Synthesis, characterization and electroluminescence of polyfluorene copolymers containing t-shaped lsophorone derivatives

Article abstract of DOI:10.1002/pola.23761

We have successfully synthesized a series of new fluorene-based copolymers, poly[(9,9-bls(4-octyloxy-phenyl)fluorene-2,7-diyl)-co- [2(3{2[4(2{4[bis(bromophenyl-4yl) amino]phenyl}vinyl)-2,5-blsoctyloxyphenyl] vinyl}-5,5-dimethyl-cyclohex-2enylidene)malonon

Full text of DOI:10.1002/pola.23761

Synthesis, Characterization, and Electroluminescence of Polyfluorene
Copolymers Containing T-Shaped Isophorone Derivatives
MOO-JIN PARK,1 JONGHEE LEE,2* IN HWAN JUNG,2 JONG-HWA PARK,2 HOYOUL KONG,2
JI-YOUNG OH,2* DO-HOON HWANG,3 HONG-KU SHIM2
1Polymer Science and Engineering Program, Korea Advanced Institute of Science and Technology,
Daejeon 305-701, Korea
2Department of Chemistry, Korea Advanced Institute of Science and Technology, Daejeon 305-701, Korea
3Department of Applied Chemistry, Kumoh National Institute of Technology, Gumi 730-701, Korea
Received 6 September 2009; accepted 25 September 2009
DOI: 10.1002/pola.23761
Published online in Wiley InterScience (www.interscience.wiley.com).
ABSTRACT: We have successfully synthesized a series of new fluo-
rene-based copolymers, poly[(9,9-bis(4-octyloxy-phenyl)fluor-
ene-2,7-diyl)-co-[2(3{2[4(2{4[bis(bromophenyl-4yl) amino]phe-
nyl}vinyl)-2,5-bisoctyloxyphenyl]vinyl}-5,5-dimethyl-cyclohex-2-
enylidene)malononitrile] (PFTBMs), with varying molar ratios
of the low-energy band gap comonomer, 2(3{2[4(2{4[bis(4-bromo-
phenyl)amino]phenyl}vinyl)-2,5-bisoctyloxyphenyl]vinyl}-5,5-
dimethyl-cyclohex-2-enylidene)malononitrile (BTBM). To prepare
BTBM (which has a T-shaped structure) from triphenylamine,
dialkoxy phenyl, and isophorone, we introduced three individual
segments of an isophorone derivative containing two cyanide
groups at the carbonyl position, a dialkoxy phenyl group for
increased solubility, and a triphenyl amine for effective charge
transfer. Furthermore, we introduced vinyl linkages between
each segment to increase the length of p-conjugation. The
synthesized polyfluorene copolymers with the BTBM, PFTBMs,
were synthesized via palladium-catalyzed Suzuki coupling reac-
tions. The photoluminescence emission spectra of the synthe-
sized polymers in solution did not show significant energy
transfer from PBOPF segments to the BTBM units. Light-emitting
devices based on these polymers were fabricated with an indium
tin oxide/poly(3,4-ethylene dioxythiophene):poly(styrene sulfo-
nate) (PEDOT:PSS)/polymers/Balq/LiF/Al configuration. Examina-
tion of the electroluminescence emission of the synthesized
polymers showed that the maximum wavelength shifted contin-
uously toward long wavelengths with as the number of BTBM
units in the polymer main chain was increased. In particular, a
device using PFTBM 05 exhibited a maximum brightness of 510
cd/m2 and a maximum current efficiency of 0.57 cd/A.
2009
C
V
Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 48:
82–90, 2010
KEYWORDS: conducting polymers; conjugated polymers; fluo-
rescence; isophorone; light-emitting diodes; polyfluorene
INTRODUCTION Over the past several years, conjugated
polymers have attracted strong interest in scientific and
technological fields because of their potential use as semi-
conductor and electroactive materials in a variety of applica-
tions, such as organic thin-film transistors,1 organic bulk het-
erojunction photovoltaic cells,2 nonlinear optical devices,3
and organic polymer light-emitting diodes (PLEDs).4 In par-
ticular, interest in PLED devices using conjugated polymers5
has increased because such PLEDs have properties that are
suitable for flat panel displays; easy processing from poly-
mer solutions, low operating voltages compared with small
molecules, faster response times than liquid crystal displays,
and facile color tuning over the full visible range from blue
to red via introduction of a diversity of comonomers.
(PL) and electroluminescence efficiencies, thermal and elec-
trical stabilities, and facilitating the introduction of diverse
functional groups at the C-9 position of fluorene.6,7 Further-
more, the properties of polyfluorene are easily modulated by
introducing diverse low band gap comonomers because of
its wide band gap of ꢀ3.0 eV. This approach use methods
widely used in color tuning, which involve the covalent
attachment of a chromophore to the polymer. To date, the
most widely used narrow energy band gap comonomers
have been those containing aromatic heterocycles, such as
thiophene, bithiophene, benzothiazole, and benzothidazoloe
derivatives.8,9 To enhance polyfluorene efficiencies, several
studies have used strategies of blending, copolymerization,
and end-capping with charge-transporting materials to
achieve efficient charge injection.10 We have reported that
fluorene derivatives with bulky alkoxyphenyl substituents at
the 9-position exhibit enhanced blue emission stability and
Recently, studies of polyfluorenes and fluorene oligomers
have explored the advantages of these materials over other
conjugated polymers, yielding improved photoluminescence
*Present address: Convergence Components and Materials Lab., Electronics and Telecommunications Research Institute, Daejeon 305-350, Korea
Correspondence to: H.-K. Shim (E-mail: hkshim@kaist.ac.kr) or D.-H. Hwang (E-mail: dhhwang@kumoh.ac.kr)
C
V
Journal of Polymer Science: Part A: Polymer Chemistry, Vol. 48, 82–90 (2010) 2009 Wiley Periodicals, Inc.
82
INTERSCIENCE.WILEY.COM/JOURNAL/JPOLA

ARTICLE
SCHEME 1 The synthetic routs of the BTBM.
superior device performance compared with alkyl-substituted
polyfluorenes.11
the efficient red-light emission EL properties of isophorone-
based dopants.
