Carbazole and arylamine functionalized iridium complexes for efficient electro-phosphorescent light-emitting diodes

Article abstract of DOI:10.1016/j.ica.2011.01.095

We report the synthesis and characterization of four cyclometalated iridium complexes based on carbazole and arylamine modified 2-phenylpyridine. The carbazole and arylamine groups are linked to 2-phenyl pyridine backbone to enhance the energy harvesting and transfer from host to guest materials. The electrochemical and photophysical properties of the complexes are studied and electroluminescent devices are fabricated. The results show that the complexes with ligands containing carbazole moieties have desirable phosphorescent properties. The device with complex 3 doped PVK (poly (vinylcarbazole)) as emission layer achieves maximum luminous efficiency of 6.56 cd A^-1 and maximum brightness of 14448 cd m^-2.

Full text of DOI:10.1016/j.ica.2011.01.095

Inorganica Chimica Acta 370 (2011) 340–345
Contents lists available at ScienceDirect
Inorganica Chimica Acta
journal homepage: www.elsevier.com/locate/ica
Carbazole and arylamine functionalized iridium complexes for efficient
electro-phosphorescent light-emitting diodes
a,
Dan Wang a, Jian Wang b, He-Liang Fan b, Hai-Fang Huang b, Zeng-Ze Chu a, Xi-Cun Gao b, , De-Chun Zou
⇑
⇑
a Beijing National Laboratory for Molecular Sciences, Key Laboratory of Polymer Chemistry and Physics of Ministry of Education,
College of Chemistry and Molecular Engineering, Peking University, Beijing 100871, China
b Department of Chemistry, School of Science, Nanchang University, Nanchang 330031, China
a r t i c l e i n f o
a b s t r a c t
Article history:
Received 11 June 2010
Received in revised form 5 January 2011
Accepted 26 January 2011
Available online 3 February 2011
We report the synthesis and characterization of four cyclometalated iridium complexes based on carba-
zole and arylamine modified 2-phenylpyridine. The carbazole and arylamine groups are linked to 2-phe-
nyl pyridine backbone to enhance the energy harvesting and transfer from host to guest materials. The
electrochemical and photophysical properties of the complexes are studied and electroluminescent
devices are fabricated. The results show that the complexes with ligands containing carbazole moieties
have desirable phosphorescent properties. The device with complex 3 doped PVK (poly (vinylcarbazole))
as emission layer achieves maximum luminous efficiency of 6.56 cd Aꢀ1 and maximum brightness of
Keywords:
Iridium complex
Carbazole
Phosphorescent materials
Organic light-emitting diode
14448 cd mꢀ2
.
Ó 2011 Elsevier B.V. All rights reserved.
1. Introduction
4,40-Bis(N-carbazolyl)biphenyl (CBP) is a commonly used host
material, and many excellent devices with CBP as host exhibiting
high efficiencies were reported [15–20]. The green phosphorescent
device with heteroleptic complex, Ir(ppy)2acac, doped into CBP has
In the past decades, organic light-emitting diodes (OLEDs)
based on phosphorescent complexes have attracted increasing
attentions. The phosphorescent materials are doped as emitting
guests into charge-transporting host materials to obtain high effi-
ciency. The presence of a heavy-metal atom in the phosphorescent
complex provides a significant spin–orbit interaction that allows
the decay of normally spin-forbidden radiative triplet to happen.
Due to both singlet and triplet excited states participating in the
emission, the internal quantum efficiency can potentially reach
as high as 100% [1–6].
Of all these phosphorescent complexes, cyclometalated iridium
(III) complexes are the most promising candidates. Because of the
comparatively short excited state and high phosphorescent effi-
ciency, the quenching of the triplet excitons is decreased, leading
to the effective phosphorescent emission in OLEDs [7–14]. Gener-
ally, it is necessary to disperse the iridium complexes as guest into
a suitable host material to reduce triplet–triplet annihilation and
concentration quenching so that the efficiency of energy-harvest-
ing and the completeness of energy transfer from hosts to guests
are can be effectively improved for highly efficient electrophospho-
rescent devices.
been reported with a high gext of 19% and a power efficiency (gp) of
60 lm Wꢀ1 (ppy = 2-phenyl pyridine, acac = acetylacetone) [21,22].
