mCP devices with fac-Ir(ppz)
3
as a blocking layer
are voltage-dependent. As the voltage increases, the green emission part is
more dominant (Figure 3.28).

Figure 3.28. The EL Spectra of flz
2
Ir(pypzCF
3
)-doped mCP Device with
fac-Ir(ppz)
3
as an Electron Blocking Layer

400 500 600 700
0.0
0.2
0.4
0.6
0.8
1.0
1E-3 0.01 0.1 1 10 100 1000
1E-3
0.01
0.1
1
0.1 1 10
1E-7
1E-6
1E-5
1E-4
1E-3
0.01
0.1
1
10
100
1000
110
1E-3
0.01
0.1
1
10
100
1000

Normalized Intensity
Wavelength (nm)
8V

Q.E. (%)
Current Density (mA/cm
2
)
Q.E. max= 0.654%

Current Density (mA/cm
2
)
Voltage (V)

Brightness (Cd/m
2
)
Voltage (V)
Turn-On 3.7V
300 400 500 600 700
0.0
0.2
0.4
0.6
0.8
1.0

Normalized Intensity
Wavelength (nm)
7V
8V
9V
10V
11V
12V
13V
14V
ITO/ NPD (400A)/ Ir(ppz)
3
(100A)/ flz
2
IrpypzCF
3
: mCP (8%, 250A)/ BCP (400A)/ LiF (10A)/ Al (1100A)

108
Analogous (flz)
2
Ir(pypzCF
3
)-doped devices with CBP as a host
material have also been fabricated with a device structure of ITO/
NPD(400Å)/ (flz)
2
Ir(pypzCF
3
): CBP (8%, 250 Å)/ BCP(400 Å)/ LiF(10 Å)/ Al
(1100 Å). According to the EL spectra, there is only NPD emission, therefore
the recombination only occurs on NPD layer. The device performance of
(flz)
2
Ir(pypzCF
3
)-doped CBP device is shown in Figure 3.29.

Figure 3.29. The Performance of flz
2
Ir(pypzCF
3
)-doped CBP Device

Adding 100 Å of mCP as an electron blocking layer in the
(flz)
2
Ir(pypzCF
3
)-doped mCP device could not improve the device
performance. The NPD emission is still more dominant than the dopant
emission (Figure 3.30). Thus, mCP is not a good electron blocker for this
CBP doped device.
400 450 500 550 600 650 700
0.0
0.2
0.4
0.6
0.8
1.0
1E-3 0.01 0.1 1 10 100
0.01
0.1
1
110
1E-6
1E-5
1E-4
1E-3
0.01
0.1
1
10
100
1000
0.1 1 10
1E-4
1E-3
0.01
0.1
1
10
100
1000
10000

Normalized Intensity
Wavelength (nm)
EL

Q.E. (%)
Current Density (mA/cm
2
)
Q.E. max= 0.7 %

Current Density (mA/cm
2
)
Voltage (V)

Brightness (Cd/m
2
)
Voltage (V)

109

Figure 3.30. The Performance of flz
2
Ir(pypzCF
3
)-doped CBP Device with
mCP as an Electron Blocking Layer
Analogous device structure with 100 Å of Ir(ppz)
2
acac as an electron
blocking layer in the (flz)
2
Ir(pypzCF
3
)-doped mCP device has also been
fabricated. The EL spectra shows the green emission from Ir(ppz)
2
(acac)
(Figure 3.31). Thus, the recombination occurs on the Ir(ppz)
2
(acac) layer.

Figure 3.31. The Performance of flz
2
Ir(pypzCF
3
)-doped CBP Device with
Ir(ppz)
2
acac as an Electron Blocking Layer
400 500 600 700 800
0.0
0.2
0.4
0.6
0.8
1.0
0.01 0.1 1 10 100
1E-3
0.01
0.1
1
110
1E-3
0.01
0.1
1
10
100
1000
0.1 1 10
1E-6
1E-5
1E-4
1E-3
0.01
0.1
1
10
100

Normalized Intensity
Wavelength (nm)
EL

Q.E. (%)
Current Density (mA/cm
2
)
Q.E. max= 0.7%

Brightness (Cd/m
2
)
Voltage (V)

Current Density (mA/cm
2
)
Voltage (V)
400 500 600 700 800
0.0
0.2
0.4
0.6
0.8
1.0
0.1 1 10 100
1E-3
0.01
0.1
1
110
1E-3
0.01
0.1
1
10
100
0.1 1 10
1E-4
1E-3
0.01
0.1
1
10
100

Normalized Intensity
Wavelength (nm)
EL

Q.E. (%)
Current Density (mA/cm
2
)
Q.E. max= 0.27%

Brightness (Cd/m
2
)
Voltage (V)

Current Density (mA/cm
2
)
Voltage (V)

110
The devices with Ir(ppz)
2
acac as a blocking layer described above are
voltage dependent. The higher the voltage is, the more recombination can
occur on the NPD layer (Figure 3.32). Because of this result, the
Ir(ppz)
2
(acac) is also not an ideal blocking layer.

Figure 3.32. The EL Spectra of (flz)
2
Ir(pypzCF
3
)-doped CBP Device with
Ir(ppz)
2
acac as an Electron Blocking Layer

3.4. Conclusion

Heteroleptic Ir(III) complexes could be easily prepared. Incorporation
of high energy triplet energy ancillary ligands (i.e. pmi) on ppz
2
Ir(III)
derivatives gives emission at RT (i.e. Φ of flz
2
Ir(pmi) = 0.31). Three new
reducible flz
2
Ir(III) complexes could be achieved by incorporating high triplet
energy, more reducible ancillary ligands (L^Xs), i.e pypz, pypzCF
3
, pic1. The
flz
2
Ir(L^X) are redox active: the oxidation is localized on flz
2
moiety while the
reduction is localized on the L^X moiety. The electrochemical properties and
quantum yields of flz-based more reducible Ir(III) Complexes are shown in
400 500 600 700 800
0.0
0.2
0.4
0.6
0.8
1.0

Normalized Intensity
Wavelength (nm)
7V
8V
9V
10V
11V
12V

111
Table 3.1. OLED Performance of flz
2
Ir(pypz) and flz
2
Ir(pypzCF
3
) as dopants
are not as efficient as Ir(flz)
3
.
Table 3.1. Electrochemical Properties and Quantum Yields of flz-based
Ir (III) Complexes

In comparison to Ir(flz)
3
, all more reducible heteroleptic flz-based Ir(III)
complexes have low Φ
RT
. The low Ф
RT
hypothesis is shown in Figure 3.33
below. The LUMO of flz
2
Ir(pmi) complex lies on carbene (pmi) moiety while
the LUMO of flz2Ir(pic1) complex lies on the reducible ancillary ligand (pic1)
moiety. Since the LUMO of pic1 is lower than T
1
, it can undergo charge
transfer from the flz ligand to the pic1 ligand leading to no emission. On the
other hand, the LUMO of carbene (pmi) is higher than T
1
, so there is too
large of a barrier for charge transfer to occur in the case of flz
2
Irpmi. This
results in a higher Φ
RT
of flz
2
Irpmi compared to that of flz
2
Ir(pic1).

0.52 -2.41 flz
2
pic1
0.58 -2.61 flz
2
pypzCF
3
0.50 -2.70 flz
2
pypz
0.31 -3.10 Ir(flz)
3
E° oxidation (V) E° reduction (V) Ir-complexes
0.52 -2.41 flz
2
pic1
0.58 -2.61 flz
2
pypzCF
3
0.50 -2.70 flz
2
pypz
0.31 -3.10 Ir(flz)
3
E° oxidation (V) E° reduction (V) Ir-complexes
0.17
0.19
0.13
0.81
Φ
RT
0.17
0.19
0.13
0.81
Φ
RT

112

Figure 3.33. The Low Ф
RT
Hypothesis for More Reducible flz-based Ir(III)
Complexes
N
N
Ir
3
N
N
Ir
2
N
O
O
HOMO
LUMO
CS
LUMO
reducible
ancillary ligand
LUMO
carbene
(charge transfer state)
3
LC
3
LC
L^X= flz
L^X= pmi
L^X = pic1
T1
No Emission
LUMO HOMO
N
N
Ir
2
N
N
Φ
RT
= 0.17
CS
hυ
LUMO HOMO
Φ
RT
= 0.31
Φ
RT
= 0.81
(flz)
2
Irpic1
(flz)
2
Ir(pmi)
Ir(flz)
3

113
Chapter 3 References

1. Lamansky, S.; Djurovich, P.I.; Murphy, D.; Abdel-Razaq, F.; Kwong, R.;
Tsyba, I.; Bortz, M.; Mui, B.; Bau.R.; Thompson, M.E. Inorg. Chem. 2001, 40,
1704-1711.

2. Tamayo, Arnold B.; Alleyne, Bert D.; Djurovich, Peter I.; Lamansky,
Sergey; Tsyba, Irina; Ho, Nam N.; Bau, Robert; Thompson, Mark E J. Am.
Chem. Soc. 2003, 125(24), 7377-7387.

3. Li, J.; Djurovich, P.I.; Alleyne, B.D.; Yousufuddin, M.; Ho, N.N. ; Thomas,
J.C.; Peters, J.C.; Bau, R.; Thompson, M.E. Inorg. Chem. 2005, 44, 1713-
1727.

4. Sajoto, T.; Djurovich, P.I.; Tamayo, A.; Yousufudddin, M.; Bau, R.;
Thompson, M.E. Inorg. Chem. 2005, 44, 7992-8003.

5. Klapars, A.; Antilla, J. C.; Huang, X.; Buchwald, S. L. J. Am. Chem. Soc.,
2001, 123; 7727-7729.

6. (a) Demas, J.N.; Crosby, G.A. J. Phys. Chem. 1978, 82, 991. (b) DePriest,
J.; Zheng, G.Y.; Goswami, N.; Eichhorn, D.M.; Woods, C.; Rillema, D.P.
Inorg. Chem. 2000, 39, 1955.

7. (a) Gagne, R.R.; Koval, C.A.; Lisensky, G.C. Inorg. Chem. 1980, 19, 2854.
(b) Sawyer, D.T.; Sokkowiak, A.; Roberts, J.L., Jr. Electrochemistry for
Chemists, 2
nd
ed.: John Wiley and Sons: New York, 1995; p 467.

114
Chapter 4. Broad Band Phosphorescent Tris-cyclometalated
Iridium (III) Benzoquinoline Complex: Synthesis,
Characterization and Their Applications in White OLEDs

4.1. Introduction

Luminescent cyclometalated Ir(III) complexes have been given
significant attention due to their applications in phosphorescent organic light
emitting devices (OLEDs).
1,2
For display applications, narrow band
luminescent materials are desirable to achieve good color purity. However,
for general lighting applications, broad band luminescent materials would be
beneficial--especially to simplify device architectures where white light can be
produced by using only two emitters, one blue and one broad band (yellow-
red).
In general, featureless broad band luminescence comes from
complexes that have more metal to ligand charge transfer (MLCT)
characteristics than ligand-centered (LC) characteristics. Featureless broad
band emission indicates the presence of a distorted excited state in the
complexes. There are only a few examples of broad band tris-cyclometalated
Ir(III) complexes that have been reported thus far.
3

In this chapter, tris-cyclometalated iridium (III) benzoquinoline
complexes, mer-Ir(bzq)
3
and fac-Ir(bzq)
3
,

have been synthesized and their
photophysical properties have been fully investigated. Some white
phosphorescent OLEDs with mer-Ir(bzq)
3
as the broad band emitter and fac-
flzIr, fac-flimIr (in Chapter 2) or DTIC as the blue-green emitter have also

115
been fabricated and their performances are discussed in this chapter. These
devices emit white light with maximum quantum efficiency of ~12%.
Chemical structure of Ir(bzq)
3
is shown in Figure 4.1.

Figure 4.1. Chemical Structure of Ir(bzq)
3
; mer- and fac- isomers

4.2. Experimental

Reagents and Ligands. Solvents and reagents were purchased from
Aldrich, Matrix Scientific, and EM Science, and were used without further
purification. N,N-dimethylformamide (EM Science, anhydrous – 99.8%) and
tetra-n-butylammonium hexafluorophosphate – (TBAH) (Fluka,
electrochemistry grade) were used for electrochemical measurements.
IrCl
3
·nH
2
O was purchased from Next Chimica. 7,8-benzoquinolines were
purchased from Aldrich Chemical Co. and used as received. Ir(acac)
3
was
purchased from Next Chimica and used as without further purification.
Synthesis of (bzq)
2
Ir(μ-Cl)Ir(bzq)
2
:

A 250 ml round-bottomed flask was
charged with iridium trichloride hydrate (2.53 g, 7.175 mmol), 7,8-
benzoquinoline (2.7 g, 15.065 mmol) and 125 ml of a 2-ethoxyethanol-water-
Ir
N
N
C
C
C N
mer- Ir(C^N)
3
N
Ir
3
Ir
N
C
C
C
N N
fac- Ir(C^N)
3

116
mixture (3:1). The reaction mixture was stirred and heated with an oil bath at
110ºC for 4 hours under nitrogen. The reaction mixture turned color from
dark green to brown to orange solution with dark yellow precipitates within 4
hours of refluxing. After 4 hours refluxing, the reaction mixture was allowed to
cool to ambient temperature. Deionized water (50ml) was added onto the
reaction mixture. The dark yellow orange solid was vacuum-filtered and
washed with methanol (3x50 ml) and hexanes (3x50ml). It gave 3.548 g of
(bzq)
2
Ir(μ-Cl)Ir(bzq)
2
(85% yield) as dark yellow-orange solid, which was
used without further purification in the next step to prepare the tris-Ir(III)
benzoquinoline complex, mer-Ir(bzq)
3
.
Synthesis of mer-Ir(bzq)
3
: A 250 ml round-bottomed flask was charged with
(bzq)
2
Ir(μ-Cl)Ir(bzq)
2
(1.2 g, 1.031 mmol), 7,8-benzoquinoline (0.388 g, 2.165
mmol), excess potassium carbonate (1.2 g, 8.682 mmol) and 125 ml of 2-
ethoxyethanol. The reaction was stirred and heated with an oil bath at 160ºC
for 24 hours under nitrogen. The reaction mixture was cooled to ambient
temperature and deionized water (100 ml) was added to the reaction mixture
to dissolve excess K
2
CO
3
. The orange solid was vacuum-filtered, washed
with methanol (3x15ml) and hexanes (3x15ml), and air-dried. It was further
purified by column chromatography on silica gel using dichloromethane as
the eluent. Orange band fractions were collected and concentrated under
reduced pressure. Some hexanes were added onto the solid and the orange
solid was vacuum-filtered and air-dried. It gave 0.330 g (44% yield) of mer-

117
Ir(bzq)
3
.
1
H NMR in CDCl
3
was obtained and shown in Figure 4.2.
Crystallographic data for mer-Ir(bzq)
3
is shown in Table 4.2.
Synthesis of fac-Ir(bzq)
3
: A 200 ml round-bottomed flask was charged with
Ir(acac)
3
(0.500 g), 7,8-benzoquinoline (0.915 g), 100 ml of glycerol and a
stirbar. The reaction was stirred and heated with an oil bath at 205ºC for 18
hours under nitrogen. Yellow solution turned orange with some precipitates.
The reaction mixture was cooled to ambient temperature and methanol (100
ml) was added. The yellow-orange precipitates were then vacuum-filtered,
washed with methanol (3x15ml), ethanol (3x15ml), and hexanes (3x15ml),
and air-dried. It gave 0.464 g (63% yield) of fac-Ir(bzq)
3
. This complex is
hardly soluble in any organic solvents. NMR spectra could not be obtained.
Its mass spectrum indicates a mass of 727 at the major peak.
Crystallographic data for fac-Ir(bzq)
3
is shown in Table 4.3. The crystal
structure could not be resolved completely, Ir-N and Ir-C bonds are almost
identical for the crystal so it is hard to identify if it is really the facial isomer.
However, since the NMR unobtainable due to its insolubility and it has the
same mass as Ir(bzq)
3
, we can presume it is the facial isomer. The
photophysical properties of both isomers are also very distinct from each
other.
Photophysics. The UV-visible spectra were recorded on a Hewlett-Packard
4853 diode array spectrophotometer. Steady state emission at room
temperature and 77K were determined using a Photon Technology
International QuantaMaster Model C-60SE spectrofluorimeter.

118
Phosphorescence lifetime measurements were performed on an IBH
Fluorocube lifetime instrument by a time correlated single photon counting
method using a 405 nm LED excitation source. The absolute quantum yields
in fluid solution have been measured using a more reliant method compared
to those of previously reported.
4
The quantum yield measurement
experiments were carried out in dilute 2-MeTHF solution. The sample was
placed in a 1 cm
2
quartz cell and degassed with N
2
. The quantum yields and
the lifetimes of 2-3wt% doped thin films for mer-Ir(bzq)
3
in poly-
(methylmetacrylate) have also been measured. 2 mg of the sample along
with 100 mg of poly-(methylmetacrylate) were dissolved in 1 ml of toluene;
the dissolved sample was spincoated on a 0.5x0.5cm
2
quartz substrate at
3000 rpm for 40 seconds. The quantum efficiencies were measured using a
calibrated Hamamatsu integrating sphere equipped with a xenon lamp (with
a 380 nm excitation wavelength) and photonic multi-channel analyzer
C10027. The accuracy of the quantum efficiency measurements is + 5-10%
error of measurements. The quantum efficiencies data have been processed
with PLQY measurement software U6039-05.
NMR. NMR spectra were recorded on Bruker AMX 250 MHz instrument, and
chemical shifts were referenced to residual protiated solvent.
1
H NMR
spectra of (bzq)
2
Ir(μ-Cl)Ir(bzq)
2
and mer-Ir(bzq)
3
are shown in Figure 4.2.

