Iridium(III) complexes bearing quinoxaline ligands with efficient red luminescence properties

Article abstract of DOI:10.1246/bcsj.80.783

Newly designed cyclometalated iridium(III) complexes bearing 2,3-diphenylquinoxalines, which were shown to be highly efficient and pure-red emitting materials for electrophosphorescent organic light-emitting diodes (OLEDs), were synthesized and characteri

Full text of DOI:10.1246/bcsj.80.783

ꢀ 2007 The Chemical Society of Japan
Bull. Chem. Soc. Jpn. Vol. 80, No. 4, 783–788 (2007)
783
Iridium(III) Complexes Bearing Quinoxaline Ligands
with Efficient Red Luminescence Properties
Kazuyasu Tani,2 Hiroyuki Fujii,3 Lisheng Mao,2 Hidehiro Sakurai,y and Toshikazu Hirao
;1;2
ꢀ1;2
1Department of Applied Chemistry, Graduate School of Engineering, Osaka University,
Yamada-oka, Suita, Osaka 565-0871
2Handai Frontier Research Center, Graduate School of Engineering, Osaka University,
Yamada-oka, Suita, Osaka 565-0871
3SANYO Electric Co., Ltd., 1-18-13 Hashiridani, Hirakata, Osaka 573-8534
Received July 3, 2006; E-mail: hirao@chem.eng.osaka-u.ac.jp
Newly designed cyclometalated iridium(III) complexes bearing 2,3-diphenylquinoxalines, which were shown to be
highly efficient and pure-red emitting materials for electrophosphorescent organic light-emitting diodes (OLEDs), were
synthesized and characterized. Excellent quantum efficiencies for photoluminescence within the range of 50–79% were
attained in dichloromethane solution at room temperature. Luminescence peak wavelengths of the complexes were with-
in the preferred range of 653–671 nm in thin films. The most vivid red electrophosphorescence with CIE chromaticity
coordinates x ¼ 0:70 and y ¼ 0:28, which are the closest to the ultimate limit of pure red among reported OLEDs, was
achieved with the acetylacetonatoiridium complex bearing 2,3-diphenylquinoxaline.
ortho-Metalated complexes have attracted much attention
for use in organic light-emitting diodes (OLEDs) because
Results and Discussion
they are strong electroluminescent emitters.1 Especially, iri-
dium(III) complexes bearing o-pyridine-arene or o-pyridine-
heterocycle derivatives2,3 have been reported to show highly
efficient phosphorescence due to emission from the triplet
metal to ligand charge transfer (3MLCT) excited state and
triplet ligand centered (3LC) excited state.1 Quinoxalines
are considered to be building blocks for functional materials,
and so, homo- and co-polymers containing a quinoxaline unit
have been investigated.4–9 Red emission complexes with
larger quantum yields have been studied towards the devel-
opment of highly efficient red emissive OLEDs.10–14 A phos-
phorescent organoiridium compound, bis(2-(20-benzothienyl)-
pyridinato-N,C30)iridium(acetylacetonate) ([Ir(btp)2(acac)]),
has been reported to give red photoluminescence (PL) with
a PL quantum yield of 0.21.2 The orange-red iridium com-
plex bearing dibenzo[f,h]quinoxaline (dbq) has been report-
ed to give a PL quantum yield of 0.53 in dichloromethane
and chromaticity of (x ¼ 0:62, y ¼ 0:38) on electrolumines-
cence.10 Since 2,3-diphenylquinoxalines14 possess a higher
energy highest occupied molecular orbital (HOMO) and low-
er energy lowest unoccupied molecular orbital (LUMO) due
to their ꢀ orbital and susceptibility to reduction, iridium(III)
complexes with 2,3-diphenylquinoxaline ligands should ex-
hibit pure red emission.11–15 We now report the synthesis
and characterization of acetylacetonatoiridium(III) complexes
with 2,3-diphenylquinoxalines.
Synthesis of Acetylacetonatoiridium(III) Complexes.
Acetylacetonatoiridium(III) complex 3 was synthesized as
shown in Scheme 1.16 2,3-Diphenylquinoxaline5 reacted with
IrCl3 nH2O in a mixed solvent of 2-ethoxyethanol and H2O
ꢁ
(v/v = 3:1) at 100 ꢂC. Filtration of the solid gave the iridium
chloride-bridged dimer 2 as a main product with small
amounts of fac- and/or mer-tris(2,3-diphenylquinoxalinato)-
iridium(III). Due to insolubility of 2, excess ligand and other
iridium complexes were readily removed by washing with
ethanol. Although two coordination sites are available with
the quinoxaline ligand, only one nitrogen atom of the quinoxa-
line coordinated under the reaction conditions. Then, 2 reacted
with acetylacetone in the presence of Na2CO3 to give the cor-
responding acetylacetonatoiridium(III) complex 3, which was
1
identified by H and 13C NMR, and elemental analysis.
