Synthesis of benzo[1,2-b:4,3-b′]dithiophene/triphenylamine copolymers: Effects of substituents on optical and EL properties

Article abstract of DOI:10.1246/bcsj.81.1322

Benzo[1,2-b:4,3-b′]dithiophene/triphenylamine copolymers P-2eh (with no methyl substituents) and P-Me and P-2Me (with methyl substituents at triphenylamine sites) were synthesized by Stille coupling reactions. In the ground state, the methyl substituents at the ortho positions to the BDT unit on the triphenylamine (TPA) moiety in P-Me and P-2Me caused twisting of the polymer structure and clearly limited conjugation of the polymer backbones. However, in their excited states, all of these copolymers were shown to have planar structures, and almost the same emission maxima were observed. This result indicates that, in the excited states, π-conjugation of the polymer backbone results in the adoption of a more stable planar structure rather than the twisted structure observed in the ground state. The maximum EL efficiencies of devices based on P-Me and P-2Me were about three times higher than that of P-2eh due to restricted π-stacking/aggregation of the conjugated copolymers in the solid state and improvements in thermal and electrochemical stability.

Full text of DOI:10.1246/bcsj.81.1322

1322 Bull. Chem. Soc. Jpn. Vol. 81, No. 10, 1322–1330 (2008)
Ó 2008 The Chemical Society of Japan
Synthesis of Benzo[1,2-b:4,3-b0]dithiophene/triphenylamine Copolymers:
Effects of Substituents on Optical and EL Properties
ꢀ
Yosuke Nishide, Hideji Osuga, Kunihiro Iwata, Kazuhiko Tanaka, and Hidefumi Sakamoto
Department of Material Science and Chemistry, Faculty of Systems Engineering,
Wakayama University, 930 Sakaedani, Wakayama 640-8510
Received February 21, 2008; E-mail: osuga@sys.wakayama-u.ac.jp
Benzo[1,2-b:4,3-b0]dithiophene/triphenylamine copolymers P-2eh (with no methyl substituents) and P-Me and
P-2Me (with methyl substituents at triphenylamine sites) were synthesized by Stille coupling reactions. In the ground
state, the methyl substituents at the ortho positions to the BDT unit on the triphenylamine (TPA) moiety in P-Me
and P-2Me caused twisting of the polymer structure and clearly limited conjugation of the polymer backbones. However,
in their excited states, all of these copolymers were shown to have planar structures, and almost the same emission
maxima were observed. This result indicates that, in the excited states, ꢀ-conjugation of the polymer backbone results
in the adoption of a more stable planar structure rather than the twisted structure observed in the ground state. The
maximum EL efficiencies of devices based on P-Me and P-2Me were about three times higher than that of P-2eh
due to restricted ꢀ-stacking/aggregation of the conjugated copolymers in the solid state and improvements in thermal
and electrochemical stability.
Since Tang and VanSlyke reported the first practical multi-
layered organic light-emitting diodes (OLEDs),1 various types
of organic material for OLEDs have been developed.2 In 1990,
the Cambridge group reported the preparation of polymer
(poly(phenylenevinylene), PPV)-based organic light-emitting
diodes (PLEDs),3 which have attracted much scientific and
technological research interest during the past decade due to
their simplicity and low-cost fabrication using wet processes,
such as inkjet printing as well as their possible application in
flexible displays.4 The main advantages of electroluminescent
(EL) conjugated polymers over inorganic and organic small-
molecule-based materials in OLEDs are easy processability,
ease of formation of large-area thin films, and simple molecu-
lar structure design.5–7 Although many polymers have been
investigated for application in PLEDs, further improvements
in efficiency, color purity, and durability are still necessary
in order to allow development to proceed to the commercial
stage for application in full-color flat-panel displays and sol-
id-state lighting. Therefore, detailed investigation of struc-
ture–property relationships in EL polymers is required.
We previously reported the fabrication and EL properties
of OLEDs using 1,2-diarylethylene derived from the ortho
fused heterocyclic compound benzo[1,2-b:4,3-b0]dithiophene
(BDT).8 This device was shown to give strong emissions
(25000 cd mꢁ2), with Commission International de l’Eclairage
(CIE) chromaticity coordinates at (0.19, 0.27), in the greenish-
blue region. However, this kind of material cannot be used as a
single material for an emission layer due to quenching arising
from its high planarity and ꢀ–ꢀ stacking in solid thin films.
We also found that 4,5-diphenyl BDT, which contains phenyl
groups on the benzene ring, has a non-planar structure due to
the torsion angle between BDT and the phenyl groups.
copolymers. Triphenylamine (TPA) derivatives have high
hole-transporting abilities9–17 and large volumes arising from
their pyramidal structures.17–21 Therefore, copolymers with
combinations of BDT and TPA moieties are expected to show
suppression of inter- or intramolecular interactions due to the
non-planar structure of the strained phenyl groups on the
benzene ring of BDT and the bulkiness of TPA. The purpose
of this study was to investigate the substitution effect on the
optical, electrochemical, and EL properties of these materials
by synthesis of copolymers containing methyl groups on a
polymer backbone.
Results and Discussion
Synthesis and Characterization. The syntheses of the
monomers and corresponding polymers are outlined in
Schemes 1–4. Monobromination of triphenylamine (1) with
N-bromosuccinimide (NBS)22 and subsequent alkylation by
the appropriate Grignard reagent in the presence of a NiII
catalyst gave 3.23 Monomer 4 was obtained by dibromination
of 3 with NBS; the overall yield from the starting material 1
was 31%. We attempted to synthesize the dimethyl monomer
7 from 4-hexylaniline (5) by palladium-catalyzed amination
using 5 equivalents of 2,5-dibromotoluene (6),24 but an
isomeric mixture of 7 and 8 was obtained (47% yield) from
which the desired compound 7 could not be isolated. Tetra-
methyl monomer 11 (19% overall final yield) was also pre-
pared by an amination reaction under similar conditions to
the synthesis of 7, but a 2-step reaction was necessary due to
the poor reactivity of sterically hindered bromide 9. The 2-
ethylhexyl group was attached to monomer 4 in order to
suppress intermolecular interactions, because it had no methyl
substituents which could strain the polymer backbones. 4,5-
Diphenylbenzo[1,2-b:4,3-b0]dithiophene (14) was prepared
by McMurry coupling of 2-benzoylthiophene (12) followed
We report herein the synthesis and structure–property rela-
tionships of benzo[1,2-b:4,3-b0]dithiophene/triphenylamine
Published on the web October 10, 2008; doi:10.1246/bcsj.81.1322

