High-efficient phosphorescent iridium(III) complexes with benzimidazole ligand for organic light-emitting diodes: Synthesis, electrochemistry and electroluminescent properties

Article abstract of DOI:10.1016/j.jorganchem.2009.03.022

Two phosphorescent complexes Ir(FFBI)₂(pmp) and Ir(FFBI)₂(pti) based on cyclometalated ligand 1-(4-fluorobenzyl)-2-(4-fluorophenyl)-1H-benzo[d]imidazole (FFBI) and ancillary ligands 2-(phenyliminomethyl)phenol (pmp) or 3-(pyridin-2-y

Full text of DOI:10.1016/j.jorganchem.2009.03.022

Journal of Organometallic Chemistry 694 (2009) 2415–2420
Contents lists available at ScienceDirect
Journal of Organometallic Chemistry
journal homepage: www.elsevier.com/locate/jorganchem
High-efficient phosphorescent iridium(III) complexes with benzimidazole
ligand for organic light-emitting diodes: Synthesis, electrochemistry
and electroluminescent properties
c,
Chunxiang Li a, Guanghui Zhang b, Hung-Hsin Shih d, Xiaoqing Jiang b, Peipei Sun b, , Yi Pan
,
*
*
Chien-Hong Cheng d
a College of Chemistry and Molecular Engineering, Qingdao University of Science and Technology, Qingdao 266042, PR China
b Jiangsu Key Laboratory of Biofunctional Materials, College of Chemistry and Environmental Science, Nanjing Normal University, 122, Ninghai Road, Nanjing, Jiangsu 210097, PR China
c School of Chemistry and Chemical Engineering, Nanjing University, Nanjing 210093, PR China
d Department of Chemistry, Tsing Hua University, Hsinchu 300, Taiwan
a r t i c l e i n f o
a b s t r a c t
Article history:
Two phosphorescent complexes Ir(FFBI)2(pmp) and Ir(FFBI)2(pti) based on cyclometalated ligand 1-(4-
fluorobenzyl)-2-(4-fluorophenyl)-1H-benzo[d]imidazole (FFBI) and ancillary ligands 2-(phenyliminom-
ethyl)phenol (pmp) or 3-(pyridin-2-yl)-4,5,6,7-tetrahydro-2H-indazole (pti) were synthesized. The single
crystal of Ir(FFBI)2(pmp) was obtained. The light emitting and electrochemical properties of these com-
plexes were studied. The electroluminescent devices based on these two complexes with the structure of
ITO/NPB (40 nm)/Ir complex: CBP (30 nm)/BCP (15 nm)/Alq (30 nm)/LiF (1 nm)/Al (100 nm) emitted cyan
color, with high brightness and efficiencies. The maximum external quantum efficiencies reached to 6.8%
and 11.6%, respectively.
Received 28 November 2008
Received in revised form 9 March 2009
Accepted 16 March 2009
Available online 21 March 2009
Keywords:
Electrophosphorescence
Ir-complex
Ó 2009 Elsevier B.V. All rights reserved.
Synthesis
OLEDs
1. Introduction
we recently reported [11], to get high efficient and full-color emit-
ting materials, while the study to the ancillary ligand was deficient
Electrophosphorescent materials incorporating complexes of
heavy metals have been aroused particularly attention in last dec-
ade due to their extremely high efficiency as electroluminescent
emitters. They mainly include square planar d8 or octahedral d6
complexes of heavy-metals such as Pt(II), Ru(II), Os(II), and Ir(III)
[1–6]. Of these materials, iridium complexes have been regarded
as the most appropriate phosphorescent materials because of their
relatively short lifetime and high quantum efficiency. These Ir com-
though it was shown that the ancillary ligand has an evident effect
on the properties of materials [12–14]. And also, a majority of
complexes obtained by modifying cyclometalated ligand emit
green or red color, while blue-emitting iridium complexes, which
are important for the realization of RGB full-color displays and
the creation of white light-emitting devices (WOLEDs), are still
scarce. In our previous report, a complex Ir(FFBI)2(acac) with green
emitting and high efficiencies was studied [15]. In this work, using
1-(4-fluorobenzyl)-2-(4-fluorophenyl)-1H-benzo[d]imidazole (FFBI)
as cyclometalated ligand, by introducing two novel ancillary
ligands, two new complexes were synthesized. They showed
obvious blue shift compared to Ir(FFBI)2(acac). The devices based
on these two complexes gave high brightness and external quan-
tum efficiencies.
