Polymers with alkyl main chain pendent biphenyl carbazole or triphenylamine unit as host for polymer light emitting diodes

Article abstract of DOI:10.1016/j.polymer.2012.08.042

The soluble styrene polymers, bearing dicarbazole, phenylcarbazole or phenyltriphenylamine side groups were investigated as a host material for green emitter in phosphorescent PLED devices. Those polymers were synthesized by free radical polymerization via azobisisobutyronitrile (AIBN) as initiator under 75 °C. All of the host materials exhibit high thermal stability with high decomposition (T_{d,5% weight loss} > 398 °C) and glass transition temperatures (T_g > 172 °C). The HOMO (ca. -5.39 -5.69 eV) and LUMO (ca. -2.22 -2.41 eV) levels with the triplet energy of ca. 2.50-2.93 eV suggest that polymers are suitable for host materials for green emitter. The devices based on the emissive layers containing host materials doped with Ir(ppy)₃ (4 wt%) display stable green emission with high device performances. The brightness and current efficiency reach 15,800 cd/m² and 17.5 cd/A, respectively, at the optimum blending with 40 wt% 2-(4-biphenyl)-5-(4-tert-butylphenyl)-1,3,4-oxadiazol (t-PBD). Furthermore, the device performance reached higher brightness (23,400 cd/m²) and current efficiency (12.3 cd/A) when mixture with 2,4,6-triphenyl-1,3,5-triazine (TRZ) and t-PBD.

Full text of DOI:10.1016/j.polymer.2012.08.042

Polymer 53 (2012) 4983e4992
Contents lists available at SciVerse ScienceDirect
Polymer
journal homepage: www.elsevier.com/locate/polymer
Polymers with alkyl main chain pendent biphenyl carbazole or triphenylamine
unit as host for polymer light emitting diodes
Ching-Nan Chuang a, Hsin-Jou Chuang a, Yu-Xun Wang c, Szu-Hsien Chen a, Jau-Jiun Huang c,
,
c
,
a,b,
*
Man-kit Leung a
**
, Kuo-Huang Hsieh
a Institute of Polymer Science and Engineering, National Taiwan University, Taipei 106, Taiwan
b Department of Chemical Engineering, National Taiwan University, Taipei 106, Taiwan
c Department of Chemistry, National Taiwan University, Taipei 106, Taiwan
a r t i c l e i n f o
a b s t r a c t
Article history:
The soluble styrene polymers, bearing dicarbazole, phenylcarbazole or phenyltriphenylamine side
groups were investigated as a host material for green emitter in phosphorescent PLED devices. Those
polymers were synthesized by free radical polymerization via azobisisobutyronitrile (AIBN) as initiator
under 75 ꢀC. All of the host materials exhibit high thermal stability with high decomposition (Td,5% weight
Received 16 May 2012
Received in revised form
14 August 2012
Accepted 18 August 2012
Available online 24 August 2012
> 398 ꢀC) and glass transition temperatures (Tg > 172 ꢀC). The HOMO (ca. ꢁ5.39 ‒ ꢁ5.69 eV) and
loss
LUMO (ca. ꢁ2.22 ‒ ꢁ2.41 eV) levels with the triplet energy of ca. 2.50e2.93 eV suggest that polymers are
suitable for host materials for green emitter. The devices based on the emissive layers containing host
materials doped with Ir(ppy)3 (4 wt%) display stable green emission with high device performances. The
brightness and current efficiency reach 15,800 cd/m2 and 17.5 cd/A, respectively, at the optimum
blending with 40 wt% 2-(4-biphenyl)-5-(4-tert-butylphenyl)-1,3,4-oxadiazol (t-PBD). Furthermore, the
device performance reached higher brightness (23,400 cd/m2) and current efficiency (12.3 cd/A) when
mixture with 2,4,6-triphenyl-1,3,5-triazine (TRZ) and t-PBD.
Keywords:
Host material
Light-emitting diodes
Ó 2012 Elsevier Ltd. All rights reserved.
1. Introduction
singlet and triplet excitons of emitting layer zone. The suitable
polymer host not only should possess proper HOMO/LUMO energy
Polymer light-emitting diodes (PLEDs) promise new flat-panel
or flexible display and solid-state lighting technologies fabricated
by low-cost solution processing [1]. The efficiencies of phospho-
rescent PLEDs (PhPLEDs) have advanced rapidly in recent years
because of the phosphorescent dopants dispersed in a polymeric
host have attracted extensive attention because of their inexpen-
sive solution-processing techniques and harvest both singlet and
triplet excitons and achieve an internal electron-to-photon
quantum efficiency of 100% [2e16]. However, the solution pro-
cessing in fabrication of PhPLEDs has a single-layer configuration
with the emissive layer sandwiched between the cathode and
anode. During the device operation, electrons and holes are injec-
ted from cathode and anode to the polymer host and generate
levels matching with the anode/cathode to facilitate charge carrier
injection but also have a high triplet energy level (ET) to prevent
triplet energy back transfer from the dopant to the host and the
consequent quenching of triplet excitons [17e19]. Disappointedly,
almost of polymer host materials with both high ET and proper
LUMO/HOMO energy levels are scarce. In general,
p-conjugated
polymers usually have low ET levels, which are not suitable as host
materials for blue and green phosphorescent heavyemetal
complexes [19,20], such as polyfluorene and its derivatives which
are the widely used
p-conjugated polymer host materials possess
low ET of 2.15e2.3 eV [21,22]. One effective strategy to improve
the ET levels of polymer host materials is to design the nonlinear
p-conjugated polymers via limiting the delocalization length of
carriers and excitons [23].
However, poly(n-vinylcarbazole) (PVK) has a low lying HOMO
energy level of ꢁ5.8 eV (ET of 2.5 eV), which mismatches work
function of common anode and results in difficult hole injection
[20]. Moreover, PhPLEDs using PVK all exhibit short lifetime.
Therefore, it is strongly required to develop polymer host with both
high ET and proper LUMO/HOMO energy levels. Highly efficient and
* Corresponding author. Department of Chemical Engineering, National Taiwan
University, Taipei 106, Taiwan. Tel.: þ886 2 33663044; fax: þ886 2 3366 5237.
** Corresponding author. Department of Chemistry, National Taiwan University,
Taipei 106, Taiwan. Tel.: þ886 2 33661673; fax: þ886 2 3366 5237.
E-mail addresses: mkleung@ntu.edu.tw (M.-k. Leung), khhsieh@ntu.edu.tw
(K.-H. Hsieh).
0032-3861/$ e see front matter Ó 2012 Elsevier Ltd. All rights reserved.
http://dx.doi.org/10.1016/j.polymer.2012.08.042

4984
C.-N. Chuang et al. / Polymer 53 (2012) 4983e4992
bright PLEDs have been reported by blending a PVK-matrix with
phosphorescent dopants, electron-, and additional hole-
transporting molecules [5,24e25]. Following this idea, a phospho-
rescent dopant blended together with an electron and a hole
transporting material can be considered as an emissive layer in
a single layer device. This approach opens an easy way to investi-
gate new polymer charge transport materials for PLEDs. Charge-
transporting materials have to meet a wide range of demands,
primarily electronic characteristics in respect to efficiency and
brightness, adaptable energy levels, high purity, availability, proc-
essability, high glass-transition temperatures, and a long-term
stability. Polystyrene is known to be a chemically stable and opti-
cally inert polymer. Therefore, Chen et al. [26e28] reported
a polymer matrix system based on polystyrene with covalently
fixed electron- and hole-transporting side functionalities, but the
system had a drawback of the random copolymer that creates
exciplex emission to result in device performance drop down.
