Synthesis and characterization of poly(N-arylcarbazole-alt-aniline) copolymers as Blue-emitting host matrix for polymer light-emitting diodes

Article abstract of DOI:10.1080/15421400600930417

Thermally stable and solution-processable poly(N-arylcarbazole-alt-aniline) copolymers with high structural integrity were synthesized in good yields via palladium-catalyzed polycondensation of aniline with corresponding N-arylcarbazole monomers such as N-(2-ethylhexyloxyphenyl)-3,6-dibromocarbazole, bis[6-bromo-N-(2-ethylhexyloxyphenyl)carbazole-3-yl] and N-(4-(2-ethylhexyl)-3, 5-dibromomethylene-phenyl)carbazole, respectively. The optical and electrochemical properties of these copolymers were measured and compared with those of poly(N-alkylcarbazole-alt-aniline) copolymer. All synthesized poly(N-arylcarbazole-alt-aniline) copolymers showed maximum UV-Vis absorption peaks at around 300 nm in THF solution, and exhibited maximum photoluminescence peaks in the blue emission range from 430 to 460 nm. It was also found that poly(N-arylcarbazole-alt-aniline) copolymers had wider band gap energy than poly(N-alkylcarbazole-alt-aniline) copolymer.

Full text of DOI:10.1080/15421400600930417

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Synthesis and Characterization
of Poly(N-arylcarbazole-alt-
aniline) Copolymers as Blue-
Emitting Host Matrix for
Polymer Light-Emitting Diodes
Hui Wang a , Jeong-Tak Ryu a , Yoon Soo Han b , Dae-
Hwan Kim b , Byeong Dae Choi b , Lee Soon Park c
Dayong Teng d & Younghwan Kwon d
a College of Information and Communication
,
Engineering , Daegu University , Gyeongbuk, Korea
b Department of Display & Nano Materials , Daegu
Gyeongbuk Institute of Science & Technology ,
Daegu, Korea
c ADMRC, Department of Polymer Science ,
Kyungpook National University , Daegu, Korea
d ADMRC, Department of Chemical Engineering ,
Daegu University , Gyeongsan, Gyeongbuk, Korea
Published online: 31 Jan 2007.
To cite this article: Hui Wang , Jeong-Tak Ryu , Yoon Soo Han , Dae-Hwan Kim ,
Byeong Dae Choi , Lee Soon Park , Dayong Teng & Younghwan Kwon (2006) Synthesis
and Characterization of Poly(N-arylcarbazole-alt-aniline) Copolymers as Blue-Emitting
Host Matrix for Polymer Light-Emitting Diodes, Molecular Crystals and Liquid Crystals,
459:1, 95/[375]-107/[387], DOI: 10.1080/15421400600930417
To link to this article: http://dx.doi.org/10.1080/15421400600930417

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Mol. Cryst. Liq. Cryst., Vol. 459, pp. 95=[375]–107=[387], 2006
Copyright # Taylor & Francis Group, LLC
ISSN: 1542-1406 print=1563-5287 online
DOI: 10.1080/15421400600930417
Synthesis and Characterization of Poly(N-arylcarbazole-
alt-aniline) Copolymers as Blue-Emitting Host Matrix
for Polymer Light-Emitting Diodes
Hui Wang
Jeong-Tak Ryu
College of Information and Communication Engineering,
Daegu University, Gyeongbuk, Korea
Yoon Soo Han
Dae-Hwan Kim
Byeong Dae Choi
Department of Display & Nano Materials, Daegu Gyeongbuk Institute
of Science & Technology, Daegu, Korea
Lee Soon Park
ADMRC, Department of Polymer Science, Kyungpook National
University, Daegu, Korea
Dayong Teng
Younghwan Kwon
ADMRC, Department of Chemical Engineering, Daegu University,
Gyeongsan, Gyeongbuk, Korea
Thermally stable and solution-processable poly(N-arylcarbazole-alt-aniline)
copolymers with high structural integrity were synthesized in good yields via pal-
ladium-catalyzed polycondensation of aniline with corresponding N-arylcarbazole
monomers such as N-(2-ethylhexyloxyphenyl)-3,6-dibromocarbazole, bis[6-bromo-
N-(2-ethylhexyloxyphenyl)carbazole-3-yl] and N-(4-(2-ethylhexyl)-3,5-dibromo-
methylene-phenyl)carbazole, respectively. The optical and electrochemical proper-
ties of these copolymers were measured and compared with those of poly
(N-alkylcarbazole-alt-aniline) copolymer. All synthesized poly(N-arylcarbazole-
alt-aniline) copolymers showed maximum UV-Vis absorption peaks at around
300 nm in THF solution, and exhibited maximum photoluminescence peaks in
Financial support from Daegu Gyeongbuk Institute of Science & Technology (DGIST)
was gratefully acknowledged.
Address correspondence to Prof. Y. Kwon, ADMRC, Department of Chemical Engineer-
ing, Daegu University, Gyeongsan, Gyeongbuk 712-714, Korea. E-mail: y_kwon@daegu.
ac.kr
95=[375]

