New ladder-type poly(p-phenylene)s containing fluorene unit exhibiting high efficient electroluminescence

Article abstract of DOI:10.1021/ma034929q

A type of soluble and thermally stable ladder-type poly(p-phenylene) (LPF) with fluorene units in polymer backbone has been synthesized by Suzuki coupling and Friedel-Crafts ring-closing reaction. The full characterization of structures and properties as

Full text of DOI:10.1021/ma034929q

Macromolecules 2003, 36, 9823-9829
9823
New Ladder-Type Poly(p-phenylene)s Containing Fluorene Unit
Exhibiting High Efficient Electroluminescence
Son g Qiu , P in g Lu , Xia o Liu , F a n gzh on g Sh en , Lin lin Liu , Yu gu a n g Ma ,* a n d
J ia con g Sh en
Key Lab of Supramolecular Structure and Materials, J ilin University,
Changchun 130023, P. R. China
Received J uly 3, 2003; Revised Manuscript Received August 28, 2003
ABSTRACT: A type of soluble and thermally stable ladder-type poly(p-phenylene) (LPF) with fluorene
units in polymer backbone has been synthesized by Suzuki coupling and Friedel-Crafts ring-closing
reaction. The full characterization of structures and properties as well as the performances of
electroluminescence devices of the new ladder polymers are presented. LPFs show the well-defined
structures, high molecular weights, excellent thermal stability, and good solubility in common organic
solvents. The high-efficiency emission and absence of low-energy emission band in photoluminescence
spectra are observed from LPFs both in the solution and in the solid film. Furthermore, the single layer
light-emitting device using LPFs as the active layer shows very stable blue-green emission with maximum
luminescence of 5400 cd/m2 and maximum luminance efficiency of 0.66 cd/A. The extraordinary low
concentration of keto defects in LPFs may be corresponding to the improvement in optical and device
properties. The attractive properties exhibited by new ladder-type poly(p-phenylene)s establish them as
good candidates for active layers in light-emitting devices.
In tr od u ction
photophysical properties of conjugated polymers because
the excited energy migration along conjugated polymer
chains and a transfer to defects are more efficient,
especially in the solid state due to an additional inter-
chain energy migration process. These results let us
reconsider the possible defects in LPPP and search the
possible route to depress the defect sites in LPPP. To
look back at each step in the synthesis of LPPP, the
incomplete reaction of keto groups in the reduction
process and incomplete cyclization in the final Friedel-
Crafts ring-closing reaction may induce the keto survi-
vors. Thus, a careful study on both reactions is strongly
required.
In this paper, we introduce a type of LPPP derivative
(LPF, as shown in Chart 1d,e). Identical LPPP deriva-
tives have been prepared by Forster (Scherf group) in
2000,10 but the detailed characteristics of polymer
structure and measurement in physical properties, e.g.,
electroluminescence, are not studied. Different from
LPPPs that were built from the phenylene units, the
LPFs were obtained by the fluorene monomer as one of
the initial building blocks. Since fluorene units are
rigidly bridged and they occupy half of the skeleton in
the precursor polymer before ring-closing reaction, this
change can partially reduce the probability of the
formation of defects originating from incomplete cy-
clization. The resultant LPFs exhibit distinct improve-
ment in color purity, spectral stability, and the perfor-
mance of LED devices. On the other hand, the incorp-
orated fluorene units in LPFs backbone also provide the
opportunity to modify the polymer properties by chang-
ing the substitutes at the active C-9 position of fluorene
rings, as has been extensively used for the modification
of fluorene-based conjugated polymers.11
In the past few decades, conjugated polymers have
attracted broad interest due to their potential applica-
tion to full color flat panel displays.1 Among these
conjugated polymers, ladder-type poly(p-phenylene)
(LPPP) and its derivatives are an important class of
polymers materials served as active layer of light-
emitting diodes (LEDs),2 energy-transfer host material,3
and important model compound in photophysical re-
search fields.4 In 1991, for the first time, Scherf and
Mu¨llen showed that structural regular LPPP (Chart 1a)
can be obtained by intramolecular Friedel-Crafts ring-
closing reaction of a designed soluble poly(p-phenylene).5
The original LPPP showed an unstructured broad
emission from 460 to 600 nm in the solid state compared
to its sharp fluorescence emission around 460 nm in
solution. The low-energy emission band of LPPP con-
tributed to the formation of the excimer owing to
interchain interactions and π-π stacking interaction
between the planar conjugated segments.6 Conse-
quently, the distinct reduction of the low-energy emis-
sion band in the LPPP derivatives with slight structure
variations such as MeLPPP (introduction of a methyl
group at the methylene bridge) (Chart 1b) was obtained
through introduction of spatial hindrance to inhibit the
aggregation of planar conjugated polymers.7 Within the
past 5 or 6 years MeLPPP has been intensively tested
for many potential applications.8
However, recently Scherf et al. provided more power-
ful evidence indicating that the low-energy emission
bands are due to keto defect sites in the polymer
backbone, especially for the polyfluorene (PF) deriva-
tives with methylene-bridged hydrogen substituents.9
It is reasonable that the defects in very low concentra-
tion (even no indication in the general analysis method,
ca. IR and NMR) play a more important role for
Resu lts a n d Discu ssion
Syn th esis a n d Ch a r a cter iza tion . Scheme 1 shows
the synthetic routes to the monomers for LPFs. 1,4-
Dibromo-2,5-benzenedicarboxylic acid (1) was synthe-
* Corresponding author: Fax +86-431-8980729, e-mail ygma@
jlu.edu.cn.