119

ppm (t1)
6.00 6.50 7.00 7.50 8.00 8.50 9.00 9.50

Figure 4.2.
1
H NMR of (a)

(bzq)
2
Ir(μ-Cl)Ir(bzq)
2
in CDCl
3
; (b) mer-Ir(bzq)
3
in CD
2
Cl
2

Mass Spectroscopy. Mass Spectra were taken with a Hewlett-Packard
GC/MS instrument with electron impact ionization and a model 5873 mass
sensitive detector.
X-ray Crystallography. Diffraction data for mer-Ir(bzq)
3
and fac-Ir(bzq)
3

ppm (t1)
6.0 7.0 8.0 9.0

120
were collected at T = 423(2)K and 110(2)K, respectively. The data set were
collected on a Bruker SMART APEX CCD diffractometer with graphite
monochromated Mo Kα radiation (λ = 0.71073 Å). The cell parameters for the
iridium complexes were obtained from a least-squares refinement of the
spots (from 60 collected frames) using the SMART program. One
hemisphere of crystal data for each of the three compounds was collected up
to a resolution of 0.86 Å, and the intensity data were processed using the
Saint Plus program. All of the calculations for the structure determination
were carried out using the SHELXTL package (version 5.1).
5
Initial atomic
positions were located by Patterson methods using XS and the structures of
the compounds were refined by the least squares method using SHELX93
with 12321-16935 independent reflections within the range of θ = 1.80 to
27.50°. Absorption corrections were applied using SADABS.
6
In most cases,
hydrogen positions were input and refined in a riding manner along with the
attached carbons.

Electrochemistry. Cyclic voltammetry and differential pulsed voltammetry
were performed using an EG&G potentiostat/galvanostat model 283.
Anhydrous DMF was used as solvent under inert atmosphere and 0.1 M
tetra-n-butylammonium hexafluorophosphate was used as the supporting
electrolyte. A glassy carbon rod was used as the working electrode, a
platinum wire used as the counter electrode, and a silver wire was used as a
pseudo-reference electrode. The redox potentials are based on values

121
measured from differential pulsed voltammetry and are reported relative to
either a ferrocenium/ferrocene (Cp
2
Fe
+
/Cp
2
Fe) redox couple or a
decamethylferrocenium/decamethylferrocene (Me
5
Cp
2
Fe
+
/Me
5
Cp
2
Fe) redox
couple used as an internal reference,
7
while electrochemical reversibility was
determined using cyclic voltammetry.
OLED Fabrication. N,N’-diphenyl-N,N’-bis(1-naphthyl)benzidine (NPD),
N,N’-dicarbazolyl-3,5-benzene (mCP), and 4,4'-bis(carbazol-9-yl)biphenyl
(CBP) were provided by Universal Display Corporation and used without
further purifications. 2,9-dimethyl-4,7-diphenyl-1,10-phenanthroline (BCP)
was purchased from the Aldrich Chemical Company and was purified by
temperature gradient vacuum sublimation. Other materials such fac-flzIr, fac-
flimIr, mer-Ir(bzq)
3
and DTIC were also purified by sublimation before use in
the chamber. Prior to device fabrication, purchased 2mm wide striped pre-
patterned ITO substrates were cleaned by sonication in soap solution, rinsed
with deionized water and acetone, and then dried with N
2
. Then, photoresists
were spincoated onto each substrate. The substrates were then placed in the
vacuum-oven for 45 minutes. The photoresists were washed off with acetone
and N
2
-dried. They were then treated with UV ozone for 10 min. Organic
layers were deposited sequentially by thermal evaporation from resistively
heated tantalum boats at a rate of 2-2.5 Å S
-1
. After organic film deposition,
the chamber was vented and a shadow mask with a 2mm wide stripe was
put on the substrate perpendicular to the ITO stripes. Cathodes consisted of
a 10 Å thick layer of LiF followed by a 1000 Å thick of Al. The devices were

122
tested in air within 2 hours of fabrication. Device current-voltage and light-
intensity characteristics were measured using the program LabVIEW by
National Instruments with a Keithley 2400 SourceMeter/2000 Multimeter
coupled to a Newport 1835-C Optical Meter and equipped with a UV-818 Si
photocathode. Only light emitting from the front face of the devices was
collected and used in subsequent calculation. The electroluminescence
spectra were measured on a PTI QuantaMasterTM Model C-60SE
spectrofluorimeter equipped with a 928 PMT detector and corrected for
detector response.

4.3. Results and Discussion

4.3.1. Synthesis of Ir(bzq)
3
complex

Synthesis of Ir(bzq)
3
. Cyclometalated Ir (III) µ-chloro-bridged dimers of
benzoquinoline with a formula of (bzq)
2
Ir(µ-Cl)
2
Ir(bzq)
2
(where bzq
represents a 7,8-benzoquinoline cyclometalating ligand) were synthesized
first before the synthesis of Ir(bzq)
3
. The (bzq)
2
Ir(µ-Cl)
2
Ir(bzq)
2
was
synthesized by a method similar to the one reported by Nonoyama,
8
which
involves heating to 110
°
C IrCl
3
·H
2
O with 2-2.5 equivalents of cyclometallating
ligand in a 3:1 mixture of 2-ethoxyethanol and deionized water under inert
atmosphere. Tris-cyclometalated Iridium (III) benzoquinoline complex, mer-
Ir(bzq)
3
can be prepared from cyclometalated Ir (III) µ-chloro-bridged dimers
of benzoquinoline or through bis-cyclometallated iridium acetylacetonate

123
complexes, (bzq)
2
Ir(acac)
9
(Scheme 4.1). Detailed synthesis and
characterization of fac- and mer-Ir(bzq)
3
, are given in the experimental
section. Meridional isomer of Ir(bzq)
3
is synthesized by methods shown in
Scheme 4.1, whereas, the facial isomer of Ir(bzq)
3
was synthesized by
methods described in Scheme 4.2.

Scheme 4.1. Synthesis of mer-Ir(bzq)
3

Scheme 4.2. Synthesis of fac-Ir(bzq)
3

(C^N)
2
Ir(O^O) + HC^N
Ir(C^N)
3
+ O^OH
glycerol
@ 140-150 degrees C
N
2
+
@ 210-220 degrees C
2 HC^N + IrCl
3.
H
2
O
(N^C)
2
Ir
Cl
Ir(C^N)
2
Cl
2-EthoxyEtOH : H
2
O(3:1)
reflux
(N^C)
2
Ir
Cl
Ir(C^N)
2
Cl
+
O
O
(N^C)
2
Ir
O
O
K
2
CO
3
Dichloroethane
reflux
Ir(acac)
3 + 3N^CH
Ir(C^N)
3
glycerol
@ 210-220 degrees C
N
2
+
3 acacH

124
4.3.2. Photophysical Properties

4.3.2.1. Emission Spectra

The mer-Ir(bzq)
3
displays broad featureless phosphorescence (500-700 nm),
whereas the facial (fac) isomer exhibits narrower, more structured emission.
The featureless emission from the mer-isomers indicates the presence of a
distorted excited state in this species. The luminescent quantum yield (QY) of
mer-isomers of tris-cyclometalated Ir complexes are generally lower than the
fac-counterparts, e.g. mer-Ir(ppy)
3
, QY= 0.04; fac-Ir(ppy)
3
, QY= 1.0. At the
same token, mer-Ir(bzq)
3
, QY= 0.40; fac-Ir(bzq)
3
, QY= 0.80. However, the
luminescent efficiency of mer-Ir(bzq)
3
in dilute solution is about 10 orders of
magnitude greater than that of mer-Ir(ppy)
3
. Likewise, the luminescent
lifetime of mer-Ir(bzq)
3
in fluid solution at 300K (~5μs) is longer than that of
mer-Ir(ppy)
3
(250 ns). Clearly, nonradiative processes in mer-Ir(ppy)
3
are
suppressed in mer-Ir(bzq)
3
. Since mer-Ir(bzq)
3
displays broadband
phosphorescence (~500-750 nm) at RT, it would be beneficial as a broad
band emitter for white electroluminescent OLED applications. In comparison
to fac-Ir(bzq)
3
, mer-Ir(bzq)
3
displays more featureless 77K emission and
more broadened RT emission (Figure 4.3). The broadband
phosphorescence of mer-Ir(bzq)
3
(500-700nm) makes it a better candidate
for white electroluminescent OLED applications compared to its facial
isomer.

125

Figure 4.3. Excitation and Emission Spectra of fac-Ir(bzq)
3
and mer-
Ir(bzq)
3
, in dilute 2-MeTHF solution (77K and RT)

4.3.2.2. Absorption Spectra

Just like the emission characteristics, the facial (fac) isomer of Ir(bzq)
3

also exhibits more structured absorption compared to the mer- analog
(Figure 4.4). This means that the facial isomer has more ligand character in
the complex compared to the meridional isomer.

Figure 4.4. Absorption Spectra of fac-Ir(bzq)
3
and mer-Ir(bzq)
3

300 400 500 600
0.0
0.2
0.4
0.6
0.8
1.0

Normalized Absorbance
Wavelength (nm)
mer-Ir(bzq)
3
fac-Ir(bzq)
3
300 350 400 450 500 550 600 650 700
0.0
0.2
0.4
0.6
0.8
1.0

Normalized Intensity
Wavelength (nm)
77K Emission (facial)
77K Excitation (facial)
RT Emission (facial)
RT Excitation (facial)
77K Emission (meridional)
77K Excitation (meridional)
RT Emission (meridional)
RT Excitation (meridional)
fac-Ir(bzq)
3

at RT
mer-Ir(bzq)
3
at RT

126
4.3.3. Electrochemical Properties

The cyclic voltammogram (CV) and the different pulse voltammogram
(DPV) for mer-Ir(bzq)
3
in DMF gives a quasi-reversible oxidation at 0.25 V
and a quasi-reversible reduction at -2.41 V (Figure 4.5). The overall band
gap is 2.66 eV, which is a bit lower than the triplet energy (E
0-0
) of the
benzoquinoline ligand (459 nm, 2.70 eV). Since the overall band gap is lower
than the triplet energy of the cyclometalating ligand in the complex, we can
expect that mer-Ir(bzq)
3
would have more metal to ligand charge transfer
(MLCT) characteristics than the ligand-centered (LC) characteristics. This
phenomena also reflects in the photophysical properties of mer-Ir(bzq)
3
,
where it gives featureless broadband emission.

Figure 4.5. CV and DPV Trace of mer-Ir(bzq)
3
in DMF

-3.5 -3.0 -2.5 -2.0 -1.5 -1.0 -0.5 0.0 0.5 1.0
-0.0003
-0.0002
-0.0001
0.0000
0.0001
0.0002

Current (A)
mer-Ir(bzq)
3
Voltage (vs Fc
+
/Fc)
-3.0 -2.5 -2.0 -1.5 -1.0 -0.5 0.0 0.5
-0.00008
-0.00006
-0.00004
-0.00002
0.00000
0.00002
0.00004
0.00006
0.00008

Current (A)
Voltage (vs. Fc
+
/Fc)
DPV1
DPV2

127
4.3.4. X-ray Crystallography

A molecular plot for mer-Ir(bzq)
3
is shown in Figure 4.6. Selected
bond lengths and bond angles of the mer-Ir(bzq)
3
are listed in Table 4.1. The
crystal structure of mer-Ir(bzq)
3
shows a pseudo-octahedral coordination of
three benzoquinoline ligands in a meridional arrangement (Figure 4.1). From
Table 4.1., Ir-N1 (2.096(4) Å) is longer thus weaker compared to the other Ir-
N bond lengths (2.067(4) and 2.060(4) Å) at the iridium center. However, in
order to isomerize to the facial form, Ir-N3 needs to break, rotate and reform.
Unfortunately, in the case of mer-Ir(bzq)
3
, Ir-N3 (2.060(4) Å) seems to be too
strong of a bond to break. Ir-N1 will more likely to break in this complex,
however, the facial isomer will not be able to form since the breaking,
rotation, and reformation of Ir-N1 in this complex will still give another
meridional form of the complex. The attempts to do mer- to fac- isomerization
have been performed but so far there has not been any evidence of the mer-
to fac- isomerization.

Figure 4.6. ORTEP Plot of mer-Ir(bzq)
3
; The hydrogen atoms have been
omitted for clarity

Ir
N1
N2
N3
C37
C24
C11
Ir
N1
N2
N3
C37
C24
Ir
N1
N2
N3
C37
C24
C11

128
Table 4.1. Selected Bond Distances and Bond Angles for mer-Ir(bzq)
3

Bond Type Bond Distances (Å)
Ir-N1 2.096(4)
Ir-N2 2.067(4)
Ir-N3 2.060(4)
Ir-C11 2.090(4)
Ir-C24 2.061(4)
Ir-C37 2.049(4)
Bond Angles (Degrees)
N3-Ir-N2 173.65(15)
C37-Ir-C11 170.01(17)

Table 4.2. Crystallographic data for mer-Ir(bzq)
3
Empirical formula C
39
H
24
IrN
3

Formula weight 726.81
Temperature 423(2) K
Wavelength 0.71073 Å
Crystal system Monoclinic
Space group P2(1)/n
Unit cell dimensions a = 10.3096(17) Å; α = 90°.
b = 13.609(2) Å; β = 102.899(3)°.
c = 20.504(3) Å; γ = 90°.
Volume
2804.2(8) Å
3

Z 4
Density (calculated)
1.722 Mg/m
3

Absorption coefficient
4.796 mm
-1

F(000) 1424
Crystal size
0.1 x 0.1 x 0.05 mm
3

Theta range for data collection 1.81 to 23.27°.
Index ranges -11<=h<=10, -10<=k<=15, -22<=l<=22
Reflections collected 12321
Independent reflections 4030 [R(int) = 0.0348]
Completeness to theta = 23.27° 99.9 %
Absorption correction Semi
Refinement method
Full-matrix least-squares on F
2

Data / restraints / parameters 4030 / 0 / 388
Goodness-of-fit on F
2

0.948
Final R indices [I>2sigma(I)] R1 = 0.0266, wR2 = 0.0480
R indices (all data) R1 = 0.0361, wR2 = 0.0500
Largest diff. peak and hole
0.919 and -0.741 e.Å
-3

129
Table 4.3. Crystallographic data for fac-Ir(bzq)
3

Empirical formula IrN
3
C
39
H
24

Formula weight 726.81
Temperature 110(2) K
Wavelength 0.71073 Å
Crystal system Monoclinic
Space group P2(1)/n
Unit cell dimensions a = 10.1921(18) Å; α = 90°.
b = 13.708(3) Å; β = 102.429(3)°.
c = 20.474(4) Å; γ = 90°.
Volume
2793.4(9) Å
3

Z 4
Density (calculated)
1.728 Mg/m
3

Absorption coefficient
4.815 mm
-1

F(000) 1424
Crystal size
0.25 x 0.30 x 0.10 mm
3

Theta range for data collection 1.80 to 27.50°.
Index ranges -12<=h<=13, -17<=k<=15, -26<=l<=19
Reflections collected 16935
Independent reflections 6263 [R(int) = 0.0298]
Completeness to theta = 27.50° 97.7 %
Absorption correction max/min= 0.850096
Refinement method
Full-matrix least-squares on F
2

Data / restraints / parameters 6263 / 0 / 388
Goodness-of-fit on F
2

1.039
Final R indices [I>2sigma(I)] R1 = 0.0275, wR2 = 0.0651
R indices (all data) R1 = 0.0322, wR2 = 0.0670
Largest diff. peak and hole
1.067 and -0.600 e.Å
-3

4.3.5. OLED Studies

The monochrome mer-Ir(bzq)
3
-doped CBP devices have been
fabricated with a device structure of ITO/ NPD(400Å)/ mer-Ir(bzq)
3
:CBP (8%,
250 Å)/ BCP(400 Å)/ LiF(10 Å)/ Al (1100 Å). This monochrome device turns
on at a low voltage of 2-3V and the electroluminescence comes from the
broadband emitter, mer-Ir(bzq)
3
with a maximum external quantum efficiency

130
of 7.43% and a maximum brightness of about 10,000 Cd/m
2
with CIE
coordinates: x= 0.33, y= 0.63 (Figure 4.7.). Analogous mCP devices were
also fabricated, but they do not perform as well as the mer-Ir(bzq)
3
-doped
CBP devices due to their low external quantum efficiencies and high current
shortages.