Triarylamines, in amorphous glassy film states, show excel-
lent hole mobilities at room temperature through time-of-
flight measurements.25 These materials have attracted con-
siderable interest as hole-transport materials for use in mul-
tilayer organic electroluminescence (EL) devices12,13 because
of the low levels of their highest occupied molecular orbitals
(HOMO) and high hole mobility. The former allows efficient
hole injection from indium tin oxide (ITO) transparent ano-
des and reduces the likelihood of trapping.14 Pernius et al.15
reported the efficient blue-light emission EL properties of
polyfluorenes containing a triphenyl amine derivative that
enhanced hole-transporting abilities in the polymer chains.
In this article, we report the synthesis of polyfluorene co-
polymers containing isophorone derivatives, 2(3{2[4(2{4
[bis(4-bromophenyl)amino]phenyl}vinyl)-2,5-bisoctyloxyphenyl]-
vinyl}-5,5-dimethyl-cyclohex-2-enylidene)malononitrile (BTBM).
BTBM contains a long conjugated system. It has three indi-
vidual segments with an isophorone derivative containing
two cyanide groups at the carbonyl position, a dialkoxy
phenyl group for increased solubility, and a triphenyl amine
for effective charge transfer. Furthermore, we introduced a
vinyl linkage between each segment to increase the p-con-
jugation length. We systematically investigated the synthe-
sis, thermal stability, optical properties, and electrical prop-
erties of the resulting polymers. The synthetic routes for
the new PBOPF-based copolymers, PFTBMs, are given in
Schemes 1 and 2.
The well-known pyran-containing laser dyes, such as
4(dicyanomethylene)2-methyl-6[p(dimethylamino)styryl]4H-
pyran (DCM) derivatives, have been widely used and are
regarded as progressive red-emitting materials for OLED
applications.16 All DCM derivatives consist of two cyanide
groups as the acceptor and a pyran ring as the donor, where
the donor and acceptor are connected by a vinylene group.
The architectures of these DCM derivatives yield a pure red
color when combined with a suitable host material. They are
usually synthesized by condensation reactions between alde-
hyde groups and dicyanomethylidenepyrans, which produce
a doubly condensed product. A one-to-one stoichiometric ra-
tio, however, tends to produce unwanted double-condensed
products. These products are difficult to separate using chro-
matography or sublimation isolation.17 The isophorone is not
only similar in structure to DCM but also avoids forming the
double-condensation byproduct because of its asymmetric
structure. Lee and coworkers17 and Ermer et al.18 reported
EXPERIMENTAL
Measurements
NMR spectra were recorded using a Bruker AM 300 MHz
spectrometer with tetramethylsilane as an internal reference.
Elemental analysis was performed using an EA 1110 Fisons
analyzer. UV–vis and PL spectra were recorded using Jasco V-
530 and Spex Fluorolog-3 spectrofluorometers. Thermogravi-
metric analysis (TGA) was performed using a TA Q500 ana-
lyzer with a heating rate of 10 ꢁC/min under nitrogen
atmosphere. Differential scanning calorimetric measurements
were made using TA Q100 instrument and operated under
nitrogen atmosphere at a heating rate of 10 ꢁC/min. The
number- and weight-average molecular weights of the poly-
mers were determined by gel permeation chromatography
SYNTHESIS AND PROPERTIES OF POLYFLUORENE COPOLYMERS, PARK ET AL.
83

JOURNAL OF POLYMER SCIENCE: PART A: POLYMER CHEMISTRY DOI 10.1002/POLA
SCHEME 2 The synthetic routs of the copolymers, PFTBMs.
(GPC) on Viscotek T60A instrument, using tetrahydrofuran
(THF) as eluent and polystyrene as standard. Cyclic voltam-
metry (CV) was performed on an AUTOLAB/PG-STAT12
model system with a three-electrode cell in a solution of
Bu4NBF4 (0.10 M) in acetonitrile at a scan rate of 50 mV/s.
A film of each polymer was coated onto a Pt wire electrode by
dipping the electrode into a solution of the polymer. The meas-
urements were calibrated using ferrocene as standard. LED
devices were fabricated on glass substrates coated with ITO.
The device configuration was ITO/PEDOT:PSS/polymer/Balq/
LiF/Al structures. The procedure for cleaning the ITO surface
included sonication and rinsing in deionized water, methanol,
and acetone. The hole-transporting PEDOT:PSS layer was spin-
coated onto each ITO anode from a solution purchased from
Bayer. Each polymer solution in chlorobenzene was then spin-
coated onto the PEDOT:PSS layer. The spin-casting yielded uni-
form polymer films with thicknesses of ꢀ40 nm. A 40-nm-
thick bis(2-methyl-8-quinolinolate)-4-(phenylphenolata)alu-
minum (Balq) electron-transporting layer was deposited, and
a 1-nm-thick lithium fluoride layer and a 70-nm-thick alumi-
num layer were subsequently deposited at pressures below
10ꢂ6 Torr. EL spectra of the devices were obtained using a
Minolta CS-1000. Current–voltage–luminance (I-V-L) charac-
teristics were recorded simultaneously with the measurement
of the EL intensity by attaching the photospectrometer to a
Keithley 238 and a Minolta LS-100 as the luminance detector.
were synthesized according to procedures outlined in the
literature.11,19,20 Solvents with analytical grade were used
during the whole experiments, and all chemicals were used
without further purification.
Synthesis of Bis(4-bromophenyl)-
(4-vinylphenyl)amine (3)
4[Bis-(4-bromophenyl)amino]benzaldehyde (2) (3 g, 6.96
mmol) and methyltriphenylphosphonium bromide (7.45 g,
20 mmol) were dissolved in 10 mL of dry THF. Potassium
tert-butoxide (50 mL, 1.0 M solution in THF) was added
dropwise slowly to the resulting solution at 0 ꢁC, then the
reaction mixture was warmed to room temperature and
stirred under N2 for 12 h. The reaction mixture was poured
into water and extracted with ethyl acetate. The combined
organic extracts were washed with brine, dried (MgSO4), and
concentrated to dryness under vacuum. The crude product
was purified by column chromatography (petroleum ether/
dichloromethane ¼ 4:1) to give product (3) as a white solid.
The resulting product yield was 80% (2.39 g).