96=[376]
H. Wang et al.
the blue emission range from 430 to 460 nm. It was also found that poly(N-arylcar-
bazole-alt-aniline) copolymers had wider band gap energy than poly(N-alkylcarba-
zole-alt-aniline) copolymer.
Keywords: blue emission; host matrix; N-arylcarbazole; triarylamine
INTRODUCTION
Since the first report on conjugated polymers as a new class of electro-
luminescent materials for diodes, the research in this field has been
advancing rapidly over the past 15 years [1–3]. So far, a lot of polymers
such as poly(phenylene vinylene)s [4], polyphenylenes [5] and poly
(fluorene-2,7-diyl) [6] have been paid much attention and have been
studied as promising materials for commercial displays. Due to low
cost and simplified manufacturing process, polymer light-emitting
diodes (PLEDs) have been commercially applied in the fields of display
manufacture, digital cameras, portable electronics, consumer goods,
automotive systems and communication systems [7].
Carbazole-containing polymers have been widely investigated,
since the discovery of good photoconductive properties of poly
(N-vinylcarbazole) (PVK) [8,9]. It has been generally known that
carbazole systems have chemical stability, hole-transporting pro-
perty and wide band gap energy close to blue light emission. Among
them, N-arylcarbazoles, resembling the structure of substituted
triphenylene derivatives, could be obtained by introducing a phenyl
´
substituent on N atom of carbazole units [10,11]. Martınez et al.
reported the synthesis of a series of different polysubstituted
N-arylcarbazole derivatives by a highly efficient carbazole arylation
method [12]. Wong et al. prepared new 9,9-dihehexylfluorene=
9-arylcarbazole hybrid copolymers [13]. They pointed out that incor-
porating the electron-rich N-arylcarbazole groups into polyfluorene
main chain can increase the HOMO levels as well as retain their
blue emission. They also noted that advantage of the robust N-
arylcarbazole groups increased the thermal stability and glass
transition temperature of the resulting polymers compared to the
N-alkyl-substituted polymers.
In this paper, we synthesized and characterized different types of
poly(N-arylcarbazole-alt-aniline) copolymers as blue-emitting host
matrix polymers for PLEDs. The optical and electrochemical proper-
ties of these copolymers were discussed with those of N-alkyl substi-
tuted polymer.

