Novel orange-red light-emitting polymers with cyclometaled iridium complex grafted in alkyl chain

Article abstract of DOI:10.1016/j.jorganchem.2009.05.007

Novel poly(fluorene-alt-carbazole) (PFCz) based copolymers with 3,6-carbazole-N-alkyl grafted iridium complex using 2,3-diphenylpyrazine as ligand (IrBpz) were synthesized by Suzuki polycondensation. The emission of host polymer, PFCz, was completely quen

Full text of DOI:10.1016/j.jorganchem.2009.05.007

Journal of Organometallic Chemistry 694 (2009) 2727–2734
Contents lists available at ScienceDirect
Journal of Organometallic Chemistry
journal homepage: www.elsevier.com/locate/jorganchem
Novel orange-red light-emitting polymers with cyclometaled iridium
complex grafted in alkyl chain
*
Lei Ying, Jianhua Zou, Anqi Zhang, Bing Chen, Wei Yang , Yong Cao
Institute of Polymer Optoelectronic Materials and Devices, Key Laboratory of Specially Functional Materials, Ministry of Education, South China University of Technology,
Guangzhou 510640, China
a r t i c l e i n f o
a b s t r a c t
Article history:
Novel poly(fluorene-alt-carbazole) (PFCz) based copolymers with 3,6-carbazole-N-alkyl grafted iridium
complex using 2,3-diphenylpyrazine as ligand (IrBpz) were synthesized by Suzuki polycondensation.
The emission of host polymer, PFCz, was completely quenched when the copolymer with 1 mol% of irid-
ium complex. An orange-red emission with CIE coordinate of (0.56, 0.42) was observed from Phosphores-
cent polymer light-emitting diodes (PhPLEDs). The PhPLEDs made by this copolymer–iridium complex
showed a maximum luminous efficiency (LE) of 5.58 cd/A and a maximal luminance of 8625 cd/m2.
White light with CIE coordinate of (0.33, 0.27) was observed from white PhPLEDs (WPhPLEDs) made
by the copolymer containing 0.4 mol% iridium complex. A LE of 2.30 cd/A with luminance of 2068 cd/
m2 was observed from WPhPLEDs.
Received 19 January 2009
Received in revised form 7 May 2009
Accepted 8 May 2009
Available online 15 May 2009
Keywords:
Fluorene-alt-carbazole copolymer
Ir complex
Light-emitting diode (LED)
Ó 2009 Elsevier B.V. All rights reserved.
1. Introduction
by one conjugated polymers containing phosphorescent dyes in
polymer main chain. Recently, our group reported the poly(2,7-flu-
Phosphorescent polymer light-emitting diodes (PhPLEDs) have
been attracted the attention of scientist during last decade because
their internal quantum efficiency is theoretically 100% and they
can be fabricated by low-cost wet process techniques [1,2]. In Gen-
eral, the emissive layer of PhPLEDs was fabricated by conjugated
polymers blended with phosphorescent dyes [3]. These PhPLEDs
exhibited high luminous efficiency (LE) and high brightness, how-
ever, these PhPLEDs are unstable because phase separation and
triplet–triplet annihilation at the bias of high current densities. In
order to resolve this problem, an alternative approach is to fabri-
cate PhPLEDs by conjugated polymers chemically bonded with
phosphorescent dyes, i.e. to copolymerize phosphorescent dyes
in conjugated polymer backbone [4] or to graft phosphorescent
dyes into polymer side chain by a long alkyl chain [5]. These con-
jugated polymers containing phosphorescent dyes allow for the
formation of well-designed solid-state materials while the phase
separation or dopant aggregation could be restrained and the
PhPLEDs with high LE and brightness are expected.
orene-alt-3,6-carbazole) (PFCz) derivatives with phosphorescent
iridium complexes in polymer side chain [9]. In these new materi-
als, the emission from the host PFCz is completely quenched by the
incorporated iridium complexes, and emissions of these polymers
are mainly relied on the incorporated iridium complexes [10].