1H NMR (CDCl3, ppm) 7.32–7.28 (m, 6H), 7.00 (d, 2H), 6.94–
6.92 (m, 4H), 6.64–6.61 (m, 1H), 5.67–5.63 (d, 1H), 5.28–
5.17 (d, 1H). 13C NMR (CDCl3, ppm) 146.38, 146.25, 135.92,
132.93, 132.34, 127.29, 125.51, 124.13, 115.64, 112.91. Anal.
Calcd for C20H15Br2N; C, 55.97; H, 3.52; N, 3.26. Found: C,
55.87; H, 3.61; N, 3.24.
Synthesis of 2,5-Diiodo-1,4-bis-octyloxy-benzene (5)
A solution of compound (4) (10 g, 30 mmol), KIO3 (2.55 g,
12 mmol), and I2 (8.35 g, 32.7 mmol) in acetic acid (100
mL)/conc. H2SO4 (1 mL)/H2O (4 mL) was stirred at 80 ꢁC
for 24 h. After cooling, Na2S2O3 aqueous solution was added
until the purple color disappeared, then the mixture was
poured into H2O (250 mL) and extracted with dichlorome-
thane. The combined organic extracts were washed with
brine, dried (MgSO4), and concentrated to dryness under
vacuum. Recrystallization from dichloromethane and hexane
afforded product (5). The resulting product yield was 59%
(10 g).
Materials
Triphenyl amine, malononitrile, isophorone, hydroquinone, 1-
bromooctane, 2,7-dibromofluorenone, toluene (99.8%, anhy-
drous), N,N-dimethylformamide (99.8%, anhydrous), 2-iso-
propoxy-4,4,5,5,-tetramethyl-1,3,2-dioxaborolane, methyltri-
phenylphosphonium bromide, tetrakis-(triphenyl-phosphine)-
palladium (0), palladium (II) acetate, triphenylphosphine,
R
triethylamine, N-bromosuccinimide, and AliquatV336 were
purchased from Aldrich. All chemicals were used without
further purification. 4-Diphenylamino-benzaldehyde (1),
4[bis(4-bromophenyl)amino] benzaldehyde (2), 1,4-bis-
octyloxy-benzene (4), 2(3,5,5-trimethyl-cyclohex-2-enylide-
ne)malononitrile (7), 2,7-dibromo-9,9-bis(4-octyloxyphenyl)-
fluorene (BOPF) (10), and 2,7-bis(4,4,5,5-tetramethyl-1,3,2-
1H NMR (CDCl3, ppm) 7.14 (s, 2H), 3.89 (t, 4H), 1.76 (m,
4H), 1.53–1.28 (m, 20H), 0.88 (t, 6H). 13C NMR (CDCl3, ppm)
152.84, 121.70, 85.67, 69.99, 32.01, 28.98, 28.01, 25.89,
dioxaborolan-2-yl)-9,9-bis(4-octyloxy-phenyl)fluorene
(11)
84
INTERSCIENCE.WILEY.COM/JOURNAL/JPOLA

ARTICLE
22.14, 13.89. Anal. Calcd for C22H36I2O2; C, 45.07; H, 6.19.
Found: C, 45.15; H, 6.23.
Recrystallization from dichloromethane and methanol
afforded product (9). The resulting product yield was 30%
(0.6 g).
Synthesis of 4-Iodo-2,5-bis-octyloxy-benzaldehyde (6)
The obtained compound (5) (3.5 g, 5.97 mmol) was dissolved
1H NMR (CDCl3, ppm) 7.43–7.33 (m 8H), 7.08–6.83 (m, 11H),
4.07–4.01 (m, 4H), 2.58 (s, 2H), 2.47 (s, 2H), 1.88–1.81 (m,
4H), 1.51–0.95 (m, 26H), 0.87–0.84 (m, 6H). Anal. Calcd for
C55H63Br2N3O2; C, 68.96; H, 6.63; N, 4.39. Found: C, 68.86; H,
6.54; N, 4.32. m/z ¼ 957.85 (Mþ).
ꢁ
in diethyl ether (100 mL) at ꢂ78 C. To a solution was added
3.75 mL (5.97 mmol) of butyllithium (1.6 M in hexane) by sy-
ringe. The mixture was stirred at ꢂ78 ꢁC for 2 h. N,N-Di-
methylformamide (0.66 mL, 8.96 mmol) was added to the solu-
ꢁ
tion, and the resulting mixture was stirred at ꢂ78 C for 1 h,
warmed to room temperature, and stirred for 40 h. The mix-
ture was poured into water, extracted with dichloromethane,
and dried over MgSO4. The solvent was removed by solvent
evaporation, and the residue was purified by column chroma-
tography using ethylacetate/hexane (2/8, v/v) as the eluent.
Recrystallization from dichloromethane and hexane afforded
product (6). The resulting product yield was 85% (2.48 g).
General Polymerization Procedure
Into 100-mL two-neck flask was added dibromo compounds
and diborolan compound in 25 mL of anhydrous toluene.
Water-soluble Pd (0) complex, tetrakis-(triphenylphosphine)-
palladiuim (1 mol %), was transferred into the mixture in a
dry box. Subsequently, 2 M aqueous sodium carbonate
deaerated for 30 min and the phase transfer catalyst,
R
AliquatV336 (several drops), in toluene purged under nitro-
1H NMR (CDCl3, ppm) 10.21 (s, 1H), 7.47 (s, 1H), 7.21 (s,
1H), 4.08 (t, 2H), 4.02 (t, 2H), 1.91 (m, 4H), 1.59–1.31 (m,
20H), 0.87 (t, 6H). 13C NMR (CDCl3, ppm) 189.02, 154.92,
152.02, 124.98, 124.58, 109.01, 96.65, 69.79, 69.22, 31.58,
28.92, 28.49, 28.38, 26.02, 25.99, 21.94, 13.80. Anal. Calcd
for C23H37I2O3: C, 44.89; H, 6.06. Found: C, 45.02; H, 6.08.
gen for 1 h was transferred via cannula. The reaction mix-
ture was stirred at 80 ꢁC for 3 days, and then the excess
amount of bromobenzene, the end-capper, dissolved in 1 mL
of anhydrous toluene was added and stirring continued for
12 h. The reaction mixture is cooled to about 50 ꢁC and
added slowly to a vigorously stirred mixture of 200 mL of
methanol. The polymer fibers are collected by filtration and
reprecipitation from methanol and acetone. The polymers
are purified further by washing for 2 days in a Soxhlet appa-
ratus with acetone to remove oligomers and catalyst resi-
dues, and column chromatography with a chloroform solu-
tion of the polymer. The reprecipitation procedure in
chloroform/methanol is then repeated several times. The
resulting polymers were soluble in common organic solvents.
