Synthesis and electroluminescence properties of fac-tris(2-phenylpyridine)- iridium derivatives containing hole-trapping moieties

Article abstract of DOI:10.1002/ejic.200600285

In order to investigate an effective method for carrier injection into the phosphor of organic electroluminescent (EL) devices, we synthesized fac-tris(2-phenylpyridine)iridium [Ir(ppy)₃] derivatives containing hole-trapping moieties, such as d

Full text of DOI:10.1002/ejic.200600285

FULL PAPER
DOI: 10.1002/ejic.200600285
Synthesis and Electroluminescence Properties of fac-Tris(2-phenylpyridine)-
iridium Derivatives Containing Hole-Trapping Moieties
Katsuhiko Ono,*[a] Michitoshi Joho,[a] Katsuhiro Saito,[a] Masaaki Tomura,[b]
Yosuke Matsushita,[c] Shigeki Naka,[c] Hiroyuki Okada,[c] and Hiroyoshi Onnagawa[c]
Keywords: Amines / Charge-carrier injection / Doping / Iridium / Luminescence
In order to investigate an effective method for carrier injec-
tion into the phosphor of organic electroluminescent (EL)
devices, we synthesized fac-tris(2-phenylpyridine)iridium
[Ir(ppy)3] derivatives containing hole-trapping moieties, such
cyclic voltammetry. EL devices using an Ir complex with di-
phenylamine exhibited high EL performance because 1,1-
bis[4-(di-p-tolylamino)phenyl]cyclohexane (TAPC) was em-
ployed as a hole-transporting layer. The maximum external
as diphenylamine, carbazole, and phenoxazine. Their photo- quantum efficiency (ηext) was recorded as 12.2%. This value
luminescent maxima were observed around the maximum of
Ir(ppy)3. These values were slightly shifted depending on the
hole-trapping moieties: redshifted due to diphenylamine and
blueshifted due to carbazole and phenoxazine. Further, these
moieties affected the oxidation potentials of Ir complexes in
is comparable to that observed in a device using Ir(ppy)3.
These results indicate that the diphenylamino substituent is
favorable to serve as a hole-trapping moiety of Ir(ppy)3.
(© Wiley-VCH Verlag GmbH & Co. KGaA, 69451 Weinheim,
Germany, 2006)
triplet states to the phosphor triplet state at the emitting
Introduction
layer.[4,5] fac-Tris(2-phenylpyridine)iridium [Ir(ppy)3] is a
Currently, organic electroluminescent (EL) devices are an well-known green emitter.[3,6] A phosphorescent EL device
active area of research because of their potential applica- using Ir(ppy)3 demonstrated a high performance with a
tions in flat-panel displays.[1] The research to synthesize maximum external quantum efficiency of 19.2%.[3e] This
phosphorescent materials with heavy metals such as plati- value was comparable to the theoretical limit of around
num and iridium has attracted considerable attention[2,3] be- 20% obtained from simple classical optics.[7] However, fur-
cause an internal quantum efficiency of 100% can be ther investigation of phosphorescent materials is still re-
achieved by the energy transfer from both the singlet and quired for the research and development of phosphorescent
Scheme 1. Structures of Ir complexes 1.
EL devices. Also, synthetic studies on various materi-
[a] Department of Materials Science and Engineering, Nagoya In-
als such as Ir,[8,9] Pt,[10] and other metal[11] complexes have
stitute of Technology, Gokiso,
Showa-ku, Nagoya 466-8555, Japan
Fax: +81-52-735-5407
been conducted. These substances are used as dopants at
the emitting layer. For example, the addition of an amount
of ca. 6 wt.-% of Ir(ppy)3 to the host material afforded the
highest external quantum efficiency.[3a,3b] Therefore, the
combination of phosphorescent and host materials is cru-
cial for effective injection of holes and electrons into the
E-mail: ono.katsuhiko@nitech.ac.jp
[b] Institute for Molecular Science,
Myodaiji, Okazaki 444-8585, Japan
[c] Department of Electric and Electronic Engineering, Faculty of
Engineering, University of Toyama,
Gofuku, Toyama 930-8555, Japan
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fac-Tris(2-phenylpyridine)iridium Derivatives Containing Hole-Trapping Moieties
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4a–d were prepared with yields of 82–91% by the Pd-cata-
lyzed cross-coupling reaction of 3 with aromatic amines
such as diphenylamine, carbazole, phenoxazine, and pheno-
thiazine.[16] This reaction required a selective use of an addi-
tive base. Sodium tert-butoxide was selected for the reaction
of diphenylamine, and potassium carbonate was employed
for those of rigid amines, namely, carbazole, phenoxazine,
and phenothiazine. The ligands 4a–c produced the cyclo-
metalated IrIII µ-chloro-bridged dimers 5a–c with yields of
80–88% by treatment with IrCl3·nH2O in 2-ethoxyethanol
and water at 120 °C.[6a] However, the Ir dimer 5d was not
obtained. The Ir complexes 1a–c were prepared with yields
of 48–78% by stirring 4 and 5 in glycerol with K2CO3 at
240 °C.[17] These Ir complexes were obtained in the form of
orange solids for 1a and yellow solids for 1b and 1c. Their
melting points were above 300 °C. Structural determination
was performed by using 1H NMR, MALDI-TOF mass
spectrometry, and elemental analysis. The stereochemistry
of these complexes was determined to be that of facial iso-
mers because the NMR chemical shifts observed in the
three ligands were equivalent. In order to investigate the
molecular structures of the Ir complexes, an X-ray crystal-
lographic analysis of 1a was performed. Two crystallo-
graphically independent molecules existed in this crystal.
