Synthesis of new fluorene-based copolymers containing an anthracene derivative and their applications in polymeric light-emitting diodes

Article abstract of DOI:10.1166/jnn.2011.3709

We report the synthesis of copolymers containing fluorene and highly soluble anthracene derivatives, of general formula, poly{9,9′-bis-(4- octoloxy-phenyl)-fluorene-2,7-diyl-co-9,10-bis-(decy-1-ynyl)-anthracene-2, 6-diyl}s (PFAnts). The PFAnts were synthesized via Suzuki coupling and the feed ratios of the anthracene derivative (Ant) were 1, 5, 10, 30, and 50 mol % of the total amount of monomer. PFAnts showed well-defined high molecular weights and were more soluble in conventional organic solvents. The photoluminescence spectra of PFAnts shifted to longer wavelengths with increases in Ant proportion and the PFAnts emitted various colors varying from greenish-blue to orange. The highest occupied molecular orbital and lowest unoccupied molecular orbital energy levels trended toward enhanced hole and electron recombination balance as the Ant proportion increased, due to the better electron-accepting ability of the anthracene moiety compared to the fluorene moiety. Polymeric light-emitting diodes with the configurations ITO/PEDOT:PSS(40 nm)/polymer(60 nm)/Ca(10 nm)/Al(100 nm) (Device A) and ITO/PEDOT:PSS(40 nm)/polymer(60 nm)/Balq(40 nm)/LiF(1 nm)/Al(100 nm) (Device B) were fabricated using the polymers as emissive layers. Especially, Device B with PFAnt01 exhibited the highest measured maximum brightness of 1760 cd/m² at 14 V, a maximum current efficiency of 1.66 cd/A, and a maximum external quantum efficiency of 0.70%. Copyright

Full text of DOI:10.1166/jnn.2011.3709

Copyright © 2011 American Scientific Publishers
All rights reserved
Printed in the United States of America
Journal of
Nanoscience and Nanotechnology
Vol. 11, 4648–4657, 2011
Synthesis of New Fluorene-Based Copolymers
Containing an Anthracene Derivative and Their
Applications in Polymeric Light-Emitting Diodes
Kyoungmi Lee1, Jong- Hwa Park1, Moo-Jin Park2, Jonghee Lee3, and Hong-Ku Shim1ꢀ∗
1Department of Chemistry and School of Molecular Science (BK21), Active Polymer Center for Pattern Integration,
Korea Advanced Institute of Science and Technology, Daejeon, 305-701, Republic of Korea
2Polymer Science and Engineering Program, Active Polymer Center for Pattern Integration, Korea Advanced
Institute of Science and Technology, Daejeon, 305-701, Republic of Korea
3Convergence Components and Materials Research Laboratory,
Electronics and Telecommunications Research Institute Daejeon, 305-700, Republic of Korea
We report the synthesis of copolymers containing fluorene and highly soluble anthracene
derivatives, of general formula, poly{9,9ꢀ-bis-(4-octoloxy-phenyl)-fluorene-2,7-diyl-co-9,10-bis-(decy-
1-ynyl)-anthracene-2,6-diyl}s (PFAnts). The PFAnts were synthesized via Suzuki coupling and
the feed ratios of the anthracene derivative (Ant) were 1, 5, 10, 30, and 50 mol % of the
total amount of monomer. PFAnts showed well-defined high molecular weights and were more
soluble in conventional organic solvents. The photoluminescence spectra of PFAnts shifted to
longer wavelengths with increases in Ant proportion and the PFAnts emitted various colors
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varying from greenish-blue to orange. The highest occupied molecular orbital and lowest unoc-
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cupied molecular orbital energy levels trended toward enhanced hole and electron recombina-
Copyright: American Scientific Publishers
tion balance as the Ant proportion increased, due to the better electron-accepting ability of the
anthracene moiety compared to the fluorene moiety. Polymeric light-emitting diodes with the
configurations ITO/PEDOT:PSS(40 nm)/polymer(60 nm)/Ca(10 nm)/Al(100 nm) (Device A) and
ITO/PEDOT:PSS(40 nm)/polymer(60 nm)/Balq(40 nm)/LiF(1 nm)/Al(100 nm) (Device B) were fab-
ricated using the polymers as emissive layers. Especially, Device B with PFAnt01 exhibited the
highest measured maximum brightness of 1760 cd/m2 at 14 V, a maximum current efficiency of
1.66 cd/A, and a maximum external quantum efficiency of 0.70%.
Keywords: Conjugated Polymers, Light-Emitting Diodes (LED), Polyfluorenes, Anthracene.
1. INTRODUCTION
Polyfluorenes (PFs) have typically been used as polymer
backbones for PLEDs because of their large band gaps,
high photoluminescence (PL) and electroluminescence
(EL) quantum yields, excellent chemical and thermal sta-
bility, good solubility and film-forming properties, and
prompt availability from high-yielding synthetic routes,
such as Suzuki coupling, of well-defined high molar-mass
polymers.4ꢀ5 Recently, Hwang and colleagues reported that
PF derivatives with bulky alkoxyphenyl groups at the
9-position showed more stable blue emission and better
device performance than did alkyl-substituted fluorenes.6
However, PFs and derivatives thereof differ in charge
carrier mobility, and hence in the relative proportions
of holes and electrons because holes are usually faster
than electrons. This poor charge balance can lower EL
performance.
Conducting polymers have been extensively developed
since the time doped polyacetylene was first used as a
metallic conducting organic material in 1977.1 Such con-
jugated conducting polymers are very important as active
materials in polymeric electronic device applications.
