Synthesis and luminescent properties of block copolymers based on polyfluorene and polytriphenylamine

Article abstract of DOI:10.1016/j.polymer.2012.02.021

For the preparation of block copolymers containing polyfluorene (PF) and hole transporting segment, PF homopolymers with diphenylamine terminals were synthesized by Suzuki coupling polymerization. The terminals of PF were converted to polytriphenylamine (PTPA) block by C-N coupling polymerization to give PTPA-block-PF-block-PTPA (PF-PTPA) triblock copolymers with different PTPA chain lengths. These polymers were soluble in common organic solvents and readily formed thin films by solution processing. All of the polymers exhibited similar UV absorption and PL emission properties both in chloroform solution and in film state. PF-PTPA block copolymers showed relatively high HOMO compared with that of PF by cyclic voltammetry. Compared with corresponding PF homopolymers, the EL devices based on PF-PTPA block copolymers showed higher luminance and current efficiency than those of PF homopolymers because of the improvement of hole injection by the introduction of PTPA segment.

Full text of DOI:10.1016/j.polymer.2012.02.021

Polymer 53 (2012) 1444e1452
Contents lists available at SciVerse ScienceDirect
Polymer
journal homepage: www.elsevier.com/locate/polymer
Synthesis and luminescent properties of block copolymers based on polyfluorene
and polytriphenylamine
*
Ying Tan, Zhijie Gu, Kousuke Tsuchiya, Kenji Ogino
Graduate School of Bio-Applications and Systems Engineering, Tokyo University of Agriculture and Technology, 2-24-16 Nakacho, Koganei-shi, Tokyo 184-8588, Japan
a r t i c l e i n f o
a b s t r a c t
Article history:
For the preparation of block copolymers containing polyfluorene (PF) and hole transporting segment, PF
homopolymers with diphenylamine terminals were synthesized by Suzuki coupling polymerization. The
terminals of PF were converted to polytriphenylamine (PTPA) block by CeN coupling polymerization to
give PTPA-block-PF-block-PTPA (PF-PTPA) triblock copolymers with different PTPA chain lengths. These
polymers were soluble in common organic solvents and readily formed thin films by solution processing.
All of the polymers exhibited similar UV absorption and PL emission properties both in chloroform solution
and in film state. PF-PTPA block copolymers showed relatively high HOMO compared with that of PF by
cyclic voltammetry. Compared with corresponding PF homopolymers, the EL devices based on PF-PTPA
block copolymers showed higher luminance and current efficiency than those of PF homopolymers
because of the improvement of hole injection by the introduction of PTPA segment.
Received 15 December 2011
Received in revised form
10 February 2012
Accepted 14 February 2012
Available online 21 February 2012
Keywords:
Polyfluorene
Polytriphenylamine
Block copolymer
Ó 2012 Elsevier Ltd. All rights reserved.
1. Introduction
Triphenylmaine (TPA) derivatives have been known as candi-
dates for hole transporting materials to be used in organic EL and
Polyfluorenes (PFs), which possess a relatively large band gap,
have been widely investigated as a blue PLED material because of
their superior properties, such as highly efficient photo-
luminescence (PL), excellent thermal stability, and good solubility in
common organic solvents [1,2]. However, they exhibit insufficient
color stability causing troublesome long wavelength emission band
(520e560 nm), assigned to aggregates/excimers, interchain inter-
actions, and/or an emissive keto defect generated by thermo-,
photo-, or electro-oxidative degradation during device operation
[3e6]. In fact, various kinds of modifications were proposed to
prepare polyfluorene-based copolymers to improve the perfor-
mance. For example, an alkyl/phenyl structure was introduced at
the C-9 position to reduce the aggregation and keto defect [7e10], or
end-capping groups were attached to PF backbones to suppress the
green emission by keeping the recombination zone away from the
polymer/anode interface and by increasing the hole-trap efficiency
[11]. Another serious problem associated with PF is poor electro-
luminescence (EL) efficiency due to an imbalance in charge carriers
caused by large hole injection barriers and different charge carrier
mobilities [12]. Therefore, PFs require additional hole-transporting
layers to obtain efficient hole injection/transport in EL device.
photovoltaic cell devices. Many compounds containing the TPA
moiety for EL devices have been reported for decades [13e16].
Furthermore, some researchers employed triphenylamine as
a polymer backbone for building up the
p-conjugated structure of
poly(triphenylamine) (PTPA) [17e20] because PTPA has been found
to a) facilitate hole injection and transport from the anode and b)
serve as an electron-blocking layer, which blocks electron move-
ment to the anode and confines excitons within the emission layer
to reduce green emission [5,6]. Previously, we reported that PTPA
can be synthesized via CeN coupling polymerization of a self-
condensing monomer by palladium catalyst [21]. This technique
allows us to assemble PTPA into the block copolymer architectures
by the chain elongation from terminals of the other polymer.
Incorporating some functional components such as charge
transport and luminescent moieties into a copolymer can easily
adjust the balance between hole and electron injections in the
emitting layer in polymer EL devices. For example, multilayer blue-
emitting EL device based on fluorene-triarylamine alternating
copolymer with a high hole mobility showed a high current effi-
ciency as 8.7 cd/A [22]. Moreover, we demonstrated that the device
based on bipolar charge transporting block copolymers showed
higher external quantum efficiency compared with random copoly-
mers or polymer blends with the same composition [23,24]. The
microphase-separated structure built in the block copolymer layer
afforded the effective charge recombination [25,26]. The block
* Corresponding author. Tel./fax: þ81 42 388 7404.
E-mail address: kogino@cc.tuat.ac.jp (K. Ogino).
0032-3861/$ e see front matter Ó 2012 Elsevier Ltd. All rights reserved.
doi:10.1016/j.polymer.2012.02.021

Y. Tan et al. / Polymer 53 (2012) 1444e1452
1445
copolymer containing polyfluorene segment was also reported by
theotherauthors[27]. Inthiswork, blockcopolymersconsistingofPF
and PTPA were synthesized for a luminescent material in EL devices.
PTPA segments were introduced at the terminals of PF for improve-
ment of hole injection/transport at the PF layer. In order to convert
the terminals of PF to diphenylamine group, polymerization method
of the fluorene monomer(s) was optimized. The terminal-modified
PFs were sequentially altered to the block copolymers by CeN
coupling polymerization. The structures of PF homopolymers and
block copolymers were characterized by GPC and 1H NMR. The
photophysical and electrical properties of the polymers as well as
performance of the EL device based on them were examined.