Therefore Ogino et al. [46] and Fréchet et al. [47] reported some
block copolymers to avoid exciplex to produce. Further, to avoid
phase separation and degradation during PLED operation, the
phosphorescent complex was attached to the polystyrene back-
bone and for those systems current efficiencies up to 17 cd/A were
observed.
rate of 10 ꢀC minꢁ1 under a nitrogen atmosphere. The temperature
of degradation (Td) corresponds to a 5% weight loss. UVevis
absorption spectra were taken using a Jasco V-570 UVeVis spec-
trophotometer. Fluorescence spectra were recorded on a Hitachi-
4500 spectrofluorometer. Phosphorescence spectra were recorded
on a Hitachi-4500 spectrofluorometer. Triplet energy level esti-
mated from the first peak of highest-energy phosphorescence at
77 K in THF [34]. Cyclic voltammograms (CVs) were recorded on
a CHI Instruments Electrochemical Analyzer CHI1127 using plat-
inum and platinum wire as working and counter electrodes at
a scan rate of 100 mV sꢁ1 and a Ag/Agþ (0.10 M of AgCl solution) as
reference electrode in an anhydrous and argon-saturated solution
of 0.1 M of tetrabutylammonium perchlorate (Bu4NClO4) in ben-
zonitrile as the supporting electrolyte. In these conditions, the
oxidation potential (E1/2,Ox) of ferrocene was 0.43 V versus SCE. The
HOMO energy level was determined from the oxidation onset from
CV data taking into account the SCE level at ꢁ4.8 eV [29,30]. Elec-
trochemical onsets were determined at the position where the
current starts to differ from the baseline. The thickness of the
polymer films was measured using an Alpha step Dektak 3030
profilometer. Electroluminscence was recorded on a Minolta CS-
100A instrument. The morphology of cross-sectioned thin film
samples was observed using a FEI Tecnai operated at 200 kV. A
multimode AFM (Veeco) was used in a tapping mode to investigate
the two-dimensional surface topology of the SCzCz, SDBCz and
STPA films on ITO/glass substrate as used for device fabrication. The
IeV and LeV characteristics of the devices were measured by
integrating a Keithley 2400 source-meter as the voltage and current
source and a Minolta CS100A instrument as the Luminance
detector. All the measurements and device fabrications were per-
formed in air at room temperature under a dust-controlled
environment.
Following this method, we established
a series of hole-
transporting monomers (carbazole and triphenylamine) by
attaching these materials directly at the polystyrene chain. In this
article, we present the monomer and polymer syntheses and
investigated the electrochemical, optical, thermal property and
electroluminescent behavior of the host materials in blend systems
with t-PBD and TRZ as electron transporting materials, Ir(ppy)3 as
phosphorescent dopant and compare the results with the well-
known polymer of PVK.
Device fabrication: The indium-tin oxide (ITO) glass plates were
cleanedbysonicationandrinsingindeionizedwater, Triton-100water
solution, deionized water, acetone, and then methanol. A 30 nm thick
ITO-modifying layer of poly(ethylenedioxythiophene):poly(styrene
sulfonic acid) (PEDOT:PSS) with Triton-100 (10:1 Vol.%) was spin-
coated (5000 rpm, 60 s) on top of the ITO and then baked for 30 min
at 130 ꢀC under vacuum. Thin films of the emitting layer (EML) were
spin-coated from their solution in chloroform (10 mg/mL) was filtered
2. Experimental
2.1. Materials and characterization
Materials: Chemicals and solvents were reagent grades and
purchased from Aldrich, ACROS, Fluka, and Lancaster Chemical Co.
THF, dichloromethane, NMP and benzonitrile were distilled over
sodium/benzophenone, P2O5 calcium hydride and magnesium
sulfate respectively and freshly distilled before use. Azobisisobu-
tyronitrile (AIBN) and tetrabutylammonium perchlorate (Bu4NClO4)
were recrystallized twice from ethanol and ethyl acetate and further
dried for one day under vacuum. PEDOT:PSS (CLEVIOUS P VP. AI
4083) was purchased from Heraeus. The other chemicals were used
without further purification. Column chromatography was carried
through a membrane filter with the channel size of 0.45 mm. The
substrate was then thermally annealed in vacuum at 80 ꢀC for 5 min.
After being cooled, the substrate was transferred to a vacuum thermal
evaporator. A2nmthicklayerofMgwasdepositedatapressurebelow
5ꢂ10ꢁ6 torrthroughamask,andanotherlayerof100nmthickAgwas
deposited on the top as a protecting layer for Mg. The deposition rates
for Mg and Ag cathodes are 1 and 4 Å/s, giving an active area of
0.126 cm2. The thicknessforeachlayer was measured byanAlpha step
instrument.
out on silica gel (size 40e63
mm, pore size 60 Å, Silicycle). The
chemical structures for all products were confirmed by 1H and 13C
NMR spectroscopy, mass spectra (FAB) and elemental analyses.
Characterization: 1H and 13C NMR spectra were recorded on
2.2. Monomer synthesis
a
Bruker 400 MHz spectrometer apparatus in appropriated
deuterated solvent solution at 298 K, unless specified otherwise.
Chemical shifts were reported as values (ppm) relative to an
2.2.1. 3,6-Diiodocarbazole (1) [31,32]
d
To a round bottom flask (250 mL, two-neck), equipped with
a magnetic stir under atmosphere, was loading a solution of
carbazole (15 g, 89.71 mmol), KI (19.36 g, 116.62 mmol), KIO3
(19.20 g，89.71 mmol), acetic acid (100 mL) and deionized water
(10 mL). The iodination reaction was continued at 80 ꢀC for 48 h.
After cooling to room temperature, the mixture was filtered,
washed with deionized water, saturated Na2CO3 solution, and
methanol to afford a white powder 1 (24.4 g, yield 65%), m.p. 208e
internal tetramethylsilane (TMS) standard. Number-average (Mn)
and weight-average (Mw) molecular weights were determined
a Waters GPC-480 system with a column of AM GPC Gel (10 mm)
from American Polymer Standard Company. The calibration curve
was made with a series of monodispersed polystyrene standards
and tetrahydrofuran (THF) as eluent were used in the GPC experi-
ments. Differential scanning calorimetry (DSC) analyses were per-
formed on a TA Q20 instrument. Glass transition temperatures (Tg)
were measured at a scanning rate of 10 ꢀC minꢁ1, under a nitrogen
flow. Thermogravimetric analysis (TGA) measurements were
carried out with a TGA PerkineElmer TGA-7 apparatus at a heating
209 ꢀC. 1H NMR (400 MHz, CDCl3):
d
¼ 8.29 (s, 2H), 8.09 (br, 1H),
7.65 (d, 2H), 7.18 (d, 2H). 13C NMR (100 MHz, CDCl3):
d
¼ 138.52,
134.80, 129.37, 124.56, 112.68, 82.41. HRMS (m/z): calcd for
C12H7I2N: 418.8668. Found: 418.8678.