ˆ
plexes generally contain two cyclometalated ligands (CN) and a sin-
gle bidentate, monoanionic ancillary ligand, or with three
cyclometalated ligands. The cyclometalated ligands used in the
complexes are well known as heterocycle derivatives that coordi-
nated to the metal center via formation of Ir–N and Ir–C bonds.
Therefore, design of ligands for Ir complexes is of great importance
in order to achieve high efficiency and color purity for OLEDs. To
date, most researches were focused on the design and synthesis
2. Results and discussion
of the cyclometalated ligand, such as changing
p conjugation, intro-
ducing electron donating or withdrawing group on the appropriate
position of the aromatic ring [7–10], and adopting rigid structure, as
2.1. Synthesis and structural characterization of the complexes
Scheme 1 shows the synthetic procedure for the ligands and the
corresponding iridium complexes. The cyclometalated ligand 1-(4-
* Corresponding authors. Tel./fax: +86 25 83598280 (P.P. Sun).
E-mail address: sunpeipei@njnu.edu.cn (P.P. Sun).
fluorobenzyl)-2-(4-fluorophenyl)-1H-benzo[d]imidazole
(FFBI)
0022-328X/$ - see front matter Ó 2009 Elsevier B.V. All rights reserved.
doi:10.1016/j.jorganchem.2009.03.022

2416
C. Li et al. / Journal of Organometallic Chemistry 694 (2009) 2415–2420
N
NH2
NH2
I2
THF/H2O
F
+
F
CHO
N
F
FFBI
OH
OH
N
NH2
EtOH
+
CHO
pmp
N
(i) NaH, THF
+
O
HN
N
N
COOEt
(ii) N2H4, EtOH
pti
IrIr
F
F
N
N
IrCl
N
3
N
Cl
Cl
2-ethoxyethanol, H O
2
o
120 C, 24 h
N
N
F
2
F
2
F
F
N
N
N
N
N
pmp, Na2CO3
O
N
N
Ir
Ir
2-ethoxyethanol
120 oC, 12 h
N
F
F
2
2
F
F
Ir(FFBI)2(pmp)
Ir(FFBI)2(pti)
Scheme 1. Synthesis of the iridium complexes.
was conveniently prepared by the reaction of 1,2-phenylenedi-
amine and 4-fluorobenzaldehyde catalyzed by iodine [16]. The
ancillary ligand 2-(phenyliminomethyl)phenol (pmp) was easily
achieved by the condensation of salicylaldehyde with aniline. The
ligand 3-(pyridin-2-yl)-4,5,6,7-tetrahydro-2H-indazole (pti) was
synthesized by the condensation of ethyl picolinate and cyclohex-
anone, followed by treatment with hydrazine hydrate in refluxing
ethanol [17]. The complexes were synthesized by a general proce-
dure [18]. The reaction of iridium trichloride hydrate with cylco-
of trans ligands at the metal center range between 171.2 and
179.4° and the bond lengths range between 2.005 and 2.147 Å.
The atoms are nearly planar with the torsion angles of N4–N1–
N2–C46 2.69 (0.11)°, O1–N2–C26–N4 3.88 (0.13)°, and O1–N1–
C26–C46 2.12 (0.15)°. The two phenyl groups of pmp are perpen-
dicular each other with dihedral angle of 90.09°.
2.2. Electrochemical properties
metalated ligands FFBI gave the Ir(III)
l
-chlorobridged dimer.
In order to investigate the highest occupied molecular orbital
(HOMO) and the lowest unoccupied molecular orbital (LUMO) en-
ergy levels of the two complexes, cyclic voltammetry was carried
out. On the basis of the onset potential of the oxidation, HOMO en-
ergy level of the two Ir complexes can be estimated with regard to
the energy level of the ferrocenium/ferrocene redox couple (being
approximately 4.8 eV negative to the vacuum level) [19].