In this paper, we reported the synthesis of PFCz–IrBpz, an irid-
0
ium(III)bis(2,3-diphenylpyrazine-N,C2 )-2,4-pentadiketone (IrBpz)
as an phosphorescent dyes chemically bonded with PFCz side chain
by alkyl side chain. We demonstrated that the PhPLEDs with CIE
coordinate of (0.56, 0.42) and a LE of 5.58 cd/A due to the emission
of IrBpz from PFCz–IrBpz was observed by carefully tune the con-
tent of IrBpz in PFCz. Moreover, WPhPLEDs with CIE coordinate of
(0.33, 0.27) and a LE of 2.30 cd/A was achieved from PFCz–IrBpz via
further tuning the content of IrBpz in PFCz to realize the emission
from PFCz and IrBpz.
2. Results and discussion
Among PhPLEDs, white PhPLEDs (WPhPLEDs) are of particular
interests because their potential applications in full-color flat panel
displays and solid state lighting sources [6]. Various approaches
including a simultaneously incorporating three primary colors
(red, green and blue) [7] or two complementary colors [8] into
one polymer main chain have been reported to realize WPhPLEDs
2.1. Synthesis of monomers and polymers
The ligand 2,3-diphenylpyrazine (2) was prepared in high
yield from dehydration of 2,3-diphenyl-5,6-dihydropyrazine (1)
with FeCl3 in dehydrate ethanol. By treatment of the bisenolate
of 2,4-pentanedione with 3,6-dibromo-9-(100-bromodecane)car-
bazole with sodium hydro in absolute THF, the b-diketone was
successfully tethered into the side chain of carbazole-N of com-
pound 5 by long alkyl chain with 70% yield. The reaction of the
* Corresponding author. Fax: +86 20 87110606.
E-mail address: pswyang@scut.edu.cn (W. Yang).
0022-328X/$ - see front matter Ó 2009 Elsevier B.V. All rights reserved.
doi:10.1016/j.jorganchem.2009.05.007

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L. Ying et al. / Journal of Organometallic Chemistry 694 (2009) 2727–2734
b-diketone ligand 5 with the crude chloro-bridged iridium dimer
3 in 2-ethoxyethanol under reflux for 16 h given the 3,6-dibro-
mocarbazole-N-decamethylene-tethered iridium complex (6) a
yield of 38%. The model iridium complex 4 was synthesized in
similar yield from this approach, and the yield was still as low
as 42%. The synthetic routes of these compounds are shown in
Scheme 1.
The reason for the low yield might be attribute to the side reac-
tion of generated hydrodebrominated derivatives, which has been
previously evidenced by Evans et al. [11]. Although the yield was
much lower than expectation, the 1H NMR spectrum of the 3,6-
dibromocarbazole-N-decamethylene-tethered iridium complex
(6) was well accordance with the target molecular structure while
only a trace of impurities was found. Molecular structure of 6 was
Scheme 1. Synthetic route for the compounds and polymers.

L. Ying et al. / Journal of Organometallic Chemistry 694 (2009) 2727–2734
2729
further verified by the data from both ESI-MS and elemental
analysis. In addition, a 1H–1H COSY spectrum enables the near-
complete assignment of all aromatic protons for the 3,6-dibromo-
carbazole-N-decamethylene-tethered iridium complex (6) in
deuterated chloroform except the detailed splitting of protons in
pyrazine ligand (adjacent to the aromatic phenyl carbon atoms
which coordinated with iridium core), which might caused by
face-to-face conformation of the iridium complex. Combining the
integral values of each of the peaks in the one-dimensional 1H
NMR spectrum and the coherence peaks of protons coupled over
two (geminal) or three (vicinal) bonds in 1H–1H COSY spectrum,
the assignment along with the protons chemical shifts of complex
6 is attained and the results are shown in Fig. 1.
The copolymers were prepared from 3,6-dibromo-9-(irid-
0
ium(III)bis(2,3-diphenylpyrazine-N,C2 ))-12,14-pentadecyldike-
tone)carbazole (6), 3,6-dibromo-9-(2-ethylhexyl)-carbazole [12]
(7), and 2,7-bis(4,4,5,5-tetramethyl-1,3,2-dixaborolan-2-yl)-9,9-
dioctylfluorene [13] (8) by Suzuki polycondensation (Scheme 1).
