Novel efficient green electroluminescent conjugated polymers based on fluorene and triarylpyrazoline for light-emitting diodes

Article abstract of DOI:10.1039/B313160B

A series of novel light-emitting conjugated polymers based on fluorene and triarylpyrazoline were synthesized in good yields through Suzuki coupling reactions. The resulting polymers were characterized by NMR, FT-IR, elemental analysis, DSC, TGA and GPC.

Full text of DOI:10.1039/B313160B

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A R T I C L E
Novel efficient green electroluminescent conjugated polymers
based on fluorene and triarylpyrazoline for light-emitting
diodes{
Qiang Peng,a Zhi-Yun Lu,a Yan Huang,a Ming-Gui Xie,*a Dan Xiao,b Shao-Hu Han,c
Jun-Biao Pengc and Yong Caoc
aDepartment of Chemistry, Sichuan University, Chengdu 610064, China.
E-mail: xiemingg@mail.sc.cninfo.net.; Fax: 186 02885413601; Tel: 186 02885410059
bDepartment of Chemical Engineering, Sichuan University, Chengdu 610065, China
cInstitute of Polymer Optoelectronic Materials and Devices, South China University of
Technology, Guang Zhou 510640, China
Received 18th October 2003, Accepted 3rd December 2003
First published as an Advance Article on the web 8th January 2004
A series of novel light-emitting conjugated polymers based on fluorene and triarylpyrazoline were synthesized in
good yields through Suzuki coupling reactions. The resulting polymers were characterized by NMR, FT-IR,
elemental analysis, DSC, TGA and GPC. These polymers possess excellent thermal stability with glass
transition temperatures (Tg) of 80–162 uC and onset decomposition temperatures (Td) of 376–387 uC. Cyclic
voltammetry studies revealed that these polymers have good hole and electron transporting properties with
LUMO energy levels of 22.97 to 22.98 eV and HOMO energy levels of 25.71 to 25.81 eV. All the polymers
emit green fluorescence with very high photoluminescence (PL) quantum yields of 45–59%. Polymer light-
emitting diodes (PLEDs) with the configuration ITO/PEDOT/polymer/Ba/Al were fabricated. All these devices
showed bright green emission peaking at 494–500 nm with high maximum external quantum efficiencies of
0.6–2.53% and low turn-on bias voltages. The good light-emitting properties indicate that these polymers are
new and promising candidates for electroluminescent materials that can be used to fabricate efficient polymer
light-emitting diodes.
high fluorescence yield. These compounds exhibit twisted
Introduction
intramolecular charge transfer (TICT).25 Upon excitation,
molecules with TICT will twist and form an electron donor–
accepter system. Therefore, these compounds with nonplanar
structure can be used as carrier-transporting as well as emitting
materials.26–28 However, pyrazoline compounds tend to
recrystallize easily leading to device degradation. From the
chemical viewpoint, this problem may be avoided by
incorporating these moieties into the polymer main chain by
chemical doping.
Since the discovery of polymer light-emitting diodes (PLEDs)
by the Cambridge group,1 great progress has been made in
developing all kinds of conjugated polymers in order to
obtain three primary (RGB) colors for large-area flat panel
displays. Among these polymers, polyfluorene (PF) derivatives
show interesting and unique chemical and physical pro-
perties because they contain a rigid planar biphenyl unit and
facile substitution at the remote C-9 position can improve
the solubility and processability of polymers without signifi-
cantly increasing the steric interactions in the polymer back-
bone.2 As a result, fluorene-based conjugated polymers have
emerged as the most promising blue light-emitting materials
because of their high quantum yield, good film-forming
and excellent thermal stability.3–14 Color-tuning in these
polymers can be achieved by incorporating other moieties,
such as benzodithiazole, oxadiazole, quinoline and quinoxaline
units, into the polymer backbone.15–22 However, most of
these moieties are electron-deficient units, which can easily
form trapping centers that reduce the quantum efficiencies
of the polymers. On the other hand, fluorene-based polymers
often suffer from serious aggregation formation, which
leads to enhanced excimer emission in the EL process
and reduced quantum efficiency.23,24 So modification of
polyfluorene and their derivatives are still receiving consider-
able interest.