THF (37 mL) and 2 (2.80 g, 8.3 mmol) were added and the mixture
was refluxed for 16 h. After reaction for 2 h at r.t., the mixture was
treated with saturated NH4Cl aq., extracted with diethyl ether. The
organic layer was washed with brine, dried with MgSO4, and
concentrated by rotary evaporator. The crude product was purified
by column chromatography (chloroform:hexane ¼ 1:1). White solid
was obtained. The yield was 2.35 g (54%). 1H NMR (300 MHz, CDCl3)
d
(ppm): 7.49 (s, 4H, ArH), 7.45 (s, 2H, ArH), 7.25 (d, J ¼ 6.0 Hz, 2H,
ArH), 7.11 (d, J ¼ 6.0 Hz, 2H, ArH), 2.56 (t, J ¼ 6.0 Hz, 2H, CH2), 2.49 (s,
1H, eOH),1.58 (m, 2H, CH2),1.27 (m,10H, CH2), 0.87 (t, J ¼ 6.0 Hz, 3H,
CH3). 13C NMR (75 MHz, CDCl3)
d (ppm): 152.26, 142.70, 138.93,
137.57, 132.42, 128.64, 128.42, 125.23, 122.58, 121.61, 83.37, 35.74,
32.00, 31.51, 29.58, 29.54, 29.37, 22.80, 14.26. HR-MS (m/z): calcd for
C27H28Br2O, 526.0507; found, 526.0549 [M]þ.
2. Experimental
2.1. Materials
2.5. Synthesis of 2,7-dibromo-9-(4-methylphenyl)-9-(4-octylphenyl)
fluorene (4)
All reagents and solvents were used without further purification
unless stated otherwise. Tetrahydrofuran (THF) was distilled over
sodium and benzophenone, and stored under nitrogen atmosphere.
Toluene was distilled over calcium hydride, and stored under
nitrogen atmosphere. The other reagents and solvents were ob-
tained commercially and were used as received.
To a flask equipped with a stopcock were placed 3 (2.00 g,
3.92 mmol) and distilled toluene (48 mL) under nitrogen atmo-
sphere, heated up to 60 ꢁC. After trifluoromethanesulfonic acid
(0.68 mL, 7.75 mmol) was added, the mixture was stirred for 2 h.
The solution was neutralized with sodium bicarbonate aq. and
extracted with ethyl acetate, and the organic layer was dried with
MgSO4. After ethyl acetate was removed by rotary evaporator, the
crude product was purified by column chromatography (hex-
ane:ethyl acetate ¼ 30:1). White solid was obtained. The yield was
2.2. Synthesis of 2,7-dibromofluorene (1)
Fluorene (16.62 g, 0.10 mol), 2,6-t-butyl-4-cresol (0.04 g,
0.182 mmol), FeCl3 (0.4010 g, 2.48 mmol), and chloroform (300 mL)
were added into a flask under nitrogen atmosphere and cooled
down to ꢀ78 ꢁC, and then bromine (12.5 mL, 0.244 mmol) was
added dropwise slowly. After reaction for 24 h at r.t., NaHSO3 aq.
(300 mL) was added. The product was extracted with chloroform
and dichloromethane, and the organic layer was dried with MgSO4.
After the organic layer was concentrated by rotary evaporator, the
crude product was recrystallized from methanol once or twice.
White crystal (26.64 g in total) was obtained. The yield was 82%. 1H
1.91 g (83%). 1H NMR (300 MHz, CDCl3)
d
(ppm): 7.57 (d, J ¼ 6.0 Hz,
2H, ArH), 7.48 (d, J ¼ 3.0 Hz, 2H, ArH), 7.46 (s, 2H, ArH), 7.04 (m,
J ¼ 3.0 Hz, 8H, ArH), 2.55 (t, J ¼ 6.0 Hz, 2H, CH2), 2.31 (s, 3H, CH3),
1.55 (m, 2H, CH2), 1.27 (m, 10H, CH2), 0.87 (t, J ¼ 6.0 Hz, 3H, CH3). 13
C
NMR (75 MHz, CDCl3) d (ppm): 153.53, 141.98, 141.74, 141.69, 138.13,
136.90, 130.91, 129.51, 129.33, 128.61, 128.00, 127.95, 121.92, 121.63,
65.18, 35.65, 32.04, 31.50, 29.60, 29.38, 22.82, 21.12, 14.27. HR-MS
(m/z): calcd for C34H34Br2, 600.1027; found, 600.1088 [M]þ.
NMR (300 MHz, CDCl3)
d
(ppm): 7.68 (s, 2H, ArH), 7.60 (d, J ¼ 9.0 Hz,
2.6. Synthesis of 2,7-bis(4,4,5,5-tetramethyl-1,3,2-dioxaborolan-2-
yl)-9- (4-methylphenyl)-9-(4-octylphenyl)fluorene (5)
2H, ArH), 7.52 (d, J ¼ 9.0 Hz, 2H, ArH), 3.87 (s, 2H, CH2). 13C NMR
(75 MHz, CDCl3)
d (ppm): 144.87, 139.78, 130.24, 128.40, 121.30,
121.02, 36.65. HR-MS (m/z): calcd for C13H8Br2, 321.8993; found,
A solution of 4 (0.903 g, 1.5 mmol) dissolved in 10 mL of THF was
added to a flask equipped with a stopcock under nitrogen atmo-
sphere, and cooled to ꢀ78 ꢁC. Then, n-butyllithium (1.34 mL, 2.6 M
solution in hexane) was added dropwise, and the mixture was
stirred for 30 min. To this mixture, 2-isopropoxy-4,4,5,5-
tetramethyl-1,3,2-dioxaborolane (1.674 g, 9.0 mmol) was added,
and the mixture was stirred for 12 h. The reaction mixture was
quenched with brine, and extracted with diethyl ether. The organic
layer was washed with brine, dried with MgSO4, and concentrated
by rotary evaporator. The crude product was purified by column
chromatography on silica gel with hexane:ethyl acetate ¼ 10:1 as
an eluent. White solid was obtained. The yield was 0.41 g (39%). 1H
323.8999 [M]þ.