Examples are polymeric light-emitting diodes (PLEDs),
photovoltaic cells, photodetectors, biosensors, and thin-
film transistors.2ꢀ3 The polymers permit rapid and low cost
fabrication because film-forming polymer solutions can be
employed. In recent years, enormous interest and effort
has driven the synthesis and characterization of conducting
polymers for PLEDs.
∗Author to whom correspondence should be addressed.
4648
J. Nanosci. Nanotechnol. 2011, Vol. 11, No. 5
1533-4880/2011/11/4648/010
doi:10.1166/jnn.2011.3709

Lee et al.
Synthesis of New Fluorene-Based Copolymers Containing an Anthracene Derivative and Their Applications in PLEDs
Anthracene is one of the well-known fused aromatics used
on a Spex Fluorolog-3 spectrofluorometer (model FL3-11)
using spin-coated films. And PL measurements were pre-
pared by spin-coating with the molecules dissolved in
chloroform solution (1 wt%). Cyclic voltammograms were
recorded at a scan rate of 50 mV/s at room temperature
in a solution of tetrabutylammonium hexafluorophosphate
(Bu4NPF6ꢁ dissolved in acetonitrile. A Pt wire was used
as the counter electrode and an Ag/AgCl electrode was
used as the reference electrode. The oxidation potentials
were calibrated using the ferrocene (Fc) value of −4.8 eV
as the standard. A film of each polymer was coated onto a
Pt wire electrode by dipping the electrode into a solution
of the polymer. Film thickness was measured with a TEN-
COR alpha-step 500 surface profiler. EL spectra of the
devices were obtained using a Minolta CS-1000. Current–
voltage–luminance (I–V–L) characteristics 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. All measure-
ments were carried out at room temperature under ambient
atmosphere.
in organic electronic device applications. In 1963, Pope and
co-workers reported the first use of anthracene in this con-
text. They applied a high voltage to an anthracene single
crystal, used as an organic electroluminescent material,
causing blue light to be emitted.7 Moreover, single-crystal
anthracene shows charge carrier mobility up to 3 cm2/Vs
at 300 K.8 Several oligomers and polymers of anthracene
derivatives, such as poly(anthrylene)s, poly(anthrylene-
vinylene)s, and poly(anthryleneethynylene)s, have been
reported.9ꢀ10 Despite good conducting properties, polyan-
thrylenes and their derivatives have some drawbacks
in that anthracene derivatives show low solubility and
polymerization reactivity because of their rigid pla-
nar structures.11 Recently, several attempts have been
made to deal with these problems. Yang and col-
leagues synthesized a novel soluble poly(9,10-bis(p-(2-
ethylhexyloxy)phenyl)-2,6-anthracenevinylene) (2,6-PAV)
for EL applications, but EL performance was not
impressive.12
Here,wereportthesynthesisofahighlysolubleanthracene
(Ant) derivative, and poly(fluorene-co-anthracene)s, specif-
ically poly{9,9ꢀ-bis-(4-octoloxy-phenyl)-fluorene-2,7-diyl-
co-9,10-bis-(decy-1-ynyl)-anthracene-2,6-diyl}s (PFAnts).
To improve EL properties, we copolymerized the fluo-
rene and Ant, with control of relative proportions of these
materials, to minimize problems associated with the poor
charge balance of PFs and the low solubility and reactiv-
2.2. Fabrication of EL Devices
In this study, single layer EL devices were fabricated on
glass substrates patterned with indium-tin oxide (ITO).
The device configurations of Device A: ITO/PEDOT:
PSS/polymer/Ca/Al and Device B: ITO/PEDOT:
PSS/polymer/Balq/LiF/Al. A hole injection layer of
poly(3,4-ethylenedioxythiophene) (PEDOT) doped with
poly(styrenesulfonicacid) (PSS) (PEDOT:PSS, Bayer Al
4083) was spincoated onto each ITO anode from a solu-
tion. Each polymer solution was then spin-coated onto
the PEDOT:PSS layer. The polymer solution for spin
coating was prepared by the dissolution of the polymer
(2.0 wt%) in chlorobenzene. In the Device A, calcium and
aluminum contacts were formed by vacuum deposition at
pressures below 10−6 Torr. In Device B, a bis(2-methyl-
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ity of poly(anthrylene)s. In this paper, we systematically
investigate the synthesis, thermal stability, and optical prop-
erties of the resulting polymers using PL tests. Finally, we
study EL applications with or without an electron transport
layer.
Copyright: American Scientific Publishers
2. EXPERIMENTAL DETAILS
2.1. Measurements
1H and 13C NMR spectra were recorded on Bruker
AVANCE 300 and 400 spectrometers, respectively, with
tetramethylsilane as an internal reference. Elemental anal-
yses were performed by the Seoul Branch Analytical
Laboratory of the Korea Basic Science Institute. The
number- and weight-average molecular weights of the
polymers were determined by gel permeation chromatog-
raphy (GPC) on a Waters GPC-150C instrument, using
THF as eluent and polystyrene as standard. Mass spec-
tra were obtained with an Autospec ultra spectrometer.
Thermogravimetric analysis (TGA) measurements of the
polymers were perꢁformed under nitrogen atmosphere at a
heating rate of 10 C/min using TA Q500 instrument, and
the differential scanning calorimetric (DSC) measurements
were made using TA Q100 instrument and operated under
nitrogen. UV-vis spectra were measured on a Jasco V-530
UV/Vis spectrometer and photoluminescence (PL) spec-
tra of the polymers were measured at room temperature
8-quinolinolate)-4-(phenylphenolata)aluminum
electron-transporting layer (ETL), lithium fluoride and
aluminuim were deposited in the same condition.