10.1021/ma034929q CCC: $25.00 © 2003 American Chemical Society
Published on Web 12/06/2003

9824 Qiu et al.
Macromolecules, Vol. 36, No. 26, 2003
Ch a r t 1
Sch em e 1. Syn th etic Rou te to th e Mon om er s, Rea gen ts, a n d Con d ition s
sized via a two-step oxidation of 1,4-dibromo-p-xylene.12
1 was then conversed to the 2,5-dibromoterephthaloyl
dichloride (2) by treatment with thionyl chloride. To
obtain 2′,5′-dibromo-4-decyl-4′-(4-decylbenzoyl)benzophe-
none (3), the reaction of 2 with decylbenzene via
Friedel-Crafts acylation in CH2Cl2 according to the
literature was unsuccessful; however, in benzene sol-
vent, 3 was obtained with a satisfactory yield of 72.3%.
The copolymerized monomer 2,7-bis(4,4,5,5-tetramethyl-
1,3,2-dioxaborolan-2-yl)-9,9-dihexylfluorene (4) was pre-
pared using the well-known route.13
Scheme 2 shows the preparation of novel ladder poly-
(p-phenylene) with the well-known process.5,7 For the
first step, the alternating copolymer P 1 can be prepared
from a Suzuki coupling reaction between 3 and 4 using
(PPh3)4Pd(0) as catalyst in a mixture of toluene and 2
M K2CO3 aqueous solution for 2 days. For the second
step, there exist two routes. One is the keto group
alkylated with methyllithium to give P 2a , and the other
is the keto group reduced with lithium aluminum
hydride to give P 2b. To obtain good quality LPFs, the
remaining keto groups must be reduced completely in
this step, so the reducing agents methyllithium and
lithium aluminum hydride are need largely excessive
to ensure complete reduction of keto groups. For the last
step, the final products, MeLPF and HLPF, were
obtained by the ring-closure reaction of P 2a (P 2b) with
boron trifluoride etherate via a polymer-analogous
intramolecular Friedel-Crafts alkylation. The polymers
are yellow-green powder after repeated precipitation
with CHCl3/methanol and are readily dissolved in
common organic solvents such as chloroform, dichloro-
methane, tetrahydrofuran, toluene, and xylene.
The number-average molecular weights (Mn) and the
weight-average molecular weights (Mw) of the polymers
were measured by gel permeation chromatography
(GPC) using polystyrene as a standard (Table 1). The
Mn of MeLPF is 22 000, corresponding to about 70

Macromolecules, Vol. 36, No. 26, 2003
Ladder-Type Poly(p-phenylene)s 9825
Sch em e 2. Syn th etic Rou te to MeLP F a n d HLP F
Ta ble 1. Molecu la r Weigh t a n d th e Th er m ogr a vim etr ic
An a lysis Da ta of MeLP F a n d HLP F
in the low-energy range can be explained by the interac-
tion between the n-π* orbital of the keto substituents
and the π-π* orbital of the conjugated backbone, and
such interaction was absent in its reduced products P 2a
and P 2b, resulting in an increase in absorption energy.