C.-N. Chuang et al. / Polymer 53 (2012) 4983e4992
4985
2.2.2. 9-Butyl-3,6-diiodo-9H-carbazole (2) [31,32]
7.04 (m, 6H), 6.99e6.96 (m, 2H); 13C NMR (100 MHz,CDCl3):
3,6-Diiodocarbazole (1) (5 g, 11.93 mmol), powdered potassium
hydroxide (1.34 g, 23.87 mmol) and [(n-Bu)4N]HSO4 (0.11 g,
0.32 mmol) were mixed in a flask containing acetone (18 mL) stirrer
under an atmosphere of N2. After stirred for 1 h, 1-bromobutane
(2.98 g, 21.78 mmol) was added slowly. The solution was heated
to reflux for 3 h. After cooling to room temperature, the mixture
was extracted with dichloromethane and the organic phase evap-
orated to dryness. The product (5.04 g, yield 89%) was obtained
after recrystallization (MeOH/hexane, 1:1).
d
¼ 147.26, 146.91, 132.25, 132.06, 125.31, 125.02, 124.31, 123.14,
HRMS (m/z): calcd for C18H14BrN: 323.0310. Found: 323.0318.
2.2.6. 9-Butyl-6-(4-vinylphenyl)-9H-3,90-bicarbazole (M1)
9-Butyl-6-iodo-9H-3,90-bicarbazole (3.00 g, 6.42 mmol), 4-vinyl
phenylboronic acid (1.05 g, 7.06 mmol), and tetrakis(triphenyl
phosphine)palladium(0) (0.68 g) were stirred in 54 mL of THF. After
adding 32 mL of aqueous 1 M K2CO3, the reaction mixture was
reacted at 80 ꢀC for 24 h. The crude mixture was cooled to ambient
temperature. The solvent was removed by evaporation under
reduced pressure, and the reaction mixture was poured into water
and extracted with CH2Cl2 three times. The combined organic
solution was dried over anhydrous MgSO4 and filtered. After
evaporation of the solvent, the residue was purified by silica
column chromatography with n-hexane and CH2Cl2 (4:1) to give
1H NMR (400 MHz, CDCl3):
(d, 2H), 4.16e4.20 (t, 2H), 1.77 (qn, 2H), 1.31 (sex, 2H), 0.88e0.92
(t, 3H); 13C NMR (100 MHz, CDCl3):
d
¼ 8.29 (s, 2H), 7.68 (d, 2H), 7.13
d
¼ 139.35, 134.36, 129.20,
123.83, 110.79, 81.60, 42.87, 30.90, 20.39, 13.77. HRMS (m/z): calcd
for C16H15I2N: 475.1059. Found: 475.1066.
2.2.3. 9-Butyl-6-iodo-9H-3,90-bicarbazole (3)
a white solid (2.51 g, 80%). 1H NMR (400 MHz, DMSO-d6):
d
¼ 8.54
A mixture of carbazole (1.00 g, 6.02 mmol), 9-butyl-3,6-diiodo-
9H-carbazole (2) (3.14 g, 6.62 mmol), Cu powder (0.38 g,
6.02 mmol), 18-crown-6 (0.025 g, 0.09 mmol), K2CO3 (1.66 g,
12.03 mmol), and 1,2-dichlorobenzene (5 mL) were heated to
180 ꢀC for 24 h under an atmosphere of N2. After cooling to room
temperature, the crude mixture was filtered, and the residue was
washed with dichloromethane. The combined filtrates were then
evaporated to dryness. The product was purified by flash column
chromatography (silica gel, hexane) to afford compound (3) (1.33 g,
yield 43%) as a white solid.
(s, 1H), 8.53 (s, 1H), 8.26e8.28 (d, 2H), 7.85e7.89 (m, 2H), 7.74e7.78
(m, 3H), 7.62e7.65 (d, 1H), 7.53e7.55 (d, 2H), 7.27e7.44 (m, 6H),
6.72e6.80 (dd, 1H), 5.83e5.88 (d, 1H), 5.24e5.27 (d, 1H), 4.51
(t, 2H), 1.83 (quint, 2H), 1.38 (sext, 2H), 0.93e0.97 (t, 3H). 13C NMR
(100 MHz, CDCl3):
d
¼ 184.68, 180.26, 178.34, 165.60, 159.47, 156.86,
143.93, 141.93, 140.91, 140.1, 139.32, 136.04, 135.06, 130.54, 127.93,
126.43, 125.90, 123.15, 122.31, 122.21, 120.24, 119.46, 109.54, 52.93,
19.93, 14.14. HRMS (m/z): calcd for C36H30N2: 490.2409. Found:
490.2422.
1H NMR (400 MHz, DMSO-d6):
d
¼ 8.66 (s, 1H), 8.49 (s, 1H), 8.26
2.2.7. 9-(40-Vinylbiphenyl-4-yl)-9H-carbazole (M2)
(d, 2H), 7.87 (d, 1H), 7.76 (d, 1H), 7.64 (d, 1H), 7.56 (d, 1H), 7.39e7.43
(t, 2H), 7.34 (d, 2H), 7.26e7.30 (t, 2H), 4.47 (t, 2H), 1.81 (qn, 2H), 1.36
9-(4-Bromophenyl)-9H-carbazole (2 g, 6.2 mmol), 4-
vinylphenylboronic acid (1 g, 6.8 mmol), and tetrakis(triphenyl
phosphine)palladium(0) (0.65 g) were stirred in 52 mL of THF. After
adding 31 mL of aqueous 1 M K2CO3, the reaction mixture was
reacted at 80 ꢀC for 24 h. The crude mixture was cooled to ambient
temperature. The solvent was removed by evaporation under
reduced pressure, and the reaction mixture was poured into water
and extracted with CH2Cl2 three times. The combined organic
solution was dried over anhydrous MgSO4 and filtered. After
evaporation of the solvent, the residue was purified by silica
column chromatography with n-hexane and CH2Cl2 (4:1) to give
(sex, 2H), 0.90e0.93 (t, 3H); 13C NMR (100 MHz, CDCl3):
d
¼ 141.80,
140.22,139.44,134.48,129.46,129.34,125.85, 124.92, 123.11,122.43,
120.26, 119.62, 119.59, 111.08, 109.88, 109.75, 81.56, 43.21, 31.12,
20.57, 13.88. HRMS (m/z): calcd for C28H23IN2: 514.0906. Found:
514.0926.