Herein, we present
a series of novel fluorene-based
conjugated polymers containing the triarylpyrazoline moiety
in the main chain. The twisted triarylpyrazoline unit is
introduced to avoid the aggregation of PFs and to increase
their quantum yield. On the other hand, the often-observed
recrystallization of small molecular pyrazoline compounds can
be resolved in polymer films. The resulting polymer can emit
green light with very high absolute PL quantum efficiency
and an EL maximum external quantum efficiency in solid
films. To our knowledge, this work will be the first report of
pyrazoline-based conjugated polymers used in polymer light-
emitting diodes.
Experimental
Chemicals
All the chemicals were purchased from Aldrich and Acros
chemical company and were used without any further
purification. All the solvents such as toluene and DMF were
dried with appropriate drying agents, then distilled under
Triarylpyrazoline compounds have been widely used as
fluorescent dyes in the textile industry because of their very
{ Electronic supplementary information (ESI) available: The detailed
synthesis procedures and characterization data of intermediate
compounds 2, 3, 5–7. See http://www.rsc.org/suppdata/jm/b3/
b313160b/
˚
reduced pressure, and stored over 4 A molecular sieves. The
29
catalyst tetrakis(triphenylphosphine)palladium Pd(PPh3)4
and 9,9-dihexylfluorene-2,7-bis(trimethylene boronates) (8)8
3 9 6
J . M a t e r . C h e m . , 2 0 0 4 , 1 4 , 3 9 6 – 4 0 1
T h i s j o u r n a l i s ß T h e R o y a l S o c i e t y o f C h e m i s t r y 2 0 0 4

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Scheme 1 Synthetic route to the monomers and polymers.
were synthesized according to the literature. The detailed
synthesis procedures and characterization data of intermediate
compounds 2, 3, 5–7 (Scheme 1) are given in the electronic
supplementary information (ESI) section.{
potential/galvanostat model 283. The thicknesses of the films
were measured with a Dektak surface profilometer.
Poly{(9,9-dihexyl-9H-fluoren-2,7-ylene)-alt-[3,5-bis(1,4-
phenylene)-4,5-dihydro-1-phenyl-1H-pyrazole]} (PFPZ1)
Instrumentation
To a mixture of 8 (502.3 mg, 1.0 mmol), 3 (456.2 mg, 1.0 mmol)
and Pd(PPh3)4 (12 mg, 1.0 mol%) was added a mixture of
toluene (5 mL) and aqueous 2 M potassium carbonate (5 mL).
The mixture was vigorously stirred at 85–90 uC for 48 h. After
the mixture was cooled down to room temperature, it was
poured into 200 mL of methanol and deionized water (10 : 1). A
fibrous solid was obtained by filtration, the solid was washed
with methanol, water and then methanol. After washing for
24 h in a Soxhlet apparatus with acetone, the resulting polymer
PFPZ1 was obtained as a bright yellow powder with a yield of
85% after drying under a vacuum. 1H NMR (CDCl3, 400 MHz,
d/ppm): 8.27–7.97 (m, 4 H), 7.85–7.05 (m, 13 H), 7.00–6.80 (m,
2 H), 5.38 (m, 1 H), 3.91 (m, 2 H), 2.05 (br, 4 H), 1.95–0.74 (m,
22 H). 13C NMR (CDCl3, 400 MHz, d/ppm): 151.78, 146.46,
144.76, 144.41, 141.57, 140.90, 140.54, 139.79, 132.07, 131.97,
131.36, 130.53, 129.06, 128.93, 128.73, 128.48, 128.26, 127.78,
127.36, 127.13, 126.38, 126.21, 125.94, 125.58, 125.39, 125.24,
121.50, 121.26, 121.10, 119.20, 113.47, 64.26, 55.33, 43.57,
40.40, 31.40, 29.64, 23.77, 22.51, 13.94. FT-IR (KBr, n/cm21):
3070, 3028, 2922, 2852, 1633, 1595, 1495, 1460, 1384, 1262,
1098, 1066, 1024, 872, 742, 689. Anal. Calcd for (C48H48N2)n:
C, 87.85; H, 7.69; N, 4.45. Found: C, 86.12; H, 7.76; N, 4.49%.
