Phosphorescence color tuning of oxadiazole-based iridium(III) complexes for organic light emitting diode

Article abstract of DOI:10.1166/jnn.2012.6301

The new heteroleptic iridium complexes bearing 2-(5-phenyl-1,3,4-oxadiazol- 2-yl)phenolate (ODZ), were synthesized and characterized for application to organic light-emitting diodes (OLEDs). As main ligands (C^{^}N), the anions of 2-phenylpyridine

Full text of DOI:10.1166/jnn.2012.6301

Copyright © 2012 American Scientific Publishers
All rights reserved
Printed in the United States of America
Journal of
Nanoscience and Nanotechnology
Vol. 12, 5613–5618, 2012
Phosphorescence Color Tuning of
Oxadiazole-Based Iridium(III) Complexes for
Organic Light Emitting Diode
∗
Hye Rim Park, Bo Young Kim, Young Kwan Kim, and Yunkyoung Ha
Department of Information Display Engineering, Hongik University, Seoul 121-791, Korea
The new heteroleptic iridium complexes bearing 2-(5-phenyl-1,3,4-oxadiazol-2-yl)phenolate (ODZ),
were synthesized and characterized for application to organic light-emitting diodes (OLEDs).
∧
As main ligands (C N), the anions of 2-phenylpyridine (ppy), 2-phenylquinoline (pq) and
2
-(2,4-difluorophenyl)pyridine (F -ppy) were chelated to the iridium center and 2-(5-phenyl-1,3,4-
2
oxadiazol-2-yl)phenolate (ODZ) was introduced as an ancillary ligand for luminescence modulation
of their iridium complexes. We expected that the relative energy levels of the main and ancillary
ligands in the complexes could lead to emission color tuning and luminous efficiency improvement
by possible inter-ligand energy transfer (ILET). The photoabsorption, photoluminescence and elec-
troluminescence of the complexes were studied. Ir(F -ppy) (ODZ), Ir(ppy) (ODZ) and Ir(pq) (ODZ)
2
2
2
2
exhibited the photoluminescence maxima between 505–610 nm at room temperature in CH Cl ,
2
2
depending on both main and ancillary ligands. The longer ꢀ conjugation in the cyclometallating pq
ligands leads to the bathochromic shift in luminescence of their iridium complexes. The electrolu-
Delivered by Publishing Technology to: University of Waterloo
minescent properties of the complexes were influenced by ILET.
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Keywords: Organic Lig Ch to- Ep my ri it gt i nh gt : DA imo de er ,i cI ar i dn i uSmc i eC no tmi f ipc le Px u, bO l xi sa hd ei ar zs olylphenolate, Inter-Ligand
Energy Transfer.
1
. INTRODUCTION
complexes are particularly important in achieving high-
efficiency of the OLEDs.
8
In the last few years, organic light emitting materials have
been extensively studied owing to their excellent phos-
phorescent quantum yields and easy tuning of emission
color by their molecular structures. The iridium com-
plexes have attracted increasing interests as highly emis-
For the development of full-color, and efficient emit-
ting materials of OLEDs, we have introduced various main
∧
ligands (C N) and a new ancillary ligand to the irid-
1
–2
∧
ium complexes. The C N ligands have been known for
their major contribution to emission color determination
of their complexes while the ancillary ligand has shown
a minor effect on the color tuning. On the other hand,
the recent reports on inter-ligand energy transfer (ILET)
between the main and ancillary ligands emphasize the con-
3
–4
sive dopants in organic light emitting diodes (OLEDs).
Because the heavy iridium center allows both singlet and
triplet excitons to be used in an electroluminescence pro-
cess, internal quantum efficiency of 100% is theoretically
possible.
In general, OLEDs exhibit several advantages such as
a wider viewing angle, faster response time, and self-
emission over liquid crystal display (LCD). However, full-
color OLEDs still require improvement in terms of device
efficiency, color purity, manufacturing process, and low
cost. These factors in turn depend on the development of
efficient OLED materials, including red, green, and blue
tribution of the ancillary ligand to the emission color and
9–10
efficiency.
Thus, the modulation of the relative triplet
∧
states of the C N and ancillary ligands could be considered
an important factor in determining the emission color of
their iridium complexes. We applied these concepts to the
design of the iridium complexes and prepared them con-
taining the anions of F -ppy, ppy and pq as main ligands
2
and 2-(5-phenyl-1,3,4-oxadiazol-2-yl)phenolate (ODZ) as
an ancillary ligand.
