Facile synthesis of carbazole-containing semiladder polyphenylenes for pure-blue electroluminescence

Article abstract of DOI:10.1021/ma050821u

A type of soluble and thermally stable semiladder polyphenylenes containing carbazole moieties (SLPFCs) have been prepared with a facile and short synthetic route. The full characterizations of structures and properties as well as the performances of elec

Full text of DOI:10.1021/ma050821u

6782
Macromolecules 2005, 38, 6782-6788
Articles
Facile Synthesis of Carbazole-Containing Semiladder Polyphenylenes
for Pure-Blue Electroluminescence
Song Qiu, Linlin Liu, Baoling Wang, Fangzhong Shen, Wu Zhang, Mao Li, and
Yuguang Ma*
Key Lab of Supramolecular Structure and Materials, Jilin University,
Changchun 130012, P. R. China
Received April 19, 2005; Revised Manuscript Received May 27, 2005
ABSTRACT: A type of soluble and thermally stable semiladder polyphenylenes containing carbazole
moieties (SLPFCs) have been prepared with a facile and short synthetic route. The full characterizations
of structures and properties as well as the performances of electroluminescence devices of the new polymers
are presented. The conjugated backbone of the SLPFCs contained three kinds of constituents: fluorene,
ladder-type tetraphenylene, and ladder-type hexaphenylene. The SLPFCs exhibit pure-blue fluorescence
(λmax ) 445 nm) with high efficiency up to 90% in solution. Electrochemical studies indicate that the
introduction of carbazole moieties raises the HOMO energy levels. Furthermore, the single-layer light-
emitting devices using the SLPFCs as the active layer show pure-blue emission (λmax ) 447 nm, CIE
coordinates: 0.15, 0.05) with maximum luminescence of 5500 cd/m2 and maximum luminance efficiency
of 0.556 cd/A. The attractive properties exhibited by the new semiladder polymers establish them as
good candidates for active layers in stable pure-blue light-emitting devices.
Introduction
stacking interactions between the planar-conjugated
main chains,3b,6 but more recently, it has been confirmed
that the long-wavelength emission arises from ketone
defects formed by oxidative electro- and photodegrada-
tion at the methine bridge when nonsubstituted or
monosubstituted fluorene units are present in the
polymer main chain.7
Conjugated polymers have attracted much attention
because of their potential application to large-area flat-
panel displays at low power consumption.1 One of the
most important goals of research on conjugated poly-
mers is the obtaining of a stable blue emission,2 which
is particularly required for full-color displays. Much
research into blue-emitting conjugated polymer materi-
als has centered on phenylene-based polymers such as
polyfluorenes (PF),3 ladder-type polyphenylenes,4 and
semiladder polyphenylenes5 because of their wide band
gap, well-defined structures, high-luminescence quan-
tum yield, and color tunability. In the past few decades,
Grimsdale and Mullen developed a series of semiladder
polyphenylenes with a structure intermediate between
PF and ladder-type polyphenylenes. These semiladder
polyphenylenes with the repeat units from indenofluo-
rene to bridged pentaphenylene show the emission color
from 430 to 460 nm, which red-shifts with increasing
the rigidity of the polymer chains. Among them, the
polymer of bridged pentaphenylene (Chart 1 a) can give
the emission maximum of 445 nm that has the opti-
mized pure-blue observable by the human eye.5d
As an alternative, increasing interest has been paid
to 2,7-substituted carbazole building blocks. In 2001,
Leclerc reported the first syntheses of 2,7-carbazole-
based conjugated polymers. After that, many studies
have been devoted to the development of novel 2,7-
carbazole-based homopolymers,8,9 copolymers,10 and oli-
gomers11 as potential active materials in electronic
applications such as organic light-emitting diodes (OLE-
Ds), field-effect transistors, and photovoltaic devices.