At the end of the polymerization, phenylboric acid and bromoben-
zene are added subsequently to remove the possible ended bromo-
or boric ester groups in the resulted polymers. The feed ratio of Ir
complex in the polycondensation are 0, 0.2, 0.4, 0.6, 1 and 2 mol%,
and the corresponding copolymers are named PFCz, PFCzIrBpz-02,
PFCzIrBpz-04, PFCzIrBpz-06, PFCzIrBpz-1 and PFCzIrBpz-2, respec-
tively. Average molecular weights (Mn) of these copolymers are
from 8200 to 10 200 with the polydispersity (PDI) in the range of
Fig. 1. 1H NMR (a) and 1H–1H COSY (b) of monomer 6.

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L. Ying et al. / Journal of Organometallic Chemistry 694 (2009) 2727–2734
Table 1
Molecular weight and electrochemical properties of polymers.
Polymer
Mn (ꢁ103)
PDI
Eox (V)
HOMO (eV)
LUMO (eV)
Eogpt (eV)
PFCzIrBpz-02
PFCzIrBpz-04
PFCzIrBpz-06
PFCzIrBpz-1
PFCzIrBpz-2
9.3
8.2
8.5
10.2
9.0
1.8
2.0
1.7
1.8
1.6
1.02
1.00
1.03
1.10
1.12
ꢀ5.42
ꢀ5.40
ꢀ5.43
ꢀ5.45
ꢀ5.47
ꢀ2.30
ꢀ2.27
ꢀ2.31
ꢀ2.33
ꢀ2.35
3.12
3.13
3.12
3.12
3.12
1.6–2.0, which is consistent with the Suzuki polycondesation pro-
cedure [14] (see Table 1).
The electrochemical behaviors of copolymers were investigated
by cyclic voltammetry (CV) in 0.1 M of tetrabutylammonium hexa-
fluorophosphate (Bu4NPF6) acetonitrile (CH3CN) solution. The CV
curves were referred to an Ag quasireference electrode, which
was calibrated using the ferrocene/ferrocenium redox couple
(0.35 V vs. Ag/AgCl) as an internal standard prior to measurements.
The photophysical and electrochemical properties of Ir complexes
and the redox potentials of copolymers derived from the onset in
the cyclic voltammetry are summarized in Table 1. The HOMO en-
ergy levels of polymers can be estimated using the empirical equa-
tion EHOMO = ꢀe(Eox + 4.40) (eV) [15]. However, since the redox
peaks cannot be recorded corresponding to Ir complex in the
copolymers, so the LUMO energy levels (ELUMO) is estimated from
both of the absorption onset (the optical energy gap, Eogpt) and
EHOMO. The oxidation for IrBpz observed at 0.96 V, thus the HOMO
energy level of IrBpz was calculated as ꢀ5.26 eV, which was slight
lower than that of PEDOT:PSS (ꢀ5.20 eV) but higher than that of host
PFCz (ꢀ5.47 eV). The LUMO energy level (ELUMO) was estimated to be
2.2. Photophysical and electrochemical properties
Fig. 2 shows the UV–vis absorption spectra of copolymer
PFCzIrBpz and Ir complex (IrBpz) and the PL spectrum of PFCz. It
was found that all of these copolymers have very similar UV–vis
spectra, and the characteristic absorption of IrBpz cannot be ob-
served because of their fairly low content level in copolymers.
The model Ir complex (IrBpz) has broad absorption band ranged
from 270 nm to 570 nm. An intense absorption band below
350 nm is attributed to the spin-allowed singlet state 1 * transi-
p–p
tion of cyclometalated ligands. A weak absorption band around
410 nm is assigned to the spin-allowed singlet metal-to-ligand
charge-transfer (1MLCT) transition. The strong absorption peaked
at 512 nm for IrBpz is originated from triplet metal-to-ligand
change-transfer (3MLCT) transition. Fig. 2 shows clearly that there
is a good spectral overlap between the PL emission of the host
copolymer PFCz and the absorption spectra of the guests (IrBpz)
which was shown clearly in Fig. 1. This good spectra overlap indi-
cated an efficient Förster energy transfer from the PFCz host to Ir
complex guests is expected [14].