5
–7
(RGB) emitters. Therefore, the design and synthesis of
phosphorescent emitting materials containing heavy-metal
The main ligands, F -ppy, ppy and pq, which have
2
drastically different energy gaps between the HOMO and
LUMO energy levels were chosen. As an ancillary ligand,
∗
Author to whom correspondence should be addressed.
J. Nanosci. Nanotechnol. 2012, Vol. 12, No. 7
1533-4880/2012/12/5613/006
doi:10.1166/jnn.2012.6301
5613

Phosphorescence Color Tuning of Oxadiazole-Based Iridium(III) Complexes for OLED
Park et al.
an oxadiazole derivative, ODZ, was introduced; it is
known to have promising electron transport and emis-
sion characteristics when used in organic EL devices.
ODZ can form a stable six-membered metallacycle when
chelated. This class of compounds can offer numerous
attractive properties such as a double role of electron trans-
port and phosphor, high thermal stability, and ease of
sublimation.
on silica gel column with dichloromethane and purified by
recrystallization.
1
1–13
Data for [Ir(F -ppy) (ODZ)]: Yield: 68%. FAB-MS:
2
2
1
calculated 809; found 810. H NMR(CDCl , 400 MHz):
3
ꢁ8.21 (d, 3 H) 8.12 (d, 2 H) 7.98 (d, 3 H) 7.82 (d, 3 H)
7.66 (d, 1 H) 7.56 (s, 4 H) 7.43 (t, 2 H) 7.20 (d, 2 H)
6.87 (d, 1 H).
Data for [Ir(ppy) (ODZ)]: Yield: 65%. FAB-MS: calcu-
2
1
We investigated the photoabsorption properties of the
iridium complexes with their UV-Vis spectra and studied
the electrochemical characteristics with their cyclic voltam-
metric diagrams. The photoluminescence (PL) and electro-
luminescence (EL) of the complexes were also investigated.
The emitting colors and the device performances of
the complexes, Ir(F -ppy) (ODZ), Ir(ppy) (ODZ) and
lated 737; found 738. H NMR(CDCl , 400 MHz): ꢁ8.63
3
(d, 1 H) 8.38 (d, 1 H) 8.13 (d, 2 H) 7.87 (d, 2 H) 7.79
(m, 3 H) 7.72 (d, 2 H) 7.55 (d, 3 H) 7.30 (t, 1 H) 7.17
(t, 2 H) 6.81 (m, 2 H) 6.66 (d, 2 H) 6.55 (d, 1 H) 6.43
(t, 1 H) 6.18 (d, 1 H) 6.05 (d, 1 H).
Data for [Ir(pq) (ODZ)]: Yield: 71%. FAB-MS: calcu-
2
1
lated 837; found 838. H NMR(CDCl , 400 MHz): ꢁ8.48
2
2
2
3
Ir(pq) (ODZ), were compared to find the effects of the
main ligands and the new ancillary ligand, ODZ, on the
luminescence properties of their complexes.
(d, 2 H) 8.37 (d, 2 H) 8.13 (d, 1 H) 8.01 (d, 1 H) 7.91
(d, 1 H) 7.85 (d, 1 H) 7.74 (d, 2 H) 7.64 (d, 1 H) 7.55
(m, 3 H) 7.42 (t, 1 H) 7.33 (d, 2 H) 7.16 (d, 2 H) 6.94
2
(
(
d, 2 H) 6.87 (t, 1 H) 6.59 (m, 3 H) 6.25 (d, 1 H) 6.19
d, 1 H) 6.05 (t, 1 H) 5.76 (s, 1 H).