UV–Vis and Emission Spectra. In the UV–vis spectra of
the acetylacetonatoiridium(III) complexes 3a–3d, a new ab-
sorption appeared at 470–480 nm, which was assigned to
MLCT (Fig. 1 and Table 1).2 Other absorption maxima around
ꢀ
ꢀ
230–400 nm may be ligand transitions (ꢀ–ꢀ and n–ꢀ tran-
sition), as compared with the absorptions of the corresponding
free ligands 1a–1d.6 No emission was observed with 1a–1d
when excited at ꢁ ¼ 390 nm. The emission of the fluoro deriv-
ative 3b was 10–20 nm blue-shifted from the other complexes
3a, 3c, and 3d (Fig. 2). It should be noted that the complexes 3
showed relatively high quantum yields, which were deter-
mined to be 0.50–0.79 on the basis of quinine sulfate/0.1 M
H2SO4 solution. These findings also suggest that emission
depends on the MLCT excited state. In thin film states, the ab-
sorption maxima of the MLCT were nearly the same (Fig. 3).
However, these absorption maxima for 3 were 15 nm red-shift-
y Present address: Research Center for Molecular-Scale Nano-
science, Institute for Molecular Science, Myodaiji, Okazaki
444-8787
Published on the web April 13, 2007; doi:10.1246/bcsj.80.783

784 Bull. Chem. Soc. Jpn. Vol. 80, No. 4 (2007)
Iridium(III) Complexes with Efficient Luminescence
R
Cl
Cl
N
N
Ir
N
Ir
.
N
IrCl3 nH2O
N
2-ethoxyethanol/H2O
(3 : 1)
N
R
R
100 °C, 18 h
R
R
R
1
2
2
2
R = H, 80% (2a)
R = F, 63% (2b)
R = MeO, 84% (2c)
R = Me, 82% (2d)
O
O
O
O
N
Ir
N
2-ethoxyethanol
Na2CO3
R
100 °C, 18 h
R
2
3
R = H, 95% (3a)
R = F, 79% (3b)
R = MeO, 85% (3c)
R = Me, 89% (3d)
Scheme 1. Synthesis of iridium(III) complexes 2 and 3.
Table 1. UV–Vis Spectra and Luminescent Properties for Acetylacetonatoiridium Complexes 3a–3da)
Solutionb)
Thin filmd)
Complex
UV–vis spectra
max/nm (log ")
Emission
max/nmc)
ꢀ
UV–vis spectra
max/nm
Emission
max/nme)
ꢁ
ꢁ
ꢁ
ꢁ
3a
3b
3c
3d
233 (5.43), 257 (5.15), 281 (5.11), 306 (4.93),
325 (4.79), 378 (4.41), 488 (3.93)
232 (5.37), 257 (5.08), 279 (5.03), 304 (4.91),
322 (4.79), 360 (4.35), 471 (3.99)
232 (5.36), 254 (5.15), 280 (5.03), 380 (4.53),
477 (4.07)
670
0.50
0.71
0.67
0.79
277, 374, 483
277, 377, 473
278, 393, 481
276, 374, 481
671
647
659
669
653
664
670
230 (5.27), 262 (5.05), 287 (4.90), 389 (4.31),
414 (4.35), 477 (4.04)
a) 298 K. b) 1:0 ꢃ 10ꢄ5 M in dichloromethane. c) Excitation at ꢁmax 390 nm. d) 20 nm thin film. e) Excitation at ꢁmax 470 nm.
3
ed as compared with those in solution states, suggesting that
there is a contribution from intermolecular ꢀ interactions in
solid states. The emission maxima in thin film states appeared
between 653 and 671 nm, which are about 5 nm red-shifted
3a
3b
3c
3d
2
1
from the solution state emission (Fig. 4). These emission proc-
3
esses are mainly due to the MLCT transition. In general, the
luminescence quantum yields decreased with an increase in the
emission peak wavelength according to the energy gap law.6
Therefore, these acetylacetonatoiridium(III) complexes 3a–
3d bearing the quinoxaline ligands appear to be promising as
red luminescent materials.
OLED Performance. As described below, two types of
OLEDs were fabricated with a multilayered structure by vacu-
um thermal evaporation on indium–tin oxide (ITO) anode pre-
patterned glass substrates. The organic layers between the
anode and the cathode were composed of a hole-injection layer
(HIL), a light-emitting layer, and an electron-injection layer
(EIL). The light-emitting layer was either a doped light-emit-
0
250
300
400
500
600
nm
Fig. 1. UV–vis spectra of acetylacetonatoiridium(III) com-
plexes 3a–3d in dichloromethane solution.

K. Tani et al.
Bull. Chem. Soc. Jpn. Vol. 80, No. 4 (2007)
785
Cathode
EIL(BPhen)
EETL(TAZ)
HIL(NPD)
Anode
Cathode
EIL(BPhen)
EBL(CBP)
HIL(NPD)
Anode
3a
3b
3c
3d
N
N
N
N
N
CBP
TAZ
Fig. 5. The device structures and chemical structures of
CBP and TAZ.