Figure 4.7. The Monochrome mer-Ir(bzq)
3
Device Performances in CBP
To achieve white electroluminescent OLEDs, we demonstrated two
different approaches. One is to use two phosphorescent dopants in one
device structure such as the broadband phosphorescent emitter, mer-
Ir(bzq)
3
, with the efficient blue-green phosphor (flzIr; CIE, x= 0.16, y= 0.50).
The phosphorescent molecules harness the triplet excitons constituting 75%
of the bound electron-hole pairs that form during charge injection; the all-
0.1 1 10
1E-4
1E-3
0.01
0.1
1
10
100
0.1 1 10 100
0.01
0.1
1
10
0.1 1 10
1E-3
0.01
0.1
1
10
100
1000
10000
400 450 500 550 600 650 700 750
0.0
0.2
0.4
0.6
0.8
1.0

Current Density, mA/cm
2
Voltage, V
Device 1
Device 2
Device 3

Q.E. (%)
Current Density, mA/cm
2
Device 1
Device 2
Device 3

Brightness, Cd/m
2
Voltage, V
Device 1
Device 2
Device 3

Normalized Intensity
Wavelength, nm
7V
8V
9V
10V
12V
11V-back
9V-back
7V-back
ITO/ NPD (400 Å)/ mer-ir(bzq)
3
: CBP (8%, 250 Å) / BCP (400 Å)/ LiF/ Al
0.1 1 10
1E-4
1E-3
0.01
0.1
1
10
100
0.1 1 10 100
0.01
0.1
1
10
0.1 1 10
1E-3
0.01
0.1
1
10
100
1000
10000
400 450 500 550 600 650 700 750
0.0
0.2
0.4
0.6
0.8
1.0

Current Density, mA/cm
2
Voltage, V
Device 1
Device 2
Device 3

Q.E. (%)
Current Density, mA/cm
2
Device 1
Device 2
Device 3

Brightness, Cd/m
2
Voltage, V
Device 1
Device 2
Device 3

Normalized Intensity
Wavelength, nm
7V
8V
9V
10V
12V
11V-back
9V-back
7V-back
ITO/ NPD (400 Å)/ mer-ir(bzq)
3
: CBP (8%, 250 Å) / BCP (400 Å)/ LiF/ Al

131
phosphor-doped devices have the potential for 100% internal quantum
efficiency. One of the phosphors-doped WOLED device structures consisting
of ITO/ NPD(400Å)/ flzIr: mCP (8%, 100 Å)/ mer-Ir(bzq)
3
:CBP (8%, 100 Å)/
BCP(400 Å)/ LiF(10 Å)/ Al (800 Å) turns on at a low voltage of 2-3V and the
electroluminescence comes from both phosphorescent emitters, flzIr and
mer-Ir(bzq)
3
, with a maximum external quantum efficiency of 11.6% and a
maximum brightness of roughly 10,000 Cd/m
2
with CIE coordinates: x= 0.38,
y= 0.50. In addition, these flzIr-mer-Ir(bzq)
3
-doped devices are not voltage-
dependent. However, the NPD emission shows more significantly as the
voltage increases (Figure 4.8). A good blocking layer such as fac-Ir(ppz)
3

can definitely solve this issue without decreasing the device efficiencies.

Figure 4.8. flzIr-mer-Ir(bzq)
3
-doped Devices Performance in Two
Different Hosts, mCP and CBP

110 100
0.1
1
10
0.1 1 10
1E-6
1E-5
1E-4
1E-3
0.01
0.1
1
10
100
0.1 1 10
1E-4
1E-3
0.01
0.1
1
10
100
1000
10000
400 500 600 700 800
0.0
0.2
0.4
0.6
0.8
1.0

Q.E. (%)
Current Density, mA/cm
2
Device 1
Device 2
Device 3a
Device 3b

Current Density, mA/cm
2
Voltage, V
Device 1
Device 2
Device 3a
Device 3b

Brightness, Cd/m
2
Voltage, V
Device 1
Device 2
Device 3a
Device 3b

Normalized Intensity
Wavelength, nm
7V
8V
9V
10V
11V
12V
10V-back
ITO/ NPD (400 Å)/ flzIr: mCP (8%, 100 Å) / mer-ir(bzq)
3
: CBP (8%, 100Å) / BCP (400 Å)/LiF/Al
Q.E. (max)= 11.6%
110 100
0.1
1
10
0.1 1 10
1E-6
1E-5
1E-4
1E-3
0.01
0.1
1
10
100
0.1 1 10
1E-4
1E-3
0.01
0.1
1
10
100
1000
10000
400 500 600 700 800
0.0
0.2
0.4
0.6
0.8
1.0

Q.E. (%)
Current Density, mA/cm
2
Device 1
Device 2
Device 3a
Device 3b

Current Density, mA/cm
2
Voltage, V
Device 1
Device 2
Device 3a
Device 3b

Brightness, Cd/m
2
Voltage, V
Device 1
Device 2
Device 3a
Device 3b

Normalized Intensity
Wavelength, nm
7V
8V
9V
10V
11V
12V
10V-back
ITO/ NPD (400 Å)/ flzIr: mCP (8%, 100 Å) / mer-ir(bzq)
3
: CBP (8%, 100Å) / BCP (400 Å)/LiF/Al
110 100
0.1
1
10
0.1 1 10
1E-6
1E-5
1E-4
1E-3
0.01
0.1
1
10
100
0.1 1 10
1E-4
1E-3
0.01
0.1
1
10
100
1000
10000
400 500 600 700 800
0.0
0.2
0.4
0.6
0.8
1.0

Q.E. (%)
Current Density, mA/cm
2
Device 1
Device 2
Device 3a
Device 3b

Current Density, mA/cm
2
Voltage, V
Device 1
Device 2
Device 3a
Device 3b

Brightness, Cd/m
2
Voltage, V
Device 1
Device 2
Device 3a
Device 3b

Normalized Intensity
Wavelength, nm
7V
8V
9V
10V
11V
12V
10V-back
ITO/ NPD (400 Å)/ flzIr: mCP (8%, 100 Å) / mer-ir(bzq)
3
: CBP (8%, 100Å) / BCP (400 Å)/LiF/Al
Q.E. (max)= 11.6%

132
In addition, we also fabricated devices in which the mer-Ir(bzq)
3
-doped
layer is sandwiched between two flzIr-doped layers; the device performance
is similar to the simple double-doped layers devices except for the
electroluminescent performance (CIE coordinates: x= 0.47, y= 0.48). The
mer-Ir(bzq)
3
sandwiched type devices show more broadening effects on the
EL, up to 750 nm (Figure 4.9).

Figure 4.9. Devices with mer-Ir(bzq)
3
Sandwiched Between flzIr

Additionally, mer-Ir(bzq)
3
-flzIr doped devices perform in two different
hosts, mCP and CBP with similar thicknesses, as devices in Figure 4.8, but
with switched doped layers (Figure 4.10). For these devices, the exciton
recombinations occur more in the mer-Ir(bzq)
3
doped layer rather than in the
400 500 600 700 800
0.0
0.2
0.4
0.6
0.8
1.0
0.1 1 10
1E-6
1E-5
1E-4
1E-3
0.01
0.1
1
10
100
0.1 1 10
1E-3
0.01
0.1
1
10
100
1000
10000
0.1 1 10 100
0.01
0.1
1
10

Normalized Intensity
Wavelength, nm
7V
8V
9V
10V
11V
12V
10V-back
8V-back

Current Density, mA/cm
2

Voltage, V
Device 1
Device 2
Device 3

Brightness, Cd/m
2
Voltage, V
Device 1
Device 2
Device 3

Q.E. (%)
Current Density, mA/cm
2
Device 1
Device 2
Device 3
ITO/ NPD (400 Å)/ flzIr: mCP (8%, 100 Å) / mer-ir(bzq)
3
: CBP (8%, 100Å) / flzIr: mCP (8%, 100 Å) / BCP (400 Å)/ LiF/ Al
Q.E. (max)= 10.18 %
400 500 600 700 800
0.0
0.2
0.4
0.6
0.8
1.0
0.1 1 10
1E-6
1E-5
1E-4
1E-3
0.01
0.1
1
10
100
0.1 1 10
1E-3
0.01
0.1
1
10
100
1000
10000
0.1 1 10 100
0.01
0.1
1
10

Normalized Intensity
Wavelength, nm
7V
8V
9V
10V
11V
12V
10V-back
8V-back

Current Density, mA/cm
2

Voltage, V
Device 1
Device 2
Device 3

Brightness, Cd/m
2
Voltage, V
Device 1
Device 2
Device 3

Q.E. (%)
Current Density, mA/cm
2
Device 1
Device 2
Device 3
ITO/ NPD (400 Å)/ flzIr: mCP (8%, 100 Å) / mer-ir(bzq)
3
: CBP (8%, 100Å) / flzIr: mCP (8%, 100 Å) / BCP (400 Å)/ LiF/ Al
Q.E. (max)= 10.18 %

133
interface between mer-Ir(bzq)
3
and flzIr doped layers. The device efficiencies
are also lower than the devices mentioned previously.

Figure 4.10. mer-Ir(bzq)
3
-flzIr Doped Devices Performance in Two
Different Hosts, CBP and mCP
The second approach introduces a different concept by incorporating
a blue fluorescent emitter such as DTIC in exchange for a phosphorescent
dopant, and combining it with the broadband phosphorescent emitter, mer-
Ir(bzq)
3
, to obtain high power efficiency and stable color balance while
maintaining the potential for 100% internal quantum efficiency. Energy
transfers within this second type of device channel nearly all of the triplet
energy onto the phosphorescent dopant, retaining the singlet energy
exclusively on the blue fluorescent dopant. Eliminating the exchange energy
loss to the blue fluorophore allows for about 20% increased power efficiency
compared to a fully phosphorescent device. Devices consisting of ITO/
400 450 500 550 600 650 700 750 800
0.0
0.2
0.4
0.6
0.8
1.0
110 100
1
2
3
4
5
6
0.1 1 10
1E-4
1E-3
0.01
0.1
1
10
100
0.1 1 10
1E-3
0.01
0.1
1
10
100
1000
10000

Normalized Intensity
Wavelength, nm
7V
8V
9V
10V
11V
12V
10V-back
8V-back

Q.E. (%)
Current Density, mA/cm
2
Device 1
Device 2a
Device 2b

Current Density, mA/cm
2
Voltage, V
Device 1
Device 2a
Device 2b

Brightness, Cd/m
2
Voltage, V
Device 1
Device 2a
Device 2b
ITO/ NPD (400 Å)/ mer-ir(bzq)
3
: CBP (8%, 100Å) / flzIr: mCP (8%, 100 Å) / BCP (400 Å)/LiF/Al
Q.E. (max)= 5.62 %
400 450 500 550 600 650 700 750 800
0.0
0.2
0.4
0.6
0.8
1.0
110 100
1
2
3
4
5
6
0.1 1 10
1E-4
1E-3
0.01
0.1
1
10
100
0.1 1 10
1E-3
0.01
0.1
1
10
100
1000
10000

Normalized Intensity
Wavelength, nm
7V
8V
9V
10V
11V
12V
10V-back
8V-back

Q.E. (%)
Current Density, mA/cm
2
Device 1
Device 2a
Device 2b

Current Density, mA/cm
2
Voltage, V
Device 1
Device 2a
Device 2b

Brightness, Cd/m
2
Voltage, V
Device 1
Device 2a
Device 2b
ITO/ NPD (400 Å)/ mer-ir(bzq)
3
: CBP (8%, 100Å) / flzIr: mCP (8%, 100 Å) / BCP (400 Å)/LiF/Al
Q.E. (max)= 5.62 %

134
NPD(400Å)/ DTIC: CBP (8%, 200 Å)/ CBP (50 Å)/ mer-Ir(bzq)
3
:CBP (8%, 50
Å)/ BCP(400 Å)/ LiF(10 Å)/ Al (1100 Å) were fabricated and they turn on at a
low voltage of 2-3 V, giving a maximum external quantum efficiency of about
5% and a maximum brightness of roughly 5,000 Cd/m
2
with CIE coordinates:
x= 0.29, y= 0.35. These fluorescent-phosphorescent doped devices are
voltage dependent (Figure 4.11).

Figure 4.11. DTIC: mer-Ir(bzq)
3
Doped Devices Performance Using the
Same Hosts, CBP
The mer-Ir(bzq)
3
-doped layer sandwiched between DTIC-doped layers
devices were also demonstrated with a device structure consisting of ITO/
NPD(400Å)/ DTIC: CBP (8%, 100 Å)/ CBP (50 Å)/ mer-Ir(bzq)
3
:CBP (8%, 50
Å)/ CBP (50 Å)/ DTIC: CBP (8%, 100 Å)/ BCP(400 Å)/ LiF(10 Å)/ Al (1100 Å).
The CIE coordinates of these sandwiched devices is: x= 0.52, y= 0.34. The
300 400 500 600 700
0.0
0.2
0.4
0.6
0.8
1.0
0.1 1 10
1E -5
1E -4
1E -3
0.01
0.1
1
10
100
0.1 1 10
1E -3
0.01
0.1
1
10
100
1000
1 10 100
0.1
1
10

Normalized Intensity
Wavelength, nm
7V
8V
9V
10V
11V
12V
10V-back
8V-back

Current Density, mA/cm
2
Voltage, V
Device 1
Device 2
Device 3

Brightness, Cd/m
2
Voltage, V
Device 1
Device 2
Device 3

Q.E. (%)
C urrent D ensity, mA /cm
2
Device 1
Device 2
Device 3
NPD (400 Å)/DTIC: CBP (8%, 200 Å)/CBP(50 Å)/mer-ir(bzq)
3
: CBP (8%, 50Å)/BCP (400 Å)/LiF/Al

135
device performances of the sandwiched devices are inferior to the simple
double-doped layer devices and are still voltage dependent (Figure 4.12.)

Figure 4.12. Devices with mer-Ir(bzq)
3
Sandwiched Between DTIC

In addition, analogous device structures with a carbene analog of fac-
flzIr (fac-flimIr) as a blue-green phosphor have been fabricated. Since the
emission of fac-flimIr is about 15nm blue-shifted from that of fac-flzIr at 77K
and RT (see Chapter 2), it is very tempting to apply this carbene analog of
flzIr for the white OLED applications especially to achieve better CIE
coordinates.
Just like the monochrome fac-flzIr: mCP device, monochrome fac-
flimIr: mCP device also emits from the dopant itself (fac-flimIr) and turns on
0.1 1 10
1E -5
1E -4
1E -3
0.01
0.1
1
10
100
1 10 100
0.1
1
10
0.1 1 10
1E -3
0.01
0.1
1
10
100
1000
300 400 500 600 700
0.0
0.2
0.4
0.6
0.8
1.0

Current Density, mA/cm
2
Voltage, V
Dev ice 1
Dev ice 2
Dev ice 3

Q.E. (%)
Current Density, mA /cm
2
D evice 1
D evice 2
D evice 3

Brightness, Cd/m
2
Voltage, V
D evice 1
D evice 2
D evice 3

Normalized Intensity
Wavelength, nm
7V
8V
9V
10V
11V
12V
10V-back
8V-back
NPD (400 Å)/DTIC: CBP (8%, 100 Å)/CBP(50 Å)/mer-ir(bzq)
3
: CBP (8%, 50Å)/CBP(50Å)/DTIC:CBP(8%, 100 Å)/ BCP (400 Å)/LiF/Al

136
at a low voltage of 2-3V. As an advantage over flzIr device, flimIr device
emits in a bluer region (~466nm). As drawbacks, flimIr: mCP device gives a
lower brightness and a lower external quantum efficiency compared to those
of flzIr: mCP device (Figure 4.13.)

Figure 4.13. Monochrome Device for flimIr vs. flzIr in mCP
The first fac-flimIr : mer-Ir(bzq)
3
devices fabricated consist of ITO/
NPD(400Å)/ 8% fac-flimIr in mCP (150 Å)/ 8% mer-Ir(bzq)
3
:CBP (100 Å)/
BCP(400 Å)/ LiF(10 Å)/ Al (1000 Å). This device has a maximum external
quantum efficiency of about 7% and a maximum brightness of roughly 5,000
Cd/m
2
with CIE coordinates: x= 0.29, y= 0.37 (Figure 4.15). Compared to
fac-flzIr: mer-Ir(bzq)
3
devices, this device has a lower quantum efficiency and
brightness. However, the turn-on voltage is still quite low (2-3V) and the EL
still comes from both phosphorescent dopants. This device is voltage-

ITO/ NPD (400 Å)/ 8% DOPANT: mCP (250 Å) / BCP (400 Å)/ LiF/ Al
400 500 600 700
0.0
0.2
0.4
0.6
0.8
1.0
0.1 1 10 100
1
2
3
4
5
6
7
8
110
1E-7
1E-6
1E-5
1E-4
1E-3
0.01
0.1
1
10
100
0.1 1 10
1E-3
0.01
0.1
1
10
100
1000
10000

Normalized Intensity
Wavelength (nm)
7V
8V
9V
10V
11V
12V
10Vback
flzIr

Q.E. (%)
Current Density (mA/cm
2
)
flzIr in mCP
flimIr in mCP

Current Density (mA/cm
2
)
Voltage (V)
flzIr in mCP
flimIr in mCP

Brightness (Cd/m
2
)
Voltage (V)
flzIr in mCP
flimIr in mCP

137
independent and the NPD emission shows more significantly as the voltage
increases. A good blocking layer such as fac-Ir(ppz)
3
can definitely solve this
issue without decreasing the device efficiencies. The CIE coordinates for this
fac-flimIr: mer-Ir(bzq)
3
device are x=0.29, y=0.37, getting closer to the CIE of
RGB White (x=0.30, y=0.30). The CIE coordinates of this fac-flimIr: mer-
Ir(bzq)
3
has been improved compared to previously reported fac-flzIr: mer-
Ir(bzq)
3
devices. A change in fac-flimIr: mCP layer thickness can definitely
affect the recombination zone. By changing fac-flimIr: mCP layer from 150 Å
to 100 Å and leaving the mer-Ir(bzq)
3
: CBP layer constant, more exciton
recombinations happen in mer-Ir(bzq)
3
:CBP layer (Figure 4.14).