2. EXPERIMENTAL DETAILS
2
.1. Synthesis and Characterization
2.2. Optical Measurements
All reagents, purchased from Aldrich Co. and Strem
Co., were used without further purification. All reactions
were carried out under an argon atmosphere. Solvents
were dried by standard procedures. Mass spectra were
UV-visible absorption spectra were obtained from Hewlett
Packard 8425A spectrometer. PL spectra were measured
on a Perkin Elmer LS 50B spectrometer. The UV-Vis
and PL spectra of iridium complexes were measured in
Delivered by Publishing Technology to: University of Waterloo
−
10 M dilute CH Cl solution. Cyclic voltammograms
2 2
5
determined on JEOL, JMS-AX505WA, HP 5890 Series
IP: 23.24.70.177 On: Wed, 14 Oct 2015 07:09:55
II Hewlett-Packard 5890A at Seoul National University.
were obtained at a scan rate of 100 mV/s with electro-
Copyright: American Scientific Publishers
H NMR was taken with a 400 MHz NMR spectrometer
1
1
chemical Analyzer of CH Instruments. H NMR spec-
tra were obtained from a 400 MHz NMR at Sogang
University, and mass spectra were determined on JEOL,
JMS-AX505WA, HP 5890 Series II Hewlett-Packard
at Sogang University in Korea.
2
.1.1. Synthesis of Ligands and Iridium Complexes
5890A (capillary column) at Seoul National University in
Synthesis of F -ppy. 2,4-difluoro-2-phenylpyridine was
2
Korea.
obtained from the reaction of 2-chloropyridine and
2
,4-difluorophenylboronic acid by Suzuki coupling.14
2.3. Device Fabrication and Measurements
Yield: 69%.
Synthesis of ODZ.13 In 25-ml anhydrous pyridine,
acetylsalicyloyl chloride (10.0 g, 50.3 mmol) and
The OLEDs containing the heteroleptic iridium com-
plexes as a dopant in emitting layers were fabricated.
Glass substrate coated with a 180-nm-thick indium tin
oxide (ITO) layer had a sheet resistance of 12 ꢂ/sq. All
organic layers were sequentially deposited onto the sub-
strate without breaking vacuum at a pressure of about
5
-phenyl-1,2,3,4-tetrazole (7.5 g, 51.3 mmol) were added
and stirred at reflux for 2 h under an argon atmosphere.
After removal of the solvent under reduced pressure, the
residue was treated with aqueous sodium hydroxide solu-
tion (3.5 g) in ethanol at reflux for 1 h. The precipitates
were collected by glass filter and acidified in methanol.
Yield: 71%.
−
7
5 × 10 torr, using the thermal evaporation equipment.
The organic materials were deposited as the following
ꢀ
structure: 4,4 -bis[N-(naphthyl)-N-phenylamino]biphenyl
∧
∧
ꢀ
ꢀꢀ
Synthesis of Ir(C N) (ODZ) (C N = F -ppy, ppy, pq).
(NPB, 50 nm) as hole transporting layer (HTL)/4,4 ,4 -
2
2
The cyclometallated Ir(III) ꢀ-chloro-bridged dimer,
tris(N-carbazolyl)triphenylamine (TCTA, 10 nm) as buffer
∧
∧
ꢀ
(
C N) Ir(ꢀ-Cl) Ir(C N) (0.5 mmol), was first prepared
layer/iridium complex phosphors (10%) doped in 4,4 -
2
2
2
1
5
ꢀ
according to the Nonoyama method. The resulting
dimer (1.73 g, 1.9 mmol) and an excess of the ancil-
lary ligands were next mixed with Na CO (500 mg) in
bis(9-carbazolyl)-1,1 -biphenyl (CBP, 30 nm) as emitting
layer/4,7-Diphenyl-1,10-phenanthroline (Bphen, 30 nm) as
electron transporting layer (ETL)/lithium quinolate (Liq,
2 nm) as electron injection layer (EIL). The deposition
rates were 1.0–1.1 and 0.1 Å/sec for organic materials and
lithium quinolate (Liq), respectively. Finally, the aluminum
2
3
2
2
-ethoxyethanol (30 mL). The mixture was refluxed for
h. The solution was cooled to room temperature and the
solid was filtered. The crude product was chromatographed
5
614
J. Nanosci. Nanotechnol. 12, 5613–5618, 2012

Park et al.
Phosphorescence Color Tuning of Oxadiazole-Based Iridium(III) Complexes for OLED
cathode was deposited at a rate of 10 Å/sec. The devices
were encapsulated in a glove box with O and H O at con-
Ir(F -ppy) (ODZ)
2 2
3
.0
Ir(ppy)2(ODZ)
Ir(pq) (ODZ)
2
2
2
centrations below 1 ppm. The devices had emission areas
2.5
2
of 3×3 mm . The electrical characteristics of devices and
2
1
1
0
.0
.5
.0
.5
the EL spectra were measured and immediately recorded
with a Chroma meter CS-1000A (Minolta). The current
and voltage were controlled with a measurement unit
(model 236, Keithely).