500
600
700
800
900
nm
1
Fig. 2. Emission spectra of acetylacetonatoiridium(III)
complexes 3a–3d in dichloromethane solution.
3a
[Ir(acac)(btp)2]
0.3
0
0.2
0.1
3a
3b
3c
3d
380
480
580
680
780
nm
Fig. 6. Electroluminescence spectra of [Ir(acac)(btp)2]
(square) and 3a (circle) doped EBL OLEDs at room tem-
perature.
ting bipolar layer (EBL) with 4,40-di-9-carbazolylbiphenyl
(CBP) or a doped light-emitting electron-transport layer
(EETL) with 3-(4-biphenylyl)-4-phenyl-5-(4-tert-butylphen-
yl)-1,2,4-triazole (TAZ) as shown in Fig. 5. The acetylaceto-
natoiridium(III) complex 3a was doped into the light-emitting
layer at a doping concentration of 9 wt %. The cathode was
0.5 nm thick lithium fluoride for efficient electron injection
and 150 nm thick aluminum. The materials for organic layers
were 4,40-bis[N-(1-naphthyl)-N-phenylamino]biphenyl (NPD)
for HIL (thickness: 60 nm), CBP for EBL (35 nm), TAZ for
EETL (35 nm), and 4,7-diphenyl-1,10-phenanthroline (BPhen)
for EIL (60 nm).
The electroluminescence spectra for 3a and [Ir(acac)(btp)2]
(btp: benzothienylpyridine) doped devices are shown in Fig. 6.
The featureless broad emission peak of 3a suggests that the
electrophosphorescence predominantly originated from the
3MLCT excited state. On the contrary, the electrolumines-
cence of a conventional red complex, [Ir(acac)(btp)2], has been
reported to originate dominantly from the 3LC excited state as
observed in the vibronic peaks.2,17
0
300
400
500
600
nm
Fig. 3. UV–vis spectra of acetylacetonatoiridium(III) com-
plexes 3a–3d in 20 nm thin film states.
3a
3b
3c
3d
In relation to pure-red luminescence, the electrolumines-
cence peak wavelength of 675 nm for 3a is clearly superior
to the one of 616 nm for [Ir(acac)(btp)2]. To the best of our
knowledge, 3a exhibited the most vivid-red electrolumines-
cence with the 1931 CIE chromaticity coordinates of (0.70,
0.28).
600
700
800
nm
Fig. 4. Emission spectra of acetylacetonatoiridium(III)
complexes 3a–3d in 20 nm thin film states.
Figure 7 shows a comparison of the electrophosphorescence

786 Bull. Chem. Soc. Jpn. Vol. 80, No. 4 (2007)
Iridium(III) Complexes with Efficient Luminescence
rious radiation becomes possible. This may be another reason
for the higher color purity for the EETL OLED with TAZ.
1
Conclusion
We synthesized and characterized acetylacetonatoiri-
dium(III) complexes 3. Complexes 3 showed red luminescence
between 647 and 670 nm in dichloromethane solution. A pure-
red OLED was produced by using 3a with 2,3-diphenylqui-
noxaline. The new organoiridium compound is promising as
a pure-red emitting material, for use in various applica-
tions, such as surgical illumination with enhanced color repro-
ducibility.
0
380
480
580
680
780
nm
Fig. 7. Comparison of electrophosphorescence spectra for
two types of 3a doped OLEDs at luminance of 600
cd mꢄ2. Fine curve: the light-emitting electron-transport
layer (EETL) OLED, dashed curve: the light-emitting bi-
polar layer (EBL) OLED.
Experimental
All reagents and solvents were purchased from commercial
sources and were further purified by the standard methods, if nec-
essary. Melting points were determined on a Yanagimoto Micro-
melting Point Apparatus and are uncorrected. Infrared spectra
were obtained with a JASCO FT/IR-480 plus. The 1H NMR
(300 MHz) and 13C NMR (75.5 MHz) spectra were recorded on
a Varian MERCURY 300 spectrometer. Mass spectra were run
on a JEOL JMS-DX303HF mass spectrometer. UV–vis spectra
were obtained by using a Hitachi U-3500 spectrophotometer at
1:0 ꢃ 10ꢄ5 M concentration in dichloromethane at 298 K. Emis-
sion spectra were taken on a Shimadzu RF-5300PC spectrofluoro-
photometer with a sample concentration of 1:0 ꢃ 10ꢄ5 M in di-
chloromethane at 298 K. Thin films (20 nm) were prepared by sub-
limation at 4 ꢃ 10ꢄ2 Pa. Emission spectra of the thin films on
glass were taken on a Shimadzu RF-5300PC spectrofluorophotom-
eter at 298 K. Emission quantum yields in solution were estimated
by using a solution with a concentration of 1:0 ꢃ 10ꢄ5 M concen-
tration of (ꢄ)-quinine sulfate/0.1 M H2SO4 aq as a reference.
