Highly efficient iridium(III) complexes with diphenylquinoline ligands for organic light-emitting diodes: Synthesis and effect of fluorinated substitutes on electrochemistry, photophysics and electroluminescence

Article abstract of DOI:10.1016/j.jorganchem.2006.07.008

A series of novel cyclometalated iridium(III) complexes bearing 2,4-diphenylquinoline ligands with fluorinated substituent were prepared and characterized by elemental analysis, NMR and mass spectroscopy. The cyclic voltammetry, absorption, emission and e

Full text of DOI:10.1016/j.jorganchem.2006.07.008

Journal of Organometallic Chemistry 691 (2006) 4312–4319
www.elsevier.com/locate/jorganchem
Highly efficient iridium(III) complexes with diphenylquinoline
ligands for organic light-emitting diodes: Synthesis and effect
of fluorinated substitutes on electrochemistry,
photophysics and electroluminescence
a
b
a,
a
a
Xiaowei Zhang , Jia Gao , Chuluo Yang *, Linna Zhu , Zhongan Li ,
a
a
b
b,
*
Kai Zhang , Jingui Qin , Han You , Dongge Ma
a
Department of Chemistry, Hubei Key Lab on Organic and Polymeric Optoelectronic Materials, Wuhan University, Wuhan 430072, China
b
State Key Laboratory of Polymer Physics and Chemistry, Changchun Institute of Applied Chemistry, Chinese Academy of Sciences,
Changchun 130022, China
Received 4 May 2006; received in revised form 22 June 2006; accepted 7 July 2006
Available online 18 July 2006
Abstract
A series of novel cyclometalated iridium(III) complexes bearing 2,4-diphenylquinoline ligands with fluorinated substituent were pre-
pared and characterized by elemental analysis, NMR and mass spectroscopy. The cyclic voltammetry, absorption, emission and electro-
luminescent properties of these complexes were systematically investigated. Electrochemical studies showed that the oxidation of the
fluorinated complexes occurred at more positive potentials (in the range 0.57–0.69 V) than the unfluorinated complex 1 (0.42 V). In view
of the energy level, the lowering of the LUMO by fluorination is significantly less than that of the HOMO. The weak and low energies
3
absorption bands in the range of 300–600 nm are well resolved, likely associated with MLCT and p–p* transitions. These complexes
show strong orange red emission both in the solution and solid state. The emission maxima of the fluorinated complexes showed blue
shift by 9, 24 and 15 nm for 2, 3 and 4, respectively, with respect to the unfluorinated analogous 1. Multilayered organic light-emitting
diodes (OLEDs) were fabricated by using the complexes as dopant materials. Significantly higher performance and lower turn-on voltage
were achieved using the fluorinated complexes as the emitter than that using the unfluorinated counterpart 1 under the same doping level.
OLED devices using complexes 2 and 3 as the phosphorescent dopant at 3 wt% doping level exhibit very high performance. To complex
2, the maximum luminance is 16410 cd/m2 at a current density of 210 mA/cm2, and the maximum luminance efficiency and power effi-
ciency are 9.34 cd/A and 5.20 lm/W, respectively, with the emission of 605 nm. To complex 3, those data are 16797 cd/m2 at a current
density of 211 mA/cm2, 11.12 cd/A and 4.97 lm/W, respectively, with the emission of 593 nm.
Ó 2006 Elsevier B.V. All rights reserved.
Keywords: Iridium complexes; Phenylquinoline; Fluorination; Electrochemistry; Photophysics; Electroluminescence
1. Introduction
nylpyridine)iridium [Ir(ppy)3] [1]. The frequency of
emission of the iridium complexes can usually be tuned
by modification or variation of cyclometalated ligands of
2-phenylpyridine or its analogical ligands, such as benzo-
isoquinolines [2], 2-phenylbenzothiazole [3], benzoimidaz-
ole [4], etc. Several groups have studied the mechanism of
the OLEDs based on phosphorescent heavy metal com-
plexes [5]. It has been demonstrated that the Fo¨rster energy
transfer plays minor role in achieving high efficiency in
Recently, the iridium complexes as phosphorescent
emitter in organic light-emitting diodes (OLEDs) have
attracted much attention since the realization of a high effi-
ciency OLED device based on the complex fac-tris(2-phe-
*
Corresponding authors. Tel./fax: +86 27 68756757.