2.3. Synthesis of 2,7-dibromofluoren-9-one (2)
To a flask equipped with a stopcock were added 1 (20.0 g,
61.7 mmol) and acetic acid (150 mL) under nitrogen atmosphere. A
solution of CrO3 (15 g, 150 mmol) dissolved in acetic acid (120 mL)
was added. After reaction for 24 h at r.t., the solution was
neutralized with sodium bicarbonate aq. and the precipitate was
filtrated. The crude product was recrystallized from ethanol and
chloroform twice. Yellow crystal (10.02 g in total) was obtained. The
yield was 48%. 1H NMR (300 MHz, CDCl3)
J ¼ 3.0 Hz, 2H, ArH), 7.60 (dd, J ¼ 6.0 Hz, 2H, ArH), 7.35 (d, J ¼ 9.0 Hz,
2H, ArH). 13C NMR (75 MHz, CDCl3)
(ppm): 191.01, 142.28, 137.57,
d
(ppm): 7.72 (d,
NMR (300 MHz, CDCl3)
d
(ppm): 7.81 (d, J ¼ 6.0 Hz, 4H, ArH), 7.77 (d,
J ¼ 6.0 Hz, 2H, ArH), 7.11 (dd, J ¼ 3.0 Hz, 4H, ArH), 7.01 (dd, J ¼ 3.0 Hz,
d
4H, ArH), 2.25 (s, 3H, CH3),1.55 (m, 2H, CH2),1.31 (m, 24H, CH3),1.28
135.30, 127.88, 123.42, 121.96. HR-MS (m/z): calcd for C13H7Br2O,
(m, 10H, CH2), 0.87 (m, 3H, CH3). 13C NMR (75 MHz, CDCl3)
d (ppm):
336.8864; found, 336.8864 [M þ H]þ.
151.63, 143.03, 142.96, 142.90, 141.09, 135.99, 134.26, 132.47, 128.95,
128.48, 128.40, 128.23, 119.90, 119.89, 83.80, 65.01, 35.67, 32.06,
31.53, 29.62, 29.43, 25.05, 25.03, 22.81, 21.11, 14.28. Anal. Calcd for
C46H58B2O4: C, 78.24, H, 7.08; Found: C, 78.07, H, 6.80.
2.4. Synthesis of 2,7-dibromo-9-(4-octylphenyl)fluoren-9-ol (3)
To a 100-mL flask equipped with a stopcock and a condenser
were placed Mg (0.28 g, 12.0 mmol), 1,2-dibromoethane (0.020 mL,
0.23 mmol), and THF (2.0 mL) under nitrogen atmosphere. When Mg
began to react, a solution of 4-bromooctylbenzene (3.0 g, 11 mmol)
dissolved in THF (2.0 mL) was added, and the mixture was refluxed
until Mg reacted completely. The solution was cooled down to r.t.,
2.7. Synthesis of 1-{2-(2-(2-methoxyethoxy)ethoxy)ethoxy}-4-
nitrobenzene (6)
To a flask equipped with a DeaneStark apparatus were placed
triethylene glycol monomethyl ether (16.32 g, 0.1 mol), potassium

1446
Y. Tan et al. / Polymer 53 (2012) 1444e1452
carbonate (33.0 g, 0.246 mol), dimethylacetamide (DMAc)
(180 mL), and toluene (180 mL) and heated up to 150 ꢁC. After water
and toluene were removed completely, 4-fluoronitrobenzene
(8.60 mL, 0.081 mol) was added and the mixture was stirred for
24 h. The mixture was put in ice bath and neutralized with 1 N HCl,
extracted with chloroform, and the organic layer was dried with
MgSO4. After chloroform was removed by rotary evaporator, the
crude product was purified by column chromatography (hex-
ane:ethyl acetate ¼ 1:5). Light yellow liquid was obtained. The yield
added and reflux was continued for 12 h. After the reaction chlo-
roform was added, and the resulting solution was washed with sat.
NaCl aq. and dried with MgSO4. The solvent was removed by rotary
evaporator, and the product was obtained by the precipitation into
methanol and acetone. The yield was 0.13 g (89%). 1H NMR
(300 MHz, CDCl3) d (ppm): 7.81-7.67 (m, 2H, ArH), 7.65-7.41 (m, 4H,
ArH), 7.18-6.91 (m, 8H, ArH), 4.31-3.37 (m, 16H, CH2O), 2.58-2.42
(m, 2H, CH2), 2.34-2.19 (m, 3H, CH3), 1.66-1.42 (m, 2H, CH2), 1.42-
1.12 (m, 10H, CH2), 0.85-0.91 (m, 3H, CH3).
was 14.04 g (93%). 1H NMR (300 MHz, CDCl3)
d (ppm): 8.19 (d,
J ¼ 6.0 Hz, 2H, ArH), 6.97 (d, J ¼ 6.0 Hz, 2H, ArH), 4.21 (t, J ¼ 6.0 Hz,
2H, CH2O), 3.89 (t, J ¼ 6.0 Hz, 2H, CH2O), 3.74 (t, J ¼ 6.0 Hz, 2H,
CH2O), 3.67 (m, J ¼ 6.0 Hz, 2H, CH2O), 3.65 (m, J ¼ 6.0 Hz, 2H, CH2O),
3.54 (t, J ¼ 6.0 Hz, 2H, CH2O), 3.37 (s, 2H, CH3). 13C NMR (75 MHz,
2.11. Synthesis of PF homopolymer (PF2) via Suzuki coupling
polymerization
To a 20 mL three-necked round-bottom flask equipped with
a stopcock and a condenser were added 4 (0.166 g, 0.276 mmol), 5
(0.226 g, 0.324 mmol), Pd (PPh3)4 (3.46 mg, 0.003 mmol, 0.5%), 2N
K2CO3 aq. (4 mL), and toluene (4 mL) under nitrogen atmosphere,
and the mixture was refluxed for 48 h. Then, 8 (0.15 g, 0.3 mmol)
was added and reflux was continued for 12 h. After the reaction,
chloroform was added, the resulting solution was washed with sat.
NaCl aq. and dried with MgSO4. The solvent was removed by rotary
evaporator, the product was obtained by precipitation into meth-
anol. The yield was 0.221 g (83%). 1H NMR (300 MHz, CDCl3)
CDCl3)
d (ppm): 163.71, 141.26, 125.63, 114.43, 71.66, 70.64, 70.38,
70.31, 69.14, 68.03, 58.79. HR-MS (m/z): calcd for C13H20NO6,
286.1291; found, 286.1309 [M þ H]þ.
2.8. Synthesis of 4-{2-[2-(2-methoxyethoxy)ethoxy]ethoxy}
phenylamine (7)
To a flask equipped with a stopcock were added 6 (5.60 g,
19.6 mmol), ethanol (108 mL), and Pd/C (0.12 g, 10% of palladium
loading) under hydrogen atmosphere. After reaction for 24 h at r.t.,
the catalyst was removed by filtration for three times. The product
was extracted by chloroform, dried with MgSO4. After the solution
was concentrated by rotary evaporator, the crude product was
purified by column chromatography (hexane:ethyl acetate ¼ 1:5).