ꢀ3.08 eV based on EHOMO and corresponding optical band gap ðEoptÞ.
g
In considering that the iridium complex (IrBpz) was tethered to PFCz
side chain by a long alkyl spacer, thus its EHOMO and ELUMO would not
distinctly change. In this case, both of the EHOMO and ELUMO would
fall within that of PFCz, so that the grafted IrBpz is expected to func-
tion as both hole and electron trapping center.
The photoluminescent (PL) spectra of the copolymers were
shown in Fig. 3. All of the emissions of copolymers are dominant
at 420 with a small shoulder at 585 nm. The emission peaked at
420 nm is attributed to the emission of host PFCz, while the
585 nm peaks are ascribed to the emission of grafted IrBpz com-
plex. The relative intensities at 420 nm remain almost independent
with the Ir complex (IrBpz) contents in the copolymers and the
emission at 585 nm increased gradually with the grafted IrBpz con-
tents. The PL quantum efficiencies of PFCz–IrBpz and PFCzIrBpz are
in the range of 45–60%.
2.3. Electroluminescent properties
In order to balance the carrier’s transporting, 30 wt% of 2-tert-
butylphenyl-5-biphenyl-1,3,4-oxadiazole (PBD) was blended with
the copolymers to make in the emissive layer because copolymer
exhibited a good hole transport property due to the incorporated
carbazole moiety into main chain of polymer, and PBD is well-
know electron transporting molecule [16]. The electroluminescent
(EL) spectra observed from the devices with a configuration of ITO/
Fig. 2. UV–vis of IrBpz and PL of IrBpz and PFCz.
Table 2
Electroluminescent properties of polymers.
Polymer
At maximal luminous efficiency
Lmax (cd/m2)
CIE (x, y)
Bias (V)
J (mA/cm2)
QE (%)
LE (cd/A)
PFCzIrBpz-02
PFCzIrBpz-04
PFCzIrBpz-06
PFCzIrBpz-1
PFCzIrBpz-2
6.4
5.4
6.0
5.6
5.2
1.7
8.7
12.8
7.7
8.0
0.18
1.84
2.80
4.46
2.91
0.23
2.30
3.50
5.58
3.64
136
(0.20, 0.12)
(0.33, 0.27)
(0.48, 0.38)
(0.56, 0.42)
(0.56, 0.43)
2068
4416
8625
5025
Device structure: ITO/PEDOT/polymer + PBD (30 wt%)/Ba/Al.

L. Ying et al. / Journal of Organometallic Chemistry 694 (2009) 2727–2734
2731
Fig. 3. PL spectra of copolymers.
Fig. 5. CIE coordinates (x, y) of polymers.
from IrBpz phosphorescent. Observed white light has CIE of
(0.33, 0.27) which is very close to that from pure white light
(0.33, 0.33). The observed CIE coordinates were shown in Fig. 5.
The devices performances were summarized in Table 2. The ap-
plied voltages from these devices made by various copolymers
were relatively low. This was probably due to the incorporated car-
bazole moiety in main chain of polymer resulting in high HOMO as
compared with polyfluorene homopolymers. The best device per-
formance was observed from PhPLEDs made by PFCzIrBpz-1. The
light observed from this device has
a CIE coordinate of
(0.56, 0.42). The devices exhibited a maximum LE of 5.58 cd/A with
brightness of 8625 cd/m2 at current density of 7.7 mA/cm2. The de-
vice performance became poor when a high content of IrBpz was
incorporated with copolymers. However, the white light was ob-
served from PhPLED made by PFCzIrBpz-04. The white light has
CIE coordinate of (0.33, 0.27). The WPhPLEDs exhibited a LEmax of
2.30 cd/A and brightness of 2068 cd/m2 at current density of
8.7 mA/cm2. We also observed a stable color when PhPLEDs and
WPhPLEDs were biased at different current densities. For the fabri-
cated WPhPLEDs based on PFCzIrBpz-04 as active layer, the CIE
coordinates varied from (0.33, 0.27) to (0.34, 0.25) while the corre-
sponding current density increased from 5 mA/cm2 to 100 mA/
cm2. These results demonstrated that the graft of phosphorescent
complexes by long alkyl side chain into polymer backbone is an
effective approach to obtain stable white light from WPhPLEDs,
particularly, at the bias of high current density [18].