(Balq)
2.3. Materials
Acetic anhydride, chromium oxide, zinc chloride,
1-bromooctane,
t-butyllithum,
2-isopropoxy-4,4,5,5-
tetramethyl-1,3,2-dioxaborolane, n-butyllithum, copper
bromide, t-butyl nitrite, tetrakis(triphenylphosphine)palla-
dium, toluene, aliquat®336, 1-decyne, tin chloride dehy-
drate were purchased from Aldrich Co. hydrochloric
acid, potassium iodide (KI), acetonitrile, magnesium sul-
fate anhydrous (MgSO4ꢁ were purchased from Junsei
Co. potassium carbonate (K2CO3ꢁ, sodium carbonate
(Na2CO3ꢁ were purchased from Daejung Co. All reagents
purchased commercially were used without further purifi-
cation except for tetrahydrofuran (THF) dried over
J. Nanosci. Nanotechnol. 11, 4648–4657, 2011
4649

Synthesis of New Fluorene-Based Copolymers Containing an Anthracene Derivative and Their Applications in PLEDs
Lee et al.
sodium/benzophenone. 2,6-Dibromoanthraquinone (1)
and 2,7-dibromo-9,9-bis-(4-octyloxy-phenyl)-fluorene (3)
were synthesized according to procedures outlined in the
literature.13
(t, 4H), 1.71 (m, 4H), 1.38 (m, 4H), 1.27 (m, 40H), 0.85
(m, 6H). 13C NMR (CDCl3, ppm) 157.71, 151.86, 142.61,
137.62, 134.04, 132.21, 129.39, 119.74, 113.98, 83.67,
67.85, 64.16, 31.79, 29.33, 29.29, 29.21, 26.04, 24.88,
22.63, 14.07. Anal. Calcd for C53H72B2O6 : C, 77.00; H,
8.78. Found : C, 78.91; H, 8.93.
2.4. Synthesis of Fluorene Derivative Monomers
2.4.1. 2, 6-Dibromo-9, 10-bis(decy-1-ynyl)
anthracene (2)
2.4.3. Poly(9,9ꢀ-bis-4-octoloxy-phenyl-fluorene)
(PBOPF)
To a solution of 1-decyne (6.35 mL, ꢁ31.75 mmol) in
dry tetrahydrofurane (150 mL) at −78 C was added by
syringe, 21.9 mL (38.35 mmol) of n-butyllithium (2.6 M
in hexane). The mixture was stirred at −78 ꢁC for 2 hours.
2, 6-dibromoanthraquinone (1) (5 g, 13.65 mmol) was
added to the solution, and the resulting mixture was stirred
at 0 ꢁC for 1 hour and warmed to room temperature
slowly and stirred for 5 h. The mixture was extracted with
petroleum ether (PE)/brine and then dried over MgSO4.
After the solvent being evaporated, the residue was dis-
solved in tetrahudrofuran (20 mL), and then dropwised
into SnCl2 ·2H2O (15.4 g, 68.35 mmol, in 50 mL of 50%
acetic acid). The mixture was stirred at room temperature
overnight, and poured into water and extracted with ethyl
ether. The organic layer was washed with brine and dried
over anhydrous MgSO4. Solvent was removed and the
crude product was purified with column chromatography
Into a 150 mL two-neck flask were added 0.5 g (0.817 mmol)
of the dibromo compounds, 2,7-Dibromo-9,9-bis-(4-
octyloxy-phenyl)-fluorene (3) and 0.675 g (0.817 mmol)
of
2,7-bis(4,4,5,5-tetramethyl-1,3,2-dioxaborolan-2-yl)-
9,9-bis-(4-octyloxy-phenyl)-fluorene (4) in 8 mL of anhy-
drous toluene. The air-sensitive and water soluble Pd(0)
complex, tetrakis(triphenylphosphine)palladium (2 mol%),
was transferred in a dry box. Subsequently, 2 M aqueous
sodium carbonate deaerated for 30 min and the phase-
transfer catalyst, Aliquat®336 (several drops), in toluene
purged under nitrogen for 1 h was transꢁferred via cannula.
The reaction mixture 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 stir-
ring continued for 12 h. The reaction mixture was cooled to
ꢁ
about 50 C and added slowly to a vigorously stirred mixture
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on silica with PE as eluent, and the residue was purified
of 200 mL of methanol. The polymer fibers were collected
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by several reprecipitation in PE to provide yellow solid.
by filtration and reprecipitation from methanol and acetone.
The polymers were purified further by washing for 2 days
in a Soxhlet apparatus with acetone to remove oligomers
and catalyst residues, and column chromatographied with
a chloroform solution of the polymer. The reprecipita-
tion procedure in chloroform/methanol is then repeated
several times. The resulting polymers were soluble in com-
Copyright: American Scientific Publishers
1
(6.34 g, 73%) H NMR (CDCl3, ppm) 8.66 (d, 2H), 8.36
(d, 2H), 7.57 (dd, 2H), 2.73 (t, 4H), 1.78 (m, 4H), 1.59 (m,
4H), 1.34 (m, 16H), 0.87 (m, 6H). 13C NMR (CDCl3, ppm)
132.72, 130.61, 130.10, 129.17, 129.02, 121.34, 118.05,
104.33, 76.55, 31.89, 29.31, 29.22, 28.92, 22.70, 20.25,
14.12. Calcd for C34H40Br2:C, 67.11; H, 6.63. Found:C,
66.53; H, 6.55.
1
mon organic solvents. (0.64 g, 67.9%) H NMR (CDCl3,
ppm) 7.74–7.72(2H), 7.54–7.49(4H), 7.15–7.10(4H), 6.75–
6.71(4H), 3.88–3.85(4H), 1.75–1.68(4H), 1.41–1.36(4H),
1.29–1.25(4H), 0.87–0.83(6H). Element Anal. Found: C,
87.98; H, 8.78.