2,7-Substituted carbazoles contain a rigid biphenyl unit
like fluorene that can lead to a large band gap with
efficient blue emission and improves the hole-accepting
and transporting properties. The nitrogen bridge is not
oxidizable to a carbonyl like fluorene and facile substi-
tution to improving the solubility and processability of
polymers. Several conjugated ladder-type polyphe-
nylenes containing carbazole moieties have been present
recently (Chart 1b).12 These polymers show blue-green
or yellow-green emission and obviously aggregation
behavior, leading to both color instability and reduced
efficiency.12b
However, polyfluorene derivatives often show a tailed
emission band at long wavelengths in solid-state or
light-emitting devices, leading to both color instability
and reduced efficiency.3 The source of this long wave-
length emission was initially attributed to the formation
of an excimer, owing to interchain interactions and π-π
In this paper, we present a novel kind of semiladder
poly(p-phenylene)s containing carbazole and fluorene
moieties (SLPFCs) with a facile and short synthetic
strategy. The conjugated backbone of the polymers
contained three kinds of constituents: fluorene, ladder-
* Author to whom correspondence should be addressed. E-
mail: ygma@jlu.edu.cn.
10.1021/ma050821u CCC: $30.25 © 2005 American Chemical Society
Published on Web 06/21/2005

Macromolecules, Vol. 38, No. 16, 2005
Semiladder Polyphenylenes for Pure-Blue Electroluminescence 6783
Chart 1
type tetraphenylene, and ladder-type hexaphenylene.
The polymer backbone with such multiform constituents
is expected to be useful for inhibiting the aggregation
of planar-conjugated polymers such as the correspond-
ing ladder polymers. The full characterizations of
structures and properties as well as the performances
of electroluminescence devices of the SLPFCs are pre-
sented. The attractive properties of this class of new
semiladder polymers establish them as good candidates
for active materials in stable pure-blue polymer light-
emitting diodes and other polymer-based optical and
electrooptical applications.
are outlined in Scheme 1. We prepared 2,7-dibromo-
carbazole with an efficient route developed by Dierschke
et al.13 The N-alkylation of the 2,7-dibromo-carbazole
in N,N-dimethylformamide (DMF) by K2CO3 and 2-eth-
ylbromohexane leads to 2,7-dibromo-9-ethylhexylcar-
bazole (1) in 78% yield. Then, a Friedel-Crafts acylation
of compound 1 with benzoic anhydride or 4-tert-butyl-
benzoyl chloride using an AlCl3 catalyst in 1,2-dichlo-
roethane gives monoacylation products 2a and 2b in
good yields by a rigorous 1:1 feed rate. The copolymer-
ized monomer 2,7-bis(4,4,5,5-tetramethyl-1,3,2-diox-
aborolan-2-yl)-9,9-bis(2-ethylhexyl)-fluorene (3) was pre-
pared according to the literature.14
Results and Discussion
To prepare the novel carbazole-based semiladder
polymers, we adapted the synthetic approach developed
by Scherf.4 The first step is a Pd0-catalyzed Suzuki
Synthesis and Characterization. The synthetic
procedures used to prepare the monomers and polymers
Scheme 1. Synthesis of Semiladder Polymers (SLPFCs)

6784 Qiu et al.
Macromolecules, Vol. 38, No. 16, 2005
Scheme 2. Structure Analysis of Semiladder Polymers SLPFCs
cross-coupling for the synthesis of the precursor alter-
nating copolymer P1. Then the precursor P1 was trans-
formed into the polyalcohol P2 with methyllithium. The
final semiladder polymers (SLPFCs) were obtained by
the ring-closure reaction of P2 with boron trifluoride
proportion of the four constituents of SLPFCs will be
25% each. Neither constituents C3 nor F can continu-
ously present with itself in the SLPFC’s backbone
because the fluorene and carbazole moieties have to be
the adjoining moieties defined by the Suzuki polymer-
ization reaction. The constituents C2 can continuously
present and occupy the half proportion of SLPFCs; as a
result, the properties of final product SLPFCs will be
analogous to that of the polymer of ladder-type tet-
raphenylenes (C2). Such an irregular conjugated back-
bone will inhibit the formation of aggregation like the
corresponding ladder polymers.4,12
etherate via
a polymer-analogous intramolecular
Friedel-Crafts alkylation. Immediately after the addi-
tion of boron trifluoride, a strong blue fluorescent
solution is obtained, indicating the formation of the
SLPFCs.
Polymer SLPFC-a is readily dissolved in common
organic solvents such as chloroform, dichloromethane,
tetrahydrofuran (THF), and toluene, while the polymer
SLPFC-b can only be readily dissolved in chloroform
and partially dissolved in THF. The number-average
molecular weights (Mn) and the weight-average molec-
ular weights (Mw) of the polymers were measured by
gel-permeation chromatography (GPC) using polysty-
rene as a standard. The Mn and Mw of SLPFC-a are
estimated to be 7895 and 10339, respectively, corre-
sponding to about 44 benzene rings in the backbone.