However, these devices have a complicated structure and consist of
multiple layers deposited sequentially by thermal evaporation un-
der high vacuum conditions. PLEDs that are made by processing
polymeric materials from solution, such as by spin-coating or
ink-jet printing techniques, have the advantages of easy fabrication
and low cost. This inspires the exploration of the solution process-
able approach by incorporation of iridium complexes either by
physical blending in polymeric host materials like PVK [23–29]
or chemical bonding on polymer chains [30–34]. However, poly-
meric materials have disadvantages such as uncertain molecular
structure and purity. In contrast, small molecule materials have de-
fined molecular structure and can be easily purified. In order to
combine both the advantages of small molecules with high purity
and the convenience of solution-processible PLEDs, we synthesized
a series of iridium complexes that can form uniform films through
spin-coating. Owing to the high solubility, high thermal stability of
the complexes and fine film morphology, the devices with solu-
tion-processible phosphorescent light-emitting layers show excel-
lent properties.
In addition, because the balanced injection and transport of
holes and electrons are key factors in the high efficiency OLED de-
vices, it would be desirable to prepare phosphorescent complexes
⇑
Corresponding authors. Tel./fax: +86 791 3969386 (X.C. Gao), tel./fax: +86 10
62759799 (D.C. Zou).
E-mail addresses: xcgao@ncu.edu.cn (X.-C. Gao), dczou@pku.edu.cn (D.-C. Zou).
0020-1693/$ - see front matter Ó 2011 Elsevier B.V. All rights reserved.
doi:10.1016/j.ica.2011.01.095

D. Wang et al. / Inorganica Chimica Acta 370 (2011) 340–345
341
Scheme 1. Synthetic route to the iridium complexes 1–4.
containing structures that are beneficial for charge injection and
shorter than 400 nm due to the
The p–
tions extending into the visible region longer than 450 nm, which
can be assigned to MLCT transitions. The complexes with
carbazole-substituted phenyl pyridine ligands showed more
p
–
p⁄ transition of the ligands.
transport. Carbazole- and arylamine-based compounds are com-
monly used as host materials for both small-molecule OLEDs (such
as CBP) and PLEDs (such as PVK), because of their good hole-trans-
porting ability and high triplet energy that effectively confines
triplet excitons on phosphorescent dopants [14,35–40]. In this
work, we introduced carbazole and arylamine functionalized
groups directly into the ligands to increase energy transfer
efficiency and hole-transporting ability. A series of novel iridium
p⁄ bands are accompanied by weaker, lower energy absorp-
(a)
reference
1.0
0.8
0.6
0.4
0.2
0.0
1
2
3
4
´
complexes with formula Ir(L)2(acac) (L = 2,5-bis(4,4’’-N,N-diphen-
ylamino) phenyl pyridine (1); L = 2-(40-(400-N,N-dipheny-lami-
no)phenyl)phenyl-5-(4000-N,N-diphenylamino)phenyl-pyridine (2);
0
00
´
L = 2,5-bis(4,4’’-9H-9-carbazolyl)phenyl pyridine (3); L = 2-(4 -(4 -
(9H-9-carbazolyl)phenyl)phenyl-5-(4000-(9H-9-carbazole))phenyl
pyridine (4) have been synthesized. The photophysical and
electro-chemical properties were studied and electrolumines-
cent devices were fabricated. The device based on complex 3
showed a maximum luminous efficiency of 6.56 cd Aꢀ1 and a
maximum brightness of 14448 cd mꢀ2
.
250
300
350
400
450
500
550
600
Wavelentgh(nm)
2. Results and discussion
(b)
reference
1.0
0.8
0.6
0.4
0.2
0.0
2.1. Synthesis
1
2
3
4
The target compounds were synthesized through typically four
key steps (Scheme 1). First, 4-N,N-diphenylaminophenylboronic
acid and 4-(9H-9-carbazole)phenylboronic acid were synthesized
in good yields. Then, the ligands were obtained via Suzuki coupling
under mild conditions. The third step was to obtain
bridged dimers of a general formula (C^N)2 Ir( -Cl)2Ir(C^N)2. Final-
ly, the complexes were obtained through the reaction of the
l-chloro-
l
l
-
chloro-bridged dimmers with the second ligand, acac b-diketone.
The overall yield for complexes 1–4 over these steps was about 30%.