Synthesis and Characterization of Poly(N-arylcarbazole-alt-aniline)
97=[377]
EXPERIMENTAL
Synthesis of Monomers
N-(2-ethylhexyl)-3, 6-dibromocarbazole (Monomer 1)
As shown in Scheme 1, a mixture of 3, 6-dibromocarbazole
(18.46 mmol) and K2CO3 (37 mmol) in DMF (20 ml) was refluxed in
N2 atmosphere and heated to 80ꢀC. 2-Ethylhexylbromide (28 mmol)
was added dropwise. After complete addition, heating was continued
for 16 h. The product was isolated by diethyl ether=water extraction.
The organic layer was dried with MgSO4, then filtered and concen-
trated. The pure white viscous liquid, monomer 1, was obtained by sil-
1
ica column chromatography (eluent: hexane). (Yield: 56%,). H NMR
(300 MHz in CDCl3): d 8.11 (2H, ArꢁH), 7.48 (2H, ArꢁH), 7.22 (2H,
ArꢁH), 4.18 (2H, ꢁNꢁCH2ꢁ), 1.23 ꢂ 1.44 (9H, ꢁCHꢁ, ꢁCH2ꢁ),
0.91 (6H, ꢁCH3).
N-(2-Ethylhexyloxylphenyl)-3,6-dibromocarbazole
(Monomer 2)
Synthetic procedure for monomer 2 was presented in Scheme 2. In
the first step, 4-bromophenol (1.5 mmol) was dissolved in 100 ml of
acetonitrile, then K2CO3 (4.5 mmol) was added. The mixture was stir-
red in N2 atmosphere at 60ꢀC. After 30 min, 2-ethylhexylbromide
(4.5 mmol) was dissolved in 25 ml of acetonitrile and added to the flask
dropwise. After 48 h of reaction, K2CO3 was filtered out, and the sol-
vent was evaporated, then the crude product was washed with water
and dried with MgSO4. The pure white liquid product, 4-bromo-(2-
ethylhexyloxyl)-benzene (1), was obtained by silica column chromato-
graphy (eluent: hexane). (Yield: 66%). 1H NMR (300 MHz in CDCl3): d
7.33 (2H, ArꢁH), 6.79 (2H, ArꢁH), 3.79 (2H,ꢁOꢁCH2ꢁ), 1.71(1H,
ꢁCHꢁ), 1.29ꢂ1.46 (8H, ꢁCH2ꢁ), 0.91 (6H, ꢁCH3); 13C NMR
(300 MHz in CDCl3): 158.4, 132.0, 116.2, 112.4, 70.6, 39.2, 30.4, 29.0,
23.8, 23.0, 14.1, 11.1.
SCHEME 1 Synthetic route to monomer 1.

98=[378]
H. Wang et al.
SCHEME 2 Synthetic route to monomer 2.
4-Bromo-(2-ethylhexyloxyl)-benzene (1) (56.4 mmole), carbazole
(7.6 mmol), K3PO4 (13.4 mmol), CuI (0.32 mmol) and trans-1, 2-cyclo-
hexanediamine (1.27 mmol) were used in the second step. The reaction
and workup procedure were carried out as described [14,15]. White
solid product, N-(2-Ethylhexyloxylphenyl)-carbazole (2), was obtained
(Yield: 29%). 1H NMR (300 MHz in CDCl3): d 8.15 (2H, ArꢁH),
7.44ꢂ7.24 (8H, ArꢁH), 7.08 (2H, ArꢁH), 3.94 (2H, ꢁOꢁCH2ꢁ),
1.77(1H, ꢁCHꢁ), 1.26ꢂ1.57 (8H, ꢁCH2ꢁ), 0.91 (6H, ꢁCH3); 13C
NMR (300 MHz in CDCl3): 158.6, 141.3, 129.9, 128.5, 125.8, 123.0,
120.2, 119.5, 115.5, 109.7, 70.8, 39.2, 30.4, 29.0, 23.8, 23.0, 14.1, 11.1.
In a flask, covered with aluminum oil, a stirred solution of 2
(2.43 mmol) in 60 ml of THF was cooled to 0ꢀC. N-bromosuccinimide
(NBS, 4.86 mmol) was added in small portion. The mixture was allowed
to warm to room temperature overnight. THF was evaporated and the
product was purified by extraction with diethyl ether and water. The
organic layer was dried MgSO4. The product, monomer 2, was obtained
by column chromatography (eluent: hexane=methylene chloride).
1
(Yield: 59%). H NMR (300MHz in CDCl3): d 8.18 (2H, ArꢁH), 7.47
(2H, ArꢁH), 7.36 (2H, ArꢁH) 7.16 (2H, ArꢁH), 7.08 (2H, ArꢁH),
3.94 (2H,ꢁOꢁCH2ꢁ), 1.77(1H, ꢁCHꢁ), 1.26 ꢂ 1.57 (8H, ꢁCH2ꢁ),