Then the dimer reacted with ancillary ligand pmp or pti in the
presence of base to afford the desired iridium complexes Ir(FF-
BI)2(pmp) and Ir(FFBI)2(pti) in moderate yields. The complexes
were purified by column chromatography then sublimated at
300–320 °C and 4 ꢀ 10ꢁ3 Pa. Their structures were characterized
by 1H NMR, IR, mass spectra and elemental analyses.
X-ray crystallographic studies have been carried out for Ir(FF-
BI)2(pmp). The crystal structure and crystal packing diagram of
Ir(FFBI)2(pmp) are shown in Figs. 1 and 2. Selected bond distances
and bond angles are listed in Table 1. The complex exhibits slightly
distorted octahedral coordination geometry around Ir atom with
the cis-O, N, cis-C, C, and trans-N, N chelate disposition. The angles
The HOMO energy level of Ir(FFBI)2(pti) was calculated to be
ꢁ5.04 eV which is very close to that of Ir(FFBI)2(pmp). This is con-
sistent with the reported electrochemical studies and theoretical
calculations that the one-electron oxidation of such d6 complexes
would mainly occur at the metal site, together with a minor contri-
bution from the surrounding chelates [12,20].

C. Li et al. / Journal of Organometallic Chemistry 694 (2009) 2415–2420
2417
Table 1
The selected bond lengths (Å), angles (°).
Bond distance (Å)
Ir(1)–O(1)
Ir(1)–N(1)
Ir(1)–N(2)
Ir(1)–N(4)
2.138(4)
2.147(5)
2.052(5)
2.071(4)
2.005(6)
Ir(1)–C(46)
F(1)–C(24)
F(2)–C(31)
F(3)–C(44)
F(4)–C(51)
2.073(5)
1.404(7)
1.349(8)
1.438(8)
1.337(4)
Ir(1)–C(26)
Bond angle (°)
O(1)–Ir(1)–N(1)
O(1)–Ir(1)–N(2)
O(1)–Ir(1)–N(4)
O(1)–Ir(1)–C(26)
O(1)–Ir(1)–C(46)
N(1)–Ir(1)–N(2)
N(1)–Ir(1)–N(4)
N(1)–Ir(1)–C(26)
86.42(15)
96.83(15)
87.73(16)
177.2(2)
93.28(19)
87.54(19)
100.29(18)
95.3(2)
N(1)–Ir(1)–C(46)
N(2)–Ir(1)–N(4)
N(2)–Ir(1)–C(26)
N(2)–Ir(1)–C(46)
N(4)–Ir(1)–C(26)
N(4)–Ir(1)–C(46)
C(26)–Ir(1)–C(46)
Ir(1)–O(1)–C(1)
179.4(2)
171.21(18)
81.0(2)
93.1(2)
94.2(2)
79.1(2)
85.1(2)
128.3(3)
Table 2
The electrochemical behavior of Ir(FFBI)2(pmp) and Ir(FFBI)2(pti).
Complex
Eonset
(V)
E1/2
(V)
k
Eg
HOMO
(eV)c
LUMO
(eV)d
(nm)a
(eV)b
Ir(FFBI)2(pti)
Ir(FFBI)2(pmp)
0.24
0.27
0.37
0.38
444
461
2.79
2.69
ꢁ5.04
ꢁ5.07
ꢁ2.25
ꢁ2.38
a
Obtained from the wavelength at the intersection of absorption and emission
spectra.
b
c
Eg = hc/k = 1241/k (nm).
Calculated from onset oxidation potential.
Calculated from Eg and HOMO energy level.
d
From the HOMO energy level and the energy gap calculated
from the wavelength at the intersection of UV–Vis absorption
and emission spectra, the LUMO energy level can be estimated
[21] (Table 2). For the two complexes, Ir(FFBI)2(pti) has a greater
energy gap so a blue shift of the PL spectrum was observed.