350
400
450
500
550
600
650
2.2. Photophysical properties
Wavelentgh(nm)
The absorption spectra of Ir(ppy)2 (acac) and complexes 1–4 are
shown in Fig. 1a. Complexes 1–4 have characteristic absorptions
Fig. 1. Absorption spectra (a) and photoluminescence spectra (b) of iridium
complexes 1–4 in CHCl3 at 293 K with Ir(ppy)2 (acac) as a reference.

342
D. Wang et al. / Inorganica Chimica Acta 370 (2011) 340–345
distinguishable MLCT absorption features at about 460 nm, which
are likely due to the 3MLCT transitions [18]. The similarity of MLCT
energies for complexes 1, 2 and complexes 3, 4 is not surprising,
since each pair of complexes has MLCT states involving very simi-
lar acceptors. Meanwhile, the absorption spectra matched well
with the emission spectra of the host material PVK (main peak at
370 nm), ensuring efficient energy transfer from host materials
to guest materials. The PL spectra of complexes 1–4 are shown in
Fig. 1b. All the complexes have two emission peaks with one at
the longer wavelength and another at the shorter wavelength.
The high energy emission at shorter wavelength can be assigned
to the ligand emission and the low energy emission at longer
wavelength can be assigned to the 3MLCT emission. The corre-
sponding maximum emission wavelengths of complex 1 in CH2Cl2
are near 475 and 580 nm. For complex 2, the main emissions are
near 450 and 580 nm. Complexes 3 and 4 have similar maximum
emission wavelengths, with peaks at near 410 and 550 nm. All
According to the literature [41,42], the HOMO energy level can
ox
be estimated from the onset potentials (E
) through the follow-
onset
1.0
0.8
0.6
0.4
0.2
0.0
(
a)
1
2
3
4
400 450 500 550 600 650 700 750 800
Wavelength(nm)
complexes emit from a mixed 3MLCT-3 state with more 3p
p–p –p
characteristics than those in the known complex Ir(ppy)2(acac)
and have an emission wavelength longer than the PL wavelength
of Ir(ppy)2(acac) (518 nm), due to the enlarged conjugation system
and increased size of the ligands.
The phosphorescence quantum yields of complex 3 and com-
plex 4 are high (0.18 and 0.29), measured by using Ir(ppy)2(acac)
as a reference, which has a value of 0.34 [19]. Complexes 1 and 2
have a relatively low quantum yield (about 0.038 and 0.10). The re-
sults show that the phosphorescence emissions of complex 3 and
complex 4 are stronger due to the rigid carbazole group.
2000
(b)
1
2
3
4
1800
1600
1400
1200
1000
800
600
400
200
0
-200
2.3. Electrochemical properties
-5
0
5
10
15
20
25
30
35
40
Cyclic voltammetry (CV) was used to evaluate the electrochem-
ical behavior of the four complexes and the results were shown in
Fig. 2. It was recorded with a glass-carbon electrode in CH2Cl2 solu-
tions containing 0.001 M of the Ir-complex and 0.10 M n-Bu4NClO4
against Ag/AgCl using ferrocene (Fc) as the internal standard.
Voltage(V)
(c)
10000
1000
100
10
1
2
3
4
80
60
40
20
0
1
-20
0.1
-5
0
5
10
15
20
25
30
35
40
-40
-60
1
Voltage(V)
2
3
4
10
1
-80
1
2
3
4
(d)
(PPY)2Ir(acac)
-100
-200
0
200 400 600 800 1000 1200 1400
Potential(mV)
Fig. 2. Cyclic voltammograms of complexes 1, 2, 3, 4, with n-Bu4NClO4 as
electrolytes.
0.1
0.01
Table 1
Electrochemical potentials and energy levels of the iridium complexes.
HOMO/LUMO(eV)
Eg(eV)
0
500
1000
1500
2000
Complex 1
Complex 2
Complex 3
Complex 4
Ir(ppy)2(acac)
ꢀ5.04/ꢀ2.65
ꢀ5.13/ꢀ2.77
ꢀ5.19/ꢀ2.76
ꢀ5.23/ꢀ2.58
ꢀ5.15/ꢀ2.34
2.39
2.36
2.43
2.38
2.81
Current Density(mA/cm2)
Fig. 3. (a) EL spectra of devices using iridium complexes as guest and PVK as host
with a concentration of 5 wt% and (b and c) current–voltage and luminance–voltage
characteristics (d) current efficiency–current density characteristics.