1H NMR and 13C NMR spectra were performed on a Varian
Unity INOVA-400. FT-IR spectra were recorded on a Perkin-
Elmer 2000 spectrometer as KBr pellets. Elemental analysis
studies were carried out with a Carlo Erba 116 Elemental
Analyzer. UV-Vis spectra of the polymers in solution and as
thin films were taken on a Shimadzu UV2100 UV-Vis
recording spectrophotometer. Photoluminescence (PL) spectra
of the polymers in solutions and thin films were measured on
a
Hitachi 850 fluorescence spectrophotometer. The PL
quantum yields in neat films were measured in an integrating
sphere at room temperature. Thermal gravimetric analysis
(TGA) measurements were performed on Perkin-Elmer
series 7 thermal analysis system under N2 at a heating rate
of 10 uC min21. Differential scanning calorimetry (DSC)
measurements were performed on a Perkin-Elmer DSC 7 under
N2 at a heating rate of 10 uC min21. The weight-average
molecular weights (Mw) and polydispersity indices (Mw/Mn)
of the polymers were measured on
210 chromatograph at 25 uC, using THF as the eluent and
standard polystyrene as the reference. The cyclic voltammo-
a PL-GPC model
grams were recorded on
a computer-controlled EG&G
J . M a t e r . C h e m . , 2 0 0 4 , 1 4 , 3 9 6 – 4 0 1
3 9 7

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Poly{(9,9-dihexyl-9H-fluoren-2,7-ylene)-alt-[3-(2-hexyloxy-1,5-
phenylene)-5-(1,4-phenylene)-4,5-dihydro-1-phenyl-1H-
pyrazole]} (PFPZ2)
Table 1 Molecular weights and thermal properties of the polymers
a
a
Polymers
Yield (%)
Mw
Mw/Mn
Tdb/uC
Tgc/uC
PFPZ1
PFPZ2
PFPZ3
85
80
81
39100
33200
37100
2.33
1.53
1.45
387
376
380
162
111
80
PFPZ2 was obtained as a bright yellow powder with a yield of
80% from the reaction of 7a with 8 according to the procedure
described for the synthesis of polymer PFPZ1. 1H NMR
(CDCl3, 400 MHz, d/ppm): 8.33–8.00 (m, 4 H), 7.79–7.11 (m,
12 H), 7.01–6.81 (m, 2 H), 5.60 (m, 1 H), 4.29–4.20 (m, 2 H),
3.82–3.80 (m, 2 H), 2.05 (br, 4 H), 1.95–0.74 (m, 33 H). 13C
NMR (CDCl3, 400 MHz, d/ppm): 151.75, 151.60, 151.53,
147.22, 147.04, 145.08, 144.25, 143.62, 141.70, 141.62, 141.08,
139.76, 139.44, 139.19, 139.10, 135.82, 134.11, 131.82, 131.73,
131.63, 130.07, 128.93, 128.74, 128.70, 128.39, 128.27, 127.32,
127.14, 126.10, 125.89, 125.57, 124.08, 121.49, 121.20, 121.07,
120.01, 119.80, 118.93, 113.44, 111.71, 68.45, 68.23, 55.26,
55.11, 42.09, 40.39, 40.25, 36.99, 31.54, 31.39, 29.65, 29.33,
29.09, 28.77, 25.95, 25.86, 25.52, 23.75, 22.66, 22.53, 21.98,
14.07, 13.96. FT-IR (KBr, n/cm21): 3073, 3030, 2927, 2855,
1598, 1571, 1499, 1465, 1391, 1324, 1248, 1118, 1070, 999, 872,
816, 746, 724, 692, 542. Anal. Calcd for (C52H60N2O)n: C,
85.67; H, 8.30; N, 3.84. Found: C, 85.09; H, 8.41; N, 3.88%.
a Molecular weights and polydispersity indices were determined by
GPC in THF using polystyrene as the standard. b Onset decomposi-
tion temperature measured by TGA under N2. c Glass transition
temperature measured by DSC under N2.