Yield: 50–68%.
Synthesis of 2{3[2(4-Iodo-2,5-bisoctyloxyphenyl)vinyl]-
5,5-dimethyl-cyclohex-2-enylidene}malononitrile (8)
To a solution of compound (6) (5 g, 10.2 mmol) and com-
pound (7) (2 g, 10.7 mmol) in 13 mL of N,N-dimethylforma-
mide, 2.6 mL of acetic acid, 2.6 mL of piperidine, and 1.3 mL
of acetic anhydride were added. The reaction mixture was
heated at 80 ꢁC for 8 h under stirring, cooled, and poured
into water. After filtration, the crude reaction product was
purified first by column chromatography onto silica gel using
dichloromethane/ethyl acetate (4/1, v/v) as eluent. After
evaporation of the solvent, the remaining reaction product
was recrystallized from ethanol to obtain the pure product
(8). The resulting product yield was 60% (3.98 g).
1H NMR (CDCl3, ppm) 7.32 (t, 2H), 6.95 (t, 2H), 6.82 (s, 1H),
4.00–3.92 (m, 4H), 2.56 (s, 2H), 2.43 (s, 2H), 1.84–1.77 (m,
4H), 1.37–1.27 (m, 16H), 0.87 (s, 6H), 0.87–0.84 (t, 6H). 13C
NMR (CDCl3, ppm) 169.20, 154.23, 152.23, 151.76, 131.21,
129.34, 125.45, 123.89, 123.54, 113.47, 112.81, 109.14,
89.44, 70.06, 69.49, 42.90, 38.93, 31.96, 31.73, 31.71, 29.27,
29.26, 29.22, 29.16, 29.12, 27.94, 26.13, 26.02, 22.60, 22.58,
14.07, 14.05. Anal. Calcd for C35H49IN2O2: C, 64.02; H, 7.52;
N, 4.27. Found: C, 64.15; H, 7.64; N, 4.15.
PFTBM 05
2,7-Bis(4,4,5,5-tetramethyl-1,3,2-dioxaborolan-2-yl)-9,9-bis-(4-
octyloxy-phenyl)-fluorene (11) (1 equiv), 2,7-dibromo-9,9-
bis-(4-octyloxy-phenyl)-fluorene (10) (0.995 equiv), and
BTBM (9) (0.005 equiv) were used in this polymerization.
1H NMR (CDCl3, ppm) aromatic and vinylene; 7.76–6.75
(ꢀ33H), aliphatic; 3.90–3.85 (ꢀ8H), 1.74–0.84 (ꢀ70H). ELEM.
ANAL. Found: C, 87.12; H, 9.04; N, 0.04.
PFTBM 1
2,7-Bis(4,4,5,5-tetramethyl-1,3,2-dioxaborolan-2-yl)-9,9-bis-(4-
octyloxy-phenyl)-fluorene (11) (1 equiv), 2,7-dibromo-9,9-
bis-(4-octyloxy-phenyl)-fluorene (10) (0.99 equiv), and
BTBM (9) (0.01 equiv) were used in this polymerization.
Synthesis of 2(3{2[4(2{4[Bis(4-bromophenyl)
amino]phenyl}vinyl)-2,5-bisoctyloxyphenyl]vinyl}-5,5-
dimethyl-cyclohex-2-enylidene)malononitril (9) (BTBM)
A solution of compound (3) (1 g, 2.33 mmol), compound (8)
(1.6 g, 2.33 mmol), palladium (II) acetate (0.16 g, 0.24
mmol), triphenyphosphine (0.1 g, 0.38 mmol), and triethyl-
amine (7 mL) in N,N-dimethylformamide (30 mL) was
stirred at 130 ꢁC for 24 h. The mixture was poured into
water, extracted with dichloromethane, and dried over
MgSO4. The solvent was removed by solvent evaporation,
and the residue was purified by column chromatography
using dichloromethane/ethylacetate (4/1, v/v) as the eluent.
1H NMR (CDCl3, ppm) aromatic and vinylene; 7.76–6.75
(ꢀ33H), aliphatic; 3.90–3.85 (ꢀ8H), 1.74–0.84 (ꢀ70H). ELEM.
ANAL. Found: C, 86.04; H, 8.90; N, 0.14.
PFTBM 5
2,7-Bis(4,4,5,5-tetramethyl-1,3,2-dioxaborolan-2-yl)-9,9-bis-(4-
octyloxy-phenyl)-fluorene (11) (1 equiv), 2,7-dibromo-9,9-
bis-(4-octyloxy-phenyl)-fluorene (10) (0.95 equiv), and
BTBM (9) (0.05 equiv) were used in this polymerization.
SYNTHESIS AND PROPERTIES OF POLYFLUORENE COPOLYMERS, PARK ET AL.
85

JOURNAL OF POLYMER SCIENCE: PART A: POLYMER CHEMISTRY DOI 10.1002/POLA
1H NMR (CDCl3, ppm) aromatic and vinylene; 7.76–6.75
(ꢀ33H), aliphatic; 3.90–3.85 (ꢀ8H), 1.74–0.84 (ꢀ70H). ELEM.
ANAL. Found: C, 84.62; H, 8.41; N, 0.62.
PFTBM 10
2,7-Bis(4,4,5,5-tetramethyl-1,3,2-dioxaborolan-2-yl)-9,9-bis-(4-
octyloxy-phenyl)-fluorene (11) (1 equiv), 2,7-dibromo-9,9-
bis-(4-octyloxy-phenyl)-fluorene (10) (0.90 equiv), and
BTBM (9) (0.10 equiv) were used in this polymerization.
1H NMR (CDCl3, ppm) aromatic and vinylene; 7.76–6.75
(ꢀ33H), aliphatic; 3.90–3.85 (ꢀ8H), 1.74–0.84 (ꢀ70H). ELEM.
ANAL. Found: C, 83.88; H, 8.33; N, 0.74.