The structure of one of these molecules is shown in Fig-
ure 1. Three sets of linear C–Ir–N bonds are observed, indi-
phosphor. 4,4Ј-Bis(carbazol-9-yl)-1,1Ј-biphenyl (CBP),
which is an aromatic amine, is generally employed as the
host material.[2b] Thus, we synthesized Ir(ppy)3 derivatives
as new types of phosphorescent materials, which are com-
posed of aromatic amines such as diphenylamine, carbazole,
phenoxazine, and phenothiazine[12] (see Scheme 1); these
amine units act as effective hole-trapping moieties.[13] As a
compound related to 1a, its acetylacetonate (acac) complex
[Ir(ppy-NPh2)2(acac)] has been recently synthesized.[14] It
was reported that the phosphorescent EL performance of
this complex was better than that of Ir(ppy)2(acac). In this
paper, we report the synthesis and properties of Ir com-
plexes 1 and their applications in the study of phosphores-
cent EL devices.
Results and Discussion
Preparation and Properties of Ir Complexes Containing
Hole-Trapping Moieties
The synthesis of the Ir complexes 1 is illustrated in
Scheme 2. 2-(4-Bromophenyl)pyridine (3) was synthesized
with a yield of 43% by the reaction of 2-fluoropyridine (2)
with 4-bromophenyllithium;[15] this was utilized as the key
compound in the following amination reaction. The ligands
Scheme 2. Synthesis of ligands 4 and Ir complexes 1.
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Figure 1. Molecular structure of Ir complex 1a (stereo view). Ir and N atoms are depicted as shaded octants.
cating that complex 1a is a facial isomer. Three diphenyl- Table 1. PL and absorption maxima of ligands 4.[a]
amine moieties, resembling antennas, exist on the side of
the Ir(ppy)3 core.
Ligand
λem [nm]
λabs [nm]
∆ [nm]
4a
4b
4c
4d
435
406
520
535
346
318
326
320
89
88
194
215
The ligands 4 exhibited photoluminescence (PL) maxima
between 400 and 540 nm in dichloromethane. The emission
and absorption maxima are listed in Table 1. The Stokes
shifts (∆) for 4c–d are greater than those for 4a–b, indicating
that the insertion of chalcogens such as O and S atoms into
the carbazole moieties results in large Stokes shifts. The PL
spectra of Ir complexes 1 are shown in Figure 2, and their
emission and absorption maxima are listed in Table 2. The
absorption maxima of the Ir complexes are redshifted as
compared to those of the ligands. These maxima can be
attributed to the metal–ligand charge-transfer (MLCT) ex-
citation. The PL maxima of 1 are almost similar to that of
Ir(ppy)3, indicating the Ir(ppy)3 cores as the source of the
emission. The emission maxima marginally shifted de-
pending on the molecular structure of the hole-trapping
moiety. The maximum of 1a, possessing a flexible amine, is
redshifted from that of Ir(ppy)3, and the maxima of 1b and
1c, possessing rigid amines, are blueshifted. The redshift is
attributed to the resonance effect of the diphenylamino sub-
stituent, which reduced the energy gap between HOMO
and LUMO. On the other hand, the π-conjugation on the
rigid frameworks of carbazole and phenoxazine prevents
the electron donation to the phenylpyridine (ppy) chelates.
Furthermore, the emission maxima of the Ir complexes 1a
and 1b are redshifted by ca. 100 nm from those of the li-
gands 4a and 4b, and the maximum of 1c is similar to that
of 4c because of the large Stokes shift in the ligand. In ad-
dition, the emission maximum of 1a is comparable to that
of Ir(ppy-NPh2)2(acac) (λem = 530 nm).[14] The PL quantum
[a] In CH2Cl2.
Figure 2. PL spectra of Ir complexes 1 in dichloromethane.