Brown liquid was obtained. The yield was 4.80 g (86%). 1H NMR
d
(ppm): 7.81-7.67 (m, 2H, ArH), 7.65-7.41 (m, 4H, ArH), 7.18-6.91
(m, 8H, ArH), 4.31-3.37 (m, 16H, CH2O), 2.58-2.42 (m, 2H, CH2),
2.34-2.19 (m, 3H, CH3), 1.66-1.42 (m, 2H, CH2), 1.42-1.12 (m, 10H,
CH2), 0.85-0.91 (m, 3H, CH3). The homopolymers PF4 and PF5 were
synthesized by the same procedure as PF2 with different feed ratios
of 4 and 5. The yield of PF4 was 0.210 g (79%); that of PF5 was
0.226 g (85%).
(300 MHz, CDCl3)
d
(ppm): 6.77 (d, J ¼ 6.0 Hz, 2H, ArH), 6.62 (d,
J ¼ 6.0 Hz, 2H, ArH), 4.08 (t, J ¼ 6.0 Hz, 2H, CH2O), 3.82 (t, J ¼ 6.0 Hz,
2H, CH2O), 3.73 (t, J ¼ 6.0 Hz, 2H, CH2O), 3.67 (m, J ¼ 6.0 Hz, 4H,
CH2O), 3.54 (t, J ¼ 6.0 Hz, 2H, CH2O), 3.38 (s, 2H, NH2), 3.37 (s, 3H,
2.12. Synthesis of PF homopolymer (PF3) via one-pot Suzuki
coupling polymerization
CH3). 13C NMR (75 MHz, CDCl3)
d (ppm): 151.34, 140.32, 115.91,
115.48, 71.60, 70.42, 70.31, 70.22, 69.60, 67.77, 58.71.
To a 20 mL three-necked round-bottom flask equipped with
a stopcock and a condenser were added 4 (0.337 g, 0.56 mmol),
bis(pinacolato)diboron (0.166 g, 0.655 mmol), Pd(PPh3)4 (3.2 mg,
0.0028 mmol, 0.5 mol%), 2N K2CO3 aq. (3 mL), and toluene (3 mL)
under nitrogen atmosphere and the mixture was refluxed for 48 h.
Then, 8 (0.15 g, 0.3 mmol) was added and reflux was continued for
12 h. After the reaction chloroform was added, the resulting solu-
tion was washed with sat. NaCl aq. and dried with MgSO4. The
solvent was removed by rotary evaporator, and the product was
obtained by precipitation into methanol. The yield was 0.176 g
2.9. Synthesis of (40-bromobiphenyl-4-yl)-(4-{2-[2-(2-methoxy-
ethoxy)ethoxy]ethoxy}phenyl)amine (8)
To a flask equipped with a stopcock and a condenser were
placed 7 (3.00 g,12 mmol), 4,40-dibromobiphenyl (3.75 g,12 mmol),
sodium tert-butoxide (1.70 g, 1.7 mmol), Pd(dppf)Cl2 (0.10 g,
0.12 mmol), and toluene (5 mL) under nitogen atmosphere. After
reaction for 24 h at reflux, the mixture was washed with 1 N HCl
and brine. The organic layer was dried with MgSO4, and concen-
trated by rotary evaporator. The crude product was purified by
column chromatography (hexane:ethyl acetate ¼ 1:5). Reddish
brown solid was obtained. The yield was 2.01 g (28%). 1H NMR
(71%). 1H NMR (300 MHz, CDCl3)
d (ppm): 7.81-7.67 (m, 2H, ArH),
7.65-7.41 (m, 4H, ArH), 7.18-6.91 (m, 8H, ArH), 4.31-3.37 (m, 16H,
CH2O), 2.58-2.42 (m, 2H, CH2), 2.34-2.19 (m, 3H, CH3), 1.66-1.42 (m,
2H, CH2), 1.42-1.12 (m, 10H, CH2), 0.85-0.91 (m, 3H, CH3).
(300 MHz, CDCl3)
d
(ppm): 7.53 (d, J ¼ 9.0 Hz, 2H, ArH), 7.37 (d,
J ¼ 9.0 Hz, 4H, ArH), 7.13 (d, J ¼ 9.0 Hz, 4H, ArH), 6.90 (d, J ¼ 9.0 Hz,
2H, ArH), 5.71 (s, 1H, NH), 4.14 (s, 2H, CH2O), 3.87 (t, J ¼ 6.0 Hz, 2H,
CH2O), 3.76 (m, 2H, CH2O), 3.65 (m, 4H, CH2O), 3.57 (m, J ¼ 6.0 Hz,
2.13. Synthesis of PF-b-PTPA block copolymer (PF-PTPA2)
To a 10 mL two-necked round-bottom flask equipped with
a stopcock and a condenser were added PF2 (0.134 g, 0.30 mmol of
2H, CH2O), 3.37 (s, 2H, CH3). 13C NMR (75 MHz, CDCl3)
d (ppm):
154.72, 145.04, 139.99, 135.50, 131.85, 130.83, 127.99, 127.84, 122.41,
120.41,115.74,115.64, 72.02, 70.91, 70.77, 70.67, 69.92, 67.90. HR-MS
(m/z): calcd for C25H28BrNO4, 485.1202; found, 485.1209 [M]þ.
repeating unit), 8 (0.146 g, 0.3 mmol), P(t-Bu)3 (7.5 mL, 0.01 mmol),
Pd(OAc)2 (0.0014 g, 0.006 mmol), t-BuONa (0.032 g, 0.33 mmol),
and THF (3 mL) under nitrogen atmosphere and the mixture was
stirred under reflux for 24 h. After the reaction, the resulting
solution was washed by chloroform. After removing the solvent by
rotary evaporator, the product was obtained by precipitation into
methanol and acetone. The yield of PF-PTPA2 was 0.199 g (48%).