side chain linked to the triarylpyrazoline unit. Uniform and
transparent films on substrates, such as ITO-coated glasses and
microslides, can be obtained by spin-casting the solutions in
toluene (1%) at a spin rate of 1500 rpm. Their molecular
weights were determined by gel permeation chromatography
(GPC) using polystyrene as the standard. The results are listed
in Table 1. These copolymers have weight-average molecular
weights (Mw) of 33200–39100 with polydispersity indices (Mw/
Mn) of 1.45–2.33. From GPC results, PFPZ2 and PFPZ3 have
a relative narrow polydispersity index. The reason may be that
these two polymers have a better solubility in the reaction
system due to the long alkyl side chain linked to the
triarylpyrazoline unit. Thus, the reagents can react with each
other enough and equably to afford a narrow molecular
distribution. The thermal properties of the polymers were
investigated by differential scanning calorimetry (DSC: heating
at 10 uC min21 in nitrogen) and thermogravimetric analysis
(TGA: heating at 10 uC min21 in nitrogen). As shown in
Table 1 and Fig. 1, all these polymers possess excellent thermal
stability with high onset decomposition temperatures (Td) in
the range of 376 uC to 387 uC, and no weight loss was observed
at lower temperatures. The glass transition temperatures (Tg)
of the polymers range from 80 uC to 162 uC. These Tg values
are higher than those of poly(9,9-dioctylfluorene) (POF)
(y51 uC)30 and poly(9,9-dihexylfluorene) (PHF) (y55 uC),31
in which each repeating fluorene unit contains two flexible
n-octyl or n-hexyl chains at C-9. It is evident that the incorpora-
tion of triarylpyrazoline units in the main chain can increase
the Tg of fluorene-based polymers. This is very important for
such polymers used as emissive materials in PLEDs.32
Poly{(9,9-dihexyl-9H-fluorene-2,7-ylene-alt-[3-(2-dodecyloxy-
1,5-phenylene)-5-(4-phenylene)-4,5-dihydro-1-phenyl-1H-
pyrazole]} (PFPZ3)
PFPZ3 was obtained as a bright yellow powder with a yield of
81% from the reaction of 7b with 8 according to the procedure
1
described above. H NMR (CDCl3, 400 MHz, d/ppm): 8.32–
8.01 (m, 4 H), 7.79–7.13 (m, 12 H), 7.02–6.85 (m, 2 H), 5.60 (m,
1 H), 4.21 (m, 2 H), 3.82–3.78 (m, 2 H), 2.05 (br, 4 H), 1.94–0.74
(m, 45 H). 13C NMR (CDCl3, 400 MHz, d/ppm): 151.75,
151.61, 147.24, 145.09, 141.64, 140.09, 139.76, 139.45, 133.44,
131.89, 131.87, 131.74, 130.49, 130.10, 128.94, 128.86, 128.75,
128.71, 128.62, 128.42, 128.30, 127.43, 127.16, 126.73, 126.11,
125.91, 125.56, 124.49, 121.50, 121.20, 120.01, 119.81, 118.96,
113.45, 111.72, 68.48, 68.26, 55.27, 55.11, 42.10, 40.40, 31.89,
31.40, 29.65, 29.35, 29.14, 28.82, 26.30, 26.20, 25.90, 23.77,
22.66, 22.55, 14.11, 13.96. FT-IR (KBr, n/cm21): 3071, 3029,
2925, 2853, 1637, 1598, 1499, 1464, 1389, 1326, 1250, 1117,
1069, 877, 815, 747, 693, 540. Anal. Calcd for (C58H72N2O)n: C,
85.66; H, 8.92; N, 3.44. Found: C, 85.12; H, 8.83; N, 3.49%.
The UV-Vis absorption and photoluminescence (PL) spectra
of the polymers in films (spun-cast from the corresponding
polymers in toluene at a concentration of 10 mg mL21) on
microslides are shown in Fig. 2 and 3. As shown in Fig. 2, the
absorption onsets occur at 454, 457, 458 nm for PFPZ1,
PFPZ2, PFPZ3, and give two peaks at 339, 395 nm, 337,
399 nm and 336, 398 nm for these three polymers, respectively.
The absorbances are attributed to the p–p* transitions of these
polymers. From the onset wavelengths, the optical band gaps
can be estimated to be 2.71–2.73 eV. All these films emit green
EL device fabrications
For the fabrication of the devices, glass substrates coated with
indium–tin oxide (ITO) with a sheet resistance of 30 O c21
(CSG Co. Ltd.) were cleaned sequentially in ultrasonic baths of
aqueous ionic detergent, acetone and anhydrous ethanol. A
thin film layer of PEDOT (Baytron P 4083) (90 nm) (PEDOT is
poly(ethylenedioxythiophene) doped with polystyrene sulfonic
acid) and the polymers (60 nm) (from a 10 mg mL21 solution of
the polymers in toluene solution) were spin-coated on the ITO
surface at 1500 rpm for 30 s, after which a thin layer of Ba
(4 nm)/Al (170 nm) was deposited on the polymer film by
thermal evaporation under a vacuum of 1026 Torr. The active
area of the device was about 0.15 cm2. The applied dc bias
voltages for EL devices were in a forward direction (ITO,
positive; Ba/Al, negative). The current–voltage characteristics
were measured on a voltmeter and an amperometer, respec-
tively. The EL efficiency and brightness measurements were
carried out with a calibrated silicon photodiode. All the
measurements of the EL devices were carried out in air at room
temperature.