Table 2. PL and absorption maxima and quantum yields of Ir com-
plexes 1.[a]
[b]
Complex
λem [nm]
λabs [nm]
ΦPL
1a
1b
1c
526
504
509
512
398
0.14
0.38
0.17
0.40
378 sh
375 sh
377
Ir(ppy)3
[a] In CH2Cl2. [b] Measured relative to Ir(ppy)3, λex = 380 nm.
yields of 1a–c were measured in dichloromethane using c were recorded as +0.19, +0.48, and +0.23 V vs. Fc/Fc+,
Ir(ppy)3 as the standard (ΦPL = 0.40),[6b] and these values respectively.[18] The values of 1a and 1c were lower than that
are listed in Table 2. The quantum yield of 1b is greater of Ir(ppy)3 (+0.32 V), indicating higher electron-donating
than those of 1a and 1c.
abilities of 1a and 1c. On the other hand, the electron-do-
In order to investigate the redox properties of the Ir com- nating ability of 1b was lower than that of Ir(ppy)3 owing to
plexes 1, cyclic voltammetry (CV) was performed in dimeth- the introduction of a carbazole moiety. These results were
ylformamide (DMF) with 0.1  nBu4NClO4 as the support- attributed to the redox behavior of the ligands 4a–c. The
ing electrolyte. The voltammograms of 1 indicated revers- half-wave oxidation potentials of 4a and 4c (quasi-reversible
ible redox waves. The half-wave oxidation potentials of 1a– and reversible waves) were measured to be +0.54 and
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fac-Tris(2-phenylpyridine)iridium Derivatives Containing Hole-Trapping Moieties
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+0.30 V, respectively. The peak oxidation potential of 4b ployed as the hole-transporting layer, emitter, and carrier
(irreversible wave) was observed as +0.91 V. In addition, the combination host, respectively. 2,9-Dimethyl-4,7-diphenyl-
half-wave reduction potentials of ligands 4a–c were ob- 1,10-phenanthroline (BCP) was used as an electron-trans-
served as –2.78, –2.69, and –2.64 V, respectively. Thus, the porting and hole-blocking layer. Figure 3(a) demonstrates
hole-trapping moieties affected the oxidation states of Ir the luminance/current density (L/J) characteristics of the
complexes 1.
EL devices using 1a and Ir(ppy)3 as the emitters. The EL
from 1a was over 40000 cdm–2 at 14.4 V, although the emis-
sion from 1a was weak as compared to that from Ir(ppy)3
at the same current density. This result indicated that Ir
complex 1a as well as Ir(ppy)3 were good emitters. The
turn-on voltage was 4.8 V; this value was greater than that
observed in the device with Ir(ppy)3 (3.0 V). The external
quantum efficiency (ηext) of the device with 1a also was
lower than that of the device with Ir(ppy)3 [Figure 3(b)].
Figure 3(c) shows the EL spectra. The spectrum from 1a is
similar to its PL spectrum shown in Figure 2. The EL maxi-
mum from 1a was observed at 528 nm, which was slightly
redshifted as compared to that from Ir(ppy)3 (514 nm). In
addition, a weak EL emission from TPD was observed in
the wavelength region between 390 and 470 nm. This result
indicated that an energy transfer occurred from the MLCT
singlet state of 1a to the singlet state of TPD by the Förster
mechanism.
EL Properties of Ir Complex 1a Compared to Those of
Ir(ppy)3
An organic EL device using Ir complex 1a as the emitter
was fabricated, and its performance was investigated. The
structure of ITO/TPD (50 nm)/Ir complex/CBP (20 nm)/
BCP (30 nm)/LiF (1 nm)/Al (70 nm) was examined. N,NЈ-
Diphenyl-N,NЈ-bis(3-methylphenyl)-1,1Ј-biphenyl-4,4Ј-di-
amine (TPD), Ir complex (5 wt.-%), and CBP were em-
Scope and Limitations of Ir Complexes Containing Hole-
Trapping Moieties
Because the EL emission from TPD was observed in the
device with 1a, 1,1-bis[4-(di-p-tolylamino)phenyl]cyclohex-
ane (TAPC) was employed as a hole-transporting layer. The
EL structure of ITO/TAPC (50 nm)/Ir complex/CBP
(20 nm)/BCP (30 nm)/LiF (1 nm)/Al (70 nm) was examined.
As an emitter, 5 wt.-% of 1a was employed. Figure 4(a)
shows the plots of the variation of the external quantum
efficiency (ηext) vs. the current density (J), indicating that
the efficiency increased by replacing TPD (circles) with
TAPC (triangles) as the hole-transporting layer (HTL).