An unstructured broad peak centered at ca. 500 nm was
observed from the PL spectrum of P 1 solution, which
is ascribed to keto substituents, while a pure-blue
emission peaking at 410 nm and never the 500 nm peak
was observed from P 2a and P 2b solution, suggesting
the complete reduction of the keto group to hydroxyl.
polymer
Mn
Mw
PD
Td (°C)
MeLPF
HLPF
22 307
16 359
42 864
27 044
1.92
1.65
358.3
400.9
benzene rings (25 repeated units) in the backbone,
which is a relatively high value in polymers synthesized
using the Suzuki coupling reaction.
The chemical structures of LPFs were fully character-
ized by 1H NMR, 13C NMR, FT-IR, and elemental
analysis. 1H NMR and 13C NMR spectra of polymers are
consistent with the structure of the target polymers.
Figure 4 shows the UV-vis absorption and PL spectra
in solution and film of MeLPF and HLPF. The absorp-
tion spectra of LPFs display a steep absorption edge and
a well-resolved vibrational energy band which indicates
the character of a rigid, planar, one-dimensional π-sys-
tem. The maximum absorption of MeLPF is red-shifted
by 140 nm (0.74 eV) when compared with P 2a . The PL
spectra of LPFs in dilute solution presented three
emission bands peaking around 460, 490, and 520 nm,
which are mirror-plane symmetrical with the absorption
spectra and are assigned as transition from the first
excited-state S1 to the ground-state S0 with varied
vibrational levels. At the same time, a very small Stokes
shift less than 4 nm (140 cm-1) is observed, and the
magnitude of the Stokes shift and well-resolved vibra-
tional energy band in electronic spectra can be inter-
preted as a consequence of the geometrically constrained
rigid π-electron system, which permits no major geo-
metric change in the transition from the ground state
to the excited state. The PL efficiency (ΦPL) of the
polymers in chloroform was measured compared to
quinine sulfate (ca. 2 × 10-5 M, assuming ΦPL of 0.546
at 365 nm excitation in 1 N H2SO4)14 as standard.
MeLPF and HLPF exhibited very high PL efficiencies
in chloroform in the range of 72-83% (Table 2), corre-
sponding to few routes existing for nonradiative deac-
tivation.
1
Figure 1 shows the H NMR spectrum of MeLPF. All
proton and integral areas of the peak can match the
1
polymer structure. The H NMR spectrum of HLPF is
similar to that of MeLPF; only an excessive signal
appeared around 5.07 ppm which is ascribed to the
proton in methylene bridge. The remaining -Ar-
CHOH-Ar- and keto groups were not detected in NMR
spectra. In IR spectra of LPFs (Figure 2) the keto or
hydroxyl groups in 1700 or 2500 cm-1 were not ob-
served. From above the incomplete ring-closure reaction
or defects were not found in LPFs.
MeLPF and HLPF exhibit good thermal stability
measured by thermogravimetric analysis (TGA) under
a nitrogen atmosphere. The polymers have onset deg-
radation temperatures (Td) above 358.3 and 400.9 °C,
respectively. No weight loss is observed at lower tem-
peratures. 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 glass transition process (Tg) nor
other thermal process (such as liquid-crystal phase)
from 20 to 300 °C for MeLPF and HLPF.
Sp ectr oscop ic P r op er ties. As shown in Figure 3,
the UV-vis absorption and photoluminescence (PL)
spectra of P 1 and P 2a in THF solution present an
enormous difference. The maximum absorption peak of
P 1 was at 362 nm, while P 2a and P 2b are distinctly
shifted toward high energy. The absorption band of P 1
The PL spectra in solid state of MeLPF (HLPF) are
almost identical with that in dilute solution. The slight
increase in relative intensity of 500-600 nm emission

9826 Qiu et al.
Macromolecules, Vol. 36, No. 26, 2003
F igu r e 1. 1H NMR spectra of MeLPF and HLPF in CDCl3. g* contain the proton peak of water.
F igu r e 2. FT-IR spectra of MeLPF and HLPF.
F igu r e 4. Absorption and PL spectra of MeLPF and HLPF
in dilute THF solution and spin-coating thin film.