PF-PTPA4 and PF-PTPA5 were synthesized by the same procedure
with different feed ratios. PF-PTPA4 was synthesized from PF4
(0.094 g, 0.21 mmol of repeating unit), 8 (0.0243 g, 0.05 mmol),
2.10. Synthesis of PF homopolymer (PF1) via nickel(0) mediated
polymerization
To a 20 mL three-necked round-bottom flask equipped with
a stopcock and a condenser were added 4 (0.20 g, 0.34 mmol),
Ni(cod)2 (0.20 g, 0.8 mmol), 2,20-bipyridyl (0.12 g, 1.8 mmol), and
THF (10 mL) under nitrogen atmosphere, and the mixture was
stirred under reflux for 24 h. Then, 8 (0.08 g, 0.164 mmol) was
P(t-Bu)3 (1.5
mL, 0.005 mmol), Pd(OAc)2 (0.0003 g, 0.001 mmol),
t-BuONa (0.006 g, 0.055 mmol), and THF (2 mL). The yield was

Y. Tan et al. / Polymer 53 (2012) 1444e1452
1447
0.147 g (53%). PF-PTPA5 was synthesized from PF5 (0.132 g,
0.30 mmol of repeating unit), 8 (0.146 g, 0.3 mmol), P(t-Bu)3
(7.5 L, 0.01 mmol), Pd(OAc)2 (0.0014 g, 0.006 mmol), t-BuONa
2.15. Device fabrication
m
Prior to preparation of device, a glass slide with indium tin oxide
(ITO) patterns was washed by an alkaline cleaner under sonication
and rinsed with deionized water. The substrate was subsequently
washed by 2-propanol under sonication, rinsed with clean 2-
propanol, and dried with nitrogen. PEDOT:PSS with 30 nm of
thickness was spin-coated on the substrate at 2500 rpm for 30s from
(0.032 g, 0.33 mmol), and THF (3 mL). The yield was 0.194 g (47%).
2.14. Characterizations
1H and 13C NMR spectra were obtained on a JEOL ALPHA300
instrument at 300 MHz at 25 ꢁC. Deutrated chloroform was used as
a solvent with tetramethylsilane as an internal standard. Number-
and weight-average molecular weights (Mn and Mw) and poly-
dispersity index (PDI) were determined by gel permeation chro-
matography (GPC) analysis with a JASCO RI-2031 detector eluted
with chloroform at a flow rate of 0.5 ml/min at room temperature
and calibrated by standard polystyrene samples. Thermogravi-
metric analysis (TGA) and Differential scanning calorimetry (DSC)
analysis was performed on a Rigaku DSC-8230 under nitrogen
atmosphere at heating and cooling rates of 10 ꢁC/min. UVevis
absorption spectra were obtained on a JASCO V-570 spectropho-
tometer and fluorescence spectra were obtained with JASCO FP-
6500 spectrophotometer with an excitation at 380 nm. Cyclic vol-
tammetry (CV) was conducted on a Niko Keisoku Model NPGFZ-
2501-A potentiogalvanostat. All measurements were carried out at
room temperature in a typical three-electrode cell with a working
electrode (glassy carbon electrode), a reference electrode (Ag/AgCl),
and a counter electrode (Pt wire) at a scanning rate of 0.1 V/s. In all
measurements, acetonitrile and tetrabutylammonium tetra-
fluoroborate (Bu4NBF4) (0.1 M) were used as solvent and support-
ing electrolyte, respectively.
the dispersion in water filtered by 0.2 mm of membrane filter, fol-
lowed by annealing at 200 ꢁC for 1 h. Polymer layer was laminated
on PEDOT:PSS by spin-coating at 500 rpm for 30 s from chloro-
benzene solution (12 mg/mL) filtered by 0.45 mm of membrane filter,
and annealed at 120 ꢁC for 1 h under nitrogen atmosphere. On the
polymer, 2,9-dimethyl- 4,7-diphenyl-1,10-phenanthroline (BCP)
with 50 nm thickness was deposited by thermally evaporation in
carbon pot at 240 ꢁC under vacuum with a rate of 1.5 Å/s. As
a cathode, lithium fluoride with 0.5 nm of thickness followed by a Al
with 100 nm of thickness was deposited on the organic layer with
a rate of 0.1 Å/s and a rate of 4.5 Å/s using tantalum and tungsten
boats, respectively. Finally, the polymer device was set into a metal
can with barium oxide as a drying agent under a nitrogen atmo-
sphere, and passivated with an epoxy resin (XNR 5570-B1, Nagase
ChemteX Corporation) irradiated by UV light.
3. Result and discussion
3.1. Synthesis and characterization
Scheme 1 illustrated the synthetic route of 2,7-dibromo-9-
(4-methylphenyl)-9-(4-octylphenyl)fluorene
(4)
and
(40-
O
CrO3
Br2
Br
Br
FeCl3
r.t., 12 h
CH3COOH
r.t., 12 h
Br
Br
1
2
Mg
C H
8
17
C H
8
17
CF3SO3H
H17C8
Br
HO
toluene
reflux, 3 h
THF
reflux, 12 h
Br
Br
Br
Br
4
3
C H
8
17
CH
3
CH Li
O
2
B
O
4
O
O
O
THF
r.t., 12 h
O
B
B
O
5
Pd/C
H2
K2CO3
O
O N
2
O
O
HO
O2N
H2N
F
3
DMAc
3
ethanol
r.t., 24 h
150 oC, 24 h
6
Br
Br
Pd(dppf)Cl2, t-BuONa
O
O
O
O
NH
Br
3
3
toluene
reflux, 24 h
8
7
Scheme 1. Synthetic route for monomers.

1448
Y. Tan et al. / Polymer 53 (2012) 1444e1452
Ni(cod)2
2,2'-bipyridyl
)
4
TH F
8
reflux
C H
8 17
or
8
Pd(pph3)4
4
5
)
O
O
NH
NH
O
Toluene
90
3
O
3
m
PF1, 2, 3
or
8
PF1; via scheme I), nickel(0) polymerization
PF2; via scheme II), Suzuki coupling polymerization
PF3; via scheme III), one-pot Suzuki polymerization
O
O
Pd(pph3)4
B
B
)
4
O
O
Toluene
90
8
C H
C H
17
O
8
17
O
8
Pd(OAc)2
P(t-Bu)3
t-BuONa
O
N
O
N
3
3
O
O
NH
NH
O
3
O
3
m
n
THF
reflux
n
m
PF 2, 4, 5
PF-PTPA 2, 4, 5
Scheme 2. Synthetic route for PF homopolymers and PF-PTPA block copolymers.
bromobiphenyl-4-yl)-(4-{2-[2-(2-methoxyethoxy)ethoxy]ethoxy}
phenyl)amine (8), monomers for polyfluorene and poly(triphenyl-
amine) backbones, respectively. In order to avoid the formation of
aggregates/excimers and suppress interchain interactions in PF,
octylphenyl and methylphenyl groups were introduced at the 9-
position of fluorene in 4. In the meantime, TPA monomer 8 was
modified with tri(ethylene oxide) (TEO) group, which is considered
to predominantly interact with hydrophilic PEDOT/PSS layer in EL
device to prevent the migration of an impurity from PEDOT/PSS
layer to PF emitting layer by the formation of poly(triphenylamine)
skin layer between them. Since Suzuki coupling reaction was
utilized for the preparation of PF, 2,7-bis(4,4,5,5-tetramethyl-1,3,2-
dioxaborolan-2-yl)-9-(4-methylphenyl)-9-(4-octylphenyl)fluorene
molecular weight and to convert the terminal into the diphenyl-
amine group completely. Furthermore, the tedious removal of the
large amount of nickel residue is required. In contrary, for PF2
prepared by Suzuki coupling polymerization, the molecular weight
of the polymer could be easily controlled by changing the molar
ratio of reactant monomers. Moreover, the palladium complex as
well as other residues could be removed simply by washing the
products with water and methanol. The terminals of PF2 were
designed to be boronic ester by utilizing excess amount of mono-
mer 5, and successfully converted to diphenylanime group at the
end of polymerization. Because of troublesome preparation of
boronic-acid-ester monomers, more facile one-pot Suzuki coupling
polymerization was reported recently [28]. Therefore, PF3 was
synthesized via one-pot Suzuki coupling polymerization by means
(5) were synthesized from
4 using n-butyllithium and 2-
isopropoxy-4,4,5,5-tetramethyl-1,3,2-dioxaborolane.