The Mn of SLPFC-b is 6677, indicating that the tert-
butyl group is useless for increasing the solubility and
molecular weights of the polymer.
In the backbone of the precursor P1, the acyl groups
randomly locate at the 3- or 6-position of carbazole
moieties, and there are four kinds of different arrange-
ment conformations as shown in Scheme 2. As a result,
the polymer SLPFCs present a very complex structure
with four kinds of constituents in the backbone after
the ring-closure reaction of P2. Two of these constitu-
ents (C2) are mirror images of each other with the
structure of ladder-type tetraphenylene. The other two
constituents (F and C3) are fluorene and ladder-type
hexaphenylenes, respectively. If the acyl groups in
carbazole moieties are a totally random presence, the
The structures of the polymers were characterized by
NMR, FT-IR, and elemental analysis. 1H NMR spectra
of P1 are consistent with the structure. But the well-
1
resolved H NMR spectra of SLPFCs were not obtain-
able because of the complex structure. FT-IR spectra
can help us to confirm the complete reaction of the
intramolecular ring closure. As shown in Figure 1, the
keto group in 1660 cm-1 almost disappears when
comparing the SLPFC-a with the precursor polymer
P1, while the fluorenone defect or hydroxyl groups in
1716 cm-1 or 3420 cm-1 were not observed, indicating
that the incomplete ring closure reaction or defects were
not found in SLPFCs.
SLPFCs exhibit good thermal stability measured by
thermogravimetric analysis (TGA) under a nitrogen
atmosphere. The polymers both have the onset degrada-
tion temperatures (Td) above 370 °C (Figure 2). The
phase transitions of the polymers were determined by
differential scanning calorimetry (DSC) in a nitrogen
atmosphere at a heating rate of 5 K/min, but we
observed neither a glass transition process (Tg) nor other
thermal processes (such as liquid-crystal phase) from
20 °C to 300 °C.

Macromolecules, Vol. 38, No. 16, 2005
Semiladder Polyphenylenes for Pure-Blue Electroluminescence 6785
Figure 1. FT-IR spectra of SLPFC-a. Inset: the detailed
spectra of P1 and SLPFC-a in the region of 1800-1550 cm-1
Figure 3. Absorption and emission spectra of polymer P1 in
THF.
.
Figure 2. thermogravimetric analysis (TGA) of SLPFC-a and
SLPFC-b.
Figure 4. Absorption and emission spectra of polymer
SLPFC-a in solution (THF) and film.
Spectroscopic Properties. The UV-vis absorption
and photoluminescence (PL) data of polymers are shown
in Table 1, Figure 3, and Figure 4. The optical properties
of the precursor P1a and the semiladder polymer
SLPFC-a present enormous differences that can be
attributed to the change in the conformation. The
absorption of P1a in THF shows an unstructured broad
peak centered at 365 nm, while SLPFC-a showed as
distinctly shifted toward low energy. The shape and
peak value of P1a in the PL spectrum is very similar
to those of PF, but the PL quantum efficiency of P1a is
very low.
According to expectation, the absorption spectra of
SLPFCs in THF display broad absorption bands peaking
around 382, 411, and 426 nm without the well-resolved
vibrational energy bands, which generally appear in the
spectra of the other semiladder or ladder-type polymers
with the well-defined structure. At the same time, a
steep absorption edge and a very small Stokes shift less
than 17 nm is observed, which indicates that SLPFCs
mostly remain the character of a rigid, planar, one-
dimensional π-system.