Electroluminescence spectra were measured with Konica-Minolta
CS-1000A spectroradiometer.
spectra for two types of OLEDs of 3a at luminance of 600
cd mꢄ2. The spectrum of EBL OLED had a peak at 675 nm,
while the EETL OLED afforded the purest-red electrophos-
phorescence spectrum with a maximum at 680 nm and a full
width at half maximum of 89 nm. A small peak at around
437 nm was observed in the EBL OLED with CBP under high
luminance. The small peak corresponds to the PL peak for
CBP. On the contrary, no spurious radiation was observed in
the EETL OLED. In OLEDs, holes and electrons are injected
into a light-emitting layer, and recombination of charges gen-
erates excited states. Excited energy of the host is transferred
to the dopant, and light is mainly emitted from the dopant.
However, the rate of such energy transfer is limited. Thus,
emission from the host becomes possible as the charge recom-
bination rate increases. When leakage of the charges from a
light-emitting layer is substantial, spurious radiation due to
recombination in the adjacent layers is also possible.
In the EBL OLED, the HOMO levels for the organic layers
are 5.7 eV (NPD), 6.3 eV (CBP), and 6.4 eV (BPhen), respec-
tively, and the HOMO offset between CBP and BPhen is only
0.1 eV. Therefore, substantial leakage of holes from CBP to
BPhen is possible. In contrast, the EETL had larger HOMO
offsets (0.2 eV) between TAZ and BPhen because the HOMO
level for TAZ is 6.6 eV. Therefore, leakage of holes from a
light-emitting layer to BPhen is more difficult in the EETL
OLED than the EBL OLED. This may be one reason for the
higher color purity of the EETL OLED.
In the EBL OLED, the LUMO levels for the organic layers
are 2.6 eV (NPD), 3.2 eV (CBP), and 3.0 eV (BPhen), respec-
tively. Since the LUMO offset between CBP and BPhen is
0.2 eV, electron injection from BPhen to CBP is efficient,
and recombination of charges occurs predominantly on CBP.
Thus, spurious emission from CBP is possible with high lumi-
nance. On the contrary, electron injection from BPhen to TAZ
is more difficult in the EETL OLED since the LUMO offset
between TAZ and BPhen is 0.4 eV. Direct electron injection
from BPhen to the dopant or substantial carrier trap on the
dopant may become significant in the EETL OLED because
of the high doping concentration of 9 wt % for the OLEDs.
In this case, the excited states of the dopant are directly gener-
ated on the dopant. As a result, efficient emission without spu-
Synthesis of [{Ir(Hqx)2}2(ꢀ-Cl)2] (2a). IrCl3 nH2O (10.0
ꢁ
mmol) and 2,3-diphenylquinoxaline (1a, 5.647 g, 20.0 mmol) were
stirred in a mixed solvent of 2-ethoxyethanol/water (v/v = 3:1,
200 mL) at 100 ꢂC for 18 h under argon. After the solvent was re-
moved under reduced pressure, ethanol (100 mL) and dichloro-
methane (50 mL) were added to the resulting residue. The precip-
itate was collected and dried to give 6.283 g (80% yield) of 2a as a
brown solid. Mp: >300 ꢂC; IR (KBr): 3116, 3047, 2968, 2921,
2862, 1577, 1483, 1444, 1426, 1388, 1350, 1320, 1236, 1127,
1069, 805, 758, 697, 636 cmꢄ1; 1H NMR (CDCl3): ꢂ 5.66 (d, J ¼
8:3 Hz, 1H), 6.18 (t, J ¼ 8:3 Hz, 1H), 6.45 (t, J ¼ 8:3 Hz, 1H),
6.70 (td, J ¼ 1:5, 8.3 Hz, 1H), 6.87 (t, J ¼ 8:3 Hz, 1H), 7.30 (d,
J ¼ 8:3 Hz, 1H), 7.65–7.71 (m, 4H), 8.03–8.12 (br, 2H), 8.42 (d,
J ¼ 8:3 Hz, 1H); 13C NMR (CDCl3): 121.2, 126.3, 127.8, 128.1,
128.6, 128.8, 129.1, 129.7, 130.9, 134.8, 138.2, 139.9, 140.4,
146.5, 150.0, 151.9, 163.3 ppm; Anal. Calcd for C80H52Cl2N8-
Ir2 H2O: C, 60.10; H, 3.40; N, 7.01%. Found: C, 60.00; H,
ꢁ
3.51; N, 6.90%.