E-mail address: clyang@whu.edu.cn (C. Yang).
0022-328X/$ - see front matter Ó 2006 Elsevier B.V. All rights reserved.
doi:10.1016/j.jorganchem.2006.07.008

X. Zhang et al. / Journal of Organometallic Chemistry 691 (2006) 4312–4319
4313
these devices, instead that direct charge trapping plays
dominant role in electroluminescence. Therefore, in order
to obtain high efficiency OLED devices, it would be desir-
able to design the phosphorescent complexes as energy
acceptors, more importantly, as traps for holes or/and
electrons.
suppress the aggregation-forming tendency, and the chlo-
ride or bromide in the position 6 of quinoline ring may
increase luminescent efficiency by heavy-atom effect.
2. Results and discussion
Quinoline-based compounds have received considerable
attention in optoelectronic materials due to their high elec-
tron affinities. For example, aluminum tris(8-hydroxyquin-
olate) (AlQ3) has been usually applied as electron
transporting, electron-emitting and host materials in doped
OLED systems. Most recently, phenylquinoline or phenyl-
isoquinoline based iridium complexes have been proven to
be good red emitters [2,6]. On the other hand, iridium com-
plexes carrying fluorinated phenylpyridyl ligands have
shown several benefits, such as enhancing the photolumi-
nescence efficiency and improving the sublimation [7].
In this paper, we report a series of novel iridium com-
plexes bearing 2,4-diphenylquinoline ligands with strong
electron-withdrawing fluorinated substituent, as well as
the unfluorinated analogue for comparison. We expect that
the phenyquinoline ligands modified by fluorinated substi-
tuent could improve the electron transport ability of the
complexes, consequently to facilitate the charge trapping
across the bulk for high performance OLEDs [8]. Mean-
while, it will be significant to study the effect of fluorinated
substituent on the electrochemistry, photophysics and elec-
troluminescent performance of iridium complexes in order
to understand the relationship between the structures and
properties. In addition, the bulky phenyl group in the posi-
tion 4 of quinoline ring may prevent the crystallization and
2.1. Synthesis and characterization
Phenylquinoline-based organic ligands were conve-
niently prepared from 5-chloro-2-aminobenzophenone (or
5-bromo-2-aminobenzophenone) and corresponding ace-
tophenone derivatives through Friedla¨nder reaction in
moderate yields (Scheme 1) [9]. The Ir(III) l-chloro-
bridged dimers were synthesized by the reaction of iridium
trichloride hydrate with ligands according to a conven-
tional procedure [10]. Then the diiridium complexes were
converted to mononuclear iridium complexes by replacing
the two bridging chlorides with bidentate monoanionic
acetylacetonate ligand in 50–70% yields. Elemental analysis
of each of the four complexes is consistent with the
expected formulation of their structures. The mass spectra
give corresponding molecular ion peaks at 1010 for 1, 956
for 2 and 3, and 1056 for 4. In the 1H NMR, the acetylacet-
onate CH protons appear in the region 4.69–4.79 ppm as a
sharp singlet, obviously lower than the corresponding sig-
nals usually appeared at >5.1 ppm in the other iridium
complexes with arylpyridine ligands. This is presumably
due to the weaker ligand field strength of quinoline that
inhibits effective back-donation from metal center to
ligand, consequently, metal center has larger electron den-
sity which more shields the acetylacetonate CH protons [6].
Ph
O
HOAc
+
COCH3
R'
NH2
H2SO4
R
R'
N
R
R3
R2
R1
R4
O
O
acetylacetone
IrCl3
Ir
N
Ph
2
R'
1: R'=Br R1=R2=R3=R4=H
2: R'=Cl R1=F , R2=R3=R4=H
3: R'=Cl R3=F , R1=R2=R4=H
4: R'=Cl R3=CF3
, R1=R2=R4=H
Scheme 1. Synthesis of the iridium complexes.

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X. Zhang et al. / Journal of Organometallic Chemistry 691 (2006) 4312–4319
2.2. Electrochemistry
and theoretical calculations of cyclometalated Ir(III) com-
plexes, reduction is generally considered to mainly occurs
on the heterocyclic portion of the cyclometalated CÙN
ligands, whereas oxidation process largely involves the
Ir–aryl center [12]. Consistent with this conclusion, the
fluorinated substitutes of the 2-phenyl group have less
affection on the reduction potentials, in contrast, they nota-
bly increase the oxidation potentials with respect to the
unfluorinated complex. In view of the energy level, the fluo-
rinated substitution leads to a larger decrease for the
HOMO than the LUMO orbitals, in consequence resulting
in a widening of the HOMO–LUMO gap, in comparison
with the parent complex 1.