The PL spectrum of SLPFC-a in THF shows a pure-
blue emission with a sharp peak centered at 443 nm
and a shoulder peak at 465 nm. The position of the
emission maximum is very close to that of ladder-type
pantaphenylenes (445 nm) and lies between PIF (430
nm)5b and MeLPF (460 nm).4c The absorption and PL
spectra of SLPFC-a in film are almost identical with
those in solution, and no bathochromic shift is observed,
which indicates that there is almost no change in
the conformation of the SLPFCs’ backbone from the
solution to the solid state. The slight increase in rela-
tive intensity around 500-nm emissions in films may
be ascribed to the stronger self-absorption effects than
that in solution. Generally, the low-energy emission
from the fluorenone defects around 550-570 nm was
enhanced in the film compared to the corresponding
solution because of the increased interchain energy
transfer. However, in the PL spectra of SLPFC-a in
solid film, no low-energy tailed peak is found. From
Table 1. Spectral Properties of Polymers
abs (in THF)
λmax (nm)
PL (in THF)a PL of filma
λmax (nm) λmax (nm)
PL efficiency
EL
λmax (nm)
b
polymer
in THF (ΦPL
)
P1
365
411 (426)
410 (425)
410
442 (466)
442 (466)
< 2%
93%
89%
SLPFC-ac
SLPFC-b
445 (470)
445 (470)
447 (473)
447 (473)
a Excited at 380 nm. b Calculated by relative method.15 c Peaks that appear as shoulders or weak bands shown in parentheses.

6786 Qiu et al.
Macromolecules, Vol. 38, No. 16, 2005
Figure 5. Cyclic voltammetry curves of the drop-cast films
of SLPFC-a measured in 0.1 M Bu4NBF4 acetonitrile solution
at a scan rate of 100 mV/s at room temperature (vs an Ag
quasireference electrode).
Figure 6. Electroluminescent spectra of SLPFC-a (ITO/
PEDOT/SLPFC-a/Ba/Ag) at different voltages. Inset: Cur-
rent-brightness-voltage characteristics of the device.
of the spectra is very stable in different voltages, and
no emission of the oxidative degradation of the polymers
or the ketone defects around 540-570 nm are observed.
The control of emissive layer thickness is important for
the shape of EL spectra. The thicker emissive layer
(more than 120 nm) will cause rather strong self-
absorption, resulting in a blue-green emission.19 The
best devices with the emissive layer of ca. 70-80 nm
were obtained by controlling the concentration of the
solution and the speed of the spin coating. Figure 6
shows the current-brightness-voltage curves for the
device of ITO/PEDOT:PSS/SLPFC-a/Ba/Ag. With the
increase of forward-bias voltage, the current and bright-
ness in the devices increase. Light emitting is observed
with a turn-on voltage of 5.5 V and the maximum
brightness over 5500 cd/m2 in the best devices. The
maximum luminance efficiency of 0.56 cd/A is achieved
at a brightness of 830 cd/m2. Further improvement in
device efficiency and brightness can be obtained by
adjusting the device structure and electrode metals with
more efficient injection and balanced transport of both
charge carriers.
these results, no evidence indicates that there is any
fluorenone defect or aggregation in the semiladder
polymers.
The PL efficiency (ΦPL) of the polymers in THF was
measured and compared to quinine sulfate (2 × 10-5
M, assuming ΦPL of 0.546 at 365 nm excitation in 1 N
H2SO4)15 as a standard. SLPFCs exhibited very high PL
efficiencies in THF in the range of 89-93% (Table 1),
corresponding to few routes existing for nonradiative
deactivation.
Electrochemical Study. The electrochemical be-
havior and the electrochemical stability of these poly-
mers was investigated by cyclic voltammetry (CV). The
CV measurement on drop-cast polymer film was con-
ducted in acetonitrile with 0.1 M tetrabutylammonium
tetrafluoroborate as an electrolyte at room temperature.
The CV curves were referenced to an Ag quasireference
electrode, which was calibrated using an internal stan-
dard, ferrocene/ferrocenium redox couple (0.35 V vs Ag/
AgNO3).
As shown in Figure 5, the SLPFC-a shows typical
reversible p-doping patterns similar to those reported
for the alternative copolymers of fluorene and 3,6-
carbazole.17 The onsets for reduction and oxidation
occurred at 0.786 and -2.543 V, from which we estimate
the lowest unoccupied and highest occupied molecular
orbital (LUMO and HOMO) energy levels to be 2.06 and
5.39 eV (vs SCE), respectively, given an energy level of
4.6 eV for Ag/Ag+. This corresponds to an electrochemi-
cal band gap of 3.3 eV. Compared with poly(9,9-
dioctylfluorene) (Ip ) 5.7 eV),16 the SLPFC-a has the
higher HOMO levels, so that efficient hole injection
should occur from ITO anodes (work function 5.0 eV)
or the PEDOT layer (5.2 eV). The high value of HOMO
can be attributed to the electron-donating effect of the
nitrogen atom in carbazole moieties.