D. Wang et al. / Inorganica Chimica Acta 370 (2011) 340–345
343
Table 2
EL performance of devices
Complex
Uonset (V)
Lmax (cd mꢀ2
)
gLmax (lm Wꢀ1
)
gImax (cd Aꢀ1
)
CIE coordinate
gext
(%)
k (nm) (low voltage)
max
1
2
3
4
8.3
10.75
7.6
2264
2800
14448
5768
0.49
0.38
1.70
0.81
1.84
1.76
6.56
2.75
(0.54, 0.45)
(0.58, 0.45)
(0.42, 0.57)
(0.44, 0.53)
0.69
0.64
1.81
0.80
581
589
550
557
7.8
ox
ing equation: EHOMO ¼ ꢀð4:8 þ Eref þ E
) eV, where Eref is the po-
ther proves the correct assignment of the high- and low-energy
emissions of the PL emission and that the electrophosphorescent
efficiency is higher than the electroluminescent efficiency.
The device with complex 3 as the doped material exhibits the
best performance with the lowest turn-on voltage at 7.6 V. The
maximum luminous efficiency reaches 6.56 cd Aꢀ1, with a peak
external quantum efficiency of 1.8%, while the maximum lumi-
nance reaches 14448 cd mꢀ2. These excellent properties are mainly
attributed to the high phosphorescence quantum yields and elec-
trochemical stability. Although complex 4 also has relatively high
phosphorescence quantum yields, the device with which as the
dopant shows comparatively lower performance with maximum
brightness of 5768 cd mꢀ2, a maximum external quantum effi-
ciency of 0.81%, and a luminance efficiency of 2.75 cd Aꢀ1, due to
its irreversible electrochemical process.
onset
tential of the Fc reference. The energy levels of LUMO and the
HOMO–LUMO energy gap were calculated from the spectroscopic
and electrochemical data, as shown in Table 1. The complexes with
high electron density moieties have relatively high HOMO levels,
thus high hole-transfer abilities. Consistent with the description
of pyridine-localized LUMO and metal-involved HOMO [43,44],
the direct linkage of the iridium atoms to pyridine in these com-
plexes leads to discrete striking difference in HOMO levels. In addi-
tion, the iridium complexes 1–4 show similar energy band gap due
to the similar electron-donating ability of carbazole, triphenyl-
amine and diphenylamine moieties. However, complex 4 has a nar-
rower energy gap due to the much higher LUMO, which attributes
to the modification of pyridine with 9-phenyl-carbazole that has
relatively lower electron-donating ability. As a result, the LUMO
in complex 4 is stabilized more than other complexes. Moreover,
the results showed that the complexes with the cyclometalated li-
gands containing phenylamine moieties have higher HOMO levels
than that of Ir(ppy)2 (acac) (ꢀ5.15 eV). This result confirms the im-
proved hole-transporting ability of complexes 1–2 comparing with
Ir(ppy)2 (acac). These frontier orbital levels match closely with the
energy levels for PEDOT:PSS (HOMO: ꢀ5 eV) and TPBI (LUMO:
ꢀ2.9 eV) so that the electronic-structure requirements for the
OLED devices can be satisfied.
The devices with complex 1 and 2 as emitters exhibit similar
performance, not as good as the other two. It demonstrates that
the iridium complexes with carbazole moiety based ligands have
much better electrophosphorescent properties than with the phen-
ylamine moiety. These results shown in Table 2 also agree well
with the quantum efficiencies of the complexes.
3. Conclusions
A series of iridium complexes were synthesized. Experimental
results indicate that the complexes with carbazole-substituted
2-phenyl pyridine ligands have more desirable phosphorescent
properties due to the rigid carbazole group harvesting and
transferring energy efficiently to guest. The absorption and photo-
luminescence spectra of the complexes show characteristic phos-
phorescent features. The increased HOMO level indicates that the
modification of 2-phenylpyridine ligand with carbazole or phenyl-
amine moieties increases hole-transporting ability of the phospho-
rescent center. The complexes have good solubility and can form
uniform films for device fabricating. Especially, the device with
complex 3:PVK as emission layer shows the highest brightness
(14448 cd mꢀ2) and luminous efficiency (6.56 cd Aꢀ1). This work
provides a lead for future design of the ligand structures of iridium
complexes.