2.3. Absorption and emission
Fig. 3 depicts the UV–Vis and photoluminescence (PL) spectra of
Ir(FFBI)2(pmp) and Ir(FFBI)2(pti) in dichloromethane at room tem-
perature. For Ir(FFBI)2(pmp), there are three major absorptions at
299, 377, and 431 nm in the UV–Vis spectrum. The former intense
absorption band appears to be ligand-based transition that closely
resembles the spectrum of the free ligand FFBI, whereas the latter
two absorptions are likely due to 1MLCT and 3MLCT according to
Fig. 1. (a) Molecular structure of Ir(FFBI)2(pmp) with thermal ellipsoids drawn at
the 30% probability level. (b) Packing diagram viewed from the c-axis. The broken
lines show intermolecular hydrogen bonding.
UV-Vis of Ir(FFBI)2(pti)
1.0
0.8
0.6
0.4
0.2
0.0
UV-Vis of Ir(FFBI)2(pmp)
PL of Ir(FFBI)2(pti)
PL of Ir(FFBI)2(pmp)
Fc & Ir(FBPI)(pti)
Fc & Ir(FBPI)(pmp)
Fc
1.2
0.8
0.4
0.0
-0.4
-0.8
-1.2
300
400
500
600
700
-0.8
-0.4
0.0
0.4
0.8
1.2
Wavelength (nm)
Potential (V vs Fc/Fc +)
Fig. 3. The UV–Vis absorption and photoluminescence spectra of the iridium
Fig. 2. The cyclic voltammograms of Ir(FFBI)2(pmp) and Ir(FFBI)2(pti).
complexes Ir(FFBI)2(pmp) and Ir(FFBI)2(pti) in CH2Cl2.

2418
C. Li et al. / Journal of Organometallic Chemistry 694 (2009) 2415–2420
the previous reports and the calculations of Hay [20]. Similar result
was observed for complex Ir(FFBI)2(pti). For many luminescent or-
ganic molecules, the absorption spectrum overlaps on the emission
spectrum, especially for heavy metal complexes due to their metal
to ligand charge transfer (MLCT) [11]. Based on the wavelengths at
which the UV–Vis absorption and photoluminescent spectra inter-
sect, the energy gap between LUMO and HOMO can be calculated.
On irradiation with 340 nm light, both Ir(FFBI)2(pmp) and Ir(FF-
BI)2(pti) showed strong photoluminescence in dichloromethane at
483 and 474 nm, respectively, falling in blue to cyan region. Com-
pared to Ir(FFBI)2(acac) [15], Ir(FFBI)2(pmp) and Ir(FFBI)2(pti)
exhibits 10 and 20 nm blue shift of emission maximum, respec-
tively. The results indicated that besides the cyclometalated ligand,
ancillary ligand also has an obvious effect on changing the emitting
wavelength. Through selecting appropriate ancillary ligand to get
diverse color emitting complexes, especially blue-emitting iridium
complexes will be possible.
1.0
0.8
0.6
0.4
0.2
0.0
Device A
Device B
300
350
400
450
500
550
600
650
700
750
Wavelength (nm)
Fig. 5. The electroluminescence spectra of devices.
2.4. Electroluminescent properties
To illustrate the electroluminescent properties of these com-
plexes, typical OLED devices (device A and B) using complex Ir(FF-
BI)2(pmp) and Ir(FFBI)2(pti) respectively as dopants were
fabricated. The devices had a multi-layer configuration ITO/NPB
(40 nm)/Ir complex: CBP (30 nm)/BCP (15 nm)/Alq (30 nm)/LiF
(1 nm)/Al (100 nm), in which ITO (indium tin oxide) was used as
the anode, NPB (4,40-bis[N-(1-naphthyl)-N-phenylamino]biphenyl)
was used as the hole-transporting material, CBP (4,40-N,N0-dicar-
bozole biphenyl) as the host, the iridium complexes as the dopant,
BCP (2,9-dimethyl-4,7-dipheny-1,10-phenanthroline) as the hole
blocker, Alq (tris(8-hydroxyquinolinato)aluminium) as the elec-
tron transporter, and LiF/Al as the cathode (Fig. 4). Key character-
istics of these devices are listed in Table 3.
device A L-V
device B L-V
deviceA: CD-V
deviceB: CD-V
1200
50000
40000
30000
20000
10000
0
1000
800
600
400
200
0
-2
0
2
4
6
8
10 12 14 16 18 20 22 24
Voltage(V)
Al(100 nm)
N
N
LiF(1 nm)
Alq(30 nm)
BCP(15 nm)
Ir complex: CBP(30 nm)
NPB(40 nm)
ITO
Fig. 6. The luminance–voltage–current (L–V–I) characteristics of the devices.