Conclusion
We prepared a novel kind of semiladder poly(p-
phenylene) containing carbazole moieties with a facile
and short synthetic strategy. The backbone of the
polymer contained three kinds of constituents: fluorene,
ladder-type tetraphenylene, and ladder-type hexaphe-
nylene. The polymer backbones with such multiform
constituents inhibit the aggregation of planar-conju-
gated polymers. The high-efficiency pure-blue emission
in photoluminescence spectra is observed from the
polymer both in the solution and in the solid film.
Electrochemical studies indicate that the introduction
of carbazole moieties raises the HOMO energy levels.
The single-layer light-emitting devices using the poly-
mers as the active layer show stable pure-blue emission
with maximum luminescence of 5500 cd/m2 and maxi-
mum luminance efficiency of 0.556 cd/A. The attractive
properties of this class of new semiladder polymers
establish them as good candidates for active materials
in stable pure-blue polymer light-emitting diodes and
other polymer-based optical and electrooptical applica-
tions.
Device Characteristics. The single-layer polymer
light-emitting diodes (PLEDs) with the configuration of
ITO/PEDOT:PSS/SLPFC-a/Ba/Ag were fabricated to
investigate the electroluminescent properties of the
SLPFCs. As shown in Figure 6, the EL spectra of
SLPFC-a show pure-blue emission (CIE coordinates18
0.15, 0.05) with a peak wavelength around 447 nm and
a shoulder around 472 nm, which are similar to the PL
spectra of the corresponding polymer film. The shape

Macromolecules, Vol. 38, No. 16, 2005
Semiladder Polyphenylenes for Pure-Blue Electroluminescence 6787
mixture was stirred for 8 h at room temperature and then
quenched with ice. The inorganic precipitate was dissolved in
Experimental Section
Measurement. 1H and 13C NMR spectra were recorded on
a Bruker AVANCZ 500 MHz spectrometer with chloroform-d
as solvent and tetramethylsilane (TMS) as the internal
standard. FT-IR spectra were recorded on a Bruker IFS66V
FT-IR spectrometer in the 800-4000 cm-1 region by casting
the solution of polymers on a CaF2 substrate. UV-vis and
fluorescence spectra were obtained on a Shimadzu UV-3100
spectrophotometer and a Shimadzu RF-5301PC spectropho-
tometer, respectively. Thermogravimetric analysis (TGA) was
conducted on a Perkin-Elmer Thermal Analysis system under
a heating rate of 20 K/min and a nitrogen flow rate of 80 mL/
min. Differential scanning calorimetry (DSC) was also run on
a Perkin-Elmer thermal analysis system. Elemental analysis
was performed on a Flash EA 1112, CHNSO instrument.
Number-average and weight-average molecular weights of
polymer products were determined by gel-permeation chro-
matography (GPC) with a HPLC Waters 510 using a series of
monodisperse polystyrene as standards in THF (HPLC grade)
at 308 K. Cyclic voltammetry (CV) measurements were
performed on a BAS100W with a three-electrode cell in a 0.1-M
n-Bu4NBF4 solution in acetonitrile at a scan rate of 100 mV/s
at room temperature under nitrogen. A silver wire (2-mm
diameter) sealed in a soft glass rod, a platinum wire (0.5-mm
diameter), and a platinum disk (1-mm diameter) were used
as the quasireference electrode, counter electrode, and working
electrode, respectively. The Ag quasireference electrode was
calibrated using a ferrocene/ferrocenium redox couple as an
external standard prior to measurements.
LED Device Fabrication and Characterization. PLED
devices were fabricated on glass substrates coated with ITO.
The substrate was cleaned by a general procedure, which
included sonication in detergent followed by repeated rinsing
in deionized water, acetone, and ethanol, and, prior to use,
placed in boiling H2O2 for 5 min. A conducting polymer
dispersion of poly(3,4-ethylenedioxythiophene) doped with
poly(styrene sulfonic acid) (PEDOT:PSS) was obtained from
Bayer Corp. The hole injection layer of PEDOT: PSS was
prepared from a water dispersion with the thickness of 50 nm
and baked at 170 °C for 20 min under N2 atmosphere. The
emitting layer of the polymer was spin coated from an oxygen-
free toluene solution onto the hole injection layer with a
thickness of 100 nm. Finally, a Ba and Ag cathode was vacuum
deposited onto the polymer layers at a pressure below 5 × 10-6
Torr. The emitting areas of the EL devices were 2 × 2 mm2.