2.4. Device properties
To evaluate the electroluminescent property of the iridium
complexes in OLEDs, devices using these complexes as dopant
emitters were fabricated. These phosphors are used as phosphores-
cent dopants rather than a single emission layer in OLEDs to pre-
vent the severe self-quenching expected in the solid. PVK is used
as the polymer host material for the electrophosphor because of
the excellent overlap of the absorption spectra of the iridium com-
plexes with the PL spectrum of PVK. Such a guest–host system al-
lows efficient Forster energy transfer from the PVK host singlet to
the iridium guest complex. TPBi acts as both a hole blocker and an
electron transporter, and LiF as an electron-injection layer. Com-
pared with the commonly used electron transporting materials
2,9-dimethyl-4,7-diphenyl-1, 10-phenanthroline (BCP) or tris(8-
4. Experimental part
hydroxyquinolinato)
aluminum
(Alq3),
1,3,5-tris(N-phen-
ylbenzimidazol-2-yl) benzene (TPBi) was adopted for the devices
since it shows a higher electron mobility and can efficiently confine
excitons within the emission layer.
4.1. Materials
Carbazole, n-BuLi, B(OCH3)3, were from Alfa Aesar. Pd(AcO)2,
Pd(PPh3)4, t-BuONa were from Acros. Diphenylamine, 4-bromoan-
iline, 4-bromophenylboronic acid, 1,4-dibromobenzene, 2,5-dib-
romopyridine were purchased from Sinopharm Chemical Reagent
(SCRC).
The electroluminescence (EL) spectra, current–voltage, lumi-
nance–voltage characteristics and current efficiency versus current
density curve of devices using iridium complexes as guest at a con-
centration of 5% (wt) and PVK as host are shown in Fig. 3. Com-
plexes 3 and 4 emit green light with the peak of the featureless
spectrum at about 550 nm, while complexes 1 and 2 emit orange
light with kmax at 580 nm and a shoulder at around 640 nm. The
maximum emission wavelengths of complexes 2 and 4 show slight
red shifts compared to those of complexes 1 and 3 due to the in-
4.2. Characterization and measurements
1H NMR was collected by a Bruker 400 MHz spectrometer.
Absorption spectra and photoluminescence (PL) spectra were re-
corded on a JASCO V-500 spectrophotometer and a JASCO FP-
6200 spectrofluorometer, respectively in degassed CHCl3 solutions.
creased p-conjugated system of the ligands. In addition, it should
be noted that the EL emission at the high energy region, the blue
emission from the ligand, is weak for all the complexes. This fur-

344
D. Wang et al. / Inorganica Chimica Acta 370 (2011) 340–345
The phosphorescence quantum yields were determined in CHCl3 at
293 K with Ir (ppy)2(acac) as a reference (/ = 0.34) [19]. Cyclic vol-
tammetry was performed using a Model 283 potentiostat/galvano-
stat (Princeton Applied Research) with a scan rate of 50 mV/s.
Fabrication of light-emitting devices: The etched ITO (20 O/h)
glass substrate was rinsed with detergent, deionized water, ace-
tone, and ethanol in sequence, and then treated with UV-ozone.
Next, poly(ethlyenedioxythiophene): poly (styrene-sulfonicacid)
(PEDOT:PSS) was spin-coated on the surface of the ITO substrate,
followed by thermal annealing at 120 °C for 2 h. On top of it, the
solution of the mixture of complex and PVK in chloroform
For e, as indicated in the Scheme, the starting materials were
4-bromophenylboronic acid and 2,5-dibromopyridine and the ratio
is 1:1.5. The product was white needles, yield: 61%. m.p. 78–79 °C.
1HNMR (CDCl3, 400 MHz, d: 8.73-8.72(s, H); 7.89–7.83 (m, 3H);
7.61–7.59 (d, 2H).
The synthesis of f, 2-(40-(400-N,N-diphenylamino)phenyl)phenyl-
5-(4000-N,N-diphenylamino)phenyl-pyridine (apppp) and g, 2-(40-
(400-(9H-9-carbazolyl)phenyl)
phenyl-5-(4000-(9H-9-carbazolyl))-
phenyl pyridine (cpppp) is similar to that of c and d.
For f, apppp, yellow needles, yield: 58%. m.p. 234–236 °C, 1H
NMR(CDCl3, 400 MHz), d: 8.92 (s, H); 8.11–8.09 (d, 2H); 7.93–
7.91 (d, H); 7.83–7.81 (d, 2H); 7.71–7.69 (d, 2H); 7.56–7.51 (t,
4H); 7.31–7.28 (m, 8H); 7.18–7.14 (m, 12H); 7.08–7.02 (t, 4H).