2.4.2. 2,7-bis(4,4,5,5-tetramethyl-
1,3,2-dioxaborolan-2-yl)-9,9-bis-(4-octyloxy-
phenyl)-fluorene (4)
To a solution of 2,7-Dibromo-9,9-bis-(4-octyloxy-phenyl)-
fluorene (3) (5.00 g, 6.83 mmol) in dry tetrahy-
drofurane (150 mL) at −78 ꢁC was added by
syringe, 24.7 mL (27.3 mmol) of t-butyllithium
2.4.4. Poly{9,9ꢀ-bis-(4-octoloxy-phenyl)-fluorene-2,7-
diyl-co-9,10-bis-(decy-1-ynyl)-anthracene-2,6-diyl}
(PFAnt01)
(1.7
M in hexane). The mixture was stirred at
−78 ꢁC for 2 hours. 2-Isopropoxy-4,4,5,5-tetramethyl-
1,3,2-dioxaborolane (4.18 mL, 20.5 mmol) was added
to the solution, and the resulting mixture was stirred at
−78 ꢁC for 1 hour and warmed to room temperature
slowly and stirred for 40 h. The mixture was extracted
with dichloromethane/brine and then dried over MgSO4.
The solvent was removed by solvent evaporation, and the
residue was purified by several reprecipitation in methanol
The procedure was the same as the preparation
of PBOPF but 2,7-dibromo-9,9-bis-(4-octyloxy-phenyl)-
fluorene (3) (0.98 equiv, 0.434 g), 2, 6-Dibromo-9, 10-
bis(decy-1-ynyl) anthracene (2) (0.02 equiv, 7.36 mg)
and 2,7-bis(4,4,5,5-tetramethyl-1,3,2-dioxaborolan-2-yl)-
9,9-bis-(4-octyloxy-phenyl)-fluorene (1 equiv, 0.5 g) (4)
were used in this polymerization. (0.39 g, 55.6%) 1H NMR
(CDCl3, ppm) aromatic; 7.76–6.71 (14H), aliphatic; 3.92–
3.76 (4H), 1.75–0.86 (∼22H). Element Anal. Found: C,
85.99; H, 8.55.
1
to provide white solid. (3.6 g, 63%) H NMR (CDCl3,
ppm) 7.75 (m, 6H), 7.10 (dd, 4H), 6.70 (dd, 4H), 3.86
4650
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Lee et al.
Synthesis of New Fluorene-Based Copolymers Containing an Anthracene Derivative and Their Applications in PLEDs
2.4.5. Poly{9,9ꢀ-bis-(4-octoloxy-phenyl)-fluorene-2,7-
diyl-Co-9,10-bis-(decy-1-ynyl)-anthracene-2,6-
diyl} PFAnt05)
(CDCl3, ppm) aromatic; 7.78–6.72 (13H), aliphatic; 3.86–
3.85 (∼4H), 2.74–2.73 (∼0.33H), 1,73–1.68 (4H), 1.39
(4H), 1.27–1.25 (16H), 0.87–0.83 (6H). Element Anal.
Found: C, 85.32; H, 8.47.
The procedure was the same as the preparation
of PBOPF but 2,7-dibromo-9,9-bis-(4-octyloxy-phenyl)-
fluorene (3) (0.9 equiv, 0.399 g), 2, 6-Dibromo-9, 10-
bis(decy-1-ynyl) anthracene (2) (0.1 equiv, 0.368 g)
and 2,7-bis(4,4,5,5-tetramethyl-1,3,2-dioxaborolan-2-yl)-
9,9-bis-(4-octyloxy-phenyl)-fluorene (1 equiv, 0.5 g) (4)
were used in this polymerization. (0.39 g, 55.9%) 1H NMR
(CDCl3, ppm) aromatic; 7.74–6.72 (14H), aliphatic; 3.87–
3.86 (∼4H), 2.74–2.73 (∼0.15H), 1,74–1.68 (4H), 1.40
(4H), 1.28–1.25 (16H), 0.87–0.84 (6H). Element Anal.
Found: C, 84.8; H, 8.45.
2.4.7. Poly{9,9ꢀ-bis-(4-octoloxy-phenyl)-fluorene-2,7-
diyl-co-9,10-bis-(decy-1-ynyl)-anthracene-2,6-diyl}
(PFAnt30)
The procedure was the same as the preparation
of PBOPF but 2,7-dibromo-9,9-bis-(4-octyloxy-phenyl)-
fluorene (3) (0.4 equiv, 0.0885 g), 2, 6-Dibromo-9,
10-bis(decy-1-ynyl) anthracene (2) (0.6 equiv, 0.11 g)
and 2,7-bis(4,4,5,5-tetramethyl-1,3,2-dioxaborolan-2-yl)-
9,9-bis-(4-octyloxy-phenyl)-fluorene (1 equiv, 0.25 g) (4)
were used in this polymerization. (0.10 g, 32.2%) 1H
NMR (CDCl3, ppm) aromatic; 8.73–6.74 (∼12H), 3.88
(4H), 2.73 (∼1.7H), 1,77–1.58 (8H), 1.39–1.26 (30H),
0.84 (12H). Element Anal. Found: C, 84.15; H, 8.59.