EL spectra of the devices were measured by a PR650 fluores-
cence spectrophotometer. Luminance-current density-voltage
(L-I-V) curves were recorded with a Keithley 2400 instru-
ment. All measurements were carried out at room temperature
under ambient conditions.
2 M HCl, and the product was extracted with CH2Cl2. The
organic fractions and the solvent were dried under reduced
pressure. The product was purified by column chromatography
(silica gel, 2% EtOAc in petroleum ether) to give 181 mg of 2a
as a white crystal; mp 95-96 °C (Yield: 73%). 1H NMR (CDCl3,
500 MHz): δ 8.06 (s, 1H), 7.87 (m, 3H), 7.64 (s, 1H), 7.61 (t,
1H, J ) 7.5 Hz), 7.55 (s, 1H), 7.48 (t, 2H, J ) 7.5 Hz), 7.37 (d,
1H, J ) 8.5 Hz), 4.13 (m, 2H), 2.06 (m, 1H), 1.43-1.27 (br m,
8H), 0.95 (t, 3H, J ) 7.5 Hz), 0.90 (t, 3H, J ) 7.0 Hz).
3-(4-tert-Butyl-benzoyl)-2,7-dibromo-N-(2-ethylhexyl)-
carbazole (2b). The procedure was the same as that per-
formed on 3a. The product was isolated as a white crystal;
mp 120-122 °C. (Yield: 70%). 1H NMR (CDCl3, 500 MHz): δ
8.04 (s, 1H), 7.86 (d, 1H, J ) 8.5 Hz), 7.82 (d, 2H, J ) 8.5 Hz),
7.64 (s, 1H), 7.55 (d, 1H, J ) 1.5 Hz), 7.49 (d, 2H, J ) 8.5 Hz),
7.36 (dd, 1H, J ) 8.5 Hz and J ) 1.5 Hz), 4.13 (m, 2H), 2.06
(m, 1H), 1.40-1.28 (br m, 17H), 0.95 (t, 3H, J ) 7.5 Hz), 0.90
(t, 3H, J ) 7.0 Hz).
Polymer P1a. A mixture of 2a (111.0 mg, 0.205 mmol), 2,7-
bis(4,4,5,5-tetramethyl-1,3,2-dioxaborolan)-9,9-bis(2-ethylhexy-
l)fluorene (131.9 mg, 0.205 mmol), tetrakis(triphenylphosphino)-
palladium(0) (8 mg), 3 mL of toluene, 1 mL of 1-butanol and
1 mL of aqueous K2CO3 (2 M) was refluxed for 48 h under
nitrogen. The mixture was poured into water and extracted
with dichloromethane. The organic layer was washed with
brine and water, then dried over MgSO4 and concentrated,
then the polymer was precipitated into methanol, and the
crude product was dissolved in dichloromethane and repre-
cipitated into methanol to give P1a of 102.0 mg as a yellow-
green solid (Yield: 65%). 1H NMR (CDCl3, 500 MHz): δ 8.23-
8.03 (m, 2H), 7.89-7.29 (br m, 14H), 4.31 (d, 2H), 2.25-1.80
(br m, 5H), 1.50-1.27 (br m, 8H), 1.03-0.45 (br m, 36H). Mn
7121, Mw 8693, Mw/Mn 1.13 (GPC, PS calibration).
Polymer P1b. Yellow-green solid (Yield: 67%). 1H NMR
(CDCl3, 500 MHz): δ 8.31-8.02 (m, 2H), 7.89-7.36 (br m,
13H), 4.31(d, 2H), 2.24-1.79 (br m, 5H), 1.46-1.30 (br m, 17H),
1.01-0.48 (br m, 36H). Mn 6602, Mw 7527, Mw/Mn 1.24 (GPC,
PS calibration).
Polymer P2a (Polymer P2b). A solution of polymer P1a
(P1b) (100 mg) in 40 mL of toluene was treated with a solution
of 1.6 M methyllithium in diethyl ether (1 mL, 1.6 mmol). The
mixture was stirred for 30 min at room temperature and
carefully quenched with ethanol, water, and dilute hydrochlo-
ric acid. The organic layer was washed with water and dried
with MgSO4, and the solvent was removed under reduced
pressure to give light-yellow solid (Yield: 90.2-92.1%).