NPB
CBP
Device A and B emitted strong cyan light with an emission max-
imum at 498, 492 nm, respectively (Fig. 5). It is surprising to note
that compared to the PL spectra of Ir(FFBI)2(pmp) and Ir(FFBI)2(pti)
in dichloromethane solution, the maximum emission wavelength
and the shape of the electroluminescence spectra are substantially
different, the maximum emission wavelength of device B exhibited
a red shift up to 18 nm. Though the certain reason for the differ-
ence is not yet clear, we can presume that the different environ-
ment in dichloromethane solution and in thin film had different
effect on the emission of the complex. The EL spectra of devices
do not change significantly with variation of the applied voltages
from 6 to 12 V. Based on the EL spectrum at an applied voltage
of 8 V, The Commission International de I’Eclairage (CIE) coordi-
nates of device A and B are (0.23, 0.58), (0.22, 0.54), respectively.
The CIE coordinate of both complexes are almost independent of
driving voltage.
Glass
N
N
N
O
N
O
Al
O
N
N
N
Me
Me
BCP
Alq
Fig. 4. The general structure of devices and the molecular structures of the
compounds used in the devices.
Table 3
The performance data of the Ir complex-based OLEDs.
Device
Turn-on voltage (V)
gext (%, V)
L (cd/m2, V)
gc (cd/A, V)
gp (lm/W, V)
kmax (nm)
CIE, 8 V (x, y)
A: 7.3%Ir(FFBI)2(pmp)
B: 6.7%Ir(FFBI)2(pti)
3.4
3.1
6.8, 6.5
11.6, 9.0
47100, 11.5
41150, 17.5
21.7, 6.5
35.3, 9.0
15.4, 4.0
14.8, 4.9
498
492
(0.23, 0.58)
(0.22, 0.54)
The data for external quantum efficiency (
g
ext), brightness (L), current efficiency (
g
c), and power efficiency (gp) are the maximum values of the devices.

C. Li et al. / Journal of Organometallic Chemistry 694 (2009) 2415–2420
2419
(TBAP) as the supporting electrolyte and degassed dichlorometh-
ane as the solvent. The ferrocenium/ferrocene couple was used as
the internal standard. Current, voltage, and light-intensity mea-
surements were made simultaneously using a Keithley 2400
source meter and a Newport 1835-C optical meter equipped with
a Newport 818-ST silicon photodiode.
16
14
12
10
8
12
10
8
device A: ηext-CD
device B: ηext-CD
device A: ηp-CD
device B: ηp-CD
6
4.2. Preparation of ligands
6
4
4.2.1. 1-(4-Fluorobenzyl)-2-(4-fluorophenyl)-1H- benzo[d]imidazole
(FFBI)
4
2
2
1,2-Phenylenediamine (0.54 g, 5 mmol) and 4-fluorobenzalde-
hyde (1.06 g, 10 mmol) were dissolved in THF–H2O (v/v 1:1,
20 mL), and then iodine (0.03 g, 0.1 mmol) was added. After stirred
for 3 h at room temperature, the mixture was extracted with
CH2Cl2, the solution was evaporated and the residue was then puri-
fied by column chromatography over silica gel using petroleum
ether/ethyl acetate (v/v, 4:1) as eluent to furnish pure FFBI in
72% yield. M.p. 88–90 °C. 1H NMR (CDCl3, 400 MHz) d: 8.13–8.16
(m, 1H), 7.88 (d, J = 7.4 Hz, 1H), 7.64–7.68 (m, 2H), 7.28–7.32 (m,
3H), 7.13–7.16 (m, 2H), 7.05–7.09 (m, 3H), 5.43 (s, 2H). MS (EI)
m/z: 320.1 (51.9, M+), 228.9 (7.7), 210.9 (7.3), 108.9 (100), 82.9
(19.8). Anal. Calc. for C20H14N2F2: C, 74.99; H, 4.41; N, 8.75. Found:
C, 74.95; H, 4.45; N 8.71%.