2.2.4. 9-(4-Bromophenyl)-9H-carbazole (4) [33]
A
stirred mixture of 9H-carbazole (5 g, 30 mmol), 1,4-
dibromobenzene (7.8 g, 33 mmol), K2CO3 (8.5 g, 60 mmol), Cu
powder (1.9 g, 30 mmol) and 18-crown-6 (0.13 g, 0.45 mmol) in 1,2-
dichlorobenzene (30 mL) was degassed with nitrogen for three
times. The reaction mixture was then refluxed under a nitrogen
atmosphere for 48 h. The crude mixture was filtered, and the
residue was washed with dichloromethane. The combined filtrates
were then evaporated to dryness. The product was purified by flash
column chromatography (silica gel, hexane/CH2Cl2 ¼ 5/1) to give
compound (4) (3.38 g, yield 35%) as a white solid. 1H NMR
a white solid (1.61 g, 75%). 1H NMR (400 MHz, DMSO-d6):
8.27 (d, 2H), 7.98e8.00 (d, 2H), 7.79e7.81 (d, 2H), 7.71e7.73 (d, 2H),
7.62e7.64 (d, 2H), 7.42e7.47 (m, 4H), 7.28e7.34 (m, 2H), 6.78e6.85
(dd, 1H), 5.91e5.95 (d, 1H), 5.31e5.34 (d, 1H). 13C NMR (100 MHz,
d
¼ 8.25e
DMSO-d6):
d
¼ 143.80,139.79,138.44,138.33,136.32,135.94,127.94,
127.88, 126.58, 126.06, 123.50, 122.59, 120.36, 119.92. HRMS (m/z):
calcd for C26H19N: 345.1517. Found: 345.1601.
(400 MHz, DMSO-d6):
7.42e7.45 (m, 3H), 8.0 (d, 2H), 8.22 (d, 2H). 13C NMR (100 MHz,
DMSO-d6):
d
¼ 7.26e7.31 (m, 2H), 7.38e7.41 (m, 3H),
2.2.8. 4,40-Vinylphenyltriphenylamine (M3)
4-Bromotriphenylamine
(5.98
g,
18.4
mmol),
4-
d
¼ 109.02, 119.59, 119.68, 119.95, 122.21, 125.69, 128.13,
vinylphenylboronic acid (3.00 g, 20.3 mmol), and tetrakis(triphenyl
phosphine)palladium(0) (1.94 g) were stirred in 154 mL of THF.
After adding 92.5 mL of aqueous 1 M K2CO3, the reaction mixture
was reacted at 80 ꢀC for 24 h. The crude mixture was cooled to
ambient temperature. The solvent was removed by evaporation
under reduced pressure, and the reaction mixture was poured into
water and extracted with CH2Cl2 three times. The combined
organic solution was dried over anhydrous MgSO4 and filtered.
After evaporation of the solvent, the residue was purified by
silica column chromatography with n-hexane and CH2Cl2 (4:1)
to give
CDCl3):
7.97e7.50 (m, 18H). 13C NMR (100 MHz, CDCl3):
123.80, 124.11, 124.40, 126.60, 127.51, 129.24, 134.48, 136.05, 136.40,
139.94, 147.19, 147.60. HRMS (m/z): calcd for C26H21N, 347.1674.
Found: 347.1672.
132.42, 135.46, 139.11. HRMS (m/z): calcd for C18H12BrN: 321.0153.
Found: 321.0162.
2.2.5. 4-Bromotriphenylamine (5)
Triphenylamine (5 g, 20.4 mmol) dissolved in toluene (24 mL)
was added into the round bottom flask (100 mL, two-neck) and
cooled in an ice bath. A solution of N-bromosuccinimide (4.35 g,
24.5 mmol) in DMF (12 mL) was added into the flask transfer
through the addition funnel. After reacting for 15 min, the mixture
was poured into cold water and extracted with CH2Cl2 three times.
The combined organic solution was dried over anhydrous MgSO4
and filtered. After evaporation of the solvent, the residue was
purified by recrystallized (n-hexane). The product was obtained as
a
white solid (5.31 g, 83%). 1H NMR (400 MHz,
¼ 5.19e5.22 (d, 1H), 5.70e5.75 (d, 1H), 6.67e6.73 (dd, 1H),
d
d
¼ 113.54, 122.92,
white crystals (4.89 g, 53%), 1H NMR (400 MHz, CDCl3):
（dd, J ¼ 7.64, 8.72 Hz, 2H）, 7.56（dd, J ¼ 8.12, 7.56 Hz, 4H）, 7.12e
d
¼ 7.36

4986
C.-N. Chuang et al. / Polymer 53 (2012) 4983e4992
Scheme 1. Synthetic routes of the carbazole and triphenylamine derivatives, polymers and chemical structure of the intermediates. Reagents and conditions: (i) KI, KIO3, CH3COOH,
H2O, 80 ꢀC, 48 h; (ii) C4H9Br, [(C4H9)4N]HSO4, KOH, acetone, 90 ꢀC, 24 h; (iii) Cu, K2CO3, 18-crown-6, 1,2-dichlorobenzene, 180 ꢀC, 48 h; (iv) 1,4-dibromobenzene, Cu, K2CO3, 18-
crown-6, 1,2-dichlorobenzene, 180 ꢀC, 48 h; (v) 2 M K2CO3, THF, Pd(PPh3)4; (vi) NBS, DMF, THF, r.t, 15 min; (iv) NMP, AIBN, 75 ꢀC, 24 h.

C.-N. Chuang et al. / Polymer 53 (2012) 4983e4992
4987
Table 1
3. Results and discussion
Overview of an analytical data of polymers: SCzCz, SDBCz and STPA.
3.1. Synthesis and characterization
Polymer
SCzCz
SDBCz
STPA
The synthetic routes of the host materials SCzCz, SDBCz, STPA
and the corresponding monomers are shown in Scheme 1. The iodo
compounds (1) and (2) were synthesized by two reactions
involving Tucker iodination of 9H-carbazole and alkylation of the
Approximate yield in %
60
63
75
a
GPC (g molꢁ1
Mn
)
9230
36,300
3.93
7040
15,300
2.17
7370
27,200
3.69
Mw
PDI
TGA in ꢀCb
DSC in ꢀCc
448
232
411
227
398
172
a
Determined by GPC by eluting with THF, by comparison with polystyrene
a
1.2
1.0
0.8
0.6
0.4
0.2
0.0
1.2
1.0
0.8
0.6
0.4
0.2
0.0
standards.
UV-vis
b
PL
SCzCz
SDBCz
STPA
Temperature at which a 5% weight loss occurred was determined at a heating
rate of 10 ꢀC/min under a nitrogen atmosphere.
c
The value of Tg was determined at a heating rate of 10 ꢀC/min under a nitrogen
atmosphere.