Synthesis of [{Ir(4-Fqx)2}2(ꢀ-Cl)2] (2b). IrCl3 nH2O (5.0
ꢁ
mmol) and 2,3-bis(4-fluorophenyl)quinoxaline (1b, 3.183 g, 10.0
mmol) were stirred in a mixed solvent of 2-ethoxyethanol/water
(v/v = 3:1, 100 mL) at 100 ꢂC for 18 h under argon. After the sol-
vent was removed under reduced pressure, ethanol (100 mL) was
added to the resulting residue. The precipitate was collected and
dried to give 2.713 g (63% yield) of 2b as a orange solid. Mp:
>300 ꢂC; IR (KBr): 3120, 3060, 2968, 1871, 1584, 1560, 1507,
1484, 1457, 1387, 1353, 1313, 1259, 1234, 1195, 1158, 1126,

K. Tani et al.
Bull. Chem. Soc. Jpn. Vol. 80, No. 4 (2007)
787
1096, 1066, 1015, 842, 802, 758, 733, 611, 566, 530, 521 cmꢄ1
;
2866, 1577, 1517, 1444, 1425, 1395, 1350, 1319, 1260, 1126,
1068, 1027, 807, 761, 733, 696, 637 cmꢄ1; H NMR (CDCl3): ꢂ
1H NMR (CDCl3): ꢂ 5.29 (dd, J ¼ 8:6, 2.3 Hz, 1H), 6.26 (ddd,
J ¼ 8:6, 6.9, 2.3 Hz, 1H), 6.68 (ddd, J ¼ 8:6, 6.9, 2.3 Hz, 1H),
6.91 (dd, J ¼ 8:6, 5.7 Hz, 1H), 7.32 (ddd, J ¼ 8:6, 6.9, 1.1 Hz,
1H), 7.35–7.46 (br, 2H), 7.70 (dd, J ¼ 8:6, 1.1 Hz, 1H), 7.97–
8.18 (br, 2H), 8.25 (d, J ¼ 8:6 Hz, 1H); 13C NMR (CDCl3): 109.8
1
1.62 (s, 6H, CH3), 4.69 (s, 1H, CH), 6.43 (dd, J ¼ 8:2, 1.5 Hz,
2H), 6.52 (td, J ¼ 8:2, 1.5 Hz, 2H), 6.61 (ddd, J ¼ 8:2, 7.2,
1.5 Hz, 2H), 7.08 (dd, J ¼ 8:2, 1.5 Hz, 2H), 7.50 (ddd, J ¼ 8:2,
7.2, 1.5 Hz, 2H), 7.61–7.68 (m, 8H), 8.00–8.05 (m, 4H), 8.12 (dd,
J ¼ 8:2, 1.5 Hz, 2H), 8.42 (dd, J ¼ 8:2, 1.5 Hz, 2H); 13C NMR
(CDCl3): 28.3 (CH3), 99.9 (CH), 120.6, 125.8, 128.2, 128.7,
128.9, 129.0, 129.6, 130.0, 130.4, 130.8, 136.9, 139.7, 139.9,
141.5, 146.1, 153.2, 154.3, 163.5, 185.7 (CO) ppm; Anal. Calcd
(J13C{19F ¼ 22 Hz), 115.9 (J13C{19F ¼ 22 Hz), 117.0 (J13C{19F
¼
22 Hz), 120.7 (J13C{19F ¼ 18 Hz), 125.6, 129.1 (J13C{19F ¼ 4:3
Hz), 130.6 (J13C{19F ¼ 7:7 Hz), 131.0 (J13C{19F ¼ 9:4 Hz), 132.5
(J13C{19F ¼ 8:3 Hz), 135.6 (J13C{19F ¼ 4:3 Hz), 138.2, 139.9, 142.3
(J13C{19F ¼ 2:0 Hz), 150.5, 151.3 (J13C{19F ¼ 7:5 Hz), 160.5
(J13C{19F ¼ 240 Hz), 162.2, 163.9 (J13C{19F ¼ 234 Hz) ppm; Anal.
for C45H33IrN4O2 0.5C6H14: C, 64.27; H, 4.49; N, 6.25%. Found:
ꢁ
C, 64.42; H, 4.50; N, 6.23%.
Synthesis of [Ir(4-Fqx)2(acac)] (3b).
Calcd for C80H44Cl2F8N8Ir2 0.5CH2Cl2: C, 54.72; H, 2.57; N,
[Ir(4-Fqx)2(ꢃ-Cl)2]
ꢁ
6.34%. Found: C, 54.66; H, 2.84; N, 6.30%.
Synthesis of [{Ir(4-MeOqx)2}2(ꢀ-Cl)2] (2c). IrCl3 nH2O
(2b, 117.3 mg, 0.07 mmol), acetyl acetone (20 mL, 0.19 mmol),
and Na2CO3 (206.4 mg, 1.95 mmol) were stirred in 2-ethoxyetha-
nol (5 mL) at 100 ꢂC for 18 h under argon. After removal of the
solvent under reduced pressure, the residue was extracted with
dichloromethane and washed with water. The organic layer was
separated, dried over MgSO4, and evaporated to dryness under re-
duced pressure. The residue was separated by column chromatog-
raphy on silica gel using ethyl acetate as an eluent. The obtained
solid was washed with ether (5 mL) to give 100.5 mg (79% yield)
of 3b as a black solid. Mp: >300 ꢂC; IR (KBr): 3065, 2959, 2921,
1581, 1560, 1508, 1389, 1354, 1311, 1236, 1190, 1158, 1124,
ꢁ
(5.0 mmol) and 2,3-bis(4-methoxylphenyl)quinoxaline (1c, 3.104
g, 10.0 mmol) were stirred in a mixed solvent of 2-ethoxyetha-
nol/water (v/v = 3:1, 100 mL) at 100 ꢂC for 18 h under argon.