0
0
-2
0
50
100
150
200
250
300
350
400
Current Density (mA/cm2)
Fig. 7. The external quantum efficiency (
p) characteristics of the devices.
gext)–current density–power efficiency
(g
Figs. 6 and 7 show the luminance–voltage–current (L–V–I) and
the external quantum efficiency ( ext)–current density–power effi-
ciency ( p) characteristics of the devices, respectively. Both de-
g
g
vices showed quite high efficiencies and brightness. Device A,
with 7.3% of Ir(FFBI)2(pmp), appears to show the better perfor-
mance in terms of brightness and power efficiency, with brightness
of 47100 cd/m2 at 11.5 V and 15.4 lm/W at 3.5 V. For device B, with
6.7% of Ir(FFBI)2(pti) as dopant, an extremely high external quan-
tum efficiency of 11.6%, a maximum brightness of 41150 cd/m2
at 17.5 V, and a current efficiency of 35.3 cd/A were achieved
(Table 3).
4.2.2. 2-((Phenylimino)methyl)phenol (pmp)
Salicylaldehyde (1.22 g, 10 mmol) and aniline (0.93 g, 10 mmol)
were dissolved in ethanol (20 mL). After stirred for 1 h at room
temperature, the crystal appeared. The precipitate was filtered,
recrystallized from ethanol, to give pmp in 85% yield. M.p. 50–
52 °C. 1H NMR (CDCl3, 400 MHz) d: 8.65 (s, 1H), 7.38–7.48 (m,
4H), 7.30–7.34 (m, 3H), 7.07 (d, J = 8.0 Hz, 1H), 6.97 (t, J = 7.5 Hz,
1H).
Another attractive feature of device A is the slow decay of exter-
nal quantum efficiency with increasing current density, as shown
in Fig. 6. The device gave a peak external quantum efficiency gext
of 6.8% at J = 16.62 mA/cm2. When the current density increased
4.2.3. 3-(Pyridin-2-yl)-4,5,6,7-tetrahydro-2H-indazole (pti)
To a round-bottomed flask (100 mL), NaH (1.56 g, 30 mmol) and
anhydrous THF (30 mL) were added. After cooled to 0 °C, the solu-
tion of cyclohexanone (2.94 g, 30 mmol) in THF (5 mL) was slowly
added in it. The mixture was stirred for 30 min at room tempera-
ture, ethyl picolinate (3.85 g, 28.5 mmol) was added in dropwise
at 60 °C. After refluxed for 3 h, the mixture was cooled to 0 °C,
and then poured slowly into dilute hydrochloric acid. After ad-
justed to pH 8–9 by Na2CO3, the mixture was extracted with ethyl
acetate, and the organic layer was washed with saturated NaCl and
water. The solvent was evaporated to get brown oil.
The above obtained oil was dissolved in ethanol (90 mL), heated
to boiling, 85% hydrazine hydrate (15.8 mL) was added in drops.
After the mixture was refluxed for 12 h, the solvent was evapo-
rated, and the residue was dissolved in ethyl acetate, and then
washed with water. After dried with anhydrous sodium sulfate,
the mixture was concentrated and then purified by column chro-
matography over silica gel using petroleum ether/ethyl acetate
(v/v, 5:1) as eluent to give white solid pti in 55% yield. M.p. 120–
121 °C. 1H NMR (CDCl3, 400 MHz) d: 8.64 (d, J = 6.5 Hz, 1H), 7.74
(dd, J = 7.7, 8.0 Hz, 1H), 7.60 (d, J = 8.0 Hz, 1H), 7.46–7.49 (m, 1H),
2.70–2.85 (m, 4H), 1.78–1.87 (m, 4H). Anal. Calc. for C12H13N3: C,
72.33; H, 6.58; N, 21.09. Found: C, 72.41; H, 6.52; N 20.99%.
to J = 100 mA/cm2, the external quantum efficiency
gext decreased
to 6.08% with a loss of about 10%. At J = 200 mA/cm2, the value of
gext still remained as high as 5.06%.