of simply replacing 5 with bis(pinacolato)diboron without
In order to prepare the PF homopolymer with diphenylamine
group at terminals, nickel(0) mediated polymerization of 4 (PF1)
and Suzuki coupling polymerization of 4 and 5 (PF2) were con-
ducted as shown in Scheme 2. One-pot Suzuki coupling polymer-
ization of 4 in the presence of bis(pinacolato)diboron was also
carried out (PF3). At the end of polymerizations, the terminals of
the PFs were converted to the diphenylamine moiety by the
coupling reaction with 8.
The resulting molecular weights of PF homopolymers were
summarized in Table 1. The polymers PF1, PF2, and PF3 exhibited
similar Mn ranging from 9700 to 13400. However, the PDI (Mw/Mn)
value of PF1 was 5.80, higher than those of the other two homo-
polymers (2.42 and 2.19). Therefore, it was difficult to control the
changing any reaction conditions. The polymer was obtained in
moderate yield, and the molecular weight and polydispersity of
PF3 were similar to conventionally prepared PF2. However, the
terminal modification into diphenylamine group by coupling with
8 was failed.
For the synthesis of PF with the terminals modification into
diphenylamine group, Suzuki coupling polymerization is a prior
selection to nickel(0) mediated polymerization. Therefore, we
prepared PFs with various molecular weights, and these homo-
polymers were used for the synthesis of block copolymers. It is well
known that the molecular weight of polymers in polycondensation
can be varied by deviating from the stoichiometry between two
monomers [29]. Changing molar ratio of bromo-group/boronic-
Table 1
Characterizations of PF homopolymers prepared by various polymerization methods.
a
Polymer
Molar ratio [4]/[5]
Mn
PDIa
Yield (%)
Tg (ꢁC)
Td (ꢁC)
lmax (UVevis)
lmax (PL)
Solution (nm)
Film (nm)
Solution (nm)
Film (nm)
PF1
PF2
PF3
1/0
9700
13400
10800
5.80
2.42
2.19
89
83
71
104
111
107
464
450
445
387
388
387
385
383
384
416
417
417
423
418
421
0.92/1.08
0.92/1.08b
a
Determined by GPC.
Molar ratio of [4]/[bis(pinacolato)diboron].
b

Y. Tan et al. / Polymer 53 (2012) 1444e1452
1449
Table 2
3.2. Thermal properties
Characterizations of PF-PTPA block copolymers.
b
The glass transition temperature (Tg) of the polymers was
measured by DSC under N2 atmosphere at a scan rate of 10 ꢁC/min.
The homopolymers, PF2, PF4, and PF5 showed a Tg of 111, 118, and
127 ꢁC, respectively. The Tg value slightly increased with an increase
of the molecular weight. Fig. 2 shows DSC thermograms of PF5,
PTPA, and PF-PTPA5. PTPA homopolymer exhibited relatively high
Tg of 175 ꢁC. PF-PTPA5 showed two distinct transitions at 119, and
173 ꢁC, corresponding to Tgs of PF and PTPA, respectively, which
indicates the microphase-separated structure. Other block copol-
ymers, (PF-PTPA2, PF-PTPA4) also showed double Tgs.
polymer
Molar ratio 4/5 Molar ratioa
in feed in
Mn
PDIb Yield (%) Td (ꢁC)
polymer
PF2
PF-PTPA2
PF4
PF-PTPA4
PF5
PF-PTPA5
PTPA
0.92/1.08
e
13400 2.42 83
50/50 55/45 23100 2.67 48
18700 3.24 79
81/19 89/11 20500 2.72 53
26400 3.48 85
50/50 65/35 43400 3.28 47
9700 2.80 94
450
415
448
410
451
401
406
e
0.95/1.05
e
e
0.98/1.02
e
e
e
e
a
Molar ratio of PF repeating unit to 8.
Determined by GPC.
b
3.3. Optical properties
ester-group to 0.95/1.05 and 0.98/1.02, polyfluorene homopoly-
mers PF4 and PF5 were prepared via Suzuki coupling reaction. The
CeN coupling polymerization of 8 in the presence of these three PFs
was conducted to obtain polytriphenylamine-block-polyfluorene-
block-polytriphenylamine triblock copolymers, PF-PTPA2, PF-
PTPA4, and PF-PTPA5 (Scheme 2). The feed ratios of the monomers
and the resulting molecular weights of the polymers were
summarized in Table 2. The Mn increased after the polymerization
of 8 compared with those of PF homopolymers. The polymer
structure was confirmed by 1H NMR spectra. For example, in Fig. 1,
the signals assignable to methylene protons derived from TEO
chain were observed at 3.3-4.1 ppm, clearly indicating that TPA
monomer 8 was introduced at the ends of PF backbone. The molar
ratio of the repeating unit of block copolymers were calculated
from 1H NMR spectra, depending on the area integral of ether
proton and aliphatic proton (shown in Fig. SI-5). The molar ratio of
fluorene/TPA units in PF-PTPA2, PF-PTPA4 and PF-PTPA5 were
determined as 55/45, 89/11, 65/35, respectively. The GPC chro-
matograms of block copolymers showed unimodal profiles and
a shift to higher molecular weight from homopolymers (Fig. SI-1).
This indicates that no PTPA homopolymer remained in the block
copolymers. PDI values of the six polymers were in the range from
2.42 to 3.48. All the polymers are soluble in common organic
solvents such as chloroform and THF, and formed the thin films by
solution processing.