2.4.6. Poly{9,9ꢀ-bis-(4-octoloxy-phenyl)-fluorene-2,7-
diyl-co-9,10-bis-(decy-1-ynyl)-anthracene-2,6-diyl}
(PFAnt10)
The procedure was the same as the preparation
of PBOPF but 2,7-dibromo-9,9-bis-(4-octyloxy-phenyl)-
fluorene (3) (0.8 equiv, 0.354 g), 2, 6-Dibromo-9, 10-
bis(decy-1-ynyl) anthracene (2) (0.2 equiv, 0.0736 g)
and 2,7-bis(4,4,5,5-tetramethyl-1,3,2-dioxaborolan-2-yl)-
9,9-bis-(4-octyloxy-phenyl)-fluorene (1 equiv, 0.5 g) (4)
were used in this polymerization. (0.42 g, 61.7%) 1H NMR
2.4.8. Poly{9,9ꢀ-bis-(4-octoloxy-phenyl)-fluorene-2,7-
diyl-co-9,10-bis-(decy-1-ynyl)-anthracene-2,6-diyl}
(PFAnt 50)
The procedure was the same as the preparation of PBOPF
but 2, 6-Dibromo-9, 10-bis(decy-1-ynyl) anthracene (2)
(1 equiv, 0.23 g) and 2,7-bis(4,4,5,5-tetramethyl-1,3,
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Copyright: American Scientific Publishers
O
O
O
NH2
Br
t-BuNO2, CuBr2
H2N
MeCN, 65 °C
Br
O
1
1. n-BuLi,1-decyne
2. SnCl2 2H2O
Br
Br
THF, 0 °C ~ rt
2
RO
RO
O
OR
B
OR
Br
t-BuLi/THF
O
O
Br
B
O
B
O
O
O
4
3
(R: n-octyl)
Scheme 1. Synthetic routes for monomers.
J. Nanosci. Nanotechnol. 11, 4648–4657, 2011
4651

Synthesis of New Fluorene-Based Copolymers Containing an Anthracene Derivative and Their Applications in PLEDs
Lee et al.
2-dioxaborolan-2-yl)-9,9-bis-(4-octyloxy-phenyl)-fluorene
conditions. 2-Bromobenzene was used as an end-capping
(1 equiv, 0.2659 g) (4) were used in this polymerization.
(0.32 g, 82.5%) H NMR (CDCl3, ppm) aromatic; 8.73–
6.73 (20H), 3.86 (4H), 2.74–2.73 (4H), 1,81–1.69 (8H),
1.60(4H), 1.39–1.23 (36H), 0.86–0.82 (12H). Element
Anal. Found: C, 85.34; H, 8.50.
reagent to remove monomer residues containing boronic
acid. The solubility of synthesized polymers decreased
slightly with increasing proportion of Ant, but all PFAnts
were soluble in common organic solvents including chlo-
roform, chlorobenzene, and toluene. The syntheses of all
monomers and polymers are outlined in Schemes 1 and 2,
1
1
respectively. Chemical structures were verified by H- and
3. RESULTS AND DISCUSSION
13C-NMR spectroscopy and elemental analysis. The actual
mass fractions of Ant in PFAnts, as determined by NMR
spectra after integration of copolymer peaks as shown in
Figure 1, were somewhat lower than the feed ratios. The
feed ratios were 5, 10, 30, and 50 mol% of the total
amount of monomer, and the resulting proportions of Ant
units in PFAnts were 3.67, 7.78, 29.30, and 47.68 mol%,
respectively. Unfortunately, it was not possible to calcu-
late the resulting proportion of PFAnt01, because of the
very low Ant intensity on NMR. The number-average
molecular weights (Mnꢁ of the synthesized polymers were
3.1. Synthesis and Characterization
We introduced the decyne group to 2,6-dibromoanthra-
quinone (1) at the reactive 9,10-positions and the syn-
thesized Ant showed enhanced solubility because of the
long alkyl chain. Five fluorene-based copolymers contain-
ing Ant were synthesized using the Suzuki coupling reac-
tion. For comparison, a well-known typical polyfluorene
homopolymer, poly[9,9-bis(4ꢀ-n-octyloxyphenyl)fluorene-
2,7-diyl] (PBOPF),6 was also synthesized under the same
OR
RO
RO
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Br
Copyright: American Scientific Publishers
O
O
B
B
Br
Br
O
Br
O
4
(R: n-octyl)
3
2
RO
OR
Pd(PPh3)4, Aliquat@336
Toluene, aq. 2MK2CO3, reflux
y
x
x: y = 0: 100 PBOPF
x: y = 1: 99 PFAnt01
x: y = 5: 95 PFAnt05
x: y = 10: 90 PFAnt10
x: y = 30: 70 PFAnt30
x: y = 50: 50 PFAnt50
Scheme 2. Polymerizations of PBOPF and PFAnts.
4652
J. Nanosci. Nanotechnol. 11, 4648–4657, 2011

Lee et al.
Synthesis of New Fluorene-Based Copolymers Containing an Anthracene Derivative and Their Applications in PLEDs
Table II. Physical properties of the polymers.
Polymer
Mna
Mwb
PDI
Tg (ꢁC)
T5cd (ꢁC)
PBOPF
6ꢀ400
5ꢀ100
5ꢀ400
5ꢀ300
12ꢀ000
9ꢀ300
13ꢀ000
8ꢀ300
10ꢀ000
12ꢀ000
32ꢀ000
28ꢀ000
2.01
1.63
1.93
2.23
2.69
2.99
94
93
92
97
94
92
426
411
399
407
401
389
PFAnt01
PFAnt05
PFAnt10
PFAnt30
PFAnt50
aꢀbNumber and weight average molecular weight determined by GPC using
polystyrene as the standard in THF. cDecomposition temperature determined by
TGA in N2based on 5% weight loss.
the film caused a red-shift of the spectrum because of the
rigid film structure and the interaction of Ant molecules in
the film state.
Fig. 1. 1H NMR spectra of the polymers.
Figure 3 shows the normalized UV-visible absorption
spectra of PBOPF and PFAnts. In chloroform solution, all
polymers exhibited absorption maxima at about 380 nm.