PFTBM 25
2,7-Bis(4,4,5,5-tetramethyl-1,3,2-dioxaborolan-2-yl)-9,9-bis-(4-
octyloxy-phenyl)-fluorene (11) (1 equiv), 2,7-dibromo-9,9-
bis-(4-octyloxy-phenyl)-fluorene (10) (0.75 equiv), and
BTBM (9) (0.25 equiv) were used in this polymerization.
1H NMR (CDCl3, ppm) aromatic and vinylene; 7.76–6.75
(ꢀ33H), aliphatic; 3.90–3.85 (ꢀ8H), 1.74–0.84 (ꢀ70H). ELEM.
ANAL. Found: C, 82.68; H, 8.21; N, 0.88.
FIGURE 1 TGA traces of the synthesized PFTBM polymers.
from the BTBM units in the polymer main chain, because
BTBM units have a low decomposition temperature due to
their two vinyl linkages. Additionally, we found that the
amount of weight loss at the start of thermal decomposition
increased with increasing content of BTBM units in the poly-
mer main chain. The TGA traces of the PFTBMs are shown
in Figure 1. The polymerization results of the synthesized
copolymers are summarized in Table 1.
RESULTS AND DISCUSSION
Synthesis and Characterization of the Polymers
The synthetic routes and structures of the polymers are
shown in Scheme 2. A series of conjugated copolymers were
synthesized via palladium-catalyzed Suzuki coupling reac-
tions.16,21 All PFTBMs were end-capped with bromobenzene.
The actual compositions of the polymers were determined
by elemental analysis.16,21 The feed ratios of BTBM were 0.5,
1, 5, 10, and 25 mol % of the total amount of monomer, and
the resulting ratios of BTBM units in the PFTBMs were 0.49,
1.96, 8.8, 10.69, and 12.77%, respectively. The actual ratios
of PFTBM in the copolymers are similar to the feed mono-
mer ratios in the first four cases. The lower than expected
BTBM content for the feed ratio of 25 mol % is tentatively
attributed to reduced reactivity of the bulky BTBM units
during polymerization.21 All copolymers were found to be
soluble in common organic solvents such as THF, chloroform,
and toluene, with no evidence of gel formation. Each copoly-
mer was spin-coated onto a quartz plate coated with an ITO
substrate and found to produce transparent and homogene-
ous thin films. The number-averaged molecular weights (Mn)
of the copolymers, as determined by GPC using a polystyrene
standard, were found to range from 19,300 to 22,800 with
polydispersity indices ranging from 2.1 to 2.9. The yields of
the copolymers ranged from 50 to 68%. The thermal transi-
tions of the polymers were studied using differential scan-
ning calorimetry under a nitrogen atmosphere. The thermo-
grams for PFTBMs each contained only a glass transition
around 86 ꢁC, without features characteristic of the melting
of liquid-crystalline phases. The thermal properties of the
polymers were determined using TGA. All polymers were
found to exhibit good thermal stability, losing less than 5%
of their weight upon heating from 320 to 450 ꢁC in TGA
under a nitrogen atmosphere. Interestingly, PFTBM 10 and
PFTBM 25 began decomposing at a lower temperature than
the other polymers. We assume that this result originated
Optical, Photoluminescence, and Electrochemical
Properties
The UV–vis absorption spectra of the PFTBMs exhibit
absorption maxima at 386 nm. Previous reports gave the
UV–vis absorption maxima of PBOPF homopolymers at 391
nm in the film state.11 Compared with these results, the UV–
vis absorption maxima of the PFTBMs are at lower wave-
lengths than those of the PBOPF homopolymer11 by ꢀ5 nm.
We assume that this effect is due to the linkage between the
nitrogen and phenyl groups in the diphenyl amine of the
polymer main chain. The diphenyl amine units in the main
chain disturb the conjugation of the polymer main chain
because the nonconjugated structure shortens the conjuga-
tion length of the molecules, yielding a blue-shift in the
absorption spectrum.22 The absorptions at the spectral edge,
around 425 nm, however, increased slightly with increasing
content of BTBM units in the polymer main chain. These
results indicate that the BTBM units are not involved in the
polymer main-chain processes in the solution state. The nor-
malized UV–vis absorption spectra of the polymers are
shown in Figure 2(a). The normalized PL emission spectra
are shown in Figure 2(b,c). In the solution phase [Fig. 2(b)],
the PL spectra of all polymers exhibit emission maxima at
417 nm. The shapes of the PL emission spectra of the
PFTBMs are similar to those of PBOPF homopolymers. Inter-
estingly, the intensities of PL emission of the PFTBMs at 438
and 467 nm are slightly reduced, but the intensities at 553
nm are slightly elevated compared with the PBOPF PL emis-
sion spectrum. The PL spectra for thin films of the polymers
[Fig. 2(c)], however, are quite different from the solution
spectra. The PBOPF homopolymer film has a maximum PL
emission in the blue region of the spectrum at 424 nm.11
86
INTERSCIENCE.WILEY.COM/JOURNAL/JPOLA

ARTICLE
TABLE 1 Physical Properties of the Synthesized PFTBM Polymers
Ratio (BTBM mol %)
In the Feed
Composition
In the
Copolymersc
a
Polymer
Mn
PDIa
Tg (ꢁC)
Td (ꢁC)b
PFTBM 05
PFTBM 1
PFTBM 5
PFTBM 10
PFTBM 25
a
21,200
19,700
21,300
22,800
19,300
2.3
2.1
2.8
2.7
2.9
86.1
86.5
84.5
83.2
80.2
450
450
440
412
320
0.5
1
0.49
1.96
5
8.8
10
25
10.69
12.77
c
Mn and PDI of the polymers were determined by gel permeation chro-
Calculated by elemental analysis through calculation of the amount of
matography using polystyrene standards.