On the basis of the onset potentials of the oxidation and
reduction, the HOMO and LUMO energy levels of these
iridium complexes with regard to the energy level of ferro-
cene (4.80 eV below vacuum) are estimated (Table 1) [13].
Both the HOMO and LUMO levels of the fluorinated com-
plexes are lower than that of the parent complex 1, respec-
tively. If this trend remains the same in the solid state, the
The electrochemical behaviors of the four complexes
were examined by using cyclic voltammetry. The cathodic
and anodic scans were carried out in THF and CH2Cl2
solution at 298 K, respectively (Fig. 1). The redox poten-
tials, measured relative to an internal ferrocenium/ferro-
cene reference (Fc+/Fc), are listed in Table 1.
The unfluorinated complex 1 shows three quasi-revers-
ible reduction waves, whereas the fluorinated complexes
exhibit two fully reversible reduction processes. The first
and second reduction potentials of the complexes stay in
a range of ꢀ1.99 to ꢀ2.12 V and ꢀ2.22 to ꢀ2.30 V, respec-
tively. On the other hand, each of four complexes only dis-
plays a reversible one-electron oxidation couple. The
oxidation of three fluorinated complexes occur at signifi-
cant more positive potentials (in the range 0.57–0.69 V)
than the unfluorinated complex 1 (0.42 V). These values
are similar to the reported bis-cyclometalated iridium com-
plexes [2,6,11]. As revealed previously by electrochemistry
2
1
-3
-2
-1
0
1
-2
-1
0
1
Potential (V vs. Fc/Fc+)
Potential (V vs. Fc/Fc+)
3
4
-2
-1
0
1
-2
-1
0
a
Potential ( V vs. Fc/Fc+)
Potential (V vs. Fc/Fc+)
Fig. 1. Cyclic voltammograms of the four complexes (the first reduction couple come from the solvent THF).

X. Zhang et al. / Journal of Organometallic Chemistry 691 (2006) 4312–4319
4315
Table 1
Electrochemical properties of the Ir complexes
a
a
a
a
HOMO (eV)b
LUMO (eV)c
Egap (eV)
ox
1=2
red
1=2
ox
onset
red
onset
Complex
E
ðVÞ
E
ðVÞ
E
ðVÞ
E
ðVÞ
1
2
3
4
a
0.42
0.57
0.59
0.66
ꢀ2.46, ꢀ2.28, ꢀ2.14
0.35
0.50
0.52
0.59
ꢀ2.09
ꢀ2.00
ꢀ2.05
ꢀ1.93
ꢀ5.15
ꢀ5.30
ꢀ5.32
ꢀ5.39
ꢀ2.71
ꢀ2.80
ꢀ2.75
ꢀ2.87
2.44
2.50
2.57
2.52
ꢀ2.30, ꢀ2.09
ꢀ2.30, ꢀ2.12
ꢀ2.22, ꢀ1.99
Potential values are reported vs. Fc/Fc+.
Determined from the onset oxidation potential.
Determined from the onset reduction potential.
b
c
electron injection barrier for the fluorinated complexes will
be less than their counterpart 1. This will be discussed in
Section 2.4.
The reversibility of the redox waves of the fluorinated
iridium complexes suggests good stability of both their cat-
ions and anions, which is very beneficial to the long term
stability of OLED devices fabricated from these materials.
acter from cyclometalated CÙN ligands. Relatively weaker
absorption bands in the range of 300–400 nm are well
resolved, ascribing to a spin-allowed metal-to-ligand
charge transfer (1MLCT) transition. The long tail extended
to lower energies (in the range of 400–600 nm) can be likely
3
3
associated with both MLCT and p–p* transitions, which
1
gains considerable intensity by mixing with the MLCT
transition through the spin-orbit coupling [1f,14].