Synthesis and Characterization of Poly(N-arylcarbazole-alt-aniline)
99=[379]
0.91 (6H, ꢁCH3); 13C NMR (300 MHz in CDCl3): 159.1, 140.3, 129.2,
128.9, 128.3, 123.6, 123.1, 115.7, 112.7, 111.5, 70.8, 39.3, 30.5, 29.1,
23.8, 23.1, 14.1, 11.1.
Bis[6-bromo-N-(2-ethylhexyloxyphenyl)carbazole-3-yl]
(Monomer 3)
Synthetic procedure for monomer 3 was presented in Scheme 3. To
a stirred solution of 2 (2.9 mmol) in 13 ml of chloroform, FeCl3
(8.3 mmol) was added. After stirring at room temperature for 24 h,
13 ml of water was added. The organic layer was separated, dried over
MgSO4, filtered and concentrated. Bis[N-(2-ethylhexyloxylphenyl)-
carbazole-3-yl] (3) was obtained by column chromatography (eluent:
1
hexane=dichloromethane) (Yield: 67%) H NMR (300 MHz in CDCl3):
d 8.44 (2H, ArꢁH), 8.22 (2H, ArꢁH), 7.75 (2H, ArꢁH), 7.49ꢁ7.25
(10 H, ArꢁH), 7.14 (6H, ArꢁH), 4.21 (4H, ꢁNꢁCH2ꢁ), 2.05 (2H,
ꢁCHꢁ), 1.50ꢁ1.25 (16H, ꢁCH2ꢁ), 0.91 (12H, ꢁCH3); 13C NMR
(300 MHz in CDCl3): 158.7, 141.8, 140.5, 134.1, 130.1, 128.4, 125.9,
123.6, 123.3, 120.3, 119.6, 118.8, 115.6, 109.9, 70.8, 39.4, 30.5, 29.1,
23.9, 23.1, 14.1, 11.2.
In a flask, covered with aluminum foil, a stirred solution of 3
(2.87 mmol) in 70 ml of THF was cooled to 0ꢀC. NBS (5.74 mmol) was
added in small portions. The mixture was allowed to warm to room
temperature overnight. The THF was evaporated and the product
was purified by extraction with diethylether and water. The organic
layer was dried with MgSO4 and then monomer 3 was obtained by col-
umn chromatography (eluent: hexane=dichloromethane). (Yield: 86%)
SCHEME 3 Synthetic route to monomer 3.