Figure 4.14. White OLEDs from fac-flimIr : mer-Ir(bzq)
3
in different
hosts, mCP and CBP along with their CIE coordinates

1E-3 0.01 0.1 1 10 100
1
2
3
4
5
6
7
8
9
10
11
0.1 1 10
1E-6
1E-5
1E-4
1E-3
0.01
0.1
1
10
100
0.1 1 10
1E-3
0.01
0.1
1
10
100
1000
10000
400 500 600 700
0.0
0.2
0.4
0.6
0.8
1.0

Q.E. (%)
Current Density, mA/cm
2
flimIr: mer-Ir(bzq)
3
100:100
flimIr: mer-Ir(bzq)
3
150:100

Current Density (mA/cm
2
)
Voltage (V)
flimIr: mer-Ir(bzq)
3
100:100
flimIr: mer-Ir(bzq)
3
150:100

Normalized Intensity
Voltage (V)
flimIr: mer-Ir(bzq)
3
100:100
flimIr: mer-Ir(bzq)
3
150:100

Normalized Intensity
Wavelength (nm)
8V (100: 100)
9V (100: 100)
10V (100: 100)
11V (100: 100)
12V (100:100)
8V (150:100)
9V (150:100)
10V (150:100)
11V (150:100)
12V (150: 100)

ITO/ NPD (400 Å)/ 8% flimIr: mCP (100 Å or 150 Å) / 8% mer-ir(bzq)
3
: CBP (100Å) / BCP (400 Å)/LiF/Al
unknown
520
CIE Coordinates
0
0.1
0.2
0.3
0.4
0.5
0.6
0.7
0.8
0.9
0 0.2 0.4 0.6 0.8
X
Y
CIE coords
CRT coords.
10 nm spacing
white (r=g=b)
560
600
480
150:100
100:100
CIE Coordinates
0
0.1
0.2
0.3
0.4
0.5
0.6
0.7
0.8
0.9
0 0.2 0.4 0.6 0.8
X
Y
CIE coords
CRT coords.
10 nm spacing
white (r=g=b)
560
600
480
150:100
100:100

138
4.4. Conclusion

In this chapter, tris-cyclometalated iridium (III) benzoquinoline
complexes, fac- and mer- isomers of Ir(bzq)
3,
have been synthesized and
their photophysical and electroluminescent properties have been examined.
Some white phosphorescent OLEDs with mer-Ir(bzq)
3
as the broad band
emitter and with fac-flzIr, fac-flimIr or DTIC as the blue emitter have also
been fabricated. These devices emit white light with maximum quantum
efficiency of ~12%. The mer-Ir(bzq)
3
has revealed itself to be a good
candidate as a broadband emitter for white OLED applications. The
temperature dependence study of mer-Ir(bzq)
3
is under way to seek some
explanations about what deactivation processes are occurring in mer-Ir(bzq)
3

and why mer-Ir(bzq)
3
is more efficient in solution compared to mer-Ir(ppy)
3
.

139
Chapter 4 References

1. (a) Baldo, M.A.; O’Brien, D.F.; You, Y.; Shoustikov, A.; Sibley, S.;
Thompson, M.E.; Forrest, S.R. Nature. 1998, 395, 151. (b) Baldo, M.A.;
Lamansky, S.; Burrows, P.E.; Thompson, M.E.; Forrest, S.R. Appl. Phys.
Lett. 1999, 75, 4. (c) Thompson, M.E.; Burrows, P.E.; Forrest, S.R. Curr.
Opin. Solid State Mater. Sci. 1999, 4, 369. (d) Baldo, M.A.; Thompson, M.E.;
Forrest, S.R. Nature. 2000, 403, 750.

2. (a) Lamansky, S.; Djurovich, P.I.; Abdel-Razzaq, F.; Garon, S.; Murphy,
D.L.; Thompson, M.E. J. Appl. Phys. 2002, 92, 1570. (b) Chen, F.C.; Yang,
Y.; Thompson, M.E.; Kido, J. Appl. Phys. Lett. 2002, 80, 2308. (c) Markham,
J.P.J.; Lo, S.-C.; Magennis, S.W.; Burn, P.L.; Samuel, I.D.W. Appl. Phys.
Lett. 2002, 80, 2645. (d) Zhu, W.; Mo, Y.; Yuan, M.; Yang, W.; Cao, Y. Appl.
Phys. Lett. 2002, 80, 2045. (e) Adachi, C.; Baldo, M.A.; Forrest, S.R.;
Thompson, M.E. J. Appl. Phys. 2001, 90, 4058. (f) Ikai, M.; Tokito, S.;
Sakamoto, Y.; Suzuki, T.; Taga, Y. Appl. Phys. Lett. 2001, 79, 156. (g)
Adachi, C.; Lamansky, S.; Baldo, M.A.; Kwong, R.C.; Thompson, M.E.;
Forrest, S.R. Appl. Phys. Lett. 2001, 78, 1622. (h) Lamansky, S.; Djurovich,
P.I.; Murphy, D.; Abdel-Razzaq, F.; Lee, H.E.; Adachi, C.; Burrows, P.E.;
Forrest, S.R.; Thompson, M.E. J. Am. Chem. Soc. 2001, 123, 4304.

3. Wilde, A.P.; King, K.A.; Watts, R.J. J. Phys. Chem. 1991, 95, 629-634

4. Demas, J.N.; Crosby, G.A. J. Phys. Chem. 1978, 82, 991. (b) DePriest, J.;
Zheng, G.Y.; Goswami, N.; Eichhorn, D.M.; Woods, C.; Rillema, D.P. Inorg.
Chem. 2000, 39, 1955.

5. Sheldrick, G.M. SHELXTL, version 5.1.; Bruker Analytical X-ray System,
Inc.; Madison, WI, 1997.

6. Blessing, R.H. Acta Crystallogr. 1995, A51, 33.

7. (a) Gagne, R.R.; Koval, C.A.; Lisensky, G.C. Inorg. Chem. 1980, 19, 2854.
(b) Sawyer, D.T.; Sokkowiak, A.; Roberts, J.L., Jr. Electrochemistry for
Chemists, 2
nd
ed.: John Wiley and Sons: New York, 1995; p 467.

8. Nonoyama, M., Bull. Chem. Soc. Jpn., 1974, 47, 767.

9. Lamansky, S.; Djurovich, P.I.; Murphy, D.; Abdel-Razaq, F.; Kwong, R.;
Tsyba, I.; Bortz, M.; Mui, B.; Bau.R.; Thompson, M.E. Inorg. Chem. 2001, 40,
1704-1711.

140
Chapter 5. Temperature Dependent Study of Radiative and
Nonradiative States in Neutral Phosphorescent
Cyclometalated Iridium (III) Complexes.

5.1. Introduction

One of the significant research efforts related to organic light emitting
devices (OLEDs) is the development of efficient red, green and blue
phosphorescent materials for full color display applications. It is essential to
prepare these phosphors by the incorporation of second and third row
transition metal complexes.
1
The associated strong spin orbit coupling in
heavy metals such as Ir and Pt would promote an intersystem crossing from
the singlet excited state (S
1
) to the triplet excited state (T
1
), enhance the
subsequent radiative transition from the triplet excited state (T
1
) to the
ground state (S
0
), and give good phosphorescent efficiency for these metal
complexes.

Among the phosphorescent Ir(III) complexes, green and red emitting
complexes have been well developed and studied extensively.
2
fac-Ir(ppy)
3

has been known for years as an efficient green emitter in OLEDs; OLEDs
with fac-Ir(ppy)
3
have been fabricated with 100% internal quantum
efficiency.
3
In the meantime, the red emitting Ir complexes with judicious
choices of the cyclometalating ligands have also shown good
phosphorescent efficiency despite their rapid temperature independent,
nonradiative deactivation predicted by the energy gap law.
4

141
On the other hand, there have only been a few reports on
cyclometalated Ir(III) complexes concerning types of ligands that display high
energy (near UV to sky blue) phosphorescence (400-460 nm). To achieve
high energy phosphorescent emissions from cyclometalated Ir(III)
complexes, the first strategies employed by most researchers was to alter
the emission energy of fac-Ir(ppy)
3
by the modification of its phenylpyridine
ligands. The first approach to increase the emission energy of fac-Ir(ppy)
3

focused on methods to decrease the HOMO energy while keeping the LUMO
energy relatively unchanged. The addition of electron withdrawing groups
such as fluoride on phenylpyridine ligands resulted in a blue-shift emission
from that of fac-Ir(ppy)
3
. The fac-Ir(F
2
ppy)
3
emits 50 nm higher in energy
compared to fac-Ir(ppy)
3
.
5
There are only a few other homoleptic blue
cyclometalated Ir complexes that exhibit higher emission energy than fac-
Ir(F
2
ppy)
3
; those complexes possess heterocyclic-based ligands with a high
triplet energy. Examples include phenylpyrazole ligands
5,6
, phenyltriazole
ligands
7
, phenylimidazole, and phenylbenzimidazole ligands.
8
Although the
emission energy could be significantly increased by the incorporation of
these high triplet energy heterocyclic ligands, the quantum efficiencies
declined from that of fac-Ir(ppy)
3
due to a significant increase in nonradiative
rates relative to their radiative rates. An alternate approach to decrease the
HOMO energy involves the use of different ancillary ligands on
biscyclometalated Irppy
2
derivatives. The ancillary ligands used vary from
pyrazolyl-borates and their analogues,
9
picolinate,
10
cyanide and isocyanide

142
ligands,
11
pyridyl-tetrazoles,
12
CF
3
-substituted pyridylpyrazoles or pyridyl-
triazoles.
7,13
Although efficient blue phosphors have been achieved by the
incorporation of selected ancillary ligands (i.e. cyanide and isocyanide) on
biscyclometalated Irppy
2
derivatives, there are still some limitations on how
far we can tune the emission energy and efficiency for those high energy
phosphorescent Ir complexes.
Useful information on radiative and nonradiative properties of
transition metal complexes can be obtained from temperature dependent
studies. There have been extensive studies on the photochemical and
photophysical properties of the diimine (i.e. bipyridine) chelates of Ru(II) and
Os(II).
14
Temperature dependent studies of Ru(II) and Os(II) complexes have
provided important information about two different states that exist in these
species: radiative states and nonradiative (NR) states. Temperature
dependent radiative states, which typically can be observed at a low
temperature regime (0-77K), involve the splitting of the triplet state into three
triplet substates with distinct radiative lifetimes. The splitting of a triplet state
is a consequence of spin-orbit coupling induced by the heavy metal ions. The
energy separation of triplet substate I and III is called zero-field splitting
(ZFS). The ZFS of Ru(bpy)
3
complexes is about 60 cm
-1
,
15
relatively large
compared to that of organic molecules (0.2 cm
-1
).
16
Temperature dependent
studies of Ru(II) and Os(II) complexes at higher temperatures (77K-300K)
reveal the existence of a thermally accessible, higher lying metal-to-ligand
charge transfer (MLCT) excited state. This higher lying MLCT state makes a

143
significant contribution to NR decay occuring at room temperature. For
polypyridyl complexes of Ru(II), NR decay most likely occurs through a
metal-centered ligand field (LF) state due to a photoinduced ligand loss
chemistry.
17
In contrast, this metal-centered LF excited state is relatively
inaccessible for Os (II) complexes due to its stronger ligand field strength.
The Os (II) complexes suffer more severely from temperature independent
NR decay.
18
Luminescent temperature dependence of cyclometalated Pd(II),
Rh(III), Pt(II) as well as Pt(IV) complexes have also been fully investigated.
19

Luminescent lifetimes of Pd(II), Rh(III), Pt(II) complexes are strongly
temperature dependent indicating that their deactivation pathways occur
through thermally accessible metal-centered LF excited states. In contrast,
the luminescent lifetimes of Pt (IV) complexes are only slightly temperature
dependent showing that only radiative states of these species are
temperature dependent and the LF deactivation does not occur in these
species.
Nevertheless, there have been only a few photophysical properties of
blue phosphorescent Ir(III) complexes detailed. Only recently has
luminescent temperature dependence of blue cyclometalated Ir(III)
complexes been studied.
20
Similar phenomena in Ru(II), Os(II), Pd(II), Rh(III),
Pt(II) and Pt(IV) complexes are also occurring in Ir(III) complexes.
Temperature dependent studies of Ir(III) complexes can also give important
information about their radiative and nonradiative (NR) states. Temperature
dependent radiative state involves the splitting of a triplet state, whereas the

144
temperature dependent nonradiative processes of blue phosphorescent Ir(III)
complexes involve a higher lying NR state that can be thermally populated
called a ligand field (LF) state. Temperature dependent radiative state for
cyclometalated Ir(III) complexes have been fully studied.
21
The apparent
temperature dependent lifetimes of fac-Ir(ppy)
3
at a temperature range of
77K and 300K is only for its radiative state because the fact that the quantum
yield of fac-Ir(ppy)
3
is very high (close to unity) at 300K indicates the
inaccessibility of the NR state at room temperature. Since the NR state is not
accessible, the radiative state temperature dependence of fac-Ir(ppy)
3
can
already be observed at high temperature regime (100K to 300K). The ZFS of
fac-Ir(ppy)
3
has been previously reported to be 83 cm
-1
,
21
also

relatively large
compared to ZFS of organic compounds (0.2 cm
-1
).
16
Temperature
dependent studies of homoleptics tris-pyridyl azolate and tris-phenyltriazolate
iridium (III) complexes have been investigated.
7, 20

In this chapter, we utilize extensive temperature dependent lifetime
studies to estimate the ZFS and the LF state energies for high energy
phosphorescent cyclometalated Ir(III) complexes, 1-10 (Figure 5.1). This is
the first time we can identify where the LF state is for blue cyclometalated
Ir(III) complexes. The thermal population of this LF state is most likely one of
the deactivation processes that blue cyclometalated Ir(III) complexes suffer
from. From the temperature dependence study, we learn that activation
energies (E
a
) needed to thermally populate LF state and the nonradiative

145
decay rate constant are two important factors that affect the quantum
efficiency of blue cyclometalated Ir complexes.

Figure 5.1. Structures of Compounds 1-10

Ir(ppy)
3
Ir(F
2
ppy)
3 Ir(ppz)
3
Ir(F
2
ppz)
3
(ppz)
2
Ir(ppy)
(ppz)
2
Ir(F
2
ppy)
(F
2
ppz)
2
Ir(ppy)
(F
2
ppz)
2
Ir(F
2
ppy)
Ir(flz)
3
Ir(pmb)
3
N
Ir
3
Ir
3
N
F
F
N
N
Ir
3
F
F
N
N
Ir
3
N
N
Ir
3
N
N
Ir
3
N
N
Ir
2
N
N
Ir
2 F
F
N N
N
Ir
2
F
F
N
F
F
N
N
Ir
2
N
F
F
1 2 3 4
5
6 7 8
9 10
N

146
5.2. Experimental

Synthesis. The compounds that have been studied in this chapter 1-10 were
prepared as described in chapter 2 of this thesis and also previously
reported.
5

Lifetimes Measurements. The lifetimes measurement experiments were
carried out in distilled 2-MeTHF solution, more rigid poly-THF or rigid
polystyrene. The samples were flame-sealed under vacuum in a cell after
being degassed with N
2
and repeated freeze-pump-thaw cycles. For the
temperature range of 77K-300K, the flame-sealed sample was placed inside
an Oxford OpstistatDN-V cryostat instrument, equipped with Intelligent
Temperature Controller (ITC). For the temperature range of 300K-378K, the
cell was placed in a metal sample holder that was isolated by some
Styrofoam and connected to a thermostat water bath filled with a 50:50
mixture of deionized water and ethylene glycol. All phosphorescent lifetimes
measurements in the temperature range of 77K-378K were performed on an
IBH Fluorocube by a time correlated single photon counting technique using
either a 405 (for 1-3, 5-9) or a 331 nm LED excitation source (for 4 and 10).
The lifetime measurements of thin films for 3 and 10 were performed in-
vacuum environment on an IBH Fluorocube by a time correlated single
photon counting technique using a 405 (for 3) or a 331 nm (for 10) LED
excitation source.