Anal. Calc. for C47H35N3: C, 87.99; H, 5.46; N, 6.55. Found: C,
87.95; H, 5.82; N, 6.01%.
(10 mg/mL) was spin-coated through a 0.45 lm teflon filter, fol-
lowed by thermal annealing at 120 °C for 2 h. Finally, a thin layer
of TPBi (20 nm) was used as the hole-blocking layer. A LiF layer
(1 nm) and an Al layer (80 nm) were deposited successively in a
vacuum evaporation chamber. The voltage–current density–lumi-
nance curve was measured by a measuring system composed of
the R6145 (Advantest), the multimeter 2000 (Keithley), the lumi-
nance meter LS-110 (Minolta), and the power meter 1835-C (New-
port), while the electroluminescence (EL) spectra were recorded by
the fiber optic spectrometer S2000 (Ocean Optics). All measure-
For g, cpppp, white flakes, yield: 56%. m.p. 302–304 °C. 1H NMR
(CDCl3, 400 MHz), d: 9.11 (s, H); 8.36–8.32 (d,2H); 8.18–8.16 (t,
4H); 7.92–7.90 (d, 2H); 7.85–7.83 (d, 2H); 7.81–7.79 (d, 2H);
7.75–7.73 (d, 4H); 7.52–7.50 (m, 6H); 7.46–7.43(t, 4H); 7.34–
7.30(t, 4H). Anal. Calc. for C47H31N3: C, 88.54; H, 4.87; N, 6.59.
Found: C, 88.37; H, 4.63; N, 6.55%.
ments were carried out by
environment.
a
computer under ambient
4.3.3. General procedure for the synthesis of complex 1–4 [18,19]
The synthetic procedures for complex 1–4 were quite similar.
The following is the procedure for complex 2:
4.3. Synthesis experiment
First, the synthesis of apppp2Ir(l-Cl)2Irapppp2 dimer: to a
4.3.1. General procedure for the synthesis of 4-(N,N-
diphenylamino)phenyl boronic acid (a) and 4-(N-carbazolyl)phenyl
boronic acid (b)
50 mL three-necked flask protected by N2 containing 15 mL 2-eth-
oxyethanol, 5 mL water, 1.224 g (2.2 mmol) of apppp was added.
The solution was stirred for 30 min. Then, 0.299 g (1 mmol) of
IrCl3ꢁ3H2O was added and the solution was refluxed for 25 h. After
cooling, the solution was filtered and washed by methanol, ether
and hexane. 0.88 g of yellow powder was obtained, yield: 70%.
m.p. > 300 °C.
Secondly, the complex: to a 50 mL three-necked flask equipped
with a magnetic stirrer and protected by N2, containing 15 mL 2-
ethoxyethanol, 0.06 mL (0.4 mmol) of acetylacetone (acac), 0.24 g
To a three-necked flask containing 10 mmol Ar–Br and 50 ml
THF protected by N2 and cooled by dry-ice (ꢀ78 °C), was slowly
added 16 mmol n-BuLi and the reaction was kept at ꢀ78 °C for
1 h. 30 mmol B(OCH3)3 was added to the flask rapidly and the reac-
tion was continued for 2 h. As the temperature was raised to 0 °C,
50 ml 2 M HCl was added to the flask and the reaction continued
for another 3 h. Ether was used to extract the product and the or-
ganic layer was evaporated to dryness. White powder was
obtained.
Na2CO3, was added to 0.534 g (0.2 mmol) apppp2Ir(l-Cl)2Irapppp2,
after refluxing for 48 h under N2, the solution was cooled to room
temperature, red solid powers were obtained. The powders were
filtered and washed buy water, methanol, ether and hexane. The
red residues were chromatographed on a 200–400 mesh silica
gel with dichloromethane mobile phase to yield ꢀ0.3 g (63%) pure
apppp2Ir(acac). 1H NMR(CDCl3, 400 MHz), d: 7.367–6.874 (m, 68
H); 1.280 (s, 6H). Anal. Calc. for C99H75IrN6O2: C, 75.60; H, 4.81;
N, 5.34. Found: C, 74.97; H, 5.55; N, 4.72%. ESI-MS: m/z 1572.6
[M]+.