3
. RESULTS AND DISCUSSION
0.0
2
50
300
350
400
450
500
550
As previously reported,16–19 the main and/or ancillary lig-
ands could have a significant effect on the emission prop-
erties of their complexes. Synthesis of the main ligand,
Wavelength (nm)
∧
−5
M
Fig. 2. UV-Vis absorption spectra of Ir(C N) (ODZ) in a 10
CH Cl solution (C N = F -ppy, ppy, pq).
2
∧
2
2
2
F -ppy, was straightforward, according to the modified
2
1
4
Suzuki coupling method. The ancillary ligand, ODZ,
was prepared from the reaction of acetylsalicyloyl chloride
with 5-phenyl-1,2,3,4-tetrazole, according to the reported
procedure.1 The heteroleptic iridium complexes of ODZ
were synthesized as reported by Nonoyama. The overall
synthetic schemes are illustrated in Figure 1.
Figure 2 presents the UV-Vis absorption spectra of
the complexes in CH Cl . The strong absorption bands
between 240 and 300 nm in the ultraviolet region are
attributed to the spin-allowed ꢃ–ꢃ transition of the
cyclometallated ligands, F -ppy, ppy and pq, in the
complexes. The weak band of Ir(F -ppy) (ODZ) and
Ir(ppy) (ODZ) at 350–450 nm in Ct ho ep y vr i igs hi bt l: eA mr e eg ri oi c na n Scientific Publishers
can be assigned to the spin-allowed metal-to-ligand
charge transfer band ( MLCT), and the weaker absorp-
tion bands at the longer wavelengths can be attributed
to the spin-forbidden MLCT and spin-orbit coupling
enhanced ꢃ–ꢃ transition. The absorption patterns of
Ir(F -ppy) (ODZ) and Ir(ppy) (ODZ) are similar with the
absorption maxima between 260 and 400 nm. The sim-
ilar absorption patterns indicate that change of the main
ppy-based ligands in the complexes does not make signif-
icant contribution to the absorption process. In contrast,
ascribed to the red emitting ligand, pq. The UV-Vis spec-
tra of Ir(pq) (ODZ) has also a distinct feature of strong
absorption peak around 310–370 nm.
2
3
Figure 3 shows the PL spectra of the Ir complexes
1
5
−5
in 10
M CH Cl solution. The emission maxima
2 2
of Ir(F -ppy) (ODZ), Ir(ppy) (ODZ) and Ir(pq) (ODZ)
2
2
2
2
appear at 505, 515 and 608 nm, respectively. Ir(F2-
ppy) (ODZ) and Ir(ppy) (ODZ) have similar luminescence
aspects with the emission peaks around 510 nm. Such
similarities in PL spectra of these two complexes are in
2
2
2
2
1
∗
2
fact expected, considering the similar photoabsorption pat-
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IP: 23.24.70.177 On: Wed,t e1 r 4n sOi nc tt h2 e0 i 1r 5U 0V 7- V: 0i 9s : s5p 5e ctra. The ppy-based main ligands
2
2
2
did not seem to affect luminescence as well as absorp-
tion of their complexes coordinated with ODZ. In con-
trast, Ir(pq) (ODZ) exhibited the distinct emission peak at
08 nm.
1
2
6
3
We attribute such PL difference between the ppy-based
3
∗
iridium complexes and the pq-based complex to the dif-
ferent emission mechanisms. The emission maxima of
the iridium complexes were substantially shifted to the
2
2
2
Ir(F -ppy) (ODZ)
2
2
1
0
0
0
.0
.8
.6
.4
Ir(ppy) (ODZ)
Ir(pq) (ODZ) had different absorption patterns, showing
the maxima at 275, 330 and 427 nm, which could be
2
2
Ir(pq) (ODZ)
2
Cl
C^N
LX = ODZ
IrCl3 nH2O
2
(C^N)2 Ir
Ir (C^N)2
(C^N)2 Ir (ODZ)
-ethoxyethanol:H2O
CH2Cl2/EtOH
Cl
LX =
0.2
C^N =
N
N
N
F
O
N
N
0.0
OH
ODZ
400
450
500
550
600
650
700
750
800
F
ppy
pq
F2-ppy
Wavelength (nm)
∧
−5
Fig. 1. The synthesis of main ligands, ancillary ligands and their
iridium complexes.