F igu r e 3. UV-vis absorption and PL spectra of P 1 and P 2
source of the low-energy emission in PF and LPPP,
especially in PF derivatives with methylene-bridged
hydrogen substituents.9,15 Generally, the low-energy
emission from defects was enhanced in the film com-
pared to corresponding solution because of the inter-
in THF solution.
in solid films may be ascribed to the stronger self-
absorption effects than that in solution. Recently, on-
chain chemical defects have been identified as one

Macromolecules, Vol. 36, No. 26, 2003
Ladder-Type Poly(p-phenylene)s 9827
Ta ble 2. Sp ectr a l P r op er ties of P r ecu r sor s a n d LP F s
abs (in THF)
λmax (nm)
PL (in THF)a
λmax (nm)
PL of filma
λmax (nm)
PL efficiency in
polymer
CHCl3 (ΦPL)b (%)
Egc (eV)
EL λmax (nm)
P 1
P 2a
362
318
322
(425) 455
(428) 459
500
405
403
459 (486)
464 (494)
508
415
413
460 (490)
464 (496)
3.23
3.15
3.15
2.70
2.68
P 2b
HLPFd
MeLPF
74
83
460 (490)
464 (494)
a
b
d
Excited at 360 nm. Calculated by the relative method.14 c Estimated from the onset wavelength of the optical absorption. Peaks
that appear as shoulders or weak bands shown in parentheses.
F igu r e 6. Current-brightness-voltage characteristics of the
device (ITO/PEDOT/MeLPF/Ba/Ag). Inset: dependence of the
luminance efficiency on the drive current density for the
device.
F igu r e 5. EL spectra of MeLPF (ITO/PEDOT/MeLPF/Ba/Ag)
at different voltages.
chain migration of excited energy in film state which
increased the probability of excited energy transfer to
defects. However, in the PL spectra of LPFs in solid film,
even HLPF which has hydrogen substituents at bridged
methylene, the low-energy band is very low. The spectra
are very stable even after annealing process at 180 °C
for 12 h in a nitrogen atmosphere. From these results,
no evidence indicates there is any keto defect in LPFs,
which is agreement with the conclusions by general
structural analysis, ca. IR and NMR. Sometimes we
used the LPFs solution which was deposited for several
weeks to cast film, and a new low-energy band around
540-560 nm can be observed in the PL spectra of the
film; such a low-energy band is found to disappear when
the film samples remained at room temperature for a
few hours. Since the low-energy emission from keto
defects of polymers cannot disappear, we thought the
low-energy band was mostly ascribed to an interchain
aggregate states between the planar polymer back-
bones6,16 and that aggregate state was not stable in film
state even at room temperature. We will continue the
photophysical study in following work.
Device Ch a r a cter istics. The single-layer polymer
light-emitting diodes (PLEDs) with the configuration of
ITO/PEDOT:PSS/MeLPF/Ba/Ag were fabricated to in-
vestigate the electroluminescent properties of the LPFs.
As shown in Figure 5, the EL spectra of MeLPF show a
peak wavelength around 464 nm and a shoulder around
494 and 524 nm, which are similar to the PL spectra of
the corresponding polymer film. The shape of spectra
is very stable in different voltage. Figure 6 shows the
current-brightness-voltage curves and the current
density dependence of luminance efficiency for the
device of ITO/PEDOT:PSS/MeLPF/Ba/Ag. With an in-
creasing of forward bias voltage, the current and bright-
ness in the devices increases. Light emitting is observed
with turn-on voltage ranged from 7 to 12 V and the
maximum brightness up to 5600 cd/m2 in the best
device. The luminance efficiency first increases and then
decreases with increasing current density; the maxi-
mum luminance efficiency of 0.66 cd/A is achieved at a
current density of 33 mA/cm and a brightness of 289
cd/m2. Further improvement in device efficiency and
brightness can be obtained by adjusting device structure
and electrode metals with more efficient injection and
balanced transport of both charge carriers. The HLPF
devices also show the EL spectra similar to the PL
spectra of HLPF film and keep stable at different
voltages with a lower luminance efficiency of 0.1 cd/A.
These results are obviously different from the PL and
EL spectra of the LPPP (Chart 1a) which emits an
unstructured broad band from 460 to 600 nm.2,3,5
From above, the low-energy emission band from the
aggregation of planar polymers or keto defect sites
cannot exert an effective influence to both PL and EL
spectra of LPFs. The improvement in optical and device
properties can correspond to the extraordinary low
concentration of defects in LPFs. The stable spectral
properties and the enhanced performances of devices
indicated that the LPFs can be a useful material for
light-emitting devices.