Fig. 4. EL spectra of polymers.
PEDOT:PSS (40 nm)/polymer + PBD (30 wt%) (80 nm)/Ba (4 nm)/Al
(150 nm) were shown in Fig. 4. Unlike the PL spectra, the emission
from host PFCz was completely quenched when the content of
IrBpz reaches 1 mol%. The substantial differences in PL and EL indi-
cated that the operational mechanisms in PL and EL were different.
The HOMO and LUMO of the grafted iridium complex IrBpz were
within the band gap of the host copolymer (PFCz) (whose HOMO
and LUMO are ꢀ5.47 and ꢀ2.27 eV, respectively). Therefore, the in-
jected hole from the anode and the electron from the cathode
should be readily trapped by the grafted Ir complex sites [17]. In
other words, the grafted Ir complexes functioned as both hole
and electron trapping centers and dominated electrical excitation
processes in the devices. The EL spectra shown in Fig. 4 further
demonstrated that when the content of the grafted IrBpz is larger
than 1 mol%, the EL emission from host PFCz was completely
quenched. However, the dominated electrical excitation processes
in the devices can be tuned if the content of the grafted iridium
complex were controlled at a certain level [10]. Two simulta-
neously emissions both from PFCz (blue emission) and IrBpz
(orange-red emission) are expected.
3. Conclusion
Electrophosphorescent polymers grafted iridium complex by a
long alkyl chain were synthesized by Suzuki polycondensation.
The orange-red light with a CIE coordinate of (0.56, 0.42) was ob-
served from PhPLEDs made by copolymer with 1 mol% IrBpz into
PFCz. The PhPLEDs exhibited a LE of 5.6 cd/A. White light with a
CIE coordinate of (0.33, 0.27) was observed from WPhPLEDs made
by a copolymer of PFCzIrVpz-04, in which the content of IrBpz was
tuned to be 0.4% into PFCz. WPhPLEDs exhibited a LE of 2.30 cd/A
and stabilized white light at the bias of high current densities. All
these results demonstrated that semiconducting polymer contain-
ing metal complex is an efficiency approach to realize high perfor-
mance PhPLEDs and WPhPLEDs.
In order to obtain white light form PFCz–IrBpz via combination
blue emission from PFCz and organe-red emission from IrBpz, we
synthesized PFCzIrBpz04, where the content IrBpz is as low as
0.4 mol%. The EL spectra observed from PhPLEDs made by
PFCzIrBpz-04 shown two peaks. The blue emission was from PFCz
fluorescent and the orange-red emission, peaked at 585 nm) was

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L. Ying et al. / Journal of Organometallic Chemistry 694 (2009) 2727–2734
the light-yellow powder is obtained (yield: 78%). 1H NMR
4. Experimental
(300 MHz, CDCl3) d (ppm): 7.43–7.37 (m, 4H), 7.34–7.20 (m, 6H),
3.70 (s, 4H). 13C NMR (75 MHz, CDCl3) d (ppm): 160.30, 137.78,
129.64, 128.39, 127.91, 45.84. Elemental Anal. Calc. for C16H14N2:
C, 82.02; H, 6.02; N, 11.96. Found: C, 82.32; H, 5.92; N, 11.76%.