Thus, a maximum external quantum efficiency of 9.6% was
observed at 7.4 V. The EL from 1a was over 26000 cdm–2 at
14.4 V. According to the EL spectrum shown in Figure 4(b),
emission from the hole-transporting layer (TAPC) was not
observed. This result implied that the energy transfer from
1a to the hole-transporting layer was suppressed because
the HOMO–LUMO energy gap of TAPC is larger than that
of TPD (TAPC: 3.4 eV; TPD: 3.1 eV). Further, the phos-
phor triplet excitons were effectively confined by the TAPC
layer, thereby leading to the high EL efficiency.[19]
An optimized amount of the Ir complex dopant was used
at the emitting layer. The highest EL efficiency was ob-
served when an amount of approximately 10 wt.-% of 1a
was doped. The molar ratio of the optimized amount was
slightly higher as compared to that used for Ir(ppy)3. The
luminance (L) of 1a was observed as 51900 cdm–2 at 13.0 V.
This resulted in the maximum external quantum efficiency
(ηext) of 12.2% [Figure 4(a)]. This value is comparable to
those observed in devices using Ir(ppy)3 [ηext = 11.5%, Fig-
ure 3(b)] and Ir(ppy-NPh2)2(acac) (ηext = 11.8%).[14] Table 3
Figure 3. EL characteristics of ITO/TPD (50 nm)/Ir complex
(5 wt.-%)/CBP (20 nm)/BCP (30 nm)/LiF (1 nm)/Al (70 nm). Ir
complex = 1a (circles), Ir(ppy)3 (triangles). (a) Luminance (L)/cur-
rent density (J) plots. (b) External quantum efficiency (ηext)/current
density (J) plots. (c) EL spectra.
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K. Ono et al.
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Table 3. EL properties of devices using Ir complexes 1.[a]
Complex
wt.-% [%]
Turn-on voltage [V]
ηext [%,V]
L [cd·m–2, V]
ηp [lm·W–1, V]
λmax [nm]
CIE (x, y)
1a
1b
1c
10
12
11
4.0
3.6
3.8
12.2, 6.6
9.1, 4.8
8.7, 6.4
51900, 13.0
14600, 13.6
31000, 13.0
24.8, 6.0
22.5, 4.4
15.2, 6.4
528
506
513
0.33, 0.64
0.24, 0.64
0.26, 0.64
[a] Device structure: ITO/TAPC (50 nm)/Ir complex/CBP (20 nm)/BCP (30 nm)/LiF (1 nm)/Al (70 nm).
the carbazole unit. Organic EL devices using Ir complex 1a
as the emitter exhibited stronger luminance than devices
that used 1b and 1c. Particularly, high EL efficiency was
observed when TAPC was used as the hole-transporting
layer. The maximum external quantum efficiency from the
device was comparable to that observed in a device that
used Ir(ppy)3. Therefore, the introduction of a branched
aromatic amine into phosphor is effective for the research
and development of new phosphorescent materials.
Experimental Section
General: Iridium trichloride n-hydrate (IrCl3·nH2O) was purchased
from Soekawa Chemicals. Melting points were measured with a
Yanaco micro melting point apparatus and are uncorrected. IR,
UV/Vis, and PL spectra were obtained with JASCO FT/IR-5300,
V-550, and FP-6300 spectrometers, respectively. Mass spectra were
determined with a Hitachi M-2000S mass spectrometer (EI) op-
erating at 70 eV by a direct inlet system and a Voyager-DE STR
mass spectrometer (MALDI-TOF) using dithranol as a matrix. El-
emental analyses were performed with a Perkin–Elmer 2400II ana-
1
lyzer. H and 13C NMR spectra were recorded with Varian GEM-
INI spectrometers (300 and 50 MHz) and a Bruker AVANCE 600
spectrometer (600 and 150 MHz) with tetramethylsilane as an in-
ternal standard.
Figure 4. EL characteristics of ITO/HTL (50 nm)/1a/CBP (20 nm)/
BCP (30 nm)/LiF (1 nm)/Al (70 nm). (a) External quantum effi-
ciency (ηext)/current density (J) plots. HTL/1a with TPD (5 wt.-%,
circles), TAPC (5 wt.-%, triangles), TAPC (10 wt.-%, squares). (b)
EL spectra.
Preparation of 2-(4-Bromophenyl)pyridine (3): nBuLi in hexane
(1.60 , 16.0 mL, 25.6 mmol) was added dropwise to a suspension
of 1,4-dibromobenzene (5.90 g, 25.0 mmol) in dry diethyl ether
(40 mL) at –78 °C under nitrogen. 2-Fluoropyridine (2) (1.72 mL,
20.0 mmol) was added after stirring for 30 min. The mixture was
stirred at –78 °C for 1 h and at room temperature for 1 h. The reac-
tion mixture was poured into water (50 mL), and diethyl ether
(50 mL) was added. The organic layer was separated and the aque-
ous layer was extracted with diethyl ether (50 mL×2). The com-
bined organic solutions were extracted with a 5% HCl solution
(200 mL×3), and the aqueous layer was adjusted to an alkaline
pH with KOH (63 g). The aqueous layer was extracted with diethyl
ether (200 mL×3). The organic solution was dried with MgSO4
and concentrated. The residue was sublimed at 65–70 °C under
10–2 Torr to afford compound 3 (2.02 g, 43%) as colorless needles.
summarizes the EL performances of devices with Ir com-
plexes 1a–c. The luminance increased in the following or-
der: 1b, 1c, and 1a. This may be attributed to their redox
behavior as explained in the CV study. The EL efficiency of
1a is higher than those of 1b and 1c. These results indicate
that the diphenylamine moiety with a branched structure is
acceptable as the hole-trapping moiety of Ir(ppy)3.