Fig. 3. PL spectra of Ir(C N) (ODZ) in a 10 M CH Cl solution
2
2
2
∧
(C N = F -ppy, ppy, pq).
2
J. Nanosci. Nanotechnol. 12, 5613–5618, 2012
5615

Phosphorescence Color Tuning of Oxadiazole-Based Iridium(III) Complexes for OLED
Park et al.
Table I. Physical parameters for the iridium complexes.
Ir(ppy) (ODZ) and Ir(pq) (ODZ), respectively. The energy
2
2
gap of Ir(pq) (ODZ) was the smallest among the com-
HOMO/ LUMO/
2
a
b
c
d
e
Ir complex
ꢄem/nm
E /V
eV
eV
ꢅE/eV
plexes in this study and this could be explained with the
extended ꢃ conjugation length of the pq ligand relative to
the other ligands in the respective complexes. As a result,
the pq ligand caused the bathochromic luminescence shift
and the luminescence mechanism change of its iridium
complex.
ox
Ir(F -ppy) (ODZ)
505
515
608
0.56
0.54
0.39
−5ꢆ36
−5ꢆ34
−5ꢆ19
−2ꢆ27
−2ꢆ36
−2ꢆ44
3.09
2.98
2.75
2
2
Ir(ppy) (ODZ)
2
Ir(pq) (ODZ)
2
a
b
Notes: Measured in CH Cl2 solution. Scan rate: 100 mV/s, Electrolyte: tetra-
butylammonium hexafluorophosphate. The potentials are quoted against the inter-
2
c
The EL properties of the complexes were also inves-
nal ferrocene standard. Deduced from the equation HOMO = −4ꢆ8 − Eox,
dꢇe
LUMO = −4ꢆ8 − Ered.
ꢅE = HOMO−LUMO.
Calculated from the optical edge and the relation
tigated for their OLED application. The configuration of
∧
the EL device with Ir(C N) (ODZ) used as a dopant was
2
ITO/NPB/TCTA/CBP:DOPANT 10%/Bphen/Liq/Al. In the
EL spectra, Figure 5(a) shows that the emission peaks of
Ir(F -ppy) (ODZ), Ir(ppy) (ODZ) and Ir(pq) (ODZ) were
longer wavelength upon changing the main ligand from
F2-ppy to pq. The energy gap of pq main ligand in
2
2
2
2
the complex is smaller than those of ppy and F -ppy
2
analogs, preventing the possibility of ILET. Therefore,
we assign that the resulting emission is originated mostly
from pq ligand in the complex. Previously, the emission
of the iridium complexes chelated with pq was reported
Ir(ppy) (ODZ)
2
(
a)
Ir(F -ppy) (ODZ)
1
.0
2
2
Ir(pq) (ODZ)
2
0.8
2
0
to appear at the similar red region of 597 nm. On the
other hand, Ir(F -ppy) (ODZ) and Ir(ppy) (ODZ) exhib-
0
0
.6
.4
2
2
2
ited the similar photophysical characteristics, regardless of
the main ligands, vide supra. Their similar photophysi-
cal results imply that these two complexes undergo inter-
ligand energy transfer (ILET), resulting in the emission
mainly originated from electronic transition of the ancil-
0.2
.0
0
3
00
400
500
wavelength
600
700
800
Delivered by Publishing Technology to: University of Waterloo
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lary ligand, ODZ.
We investigated the electrochemical properties of the Ir
(b)
Copyright: American Scientific Publishers
complexes with the cyclic voltammetry (CV) which could
Ir(ppy) (ODZ)
2
3
0
2
1–22
Ir(pq) (ODZ)
reveal the positions of their HOMOs and LUMOs.