100=[380]
H. Wang et al.
1H NMR (300 MHz in CDCl3): d 8.25 (2H, ArꢁH), 7.65 (2H, ArꢁH),
7.40ꢁ7.27 (10H, ArꢁH), 7.12 (2H, ArꢁH), 7.02 (4H, ArꢁH), 4.21
(4H, ꢁNꢁCH2ꢁ), 2.05 (2H, ꢁCHꢁ), 1.50-1.25 (16H, ꢁCH2ꢁ), 0.91
(12H, ꢁCH3); 13C NMR (300 MHz in CDCl3): d 158.8, 140.8, 140.4,
134.1, 129.4, 128.6, 128.3, 126.3, 124.9, 123.0, 122.6, 118.8, 115.6,
112.4, 111.3, 110.2, 70.7, 39.4, 30.5, 29.7, 23.8, 23.1, 14.1, 11.2.
N-[4-(2-Ethylhexyloxyl)-3,5-dibromomethylenephenyl]
carbazole (Monomer 4)
Synthetic procedure for monomer 4 was presented in Scheme 4.
4-Bromo-2,6-dimethylphenol (0.02 mol) in 50 ml of acetonitrile was
added to a suspension of potassium hydroxide (0.06 mol) in 200 ml of
acetonitrile which was prepared by vigorous stirring for 30 min under
N2. 2-Ethylhexyl bromide (0.02 mol) was added to the solution, fol-
lowed by refluxed for 48 h. Potassium hydroxide was filtered out,
and the solvent was evaporated, then the crude product was washed
with water and dried with MgSO4. The pure white liquid product,
5-bromo-2-(2-ethylhexyloxyl)-1,3-dimethylbenzene (4), was obtained
1
by silica column chromatography (eluent: hexane). (Yield: 63%). H
NMR (300 MHz in CDCl3): d 7.15 (2H, ArꢁH), 3.6 (2H, ꢁOꢁCH2ꢁ),
2.26 (6H, ArꢁCH3), 2.18 (9H, ꢁCHꢁ, ꢁCH2), 0.91 (6H, ꢁCH3).
SCHEME 4 Synthetic route to monomer 4.

Synthesis and Characterization of Poly(N-arylcarbazole-alt-aniline)
101=[381]
In the second step, 5-bromo-2-(2-ethylhexyloxyl)-1, 3-dimethylben-
zene (4) (112.79 mmol), carbazole (15.24 mmol), K3PO4 (26.72 mmol),
CuI (0.64 mmol) and trans-1,2-cyclohexanediamine (2.54 mmol) were
used. The reaction and workup procedure were carried out as
described [14,15]. White solid product, N-[4-(2-ethylhexyloxyl)-3,
5-dimethyl-phenyl]carbazole (5), was obtained. (Yield: 25%). 1H
NMR (300 MHz in CDCl3): d 7.38 (4H, ArꢁH), 7.26 (4H, ArꢁH), 7.16
(2H, ArꢁH), 3.6 (2H, ꢁOꢁCH2ꢁ), 2.30 (6H, ArꢁCH3), 2.18 (9H,
ꢁCHꢁ, ꢁCH2ꢁ), 0.91 (6H, ꢁCH3).
A mixture of N-[4-(2-ethylhexyloxyl)-3, 5-dimethyl-phenyl]carba-
zole (5) (3.68 mmol), NBS (8.09 mmol) and BPO (0.1618 mmol) were
added to CCl4 at room temperature. The following reaction and
workup procedure were carried out as described [14,15]. White solid
1
product, monomer 4, was obtained. (Yield: 45%). H NMR (300 MHz
in CDCl3): d 7.48 (4H, ArꢁH), 7.45 (4H, ArꢁH), 7.35 (2H, ArꢁH),
4.6 (4H, CH2Brꢁ), 3.96 (2H, ꢁOꢁCH2ꢁ), 2.25 (9H, ꢁCHꢁ, ꢁCH2ꢁ),
0.95 (6H,ꢁCH3).
Polymerization
A mixture of monomer 1 (2.60 mmol) (monomer 2, monomer 3 or mono-
mer 4) and aniline (2.60 mmol) was dissolved in toluene (30 ml). NaO-t-
Bu (7.8 mmol), Pd2(dba)3 (0.066 mmol) and P(t-Bu)3 (0.4 mmol) were
added to the solution at room temperature. The reaction mixture
was stirred at 100ꢀC for 48 h. After cooling to room temperature, the
mixture was quenched by adding aqueous ammonia (50 ml) and the
product was extracted with CHCl3. The organic fraction was concen-
trated and reprecipated from CHCl3=methonal several times. Then,
the products were filtered and dried in vacuum.
Characterization
NMR spectra were recorded on a Varian Unity Plus 300 using CDCl3.
Molecular weights and molecular weight distributions were measured
by Water gel permeation chromatograph (GPC) equipped with Styra-
gel HR 5E column using THF as an eluent against polystyrene stan-
dards at room temperature. Thermal analysis was performed on a
Seiko EXSTAR 6000 TG=DTA 6300 thermal analyzer at a heating of
20ꢀC=min for thermogravimetric analyzer (TGA) and at a heating of
10ꢀC=min for differential scanning calorimetry (DSC). UV-Visible
absorption spectra were taken by Shimadzu UV-2100. The photolumi-
nescence (PL) spectra excited by He-Cd laser at 325 nm were moni-
tored by Optical Multichannel Analyzer (Laser Photonics, OMA