Conclusions
M.p. 60–62 °C. IR (KBr): ν = 3052, 3007, 1586, 1462, 1433, 1391,
˜
1154, 1100, 1071, 1005, 841, 774 cm–1. 1H NMR (CDCl3,
300 MHz): δ = 7.23–7.28 (m, 1 H), 7.60 (dt, J = 8.8, 2.2 Hz, 2 H),
7.68–7.79 (m, 2 H), 7.88 (dt, J = 8.8, 2.2 Hz, 2 H), 8.69 (ddd, J =
4.8, 1.8, 1.1 Hz, 1 H) ppm. 13C NMR (CDCl3, 50 MHz): δ = 120.3,
122.4, 123.4, 128.4, 131.8, 136.9, 138.2, 149.7, 156.2 ppm. MS (EI):
m/z (%) = 235 (100) [M+], 233 (99) [M+], 154 (84). C11H8BrN
(234.09): calcd. C 56.44, H 3.44, N 5.98; found C 56.47, H 3.55, N
5.89.
We prepared fac-tris(2-phenylpyridine)iridium [Ir(ppy)3]
derivatives containing hole-trapping moieties such as di-
phenylamine (1a), carbazole (1b), and phenoxazine (1c).
Their PL maxima were observed around the maximum of Ir-
(ppy)3. These values were marginally shifted depending on
the hole-trapping moieties: redshifted for 1a and blueshifted
for 1b and 1c. The electron-donating ability of Ir(ppy)3 was
increased due to the diphenylamine and phenoxazine moie-
Preparation of Ligands 4a–d: A solution of Pd(OAc)2 (28 mg,
ties, and the oxidation state became more unstable due to 0.12 mmol) and tBu3P (90 mg, 0.44 mmol) in toluene (4 mL) was
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fac-Tris(2-phenylpyridine)iridium Derivatives Containing Hole-Trapping Moieties
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added to a suspension of compound 3 (0.94 g, 4.0 mmol), diphenyl-
amine (0.68 g, 4.0 mmol), and tBuONa (0.47 g, 4.9 mmol) in tolu-
ene (4 mL) under nitrogen. The mixture was refluxed for 3 h. After
cooling, the reaction mixture was poured into water (10 mL), and
ethyl acetate (10 mL) was added. The organic layer was separated
and the aqueous layer was extracted with ethyl acetate (10 mL×2).
The combined organic solutions were dried with Na2SO4 and con-
centrated. The residue was chromatographed on alumina gel (hex-
ane/CH2Cl2, 2:1) to give ligand 4a (1.17 g, 91%) as pale yellow
(d, J = 6.5 Hz, 4 H) ppm. 13C NMR (CDCl3, 50 MHz): δ = 114.3,
117.3, 120.4, 122.7, 122.9, 123.8, 125.4, 128.8, 135.4, 137.2, 146.1,
147.3, 147.7, 151.0, 167.4 ppm. MALDI-TOF MS: m/z = 1741.40
[M+ +1], 1705.41 [M+ –Cl], 870.19 [M+/2], 835.22 [M+/2–Cl].
C92H68Cl2Ir2N8 (1740.9): calcd. C 63.47, H 3.94, N 6.44; found C
63.41, H 3.83, N 6.36. Similar reaction conditions were applied to
the synthesis of Ir dimers 5b and 5c. 5b: Yield 85% (0.36 g). Yellow
solid. M.p. Ͼ 300 °C. MALDI-TOF MS: m/z = 1733.37 [M+ +1],
1697.40 [M+
–
Cl], 866.22 [M+/2], 831.25 [M+/2–Cl].
needles. M.p. 177–177.5 °C (from ethanol). IR (KBr): ν = 3057,
C92H60Cl2Ir2N8 (1732.9): calcd. C 63.77, H 3.49, N 6.47; found C
63.15, H 3.43, N 6.32. 5c: Yield 88% (0.43 g). Yellow solid. M.p.