2.3. Synthesis of polymers SCzCz, SDBCz and STPA
Homopolymers SCzCz, SDBCZ and STPA were synthesized by
free radical polymerization of M1, M2 and M3 using AIBN as an
initiator. For example, M1 (1.23 g, 2.5 mmol) and AIBN (25 mg)
were charged in a two necked flask with stirrer under N2. Injected
dry NMP (3 mL) and stirred at 75 ꢀC for 24 h, and then poured into
methanol (200 mL). The appearing precipitates were collected by
the filtered through a membrane filter with the channel size of
300
400
500
600
Wavelength (nm)
0.45 mm and then purified by extracting with methanol for 24 h
using a Soxhlet extractor. Thus-obtained polymer was further
purified by being dissolved in CHCl3 and reprecipitated from
methanol several times. The product was collected by the filtered
through a PTFE membrane filter with the channel size of 0.45 mm
and dried in vacuum to give a white powder of SCzCz. Yield
b
1.2
1.2
1.0
0.8
0.6
0.4
0.2
0.0
PL
UV-vis
SCzCz
SDBCz
STPA
1.0
0.8
0.6
0.4
0.2
0.0
was 60%.
1H NMR (400 MHz, CDCl3):
(m, NeCH2e), 0.54e1.54 (m, eCH2eCHe).
d
¼ 6.49e8.02 (m, AreH), 3.5e4.2
Other polymers (SDBCz and STPA) were prepared by a proce-
dure analogous to SCzCz using M2 and M3, and the obtained
products were white powders with yields around 63e75%.
SDBCz: 1H NMR (400 MHz, CDCl3):
1.50e2.23 (m, eCH2eCHe).
d
¼ 6.65e8.10 (m, AreH),
STPA: 1H NMR (400 MHz, CDCl3):
1.29e2.15 (m, eCH2eCHe).
d
¼ 6.42e7.50 (m, AreH),
300
400
500
600
Wavelength (nm)
100
c
1.2
SCzCz
SDBCz
SCzCz
STPA
1.0
0.8
0.6
0.4
0.2
0.0
80
SDBCz
STPA
STPA
60
SDBCz
40
SCzCz
20
150
200
Temperature ( C)
0
100
200
300
400
500
400
500
600
700
800
Temperature (oC)
Wavelength (nm)
Fig. 1. TGA curves of SCzCz, SDBCz and STPA. Inset: DSC curves of SCzCz, SDBCz and
STPA.
Fig. 2. UVevis, PL and phosphorescence spectra of the SCzCz, SDBCz and STPA poly-
mers in (a) THF solution, (b) thin films (10e15 nm), (c) 77 K in THF solution.

4988
C.-N. Chuang et al. / Polymer 53 (2012) 4983e4992
Table 2
The electrochemical and photophysical data of SCzCz, SDBCz and STPA.
Polymer
lmax,abs. solutiona (nm)
lmax,em. solutionb (nm)
lphos.,on-set (nm)c
Eg (eV)d
ET (eV)e
Eox (V)f
HOMOg/LUMOh (eV)
SCzCz
SDBCz
STPA
290(293)i
290(295)
320(330)
403(408)j
367(377)
390(439)
416
423
480
3.19
3.20
3.17
2.93
2.90
2.50
1.10
1.32
1.02
ꢁ5.47/ꢁ2.28
ꢁ5.69/ꢁ2.49
ꢁ5.39/ꢁ2.22
a
Absorption measured in dilute THF.
Recorded in solid-state on quartz.
Recorded in THF at 77 K.
Estimated from the solid-state absorption edge.
Triplet energy level estimated from the first peak of highest-energy phosphorescence.
The onset of the oxidation wave in cyclic voltammetry curves.
Calculated from Eox
Estimated from the HOMO and band-gap (Eg) energies.
The value in parentheses represents the value of lmax,abs.(nm) of the polymer as a solid film.
The value in parentheses represents the value of lmax,em. (nm) of the polymer as a solid film.
b
c
d
e
f
g
h
i
.
j
3,6-diiodocarbazole with 1-bromobutane. Compounds (3) and (4)
were prepared via Ullmann CeN coupling reaction which was
starting from carbazole coupling with compound 2 and 1,4-
dibromobenzene and 18-crown-6 as a phase transfer catalyst and
dry 1,2-dichlorobenzene as a solvent in 43% and 35% yields [33].
The final monomer of M1, M2 was synthesized via Suzuki coupling
of compounds (3), (4) and 4-vinylphenylboronic acid in dry THF at
75 ꢀC for 24 h in the presence of Pd(PPh3)4 and 2 M K2CO3. M3 was
synthesized through a two-step reaction sequence. Bromination of
triphenylamine with NBS afforded 4-bromotriphenylamine (5) in
63% yield. M3 was synthesized via Suzuki coupling of compound (5)
and 4-vinylphenylboronic acid in 83% yield [40]. The polymeriza-
tions were carried out under argon atmosphere, whereas dry NMP
acts as a solvent while the initiator was AIBN. The polymerization
temperature was 75 ꢀC for 24 h. Table 1 gives an overview of the
polymer analyses data. The approximate yields of all polymers were
above 60%. On one hand the polymers present with polydispersity
indices (PDIs) show quite higher PDIs which can be mainly attrib-
uted to poor monomer solubility observed in NMP. The maximum
quotient between the weight average molar mass Mw and the
a
b
1.0x10-5
8.0x10-6
SCzCz
SDBCz
5.0x10-6
6.0x10-6
4.0x10-6
2.0x10-6
0.0
-5.0x10-6
-1.0x10-5
-1.5x10-5
-2.0x10-5
0.0
-2.0x10-6
-4.0x10-6
-6.0x10-6
-8.0x10-6
0.0
0.2
0.4
0.6
0.8
1.0
1.2
1.4
0.0
0.5
1.0
1.5
Potential (V)
Potential (V)
1.0x10-5
c
STPA
5.0x10-6
0.0
-5.0x10-6
-1.0x10-5
-1.5x10-5
0.0
0.2
0.4
0.6
0.8
1.0
1.2
1.4
Potential (V)
Fig. 3. Oxidation part of the CV curves of (a) SCzCz, (b) SDBCz, (c) STPA in CH2Cl2 solutions.

C.-N. Chuang et al. / Polymer 53 (2012) 4983e4992
4989
number average molar mass Mn are obtained for polymer SCzCz,
with the dicarbazole unit, which has a very high PDI of 3.93. The
solubility of the dicarbazole monomer in NMP is quite good, so the
high PDI may be due to a different origin. Thesen et al. reported that
observed a bimodular distribution in the size exclusion chro-
matogram of this kind polymer, so the comparatively high PDI of
3.93 may possibly be caused by the NorrisheTrommsdorff effect or
chain-transfer mechanisms themselves [35]. These homopolymers
exhibited good thermal stability with thermal decomposition
temperature (Td) above 400 ꢀC under nitrogen atmosphere. On DSC
thermograms, SCzCz, SDBCz and STPA revealed the glass transition
temperatures (Tg) at 237, 227 and 172 ꢀC, respectively. The STPA
exhibits lower Tg than SCzCz and SDBCZ that means carbazole
structure was more rigid than triphenylamine. The high Tg values of
the present host polymers are expected to prevent morphology
deformation and degradation when used as emitting layer in PLEDs.