The optical properties of PF homopolymers and PF-PTPA block
copolymers in chloroform solution and in film state were shown in
Fig. 3 and Table 3. In the absorption spectra of solution state, both
homopolymers and block copolymers showed labs,max of 387-
389 nm. Similar results were obtained in film state. All the poly-
mers exhibited similar PL spectra in solution state, having distinct
vibronic bands at about 418 and 445 nm and a shoulder around
470 nm upon excitation at 380 nm. This is attributed to the fact that
the distance between polymer main chains in dilute solution is
sufficient to make interchain interactions negligible. In the film
state, similar emission behavior was observed in all of the polymers
(not only PF homopolymers but also PF-PTPA block copolymers)
indicating that the attachment of PTPA block to the PF backbone
gives little influence on the luminescent properties of PF, although
the emission peak width for block copolymers was slightly
increased. As Jin et al. reported, random copolymers consisting of
PF and tetraphenylbenzidine moieties show a red-shifted emission
compared with PF [5]. Taking the fact into consideration that
extensive broadening was observed in lowest molecular weight of
PF-PTPA2, peak broadening is probably resulted from the existence
of junction unit between PF and PTPA.
3.4. Electrochemical properties
The electrochemical properties of the polymers were investi-
gated by cyclic voltammetry (CV). As shown in Fig. SI-3a, the
oxidation process of PF homopolymers started at around 1.40 V,
and the reversible redox peaks in the reduction process appear at
around ꢀ0.80 V. The oxidation onset and the reduction potential for
homopolymers PF2, PF4, and PF5 slightly changed because they
possess the same PF main chain structure with an increase of
molecular weight. The same result was also found in the case of PF-
PF 5
PTPA (Mn:10K)
PF-PTPA 5
50
100
150
200
250
Temperature (oC)
Fig. 1. 1H NMR spectra of PF2 and PF-PTPA2.
Fig. 2. DSC profiles of PF, PTPA and PF-PTPA.

1450
Y. Tan et al. / Polymer 53 (2012) 1444e1452
a
b
1.0
1.0
0.8
0.6
0.4
0.2
0.0
PF 2
PF 2
PF-PTPA 2
PF-PTPA 4
PF-PTPA 5
PF-PTPA 2
PF-PTPA 4
PF-PTPA 5
0.8
0.6
0.4
0.2
0.0
350
400
450
500
550
600
350
400
450
500
550
600
Wavelength (nm)
Wavelength (nm)
c
d
1.0
0.8
0.6
0.4
0.2
0.0
1.0
0.8
0.6
0.4
0.2
0.0
PF 2
PF 2
PF-PTPA 2
PF-PTPA 4
PF-PTPA 5
PF-PTPA 2
PF-PTPA 4
PF-PTPA 5
350
400
450
500
550
600
400
450
500
550
600
wavelength (nm)
Wavelength (nm)
Fig. 3. Optical properties of PF2 and PF-PTPAs: (a) UV, soln.; (b) UV, film; (c) PL, soln.; (d) PL, film.
PTPA block copolymers (Fig. SI-3b) except that a new oxidation
peaks in the anodic sweep were observed at around 0.90 V. CV data
for block copolymers were basically coincident with those of the
previously reported polymers with fluorene and triphenylamine
backbone [30,31]. All of PF-PTPA block copolymers exhibited
a decreased oxidation onset in comparison with corresponding PF
homopolymers, which attributed to attached PTPA segment.
Furthermore, the oxidation potential of all of block copolymers
slightly increased as the PTPA segment length increased.
The energy levels of the highest occupied molecular orbital
(HOMO) of the polymers were estimated from their oxidation
potential according to an empirical formula, EHOMO ¼ - e(Eoxþ4.4)
V. HOMO levels of PF homopolymers were in the range of
from ꢀ5.79 to ꢀ5.88 eV, deeper than those of PF-PTPA block
copolymers, from ꢀ5.29 to ꢀ5.33 eV. The results indicated that the
introduction of polytriphenylamine segment into the polymer
chain ends efficiently raised their HOMO levels, thus could facilitate
the hole injection and transport from an anode to the emitting
polymer. The levels of the lowest unoccupied molecular orbital
(LUMO) for the polymers were calculated with the reduction
potential Ered from the empirical formula ELUMO ¼ - e(Ered＋4.4) V.
The electrical band gaps (Egel) of the polymers were estimated by
subtracting the HOMO levels from their respective LUMO energies.
The electrochemical properties in films were summarized in
Table 3.
Fig. 4 showed the energy level diagram for PF2 and PF-PTPA2
compared with ITO as an anode and widely used PEDOT/PSS as
a hole-injection-layer material. The HOMO levels of PF-PTPA block
copolymers suitably match the work function of PEDOT/PSS
(ꢀ5.2 eV), while there was an energy barrier over 0.50 eV between
the HOMO of PEDOT/PSS and those of PF homopolymers. This
suggests that a facile hole injection from ITO/PEDOT/PSS into
PF-PTPA layer can be expected in comparison with PF.
3.5. EL properties
The performance of the EL devices based on PF homopolymers
and PF-PTPA block copolymers with the device structure of ITO/
PEDOT:PSS/polymer/BCP/LiF/Al was evaluated. Fig.
5 showed
current density vs. voltage, luminance vs. current density, and
current efficiency vs. current density characteristics. As shown in
Fig. 5a, the current density of devices based on PF-PTPA block
Table 3
Optical and electrochemical properties of PFs and PF-PTPAs.
Polymer
lmax (UVevis)
lmax (PL)
Eox (V)
Ered (V)
EHOMO (-eV)a
ELUMO (-eV)b
Egel (eV)c
Solution (nm)
Film (nm)
Solution (nm)
Film (nm)
PF2
PF-PTPA2
PF4
PF-PTPA4
PF5
PF-PTPA5
388
389
388
389
389
386
383
386
386
384
385
383
417
418
418
418
419
418
418
416
421
415
420
416
1.39
0.89
1.40
0.85
1.48
0.93
ꢀ0.79
ꢀ0.74
ꢀ0.82
ꢀ0.71
ꢀ0.85
ꢀ0.79
5.79
5.29
5.80
5.25
5.88
5.33
3.61
3.66
3.58
3.69
3.55
3.61
2.18
1.63
2.22
1.56
2.33
1.72
a
EHOMO ¼ - e(EOxþ4.4) V.
ELUMO ¼ - e(Eredþ4.4) V.
b
c
Electrical band gap: Egel ¼ LUMO - HOMO.

Y. Tan et al. / Polymer 53 (2012) 1444e1452
1451
addition, it is suggested that the microphase-separated structure
created by the block copolymers offered large interface between PF
and PTPA segments for the efficient charge recombination [25]. The
difference of polarity between PF and PTPA with TEO moiety may
promote the microphase separation, which also contributes the
improvement of current efficiency.