Ͼ 300 °C. MALDI-TOF MS: m/z = 1761.33 [M+ –Cl], 898.23 [M+/
˜
1586, 1491, 1466, 1433, 1325, 1279, 787, 756, 698, 515 cm–1. 1H
NMR (CDCl3, 300 MHz): δ = 7.05 (tt, J = 7.3, 1.4 Hz, 2 H), 7.12–
7.20 (m, 7 H), 7.24–7.31 (m, 4 H), 7.65–7.74 (m, 2 H), 7.87 (dt, J 2], 863.26 [M+/2–Cl]. C92H60Cl2Ir2N8O4 (1796.9): calcd. C 61.50,
= 8.8, 2.4 Hz, 2 H), 8.65 (ddd, J = 4.9, 1.7, 1.0 Hz, 1 H) ppm. 13C
NMR (CDCl3, 50 MHz): δ = 117.8, 119.8, 121.4, 123.2, 124.7,
127.7, 129.3, 133.1, 136.6, 147.5, 148.7, 149.6, 157.1 ppm. MS (EI):
m/z (%) = 322 (100) [M+]. UV/Vis (CH2Cl2): λmax (logε) = 346
(4.42), 308 (4.23) nm. C23H18N2 (322.40): calcd. C 85.68, H 5.63,
N 8.69; found C 85.63, H 5.80, N 8.56. Similar reaction conditions
were applied to the synthesis of ligands 4b–d. These were carried
out using K2CO3 (3 equiv.) as a base instead of tBuONa. The reac-
tion mixtures were refluxed for 24 h. 4b: Yield 87% (0.56 g). Pale
H 3.37, N 6.24; found C 60.57, H 3.25, N 6.01.
Preparation of fac-Ir Complexes 1a–c: A mixture of Ir dimer 5a
(130 mg, 0.075 mmol), ligand 4a (49 mg, 0.15 mmol) and K2CO3
(106 mg, 0.77 mmol) in glycerol (5 mL) was stirred under nitrogen
at 240 °C for 11 h. After cooling, water (5 mL) and dichlorometh-
ane (10 mL) were added. The organic layer was separated and the
aqueous layer was extracted with dichloromethane (10 mL×2).
The combined organic solutions were dried with Na2SO4 and con-
centrated. The residue was chromatographed on silica gel (CH2Cl2)
to afford fac-Ir complex 1a (82 mg, 48%) as orange solid. M.p. Ͼ
300 °C (from CH2Cl2). 1H NMR (CDCl3, 600 MHz): δ = 6.24 (dd,
J = 8.4, 2.1 Hz, 3 H), 6.58 (d, J = 2.1 Hz, 3 H), 6.78 (t, J = 6.4 Hz,
3 H), 6.83 (d, J = 7.7 Hz, 12 H), 6.87 (t, J = 7.7 Hz, 6 H), 7.09 (t,
J = 7.7 Hz, 12 H), 7.27 (d, J = 8.4 Hz, 3 H), 7.52–7.55 (m, 6 H),
7.68 (d, J = 8.0 Hz, 3 H) ppm. 13C NMR (CDCl3, 150 MHz): δ =
114.6, 117.7, 120.5, 122.2, 124.5, 124.8, 128.6, 130.2, 135.4, 137.6,
147.2, 147.6, 148.2, 161.9, 166.2 ppm. MALDI-TOF MS: m/z =
1156.42 [M+]. UV/Vis (CH2Cl2): λmax (logε) = 398 (4.68), 367
(4.70), 320 (4.67), 261 (4.69), 227 (4.80) nm. C69H51IrN6 (1156.4):
calcd. C 71.67, H 4.45, N 7.27; found C 71.65, H 4.32, N 7.33.
Similar reaction conditions, stirring at 240 °C for 48 h and 24 h,
were applied to the synthesis of fac-Ir complexes 1b and 1c, respec-
tively. 1b: Yield 78% (0.27 g). Yellow solid. M.p. Ͼ 300 °C. 1H
NMR (CDCl3, 300 MHz): δ = 6.87 (br. m, 6 H), 6.96–7.03 (m, 18
H), 7.20 (d, J = 2.2 Hz, 3 H), 7.71 (td, J = 8.0, 1.5 Hz, 3 H), 7.76
(d, J = 4.7 Hz, 3 H), 7.81 (d, J = 8.2 Hz, 3 H), 7.94 (d, J = 7.1 Hz,
6 H), 7.99 (d, J = 8.0 Hz, 3 H) ppm. MALDI-TOF MS: m/z =
1150.35 [M+]. UV/Vis (CH2Cl2): λmax (logε) = 378 sh (4.40), 346
(4.70), 238 (5.18) nm. C69H45IrN6 (1150.4): calcd. C 72.04, H 3.94,
N 7.31; found C 72.20, H 4.03, N 7.26. 1c: Yield 54% (0.20 g).