4.1. Materials and characterization
All manipulations involving air-sensitive reagents were per-
formed under an atmosphere of dry argon. All reagents, unless
otherwise specified, were obtained from Aldrich, Acros, and TCI
Co. and were used as received. 3,6-Dibromo-9-(2-ethylhexyl)-car-
bazole [15], 2,7-bis(4,4,5,5-tetramethyl-1,3,2-dixaborolan-2-yl)-9,
9-dioctylfluorene [15], 3,6-dibromo-9-(12,14-pentadecyldike-
tone)carbazole [13] and poly(fluorene-alt-carbazole) (PFCz) were
synthesized according to similar reported procedures.
4.3.2. Synthesis of 2,3-diphenylpyrazine (Bpz, 2)
2,3-Diphenyl-5,6-dihydropyrazine (4, 10 g, 27 mmol) was put
into a 500 ml three neck flask, and 100 ml of dehydrate ethanol
was added to be dissolved. Then, iron (III) chloride (8.8 g, 54 mmol)
of was added thereto, and this mixture was heated and stirred for
30 min at 60 °C to be reacted. After the reaction, 300 ml of water
was added to the reaction mixture and the precipitated solid was
filtered followed by dissolved in toluene. After this mixture was
washed with saturated saline, the solid was obtained by concen-
trating the solvent and purified by silica column chromatography.
The eluent was concentrated to obtain 6.3 g of an orange solid of
product in the yield of 60%. 1H NMR (300 MHz, CDCl3) d (ppm):
8.60 (s, 2H), 7.47–7.42 (m, 4H), 7.33–7.29 (m, 6H). 13C NMR
(75 MHz, CDCl3) d (ppm): 152.84, 142.11, 138.62, 129.66, 128.69,
128.30. Elemental Anal. Calc. for C16H12N2: C, 82.73; H, 5.21; N,
12.06. Found: C, 82.62; H, 5.39; N, 11.98%.
1H and 13C NMR spectra were recorded on a Bruker DRX 300
spectrometer operating respectively at 300 and 75 MHz, with tetra-
methylsilane (TMS) as a reference. The H,H-COSY spectrum was re-
corded and processed in the absolute value mode 10. The spectral
width was 5208.33 Hz; 8 accumulations, 1 K ꢁ 400 data points
(t2 ꢁ t1). The data point array was F2 ꢁ F1 = 1 K ꢁ 1 K for Fourier
transformation after zero filling. The probe temperature was regu-
lated at 298 K. Direct injection mass spectra were recorded by the
electron spray impact (ESI) method on a LCQ DECA XP Liquid Chro-
matography–Mass Spectrometer (Thremo Co.). Molecular weight
determination was obtained using a Waters GPC 2410 in tetrahy-
drofuran via a calibration curve of polystyrene standards. Elemental
analyses were performed on Vario EL Elemental analysis instru-
ment (Elementar Co.). Samples were pressed as homogeneous tab-
lets ( = 30 mm) of compressed (375 MPa) powder of the
copolymers. UV–vis absorption spectra were recorded on a HP
8453 spectrophotometer. The PL quantum yields were determined
in an integrating sphere ISO80 (Labsphere) with 325 nm excitation
of HeCd laser (Mells Griot). Cyclic voltammetry was carried out on a
potentiostat/galvanostat model at a scan rate of 50 mV/s against
Ag/AgCl reference electrode with nitrogen-saturated solution of
0.1 M tetrabutylammonium hexafluorophosphate (Bu4NPF6) in
acetonitrile (CH3CN). Element analyses were performed on Vario
EL Elemental analysis instrument (Elementar Company).
4.3.3. Synthesis of chloride-bridged dimer [Ir(Bpz)2Cl]2 (3)
First, with the use of a mixture of 30 ml of 2-ethoxyethanol and
10 ml of water as a solvent, 1.86 g of the ligand 2,3-diphenylpyr-
azine (5) and 0.96 g of iridium chloride (IrCl3 3H2O) are mixed in
100 ml of flask with magnetic strirrer. Then the mixture was held
at reflux for 17 h in a nitrogen atmosphere to obtain a dinuclear
complex [Ir(Bpz)2Cl]2 (brown powder, yield: 35%). The product
was used directly for the next step without further purification.