147
Quantum Yield Measurements. The absolute quantum yields of 1-10
,
in
fluid solution have been measured using a more reliant method compared to
those of previously reported.
8
The absolute quantum yield measurement
experiments were carried out in dilute 2-MeTHF solution (~10
-5
M). The
sample was placed in a 1 cm
2
quartz cell and degassed with N
2
. The
quantum yields and the lifetimes of 1wt% doped thin films for fac-Ir(flz)
3
and
fac-Ir(pmb)
3
in poly-(methylmetacrylate) have also been measured. 2 mg of
the sample along with 180 mg of poly-(methylmetacrylate) were dissolved in
1 ml of toluene; the dissolved sample was spincoated on a 0.5x0.5cm
2
quartz
substrate at 3000 rpm for 40 seconds. The absolute quantum efficiencies
were measured using a calibrated Hamamatsu integrating sphere equipped
with a xenon lamp (with either a 330 nm (for 10) or 380 nm (for 1-9)
excitation wavelengths) and photonic multi-channel analyzer C10027. The
accuracy of the quantum efficiency measurements is + 5-10% error of
measurements. The quantum efficiencies data have been processed with
PLQY measurement software U6039-05.
Emission Intensity Measurements. The emission intensity measurement
experiments were also carried out in dilute N
2
-degassed 2-MeTHF solution
(~10
-5
M).The emission intensity measurements of fac-Ir(ppy)
3
was done
using a customized dewar. The dewar was filled with acetone for room
temperature emission intensity measurement. Some dry ice was added into
the acetone for -78ºC emission intensity measurement. For 77K emission
intensity measurement, the dewar was filled with liquid nitrogen. Steady state

148
emission measurements were done using a Photon Technology International
QuantaMaster Model C-60SE spectrofluorimeter with an excitation
wavelength of 360 nm.
5.3. Results and Discussion

5.3.1. Photophysical Properties

5.3.1.1. Emission Properties

The emission spectra of high energy phosphorescent cyclometalated
Ir(III) complexes (1-10) have been investigated. The 77K excitation and
emission spectra of 1- 8 are shown in Figure 5.2. The emission spectra of 1–
10 display highly-structured emission at low temperature (77K), with a
maxima ranging from 380 to 491 nm and luminescent decay lifetimes fall
between 2.6 to 50 μs. The highly-structured emissions imply that a
considerable LC character develops in 1–10 at low temperature and that 77K
luminescence originates from a triplet LC state of 1–10. The maximum
wavelengths of 77K emissions (E
0-0
) of 1-10 all falls in a higher energy than
500 nm. Since the maximum wavelength at 77K represents the triplet energy
of the compounds (E
0-0
), compounds 2-10 with triplet energies higher than
480 nm all meet the criteria to be blue phosphors. The lifetimes at 77K for 1-
10 are all in the microsecond regimes. The lifetimes of 1, 2, 5-8 are in
between 2.6 and 4.2 μs, indicating more charge transfer characteristics. The
lifetimes of 3, 4, and 9 are longer compared to the other iridium complexes in

149
this chapter (14, 25 and 50 μs, respectively), indicating that 3, 4 and 9 have
more ligand-centered characters than 1, 2, and 5-8.

Figure 5.2. 77K Excitation and Emission Spectra of 1-8 (in 2-MeTHF)

300 350 400 450 500 550 600 650 700
0.0
0.2
0.4
0.6
0.8
1.0

Normalized Intensity
Wavelength (nm)
Emission
Excitation
N
N
Ir
2
N
F
F
7
300 350 400 450 500 550 600 650
0.0
0.2
0.4
0.6
0.8
1.0

Normalized Intensity
Wavelength (nm)
Emission
Excitation
N
N
Ir
2
F
F
N
F
F
8
300 350 400 450 500 550 600 650 700
0.0
0.2
0.4
0.6
0.8
1.0

Normalized Intensity
Wavelength (nm)
Emission
Excitation
5
N
N
Ir
2
N
300 350 400 450 500 550 600 650 700
0.0
0.2
0.4
0.6
0.8
1.0

Normalized Intensity
Wavelength (nm)
Emission
Excitation
N
N
Ir
2
F
F
N
6
300 350 400 450 500 550 600 650 700
0.0
0.2
0.4
0.6
0.8
1.0

Normalized Intensity
Wavelength (nm)
Emission
Excitation
N
Ir
3
1
300 350 400 450 500 550 600 650 700
0.0
0.2
0.4
0.6
0.8
1.0

Normalized Intensity
Wavelength (nm)
Emision
Excitation
Ir
3
N
F
F
2
300 350 400 450 500 550 600 650
0.0
0.2
0.4
0.6
0.8
1.0

Normalized Intensity
Wavelength (nm)
Emission
Excitation
N
N
Ir
3
3
300 350 400 450 500 550 600 650
0.0
0.2
0.4
0.6
0.8
1.0

Normalized Intensity
Wavelength (nm)
Emission
Excitation
N
N
Ir
3
F
F
4

150
The room temperature emissions of 1-10 all show some bathochromic
shifts (red shifts) from 77K emissions, except for 3 and 4 where the emission
spectra were too weak to be recorded at 300K ( Ф
300K
of 3, 4 < 0.01). Some
iridium complexes show structured room temperature emission spectra and
some show featureless room temperature emission spectra. The fac-
(ppz)
2
Ir(ppy), 5 and fac-(ppz)
2
Ir(F
2
ppy), 7 show broad room temperature
emission spectra relative to their 77K emission spectra suggesting distorted
excited states in these species (Figure 5.3).

Figure 5.3. 77K and RT Emission Spectra of 5 and 7 in 2-MeTHF

400 450 500 550 600 650 700
0.0
0.2
0.4
0.6
0.8
1.0

Normalized Intensity
Wavelength (nm)
77K
RT
N
N
Ir
2
N
F
F
7
400 450 500 550 600 650 700
0.0
0.2
0.4
0.6
0.8
1.0

Normalized Intensity
Wavelength (nm)
77K
RT
5
N
N
Ir
2
N

151
Table 5.1. Photophysical Properties of Ir(III) Complexes in 2-MeTHF
complexes 77K room temperature
λ
max
(nm)
λ
max
(cm
-1
)
τ
(μs)
λ
max
(nm)
τ
(μs)
Φ
RT
k
r
( s
-1
)
k
nr
( s
-1
)
Ir(ppy)
3
491 20,370 4.0 508 1.6 1.0 6.3 × 10
5
< 3.2 × 10
4

Ir(F
2
ppy)
3
454 22,030 2.6 466 1.7 1.0 5.9 × 10
5
< 3.0 × 10
4

Ir(ppz)
3
412 24,270 14 - 0.002 < 0.01 - > 10
8

Ir(F
2
ppz)
3
388 25,770 25 - 0.007 < 0.01 - > 10
8

Ir(ppz)
2
(ppy) 479 20,8804.2 500 1.7 1.0 5.9 ×10
5
< 3.0 × 10
4

Ir(F
2
ppz)
2
(ppy) 465 21,5104.2 475 3.0 1.0 3.3 × 10
5
< 1.7 × 10
4

Ir(ppz)
2
(F
2
ppy) 463 21,600 3.4 500 1.3 0.55 4.2 × 10
5
1.9 × 10
5

Ir(F
2
ppz)
2
(F
2
ppy) 445 22,470 3.1 457 1.3 0.60 4.6 × 10
5
1.8 × 10
5

Ir(flz)
3
478 20,920 50 480 48 0.81 1.7 × 10
4
3.2 × 10
3

Ir(pmb)
3
380 26,320 3.1 400 1.1 0.37 3.4 × 10
5
2.1 × 10
5

5.3.1.2. Absolute Quantum Yields

The absolute quantum yields of cyclometalated Ir(III) complexes
studied in this chapter (1–10) have been measured in 2-MeTHF solution. The
quantum yields of 1, 2, 5, and 6 in 2-MeTHF at 300K are nearly unity.
Meanwhile, the quantum yields of 3, 4, 7–10 at 300K are <0.01, <0.01, 0.55,
0.60, 0.81, and 0.37, respectively (Table 5.1).
The quantum efficiency of fac-Ir(ppy)
3
is not dependent on
temperatures. It is shown in the emission intensity measurements at various
temperatures (room temperature, -78 °C and 77K) that the emission intensity
of fac-Ir(ppy)
3
does not change with regards to the temperature. The
integrated peak areas are similar in the three temperature measurements:
6.4 x 10
5
, 6.5 x 10
5
, and 6.4 x 10
5
(at RT, -78 °C, and 77K; see Figure 5.4).

152

Figure 5.4. Emission Intensity Measurements of fac-Ir(ppy)
3
, 1

5.3.1.3. Lifetimes Measurements

The lifetimes of 1-10 have also been measured in 2-MeTHF solution.
Although the emission intensity of fac-Ir(ppy)
3
, 1, does not change with
temperatures, the lifetimes of fac-Ir(ppy)
3
do. The lifetimes of 1 at room
temperature, -78 °C, and 77K are about 1.6 μs, 1.8 μs, and 3.8 μs,
respectively. Since only the lifetimes changes with temperature for the case
of fac-Ir(ppy)
3
, it means that its nonradiative state cannot be thermally
populated at room temperature. Therefore, the changes in the lifetimes only
correspond to its radiative states (zero field splitting). The lifetimes at 300K
for 1, 2 and 5–10 are still in the microsecond regimes (ranging from 1.1 to 48
μs). The lifetimes of 3 and 4 at 300K are in the nanosecond regimes (ranging
from 2 to 7 ns). These measurements needed particular care due to oxygen
sensitivity. All samples in dilute 2-MeTHF solution needed to be degassed
400 450 500 550 600 650 700
0.0
5.0x10
3
1.0x10
4
1.5x10
4
2.0x10
4
2.5x10
4
3.0x10
4
3.5x10
4

Emission Intensity
Wavelength (nm)
acetone (RT)
acetone-dry ice (-78 C)
liquid N
2
(77K)

153
properly to achieve the correct values for quantum yield and lifetimes. For
example, fac-Ir(flz)
3
, 9 is very sensitive to oxygen and also has a very long
lifetime (50 μs). Due to its sensitivity and long lifetime, the temperature
dependence data for 9 could not be measured accurately. These conditions
result in very poor accuracy in lifetime measurements (Figure 5.5).

50 100 150 200 250 300
1.6x10
4
1.8x10
4
2.0x10
4
2.2x10
4
2.4x10
4
2.6x10
4
2.8x10
4

decay rate (s
-1
)
Temperature (K)
flzIr, 9
9 at 300K

Figure 5.5. Temperature Dependent Luminescent Lifetimes of flzIr, 9

In Table 5.1., the radiative decay rates (k
r
) at 300K of 1, 2, 5-8, and 10
are all about 10
5
s
-1
. Compounds 3 and 4 have the fastest nonradiative
decay rate (k
nr
) at 300K (>10
8
s
-1
). Compound 9 has the slowest k
r
(10
4
s
-1
)
and the slowest k
nr
(10
3
s
-1
) at 300K.
The quantum yields of luminescent materials are generally determined
by four competing decay rates (Figure 5.6): temperature dependent radiative
decay rate, k
r
(T); temperature independent nonradiative decay rate, k
nr
;

154
temperature dependent nonradiative 1
st
order unimolecular deactivation rate,
k
nr
(T); and 2
nd
order nonradiative deactivation rate, k
nr
(Equation 5.1).
(Equation 5.1)
fac-Ir(flz)
3
, 9, is also considered as an efficient blue-green phosphor ( Φ
RT
~
0.81). However, unlike fac-Ir(ppy)
3
, fac-Ir(flz)
3
has a much longer lifetime and
is more easily quenched by oxygen as well as other molecular processes. In
addition, fac-Ir(flz)
3
emissions are more structured at room temperature as
well as at 77K compared to those of fac-Ir(ppy)
3
. This suggests that fac-
Ir(flz)
3
has less MLCT character than fac-Ir(ppy)
3
, therefore the zero-field
splitting for fac-Ir(flz)
3
should be smaller than that of fac-Ir(ppy)
3
. However,
from temperature dependence data for fac-Ir(flz)
3
, we still cannot measure
precisely how small the ZFS for fac-Ir(flz)
3
; it is very difficult to be precise
because how good the sample being degassed can affect the ZFS of fac-
Ir(flz)
3
. Although the apparent temperature dependence is also weak like fac-
Ir(ppy)
3
, the experimental E
a1
(63 cm
-1
) for fac-Ir(flz)
3
does not represent
precise value for its ZSF. Other nonradiative factors such as bimolecular
processes would be factors that affect the precision of the temperature
dependence data for fac-Ir(flz)
3
. Assuming that the LF state for fac-Ir(flz)
3
is
the same as that of fac-Ir(ppz)
3
due to similar environments around the metal
Ir center, the activation barrier to get to the LF state is about 5400 cm
-1
.
Because of this large energy barrier, we can say that the LF state is not the
state that is responsible for the temperature dependence of fac-Ir(flz)
3
.
Ф =
k
r
(T)
k
r
(T) + k
nr
+ k
nr
(T)
1st
+ k
nr
2nd

155
2
nd
order k
nr
. Temperature independent 2
nd
order nonradiative decay
processes can involve two different processes, one is oxygen-quenching and
the second is self-quenching. For complexes studied in this chapter (1-10),
all samples are in dilute concentrations (∼10
-5
M) and are degassed properly,
so the 2
nd
order nonradiative decay processes can be simply omitted from
Equation 5.1. The simplified equation for determining luminescent quantum
yields is shown in Equation 5.2 below.
(Equation 5.2)

S
1
T
1
ISC
hν
abs
k
r
(T)
NR
E
a
k
nr
k
nr
(T)

Figure 5.6. Schematic Energy Diagram with Different Decay Rates

Temperature Dependence. In general, Boltzmann analysis of the
temperature dependence data in this chapter reveals two regimes: a lower
temperature regime and a higher temperature regime. The lower temperature
regime is related to zero-field splitting (ZFS) in radiative states, and the
higher temperature regime relates to thermal population of NR state.

Ф =
k
r
(T)
k
r
(T) + k
nr
+ k
nr
(T)
1st

156
5.3.2. Radiative State

5.3.2.1. Temperature Dependence: Zero Field Splitting

Radiative Processes, k
r
. Previous assumption about all radiative processes
being temperature independent does not always hold for all transition metal
complexes. Unless the energy separation between T
I
and T
III
substates (ZFS)
is less than 3k
B
T (less than 20 cm
-1
), there would always be temperature
dependent radiative processes for transition metal complexes. To achieve a
quantum yield of nearly unity at room temperature, nonradiative decay rate
(k
nr
) at least needs to be two orders of magnitude smaller relative to its
radiative decay rates (k
r
), e.g. complexes 1, 2, 5 and 6. For example, 1, fac-
Ir(ppy)
3
, has a quantum yield of unity at room temperature. Despite its
quantum yield being unity at room temperature, temperature dependent
lifetimes between 77K-300K can still be observed for 1 (Figure 5.7). These
temperature dependent lifetimes observations only originate from its radiative
states, since nonradiative decay rates ((k
nr
) is at least two orders of
magnitude smaller relative to its radiative decay rates (k
r
). Activation energy
of 123 cm
-1
from T
I
to T
III
sublevel for fac-Ir(ppy)
3
extracted from the
Boltzmann analysis in this chapter matches closely with Yersin’s
observations. Through personal communication with Yersin, ZFS of 1 in THF
was found to be in the range of 90 and 150 cm
-1
.

157

100 150 200 250 300
3x10
5
4x10
5
5x10
5
6x10
5
0.005 0.010
12.5
13.0
13.5

ln (decay rate)
1/T (K
-1
)

1
decay rate (s
-1
)
Temperature (K)
1 at 300K

Figure 5.7. Temperature Dependent Luminescent Lifetimes of fac-
Ir(ppy)
3
, 1 (Inset: Arrhenius Plot)

5.3.3. Nonradiative State

Nonradiative Processes. There are two possible nonradiative (NR)
processes that can be responsible for deactivation occuring in transition
metal complexes. One is a temperature independent process and the other
one is a temperature dependent process.

5.3.3.1. Temperature Independence: Energy Gap Law

k
nr
. The temperature independent NR process can occur through two
different ways: surface crossing from T
1
and S
0
and/or C–H vibrational

158
deactivations. C–H vibrational modes are usually not effective for blue
phosphors. According to the energy gap law, nonradiative decay rate
decreases exponentially with increasing emission energy. The energy gap
law states that a series of complexes with similar ground and excited states
will show linearity between ln (k
nr
) and emission energy. Extrapolation of
energy gap law plot for Ru(II) complexes results in k
nr
< 10
4
s
-1
for green
phosphors (20,000 cm
-1
); if the plot is extrapolated further for blue
phosphors, k
nr
would be so much smaller than 10
4
s
-1
. As a result, the
temperature independent NR processes are not effective for blue
phosphorescent iridium (III) complexes.
5.3.3.2. Temperature Dependence: Ligand Field State

k
nr
(T). In this chapter, temperature dependent NR state for blue iridium
complexes can be approximated from lifetime measurements at higher
temperature regime, except for 1 and 9. For example, 1, fac-Ir(ppy)
3
, has
only temperature dependent radiative process, for temperature dependent
NR process is not accessible within the limitations of our temperature
dependent measurements. Only temperature independent NR may be
effective for 1, however k
nr
for 1 is < 10
4
s
-1
for possible surface crossing
from T
1
to S
0
can occurs. The rate of < 10
4
s
-1
is very slow, thus not very
likely to happen for the case of fac-Ir(ppy)
3
.