102=[382]
H. Wang et al.
system). The ionization potential (IP) was measured by a photoelec-
tron spectroscopy (Riken Keiki AC-2).
RESULTS AND DISCUSSIONS
Alternating copolymers such as poly[N-(2-ethylhexyl)-3,6-carbazole-
alt-aniline] (P1), poly[(N-(2-ethylhexyloxy)-phenyl)-3,6-carbazole-alt-
aniline] (P2), poly[bis(6-N-(4-(2-ethylhexyloxy)-phenyl)-carbazole-3-yl)-
alt-aniline] (P3) and poly[N-(4-(2-ethylhexyloxy)-3,5-dimethylene-
phenyl)-carbazole-alt-aniline] (P4) were prepared by using Pd-catalyzed
polycondensation as presented in Scheme 5. The common structural
characteristics of P1, P2 and P3 were designed to have a carbazole
and a triarylamine unit in the polymer main chain. Compared to
N-alkyl-substituted P1, however, N-arylation was employed for P2
and P3. It was reported [16] that the properties of carbazole oligomers
were affected by replacing alkyl groups on N atom of carbazole with aryl
groups. The alkyl groups on N atom activated the carbazole ring system
through increasing the electron density, compared to the corresponding
aryl-substituted compounds. On the other hand, the aryl group on
N atom was twisted to the carbazole ring and thus could not delocalize
p-electrons from carbazole. Therefore, 4, 40-bis(9-carbazolyl)-biphenyl
(CBP) was used as a blue-emitting host matrix for phosphorescent-doped
OLED. In addition, P2 and P3 were prepared to investigate the effect of
N-aryl-substituted carbazole content in the polymer backbone. The car-
bazole group in P4 was placed in the side chain and the conjugation of
the polymer was reduced by incorporating methylene groups in polymer
backbone. In all series of polymers, alkyl groups such as 2-ethylhexyl
group in P1 and 2-ethylhexyloxy groups in P2, P3 and P4 were incorpor-
ated to increase the solubility of alternating copolymers in common
organic solvents.
All synthesized copolymers were found to be soluble in common
organic solvents such as benzene, toluene, chloroform and THF, and
showed good quality of film forming. The molecular weights of the
copolymers were measured by using GPC, and summarized in
Table 1. Relatively low molecular weights of P2 and P3 might be
explained by increased rigidity of polymer backbone with substituting
2-ethylhexyloxyphenyl group on N atom, resulting in premature pre-
cipitation of the copolymers during the polymerization. The thermal
stability of the copolymers was compared with decomposition tempera-
ture (Td) measured at 5 wt% loss in TGA, as shown in Figure 1 and
Table 1. These data revealed that the copolymers had excellent ther-
mal stability under nitrogen atmosphere. P3 and P4 showed relatively

Synthesis and Characterization of Poly(N-arylcarbazole-alt-aniline)
103=[383]
SCHEME 5 Polymerizations via palladium catalyzed polycondensation;
Reaction condition (I): Toluene, NaO-t-Bu, Pd2(dba)3, P(t-Bu)3, 100ꢀC.