The emission spectra of 2, 3 and 4 in dichloromethane
show emission peak at 602, 587 and 596 nm, which blue
shifted by 9, 24 and 15 nm, respectively, when compared
with the unfluorinated counterpart 1 (Table 2 and Fig. 2
inset), falling in orange red region. The meta position on
the 2-phenyl ring, with respect to the fluoride or trifluorom-
ethyl substitutent, is electron deficient, decreasing the r
donation from the cyclometalated ligand to iridium, and
thus the HOMO levels mainly related to the Ir–aryl center
lowered in comparison with the unfluorinated analogous 1,
which is supported by the fact that the oxidation potentials
of 2–4 are significantly higher than that of 1. This results in
an energy increase of the 3MLCT emitting level in the fluo-
rinated complexes. The alteration of emission wavelength
coincides with the variation of energy gap evaluated from
the results of cyclic voltammetry (Table 1). It is noteworthy
that the complex 3 with fluorine at the meta position 3,
with respect to the coordination carbon, exhibits signifi-
cantly larger hypsochromic shift (24 nm) than complex 2
(9 nm) with fluorine at the meta position 5, indicating the
meta position 3 is more effective in tuning the emission
towards the blue region than the meta position 5. To our
knowledge, this is the first example to distinguish the effect
of different meta fluorine substitution on emission of cyclo-
metalated iridium complexes [15]. It is also interesting to
note the complex 4 with trifluoromethyl substitutent at
the meta position to iridium exhibit bathochromic shift
by 9 nm with respect to the analogue complex 3 with meta
2.3. Absorption and emission
Fig. 2 shows the absorption spectra of four complexes.
Absorption peak wavelengths and the molar extinction
coefficients are given in Table 2. Intense absorptions are
observable in the ultraviolet region of the spectra, between
250 and 300 nm, which are attributed to transitions of
ligand-centered states with mostly spin-allowed 1p–p* char-
1.2
1
2
3
4
1.0
0.8
1.0
0.8
0.6
0.4
0.2
0.0
0.6
0.4
0.2
0.0
500
550
600
650
700
Wavelength(nm)
300
400
500
600
700
Wavelength (nm)
Fig. 2. Absorption and emission (inset) spectra of the complexes in
CH2Cl2.
Table 2
Absorption and emission data for Ir complexes
Complex
Absorbance k/nm (loge)a
Emission kmax (nm)a
Quantum yielda,b
1
2
3
4
a
277 (4.7), 356 (4.5), 440 (4.0), 479 (3.7)
250 (4.3), 304 (4.6), 352 (4.3), 417 (3.5)
272 (4.7), 350 (4.2), 447 (3.8), 474 (3.8)
260 (4.8), 339 (4.2), 361 (4.1), 403 (3.9), 459 (3.8)
611
602
587
596
0.28
0.34
0.32
0.25
Measured in CH2Cl2.
b
The relative quantum yields were calculated relative to Ir(ppy)2(acac) (Uem = 0.34).

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X. Zhang et al. / Journal of Organometallic Chemistry 691 (2006) 4312–4319
fluorine substitutent. This is contrary to the corresponding
iridium complexes with fluorinated phenylpyridine ligand,
where a hypsochromic shift was observed in the same situ-
ation [7a].
250
200
150
100
50
1
2
3
4
2.4. Electroluminescent properties
The four complexes show moderate to good triplet
quantum efficiencies (Table 2). To illustrate the electrolu-
minescent properties of these complexes, typical OLED
devices using these complexes as dopants in the emitting
layer have been fabricated (Fig. 3). All device consist of
multilayer configurations ITO/NPB (40 nm)/CBP + 3–8%
dopant (30 nm)/BCP (10 nm)/AlQ3 (30 nm)/LiF(1 nm)/Al
(100 nm), in which 4,40-biscarbazolylbiphenyl (CBP) serves
as host for iridium complexes, 2,9-dimethyl-4,7-diphenyl-
1,10-phenanthroline (BCP) as hole and exciton blocker,
and 4,40-bis[N-(1-naphthyl)-N-phenylamino]biphenyl (NPD)
and tris(8-hydroxyquinoline)aluminum (AlQ3) as hole
transporting and electron transporting materials, respec-
tively [16].
All devices display intense orange-red or red emission in
the range of 593–616 nm in the EL spectra, which resem-
bled to those of the PL spectra in dichloromethane solu-
tion, indicating that the EL emissions of the device
originate from the triplet excited states of the phosphors.