159
5.3.4. Kinetic Parameters for the Luminescent Excited State
Decay

The luminescent lifetimes of 1–10 have been investigated in 2-MeTHF
solution in the temperature range of 77K–373K. Boltzmann two levels model
was used to fit temperature dependence data, plotted as 1/τ vs. T:
1/ τ = k
observed
= k
0
+ k
1
exp (-E
a1
/k
B
T) + k
2
exp (-E
a2
/k
B
T) (Equation 5.3)
1+ exp (-E
a1
/k
B
T) + exp (-E
a2
/k
B
T)
τ = experimental luminescent lifetime at a certain temperature;
k
0
= k
r
+ k
nr
at lowest temperature (77K)
k
1
, k
2
= decay rate constants; E
a1
, E
a2
= activation energies
k
B
= Boltzmann constant, 8.617x10
-5
eV/K = 0.695 cm
-1
/K; T= temperature (K)
Arrhenius kinetic model was also demonstrated to fit the plot of ln (1/ τ) vs.
1/T for 3 and 4. The values of kinetic parameters obtained from the Arrhenius
fits are similar to those obtained using the Boltzmann two levels model fits.
Arrhenius kinetic model shown below was demonstrated to fit the
temperature dependence data of 3 and 4:
1/ τ = k
0
+ k
1
exp (-E
a1
/k
B
T) + k
2
exp (-E
a2
/k
B
T)
ln(1/ τ) = ln[k
1
exp (-E
a1
/k
B
T) + k
2
exp(-E
a2
/k
B
T)]
ln(1/ τ) = [lnk
1
+ (-E
a1
/k
B
)*1/T] + [ln k
2
+ (-E
a2
/k
B
)*1/T] (Equation 5.4)

160
The kinetic parameters for the decay of the luminescent excited state can be
obtained for 1–10 using Boltzmann two levels model. The addition of a 3
rd

term did not improve the fit. The kinetic parameters for the luminescent
excited state decay in 2-MeTHF solution for 1-10 are summarized in Table
5.2.
Table 5.2. Kinetic Parameters for the Luminescent Excited State Decay
in 2-MeTHF solution.
complexes k
1
( s
-1
)
E
a1

(cm
-1
)
k
2

( s
-1
)
E
a2

(cm
-1
)
NR
(cm
-1
)
NR
(eV)
Φ
RT

Ir(ppy)
3

1.8 × 10
6

123

-

-

-

-

1.0
Ir(F
2
ppy)
3
1.3 × 10
6
100 6.1 × 10
11
4160 26,190 3.25 1.0
Ir(ppz)
3
1.4 × 10
5
40 9.7 × 10
12
2100 26,370 3.27 < 0.01
Ir(F
2
ppz)
3
1.1 × 10
5
55 4.8 × 10
14
3020 28,800 3.57 < 0.01
Ir(ppz)
2
(ppy) 1.4 × 10
6
174 1.3 × 10
14
4570 25,440 3.15 1.0
Ir(F
2
ppz)
2
(ppy) 5.8 × 10
5
74 3.1 × 10
14
5040 26,540 3.29 1.0
Ir(ppz)
2
(F
2
ppy) 8.9 × 10
5
193 4.8 × 10
13
3830 25,430 3.15 0.55
Ir(F
2
ppz)
2
(F
2
ppy) 9.4 × 10
5
92 6.0 × 10
13
3930 26,400 3.27 0.60
Ir(flz)
3
3.6 × 10
4
63 - - - - 0.81
Ir(pmb)
3
4.0 × 10
5
15 7.2 × 10
9
1900 28,220 3.50 0.37

The plots of temperature dependence data mostly consist of two
regimes: a lower temperature regime corresponds to zero-field splitting (ZSF)
and a higher temperature regime corresponds to nonradiative (NR) state.
From the temperature dependence data, the zero-field splitting of T
I
and T
III

substates of 1–10 are approximated within the range of 15 and 193 cm
-1
. The
decay rates from T
III
substate of 1–8, and 10 are all about 10
5
and 10
6
s
-1
,
except that of 9 showing the slower decay rate from T
III
substate (10
4
s
-1
).
From the temperature dependence data of compound 1–10, the energy
barriers from triplet state to the NR state could also be approximated. The

161
energy barriers to populate the NR states for 2–8, and 10 range from 1900 to
5037 cm
-1
(Table 5.2). For compound 1 and 9, the NR state still could not be
observed within the limitations of our temperature dependence
measurements. The decay rate constants from the NR state (k
2
) of 3–8 are
all about 10
13
and 10
14
s
-1
. For 2 and 10, k
2
is slower than 10
13
s
-1
(10
11
and
10
9
s
-1
, respectively).
For fac-Ir(ppz)
3
and fac-Ir(F
2
ppz)
3
(3 and 4), since their k
nr
> 10
8
s
-1
,
the room temperature emission spectra are extremely weak. This means that
temperature dependent NR state for 3 and 4 is accessible at room
temperature.
Nonradiative deactivating LF state (NR state) for fac-Ir(ppz)
3
and fac-
Ir(F
2
ppz)
3
can be thermally populated at room temperature. Meanwhile, this
NR state only starts to be populated at temperatures higher than room
temperature for 2, 5–8, and 10. Temperature dependent NR state is not
accessible for fac-Ir(ppy)
3
, 1 and fac-Ir(flz)
3
, 9 within the limitations of our
temperature dependent measurements.
The energy barrier to go to NR state from the triplet state for fac-
Ir(ppz)
3
(3) is about 1000 cm
-1
lower compared to that of fac-Ir(F
2
ppz)
3
(4).
This implies that the energy needed to break Ir–N bond in fac-Ir(F
2
ppz)
3
(4) is
higher than that of fac-Ir(ppz)
3
(3). From X-ray crystallography data, Ir-N
bonds in fac-Ir(F
2
ppz)
3
(2.095(6), 2.099(6), 2.102(5) Å) are slighter shorter
than that of fac-Ir(ppz)
3
(2.117(5), 2.135(5), 2.120(6) Å), thus stronger; it
would take more energy to break a stronger Ir–N bond in fac-Ir(F
2
ppz)
3.

162
Strong temperature dependent lifetimes are observed for fac-Ir(ppz)
3

(3) (ranging from 2 ns to 14 μs) and fac-Ir(F
2
ppz)
3
(4) (ranging from 7 ns to
25 μs), resulting in very poor luminescent emission at room temperature ( Φ <
0.01). There is certainly a higher nonradiative deactivating LF state that can
be thermally populated for 3 and 4

at room temperature. The values of kinetic
parameters for the temperature dependent lifetimes of 3

are E
a1,
E
a2
=40 cm
-1
,
2100 cm
-1
and k
1
, k
2
= 1.4 × 10
5
s
-1
, 9.7 × 10
12
s
-1
. The value of E
a1

represents the energy separation between triplet state and the LF state,
meanwhile k
1
is the deactivation rate from the LF state. A fast deactivation
rate of fac-Ir(ppz)
3
from the LF state (~10
13
s
-1
) represents the bond-breaking
features of pyrazolyl (ppz) ligands in fac-Ir(ppz)
3
. The LF state for fac-Ir(ppz)
3

is equal to 75 kcal/mol, this is close to the expected bond strength of Ir-C (80
kcal/mol).

Since Ir-N is determined to be longer thus weaker than Ir-C
phenyl
from previous reported x-ray crystal structure of fac-Ir(ppz)
3
, then Ir-N bond is
the bond that is most likely breaking during the deactivation process.

163

50 100 150 200 250 300
0.0
2.0x10
8
4.0x10
8
0.004 0.008 0.012
10
15
20
3
4

ln decay rate
1/T (K
-1
)

decay rate (s
-1
)
Temperature (K)

Figure 5.8. Temperature Dependent Luminescent Lifetimes of fac-
Ir(ppz)
3
, 3 and fac-Ir(F
2
ppz)
3
, 4 (inset: Arrhenius Plot)

The deactivation rate of NR state for 3–8 is about 10
13
or 10
14
s
-1
,
suggesting bond rupture processes are involved. Supporting the involvement
of the bond rupture process, there was a publication on DFT calculation of
fac-Ir(ppy)
3
and fac-Ir(ppz)
3
in Chemistry Letters.
22
According to this paper,
the most favorable form (lowest in energy) is when one of ppz breaks and
twists. The lowest energy minimum for fac-Ir(ppz)
3
is the ligand field state
(involving the bond rupture and rotation of one ppz ligand) (Figure 5.9).

164

2.0 kcal/mol
exp.= 6 kcal/mol
Treboux, et. al, Chem.Lett, 36 (2007)

Figure 5.9. Ligand Field State of fac-Ir(ppz)
3
, 3

In addition, temperature dependent lifetimes have also observed for
fac-Ir(F
2
ppy)
3
, 2, fac-(ppz)
2
Ir(ppy), 5, fac-(ppz)
2
Ir(F
2
ppy), 6, fac-
(F
2
ppz)
2
Ir(ppy), 7 and fac-(F
2
ppz)
2
Ir(F
2
ppy), 8 (Figure 5.10 and Figure 5.11).

50 100 150 200 250 300 350 400
4x10
5
5x10
5
6x10
5
7x10
5

decay rate (s
-1
)
Temperature (K)
2
2 at 300K

Figure 5.10. Temperature Dependent Lifetimes of fac-Ir(F
2
ppy)
3
, 2

165
50 100 150 200 250 300 350 400
0.0
5.0x10
6
1.0x10
7
1.5x10
7
2.0x10
7

decay rate (s
-1
)
Temperature (K)
7
8
7 at 300K 8 at 300K
50 100 150 200 250 300 350 400
1x10
6
2x10
6
3x10
6
5
6

decay rate (s
-1
)
Temperature (K)
6 at 300K 5 at 300K

Figure 5.11. Temperature Dependent Luminescent Lifetimes of (A) fac-
(ppz)
2
Ir(ppy), 5 and fac-(ppz)
2
Ir(F
2
ppy), 6; (B) fac-(F
2
ppz)
2
Ir(ppy), 7 and
fac-(F
2
ppz)
2
Ir(F
2
ppy), 8

For the case of fac-Ir(pmb)
3
, moderate temperature dependent
lifetimes have been observed. There is still a higher LF state that can be
thermally populated for fac-Ir(pmb)
3
. The values of kinetic parameters for the
temperature dependent lifetimes of fac-Ir(pmb)
3
are E
a1,
E
a2
= 15 cm
-1
, 1900
cm
-1
and k
1
, k
2
= 4.0 × 10
5
s
-1
, 7.2 × 10
9
s
-1
. Although the energy separation
between triplet state and LF state is similar to that of fac-Ir(ppz)
3
, a slower
deactivation rate from LF state (~10
9
s
-1
) makes room temperature emission
possible for fac-Ir(pmb)
3
. The LF state for fac-Ir(pmb)
3
is equal to 81

166
kcal/mol, which happens to be close to Ir-C
carbene
bond strength. Fac-Ir(pmb)
3

emits more efficiently at room temperature ( Φ = 0.37) than fac-Ir(ppz)
3

because its deactivation pathway is not through thermal population of the LF
state, but instead, fac-Ir(pmb)
3
undergoes a surface crossing with a rate of
10
9
s
-1
to another state, then radiates to the ground state.
0.002 0.004 0.006 0.008 0.010 0.012 0.014
12.5
13.0
13.5
14.0
14.5
15.0
15.5
T(K)
lifetime (ns)
ln (1/tau)
1/T (K
-1
)
10
500 250 167 125 100 83 71
2260
832
306
3727
1371
504
186
10 at 300K

Figure 5.12. Temperature Dependent Luminescent Lifetimes of fac-
Ir(pmb)
3
, 10
Temperature dependent lifetimes have also been studied in viscous
media (poly-THF, polystyrene) for fac-Ir(ppz)
3
and fac-Ir(pmb)
3
. There is only
a little effect on the temperature dependent characteristics from changing the
matrix; it does not change the overall qualitative picture of luminescent
temperature dependence (see Figure 5.13. and 5.14.).

167

Figure 5.13. Temperature Dependent Lifetimes of fac-Ir(ppz)
3
, 3, in
Various Matrices: Polystyrene, 2-MeTHF, and Poly-THF

0.002 0.004 0.006 0.008 0.010 0.012 0.014
12.5
13.0
13.5
14.0
14.5
15.0
15.5
T(K)
lifetime(ns)
ln (1/tau)
1/T (K
-1
)
10 in 2-MeTHF
0.5wt% 10 in PS

500 250 167 125 100 83 71
186
2260
832
306
3727
1371
504

Figure 5.14. Temperature Dependent Lifetimes of fac-Ir(pmb)
3
, 10, in
dilute 2-MeTHF solution vs. doped thin film in polystyrene matrix.
0.004 0.006 0.008 0.010 0.012 0.014
10
12
14
16
18
20
ln(decay rate)
1/T (K
-1
)
PS data
Solution data in 2-MeTHF (tau @RT = 2.74 ns)
Poly-THF data (Two-exponential fit- T2 plotted)
Poly-THF data (Single-exponential fit- T1 omitted)
N
N
Ir
3
3

168
5.4. Conclusion

In conclusion, the temperature dependent study of blue
phosphorescent cyclometalated iridium complexes in this chapter offers very
useful information regarding the deactivation pathways of these complexes.
The kinetic parameters of the nonradiative (NR) deactivating state extracted
from the temperature dependent study is very useful to evaluate various
phosphors for OLEDs or other purposes. It turns out that almost all NR states
of blue phosphorescent cyclometalated iridium complexes can be thermally
populated at around 3-4 eV (Figure 5.15), these voltages are within the turn-
on voltage range where OLEDs devices usually operate. This would set a
limit in finding good blue phosphorescent iridium complexes to be employed
as dopants in OLEDs.
cm
-1
(x10
3
)
28
26
20
4160 cm
-1
(10
11
)
4570 cm
-1
(10
14
)
2100 cm
-1
(10
13
)
22
3020 cm
-1
(10
14
)
5040 cm
-1
(10
14
)
3830 cm
-1
(10
13
)
3930 cm
-1
(10
13
)
3.5
eV
3.2
2.7
2.5
100 cm
-1
(10
6
)
40 cm
-1
(10
5
)
55 cm
-1
(10
5
)
174 cm
-1
(10
6
)
74 cm
-1
(10
5
)
193 cm
-1
(10
5
)
92 cm
-1
(10
5
)
Φ
RT
= 1.0 < 0.01 < 0.01 0.60 0.55 1.0 1.0
1900 cm
-1
(10
9
)
0.37
15 cm
-1
(10
5
)
2 3 4 5 10 8 6 7

Figure 5.15. Temperature Dependent Kinetic Parameters for 2-8, 10

169
More importantly, the temperature dependence study results and
analyses presented in this chapter indicate that nonradiative decay of high
energy (near-UV to sky blue) Ir-based phosphors typically involves a bond
rupture process. We do not know if the ruptured bond can reform, but it is
clear that in many blue cyclometalated Ir complexes, i.e. 3-8, the bond
rupture occurs with a rate of 10
13
or 10
14
s
-1
. Inhibition of the bond rupture
process in blue materials is expected to lead to more stable high energy
phosphors. Although activation energies needed to thermally populate the
ligand field (LF) states of neutral iridium (III) complexes with strong field
ligands (i.e. fac-Ir(pmb)
3
) can be similar to those of iridium (III) complexes
with weaker field ligands (i.e. fac-Ir(ppz)
3
); their nonradiative decay is quite
different. C^N type ligands shows bond rupture evidence in their nonradiative
decay rates (10
13
-10
14
s
-1
), but stronger field ligands, such as carbenes, give
nonradiative decay states that do not involve bond rupture (10
9
s
-1
). The
strong sigma bonding from the strong field ligands such as carbene to the Ir
metal center can destabilize the LF state. From the LF state, neutral iridium
(III) complexes with strong field ligands can undergo a surface crossing to
another state that would radiate to the ground state. This leads to an
increase in quantum efficiency and stability of the complex to excitation,
since the decay process does not involve bond rupture. This provides a
possible method to select high performance phosphors in the future, by
selecting for materials which do not have bond rupture in their nonradiative
decay.

170
Table 5.3. Crystallographic data for fac-Ir(F
2
ppz)
3
, 4
Empirical formula C
27
H
15
F
6
IrN
6

Formula weight 729.65
Temperature 296(2) K
Wavelength 0.71073 Å
Crystal system Monoclinic
Space group P2(1)/n
Unit cell dimensions a = 10.512(3) Å; α= 90°.
b = 16.874(4) Å; β= 90.430(4)°.
c = 13.553(4) Å; γ = 90°.
Volume
2404.0(10) Å
3

Z 4
Density (calculated)
2.016 Mg/m
3

Absorption coefficient
5.632 mm
-1

F(000) 1400
Crystal size
0.125 x 0.075 x 0.05 mm
3

Theta range for data collection 1.93 to 24.71°.
Index ranges -12<=h<=12, -18<=k<=19, -14<=l<=15

Reflections collected 12142
Independent reflections 4100 [R(int) = 0.0646]
Completeness to theta = 24.71° 100.0 %
Transmission Factors min/max ratio: 0.814322

Refinement method
Full-matrix least-squares on F
2

Data / restraints / parameters 4100 / 0 / 362
Goodness-of-fit on F
2

1.014
Final R indices [I>2sigma(I)] R1 = 0.0438, wR2 = 0.0918
R indices (all data) R1 = 0.0617, wR2 = 0.0985
Largest diff. peak and hole
0.994 and -0.883 e.Å
-3

171
Chapter 5 References

1. (a) Holder, E.; Langeveld, B.M.W.; Schubert, U.S. Adv. Mater. 2005, 17,
1109. (b) Hwang, F.-M.; Chen, H.-Y.; Chen, P.-S.; Liu, C.-S.; Chi, Y.; Shu,
C.-F.; Wu, F.-I.; Chou, P.-T.; Peng, S.-M.; Lee, G.-H. Inorg. Chem. 2005, 44,
1344. (c) Tung, Y.-L.; Lee, S.-W.; Chi, Y.; Chen, L.-S.; Shu, C.-F.; Wu, F.-I.;
Carty, A.J.; Chou, P.-T.; Peng, S.-M.; Lee, G.-H. Adv. Mater. 2005, 17, 1059.
(d) Chou, P.-T.; Chi, Y. Eur. J. Inorg. Chem. 2006, 3319.