After the solvent was removed under reduced pressure, ethanol
(100 mL) was added to the resulting residue. The precipitate was
collected and dried to give 3.740 g (82% yield) of 2c as a red solid.
Mp: >300 ꢂC; IR (KBr): 3070, 2932, 2834, 1606, 1580, 1507,
1457, 1384, 1353, 1302, 1254, 1222, 1174, 1132, 1031, 837, 758,
615, 548 cmꢄ1; 1H NMR (CDCl3): ꢂ 3.99 (s, 6H, CH3O), 5.21 (d,
J ¼ 2:6 Hz, 1H), 6.07 (dd, J ¼ 8:7, 2.6 Hz, 1H), 6.65 (dd, J ¼ 8:7,
7.5 Hz, 1H), 6.91 (d, J ¼ 8:7 Hz, 1H), 7.20 (dd, J ¼ 8:7, 7.5 Hz,
1H), 7.21–7.26 (br, 2H), 7.60 (d, J ¼ 8:7 Hz, 1H), 7.98–8.08
(br, 2H), 8.41 (d, J ¼ 8:7 Hz, 1H); 13C NMR (CDCl3): 54.3
(CH3O), 55.5 (CH3O), 109.0, 113.7, 115.1, 118.3, 126.3, 127.8,
128.5, 129.5, 130.5, 132.6, 137.9, 139.3, 140.0, 151.2, 152.7,
1065, 841, 805, 762, 734, 612, 523 cmꢄ1 1H NMR (CDCl3): ꢂ
;
1.63 (s, 6H, CH3), 4.71 (s, 1H, CH), 6.05 (dd, J ¼ 9:1, 2.2 Hz,
2H), 6.39 (ddd, J ¼ 9:1, 6.8, 2.2 Hz, 2H), 7.09 (dd, J ¼ 9:1,
5.7 Hz, 2H), 7.30–7.35 (br, 4H), 7.53 (ddd, J ¼ 9:1, 6.8, 2.2 Hz,
2H), 7.68 (ddd, J ¼ 9:1, 6.8, 1.2 Hz, 2H), 8.00 (br, 6H), 8.11 (dd,
J ¼ 6:8, 1.2 Hz, 2H), 8.20 (dd, J ¼ 6:8, 1.2 Hz, 2H); 13C NMR
(CDCl3): 28.3 (CH3), 100.2 (CH), 108.9 (J13C{19F ¼ 23 Hz),
116.2 (J13C{19F ¼ 23 Hz), 122.5 (J13C{19F ¼ 18 Hz), 125.2, 129.2
(J13C{19F ¼ 23 Hz), 130.7, 131.3, 131.8 (J13C{19F ¼ 8:9 Hz), 135.7
(J13C{19F ¼ 3:2 Hz), 139.7, 141.3, 142.0, 156.4 (J13C{19F ¼ 7:2
Hz), 161.5 (J13C{19F ¼ 271 Hz), 162.4, 163.6 (J13C{19F ¼ 250 Hz),
158.1, 160.7, 163.0 ppm; Anal. Calcd for C88H68Cl2N8O8Ir2
H2O: C, 57.48; H, 3.84; N, 6.09%. Found: C, 57.44; H, 3.91; N,
5.95%.
ꢁ
Synthesis of [{Ir(4-Meqx)2}2(ꢀ-Cl)2] (2d).
IrCl3 nH2O
ꢁ
(5.0 mmol) and 2,3-bis(4-methylphenyl)quinoxaline (1d, 3.104 g,
10.0 mmol) were stirred in a mixed solvent of 2-ethoxyethanol/
water (v/v = 3:1, 100 mL) at 100 ꢂC for 18 h under argon. After
the solvent was removed under reduced pressure, ethanol (100
mL) was added to the resulting residue. The precipitate was col-
lected and dried to give 3.572 g (84% yield) of 2d as a brown sol-
id. Mp: >300 ꢂC; IR (KBr): 3026, 2950, 2918, 2857, 1586, 1509,
1483, 1457, 1388, 1353, 1317, 1235, 1209, 1183, 1140, 1073,
185.8 (CO) ppm; Anal. Calcd for C45H29IrN4O2F4 0.5CH2Cl2: C,
ꢁ
56.43; H, 3.12; N, 5.79%. Found: C, 56.32; H, 3.09; N, 5.73%.
Synthesis of [Ir(4-MeOqx)2(acac)] (3c).