Variations in morphology due to low glass transition temperatures
upon device operation are believed to be the main causes of
degradation [36]. Fig. 1 shows TGA and DSC diagram of SCzCz,
SDBCz and STPA.
slightly blue-shifted compared to its monomer M3 (343 nm), due to
the polymerization of vinyl group reduction in -conjugation
[39,40]. This absorption spectrum is ascribed to the * transition
p
pep
of the triphenylamine moiety. All of the absorption spectra of the
three host materials in the solid state were almost identical to that
in dilute THF solution. Upon UV excitation, the PL spectrum of the
SCzCz material shows emission peak red-shifted to 408 nm with
respect to the carbazole (375 nm) monomer emission, which was
carbazole excimer emission [48]. And the other carbazole deriva-
tive, SDBCz, consists of maxima at 377 nm is carbazole emission
peak and a shoulder at 433 nm which is assigned to the excimer
emission [48]. The maximum emission peak of STPA was red-
shifted by 50 nm from the corresponding solution spectrum. Such
a phenomenon probably occurred due to intermolecular interac-
tions between polymer chains leading to better conjugation in solid
state than in solution. The highest energy phosphorescent emission
was used to calculate the triplet energy level, giving a value of
2.93 eV for SCzCz, 2.90 eV for SDBCz and 2.50 eV for STPA, higher
than the values of the commonly used triplet green-emitter
Ir(ppy)3 (2.41 eV) [20]. Using host materials that possess high
triplet energies are a provision for effective confinement of the
triplet excitons on the guest, consequently, prevention of back
energy transfer between the host and dopant molecules. Based on
the results of the measurements, the newly synthesized
compounds with high triplet energy levels are expected to serve as
appropriate hosts for Ir(ppy)3.
3.2. Photophysical properties
Fig. 2 exhibits the room-temperature absorption and fluores-
cence spectra in dilute THF and in thin film. All the results are
summarized in Table 2. The two host materials of the carbazole
derivatives in dilute solution have similar patterns with absorption
spectra spanning from 265 to 380 nm, which are nearly identical to
polyvinylcarbazole (PVK) and thus can be attributed to the nep*
3.3. Electrochemical analysis
and
p
*ep* transitions [37,38]. For STPA in THF solution, the
Cyclic voltammograms was employed to investigate the elec-
trochemical behavior and to estimate the HOMO energy level and
maximum absorption peak was observed at 320 nm, which is
EML materials
-1
STPA
SCzCz
SDBCz
-2.22
3.17
-5.39
-2.28
-2
Ir(ppy)3
-2.6
PBD
-2.6
TRZ
-2.49
-2.71
-3
3.19
3.20
-4
-5
-6
-7
-3.7
Mg
ITO
-4.8
PEDOT:
PSS
-4.2
Ag
-5.0
-5.2
-5.47
-5.69
-6.2
-6.4
N
N
N
O
N
N
Ir
N
N
N
Ir(ppy)3
PBD
TRZ
Fig. 4. Schematic energy-level diagram of the PLEDs. Also shown are the molecular structures of the EML material.

4990
C.-N. Chuang et al. / Polymer 53 (2012) 4983e4992
ELUMO ¼ EHOMO þ Eg
(3)
a
300
10000
1000
100
10
where EHOMO and ELUMO are the HOMO and the LUMO energy levels,
Eox,onset is the onset oxidation potential of the polymer, 4.8 is the
reference energy level of ferrocene (Fc, 4.8 eV below the vacuum
level), EFc is the potential of Fc/Fcþ versus Ag/AgCl (0.43 V,
measured by cyclic voltammetry), Eg is the energy bandgap of the
polymer, h is the Planck constant (6.63 ꢂ 10ꢁ34 J s), c is the speed of
light (3 ꢂ 108 m sꢁ1), and lEdge is the optical absorbance band edge
of the polymer. In this study, we used tetrabutylammonium
perchlorate (Bu4NClO4) as the supporting electrolyte and ferrocene
as the internal standard (Fig. 3) with the corresponding electro-
chemical data summarized in Table 2. The onset oxidation potential
of SCzCz, SDBCz and STPA are at 1.10, 1.32 and 1.02 V, respectively.
The HOMO energy level of SCzCz, SDBCz and STPA calculated from
their onset oxidation potentials are ꢁ5.47, ꢁ5.69 and ꢁ5.39 eV,
respectively, which are higher than that of PVK (ꢁ5.8 eV) [17]. This
seems to be attributed to pendent carbazole, phenyl substituent
group for SCzCz, SDBCz and STPA in order to extend the conjugate
length in this system. The SCzCz which pendent with dicarbazole
that the inner carbazole easier oxidization than outer carbazole.
The outer carbazole in this system acts an electron-donating group
in order to enhance the HOMO value. The SDBCz shows an irre-
versible waves and the formation of the dimer can be recognized.
The reduction peak at 1.03 V can be assigned to the reduction of the
dimer cation radical to the dimer neutral, and the small reduction
peak around 1.29 V is assigned to the dimer dication to dimer cation
radical. The STPA shows the onset oxidation potential of 1.02, this
seems be attributed to stronger hole-affinity of pendent triphe-
nylamine groups. Accordingly, the energy barrier for hole injection
from the PEDOT:PSS to emitting layers can be effectively reduced.
The LUMO energy levels of SCzCz, SDBCz and STPA, calculated from
the HOMO energy levels and the optical energy gaps (Eg),
are ꢁ2.28, ꢁ2.49 and ꢁ2.22 eV, respectively. Fig. 4 shows the
schematic energy-level diagram for the PLEDs.
250
200
150
100
50
SCzCz
SDBCz
STPA
PVK
1
0
5
10
15
20
25
30
Voltage (V)
b
20
15
10
5
10
8
SCzCz
SDBCz
STPA
PVK
6
4
2
0
0
0
50
100
150
200
Current Density (mA/cm2)
Fig. 5. (a) Brightness-voltage-current density characteristics and (b) Current
efficiency-voltage-power efficiency characteristics of EL devices A using host materials:
SCzCz, SDBCz, STPA and PVK, blends of Ir(ppy)3 (4 wt%) and t-PBD (40 wt%) as emitting
layer. Device structure: ITO/PEDOT:PSS/host materials þ Ir(ppy)3 þ t-PBD (50e90 nm)/
Mg (2 nm)/Ag (100 nm).
3.4. Electroluminescent properties
In order to assess the utility of those polymers as host materials
in PLEDs, the solution-processed electrophosphorescent devices
were using a green phosphor Ir(ppy)3 as the dopant. Single layer
optical absorption spectra of the three host polymers, according to
the following equations [41]:
devices of type
A with the configuration ITO/PEDOT:PSS/
Hosts:Ir(ppy)3(4 wt%):t-PBD(40 wt%)/Mg/Ag have been fabricated,
where ITO glass was used as a transparent anode; the conducting
polymer poly(3,4-ethylenedioxythiophene):poly(styrenesulfonate)
(PEDOT:PSS) was used as the hole-injection layer; the electron-
transporting material t-PBD was mixed into the host materials to
facilitate electron transport in the emitting layer [42], Ir(ppy)3 with
c
Eg ¼ h
(1)
(2)
lEdge
À
Á
EHOMO ¼ ꢁe Eox;onset ꢁ EFc þ ðꢁ4:8Þ eV
Fig. 6. AFM phase images of the films spin-coated from the blends the three hosts with Ir(ppy)3 and t-PBD (a) SCzCz, (b) SDBCz, (c) STPA.