Temperature resulting in 5% weight loss based on initial weight.
nitrogen contained in copolymers.
b
Interestingly, the two strong and sharp PL peaks in the blue
region of the spectrum of PBOPF are much weaker in inten-
sity in the PL spectra of the copolymers. The PL maximum
of the copolymer containing only 1% BTBM, PFTBM 1, is at
494 nm, which constitutes a large shift with respect to the
PL maximum of PBOPF. As the BTBM content of the copoly-
mers is increased, the intensities of the blue PL emission
bands in the blue decrease. These large shifts in PL emission
are probably due to intermolecular energy transfer,23,26–27
from the BOPF group to the low band gap BTBM, which
results in emission occurred mainly. The maxima of PL emis-
sion spectra are also slightly shifted to longer wavelengths
because of increased BTBM content in the polymer main
chain. This red shift in the PL emission spectrum may be
due to the increased effective BTBM content in the copoly-
mers. We assume that the differences in the solution and
film state PL spectra for PFTBMs arise from the BTBM pla-
narity, which allows more effective interchain interaction. To
explain these results, we plan to investigate the polymer con-
formations and the influence of conformation on spectral
properties. The optical properties of the synthesized poly-
mers are summarized in Table 2.
To investigate the energy levels of their HOMOs and lowest
unoccupied molecular orbitals, the electrochemical proper-
ties of PFTBMs were investigated by CV. A platinum elec-
trode was coated with the polymers and used as the working
electrode. The counter electrode was a platinum wire, and
the reference electrode was an Ag/AgNO3 (0.01 M) electrode.
The electrochemical properties of the copolymers were
investigated in an electrolyte consisting of a solution of 0.1
M tetrabutylammonium tetrafluoroborate in acetonitrile at
room temperature under nitrogen at a scan rate of 50 mV/s.
The measurements were calibrated using ferrocene as the
standard.24 Figure 3 shows the oxidation waves and energy
levels of the copolymers as a result of the p-type doping. As
shown in Figure 3, in the anodic scan and energy diagram,
the onset of oxidation of PFTBMs was found to occur
between 1.08 and 1.11 V, corresponding to ionization poten-
tials of 5.75 and 5.78 eV, respectively. The onset of oxidation
of BTBM was found to occur at 0.51 V, corresponding to
FIGURE 2 UV–vis absorption (a) and PL emission (b, solution)
and (c, film) spectra of the synthesized polymers.
SYNTHESIS AND PROPERTIES OF POLYFLUORENE COPOLYMERS, PARK ET AL.
87

JOURNAL OF POLYMER SCIENCE: PART A: POLYMER CHEMISTRY DOI 10.1002/POLA
TABLE 2 Summary of the Optical Properties and Energy Levels
of the Synthesized PFTBM Polymers
Film, kmax (nm)a
Eonset,ox EHOMO ELUMO
Polymer
Absorption Emission (V)
(eV)b
(eV)c
PFTBM 05 386
424
424
494
506
523
–
1.11
1.11
1.09
1.09
1.08
0.51
5.78
5.78
5.76
5.76
5.75
5.18
2.81
2.81
2.81
2.82
2.83
3.10
PFTBM 1
PFTBM 5
386
386
PFTBM 10 386
PFTBM 25 386
BTBM
–
a
Measured as thin films on fused quartz plate.
Determined from the onset voltage of the first oxidation potential with
b
reference to ferrocene at 4.8 eV.
c
Calculated from HOMO and energy of band gap (Eg) (Eg from UV–vis
absorption edge).
FIGURE 4 Electroluminescence spectra of PFTBM devices with
ITO/PEDOT:PSS/polymer/Balq/LiF/Al configurations.
ionization potentials of 5.18 eV. The results of CV studies of
PFTBMs show that the onset of oxidation of PFTBMs was
slightly shifted toward high HOMO levels by an increase in
BTBM content in the polymer main chain. Unfortunately, a
reduction wave was scarcely obtained. The onsets of oxida-
tion and the energies of the HOMO levels of the PFTBMs are
listed in Table 2.
the BOPF segments to the lower energy state of the BTBM
units.24 Such results are common for organic host-guest sys-
tems, in which the low-energy state unit acts as charge-trap-
ping sites.23 The maximum EL emission shifts increasingly to
the red as the fraction of BTBM units increases. In particular,
the EL emission around 650 nm increased with increasing
BTBM content in the polymer main chain. This was not
observed, however, for polymers with low BTBM content in
the polymer main chain, PFTBM 05 and PFTBM 1. We pre-
sume that the main emission process effectively occurs in
the polymer main chain between the BOPF segment and the
TPA part of the BTBM unit. Interestingly, the red emission
around 650 nm increased with increasing BTBM content in
the polymer main chain. We presume that these results were
caused by the isophorone moiety of the BTBM unit. We men-
tioned earlier that copolymers with low BTBM contents
processed through polymer main chain. The BTBM unit has
a T-shaped structure, and isophorone was introduced as part
of the red-emitting material in the BTBM. The isophorone
moiety of the BTBM unit participated in the electrolumines-
cent process with increasing BTBM content in the polymer
main chain. These results can be explained by the interchain
interactions between BTBM units and other polymer chain.
The polymer chromaticity values continuously shifted to the
red, (x ¼ 0.21, y ¼ 0.26) to (x ¼ 0.30, y ¼ 0.43). The CIE
coordinates of PFTBMs are shown in Figure 5. The voltage–
luminance (V-L) and voltage–current efficiency characteris-
tics of the devices are shown in Figure 6, and their perform-
ances are summarized in Table 3. The turn-on voltages of
the PFTBM devices range from 5.4 to 12.4 V, yielding maxi-
mum brightness values in the range 140–720 cd/m2. The
V-L and voltage–current efficiency curves shift to slightly
higher voltages when the number of BTBM units in the
copolymers is increased. PBOPF11 and the copolymers have
similar band gaps and HOMO levels, so very similar electron
and hole injection arise from the electrodes. Therefore, we
assumed that the dramatic improvement on turn-on voltage
achieved using the copolymers arise from the BTBM units in
Electroluminescence Properties and
Current–Voltage–Luminance Characteristics
To investigate the electrical properties and performances of
the copolymers in real devices, polymer EL devices with the
configuration ITO/PEDOT:PSS (40 nm)/polymer (40 nm)/
Balq (40 nm)/LiF (1 nm)/Al (70 nm) were fabricated. The
EL spectra of the synthesized polymers are similar to their
corresponding PL spectra, as shown in Figure 4. The EL
emission in the blue region shifts to longer wavelengths as a
function of increasing BTBM content in the polymer main
chain. We presume that the EL emission properties can be
explained by energy transfer from the higher energy state of
FIGURE 3 Cyclic voltammograms of the synthesized polymers
and BTBM (inset: the proposed energy levels of BTBM and
PFTBM).