[Ir(4-MeOqx)2-
(ꢃ-Cl)2] (2c, 115.6 mg, 0.07 mmol), acetyl acetone (20 mL, 0.19
mmol), and Na2CO3 (206.4 mg, 1.95 mmol) were stirred in 2-
ethoxyethanol at 100 ꢂC for 18 h under argon. After removal of
the solvent under reduced pressure, the residue was extracted with
dichloromethane and washed with water. The organic layer was
separated, dried over MgSO4, and evaporated to dryness under re-
duced pressure. The residue was separated by column chromatog-
raphy on silica gel using ethyl acetate as an eluent. The obtained
solid was washed with ether (5 mL) to give 117.9 mg (89% yield)
of 3c as a black solid. Mp: >300 ꢂC; IR (KBr): 3065, 2959, 2922,
2833, 1580, 1560, 1518, 1507, 1457, 1437, 1395, 1303, 1257,
1042, 1020, 980, 828, 809, 756, 730, 613, 512 cmꢄ1 1H NMR
;
(CDCl3): ꢂ 2.57 (s, 6H, CH3), 5.47 (d, J ¼ 1:3 Hz, 1H), 6.28
(dd, J ¼ 8:4, 1.3 Hz, 1H), 6.65 (ddd, J ¼ 8:4, 6.9, 1.3 Hz, 1H),
6.79 (d, J ¼ 8:4 Hz, 1H), 7.24 (ddd, J ¼ 8:4, 6.9, 1.3 Hz, 1H),
7.42–7.57 (br, 2H), 7.65 (dd, J ¼ 8:4, 1.3 Hz, 1H), 7.88–8.03
(br, 2H), 8.35 (d, J ¼ 8:4 Hz, 1H); 13C NMR (CDCl3): 21.2
(CH3), 21.8 (CH3), 122.3, 126.4, 128.3, 128.5, 128.7, 128.9,
129.6, 135.4, 137.3, 137.9, 138.0, 139.5, 140.3, 143.9, 150.5,
151.8, 163.3 ppm.
Synthesis of [Ir(Hqx)2(acac)] (3a). [Ir(Hqx)2(ꢃ-Cl)2] (2a,
108.0 mg, 0.07 mmol), acetyl acetone (20 mL, 0.19 mmol), and
Na2CO3 (206.4 mg, 1.95 mmol) were stirred in 2-ethoxyethanol
(5 mL) at 100 ꢂC for 18 h under argon. After removal of the sol-
vent under reduced pressure, the residue was extracted with di-
chloromethane and washed with water. The organic layer was sep-
arated, dried over MgSO4, and evaporated to dryness under re-
duced pressure. The residue was separated by column chromatog-
raphy on silica gel using ethyl acetate as an eluent. The obtained
solid was washed with ether (5 mL) to give 110.9 mg (95% yield)
of 3a as a black solid. Mp: >300 ꢂC; IR (KBr): 3042, 2986, 2926,
1
1222, 1175, 1131, 1031, 838, 765, 614 cmꢄ1; H NMR (CDCl3):
ꢂ 1.61 (s, 6H, CH3), 3.94 (s, 12H, CH3O), 4.70 (s, 1H, CH),
5.93 (d, J ¼ 2:7 Hz, 2H), 6.24 (dd, J ¼ 8:6, 2.7 Hz, 2H), 7.11
(d, J ¼ 8:6 Hz, 2H), 7.11–7.13 (m, 4H), 7.45 (ddd, J ¼ 8:6, 6.8,
1.1 Hz, 2H), 7.57 (ddd, J ¼ 8:6, 6.8, 1.1 Hz, 2H), 7.95–7.99 (br,
4H), 8.05 (dd, J ¼ 8:6, 1.7 Hz, 2H), 8.23 (d, J ¼ 8:6 Hz, 2H);
13C NMR (CDCl3): 28.3 (CH3), 54.7 (CH3O), 55.5 (CH3O), 100.0
(CH), 107.6, 114.4, 120.9, 125.5, 128.2, 128.7, 129.8, 130.7,
131.5, 132.6, 139.1, 139.4, 141.3, 152.6, 156.7, 158.7, 160.6,
163.2, 185.5 ppm; Anal. Calcd for C49H41IrN4O6: C, 60.42; H,
4.24; N, 5.75%. Found: C, 60.13; H, 4.41; N, 5.60%.
Synthesis of [Ir(4-Meqx)2(acac)] (3d). [Ir(4-Meqx)2(ꢃ-Cl)2]
(2d, 115.6 mg, 0.07 mmol), acetyl acetone (20 mL, 0.19 mmol),

788 Bull. Chem. Soc. Jpn. Vol. 80, No. 4 (2007)
Iridium(III) Complexes with Efficient Luminescence
and Na2CO3 (206.4 mg, 1.95 mmol) were stirred in 2-ethoxyetha-
nol at 100 ꢂC for 18 h under argon. After removal of the solvent
under reduced pressure, the residue was extracted with dichloro-
methane and washed with water. The organic layer was separated,
dried over MgSO4, and evaporated to dryness under reduced pres-
sure. The residue was separated by column chromatography on
silica gel using ethyl acetate as an eluent. The obtained solid
was washed with ether (5 mL) to give 106.4 mg (86% yield) of
3d as a black solid. Mp: >300 ꢂC; IR (KBr): 3028, 2927, 2857,
1583, 1560, 1522, 1391, 1352, 1316, 1261, 1183, 1140, 1072, 810,
3
A. B. Tamayo, B. D. Alleyne, P. I. Djurovich, S.
Lamansky, I. Tsyba, N. N. Ho, R. Bau, M. E. Thompson, J.