Although PF homopolymers possesses the different molecular
weights, they showed similar device performances (both lumi-
nance and current efficiency). It also should be noted that, although
PF-PTPA2, PF-PTPA4 and PF-PTPA5 possesses different PTPA
repeating units (n ¼ 15, 5, and 30), there was nearly no difference in
the UVevis and PL spectrum and a slight variation in the electro-
chemical properties. However, the EL device based on PF-PTPA2
and PF-PTPA5 exceeded that of PF-PTPA4 in the electrolumines-
cent properties. For the three block copolymers PF-PTPA2, PF-
PTPA4, and PF-PTPA5, the ratios of PF/PTPA units are roughly
calculated as 55/45, 89/11, and 65/35, respectively. With the PTPA
content increased, both luminance and current efficiency increased
(PF-PTPA2 > PF-PTPA5 > PF-PTPA4).
-3.2eV
BCP
-3.61eV
PF 2
-3.66eV
LiF/Al
-4.1eV
PF-
PTPA 2
ITO
-4.8eV
PEDOT
-5.2eV
-5.29eV
-5.79eV
-6.7eV
Fig. 4. Energy level diagram of PF2 and PF-PTPA2.
copolymers was higher than that from corresponding PF homo-
polymers. Moreover, with the PTPA content increased, the current
density of devices of block copolymers increased (PF-PTPA2 > PF-
PTPA5 > PF-PTPA4 > PFs). This fact indicates that with the
increase of PTPA content, the hole injection and transport in PF-
PTPA layer was improved more efficiently. The luminance of all
the polymers was exponentially increased with an increase in
voltage. At the similar current density (for example, 30 mA/cm2),
PF-PTPA2, PF-PTPA4, and PF-PTPA5 showed higher luminance
(532, 433, and 586 cd/m2) than corresponding PF homopolymers
(285, 226, and 274 cd/m2), respectively. Moreover, similar results
were obtained for the maximum luminance. The maximum current
efficiencies of PF hompopolymers were from 1.14 to 1.21 cd/A,
whereas those of PF-PTPA block copolymers increased from 1.60 to
2.27 cd/A. The improvement of the device performance using block
copolymers is probably attributed to an efficient hole injection,
which leads good balance between hole and electron charges in the
emitting layer, by the attachment of PTPA block to PF backbone. In
The EL spectra of the devices based on PF2 and PF-PTPA block
copolymers were shown in Fig. 6, and their corresponding CIE
coordinates were summarized in Table 4. All the devices based on
block copolymers exhibited a blue emission without unnecessary
green-emitting bands. As shown in Table 4, PF homopolymers
exhibit EL emission with CIE coordinates ranging from (0.17, 0.20)
to (0.18, 0.21); while PF-PTPA block copolymers showed slightly
deeper blue color with CIE coordinates ranging from (0.16, 0.18) to
(0.17, 0.19). The EL profiles of PF-PTPA block copolymers were
slightly narrow compared with that of PF2 as the result of
suppression of the undesired emission at 460e550 nm by the
incorporation of PTPA segment [32]. The influence of PTPA
content on the EL spectra and color purities of devices based on
block copolymers was not observed obviously. We noted that the
dominating contribution of EL properties comes from emission
peak at 450 nm, which was slightly red-shifted from that of PL
emission (425 nm) [32].
a150
b
103
102
101
100
10-1
PF-PTPA 2
PF 2
120
90
60
30
0
PF-PTPA 4
PF 4
PF-PTPA 5
PF 5
PF-PTPA 2
PF 2
PF-PTPA 4
PF 4
PF-PTPA 5
PF 5
0
25
50
75 100 125
0
5
10
Voltage (V)
15
20
Current density (mA/cm2)
c
2.5
2.0
1.5
1.0
0.5
0.0
PF-PTPA2
PF2
PF-PTPA4
PF4
PF-PTPA5
PF5
0
50
100 150 200 250
Current density (mA/cm2)
Fig. 5. Device characteristics of blue-emitting PLEDs, (a) current density e voltage characteristics; (b) luminance e current density characteristics; (c) current efficiency e current
density characteristics.

1452
Y. Tan et al. / Polymer 53 (2012) 1444e1452
showed higher luminance and current efficiency than those of
1.0
0.8
0.6
0.4
0.2
0.0
PF 2
corresponding PF homopolymers. While PF homopolymers showed
similar device performances with different molecular weights,
device performance of PF-PTPA block copolymers increased with
the PTPA content increased. These results indicates that the incor-
poration of hole transporting PTPA segments into PF backbone
improved the hole injection into PF emitting layer, which offered
the effective charge recombination.
PF-PTPA 2
PF-PTPA 4
PF-PTPA 5
Appendix. Supporting information
350 400 450 500 550 600 650
Supporting information related to this article can be found
online at doi:10.1016/j.polymer.2012.02.021.
Wavelength (nm)
Fig. 6. Electroluminescence spectra of devices based on PF2 and PF-PTPAs at 14V.
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Luminance at
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(cd/m2)
Maximum
luminance
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Maximum current
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Color
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[x, y]
PF2
PF-PTPA2
PF4
PF-PTPA4
PF5
PF-PTPA5
285
532
226
433
274
586
1001
2160
984
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1.60
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In order to prepare polyfluorene block copolymers containing
hole transporting segments for PLED devices, 2,7-dibromo-9-(4-
methylphenyl)-9-(4-octylphenyl)fluorene and (40-bromobiphenyl-
4-yl)-(4-{2-[2-(2-methoxyethoxy)ethoxy]ethoxy}phenyl)amine
were synthesized as novel monomers for PF and PTPA backbone.
For the preparation of polyfluorene homopolymer, Suzuki coupling
polymerization was selected, and the terminals were precisely
converted to diphenylamine group. PTPA block was introduced at
the terminals of PF via C-N coupling polymerization to give PTPA-
block-PF-block-PTPA triblock copolymers (PF-PTPAs) with different
PTPA chain lengths. These polymers showed good solubility in
common organic solvents, had good thermal stability, and readily
formed thin film by solution processing. All of the polymers
exhibited an absorption peak at around 385 nm both in chloroform
solution and in film state, while the PL emission were observed at
around 420 nm, the range of blue-light wavelength. The photo-
physical analysis revealed that the PTPA chains gave no influence
on the blue emission of PF segment. PF-PTPA block copolymers
showed relatively high HOMO level at around ꢀ5.3 eV compared
with those of PF by CV measurement, which provided a good match
with the work function of PEDOT/PSS (ꢀ5.2 eV). This suggests
a facile hole injection from ITO/PEDOT/PSS into the HOMO of PF-
PTPA than PF. The EL devices based on PF-PTPA block copolymers
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