2. (a) Lamansky, S.; Djurovich, P.I.; Murphy, D.; Abdel-Razzaq, F.; Lee, H.E.;
Adachi, C.; Burrows, P.E.; Forrest, S.R.; Thompson, M.E. J.Am. Chem. Soc.
2001, 123, 4304. (b) Lamansky, S.; Djurovich, P.I.; Abdel-Razzaq, F.; Garon,
S.; Murphy, D.L.; Thompson, M.E. J.Appl. Phys. 2002, 92, 1570. (c) Chen,
F.C.; Yang, Y; Thompson, M.E.; Kido, J. Appl.Phys.Lett. 2002, 80, 2308. (d)
Markham, J.P.J.; Lo, S.-C.; Magennis, S.W.; Burn, P.L.; Samuel, I.D.W.
Appl.Phys.Lett. 2002, 80, 2645. (e) Zhu, W.; Mo, Y; Yuan, M.; Yang, W.;
Cao, Y. Appl.Phys.Lett. 2002, 80, 2045. (f) Adachi, C.; Baldo, M.A.; Forrest,
S.R.; Thompson, M.E. J. Appl. Phys. 2001, 90, 4058. (g) Ikai, M.; Tokito, S.;
Sakamoto, Y.; Suzuki, T.; Taga, Y. Appl.Phys.Lett. 2001, 79, 156. (h)
D’Andrade, B.W.; Forrest, S.R. Adv. Mater. 2004, 16, 1585. (i) Gong, X.;
Robinson, M.R.; Ostrowski, J.C.; Bazan, G.C.; Heeger, A. J. Adv. Mater.
2002, 14, 581.

3. (a) Adachi, C.; Kwong, R.C.; Djurovich, P.; Adamovich, V.; Baldo, M.A.;
Thompson, M.E.; Forrest, S.R. Appl. Phys. Lett. 2001, 79, 2082. (b) Adachi,
C.; Lamansky, S.; Baldo, M.A.; Kwong, R.C.; Thompson, M.E.; Forrest, S.R.
Appl.Phys.Lett. 2001, 78, 1622. (c) Goushi, K.; Kawamura, Y.; Sasabe, H.;
Adachi, C. Japanese Journal of Applied Physics. 2004, 43, L937-L939. (d)
Marchetti, A.P.; Deaton, J.C.; Young, R.H. J. Phys.Chem. A. 2006, 110,
9828-9838. (e) Tanaka, I.; Tabata, Y.; Tokito, S. Japanese Journal of Applied
Physics. 2004, 43, L1601-L1603. (f) Baldo, M.A.; O’Brien, D.F.; You, Y.;
Shoustikov, A.; Sibley, S.; Thompson, M.E.; Forrest, S.R. Nature. 1998, 395,
151. (g) Baldo, M.A.; Lamansky, S.; Burrrows, P.E.; Thompson, M.E.;
Forrest, S.R. Appl. Phys. Lett. 1999, 75, 4. (h) Thompson, M.E.; Burrows,
P.E.; Forrest, S.R. Current Opinion in Solid State & Material Science. 1999,
4, 369. (i) Baldo, M.A.; Thompson, M.E.; Forrest, S.R. Nature. 2000, 403,
750.

4. (a) Kober, E.M.; Caspar, J.V.; Lumpkin, R.S.; Meyer, T.J. J. Phys. Chem.
1986, 90, 3722. (b) Perkins, T.A.; Pourreau, D.B.; Netzel, T.L.; Schanze, K.S.
J.Phys.Chem. 1989, 93, 4511. (c) Adachi, C.; Baldo, M.A.; Forrest, S.R.;
Lamansky, S.; Thompson, M.E.; Kwong, R.C. Appl. Phys.Lett. 2001, 78,
1622. (d) Tsuboyama, A.; Iwawaki, H.; Furugori, M.; Mukaide, T.; Kamatani,
J.; Igawa, S.; Moriyama, T.; Miura, S.; Takiguchi, T.; Okada, S.; Hoshino, M.;
Ueno, K. J. Am. Chem. Soc. 2003, 125, 12971.

172
5. Tamayo, A.B.; Alleyne, B.D.; Djurovich, P.I.; Lamansky, S.; Tsyba, I.; Ho,
N.N.; Bau, R.; Thompson, M.E. J. Am. Chem. Soc. 2003, 125, 7377-7387.

6. Chew, S.; Lee, C.S.; Lee, S.-T.; Wang, P.; He, J.; Li, W.; Pan, J.; Zhang,
X.; Kwong, H. Appl. Phys. Lett. 2006, 88, 093510.

7. Lo, S.-C; Shipley, C.P.; Bera, R.N.; Harding, R.E.; Cowley, A.R.; Burn,
P.L.; Samuel, I.D.W. Chem. Mater. 2006, 18, 5119-5129.

8. Sajoto. T.; Djurovich, P.; Tamayo, A.; Yousufuddin, M.; Bau, R.;
Thompson, M.E. Inorganic Chemistry. 2005, 44 (22), 7992 -8003.

9. Li, J.; Djurovich, P.I.; Alleyne, B.D.; Yousufuddin, M.; Ho, N.N.; Thomas,
J.C.; Peters, J.C.; Bau, R.; Thompson, M.E. Inorg. Chem. 2005, 44, 1713-
1727.

10. Yang, C.-H, Cheng, Y.-M.; Chi, Y. Hsu, C.-J.; Fang, F.-C.; Wong, K.-T.;
Chou, P.-T.; Chang, C.-H.; Tsai, M.-H.; Wu, C.-C. Angew. Chem. Int. Ed.
2007, 46, 2418-2421.

11. Dedeian, K.; Shi, J.; Forsythe, E.; Morton, D.C.; Zavalij, P.Y. Inorg.
Chem. 2007, 46, 1603-1611.

12. Wu, L.-L; Yang, C.-H.; Sun, I.-W.; Chu, S.-Y.; Kao, P.-C.; Huang, H.-H.
Organometallics. 2007, 26, 2017-2023.

13. Yang, C.-H.; Li, S.-W.; Chi, Y.; Cheng, Y.M.; Yeh, Y.-S.; Chou, P.-T.;
Lee, G.-H.; Wang, C.-H.; Shu, C.-F. Inorg. Chem. 2005, 44, 7770-7780.

14. (a) Allsopp, S.R.; Cox, A.; Kemp, T.J.; Reed, W.J. Inorganic
Photophysics in Solution. 1978, I-12, 353-362. (b) Lumpkin, R.; Kober, E.;
Worl, L.; Murtaza, Z.; Meyer, T.J. J.Phys.Chem. 1990, 94, 239-243. (c)
Barigelletti, F.; Juris, A.; Balzani, V.; Belser, P.; Zelewsky, A. J.Phys.Chem.
1986, 90, 5190-5193. (d) Van Houten, J.; Watts, R.J. J.Am.Chem.Soc. 1976,
98, 4853-4858. (e) Elfring, Jr, W.H.; Crosby, G.A. J.Am.Chem. Soc. 1981,
103, 2683-2687. (f) Yu, J.-K; Hu, Y.-H; Cheng, Y.-M; Chou, P.-T.; Peng, S.-
M.; Lee, G.-H.; Carty, A.J.; Tung, Y.-L.; Lee, S.-W.; Chi, Y.; Liu, C.-S. Chem.
Eur. J. 2004, 10, 6255-6264.

15. Hager, G.D.; Watts, R.J.; Crosby, G.A. J. Am.Chem.Soc. 1975, 97(24),
7037-7042.

16. Turro, N. J. Modern Molecular Photochemistry. 1991, p.27.

173
17. Alary, F.; Heully, J.-L.; Bijeire, L.; Vicendo, P. Inorganic Chemistry. 2007,
46, 3154-3165.

18. Yu, J.-K.; Hu, Y.-H.; Cheng, Y.-M.; Chou, P.-T.; Peng, S.-M.; Lee, G.-H.;
Carty, A.-J.; Tung, Y.-L.; Lee, S.-W.; Chi, Y.; Liu, C.-S. Chem. Eur. J. 2004,
10, 6255-6264.

19. (a) Barigelletti, F.; Sandrini, D.; Maestri, M.; Balzani, V; Zelewsky, A.;
Chassot, L.; Jolliet, P.; Maeder, U. Inorganic Chemistry. 1988, 27, 3644-
3647. (b) Brozik, J.A.; Crosby, G.A. J.Phys. Chem. A. 1998, 102, 45-50.

20. Yeh, Y.-S.; Cheng, Y.-M.; Chou, P.-T.; Lee, G.-H.; Yang, C.-H.; Chi, Y.;
Shu, C.-F.; Wang, C.-H. Chem.Phys. Chem. 2006, 7, 2294-2297.

21. Filkenzeller, W.J.; Yersin, H. Chemical Physics Letters. 2003, 377, 299-
305.

22. Treboux, G.; Mizukami, J.; Yabe, M.; Nakamura, S. Chemistry Letters.
2007, 36, 1344-1345.

174
Bibliography

Adachi, C.; Baldo, M.A.; Forrest, S.R.; Thompson, M.E. J. Appl. Phys. 2001,
90, 4058.

Adachi, C.; Kwong, R.C.; Djurovich, P.; Adamovich, V.; Baldo, M.A.;
Thompson, M.E.; Forrest, S.R. Appl. Phys. Lett. 2001, 79, 2082.

Adachi, C.; Lamansky, S.; Baldo, M.A.; Kwong, R.C.; Thompson, M.E.;
Forrest, S.R. Appl. Phys. Lett. 2001, 78, 1622.

Alary, F.; Heully, J.-L.; Bijeire, L.; Vicendo, P. Inorganic Chemistry. 2007, 46,
3154-3165.

Allsopp, S.R.; Cox, A.; Kemp, T.J.; Reed, W.J. Inorganic Photophysics in
Solution. 1978, I-12, 353-362.

Anderson, P.A.; Anderson, R.F.; Furue, M.; Junk, P.C.; Keene, F.R.;
Patterson, B.T.; Yeomans, B.D. Inorg. Chem. 2000, 39, 2721-2728.

Baldo, M.A.; Lamansky, S.; Burrows, P.E.; Thompson, M.E.; Forrest, S.R.
Appl. Phys. Lett. 1999, 75, 4.

Baldo, M.A.; O’Brien, D.F.; You, Y.; Shoustikov, A.; Sibley, S.; Thompson,
M.E.; Forrest, S.R. Nature, 1998, 395, 151.

Baldo, M. A.; O'Brien, D. F.; Thompson, M. E.; Forrest, S. R. Physical
Review B, 1999, 60, 14422.

Baldo, M.A.; Thompson, M.E.; Forrest, S.R. Nature 2000, 403, 750.

Balzani, V.; Scandola, F. Supramolecular Photochemistry; Ellis Horwood:
Chichester, U.K., 1991.

Balzani, V.; Credi, A.; Scandola, F. Transition Metals in Supramolecular
Chemistry; Fabbrizzi, L., Poggi, A., Eds.; Kluwer: Dordrecht, The
Netherlands, 1994; p1.

Balzani, V.; Juris, A.; Venturi, M.; Campagna, S.; Serroni, S. Chem. Rev.
1996, 96, 759.

Barigelletti, F.; Juris, A.; Balzani, V.; Belser, P.; Zelewsky, A. J.Phys.Chem.
1986, 90, 5190-5193.

175
Barigelletti, F.; Sandrini, D.; Maestri, M.; Balzani, V; Zelewsky, A.; Chassot,
L.; Jolliet, P.; Maeder, U. Inorganic Chemistry. 1988, 27, 3644-3647.

Belmore, K.A.; Vanderpool, R.A.; Tsai, J.C.; Khan, M.A.; Nicholas, K.M. J.
Am.Chem.Soc. 1988, 110, 2004.

Berg-Brennan, C.; Subramanian, P.; Absi, M.; Stern, C.; Hupp, J. T. Inorg.
Chem. 1996, 35, 3719-3722.

Bignozzi, C.A.; Schoonover, J.R.; Scandola, F. Prog. Inorg. Chem. 1997, 44,
1.

Blessing, R.H. Acta Crystallogr. 1995, A51, 33.

Brennaman, M.K.; Meyer, T.J.; Papanikolas, J.M. J. Phys. Chem. A. 2004,
108, 9938.

Brozik, J.A.; Crosby, G.A. J.Phys. Chem. A. 1998, 102, 45-50.

Burrows, P. E. Gu, G.; Bulovic, V.; Forrest, S. R.; Thompson, M. E. IEEE
Trans. Electron. Dev. 1997, 44, 1188.

Chen, F.C.; Yang, Y.; Thompson, M.E.; Kido, J. Appl. Phys. Lett. 2002, 80,
2308.

Chew, S.; Lee, C.S.; Lee, S.-T.; Wang, P.; He, J.; Li, W.; Pan, J.; Zhang, X.;
Kwong, H. Appl. Phys. Lett. 2006, 88, 093510.

Chin, K.-F.; Cheung, K.-K.; Yip, H.-K.; Mak, T.C.W.; Che, C.M. J.Chem.Soc.,
Dalton Trans. 1995, 4, 657-665.

Chou, P.-T.; Chi, Y. Eur. J. Inorg. Chem. 2006, 3319.

Colombo, M.G.; Brunold, T.C.; Riedener, T.; Güdel, H.U. Inorg. Chem. 1994,
33, 545.

Colombo, M.G.; Hauser, A; Güdel, H.U. Inorg. Chem. 1993, 32, 3088.

Crosby, G. A. J. Chem. Phys. 1967, 64, 160.

D’Andrade, B.W.; Forrest, S.R. Adv. Mater. 2004, 16, 1585.

Dedeian, K.; Djurovich, P.I.; Garces, F.O.; Carlson, G.; Watts, R.J. Inorg.
Chem. 1991, 30, 1685-1687.

176
Dedeian, K.; Shi, J.; Forsythe, E.; Morton, D.C.; Zavalij, P.Y. Inorg. Chem.
2007, 46, 1603-1611.

Demas, J.N.; Crosby, G.A. J. Phys. Chem. 1978, 82, 991.

Demas, J. N.; Harris, E.W.; Flynn, C.M.; Diemente, J.D. J. Am. Chem. Soc.
1975, 97, 3838.

Demas, J. N.; Harris, E.W.; McBride, R.P. J. Am. Chem. Soc. 1977, 99,
3547.

DePriest, J.; Zheng, G.Y.; Goswami, N.; Eichhorn, D.M.; Woods, C.; Rillema,
D.P. Inorg. Chem. 2000, 39, 1955.

Elfring, Jr, W.H.; Crosby, G.A. J.Am.Chem. Soc. 1981, 103, 2683-2687.

Filkenzeller, W.J.; Yersin, H. Chemical Physics Letters. 2003, 377, 299-305.

Forrest, S.R.; Burrows, P. E.; Thompson, M.E. In Organic Electroluminescent
Materials and Devices; Miyata, S., Nalwa, H. S., Eds.; Grodon and Breach:
Langhorne, PA, 1996.

Forster, L.S. Coord. Chem. Rev. 2002, 227, 59.

Gagne, R.R.; Koval, C.A.; Lisensky, G.C. Inorg. Chem. 1980, 19, 2854.

Gao, R.; Ho, D.G.; Hernandez, B.; Selke, M.; Murphy, D.; Djurovich, P.I.;
Thompson, M.E. J. Am. Chem. Soc. 2002, 124, 14828.

Garces, F.O.; King, K.A.; Watts, R.J. Inorg. Chem. 1988, 27, 3464.

Garces, F.O.; Watts, R.J. Inorg. Chem. 1990, 29, 582.

Gong, X.; Robinson, M.R.; Ostrowski, J.C.; Moses, D.; Bazan, G.C.; Heeger,
A.J.; Adv. Mater. 2002, 14, 581.

Gong, X.; Robinson, M.R.; Ostrowski, J.C.; Moses, D.; Bazan, G.C.; Heeger,
A.J.; Liu, M.S.; Jen, A.K. Adv. Mater. 2003, 15, 45.

Gong, X.; Robinson, M.R.; Ostrowski, J.C.; Moses, D.; Bazan, G.C.; Heeger,
A.J. Appl. Phys. Lett. 2005, 86, 171108.

Goushi, K.; Kawamura, Y.; Sasabe, H.; Adachi, C. Japanese Journal of
Applied Physics. 2004, 43, L937-L939.