Figs. 4 and 5 show the current–voltage curves and the lumi-
nance–current density characteristics of the devices, respec-
tively. The current efficiency (gc) as functions of current
0
0
5
10
Voltage(V)
15
20
Fig. 4. Current density vs. voltage characteristics of the devices fabricated
using the complexes 1–3 at 3 wt%, 4 at 5 wt% doping concentration.
18000
1
2
3
15000
4
12000
9000
6000
3000
0
0
50
100
Current density (mA/cm2)
Fig. 5. Luminance vs. current density characteristics of the devices
150
200
250
100nm Al
1nm LiF
30nm AlQ3
fabricated using the complexes 1–3 at 3 wt%,
concentration.
4
at 5 wt% doping
10nm BCP
30nm Ir complex: CBP
40nm NPD
12
10
8
ITO
1
2
3
4
Glass substrate
N
O
N
N
N
6
O
Al
O
N
4
CBP
AlQ3
2
H3C
CH3
N
N
0
N
N
0
50
100
150
200
Current density (mA/cm2)
NPD
Fig. 3. Device configurations and molecular structures used in the devices.
Fig. 6. Current efficiency vs. current density characteristics of the devices
BCP
fabricated using the complexes 1–3 at 3 wt%,
4 at 5 wt% doping
concentration.

X. Zhang et al. / Journal of Organometallic Chemistry 691 (2006) 4312–4319
4317
Table 3
EL performances of devices
Complex
wt%a
1
2
3
4
3
3
5
8
3
5
8
5
L (cd/m)b
Lmax (cd/m2)
gc (cd/A)b
gc (cd/A)c
gc max (cd/A)
gp (lm/W)b
gp (lm/W)c
gp max (lm/W)
Voltage (V)b
VON (V)d
1500
5107
7.41
4.47
10.79
1.39
0.62
3.40
16.7
5.7
3291
16410
8.80
6.50
9.34
2.25
1.21
5.20
12.5
4.5
1088
5423
3.09
2.12
4.36
0.74
0.34
1.37
9.5
1751
4311
4.84
2.39
5.44
0.89
0.31
1.21
17.1
8.2
3475
16797
9.58
6.64
11.12
2.23
1.16
4.97
13.5
4.5
1870
11477
5.34
3.94
6.94
1.76
0.84
4.72
9.5
2284
10113
4.55
6.33
6.44
1.32
0.76
1.54
14.9
7.3
1070
5343
2.83
1.99
3.94
0.88
0.38
2.87
10.3
4.3
5.0
5.1
kmax (nm)
a
616
605
609
611
593
596
598
605
Doping concentration of complex into host.
Recorded at 20 mA/cm2.
b
c
Recorded at 100 mA/cm2.
d
Recorded at the brightness of 1 cd/m2.
density (J) for the devices is displayed in Fig. 6. The perfor-
mance data of the devices are summarized in Table 3.
Comparing with using the unfluorinated complex 1 as
the emitter, significantly higher performance and lower
turn-on voltage were achieved when using the fluorinated
complexes under the same doping level (see Figs. 4–6 and
Table 3). The lower turn-on voltage is presumably due to
the decreasing electron injection barrier after introduction
of the fluorinated substituents, which is in agreement with
the lower LUMO level estimated from the results of cyclic
voltammetry (vide supra).
All the devices show a gradual decreasing in gc with
increasing current density, attributed to increasing trip-
let–triplet annihilation of the phosphor-bound excitons
[17]. We note that the current efficiency decrease smaller
extent for the fluorinated complexes than that for the
unfluorinated complex 1. For example, with the 3 wt%
doping level, the current efficiency lost by 40% for 1, 26%
for 2 and 30% for 3, respectively, when the current density
changed from 20 mA/cm2 to 100 mA/cm2. To complex 2,
even at high current density of 100 mA/cm2, L (luminance),
gc and gP (power efficiency) still remain as high as
11774 cd/m2, 6.50 cd/A and 1.12 lm/W, respectively, and
to complex 3, those data are 11995 cd/m2, 6.64 cd/A and
1.16 lm/W, respectively. This phenomenon implies that
the introduction of fluorinated substituent alleviates the
triplet–triplet annihilation.