2
Ir(F -ppy) (ODZ)
Table I summarizes the CV data. The oxidation poten-
tials which indicates the HOMOs of Ir(F -ppy) (ODZ) and
2
2
2
2
20
Ir(ppy) (ODZ) were irreversible at 0.56 and 0.54 V relative
2
+
to an internal ferrocenium/ferrocene reference (Fc /Fc),
respectively. By comparison, the oxidation potential of
1
0
0
Ir(pq) (ODZ) was semi-reversible at 0.39 V. The reduc-
2
tion curves of all complexes were not clearly observed
up to −2ꢆ2 V. Therefore, the LUMOs of the com-
plexes were estimated from their respective absorption
spectra, using the optical edge and band gap equation
0
20 40 60 80 100 120 140 160 180 200 220
Current density [mA/cm2]
(
ꢅE = E − E ). Their calculated reduction potentials
ox
red
3
3
2
2
1
1
5
0
5
0
5
0
5
0
Ir(ppy) (ODZ)
were −2ꢆ27, −2ꢆ36 and −2ꢆ44 eV for Ir(F -ppy) (ODZ),
2
2
2
Ir(pq) (ODZ)
2
Ir(F -ppy) (ODZ)
2
2
0
20 40 60 80 100 120 140 160 180 200 220
Current density [mA/cm2]
Fig. 5. (a) The EL spectra and (b) the power and luminous efficiencies
Fig. 4. The device structure of Ir complexes.
versus current density of the devices with the iridium complexes.
5
616
J. Nanosci. Nanotechnol. 12, 5613–5618, 2012

Park et al.
Phosphorescence Color Tuning of Oxadiazole-Based Iridium(III) Complexes for OLED
Table II. OLED device characteristics of the iridium complexes.
might exhibit various emission colors due to the main lig-
and effect among the complexes. Generally, the energy
gap of the main ligand has a major effect in determining
the emitting color of its complex. The electroluminescence
EL
Power
Quantum Luminance
Ir
ꢄmax efficiency efficiency
efficiency
(cd/A)
complex
(nm)
500
(lm/W)
(%)
CIE
spectra of Ir(F -ppy) (ODZ) and Ir(ppy) (ODZ) exhibited
Ir(F -ppy)2
5ꢆ52
2ꢆ62
7ꢆ91
35ꢆ02
9ꢆ64
(0.30, 0.56)
2
2
2
2
(
ODZ)
Ir(ppy)2
ODZ)
Ir(pq)2
ODZ)
the similar emission patterns with the maxima at 500 and
510
606
20ꢆ63
7ꢆ57
10ꢆ64
6ꢆ63
(0.33, 0.57)
(0.61, 0.38)
510 nm, while Ir(pq) (ODZ) revealed the red luminescence
2
(
around 606 nm with the CIE coordinates of (0.61, 0.38).
Considering the consistent UV and PL patterns of the irid-
ium complexes with ppy-based main ligands discussed in
this study, we could infer that the ILET might operate
in the phosphorescence process of Ir(F -ppy) (ODZ) and
(
observed at 500, 510 and 606 nm, respectively. These
results were consistent with the PL results and indicated
that EL originated from the iridium complex dopant in
the emitting layer. Figure 5(b) shows the luminance effi-
ciency versus current density characteristics of the devices
with iridium complexes. The maximum luminous efficien-
cies of the devices with Ir(F -ppy) (ODZ), Ir(ppy) (ODZ)
2
2
Ir(ppy) (ODZ). The EL device of Ir(ppy) (ODZ) showed
2
2
the best luminous efficiency of 35 cd/A. On the other
hand, the emission of Ir(pq) (ODZ) was assigned to origi-
2
nate from electronic transition in the main ligand, pq. This
study also showed the possibility of the application of irid-
ium complexes containing oxadizole-based ligand which
has a good electron transporting property to the phospho-
rescent material for OLED.
2
2
2
and Ir(pq) (ODZ) were 7.91, 35.02 and 9.64 cd/A, respec-
2
tively. The device of Ir(ppy) (ODZ) showed the best lumi-
2
nous efficiency of 35.02 cd/A. The ILET between the
ppy main ligand and the ancillary ligand, ODZ, seemed
to occur strongly, leading their iridium complex to have
substantial improvement of the device efficiencies. The
Ir complexes bearing a benzoquinoline ancillary ligand
was recently reported to show similar improvement of the
Acknowledgments: This study was supported by the
Korea Research Foundation (No. 2011-0003765).
References and Notes
2
3
device performances by I LD Ee Tl i. ver He do wb eyv eP r u, bt hl i es h di ne vg i cTe e co hf nology to: University of Waterloo
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2
2
Copyright: American Scientific Publishers
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Ir(F -ppy) (ODZ), Ir(ppy) (ODZ) and Ir(pq) (ODZ) were
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Funct. Mater. 16, 709 (2006).