Results and discussion
The resulting polymers readily dissolve in solvents, e.g., THF,
CH2Cl2, CHCl3, toluene and xylene. This is partially due to the
hexyl side chain attaching to the fluorene moiety and n-alkyl
Fig. 1 Thermal gravimetric analysis (TGA) curves of the polymers
(under a nitrogen atmosphere at a heating rate of 10 uC min21).
3 9 8
J . M a t e r . C h e m . , 2 0 0 4 , 1 4 , 3 9 6 – 4 0 1

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Fig. 2 Absorption spectra of the polymers in solid state films spin-
coated on quartz plates.
Fig. 4 Cyclic voltammograms of the polymers recorded from thin
films deposited on platinum plate electrodes at a scan rate of 50 mV s21
The potentials were measured relative to Ag/AgNO3.
.
respectively. The corresponding re-reduction peaks appeared at
1.47, 1.66 and 1.63 V. On sweeping the polymer cathodically,
the reduction (n-doping) began at 21.42, 21.42 and 21.47 V
with the cathodic current increasing quickly and produced
cathodic peaks at 22.12, 21.76 and 21.80 V for PFPZ1,
PFPZ2 and PFPZ3, respectively. The corresponding re-
oxidation peaks occurred at 21.52, 21.58 and 21.58 V. The
electrochemically measured gaps are 2.83, 2.76 and 2.78 V for
PFPZ1, PFPZ2 and PFPZ3, which are close to the optical
band gaps determined from the absorption onsets. According
to the equations,34,35 IP ~ 2([Eonset
ox
]
1 4.4) eV and EA ~
red
red
]
ox
2([Eonset
1 4.4) eV, where [Eonset
]
and [Eonset
]
are the
onset potentials for oxidation and reduction of the polymer vs.
the reference electrode, the LUMO and HOMO of the
polymers were estimated to be 22.98, 22.98, 22.93 eV and
25.81, 25.74 and 25.71 eV for PFPZ1, PFPZ2 and PFPZ3,
respectively, and therefore the HOMO and LUMO energy
levels of these polymers are quite similar. The electrochemical
data of these polymers are summarized in Table 3.
Fig. 3 PL spectra of the polymers in films.
fluorescence when they are exposed to UV light. The PL spectra
exhibit maxima at around 508–509 nm. The absolute PL
quantum yields of the neat polymer films were about 45%,
56% and 59% for PFPZ1, PFPZ2 and PFPZ3 as measured
in an integrating sphere at room temperature in air using a
HeCd laser line of 405 nm as the excitation source according
to the procedure described by Greenham et al.33 From above,
the PL efficiencies of PFPZ2 and PFPZ3 are very high. The
main features of these spectra are summarized in Table 2 and
Fig. 2 and 3.
The electrochemical behavior of the polymers was investi-
gated by cyclic voltammetry (CV). CV was performed on a thin
film of the polymer coated onto a platinum plate electrode
(about 6 mm22) in a 0.1 mol L21 tetrabutylammonium
perchlorate (Bu4NClO4) solution in acetonitrile with a scan
rate of 50 mV s21 at room temperature. A platinum wire was
used as the counter electrode, and Ag/AgNO3 (0.10 M) was
employed as the reference electrode. As shown by the cyclic
voltammograms in Fig. 4, all these polymers showed reversible
n-doping and p-doping processes. In the anodic scan, the
oxidation (p-doping) started at about 1.41, 1.34 and 1.31 V and
gave two corresponding oxidation peaks at 1.61, 2.40 V, 1.71,
2.49 V and 1.78, 2.46 V for PFPZ1, PFPZ2 and PFPZ3,
Light-emitting devices with the configuration of ITO/
PEDOT (90 nm)/polymer (60 nm)/Ba (4 nm)/Al (170 nm)
were fabricated in a glove box under a nitrogen atmosphere.