The dependence of EL performance on the doping con-
centration was studied for the devices based on the com-
plexes 2 and 3, under 3 wt%, 5 wt% and 8 wt% doping
level in host CBP, respectively. The markedly higher lumi-
nance efficiency and brightness were achieved under the
3 wt% doping concentration for both 2 and 3 (Table 3). To
complex 2, the maximum luminance (Lmax) is 16410 cd/m2
at a current density of 210 mA/cm2. The maximum lumi-
nance efficiency (gc max) and power efficiency (gp max) are
9.34 cd/A and 5.20 lm/W, respectively. To complex 3, those
data are 16797 cd/m2 at a current density of 211 mA/cm2,
11.12 cd/A and 4.97 lm/W, respectively. Neglectable red-
shift of EL emission peak implies the absence of aggregation
or stacking up to 8% doping level. The driving voltages of
these devices increase with dopant concentrations, consis-
tent with earlier reports that iridium complexes behave as
carrier traps in devices [18].
3. Conclusion
In conclusion, we have synthesized and characterized a
series of novel iridium(III) complexes bearing fluorinated
2,4-diphenylquinoline ligands. Significantly mixing of the
singlet and triplet excited states is clearly observed in both
the absorption and emission spectra of the complexes. The
emission of the complexes can be fine tuned in the orange-
red region by fluorination on the ligands frame. The alter-
ation of emission wavelength correlates with the variation
of energy gap evaluated from the results of cyclic voltam-
metry. The effect of different meta-fluorine substitution
on emission of cyclometalated iridium complexes is
clarified. Finally, very highly efficient OLED using the
complexes as the phosphorescent dopant have been dem-
onstrated. Significantly improved performance, lower
turn-on voltage and alleviatory triplet–triplet annihilation
were achieved using the fluorinated complexes as the emit-
ter than that using the unfluorinated counterpart 1 under
the same doping level, indicating the advantages of intro-
duction of fluorinated substituent on the phenylquinoline
ligand frame.
4. Experimental
4.1. General information
1H NMR spectra were measured on a MECUYR-
VX300 spectrometer in CDCl3 using tetramethylsilane as
an internal reference. Elemental analyses of carbon, hydro-
gen, and nitrogen were performed on a Carlorerba-1106

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X. Zhang et al. / Journal of Organometallic Chemistry 691 (2006) 4312–4319
microanalyzer. Mass spectra were measured on a ZAB 3F-
HF mass spectrophotometer. UV–Vis absorption spectra
were recorded on Shimadzu 160A recording spectropho-
tometer. PL spectra were recorded on Perkin–Elmer LS
55 luminescence spectrophotometer.
7.69 (s, 1H), 7.66 (s, 1H), 7.58 (dd, J = 8.7, 2.1 Hz, 1H),
7.46 (m, 5H).
4.3. Preparation of Ir complexes
Cyclic voltammetry (CV) was carried out in nitrogen-
purged anhydrous THF or dichloromethane at room tem-
perature with CHI voltammetric analyzer. Tetrabutylam-
monium hexafluorophosphate (TBAPF6) (0.1 M) was
used as supporting electrolyte. The conventional three-elec-
trode configuration consists of platinum working electrode,
a platinum wire auxiliary electrode, and an Ag wire pseu-
doreference electrode with ferrocenium/ferrocene (Fc+/
Fc) as the internal standard. Cyclic voltammograms were
obtained at scan rate of 100 mV. Formal potentials are cal-
culated as the average of cyclic voltammetric anodic and
cathodic peaks.
The mixture of organic ligand (1.42 mmol), IrCl3 Æ 3H2O
(0.21 g 0.59 mmol) in a mixed solvent of 2-ethoxyethanol
(12 ml) and water (4 ml) was stirred under argon at
120 °C for 24 h. Cooled to room temperature, the precipi-
tate was collected by filtration and washed with water, eth-
anol and hexane successively, and then dried in vacuum to
give a cyclometallated Ir(III) l-chloro-bridged dimer. The
dimer (0.12 g, 0.08 mmol), acetylacetone (0.24 mmol) and
Na2CO3 (86 mg, 0.8 mmol) were dissolved in 2-ethoxyeth-
anol (8 ml) and the mixture was then stirred under argon
at 100 °C for 16 h. After cooling to room temperature,
the precipitate was filtered off and washed with water, eth-
anol and hexane. The crude product was flash chromato-
graphed on silica gel using CH2Cl2 as eluent to afford the
desired Ir(III) complex.