Yellow solid. M.p. Ͼ 300 °C. 1H NMR (CDCl3, 300 MHz): δ =
5.69 (dd, J = 7.8, 1.4 Hz, 6 H), 6.01 (td, J = 7.8, 1.4 Hz, 6 H), 6.39
(td, J = 7.8, 1.4 Hz, 6 H), 6.52 (dd, J = 7.8, 1.4 Hz, 6 H), 6.72 (d,
J = 2.0 Hz, 3 H), 6.76 (dd, J = 8.1, 2.0 Hz, 3 H), 7.02 (t, J = 5.9 Hz,
3 H), 7.69–7.73 (m, 6 H), 7.81 (d, J = 8.1 Hz, 3 H), 7.92 (d, J =
7.7 Hz, 3 H) ppm. MALDI-TOF MS: m/z = 1198.34 [M+]. UV/Vis
(CH2Cl2): λmax (logε) = 375 sh (4.23), 330 (4.52), 283 (4.85), 241
(5.20) nm. C69H45IrN6O3 (1198.4): calcd. C 69.16, H 3.78, N 7.01;
found C 69.14, H 3.90, N 6.89.
yellow crystals (from ethanol). M.p. 179–180.5 °C. IR (KBr): ν =
˜
1603, 1516, 1453, 1366, 1335, 1318, 1235, 779, 750, 725 cm–1. 1H
NMR (CDCl3, 300 MHz): δ = 7.27–7.33 (m, 3 H), 7.40–7.51 (m, 4
H), 7.69 (dt, J = 8.8, 2.2 Hz, 2 H), 7.81–7.83 (m, 2 H), 8.16 (d, J
= 7.8 Hz, 2 H), 8.23 (dt, J = 8.8, 2.2 Hz, 2 H), 8.76 (dt, J = 4.9,
1.1 Hz, 1 H) ppm. 13C NMR (CDCl3, 50 MHz): δ = 109.8, 120.1,
120.3, 120.5, 122.4, 123.5, 126.0, 127.2, 128.4, 136.9, 138.3, 138.4,
140.7, 149.8, 156.5 ppm. MS (EI): m/z (%) = 320 (100) [M+]. UV/
Vis (CH2Cl2): λmax (logε) = 318 (4.25), 292 (4.30), 240 (4.68) nm.
C23H16N2 (320.39): calcd. C 86.22, H 5.03, N 8.74; found C 86.01,
H 5.19, N 8.62. 4c: Yield 84% (0.86 g). Pale yellow crystals (from
methanol). M.p. 173–174.5 °C. IR (KBr): ν = 1589, 1491, 1341,
˜
1
1273, 743, 729 cm–1. H NMR (CDCl3, 300 MHz): δ = 6.01 (dd, J
= 7.8, 1.5 Hz, 2 H), 6.57–6.72 (m, 6 H), 7.27–7.31 (m, 1 H), 7.45
(d, J = 8.7 Hz, 2 H), 7.80 (m, 2 H), 8.21 (d, J = 8.7 Hz, 2 H), 8.74
(d, J = 4.7 Hz, 1 H) ppm. 13C NMR (CDCl3, 50 MHz): δ = 113.3,
115.4, 120.7, 121.4, 122.5, 123.2, 129.6, 131.1, 134.2, 137.1, 139.4,
139.6, 143.9, 149.7, 156.4 ppm. MS (EI): m/z (%) = 336 (100) [M+],
182 (69). UV/Vis (CH2Cl2): λmax (logε) = 326 (3.95), 276 (4.21),
240 (4.75) nm. C23H16N2O (336.39): calcd. C 82.12, H 4.79, N 8.33;
found C 82.28, H 4.82, N 8.32. 4d: Yield 82% (0.42 g). Pale yellow
crystals (from ethanol). M.p. 174–175.5 °C. IR (KBr): ν = 1589,
˜
1
1464, 1437, 1310, 1260, 1244, 1046, 920, 783, 743 cm–1. H NMR
(CDCl3, 300 MHz): δ = 6.34 (dd, J = 7.7, 1.9 Hz, 2 H), 6.80–6.90
(m, 4 H), 7.05 (dd, J = 6.9, 2.1 Hz, 2 H), 7.25–7.30 (m, 1 H), 7.49
(dt, J = 8.7, 2.2 Hz, 2 H), 7.77–7.81 (m, 2 H), 8.20 (dt, J = 8.7,
2.2 Hz, 2 H), 8.74 (dt, J = 4.7, 1.4 Hz, 1 H) ppm. 13C NMR
(CDCl3, 50 MHz): δ = 116.6, 120.6, 120.9, 122.4, 122.7, 126.8,
126.9, 129.2, 130.5, 136.9, 139.0, 141.9, 144.0, 149.8, 156.5 ppm.
MS (EI): m/z (%) = 352 (100) [M+]. UV/Vis (CH2Cl2): λmax (logε)
= 320 (3.87), 257 (4.74) nm. C23H16N2S (352.45): calcd. C 78.38,
H 4.58, N 7.95; found C 78.32, H 4.53, N 7.89.
X-ray Crystallographic Analysis for fac-Ir Complex 1a: A single
crystal was obtained as a greenish brown platelet by recrystalli-
zation of 1a from a mixture of dichloromethane and ethyl acetate.