88
INTERSCIENCE.WILEY.COM/JOURNAL/JPOLA

ARTICLE
FIGURE 5 CIE coordinates (x,y) of PFTBMs (NTSC-dashed line).
the copolymer, which produce strong charge-trapping sites,
resulting in the higher turn-on voltages measured in the
PFTBM devices.24 The PFTBM 05 device has the best per-
formance, with a maximum brightness of 510 cd/m2 at 10 V
and a maximum current efficiency of 0.57 cd/A at 7 V. We
suggest that PFTBM 05 produces balanced electron and hole
injection in the device and that the energy transfer is effi-
cient between the blue-light–emitting BOPF segments and
the orange-light–emitting BTBM units. Although the BTBM
was shown low color tunability in the polymer main chain
because of competitive process between polymer main chain
and intermolecular interaction, we believe that these electro-
luminescence characteristics could be further improved in
future work by optimizing the film morphology, layer thick-
ness, and postproduction treatment conditions.
FIGURE 6 Voltage–luminance (V-L) (a) and voltage–current effi-
ciency (b) characteristics of the synthesized PFTBM polymers.
transfer. Furthermore, we introduced a vinyl linkage between
each segment to increase the p-conjugation length. The
PFTBMs were synthesized via palladium-catalyzed Suzuki
coupling reactions. These polymers glass transition tempera-
tures were similar to the PBOPF homopolymer and were
found to be thermally stable and readily soluble in common
organic solvents. The UV–vis absorption and PL emission
spectra of the synthesized polymers did not show significant
energy transfer from PBOPF segments to the BTBM units in
solution. PL in film and EL emissions, however, were indi-
cated that maximum spectra were shifted slightly to red due
to interchain interactions between BTBM units and other
polymer chain. The onset of oxidation of the PFTBMs was
shifted slightly to higher HOMO levels by an increase in
BTBM content in the polymer main chain. The PFTBM 05
CONCLUSIONS
We have successfully synthesized a series of new fluorene-
based copolymers (PFTBMs) with varying molar ratios of the
low-energy band gap comonomer, BTBM. To prepare a low-
energy gap comonomer, we used an isophorone derivative
containing a long conjugated system. The isophorone deriva-
tive has three individual segments containing cyanide groups
at the carbonyl position, a dialkoxy phenyl group for increas-
ing solubility, and a triphenyl amine for effective charge
TABLE 3 Summary of the EL Device Performances of the Synthesized PFTBM Polymers
Luminancemax
(cd/m2)
Current Efficiency
(cd/A)
EQE
(%)
CIE
Polymer
kmax (nm)
Coordinates (x, y)a
PFTBM 05
PFTBM 1
PFTBM 5
PFTBM 10
PFTBM 25
a
426, 456, 480
510
720
300
200
140
0.57
0.43
0.36
0.23
0.23
0.3
(0.21, 0.26)
(0.21, 0.29)
(0.27, 0.39)
(0.28, 0.40)
(0.30, 0.43)
485
492
495
501
0.23
0.17
0.11
0.11
Determined from EL spectra (Fig. 4).
SYNTHESIS AND PROPERTIES OF POLYFLUORENE COPOLYMERS, PARK ET AL.
89

JOURNAL OF POLYMER SCIENCE: PART A: POLYMER CHEMISTRY DOI 10.1002/POLA
Yeh, H.-C.; Chan, L.-H.; Wu, W.-C.; Chen, C.-T. J Mater Chem 2004, 14,
1293–1298; (d) Yeh, H.-C.; Yeh, S.-J.; Chen, C.-T. Chem Commun 2003,
2632–2633; (e) Yen, W.-C.; Pal, B.; Yang, J.-S.; Hung, Y.-C.; Lin, S.-T.;
Chao, C.-Y.; Su, W.-F. J Polym Sci Part A: Polym Chem 2009, 47,
5044–5056.
device showed the best performance, with a maximum bright-
ness of 510 cd/m2 at 10 V and a maximum current efficiency
of 0.57 cd/A at 7 V. We suggest that PFTBM 05 produces bal-
anced electron and hole injection in the device, and that
energy transfer is efficient between the blue-light–emitting
BOPF segments and the orange-light–emitting BTBM units.
10 (a) Herguth, P.; Jiang, X.; Liu, M. S.; Jen, A. K.-Y. Macromolecules 2002,
35, 6094–6100; (b) Ego, C.; Grimsdale, A. C.; Uckert, F.; Yu, G.; Srdanov,
G.; Mu¨llen, K. Adv Mater 2002, 14, 809–811; (c) Miteva, T.; Meisel, A.;
Knoll, W.; Nothofer, H. G.; Scherf, U.; Mu¨ller, C. D.; Meerholz, K.; Yasuda,
A.; Neher, D. Adv Mater 2001, 13, 565–570; (d) Grisorio, R.; Piliego, C.;
Cosma, P.; Fini, P.; Mastrorilli, P.; Gigli, G.; Suranna, G. P.; Nobile, C. F.
J Polym Sci Part A: Polym Chem 2009, 47, 2093–2104.
This work was supported by the Korea Science and Engineering
Foundation (KOSEF) grant funded by the Korea government
(MOST) (No. R11-2007-050-02003-0). The authors appreciate
Jeong-Ik Lee and Hye Yong Chu (Electronics and Telecommuni-
cations Research Institute) for EL device experiments.
11 Lee, J.-H.; Hwang, D.-H. Chem Commun 2003, 2836–2837.
12 (a) Tang, C. W. Appl Phys Lett 1986, 48, 183–185; (b) Okutsu, S.;
Onikubo, T.; Tamano, M.; Enokida, T. IEEE Trans Electron Devices
1997, 44, 1302.
REFERENCES AND NOTES
1 Sirringhaus, H.; Tessler, N.; Friend, R. H. Science 1998, 280,
13 Giebeler, C.; Antoniadis, H.; Bradley, D. D. C.; Shirota, Y. Appl Phys
1741–1744.
Lett 1998, 72, 2448–2450.