4.2. Preparation of ligands
1
6-Chloro-2-(2-fluorophenyl)-4-phenylquinoline, 6-chloro-
2-(4-fluorophenyl)-4-phenylquinoline, 6-chloro-2-(4-triflu-
oromethyl)-4-phenylquinoline were conveniently prepared
from 5-chloro-2-aminobenzophenone and corresponding
acetophenone derivatives through Friedla¨nder reaction.
5-Chloro-2-aminobenzophenone (0.93 g, 4.0 mmol) or
5-bromo-2-amino-benzophenone (1.10 g, 4.0 mmol) and
4.0 mmol acetophenone were dissolved in 15 ml of HOAC,
and then 0.25 ml of concentrated H2SO4 was added. After
refluxed for 12 h under the argon atmosphere, the solution
was poured into a mixture of 50 ml of concentrated
NH3 Æ H2O and 50 g of ice water. The resulting precipitate
was filtered and washed with water. The pure compounds
were recrystallized from THF/ethanol.
Complex 1: yield: 62%. H NMR (CDCl3, 300 MHz) d:
8.44 (d, J = 9.3 Hz, 2H), 8.01 (s, 2H), 7.99 (s, 2H), 7.82 (d,
J = 7.5 Hz, 2H), 7.66–7.62 (m, 10H), 7.48 (d, J = 9.6 Hz,
2H), 6.85 (t, J = 7.5 Hz, 2H), 6.67 (d, J = 6.9 Hz, 2H),
6.56 (d, J = 7.5 Hz, 2H), 4.76 (s, 1H), 1.56 (s, 6H). Anal.
Calc. for C47H33IrN2O2Br2: C, 55.90; H, 3.29; N, 2.77.
Found: C, 55.69; H, 3.41; N, 2.55%. MS (FAB): m/z
1010 (M+).
1
Complex 2: yield: 54%. H NMR (CDCl3, 300 MHz) d:
8.49 (d, J = 3.3 Hz, 2H), 8.40 (d, J = 9.6 Hz, 2H), 7.82 (d,
J = 2.4 Hz, 2H), 7.63–7.58 (m, 10H), 7.32 (dd, J = 9.6,
2.1 Hz, 2H), 6.64 (d, J = 5.2 Hz, 2H), 6.60 (s, 2H), 6.33
(m, 2H), 4.69 (s, 1H), 1.56 (s, 6H). Anal. Calc. for
C47H31IrN2O2Cl2F2: C, 58.99; H, 3.27; N, 2.93. Found:
C, 58.74; H, 3.43; N, 2.79%. MS (FAB): m/z: 956 (M+).
6-Bromo-2,4-diphenylquinoline: white solid, 0.93 g
(65%). 1H NMR (CDCl3, 300 MHz) d: 8.20 (d,
J = 1.5 Hz, 1H), 8.17 (s, 1H), 8.11 (d, J = 9.0 Hz, 1H),
8.04 (d, J = 2.1 Hz, 1H), 7.84 (s, 1H), 7.81 (dd, J = 9.0,
2.1 Hz, 1H), 7.58–7.48 (m, 8H).
1
Complex 3: yield: 58%. H NMR (CDCl3, 300 MHz) d:
8.46 (d, J = 9.6 Hz, 2H), 8.20–8.16 (m, 2H), 7.94 (s, 2H),
7.83–7.79 (m, 4H), 7.66–7.55 (m, 8H), 7.38 (dd, J = 9.6,
1.8 Hz, 2H), 6.90 (td, J = 9.0, 2.4 Hz, 2H), 6.18 (dd,
J = 9.6, 2.4 Hz, 2H), 4.79 (s, 1H), 1.59 (d, J = 7.8 Hz,
6H). Anal. Calc. for C47H31IrN2O2Cl2F2: C, 58.99; H,
3.27; N, 2.93. Found: C, 58.64; H, 3.05; N, 3.26%. MS
(FAB): m/z: 956 (M+).