C.-N. Chuang et al. / Polymer 53 (2012) 4983e4992
4991
Table 3
an optimized concentration of 4 wt% (for efficiency) was used as the
emitter. Fig. 5 shows the current density-voltages-brightness (J-V-
B) characteristics and current efficiency-voltage-power efficiency of
the devices of type A. According to the J-V-B characteristic curves of
the devices of type A, the turn-on voltages of SCzCz, SDBCz, STPA
and PVK were 7.2 V, 8.2 V, 6.3 V and 7.8 V, respectively (corre-
sponding to 1 cd/m2). The introduction of phenylcarbazole (SCzCz)
and diphenyl (SDBCz) substituent groups (compared with PVK) for
device A indicates that buck side group for pendent polymers
without effect the turn-on voltage in this system. Remarkable for
STPA which pendent good hole transporting property group tri-
phenylamine could enhance hole-injection and result in low turn-
on voltage. The high efficiency indicates balanced charge injection,
transport, and combination, most likely due to the HOMOs energy
levels of these hosts being better matched with the PEDOT:PSS and
thereby facilitating the hole injection of the device. The SCzCz,
SDBCz and STPA based devices show the maximum (Bmax) of
15,800 (18.5 V), 16,500 (22.5 V) and 11,000 (16 V) cd/m2, the
maximum current efficiency (hc,max) of 17.5 (15.0 V), 13.2 (18.5 V)
and 10.0 (12.0 V) cd/A, and the power efficiency (hp,max) of 3.8, 2.3
and 2.7 lm/W, respectively. The performances of the devices are far
superior to those of the corresponding PVK based devices (Bmax of
6920 cd/m2, hc,max of 11.1 cd/A and hp,max of 2.5 lm/W). However, for
electron transporting material (ETM) TRZ (LUMO of 2.71 eV) was
reported a low-lying LUMO level than t-PBD (LUMO of 2.6 eV)
material [43]. It was reported that the TRZ derivatives used as ETM
The electroluminescence characteristics of the devices of type A, B1-B4 and STD for
Ir(ppy)3 with 4 wt%.
Device
A
Host
t-PBD:TRZ
(wt%)
Vturn-on
Bmax
hc,max
hp,max
(V)a
(cd/m2)b
(cd/A)c
(lm/W)d
SCzCz
SDBCz
STPA
SCzCz
SCzCz
SCzCz
SCzCz
PVK
40:0
40:0
40:0
0:40
10:30
20:20
30:10
40:0
7.2
8.2
6.3
8.2
7.6
7.8
8.7
7.8
15,800
16,500
11,000
7480
23,400
11,300
14,000
6790
17.5
13.2
10.0
6.4
12.3
10.8
14.8
11.1
3.8
2.3
2.7
1.2
2.6
2.4
2.8
2.5
B1
B2
B3
B4
STD
a
Recorded at 1 cd/m2.
Maximum brightness.
Maximum current efficiency.
Maximum powder efficiency.
b
c
d
is expected to give negative influence on the device performance
[44,45]. The high efficiencies of the PhPLEDs were attributed to the
low electron injection barrier and balanced recombination there-
after. Fig. 6 shows the compatibility of SCzCz, SDBCz and STPA with
Ir(ppy)3 and t-PBD are explored by atom force microscopy (AFM).
The phase images exhibit a uniform surface without pinholes or
particles, indicating excellent compatibility of the three hosts with
Ir(ppy)3. This compatibility ensures good dispersion of the phos-
phorescent dopant in the hosts and is necessary for excellent device
performance. Therefore, we attribute the high performance to the
excellent film forming ability and the high triplet energy of host
materials and balanced charge recombination in the devices. It is
noteworthy that SCzCz possessed high triplet energy levels
(>2.93 eV), which is suitable to serve as appropriate hosts for green
phosphorescent emitters such as Ir(ppy)3. Therefore, we fabricated
a
350
B1
10000
B2
300
B3
B4
devices of type
B with a configuration of ITO/PEDOT:PSS/
250
A
1000
SCzCz:Ir(ppy)3 (4 wt%):t-PBD(x wt%):TRZ (y wt%)/Mg/Ag. The TRZ
was used as the electron-transporting material, blends with EML.
The devices performances are presented in Fig. 7 and summarized
in Table 3. As shown in Table 3, the present devices show turn-on
voltages of 8.2, 7.6, 7.8 and 8.7 V, the maximum (Bmax) of 7480
(20.0 V), 23,400 (19.0 V), 11,300 (16.0 V) and 14,000 (20.5 V) cd/m2,
the maximum current efficiency (hc,max) of 6.4 (17.0 V), 12.3
(15.0 V), 10.8 (14.5 V) and 14.8 (16.5 V) cd/A, and the power effi-
ciency (hp,max) of 1.2, 2.6, 2.4 and 2.8 lm/W, respectively. When TRZ
content increased from 0 to 40%, the device performances were
decreased and the TRZ crystal particle size will be large through the
polar optical micrograph (POM) observation (see Figure S20). But
the devices of B2, B3 and B4 exhibit better performance to compare
with PVK. Noteworthily, B2 reveals the maximum brightness
(23,400 cd/m2) and current efficiency maintain at 12.3 cd/A. It
demonstrated blend TRZ could increase electron transport from
cathode to EML. In this study, all of the host materials based devices
show significantly improved performance, brightness and lumi-
nance efficiency, as compared to those of PVK.
PVK
200
100
10
1
150
100
50
0
5
10
15
20
Voltage (V)
b
20
15
10
5
B1
B2
B3
B4
A
15
10
5
PVK
4. Conclusion
In conclusion, we have synthesized three polymers SCzCz,
SDBCz and STPA as host materials, for used in green electro-
phosphorescent devices. Our molecular design imparted these host
materials with high thermal stabilities, high triplet energy level and
appropriate HOMO energy level for the PLED devices. Utilizing
these compounds as hosts, Ir(ppy)3 as a dopant show a maximum
current efficiency of 17.5 cd/A and a maximum brightness to
15,800 cd/m2. This can be attributed to the high triplet energy level
well matched energy levels with the PEDOT:PSS layer and excellent
film forming ability. Moreover, we blends TRZ which provided with
0
0
0
50
100
150
200
250
300
Current Density (mA/cm2)
Fig. 7. (a) Brightness-voltage-current density characteristics and (b) Current
efficiency-voltage-power efficiency characteristics of EL devices using SCzCz as host,
blends of Ir(ppy)3 (4 wt%) and t-PBD:TRZ (x:y wt%) as emitting layer. Where x:y of 0:40,
10:30, 20:20, 30:10 and 40:0 for devices B1, B2, B3, B4 and A.

4992
C.-N. Chuang et al. / Polymer 53 (2012) 4983e4992
[18] Dijken AV, Bastiaansen JJAM, Kiggen NMM, Langeveld BMW, Rothe C,
Monkman A. J Am Chem Soc 2004;126(24):7718e27.