Con clu sion
We prepared a type of soluble, thermally stable
ladder-type poly(p-phenylene) with fluorene units in the
polymer backbone by Suzuki coupling and presented full
characterization of their structure and properties as well
as electroluminescence performances. The polymers
have high molecular weights, low defect in backbone,
excellent thermal stability, good solubility in common
organic solvents, and high PL efficiencies. Light-emit-
ting devices using LPFs as the active layer show very
stable blue-green emission. Furthermore, MeLPF de-

9828 Qiu et al.
Macromolecules, Vol. 36, No. 26, 2003
(yield: 72.3%). 1H NMR (CDCl3, 500 MHz): δ 7.76 (d, 4H),
7.582 (s, 1H), 7.32 (d, 4H), 2.69 (t, 4H), 1.65 (t, 4H), 1.26 (m,
28H), 0.88 (t, 6H). Anal. Calcd: C, 66.30; H, 7.23; O, 4.42.
Found: C, 66.47; H, 7.30; O, 4.45.
vices show a maximum luminescence of 5400 cd/m2 and
maximum luminance efficiency of 0.66 cd/A. The low-
energy emission band from the aggregation of planar
polymers or keto defect sites cannot exert an effective
influence on both PL and EL spectra of LPFs. These
attractive properties established the LPFs as widely
useful materials for polymer-based optical and elec-
trooptical applications.
P olym er P 1. A mixture of 3 (150.4 mg, 0.21 mmol), 2,7-
bis(4,4,5,5-tetramethyl-1,3,2-dioxaborolan-2-yl)-9,9-dihexyl-
fluorene (121.2 mg, 0.21 mmol), tetrakis(triphenylphosphino)-
palladium(0) (8 mg), 3 mL of toluene, and 1 mL of 1 M K2CO3
was reflexed 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; the polymer was precipitated into
methanol (1:10), and the crude product was dissolved in
dichloromethane and reprecipitated into methanol (1:10) to
Exp er im en ta l Section
1
Mea su r em en t. H and 13C NMR spectra were recorded on
a Bruker AVANCZ 500 MHz spectrometer with chloroform-d
as solvents and tetramethylsilane (TMS) as the internal
standard. FT-IR spectra were recorded on a Bruker IFS66VFT-
IR spectrometer in the 800-4000 cm-1 regions by casting the
solution of polymers on CaF substrate. UV-vis and fluores-
cence spectra were obtained on a Shimadzu UV-3100 spectro-
photometer and a Shimadzu RF-5301PC spectrophotometer,
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 an HPLC Waters 510 using a series
of monodisperse polystyrene as standards in THF (HPLC
grade) at 308 K.
LED Device F a br ica tion a n d Ch a r a cter iza tion . 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. The conducting polymer
dispersion of poly(3,4-ethylenedioxythiophene) doped with
poly(styrenesulfonic acid) (PEDOT:PSS) was obtained from
Bayer Corp. The hole injection layer of PEDOT:PSS was
prepared from a water dispersion with a thickness of 50 nm
and baked at 170 °C for 20 min under a 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, the 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
fluorescence spectrophotometer. Luminance-current density-
voltage (L-I-V) curves were recorded with a Keithley 2400
instrument. All measurements were carried out at room
temperature under ambient conditions.
1
give P 1 of 122.7 mg as a yellow-green solid (yield: 65%). H
NMR (CDCl3, 500 MHz): δ 7.588-7.573 (d, 4H), 7.529 (s, 2H),
7.390-7.374 (t, 2H), 7.249-7.236 (m, 2H), 6.975-6.958 (s, 2H).
P olym er P 2a . A solution of polymer P 1 (100 mg, 0.11
mmol) 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 30 min at room temperature and carefully
quenched with ethanol, water, and dilute hydrochloric acid.
The organic layer was washed with water, dried with MgSO4,
and concentrated to dryness. The crude polymer was redis-
solved in tetrahydrofuran and precipitated into water to give
91 mg of colorless solid (yield: 87%).
P olym er P 2b. A solution of polymer P 1 (100 mg) in 10 mL
of toluene was added to a suspension of LiAlH4 (40 mg) in 10
mL of THF. The mixture was stirred for 30 min at room
temperature and carefully quenched with ethanol, water, and
dilute hydrochloric acid. The organic layer was washed with
water, dried, and concentrated. The polymer was redissolved
in THF and precipitated in water to give 87 mg of colorless
solid (yield: 84%).