3. Conclusion
In summary, we synthesized two iridium complexes Ir(FF-
BI)2(pmp) and Ir(FFBI)2(pti) by used a cyclometalated ligand FFBI
with two novel ancillary ligands pmp and pti. The EL devices based
on these two iridium complexes emitted cyan color, with high
brightness and efficiencies. Designing novel ancillary ligands is
shown to be a direction to get high efficient diverse color emitting
electrophosphorescent complexes.
4. Experimental
4.1. Reagents and instruments
Reagents were used as purchased without further purification.
1H NMR spectra were measured on a Bruker ARX-400 spectrometer
in CDCl3 using TMS as an internal reference. Mass spectra (MS)
were measured on a VG-ZAB-HS spectrometer with electron im-
pact ionization. Elemental analysis was performed on a Perkin–El-
mer 240C elemental analyzer. The UV–Vis spectra were recorded
on a VARIAN Cary 5000 spectrometer. PL spectra were recorded
on a Perkin–Elmer LS 50B luminescence spectrophotometer. Cyclic
voltammetry (CV) measurements were carried out with a CHI660C
electrochemical analyzer (CH Instruments) at room temperature
using 0.10 M tetra(n-butyl)ammonium hexafluorophosphate
4.3. Preparation of Ir complexes
The mixture of FFBI (0.70 g, 2.2 mmol), IrCl3 3H2O (0.34 g,
1 mmol) in a mixed solvent of 2-ethoxyethanol (10 mL) and water
(3 mL) was stirred under N2 at 120 °C for 24 h. Cooled to room tem-
perature, the precipitate was collected by filtration and washed
with water, ethanol and acetone successively, and then dried in
vacuum to give a cyclometalated Ir(III) l-chloro-bridged dimer.

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C. Li et al. / Journal of Organometallic Chemistry 694 (2009) 2415–2420
The dimmer, the ancillary ligand (1 mmol) and Na2CO3 (0.3 g) were
dissolved in 2-ethoxyethanol (8 mL) and the mixture was stirred
under N2 at 120 °C for 10 h. After cooled to room temperature,
the precipitate was filtered and washed with water, ethanol and
acetone. The crude product was flash chromatographed on silica
gel using CH2Cl2 as eluent to afford the desired Ir(III) complex.
Ir(FFBI)2(pmp): Yield 65%.1H NMR (CDCl3, 400 MHz) d: 8.07 (d,
J = 7.9 Hz, 1H), 7.86 (d, J = 7.6 Hz, 1H), 7.41–7.44 (m, 2H), 7.32–
7.36 (m, 4H), 7.21–7.23 (m, 2H), 7.14–7.16 (m, 3H), 7.02–7.07
(m, 7H), 6.87–6.89 (m, 3H), 6.23–6.38 (m, 5H), 6.00–6.07 (m,
2H), 5.99 (s, 2H), 5.53–5.64 (m, 4H). MS (ESI) m/z: 1027.0 (M+).
Anal. Calc. for C53H36F4IrN5O: C, 61.98; H, 3.53; N, 6.82. Found: C,
62.12; H, 3.61; N, 6.73%. IR (KBr, cmꢁ1): 2924 (w), 2344 (w),
16079 (s), 1561 (m), 1510 (m), 1463 (m), 1433 (m), 1354 (w),
1279 (w), 1254 (w), 1230 (w), 1190 (m), 1168 (w), 1125 (w), 825
(w), 697 (w).
Acknowledgement
Financial supports from the National Natural Science Founda-
tion of China (Project Nos. 20772057 and 20773066) are gratefully
acknowledged.
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Ir(FFBI)2(pti): Yield 58%. 1H NMR (CDCl3, 400 MHz) d: 7.85 (d,
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The complexes were sublimated at 300–320 °C and 4 ꢀ 10ꢁ3 Pa
before use. The device was fabricated by vacuum deposition of the
materials at 1.3 ꢀ 10ꢁ4 Pa onto a clean glass pre-coated with a
layer of indium tin oxide with a sheet resistance of 25
X .
hꢁ1
The deposition rate for the organic compounds was 0.1–
0.2 nm sꢁ1.The cathode of LiF/Al was deposited by first evaporating
LiF at a deposition rate of 0.01 nm sꢁ1 and then evaporating alumi-
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num at a rate of 0.1–0.2 nm sꢁ1
.