[19] Sudhakar M, Djurovich PI, Hogen-Esch TE, Thompson ME. J Am Chem Soc
2003;125(26):7796e7.
good electron transport property to promote higher device
performance to 12.3 cd/A and 23,400 cd/m2.
[20] Chen FC, Chabng SC, He G, Pyo S, Yang Y, Kurotaki M. J. Polym. Sci. Part B:
Polym. phys. 2003;41(21):2681e90.
Acknowledgments
[21] Chen F, He G, Yang Y. Appl Phys Lett 2003;82(7):1006e8.
[22] Monkman A, Burrows H, Hartwell L, Horsburgh L, Hamblett I, Navaratnam S.
Phys Rev Lett 2001;86(7):1358e61.
[23] Yeh HC, Chien CH, Shih PI, Yuan MC, Shu CF. Macromolecules 2008;41(11):
3801e7.
[24] Yang XH, Neher D. Appl Phys Lett 2004;84(14):2476e8.
[25] Yang X, Müller DC, Neher D, Meerholz K. Adv Mater 2006;18(7):948e54.
[26] Lee CC, Yeh KM, Chen Y. Polymer 2008;49(24):4211e7.
[27] Yeh KM, Lee CC, Chen Y. J. Polym. Sci. Part A: Polym. Chem. 2008;46(15):
5180e93.
[28] Lee CC, Yeh KM, Chen Y. Polymer 2009;50(2):410e7.
[29] Thompson BC, Kim YG, Reynolds JR. Macromolecules 2005;38(13):5359e62.
[30] Bard AJ, Faulkner LR. Electrochemical methods: fundamentals and applica-
tions. New York: Wiley; 2001.
This work was supported by the National Science Council of
Taiwan (NSC 97-2221-E-002-025-MY3 and NSC 98-2119-M-002-
006-MY3), and the Advanced Polymer Nano-technology Research
Center (APNRC) of National Taiwan University.
Appendix A. Supplementary data
Supplementary data related to this article can be found online at
http://dx.doi.org/10.1016/j.polymer.2012.08.042.
References
[31] Li Z, Liu Y, Yu G, Wen Y, Guo Y, Ji L. Adv Funct Mater 2009;19(16):2677e83.
[32] Li Z, Jiang Z, Qiu G, Wu W, Yu G, Liu Y. Macromol Chem Phys 2010;211(16):
1820e5.
[33] Chen YH, Lin YY, Chen YC, Lin JT, Lee RH, Kuo WJ. Polymer 2011;52(4):
976e86.
[1] Kraft A, Grimsdale AC, Holmes AB. Angew Chem Int Ed 1998;37(4):402e28.
[2] Adachi C, Baldo MA, Thompson ME, Forrest SR. J Appl Phys 2001;90(10):
5048e51.
[34] Rothmann MM, Fuchs E, Schildknecht C, Langer N, Lennartz C, Munster I. P.
strohriegl. Org Electron 2011;12(7):1192e7.
[35] Thesen MW, Hofer B, Debeaux M, Janietz S, Wedel A, Kohler A. J. Polym. Sci.
Part A: Polym. Chem. 2010;48(15):3417e30.
[36] Wang D, Li W, Chu B, Su Z, Bi D, Zhang D. Appl Phys Lett 2008;92(5):
053304e6.
[37] Shen JY, Yang XL, Huang TH, Lin JT, Ke TH, Chen LY. Adv Funct Mater 2007;
17(6):983e95.
[38] Xie JH, Deng XY, Chen L, Chen SF, Liu RR, Hou XY. J. Polym. Sci. Part A: Polym.
Chem. 2009;47(20):5221e9.
[39] Sugiyama K, Hirao A, Hsu JC, Tung YC, Chen WC. Macromolecules 2009;
42(12):4053e62.
[40] Kang BG, Kang NG, Lee JS. Macromolecules 2010;43(20):8400e8.
[41] Pommerehne J, Vesweber H, Guess W, Mahrt RF, Bassler H, Porsch M. Adv
Mater 1995;7(6):551e4.
[42] Kappaun S, Slugovc C, List EJW. Int J Mol Sci 2008;9(8):1527e47.
[43] Zhong H, Xu E, Zeng D, Du J, Sun J, Ren S. Org Lett 2008;10(5):709e12.
[44] Shina DM, Noha S, Shona BC, Kima JH, Kimb C, Kimb BN. Thin Solid Films
2000;363(1e2):252e4.
[3] The special issue on organic electronics. Chem Mater 2004;16(23):4381e2.
[4] Holder E, Langeveld BMW, Schubert US. Adv Mater 2005;17(9):1109e21.
[5] Kawamura Y, Yanagida S, Forrest SR. J Appl Phys 2002;92(1):87e93.
[6] Chen XW, Liao JL, Liang YM, Ahmed MO, Tseng HE, Chen SA. J Am Chem Soc
2003;125(3):636e7.
[7] Tokito S, Suzuki M, Sato F, Kamachi M, Shirane K. Org Electron 2003;4(2e3):
105e11.
[8] Liu HM, Wang PF, He J, Zheng C, Zhang XH, Chew SL. Appl Phys Lett 2008;
92(2):023301e3.
[9] Gong X, Ma WL, Ostrowski JC, Bazan GC, Moses D, Heeger AJ. Adv Mater 2004;
16(7):615e9.
[10] Chen YC, Huang GS, Hsiao CC, Chen SA. J Am Chem Soc 2006;128(26):8549e58.
[11] Jiang JX, Xu YH, Yang W, Guan R, Liu ZQ, Zhen HY. Adv Mater 2006;18(13):
1769e73.
[12] Mathai MK, Choong VE, Choulis SA, Krummacher B, So F. Appl Phys Lett 2006;
88(24):243512e4.
[13] Chien CH, Liao SF, Wu CH, Shu CF, Chang SY, Chi Y. Adv Funct Mater 2008;
18(9):1430e9.
[14] Haldi A, Kimyonok A, Domercq B, Hayden LE, Jones SC, Marder SR. Adv Funct
Mater 2008;18(19):3056e62.
[15] Huang SP, Jen TH, Chen YC, Hsiao AE, Yin SH, Chen HY. Adv Funct Mater 2010;
20(1):138e46.
[45] Su SJ, Sasabe H, Pu YJ, Nakayama KI, Kido J. Adv Mater 2010;22(30):3311e6.
[46] Tsuchiya K, Sakaguchi K, Kasuga H, Kawakami A, Taka H, Kita H. Polymer
2010;51(3):616e22.
[47] Ma B, Kim BJ, Deng L, Poulsen DA, Thompson ME, Fréchet JMJ. Macromole-
cules 2007;40(23):8156e61.
[48] Xie LH, Ling QD, Hou XY, Huang W. J Am Chem Soc 2008;130(7):2120e1.
[16] Huang F, Shih PI, Shu CF, Chi Y, Jen AKY. Adv Mater 2009;21(3):361e5.
[17] Brunner K, van Dijken A, Börner H, Bastiaansen JJAM, Kiggen NMM,
Langeveld BMW. J Am Chem Soc 2004;126(19):6035e42.