177
Hitchcock; P.B.; Lappert, M.F.; Terreros, P.J. Organomet. Chem. 1982, 239,
C26.

Hager, G.D.; Watts, R.J.; Crosby, G.A. J. Am.Chem.Soc. 1975, 97(24), 7037-
7042.

Holder, E.; Langeveld, B.M.W.; Schubert, U.S. Adv. Mater. 2005, 17, 1109.

Holmes, R.; Forrest, S.R.; Sajoto, T.; Tamayo, A.; Djurovich, P.I.; Thompson,
M.E.; Brooks, J.; Tung, Y.-J.; D’Andrade, B.W.; Weaver, M.S.; Kwong, R.C.;
Kwong, R.C.; Brown, J.J. Appl. Phys. Lett. 2005, 87, 243507.

http://www.engadget.com/2005/05/20/samsungs-40-inch-oled-tv-pics/

Hwang, F.-M.; Chen, H.-Y.; Chen, P.-S.; Liu, C.-S.; Chi, Y.; Shu, C.-F.; Wu,
F.-I.; Chou, P.-T.; Peng, S.-M.; Lee, G.-H. Inorg. Chem. 2005, 44, 1344.

Ichimura, K.; Kobayashi, T.; King, K.A.; Watts, R.J. J. Phys. Chem. 1987, 91,
6104.

Ikai, M.; Tokito, S.; Sakamoto, Y.; Suzuki, T.; Taga, Y. Appl. Phys. Lett.
2001, 79, 156.

Kawanishi, Y.; Kitamura, N.; Tazuke, S. Inorg. Chem. 1989, 28, 2968-2975.

Kalyanasundaran, K. Coord. Chem. Rev. 1982, 46, 159.

Kalyanasundaram, K.; Gratzel, M. Coord. Chem. Rev. 1998, 177, 347-414.

King, K.A.; Spellane, P.J.; Watts, R.J. J.Am.Chem.Soc. 1985, 107, 1432.

Klapars, A.; Antilla, J. C.; Huang, X.; Buchwald, S. L. J. Am. Chem. Soc.,
2001, 123, 7727-7729.

Kober, E.M.; Caspar, J.V.; Lumpkin, R.S.; Meyer, T.J. J. Phys. Chem. 1986,
90, 3722.

Lamansky, S.; Djurovich, P.I. ; Abdel-Razzaq, F.; Garon, S.; Murphy, D.L.;
Thompson, M.E. J. Appl. Phys. 2002, 92, 1570.

Lamansky, S.; Djurovich, P.I.; Murphy, D.; Abdel-Razaq, F.; Kwong, R.;
Tsyba, I.; Bortz, M.; Mui, B.; Bau.R.; Thompson, M.E. Inorg. Chem. 2001, 40,
1704-1711.

178
Lamansky, S.; Djurovich, P.; Murphy, D.; Abdel-Razzaq, F.; Lee, H.-E.;
Adachi, C.; Burrows, P. E.; Forrest, S. R.; Thompson, M. E. J. Am. Chem.
Soc. 2001, 123, 4304-4312.

Lehn, J-M. Supramolecular Chemistry-Concepts and Properties; VCH:
Weinheim, Germany, 1995.

Lever, A.P.B. Inorganic Electronic Spectroscopy, 2
nd
Ed.: Elsevier; New
York, 1984, pp. 174-178.

Li, J.; Djurovich, P.I.; Alleyne, B.D.; Yousufuddin, M.; Ho, N.N. ; Thomas,
J.C.; Peters, J.C.; Bau, R.; Thompson, M.E. Inorg. Chem. 2005, 44, 1713-
1727.

Li, C.; Hoffman, M.Z. Inorg. Chem. 1998, 37, 830-832.

Lo, K. K. –W.; Chung, C, -K.; Lee, T. K. –M.; Lui, L. –K.; Tsang, K. H. –K.;
Zhu, N. Inorg. Chem. 2003, 42, 6886.

Lo, S.-C; Shipley, C.P.; Bera, R.N.; Harding, R.E.; Cowley, A.R.; Burn, P.L.;
Samuel, I.D.W. Chem. Mater. 2006, 18, 5119-5129.

Lumpkin, R.; Kober, E.; Worl, L.; Murtaza, Z.; Meyer, T.J. J.Phys.Chem.
1990, 94, 239-243.

Marchetti, A.P.; Deaton, J.C.; Young, R.H. J. Phys.Chem. A. 2006, 110,
9828-9838.

Markham, J.P.J,; Lo, S.-C.; Magennis, S.W.; Burn, P.L.; Samuel, I.D.W. Appl.
Phys. Lett. 2002, 80, 2645.

Meyer, T.J. Acc. Chem. Res. 1978, 11, 94.

Murov, S.L.; Carmichael, I.; Hug, G.L. Handbook of Photochemistry; Marcel
Dekker: New York, 1993.

Nolan, S.P.; Hoff, C.D.; Stoutland, P.O. ; Newman, L.J.; Buchanan, J.M.;
Bergman, R.G.; Yang, G.K.; Peters, K.S. J. Am. Chem. Soc. 1987, 109,
3143.

Nonoyama, M., Bull. Chem. Soc. Jpn., 1974, 47, 767.

Ohsawa, Y.; Sprouse, S.; King, K.A.; DeArmond, M.K.; Hanck, K.W.; Watts,
R.J. J.Phys. Chem. 1987, 91, 1047.

179
Ostrowski, J.C.; Robinson, M.R.; Heeger, A.J.; Bazan, G.C. Chem. Commun.
2002, 7, 784.

Paulose, B.M. J.S.; Rayabarapu, D.K.; Duan, J.-P. Cheng, C.-H. Adv. Mater.
2004, 16, 2003.

Pavlik, J.W.; Connors, R.E.; Burns, D.S.; Kurzwell, E.M. J.Am. Chem. Soc.
1993, 115, 7465.

Perkins, T.A.; Pourreau, D.B.; Netzel, T.L.; Schanze, K.S. J.Phys.Chem.
1989, 93, 4511.

Rothberg, L. J.; Lovinger, A. J. J. Mater. Res. 1996, 11, 3174.

Sajoto, T.; Djurovich, P.I.; Tamayo, A.; Yousufudddin, M.; Bau, R.;
Thompson, M.E. Inorg. Chem. 2005, 44, 7992-8003.

Sajoto, T.; Djurovich, P.I.; Tamayo, A.; Thompson, M.E.; Temperature
Dependence of Blue Phosphorescent Cyclometalated Iridium(III) Complexes;
manuscript in preparation, 2008.

Sawyer, D.T.; Sokkowiak, A.; Roberts, J.L., Jr. Electrochemistry for
Chemists, 2
nd
ed.: John Wiley and Sons: New York, 1995; p 467.

Schmid, B.; Garces, F.O.; Watts, R.J. Inorg. Chem. 1994, 32, 9.

Schmidt, J.; Wiedenhofer, H.; Von Zelewsky, A.; Yersin, H. J. Phys. Chem.
1995, 99, 226.

Shaw, J.R.; Sadler, G.S.; Wacholtz, W.F.; Ryu, C.K.; Schmehl, R.H. New. J.
Chem. 1996, 20, 749.

Sheldrick, G.M. SHELXTL, version 5.1.; Bruker Analytical X-ray System, Inc.;
Madison, WI, 1997.

Sibley, S.; Thompson, M. E.; Burrows, P. E.; Forrest, S. R. In “Optoelectronic
Properties of Inorganic Complexes”, Roundhill, D. M., Fakler, J. Eds.;
Plenum Press: New York.

Silavwe, N.D.; Goldman, A.S.; Ritter, R.; Tyler, D.R. Inorg. Chem. 1989, 28,
1231.

Sonoyama, N.; Karasawa, O.; Kaizu, Y. J. Chem.Soc., Faraday Trans. 1995,
91, 437.

180
Sprouse, S.; King, K.A.; Spellane, P.J.; Watts, R.J. J. Am. Chem. Soc. 1984,
106, 6647-6653.

Strouse, G.F.; Güdel, H.U.; Bertolasi, V.; Ferretti, V. Inorg. Chem. 1995, 34,
5578.

Sutin, N. Acc. Chem Res. 1968, 1, 225.

Tamayo, Arnold B.; Alleyne, Bert D.; Djurovich, Peter I.; Lamansky, Sergey;
Tsyba, Irina; Ho, Nam N.; Bau, Robert; Thompson, Mark E J. Am. Chem.
Soc. 2003, 125(24), 7377-7387.

Tanaka, I.; Tabata, Y.; Tokito, S. Japanese Journal of Applied Physics. 2004,
43, L1601-L1603.

Tan-Sien-Hee, L.; Mesmaeker, A.K.-D. J.Chem.Soc., Dalton Trans. 1994, 24,
3651-3658.

Tang, C. W. Inf. Disp. 1996, 10, 16.

Tang, C. W.; Van Slyke, S. A. Appl. Phys. Lett. 1987, 51, 913.

Tang, C. W.; Van Slyke, S. A.; Chen, C. H. Chen J. Appl. Phys. 1989, 65,
3610.

Thompson, M.E.; Burrows, P.E.; Forrest, S.R. Curr. Opin. Solid State
Mater.Sci. 1999, 4, 369.

Treboux, G.; Mizukami, J.; Yabe, M.; Nakamura, S. Chemistry Letters. 2007,
36, 1344-1345.

Tsuboyama, A.; Iwawaki, H.; Furugori, M.; Mukaide, T.; Kamatani, J.; Igawa,
S.; Moriyama, T.; Miura, S.; Takiguchi, T.; Okada, S.; Hoshino, M.; Ueno, K.
J. Am. Chem. Soc. 2003, 125, 12971.

Tung, Y.-L.; Lee, S.-W.; Chi, Y.; Chen, L.-S.; Shu, C.-F.; Wu, F.-I.; Carty,
A.J.; Chou, P.-T.; Peng, S.-M.; Lee, G.-H. Adv. Mater. 2005, 17, 1059.

Turro, N.J. Modern Molecular Photochemistry; The Benjamin/Cummings
Publishings Co., Inc.; Menlo Park, California, 1978.

Turro, N. J. Modern Molecular Photochemistry. 1991, p.27.

Van Houten, J.; Watts, R.J. J.Am.Chem.Soc. 1976, 98, 4853-4858.

181
Wang, X.-Y.; Del Guerzo, A.; Schmehl, R.H. J. Photochem. Photobiol. C.
2004, 5, 55.

Wiedenhofer, H.; Schutzenmeier S.; Von Zelewsky, A.; Yersin, H. J. Phys.
Chem. 1995, 99, 13385.

Wilde, A.P.; King, K.A.; Watts, R.J. J. Phys.Chem. 1991, 95, 629-634.

Wu, L.-L; Yang, C.-H.; Sun, I.-W.; Chu, S.-Y.; Kao, P.-C.; Huang, H.-H.
Organometallics. 2007, 26, 2017-2023.

Wu, F.; Su, H.; Shu, C.; Luo, L.; Diau, W.; Cheng, C.; Duan, J.; Lee, G. J.
Mater. Chem. 2005, 15, 1035.

Yang, C.-H.; Li, S.-W.; Chi, Y.; Cheng, Y.M.; Yeh, Y.-S.; Chou, P.-T.; Lee,
G.-H.; Wang, C.-H.; Shu, C.-F. Inorg. Chem. 2005, 44, 7770-7780.

Yang, C.-H, Cheng, Y.-M.; Chi, Y. Hsu, C.-J.; Fang, F.-C.; Wong, K.-T.;
Chou, P.-T.; Chang, C.-H.; Tsai, M.-H.; Wu, C.-C. Angew. Chem. Int. Ed.
2007, 46, 2418-2421.

Yeh, Y.-S.; Cheng, Y.-M.; Chou, P.-T.; Lee, G.-H.; Yang, C.-H.; Chi, Y.; Shu,
C.-F.; Wang, C.-H. Chem.Phys. Chem. 2006, 7, 2294-2297.

Yu, J.-K.; Hu, Y.-H.; Cheng, Y.-M.; Chou, P.-T.; Peng, S.-M.; Lee, G.-H.;
Carty, A.-J.; Tung, Y.-L.; Lee, S.-W.; Chi, Y.; Liu, C.-S. Chem. Eur. J. 2004,
10, 6255-6264.

Zhu, W.; Mo, Y.; Yuan, M.; Yang, W.; Cao, Y. Appl. Phys. Lett. 2002, 80,
2045.

Abstract (if available)

Abstract Organic light emitting devices (OLEDs) are a new type of display technology based on organic thin films. The materials that comprise these films must be able to meet certain criteria in order to be considered for these devices. The work presented here describes the development of novel phosphorescent materials along with their photophysical characterization and applications in OLEDs. Chapter 1 illustrates how these devices work, the materials used in these devices, and how the properties of these materials affect device performance. Chapter 2 describes the synthesis and characterization of high energy phosphorescent materials from Ir(III) complexes with cyclometalated pyrazolyl-based and N-heterocyclic carbene (NHC)-based ligands. Chapter 3 portrays the synthesis and characterization of heteroleptic Ir(III) complexes consisting of two chromophoric cyclometalating (C^N) ligands and a single high energy ancillary ligand (L^X). The incorporation of high energy ancillary ligands such as pmi on bis-cyclometalated Ir(ppz)2 does not lead to emission at room temperature. However, the replacement of the ppz chromophoric ligands with carbazolyl, diphenylamino, or fluorenylpyrazolyl-based chromophoric ligands leads to emission at room temperature. In Chapter 3, more reducible flz-based Ir(III) complexes have also been synthesized by incorporation of a high triplet energy, more reducible ancillary ligand. Their electrochemical, spectroscopic, and electroluminescent properties are discussed.

Linked assets

University of Southern California Dissertations and Theses

Conceptually similar

PDF

Synthesis and photophysical study of phosphorescent hetero-cyclometalated organometallic complexes involving phosphino-carbon ligands

PDF

Synthesis, structural and photophysical characterization of phosphorescent three-coordinate Cu(I)-N-heterocyclic carbene complexes

PDF

Simple complexes: synthesis and photophysical studies of luminescent, monovalent, 2-coordinate carbene-coinage metal complexes and higher coordination geometries

PDF

Photophysical properties of luminescent iridium and coinage metal complexes

PDF

High energy hosts and blue emitters for phosphorescent organic light emitting diodes

PDF

Studies of molecular orientation using iridium phosphors and integration of corannulene into organic light emitting diodes (OLEDs)

PDF

Combinatorial screening methods for metal catalysts and cyclometalated iridium and platinum complexes with non-innocent ligands

PDF

Dopants for organic light-emitting devices

PDF

Ir(III) and Pt(II) phosphorescent emitters in organic light emitting diodes: from materials development to light out-coupling

PDF

Synthesis of multifunctional heterocycles, amino phosphontes using boronic acids

PDF

Molecular design strategies for blue organic light emitting diodes

PDF

Qualitative quantum chemical description of the structure-color relationships in phosphorescent organometallic complexes

PDF

Synthesis, photophysical and electrochemical characterization of 1,3-bis(2-pyridylimino)isoindole derivatives

PDF

Development of new bifunctional iridium complexes for hydrogenation and dehydrogenation reactions

PDF

Molecular approaches to solve the blue problem in organic light emitting diode display and lighting applications

PDF

Synthesis, photo- and electroluminescence of three- and two-coordinate coinage metal complexes featuring non-N-heterocyclic carbene and non-conventional N-heterocyclic carbene ligands

PDF

Improving the sustainability of conjugated polymer synthesis via direct arylation polymerization

PDF

Hydrogen transfer reactions catalyzed by iridium and ruthenium complexes

PDF

The synthesis and characterization of [Ga]ZSM-5 by NMR spectroscopy and density functional theory

PDF

Development of N-type chromophores for organic photovoltaics, and thermally activated delayed fluorescence NHC complexes for organic light-emitting diodes

Asset Metadata

Creator Sajoto, Tissa (author)

Core Title Synthesis and photophysical characterization of phosphorescent cyclometalated iridium (III) complexes and their use in OLEDs

School College of Letters, Arts and Sciences

Degree Doctor of Philosophy

Degree Program Chemistry

Publication Date 04/21/2010

Defense Date 03/27/2008

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

Tag cyclometalated,iridium,OAI-PMH Harvest,OLEDs,phosphorescent

Language English

Advisor Thompson, Mark E. (committee chair), Bau, Robert (committee member), Goo, Edward K. (committee member), Haw, James (committee member), Prakash, Surya (committee member), Weber, William P. (committee member)

Creator Email sajoto@usc.edu

Permanent Link (DOI) https://doi.org/10.25549/usctheses-m1162

Unique identifier UC1150083

Identifier etd-Sajoto-20080421 (filename),usctheses-m40 (legacy collection record id),usctheses-c127-65899 (legacy record id),usctheses-m1162 (legacy record id)

Legacy Identifier etd-Sajoto-20080421.pdf

Dmrecord 65899

Document Type Dissertation

Rights Sajoto, Tissa

Type texts

Source University of Southern California (contributing entity), University of Southern California Dissertations and Theses (collection)

Repository Name Libraries, University of Southern California

Repository Location Los Angeles, California

Repository Email cisadmin@lib.usc.edu