Am. Chem. Soc. 2003, 125, 7377.
4
T. Yamamoto, Z.-H. Zhou, T. Kanbara, M. Shimura, K.
Kizu, T. Maruyama, Y. Nakamura, T. Fukuda, B.-L. Lee, N.
Ooba, S. Tomaru, T. Kurihara, T. Kaino, K. Kubota, S. Sasaki,
J. Am. Chem. Soc. 1996, 118, 10389.
5
C. G. Bangcuyo, J. M. Ellsworth, U. Evans, M. L. Myrick,
U. H. F. Bunz, Macromolecules 2003, 36, 546.
M. V. Kulikova, K. P. Balashev, P.-I. Kvam, J. Songstad,
Russ. J. Chem. 2000, 70, 163.
K. P. Balashev, M. V. Kulikova, P.-I. Kvam, J. Songstad,
Russ. J. Chem. 1999, 69, 1348.
A. M. Clark, C. E. F. Rickard, W. R. Roper, L. J. Wright,
J. Organomet. Chem. 2000, 598, 262.
6
1
767, 732, 612, 513 cmꢄ1; H NMR (CDCl3): ꢂ 1.59 (s, 6H, CH3),
2.51 (s, 12H, CH3), 4.67 (s, 1H, CH), 6.28 (d, J ¼ 1:1 Hz, 2H),
6.46 (dd, J ¼ 8:6, 1.7 Hz, 2H), 7.05 (d, J ¼ 8:6 Hz, 2H), 7.40–
7.59 (m, 6H), 7.61 (ddd, J ¼ 8:6, 6.8, 1.1 Hz, 2H), 7.90–7.93
(br, 4H), 8.09 (dd, J ¼ 8:6, 1.7 Hz, 2H), 8.21 (d, J ¼ 8:6 Hz, 2H);
13C NMR (CDCl3): 21.5 (CH3), 21.7 (CH3), 28.3 (CH3), 99.9
(CH), 121.9, 125.7, 128.6, 128.7, 129.6, 129.8, 130.0, 137.3,
137.5, 138.4, 139.5, 139.6, 141.5, 143.5, 153.2, 154.6, 163.5,
185.5 (CO) ppm.
7
8
9
359.
P. J. Steel, G. B. Caygill, J. Organomet. Chem. 1990, 395,
10 J.-P. Duan, P.-P. Sun, C.-H. Cheng, Adv. Mater. 2003, 15,
224.
11 G.-L. Zhang, Z.-H. Liu, H.-Q. Guo, Chin. Chem. Lett.
2004, 15, 1349.
12 G.-L. Zhang, H.-Q. Guo, Y.-T. Chuai, D.-C. Zou, Huaxue
Xuebao 2005, 63, 143.
13 S. Satoshi, H. Inoue, S. Shitagaki, N. Ohsawa, H. Abe, K.
Kojima, R. Nomura, S. Yamazaki, Dig. Tech. Pap.-Soc. Inf. Disp.
Int. Symp. 2005, 36, 806.
The use of the facilities of the Analytical Center, Graduate
School of Engineering, Osaka University is acknowledged.
The authors are grateful to Dr. Afshad Talaie, Dr. Keizo
Okada, Ms. Kana Nakamoto, Ms. Mika Gochomori, and Ms.
Shoko Wakatsuki for their help during experiments.
14 L. Mao, H. Sakurai, T. Hirao, Synthesis 2004, 2535.
15 H. Fujii, H. Sakurai, K. Tani, L. Mao, K. Wakisaka, T.
Hirao, IEICE Trans. Electron. 2004, E87-C, 2119.
16 S. D. Cummings, R. Eisenberg, J. Am. Chem. Soc. 1996,
118, 1949.
References
1
M. A. Baldo, D. F. O’Brien, Y. You, A. Shoustikov, S.
Sibley, S. M. E. Thompson, S. R. Forrest, Nature (London)
1998, 395, 151.
2
H.-E. Lee, C. Adachi, P. E. Burrows, S. R. Forrest, M. E.
Thompson, J. Am. Chem. Soc. 2001, 123, 4304.
S. Lamansky, P. Djurovich, D. Murphy, F. Abdel-Razzaq,
17 S. Lamansky, P. Djurovich, D. Murphy, F. Abdel-Razzaq,
R. Kwong, I. Tsyba, M. Bortz, B. Mui, R. Bau, M. E. Thompson,
Inorg. Chem. 2001, 40, 1704.