2
2
2
2
(0.30, 0.56), (0.33, 0.57) and (0.61, 0.38), respectively.
6
. Y. H. Kim and S. K. Kwon, J. Appl. Polm. Sci. 100, 2151
2006).
. H. S. Lee, S. Y. Ahn, H. S. Huh, and Y. Ha, J. Organomet. Chem.
94, 3325 (2009).
Table II and Figure 4 spresent the detailed data and device
structure.
We also tried to synthesize the homoleptic iridium com-
(
7
6
plex of ODZ, Ir(ODZ) , for luminescence comparison.
The synthesis of homoleptic iridium complex was however
8. S. Lamansky, P. Djurovich, D. Murphy, F. Abdel-Razzaq, H. Lee,
C. Adachi, P. E. Burrows, S. R. Forrest, and M. E. Thompson, Inorg.
Chem. 40, 1704 (2001).
3
failed. The failure in formation of Ir(ODZ) is attributed
3
9. Y. You and S. Y. Park, J. Am. Chem. Soc. 127, 12438 (2005).
to the difficulty in tri-cyclometallated six-membered ring
formation with the iridium center and steric bulkiness of
ODZ ligand.
10. Y. You, J. Seo, S. H. Kim, K. S. Kim, T. K. Ahn, D. Kim, and S. Y.
Park, Inorg. Chem. 47, 1476 (2008).
11. B. Schulz, M. Bruma, and L. Brehmer, Adv. Mater. 9, 601 (1997).
2. S. Chung, K. Kwon, S. Lee, J. Jin, C. H. Lee, C. E. Lee, and Y. Park,
1
Adv. Mater. 10, 1112 (1998).
13. N. X. Hu, M. Esteghamatian, S. Xie, Z. Popovic, A.-M. Hor, B. Ong,
and S. Wang, Adv. Mater. 11, 1460 (1999).
4. CONCLUSIONS
We have focused our research on the development of irid-
ium complexes, especially with respect to color tuning
14. G. Y. Park, J. H. Seo, Y. K. Kim, Y. S. Kim, and Y. Ha, J. Kor. Phys.
Soc. 50, 1729 (2007).
15. M. Nonoyama, J. Oranomet. Chem. 86, 263 (1975).
and efficiency improvement of luminescence for OLED.
∧
16. Y. You, K. S. Kim, T. K. Ahn, D. Kim, and S. Y. Park, J. Phys.
Chem. C 111, 4052 (2007).
17. Y. You and S. Y. Park, J. Am. Chem. Soc. 127, 12438 (2005).
Herein, we synthesized Ir(C N) (ODZ) and studied
2
their emission patterns and characteristics where F -ppy,
2
∧
ppy and pq were introduced as main ligands (C N).
18. Y. You, J. Seo, S. H. Kim, K. S. Kim, T. K. Ahn, D. Kim, and S. Y.
We expected that the complexes synthesized in this study
Park, Inorg. Chem. 47, 1476 (2008).
J. Nanosci. Nanotechnol. 12, 5613–5618, 2012
5617

Phosphorescence Color Tuning of Oxadiazole-Based Iridium(III) Complexes for OLED
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1
2
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2008).
0. F.-M. Hwang, H.-Y. Chen, P.-S. Chen, C.-S. Liu, Y. Chi, C.-F. Shu,
F.-L. Wu, P.-T. Chou, S.-M. Peng, and G.-H. Lee, Inorg. Chem.
21. K. R. J. Thomas, M. Velusamy, J. T. Lin, C. Chien, Y. Tao, Y. S.
Wen, Y. Hu, and P. Chou, Inorg. Chem. 44, 5677 (2005).
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Organnometallics 25, 3631 (2006).
(
44, 1344 (2005).
23. H. R. Park and Y. Ha, J. Nanosci. Nanotechnol. 12, 1365 (2012).
Received: 28 June 2011. Accepted: 16 January 2012.
Delivered by Publishing Technology to: University of Waterloo
IP: 23.24.70.177 On: Wed, 14 Oct 2015 07:09:55
Copyright: American Scientific Publishers
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J. Nanosci. Nanotechnol. 12, 5613–5618, 2012