Poly(3,4-ethylenedioxythiophene) (PEDOT) doped with poly-
(styrenesulfonic acid) (PSS) (Baytron P 4083) was used as the
hole injection/transporting layer. A thin layer of Ba was
employed as the cathode because it normally renders devices
with longer lifetime due to its larger atomic size and mass as
compared with Ca or Mg.36 The active area of the devices was
about 0.15 cm2. Fig. 6 show current (I) and luminance (L) as a
function of the applied voltage (V) for these devices. A typical
device with the configuration of ITO/PEDOT (90 nm)/PFPZ1
(60 nm)/Ba (4 nm)/Al (170 nm) emits visible green light starting
at about 5.5 V and reaches a brightness of 543 cd m22 at a bias
of 9 V. The maximum external quantum efficiency was
measured to be 0.60% (at 7.0 V with current indensity of
59.9 mA cm22 and brightness of 181 cd m22). As shown in
Fig. 6, the green emisssion from the device based on PFPZ2
Table 3 Electrochemical potentials and energy levels of the polymers
red
ox
c
d
e
[Ea
V
]
/
[Eb
V
]
onset
/
ELUMO
eV
/
EHOMO
eV
/
Eg
eV
/
onset
Polymer
Table 2 Absorption and emission data for the polymers
fwhma
/
PFPZ1
PFPZ2
PFPZ3
21.42
21.42
21.47
1.41
1.34
1.31
22.98
22.98
22.93
25.81
25.74
25.71
2.83
2.76
2.78
Absorption
Polymers (film) lmax/nm gap/eV
Band PL (film) Quantum
max/nm yield, wPL (%) nm
l
a Onset reduction potentials measured by cyclic voltammetry. b Onset
oxidation potentials measured by cyclic voltammetry. c Calculated
from the reduction potentials. d Calculated from the oxidation poten-
tials. e Calculated from the LUMO and HOMO energy levels.
PFPZ1
PFPZ2
PFPZ3
339, 395
337, 399
336, 398
2.73
2.71
2.71
512
508
509
45
56
59
105
95
96
a Full width at half-maximum of the film PL spectra.
J . M a t e r . C h e m . , 2 0 0 4 , 1 4 , 3 9 6 – 4 0 1
3 9 9

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green emission with high PL quantum efficiencies. Double-
layer polymer light-emitting diodes (PLEDs) were fabricated
using these polymers as the emitting layers and Ba as cathodes.
All these devices show bright green emission with high
maximum external quantum efficiencies of 0.60–2.53% and
low turn-on bias voltages of 3.7–5.5 V. The results show that
these polymers are new and promising candidates for emissive
materials that can be used to fabricate efficient polymer light-
emitting diodes.
Acknowledgements
The work was financially supported by the National Natural
Science Foundation of China (NSFC, Grant No: 20102004).
Fig. 5 EL spectra of devices with the configuration of ITO/PEDOT/
polymer/Ba/Al.
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starts at about 3.9 V and reaches a brightness of 1859 cd m22 at
a bias of 8.3 V. The maximum external quantum efficiency
was measured to be 1.56% (at 5.9 V with a current indensity of
37.4 mA cm22 and brightness of 337 cd m22). The device with
the configuration of ITO/PEDOT (90 nm)/PFPZ3 (60 nm)/
Ba (4 nm)/Al (170 nm) also emits visible green light at the
lower forward bias of about 3.7 V and reaches a brightness of
2378 cd m22 at a bias of 7.9 V. The maximum external quantum
efficiency was measured to be 2.53% (at 5 V with a current
indensity of 17 mA cm22 and brightness of 248 cd m22).
Compared with the above two devices, the device based on
PFPZ3 exhibits much higher maximum external quantum
efficiency. The EL spectra of these polymers with maxima at
500, 497 and 495 nm are very similar to the corresponding PL
spectra. The similarity of the PL and EL spectra indicates
that the same excitations are involved in both cases. From
the EL and PL spectra, no emission band appears between 600–
700 nm, which indicates that the aggregation is efficiently
suppressed in these solid films of these polymers. This may be
caused by the incorporation of twisted triarylpyrazoline units
into the polymer backbones. So further improvements could be
expected after optimization.
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Conclusion
We have synthesized a series of novel efficient light-emitting
polymers based on fluorene and triarylpyrazoline through
palladium-catalyzed Suzuki coupling polymerization. These
polymers show satisfactory thermal stability and excellent
4 0 0
J . M a t e r . C h e m . , 2 0 0 4 , 1 4 , 3 9 6 – 4 0 1

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