1H NMR (300 MHz, CDCl3) d (ppm): 8.80 (d, J = 3.24 Hz, 4H), 8.26
(d, J = 3.18 Hz, 4H), 7.75 (d, J = 3.48 Hz, 8H), 7.40 (m, 12H), 6.74
(d, J = 7.95 Hz, 4H), 6.58 (td, J = 1.26 Hz and 6.72 Hz, 4H), 6.46 (t,
J = 7.98 Hz, 4H), 6.02 (t, J = 7.26 Hz, 4H).
0
4.3.4. Synthesis of iridium(III)bis(2,3-diphenylpyrazine-N,C2 )-2,4-
4.2. Device fabrication and characterization
pentadiketone (IrBpz, 4)
Chloride-bridged dimer [Ir(Bpz)2Cl]2 (3) (0.45 g, 0.345 mmol),
2,4-pentadiketone (0.09 g, 0.885 mmol), and sodium carbonate
(0.1 g) were mixed and refluxed in 2-ethoxylethanol (30 ml) for
16 h under a nitrogen atmosphere. The solution was cooled to
room temperature and filtered before washing with water and
hexane. The crude products were purified by silica chromatogra-
phy (40% dichloromethane and 60% petroleum ether) with yield
of 42%. 1H NMR (300 MHz, CDCl3) d (ppm): 8.50 (dd, J = 0.72 Hz
and 3.15 Hz, 2H), 8.33 (d, J = 3.15 Hz, 2H), 7.69 (m, 4H), 7.52 (m,
6H), 6.86 (d, J = 8.07 Hz, 2H), 6.67 (t, J = 7.38 Hz, 2H), 6.49 (t,
J = 8.04 Hz, 2H), 6.36 (d, J = 7.62 Hz, 2H), 5.29 (s, 1H), 1.87 (s, 6H).
Polymers were dissolved in p-xylene and filtered with
a
0.45 m PTFE filter. Patterned ITO coated glass substrates were
l
cleaned with acetone, detergent, distilled water and 2-propanol
followed by in an ultrasonic bath. After treated with oxygen plas-
ma, 50 nm of poly(3,4-ethylenedioxythiophene) doped with
poly(styrenesulfonic acid) (PEDOT:PSS, Batron-P 4083, Bayer AG)
was spin-coated onto the ITO substrates followed by drying in a
vacuum oven at 80 °C for 8 h. A thin film of polymers was coated
onto the resulting PEDOT:PSS layer by spin-casting inside a glove
box filled with nitrogen. The film thickness of the active layers
was around 75–80 nm, as determined with an Alfa Step 500 sur-
face profiler (Tencor). Current–Voltage (I–V) characteristics were
recorded with a Keithley 236 source meter. EL spectra were ob-
tained by Oriel Instaspec IV CCD spectrograph. Luminance was
measured by a calibrated silicon photodiode and calibrated by a
photometer (PR705, Photo Research). The external quantum effi-
ciency was determined by a calibrated silicon photodiode in an
integrating sphere (ISO80, Labsphere).
13C NMR (75 MHz, CDCl3)
d (ppm): 185.60, 161.90, 153.31,
149.80, 142.62, 140.91, 139.91, 139.06, 132.49, 129.57, 129.49,
129.02, 128.88, 120.72, 100.73. Elemental Anal. Calc. for C37H29Ir-
N4O2: C, 58.95; H, 3.88; N, 7.43. Found: C, 58.83; H, 3.60; N, 7.60%.