Slight blue shifts in absorption maxima were seen as the
proportion of Ant increased, and vibration intensities also
increased because the Ant monomer absorption maximum
and vibration pattern contributed more to the copolymer
properties. The UV-visible spectra of the films were almost
identical to the corresponding solution spectra.
5,100 ∼ 12ꢀ000 (PDI = 1ꢂ63 ∼ 2ꢂ99ꢁ. Because of long
decyne chain, the solubility of the Ant monomer in
organic solvents, and Ant reactivity therein, were dra-
matically enhanced compared with the properties of ordi-
nary poly(anthrylene)s; as a result, the PFAnts had higher
molecular weights. PBOPF and anthracene-containing
PFAnts exhibited very good thermal stabilities, losing less
than 5% of weight on heating to approximately 400 C as
evaluated by TGA under a nitrogen atmosphere. Data on
the synthesized copolymers are summarized in Table I.
ꢁ
In the case of the PL spectra, by contrast, the solu-
tion and film spectra were dissimilar. In Figure 4(a), two
maximal emission peaks (one in the blue region at about
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3.2. Optical Properties
390 nm, from the fluorene moiety, and one in the green
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Copyright: American Scientific Publishers
region at about 515 nm, from the anthracene moiety)
are seen. Blue peak intensity fell and green peak inten-
sity rose with increasing Ant proportion. PFAnt30 and
PFAnt50 emitted almost pure green light because energy
transfers were complete, whereas energy transfers were
partial in PFAnt01, PFAnt05, and PFAnt10. In Figure 4(b),
the PL emission maxima of polymers used in films were
dramatically red-shifted compared to those in solution and
exhibited emissions ranging from blue to orange as the
proportion of Ant increased. The extents of PL spectral
red-shifts when solution and film states were compared
were 22–81 nm. Especially, the PL maximum of PFAnt50
The UV-visible absorption and PL emission properties of
the Ant monomer, and the polymers in both solution and
film states, were investigated; the results are summarized
in Table II. The normalized absorption and emission spec-
tra of Ant are shown in Figure 2. The absorption spectrum
of Ant showed the characteristic vibration pattern of the
anthracene group in both solution and film states. The Ant
thin film shows absorption onset at 491 nm. The optical
band gap of Ant, determined from absorption onset, was
calculated to be 2.52 eV. The emission spectrum of the Ant
film was markedly red-shifted (by about 60 nm) compared
to that of Ant in solution, and exhibited peak emission at
513 nm. This suggests that the aggregation of Ant units in
Table I. UV-visible absorption and PL emission spectra of Ant and
polymers in chloroform and in films.
Solution ꢃmax (nm)a
Absorption Emission
283 455
Film ꢃmax (nm)b
Polymer
Ant
Absorption
Emission
276
513
PBOPF
385
380
375
377
373
374
399
396, 454
405, 476
412, 477
478
388
382
380
380
371
369
421
477 (509)
485 (517)
487 (517)
541
PFAnt01
PFAnt05
PFAnt10
PFAnt30
PFAnt50
479
560
aDilute solution in chloroform. bSpin-coated thin film on quartz plate from chloro-
form solution for 40s at 1000 rpm.
Fig. 2. UV-visible absorption and PL emission spectra of the Ant
monomer in chloroform solution and in film.
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Synthesis of New Fluorene-Based Copolymers Containing an Anthracene Derivative and Their Applications in PLEDs
(a)
Lee et al.
(a)
(b)
(b)
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Fig. 3. UV-visible absorption spectra of PBOPF and PFAnts (a) in chlo-
roform solution and (b) in film.
Fig. 4. PL emission spectra of PBOPF and PFAnts (a) in chloroform
solution and (b) in film.
Copyright: American Scientific Publishers
shifted from 479 nm to 560 nm. Such large changes in
PL maxima probably arise not only from intramolecular
energy transfer from fluorene to Ant but also due to inter-
molecular aggregations of PFAnt molecules. In solution,
chloroform solvent molecules interrupt polymer aggrega-
tion, so that only blue and green peaks are seen, caused
by energy transfer from fluorene to anthracene. Under film
conditions, without solvent, polymer aggregation occurs
more easily than in solution because of the rigid, pla-
nar structure of Ant, and emission from the aggregates
becomes the major feature of the PL spectra as Ant content
increases.
1.203 V (vs. SCE), respectively, corresponding to ion-
ization potential (Ipꢁ values of −5.40, −5.39, −5.40,
−5.38, −5.57, and −5.87 eV, respectively, using a previ-
ously reported empirical equation.14 Usually, it is difficult
to obtain LUMO energies for fluorene-based copolymers
employing this technique; hence the LUMO values were
estimated from the HOMO energies and optical band gaps
taken from absorption onsets of polymer film UV-visible
spectra.15 Energy levels of the polymers are summarized
in Table III.
As shown in Figure 5, both HOMO and LUMO
energy levels tended to fall as the proportion of Ant
Table III. Electrochemical properties and energy levels of the
polymers.
3.3. Electrochemical Properties
The electrochemical properties of the polymers were stud-
ied to investigate redox behavior and to determine the
highest occupied molecular orbital (HOMO) and lowest
unoccupied molecular orbital (LUMO) energy levels. Elec-
trochemical processes probed by cyclic voltammetry (CV)
are similar to those involved in charge injection and trans-
port processes in LED (light-emitting diode) devices.