6-Chloro-2-(2-fluorophenyl)-4-phenylquinoline: white
solid, 0.48 g (36%). M.p.: 136–139 °C. IR [cmꢀ1, KBr]:
1
2925(s), 1629(s), 1441(s), 1383(m), 1259(m), 1097(m). H
NMR (CDCl3, 300 MHz) d: 8.12 (m, 3H), 7.89 (d,
J = 2.4 Hz, 1H), 7.79 (d, J = 2.7 Hz, 1H), 7.64 (dd,
J = 9.0, 2.4 Hz, 1H), 7.42 (m, 1H), 7.31 (td, J = 7.8,
1.2 Hz, 1H), 7.21 (m, 1H).
1
Complex 4: yield: 60%. H NMR (CDCl3, 300 MHz) d:
8.36 (d, J = 9.6 Hz, 2H), 8.07 (s, 2H), 7.93 (d, J = 8.1 Hz,
2H), 7.87 (d, J = 2.1 Hz, 2H), 7.68–7.60 (m, 10H), 7.37
(dd, J = 9.6, 3.0 Hz, 2H), 7.22 (s, 2H), 6.79 (s, 2H), 4.73
(s, 1H), 1.55 (s, 6H). Anal. Calc. for C49H31IrN2O2Cl2F6:
C, 55.68; H, 2.96; N, 2.65. Found: C, 55.74; H, 2.99; N,
2.93%. MS (FAB): m/z: 1056 (M+).
6-Chloro-2-(2-fluorophenyl)-4-phenylquinoline: white
solid, 0.66 g (49%). M.p.: 176–178 °C. IR [cmꢀ1, KBr]:
1
3008(s), 1706(s), 1451(s), 1380(m), 1259(m), 1070(m). H
NMR (CDCl3, 300 MHz) d: 8.08 (m, 3H), 7.77 (d,
J = 2.4 Hz, 1H), 7.70 (s, 1H), 7.58 (dd, J = 8.7, 1.8 Hz,
1H), 7.47 (m, 5H), 7.12 (m, 2H).
4.4. OLED fabrication
6-Chloro-2-(4-trifluoromethyl)-4-phenylquinoline: white
solid, 0.63 g (41%). M.p.: 117–119 °C. IR [cmꢀ1, KBr]:
2975(s), 1590(s), 1483(s), 1328(m), 1150(m). 1H NMR
(CDCl3, 300 MHz) d: 8.21 (s, 1H), 8.18 (s, 1H), 8.06 (d,
J = 8.7 Hz, 1H), 7.78 (d, J = 2.1 Hz, 1H), 7.74 (s, 1H),
Organic layers and metal cathode were fabricated by
high-vacuum thermal evaporation onto a pre-cleaned
indium tin oxide (ITO) glass substrate. In a vacuum cham-
ber with a pressure of <10ꢀ4 Pa, 40 nm of NPD as the hole

X. Zhang et al. / Journal of Organometallic Chemistry 691 (2006) 4312–4319
4319
[4] (a) W.S. Huang, J.T. Lin, C.H. Chien, Y.T. Tao, S.S. Sun, Y.S.
Wen, Chem. Mater. 16 (2004) 2480;
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A.J. Heeger, Phys. Rev. B 68 (2003) 115209;
transporting layer, 30 nm of the complex doped (10%) CBP
as the emitting layer, 10 nm of BCP as a hole and exciton
blacking layer, 30 nm of AlQ3 as the electron transporting
layer, and a cathode composed of 1 nm of lithium fluoride
and 100 nm of aluminum were sequentially deposited onto
the substrate to construct the device. The I–V–B of EL
devices was measured at ambient condition with a Keithey
2400 Source meter and a Keithey 2000 Source multimeter
equipped with a calibrated silicon photodiode. The EL
spectra were measured by JY SPEX CCD3000
spectrometer.
(b) X. Gong, J.C. Ostrowski, D. Moses, G.C. Bazan, A.J. Heeger,
Adv. Funct. Mater. 13 (2003) 439;
(c) P.A. Lane, L.C. Palilis, D.F. O’Brien, C. Giebeler, A.J. Cadby,
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Acknowledgments
(c) K.R.J. Thomas, M. Velusamy, J.T. Lin, C.H. Chien, Y.T. Tao,
Y.S. Wen, Y.H. Hu, P.T. Chou, Inorg. Chem. 44 (2005) 5677;
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We thank the National Natural Science Foundation of
China (Project Nos. 20371036 and 20474047), the Program
for New Century Excellent Talents in University, the Scien-
tific Research Foundation for Returned Overseas Chinese
Scholars, the Ministry of Education of China, for financial
support.
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