Yield for a: 70%. m.p. 218 °C, 1HNMR(CDCl3, 400 MHz), d: 8.02–
7.99 (d, 2H); 7.31–7.25 (m, 6H); 7.16–7.14 (d, 4H); 7.10–7.04 (m,
4H). Yield for b: 80%. m.p. 261–262 °C.
4.3.2. General procedure for the synthesis of 2,5-bis(40,400-N,N-
diphenylamino) phenyl pyridine (bppp, c), 2,5-bis(40,400-9H-9-
carbazolyl)phenyl pyridine (bcpp, d), and 5-bromo-2-(40-
bromophenyl)pyridine (e)
To a three-necked flask protected by N2 containing 2 mmol 2,5-
dibromopyridine, 4.57 mmol a, b, or 4-bromophenylboronic acid,
was added 20 ml toluene and 10 ml ethanol, 0.2 mmol Pd (PPh3)4
and 20 mmol saturated K2CO3 solution. After refluxing for 36 h,
the product was extracted and the organic phase was collected
and evaporated to dryness. Chromatography of the resulting resi-
due on 200–400 mesh silica gel eluting with dichloromethane af-
fords c, d and e. The solvent was evaporated and the solid was
recrystallized in ethanol. Pale green crystals were obtained.
For c, yield 70%. m.p. 217 °C. 1H NMR (CDCl3, 400 MHz), d: 8.87
(s, 1H, Py–H); 7.91–7.90 (t, 3H); 7.72 (s, 1H); 7.51–7.50 (d, 2H);
7.30–7.26 (m, 8H); 7.18–7.14 (m, 12H); 7.07–7.04 (m, 4H). Anal.
Calc. for C41H31N3: C, 87.05; H, 7.43; N, 5.52. Found: C, 86.5; H,
7.31; N, 5.33%.
For (bppp)2Ir(acac), 1: yellow powder, yield: 63%. m.p. > 300 °C,
dec. 1H NMR (CDCl3, 400 MHz), 7.363–7.324 (t, 7H); 7.260 (s, 9H);
7.205–7.186 (d, 7H); 7.164–7.068 (m, 12H); 7.013–6.992 (d, 6H);
6.943–6.904 (t, 7H); 6.829–6.810 (d, 6H) 6.753–6.731 (d, 3H);
6.703–6.667 (t, 3H), 1.558 (s, 6H). Anal. Calc. for C87H67IrN6O2: C,
73.57; H, 4.75; N, 5.92. Found: C, 73.61; H, 4.72; N, 6.09%. ESI-
MS: m/z 1390.5 [Mꢀ2CH3]+; 1321.5 [Mꢀacac]+.
For (bcpp)2 Ir(acac), 3, yellow powder, yield: 65%. 1H NMR
(CDCl3, TMS), d: 7.561–7.077 (m, 52H); 1.574 (s, 6H). Anal. Calc.
for C87H63IrN6O2: C, 73.97; H, 4.21; N, 5.95. Found: C, 73.87; H,
4.74; N, 6.10%. ESI-MS: m/z 1382.4 [MꢀCH3]+; 1413.4 [Mꢀacac]+.
For (cpppp)2Ir(acac), 4, yellow powder, yield: 66.0%. 1H NMR
(CDCl3, 400 MHz), d: 8.175–7.185 (m, 60H); 1.258 (s, 6H). Anal.
Calc. for C99H67IrN6O2: C, 75.99; H, 4.32; N, 5.37. Found: C, 74.41;
H, 4.11; N, 5.68%. ESI-MS: m/z 1548.4 [MꢀHꢀCH3]+.
For d: yield: 55%. m.p. 272–27 °C, 1H NMR (CDCl3, TMS), d: 9.11
(s, 1H); 8.34–8.32 (d, 2H); 8.19–8.17 (2, 4H); 8.08–8.07 (d, 1H);
7.93–7.90 (d, 1H); 7.87–7.85 (d, 2H); 7.76–7.73 (d, 4H); 7.53–
7.51 (d, 4H); 7.47–7.43 (t, 4H); 7.35–7.32 (m, 4H). Anal. Calc. for
Acknowledgements
C
41H27N3: C, 87.67; H, 4.99; N, 7.48. Found: C, 88.22; H, 4.85; N,
This work is jointly supported by NSFC (50833001, 60868001),
OST (2011CB933300) and MOE (309001), China.
7.17%.

D. Wang et al. / Inorganica Chimica Acta 370 (2011) 340–345
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