In the anodic scan, the onsets of oxidation of PBOPF,
PFAnt01, PFAnt05, PFAnt10, PFAnt30, and PFAnt50 were
found to occur at 0.725, 0.724, 0.734, 0.708, 0.904, and
Polymer
Egaꢀoptic (eV)
Eobnsetꢀox (V)
HOMO (eV)
LUMO (eV)c
PBOPF
2.95
2.93
2.53
2.51
2.50
2.49
0.725
0.724
0.734
0.708
0.904
1.203
−5ꢂ40
−5ꢂ39
−5ꢂ40
−5ꢂ38
−5ꢂ57
−5ꢂ87
−2ꢂ45
−2ꢂ46
−2ꢂ87
−2ꢂ87
−3ꢂ07
−3ꢂ38
PFAnt01
PFAnt05
PFAnt10
PFAnt30
PFAnt50
aEg,optic, calculated from the onset values of the absorption spectra of the spin-
coated films on quartz. bEonset,ox, stand for onset potential (scan rate: 50 mV/s).
cCalculated from the HOMO and Egꢀoptic
.
4654
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Lee et al.
Synthesis of New Fluorene-Based Copolymers Containing an Anthracene Derivative and Their Applications in PLEDs
Table IV. I–V–L characteristics of the polymers of Device A.
Maximum
Maximum
current
luminance efficiency Maximum
CIE
EQE (%) coordinates
Polymers ꢃmax (nm)
(cd/m2ꢁ
(cd/A)
PBOPF 425, 449 193, 9.6 V
PFAnt01 481 (515) 198, 12 V
PFAnt05 487 (522) 101, 12.6 V 0ꢂ034
PFAnt10 527, 566 100, 13 V
0ꢂ018
0ꢂ053
0ꢂ014
0ꢂ027
0ꢂ018
0ꢂ02
0ꢂ001
0ꢂ0008 (0.42, 0.48)
(0.20, 0.16)
(0.20, 0.43)
(0.31, 0.50)
(0.39, 0.50)
(0.41, 0.50)
0ꢂ045
0ꢂ0012
0ꢂ0012
PFAnt30
PFAnt50
546
551
22, 7.6 V
23, 4.4V
Fig. 5. Schematic structure of the polymer energy band gaps.
emitted orange light with an EL maximum at 551 nm
and a broad peak. The quality of emission spectra is typi-
cally defined by Commission Internationale de L’Eclairage
(CIE) 1931 chromaticity coordinates ꢄxꢀ yꢁ. The CIE
coordinates and colors of the polymer EL spectra are sum-
marized in Table IV.
As shown in Figure 7, the PFAnts, especially PFAnt01,
offered good EL performance. Moreover, as shown in
Figure 7(b), the current efficiencies of PFAnt01, PFAnt05,
and PFAnt10 were higher than that of PBOPF. However,
PFAnt30 and PFAnt50 showed poorer performances than
did the other PFAnts, because of intrinsic luminescence
quenching after aggregation. When aggregation occurs,
excitons spread out and dissociate into holes and electrons
increased. In other words, the Ant moiety of PFAnts
showed better electron-accepting ability than did PBOPF.
This indicates that electron injection from the elec-
trode to PFAnts is much easier than to PBOPF. The
good electron-accepting ability of PFAnts enhances EL
performance, because polyfluorenes usually demonstrate
electron-accepting problems arising from the abovemen-
tioned charge carrier mobility issues. In addition, the
band gap of polymers decreased gradually with increas-
ing Ant proportion. With PFAnt01, the band gap differed
only slightly from that of PBOPF. However, the band
gaps of other polymers, PFAnt05, PFAnt10, PFAnt30, and
PFAnt50, were significantly smaller than that of PFAnt01.
Such results are attributable to the rigid structure of Ant,
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which contributes to aggregation mediated by intermolec-
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ular interactions.
(a)
3.4. Electroluminescence Properties
To investigate the EL properties and current–voltage-
luminance characteristics of the synthesized polymers,
PLED devices with the configuration of Device A were
fabricated. EL spectra of PBOPF and PFAnts were similar
to the PL spectra, as shown in Figure 6. The EL emission
maxima of the polymers were red-shifted from 425 nm to
551 nm as Ant content increased. Whereas PBOPF emit-
ted blue light with an EL maximum at 425 nm and a
shoulder at 449 nm, PFAnt50, an alternating copolymer,
(b)
Fig. 7. (a) Voltage–luminance (V–L) and (b) voltage–current efficiency
Fig. 6. EL spectra of the polymers of Device A.
characteristics of the PBOPF and PFAnts forms of Device A.
J. Nanosci. Nanotechnol. 11, 4648–4657, 2011
4655

Synthesis of New Fluorene-Based Copolymers Containing an Anthracene Derivative and Their Applications in PLEDs
Lee et al.
highest maximum brightness of 1760 cd/m2 at 14 V, a
maximum current efficiency of 1.66 cd/A, and a max-
imum EQE of 0.70%. Moreover, the EL performances
of PFAnt05 and PFAnt10 also dramatically increased, as
shown in Table V. These results show that PFAnts demon-
strate improved EL performance compared with that of
previously studied poly(anthrylene)s and offer high poten-
tial for use in PLED applications.
Table V. I–V–L characteristics of the PFAnt01, PFAnt05, and PFAnt10
polymers of Device B.
Maximum
current
Maximum
luminance efficiency Maximum
CIE
Polymers ꢃmax (nm)
(cd/m2ꢁ
(cd/A)
EQE (%) coordinates
PFAnt01 485, 516 1760, 14 V
1.66
0.68
0.64
0.70
0.28
0.26
(0.22, 0.48)
(0.35, 0.53)
(0.35, 0.53)
PFAnt05
PFAnt10
524
525
280, 17 V
270, 16.5 V
4. CONCLUSION
by ꢅ-orbital overlaps between adjacent molecules. The
most interesting result is that PFAnt01 exhibitted high
PL/EL quantum yields. PFAnt01 exhibited the highest
maximum brightness of 198 cd/m2 at 12 V, a maxi-
mum current efficiency of 0.026 cd/A, and a maximum
external quantum efficiency (EQE) of 0.024%. This is
because the small Ant content minimized Ant-related prob-
lems. PFAnt01 is thus a promising material for PLED
applications.