2 Halls, J. J. M.; Walsh, C. A.; Greenham, N. C.; Marseglia, E. A.; Friend,
14 Redecker, M.; Bradley, D. D. C.; Inbasekaran, M.; Wu, W. W.; Woo,
R. H.; Moratti, S. C.; Holmes, A. B. Nature 1995, 376, 498–500.
E. P. Adv Mater 1999, 11, 241–246.
3 Prasad, P. N.; Williams, D. J. Introduction to Nonlinear Effects in
15 (a) Pernius, M.; Inbasekaran, M.; Woo, E. P.; Wu, W.; Wujkowski, L.
Proc SPIE 1999, 93, 36221; (b) Hsieh, B.-Y.; Chen, Y. J Polym Sci Part
A: Polym Chem 2009, 47, 1553–1566.
Monomers and Polymers; Wiley: New York, 1991.
4 (a) Burroughes, J. H.; Bradley, D. D. C.; Brown, A. R.; Marks, R. N.;
Mackay, K.; Friend, R. H.; Burn, P. L.; Holmes, A. B. Nature (London)
1990, 347, 539–541; (b) Gustafsson, G.; Cao, Y.; Treacy, G. M.; Klavet-
ter, F.; Colaneri, N.; Heeger, A. J. Nature (London) 1992, 357, 477–479.
16 Tang, C. W.; Van Slyke, S. A.; Chen, C. H. J Appl Phys 1989, 65,
3610–3616.
17 Li, J.; Liu, D.; Hong, Z.; Tong, S.; Wang, P.; Ma, C.; Lengyel, O.; Lee,
5 (a) Grimsdale, A. C.; Chan, K. L.; Martin, R. E.; Jokisz, P. G.; Holmes,
A. B. Chem Rev 2009, 109, 897–1091; (b) Jeong, E.; Kim, S. H.; Jung,
I. H.; Xia, Y.; Lee, K.; Suh, H.; Shim, H.-K.; Woo, H. Y. J Polym Sci Part
A: Polym Chem 2009, 47, 3467–3479.
C.-S.; Kwong, H.-L.; Lee, S. Chem Mater 2003, 15, 1486–1490.
18 Ermer, S.; Lovejoy, S. M.; Leung, D. S.; Warren, H. Chem Mater
1997, 9, 1437–1442.
6 (a) Fukuda, M.; Sawada, K.; Yoshino, K. Jpn J Appl Phys 1989, 28,
19 (a) Ahn, T.; Song, S.-Y.; Shim, H.-K. Macromolecules 2000, 33,
6764–6771; (b) Park, M.-J.; Lee, J.-H.; Hwang, D.-H. Curr Appl Phys
2006, 6, 752–755.
1433–1435; (b) Pei, Q.; Yang, Y.
J Am Chem Soc 1996, 118,
7416–7417; (c) Leclerc, M. J Polym Sci Part A: Polym Chem 2001, 39,
2867–2873; (d) Cho, H. J.; Hwang, D. H.; Lee, J. D.; Cho, N. S.; Lee, S.
K.; Lee, J.; Jung, Y. K.; Shim, H. K. J Polym Sci Part A: Polym Chem
2008, 46, 797–802.
20 Ichiki, K.; Consta, S. J Phys Chem B 2006, 39, 19176–19182.
21 Chen, C. H.; Shi, J.; Tang, C. W. Macromol Symp 1997, 125, 1.
22 Lee, R.-H.; Wang, Y.-Y. J Appl Polym Sci 2008, 107, 3459–3468.
7 (a) Tsai, L. R.; Li, C. W.; Chen, Y. J Polym Sci Part A: Polym Chem
2008, 46, 5945–5958; (b) Scherf, U.; List, E. J. W. Adv Mater 2002,
14, 477–487; (c) Bonifa¨cio, V. D. B.; Morgado, J.; Scherf, U. J Polym Sci
Part A: Polym Chem 2008, 46, 2878–2883.
23 Chuang, C.-Y.; Shih, P.; Chien, C.-H.; Wu, F.-I.; Shu, C.-F. Macromole-
cules 2007, 40, 247–252.
24 (a) Lee, J.; Lee, J.-I.; Park, M.-J.; Jung, Y. K.; Cho, N. S.; Cho, H. J.;
Hwang, D.-H.; Lee, S.-K.; Park, J.-H.; Hong, J.; Chu, H. Y.; Shim, H.-K. J
Polym Sci Part A: Polym Chem 2007, 45, 1236–1246; (b) Park, M.-J.;
Lee, J.; Jung, I. H.; Park, J.-H.; Hwang, D.-H.; Shim, H.-K. Macromole-
cules 2008, 41, 9643–9649.
8 (a) Yang, J.; Jiang, C.; Zhang, Y.; Yang, R.; Yang, W.; Hou, Q.; Cao, Y.
Macromolecules 2004, 37, 1211–1218; (b) Alam, M. M.; Tonzola, C. J.;
Jenekhe, S. A. Macromolecules 2003, 36, 6557–6587; (c) Shen, Z.;
Strauss, J.; Daub, J. Chem Commun 2002, 460–461; (d) Sun, D.; Roso-
kha, S. V.; Kochi, J. K. J Am Chem Soc 2004, 126, 1388–1401; (e) Lai,
R. Y.; Fabrizio, E. F.; Lu, L.; Jenekhe, S. A.; Bard, A. J Am Chem Soc
2001, 123, 9112–9118; (f) Hsieh, B.-Y.; Chen, Y. J Polym Sci Part A:
Polym Chem 2009, 47, 833–844.
25 Stolka, M.; Janus, J. F.; Pai, D. M.
J Phys Chem 1984, 88,
4707–4714.
26 Hwang, D.-H.; Park, M.-J.; Lee, J.-H.; Cho, N.-S.; Shim, H.-K.; Lee, C.
Synth Met 2004, 146, 145–150.
9 (a) Hou, Q.; Zhou, Q.; Zhang, Y.; Yang, W.; Yang, R.; Cao, Y. Macromo-
lecules 2004, 37, 6299–6305; (b) Cho, N. S.; Hwang, D.-H.; Jung, B.-J.;
Lim, E.; Lee, J.; Shim, H.-K. Macromolecules 2004, 37, 5265–5273; (c)
27 Pommerehe, J.; Vestweber, H.; Guss, W.; Mahrt, R. F.; Bassler, H.;
Porsch, M.; Daub, J. Adv Mater 1995, 7, 55–58.
90
INTERSCIENCE.WILEY.COM/JOURNAL/JPOLA