104=[384]
H. Wang et al.
TABLE 1 Physical Properties of Polymers
Polymers
Mw (g=mol)
Mw=Mn
Tg (ꢀC)
Td (ꢀC)a
P1
P2
P3
P4
7,100
4,100
4,900
1.3
1.3
1.1
1.6
—
—
121
132
442
415
409
327
11,500
aTemperature resulting in 5% weight loss based on initial weight.
high Tg of 121ꢀC and 132ꢀC, respectively, in Table 1. The Tg’s of P1 and
P2 could not be measured in this DSC experiment.
UV-Visible absorption and PL emission spectra of the copolymers
are presented in Figures 2 and 3, respectively. In Figure 2, the
maximum UV-Visible absorption peaks of all copolymers were
observed at around 300 nm. When excited at their UV-Visible absorp-
tion maxima, the copolymers exhibited PL emission in the blue range
from 450 nm to 460 nm. Substitution effect of alkyl and aryl groups
on N atom was observed. Compared with kmax,PL of P1, kmax,PL of P2
was blue shifted to shorter wavelength, possibly attributed to
localized electron density by twisted conformation between carbazole
and aryl groups.
Electrochemical properties of the copolymers are summarized in
Table 2. Energy levels of the copolymers are also compared as shown
in Figure 4. The copolymers showed HOMO energy levels of ꢁ5.19 eV
for P1, ꢁ5.35 eV for P2, ꢁ5.29 eV for P3 and ꢁ5.64 eV for P4. Band
gap energy levels of the copolymers were also measured from the
FIGURE 1 TGA curves of alternating copolymers.

Synthesis and Characterization of Poly(N-arylcarbazole-alt-aniline)
105=[385]
FIGURE 2 UV-Vis absorption spectra of alternating copolymers.
FIGURE 3 Photoluminescence spectra of alternating copolymers.
TABLE 2 Electronic Properties of the Polymers
Polymers kmax,UV (nm) kmax,PL (nm) Band gap (eV)a HOMO (eV)b LUMO (eV)c
P1
P2
P3
P4
309
296
305
304
452
441
433
451
2.91
3.16
3.32
3.05
ꢁ5.19
ꢁ5.35
ꢁ5.29
ꢁ5.64
ꢁ2.28
ꢁ2.19
ꢁ1.97
ꢁ2.59
aCalculated from the crosspoint of UV-Vis and PL spectrum.
bMeasured by a RIKEN Keiki AC-2.
cEstimated from the HOMO and band gap.

106=[386]
H. Wang et al.
FIGURE 4 Schematic view of energy levels of alternating copolymers.
crosspoint of UV-Visible absorption and PL emission spectra to be
2.91 eV for P1, 3.16 eV for P2, 3.32 ev for P3 and 3.05 eV for P4. It
appeared that changing the substituent group on N atom of carbazole
unit from 2-ethylhexyl group in P1 to 2-ethylhexyloxyloxy-phenyl
group in P2-P4 increased band gap energy as well as decreased
HOMO energy levels. This might be originated from the twisted con-
formation between carbazole and aryl groups in P2-P4 as mentioned
previously.
CONCLUSIONS
Synthesis of poly(N-arylcarbazole-alt-aniline) copolymers such as
poly[(N-(2-ethylhexyloxy)-phenyl)-3,6-carbazole-alt-aniline] (P2), poly
[bis(6-N-(4-(2-ethylhexyloxy)-phenyl)-carbazole-3-yl)-alt-aniline] (P3)
and poly[N-(4-(2-ethylhexyloxy)-3,5-dimethylene-phenyl)-carbazole-alt-
aniline] (P4) was successfully accomplished by using palladium-
catalyzed polycondensation. The optical and electrochemical properties
of these copolymers were characterized and compared with those of
N-alkyl substituted counterpart, poly[N-(2-ethylhexyl)-3,6-carbazole-
alt-aniline] (P1). It was observed from the optical and electrochemi-
cal properties that poly(N-arylcarbazole-alt-aniline) copolymers could
be used as blue emitting host materials for PLEDs, because they

Synthesis and Characterization of Poly(N-arylcarbazole-alt-aniline)
107=[387]
showed blue emission in PL spectra and wider band gap energy
compared to the poly(N-alkylcarbazole-alt-aniline) copolymer.
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