To improve EL performance, we developed three
PFAnts, namely PFAnt01, PFAnt05, and PFAnt10, which
showed good EL efficiencies, and fabricated Device B,
with an electron transport layer (ETL). The data are sum-
marized in Table V and Figure 8. Performance was much
better than shown in Figure 7. PFAnt01 exhibited the
We synthesized new fluorene-based copolymers, poly{9,9ꢀ-
bis-(4-octoloxy-phenyl)-fluorene-2,7-diyl-co-9,10-bis-(decy-
1-ynyl)-anthracene-2,6-diyl}s (PFAnts). The incorporation
of the long alkyl chain at the 9,10-position of anthracene,
and copolymerization with fluorene, afforded improved
solubility in common organic solvents and increased
film-forming molecular weight values, compared to
common poly(anthrylene)s. Emission colors were easily
controlled by adjusting the feed ratio of the anthracene
derivative, exploiting useful Ant properties such as long
conjugation length, small band gap, and a more rigid
and planar structure compared to the fluorene deriva-
tive. Because of these properties, the polymers showed
effective energy transfer and aggregation. Among the
materials investigated, PFAnt01, PFAnt05, and PFAnt10
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exhibited better EL efficiencies than PBOPF. Upon fur-
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ther investigation of devices made using these three
(a)
Copyright: American Scientific Publishers
PFAnts, greatly improved EL performance was noted.
Especially, PFAnt01 exhibited the highest maximum
brightness of 1760 cd/m2 at 8 V, a maximum current
efficiency of 1.66 cd/A, and a maximum EQE of 0.70%;
the enhanced electron/hole balance led to improved device
efficiency. These results suggest that copolymers contain-
ing anthracene derivatives show promise for use in PLED
displays.
Acknowledgment: This work was supported by BK
21 of the Ministry of Education and Human Resources
Development, and by the Korea Science and Engineering
Foundation (KOSEF) grant funded by the Korea govern-
ment (MEST) (No. R11-2007-050-02003-0). The authors
also appreciate Prof. Seunghyup Yoo (Department of Elec-
trical Engineering of KAIST) and Jeong-Ik Lee, Hye
Yong Chu (ETRI) for fruitful information and PLED
experiments.
(b)
References and Notes
1. C. K. Chiang, C. F. Fincher, Jr., Y. W. Park, A. J. Heeger,
H. Shirakawa, E. J. Louis, S. C. Gau, and A. G. MacDiarmid, Phys.
Rev. Lett. 39, 1098 (1977).
2. D. Braun and A. J. Heeger, Appl. Phys. Lett. 58, 1982 (1991).
3. D.-H. Hwang, M.-J. Park, J.-H. Eom, H. K. Shim, S. Lee, N. C.
Yang, D. Lian, M. C. Suh, and B. D. Chin, J. Nanosci. Nanotechnol.
8, 4649 (2008).
Fig. 8. (a) Voltage–luminance (V–L) and (b) voltage–current effi-
ciency characteristics of the PFAnt01, PFAnt05, and PFAnt10 forms of
Device B.
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Lee et al.
Synthesis of New Fluorene-Based Copolymers Containing an Anthracene Derivative and Their Applications in PLEDs
4. D. Neher, Macromol. Rapid. Commun. 22, 1365 (2001).
5. K. H. Lee, J. K. Park, G. Y. Kim, J. H. Seo, Y. K. Kim, and S. S.
Yoon, J. Nanosci. Nanotechnol. 10, 3289 (2010).
6. J.-H. Lee and D.-H. Hwang, Chem. Comm. 2836 (2003).
7. M. Pope, H. Kallmann, and P. Magnante, J. Chem. Phys. 38, 2042
(1963).
8. N. Karl and J. Marktanner, Mol. Cryst. Liq. Cryst. 355, 149 (2001).
9. M. Baumgarten, U. Müller, A. Bohnen, and K. Müllen, Angew.
Chem. Int. Ed. 31, 448 (1992).
11. W. Cui, Y. Wu, H. Tian, Y. Geng, and F. Wang, Chem. Comm. 1017
(2008).
12. J. Xu, Y. Fang, P. Ren, H. Zhang, E. Guo, and W. Yang, Macromol.
Rapid. Commun. 29, 1415 (2008).
13. J.-H. Park, D. S. Chung, J.-W. Park, T. Ahn, H. Kong, Y. K. Jung,
J. Lee, M. H. Yi, C. E. Park, S.-K. Kwon, and H.-K. Shim, Org.
Lett. 9, 2573 (2007).
14. D. M. de Leeuw, M. M. J. Simenon, A. R. Brown, and R. E. F.
Einerhand, Synth. Met. 87, 53 (1997).
10. J.-H. Eom, D. Mi, M.-J. Park, H.-J. Cho, J. Lee, J.-I. Lee, H. Y. Chu,
H.-K. Shim, and D.-H. Hwang, J. Nanosci. Nanotechnol. 9, 7029
(2009).
15. I. H. Jung, Y. K. Jung. J. Lee, J.-H. Park, H. Y. Woo, J.-I. Lee,
H. Y. Chu, and H.-K. Shim, J. Polym. Sci. Part. A : Polym. Chem.
46, 7148 (2008).
Received: 23 May 2009. Accepted: 1 December 2009.
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J. Nanosci. Nanotechnol. 11, 4648–4657, 2011
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