4.3.5. Synthesis of 3,6-dibromo-9-(12,14-
pentadecyldiketone)carbazole (5)
In a 50 ml two-neck flask with magnetic stirrer, sodium hydride
(60% dispersion in mineral oil; 320 mg, 8.00 mmol) was washed
thoroughly with tetrahydrofuran (THF) under protection of argon
to remove the mineral oil, and 20 ml THF was then added to the
flask. Subsequently, 2,4-pentanedione (0.80 ml, 7.8 mmol) was
added dropwise over 20 min to a stirred suspension of the sodium
hydride in THF (20 ml) at 0 °C. The resultant mixture was stirred
for 30 min at 0 °C. n-Butyllithium (2.5 M in hexane; 4.9 ml,
7.8 mmol) was added dropwise over 20 min to the stirred mixture
at 0 °C. The resultant solution was stirred for 25 min at 0 °C. A solu-
4.3. Synthesis of monomers
4.3.1. Synthesis of 2,3-diphenyl-5,6-dihydropyrazine (1)
First, with the use of 300 ml of dehydrated ethanol as a solvent,
21.0 g (100 mmol) of benzyl and 6.1 g (101 mmol) of ethylenedia-
mine are held at reflux in a nitrogen atmosphere for 6 h. Then the
solution is condensed to one fifth, and a produced precipitation is
collected. By washing the obtained precipitation with cool ethanol,

L. Ying et al. / Journal of Organometallic Chemistry 694 (2009) 2727–2734
2733
tion of 3,6-dibromo-9-(100-bromodecane)carbazole (1.62 g,
2.58 mmol) in THF (5 ml) was added dropwise over 10 min to the
stirred solution at 0 °C. The resultant mixture was stirred for 1 h
at 0 °C and for a further 1 h at room temperature, after which it
was quenched with aqueous ammonium chloride (10 wt%, 8 ml).
The mixture was acidified with concentrated hydrochloric acid to
pH 1 and the aqueous phase was separated and extracted with
diethyl ether. The combined organic phases were washed with sat-
urated aqueous sodium bicarbonate, dried with anhydrous magne-
sium sulfate and evaporated under reduced pressure. The crude
product was purified by silica chromatography using petroleum
ether/ethyl acetate as eluent to give the tethered ligand as white
solid in yield of 70%. 1H NMR (300 MHz, CDCl3) d (ppm): 15.51
(s, 1H, enolone 3-H3), 8.13 (d, J = 1.89 Hz, 2H), 7.54 (dd,
J = 1.89 Hz and 8.70 Hz, 2H), 7.27 (d, J = 8.70 Hz, 2H), 5.48 (s,
0.8H, enolone 3-H), 4.23(t, J = 7.14 Hz, 2H), 3.56 (s, 0.4 H, dione
3-H2), 2.49 (t, J = 7.32 Hz, 0.4 H, dione 5-H2), 2.24 (t, J = 7.41 Hz,
1.6 H, enolone 5-H2), 2.23 (s, 0.6 H, dione 1-H3), 2.05 (s, 2.4H, eno-
lone 1-H3), 1.81 (m, 2H), 1.57 (m, 2H), 1.42–1.25 (m, 14H). 13C
NMR (75 MHz, CDCl3) d (ppm): 194.32, 191.41, 139.31, 129.00,
123.44, 123.25, 111.93, 110.40, 99.76, 43.34, 38.27, 29.42, 29.39,
29.34, 29.28, 29.21, 29.18, 28.83, 27.19, 25.68, 24.99. Elemental
Anal. Calc. for C27H33Br2NO2: C, 57.56; H, 5.90; N, 2.49. Found: C,
57.29; H, 6.00; N, 2.52%.
end-capping reagent by heating for another 12 h to remove the
resident boronic ester end groups. The whole mixture was poured
into methanol. The precipitated polymer was recovered by filtra-
tion and purified by silica column chromatography with toluene
as eluent to remove small molecular fraction and residue catalyst
(yield 69%). 1H NMR (300 MHz, CDCl3) d (ppm): 8.54 (br, 2H),
7.86 (br, 2H), 7.78 (br, 2H), 7.73 (br, 2H), 7.56 (m, 2H), 7.24 (m,
2H), 4.32 (m, 2H), 2.10 (m, 1H), 1.95 (m, 4H), 1.52–0.78 (m, 44H).
Acknowledgements
We thank the National Natural Science Foundation of China
(No. 20574021 and U0634003), and the Ministry of Science and
Technology of China (Project No. 2009CB613403) for the financial
support.
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