Crystal data for 1a: 0.15×0.13×0.03 mm, C69H51IrN6, M =
1156.42, monoclinic, space group P21/n, a = 13.9742(9), b =
17.1467(9), c = 44.590(3) Å, β = 98.158(3)°, V = 10576(1) Å3, Z =
8, Dc = 1.452 gcm–3, µ = 25.82 cm–1, F(000) = 4672. A total of
Preparation of Ir Dimers 5a–c: A mixture of ligand 4a (0.65 g,
2.0 mmol) and IrCl3·nH2O (0.36 g, 1.0 mmol) in a solution of 2-
ethoxyethanol (12 mL) and water (4 mL) was stirred under nitrogen
at 120 °C for 24 h. After cooling, the precipitate was filtered and
washed with methanol, diethyl ether, and hexane to afford Ir dimer
5a (0.69 g, 80%) as yellow solid. M.p. Ͼ 300 °C. 1H NMR (CDCl3, 21884 unique reflections for 2θmax = 55° was collected [IϾ2σ(I)]
300 MHz): δ = 5.48 (d, J = 2.2 Hz, 4 H), 6.21 (t, J = 6.5 Hz, 4 H),
6.45 (dd, J = 8.5, 2.2 Hz, 4 H), 6.85–6.94 (m, 24 H), 7.09 (t, J =
7.8 Hz, 16 H), 7.22–7.28 (m, 8 H), 7.43 (d, J = 7.7 Hz, 4 H), 8.89
with a Rigaku MSC MercuryCCD diffractometer (Mo-Kα radia-
tion, λ = 0.71070 Å, graphite monochromator) at 173 K. A numeri-
cal absorption correction was applied. The structure was solved
Eur. J. Inorg. Chem. 2006, 3676–3683
© 2006 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
www.eurjic.org
3681

K. Ono et al.
FULL PAPER
using the direct method (SHELXS-97)[20] and refined by the full-
matrix least-squares analysis (SHELXL-97)[21] giving values of R1
= 0.088, Rw = 0.165, S = 1.26, ρmax/ρmin = 3.44/–2.31 e·Å–3. All
calculations were performed using the teXsan programs.[22]
CCDC-294487 contains the supplementary crystallographic
data for this paper. The data can be obtained free of charge
from the Cambridge Crystallographic Data Centre via
www.ccdc.cam.ac.uk/data_request/cif.
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Electrochemical Measurements: CV was performed with a Toho
Technical Research polarization unit PS-07 potentiostat/galvanos-
tat. The CV studies of compounds 1 and 4 were carried out in
DMF with 0.1  nBu4NClO4 using Pt and SCE electrodes. The
values are expressed in potentials vs. Fc/Fc+.
Electroluminescence Measurements: An ITO-coated glass substrate
was patterned and cleaned by scrubbing, ultrasonication, and irra-
diation in a UV/ozone chamber. Organic layers were deposited on
the ITO at an evaporating rate of 1 nm/s. The cathode of a LiF/Al
bilayer was formed by sequential deposition. The rate and thickness
of the films were monitored with a quartz oscillator. The sample
area was 2×2 mm. Current and luminance on applied voltage were
measured with an HP 4145A semiconductor parameter analyzer,
which was connected with a Topcon BM-3 luminance meter. The
electroluminescence spectra were measured with an Ocean Optics
S2000 spectrometer. The external quantum efficiency (ηext) was cal-
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[9]
[10]
Acknowledgments
This work was supported by a Grant-in-Aid (nos. 17750037,
17550033) from the Ministry of Education, Culture, Sports, Science
and Technology, Japan and a grant from Innovation Plaza Tokai
(“Investigation of organic device integration using self-alignment
technology”). K. O. wishes to thank the Yazaki Memorial Founda-
tion for Science and Technology and Research Foundation for the
Electrotechnology of Chubu for financial support. We would like
to thank the Research Center for Molecular-Scale Nanoscience,
Institute for Molecular Science, for the crystal analysis.
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© 2006 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
Eur. J. Inorg. Chem. 2006, 3676–3683

fac-Tris(2-phenylpyridine)iridium Derivatives Containing Hole-Trapping Moieties
FULL PAPER
[18] Complex 1a showed three oxidation waves with the half-wave
potential of +0.19 V and the peak potentials of +0.39 V and
+0.48 V.
[19] K. Goushi, R. Kwong, J. J. Brown, H. Sasabe, C. Adachi, J.
Appl. Phys. 2004, 95, 7798–7802.
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[21] G. M. Sheldrick, SHELXL-97, Program for the Refinement of
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[22] teXsan, Crystal Structure Analysis Package, Molecular Struc-
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Received: March 31, 2006
Published Online: August 3, 2006
Eur. J. Inorg. Chem. 2006, 3676–3683
© 2006 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
www.eurjic.org
3683