MeLP F . A solution of polymer P 2a (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. Precipitation in
methanol gives 89 mg of MeLPF as a yellow-green powder
(yield: 87.8%). 1H NMR (CDCl3, 500 MHz): δ 7.57 (d, 4H),
7.38 (s, 2H), 7.21 (t, 4H), 7.09 (t, 4H), 2.56 (s, 4H), 1.95 (s,
4H), 1.25 (m, 32H), 1.07 (m, 12H), 0.88-0.53 (m, 16H). 13C
NMR (CDCl3, 100 MHz): δ 154.5, 154.1, 151.1, 141.3, 140.2,
128.7, 127.1, 115.6, 114.6, 54.2, 36.0, 32.3, 31.7, 30.2, 29.2, 26.4,
24.2, 23.1, 14.5. Anal. Calcd: C, 90.07; H, 9.93. Found: C,
88.54; H, 9.97.
HLP F . The procedure was the same as that of MeLPF. A
1
yellow-green powder was obtained in 95.38% yield. H NMR
(CDCl3, 500 MHz): δ 7.73 (s, 2H), 7.60 (s, 2H), 7.47 (s, 2H),
7.15 (t, 8H), 5.07 (s, 2H), 2.62 (s, 4H), 2.02 (s, 4H), 1.27 (m,
32H), 1.04 (m, 12H) 0.73-0.60 (m, 16H). 13C NMR (CDCl3, 500
MHz): δ 155.4, 155.0, 151.4, 142.1, 141.0, 129.2, 129.0, 116.7,
115.0, 54.2, 36.2, 32.3, 31.9, 30.0, 29.7, 24.2, 23.1, 14.5. Anal.
Calcd: C, 90.22; H, 9.78. Found: C, 89.33; H, 10.07.
Ma ter ia ls. 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.
2,5-Dibromoterephthalic acid (1)10 and 2,7-bis(4,4,5,5-tetra-
methyl-1,3,2-dioxaborolan-2-yl)-9,9- dihexylfluorene11 were pre-
pared according to literature procedures. All other chemicals
were purchased from Aldrich and Acros and used without any
further purification.
Ack n ow led gm en t. This work is supported by Na-
tional Natural Science foundation of China (Grant
20125421, 90101026, and 600777014) and by Ministry
of Science and Technology of China (Grant 2002CB-
6134003).
Syn th esis. 3,6-Dibr om o-2,5-p h en ylen en d i(ca r boxylic
a cid ch lor id e) (2). 2,5-Dibromoterephthalic acid (3.5 g, 10.5
mmol) was treated with 16 mL of thionyl chloride (SOCl2) (205
mmol) and refluxed for 10 h. The excess SOCl2 was removed
in a vacuum to give 3.71 g of 2 as a crystalline yellow solid
Refer en ces a n d Notes
1
(yield: 95%). H NMR (CDCl3, 500 MHz): δ 8.208(s, 2H).
(1) (a) Gustafsson, G.; Cao, Y.; Treacy, G. M.; Klavetter, F.;
Colaneri, N.; Heeger, A. J . Nature (London) 1992, 357, 477.
(b) Kraft, A.; Grimsdale, A. C.; Holmes, A. B. Angew. Chem.,
Int. Ed. 1998, 37, 402. (b) Friends, R. H.; Gymer, R. W.;
Holmes, A. B.; Burroughes, J . H.; Marks, R. N.; Taliani, C.;
Bradley, D. D. C.; dos Santos, D. A.; Bredas, J . L.; Lo¨glund,
M.; Salaneck, W. R. Nature (London) 1999, 397, 121.
(2) (a) Grem, G.; Leising, G. Synth. Met. 1993, 55-57, 4105. (b)
Gru¨ner, J .; Wttmann, H. F.; Hamer, P. J .; Friend, R. H.;
Huber, J .; Scherf, U.; Mu¨llen, K.; Moratti, S. C.; Holmes, A.
2′,5′-Dib r om o-4-d e cyl-4′-(4-d e cylb e n zoyl)b e n zop h e -
n on e (3). To a solution of decylbenzene (7.2 mL, 28.4 mmol)
and aluminum trichloride (2 g, 14.98 mmol) in 15 mL of
benzene, a mixture of 2 (2.04 g, 5.67 mmol) and 5 mL of
benzene was added dropwise. After stirring at room temper-
ature for 48 h the mixture was poured into ice/2 M HCl. The
organic layer was washed with 1 M NaOH and water, then
dried over MgSO4, and concentrated. The residue was recrys-
tallized from acetone to give 3 of 2.89 g as a white crystal

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