Polymer SLPFC-a. A solution of polymer P2a (100 mg)
in 20 mL of methylene chloride was treated with boron
trifluoride etherate (300 mg, 2.11 mmol). After stirring for 5
min at room temperature, 10 mL of ethanol was added to the
mixture to destroy the catalyst. The organic layer was then
carefully washed with water, dried, and concentrated. Pre-
cipitation in methanol gave 89.0 mg SLPFC-a as a yellow-
Materials. Tetrahydrofuran (THF) for spectral study was
distilled over sodium/benzophenone, and toluene was distilled
over P2O5. Other solvents were used as commercial p.a. quality.
2,7-Dibromo-9H-carbazole was prepared according to literature
procedures. All other chemicals were purchased from Aldrich
and Acros and used without any further purification.
1
green powder (Yield: 89.2%). H NMR (CDCl3, 500 MHz): δ
Synthesis. 2,7-Dibromo-N-(2-ethylhexyl)carbazole (1).
To a solution of 2,7-dibromo-carbazole (2.0 g, 6.15 mmol) in
20 mL of DMF was added anhydrous K2CO3 (1.8 g, 13.0 mmol).
The solution was stirred at 80 °C for 2 h under N2, and then
2-ethylhexybromide (2.3 g, 12.0 mmol) was added. The mixture
was stirred at 80 °C for 24 h and then quenched with 30 mL
water. The aqueous layer was extracted with diethyl ether
three times. The organic fractions were dried over MgSO4, and
the solvent was removed under reduced pressure. The residue
was purified by column chromatography (silica gel, 10% CHCl3
in cyclohexane) to give 2.01 g of 1 as a white crystal; mp 99-
8.09-7.16 (br m), 4.33(d, 2H), 2.24-2.02 (br m, 8H), 1.53-
0.56 (br m). (C57H69N)n: Calcd C 89.12, H 9.05, N 1.82; Found
C 86.82, H 9.05, N 1.37. FTIR(KBr): 2923, 2855, 1599, 1456,
1372, 1332, 1257, 1190, 1024, 877, 809, 695. Mn 7895, Mw
10339, Mw/Mn 1.310 (GPC, PS calibration).
Polymer SLPFC-b. Precipitation in methanol gave
SLPFC-b as a yellow-green powder (Yield: 86%). 1H NMR
(CDCl3, 500 MHz): δ 8.13-7.24 (br m), 4.33 (d, 2H), 2.25-
2.02 (br m, 8H), 1.53-0.56 (br m). (C61H77N)n: Calcd C 88.88,
H 9.42, N 1.70; Found C 85.96, H 9.66, N 1.33. FTIR(KBr):
2925, 2860, 1604, 1458, 1376, 1333, 1257, 1193, 1014, 879, 807,
577. Mn 6677, Mw 7920, Mw/Mn 1.186 (GPC, PS calibration).
1
100 °C (Yield: 78%). H NMR (CDCl3, 500 MHz): δ 7.90 (d,
2H, J ) 9 Hz), 7.51 (s, 2H), 7.35 (d, 2H, J ) 9 Hz), 4.09 (m,
2H), 2.03 (m, 1H), 1.38-1.28 (m, 8H), 0.94-0.86 (m, 6H).
3-Benzoyl-2,7-dibromo-N-(2-ethylhexyl)carbazole (2a).
To a mixture of compound 2 (200 mg, 0.458 mmol) and AlCl3
(150 mg, 1.13 mmol) in 1,2-dichloroethane (3 mL) was added
benzoic anhydride (104 g, 0.46 mmol) slowly at 0 °C. The
Acknowledgment. We are grateful for financial
support from National Science Foundation of China
(grant numbers 20125421, 90101026, 50303007,
20474024), Ministry of Science and Technology and

6788 Qiu et al.
Macromolecules, Vol. 38, No. 16, 2005
(7) (a) Scherf, U.; List E. J. W. Adv. Mater. 2002, 14, 477. (b)
List, E. J. W.; Guentner, R.; Scanducci de Freitas, P.; Scherf,
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(8) Morin, J.-F.; Leclerc, M. Macromolecules 2001, 34, 4680.
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Ministry of Education of China (grant numbers
2002CB6134003 and PCSIRT).
Supporting Information Available: 1H NMR spectra of
all the new compounds synthesized. This material is available
free of charge via the Internet at http://pubs.acs.org.
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