Y. Nishide et al.
Bull. Chem. Soc. Jpn. Vol. 81, No. 10 (2008) 1323
Br
NBS
CH2Cl2, r.t.
(69%)
N
N
1
2
2-ethylhexyl
2-ethylhexyl
MgBr
NiCl2(dppp)
NBS
CH2Cl2, r.t.
(99%)
N
ether, reflux
(46%)
N
Br
Br
3
4
Pd2(dba)3
DPPF
n-hexyl
Br
NaO-t-Bu
+
CH3
toluene, 90 °C
NH2
Br
(47%)
5
6
n-hexyl
n-hexyl
CH3
+
H3C
Br
N
CH3
Br
H3C
Br
N
Br
7
8
(7 : 8 = 1.5 : 1)
Scheme 1. Synthesis of precursors for coupling reactions.
by photocyclization.25 Lithiation of 14 using butyllithium and
subsequent treatment with excess tributylstannyl chloride gave
the distannyl derivative 15. As shown in Scheme 4, all copoly-
mers (P-2eh, P-Me, and P-2Me) were synthesized by Stille
coupling reactions26 between distannyl compound 15 and the
appropriate dibromide (4, 7/8, and 11, respectively), with a
molar ratio of 1.0:1.0.
Table 1. Molecular Weights and Thermal Properties of
P-2eh, P-Me, and P-2Me
a)
a)
Copolymer
Mn
Mw
Da) Tgb)/ꢂC Tdc)/ꢂC
P-2eh
P-Me
P-2Me
6:5 ꢃ 103 1:0 ꢃ 104 1.5
3:1 ꢃ 103 4:3 ꢃ 103 1.3
4:9 ꢃ 103 7:3 ꢃ 103 1.5
—
203
259
418
474
483
The resulting polymers were quite soluble in common or-
ganic solvents such as chloroform and toluene at room temper-
ature. Table 1 summarizes their molecular weights and ther-
mal properties. The TGA curves of the polymers revealed rel-
atively high thermal stabilities. The 5% weight loss tempera-
tures (Td) of P-2eh, P-Me, and P-2Me were found to be 418,
474, and 483 ꢂC, respectively. DSC curves showed the glass-
transition temperatures (Tg) of P-Me and P-2Me to be 203
and 259 ꢂC. These values were much higher than those of poly-
fluorene derivatives, which are often used as EL materials
(e.g., the Tg of poly(2-(40-(diphenylamino)phenylenevinyl)-
1,4-phenylene-alt-9,9-n-dihexyl fluorene-2,7-diyl) (PDPF) is
reported to be about 159 ꢂC17). Although the thermal stability
is enhanced as the number of methyl groups on the triphenyl-
amine moiety increases, the different substituents (n-hexyl or
2-ethylhexyl group on the phenyl group) and the non-uniform
structure of P-Me may also have an influence on thermal sta-
a) Molecular weight and polydispersity index (D) were
determined by GPC in THF on the basis of polystyrene
standards. b) Glass-transition temperature was measured by
DSC under N2. c) 5% weight loss temperature was measured
by TGA under N2.
bility. High thermal stability of the polymers is important from
the point of view of PLED performance, as this results in a re-
duction in morphological changes, deformation, and degrada-
tion of the emitting compounds by current-induced heat during
the operation of EL devices.27
Optical and Photoluminescence Properties. The photo-
physical properties of P-2eh, P-Me, and P-2Me were deter-
mined by UV–vis and fluorescence spectroscopy in toluene
solution and in thin films, and the resulting spectra are shown
in Figure 1. All polymers had identical absorption spectra in
both toluene and thin film, with P-2eh, P-Me, and P-2Me

1324 Bull. Chem. Soc. Jpn. Vol. 81, No. 10 (2008)
Synthesis and Properties of Substituted Copolymers
Br
1) TiCl4
2) Zn
Ph
CH3
S
S
5
+
S
1,4-dioxane
(52%)
O
H3C
Ph
Ph
Ph
Ph
Br
9
12
13
n-hexyl
I2
Pd2(dba)3
DPPF
air
h
ν
S
S
NaO-t-Bu
CH3
benzene
(70%)
NH
toluene, 90 °C
(83 %)
14
Br
CH3
10
Bu3Sn
SnBu3
n-BuLi
SnBu3Cl
S
S
Pd2(dba)3
DPPF
NaO-t-Bu
THF, 0 °C
Ph
Ph
15
10
+
9
toluene, 90 °C
Scheme 3. Synthesis of precursor 15 for coupling reactions.
(23%)
n-hexyl
Table 2. Absorption Maxima (ꢁmax,abs/nm) and Fluores-
cence Maxima (ꢁmax,em/nm) of P-2eh, P-Me, and P-2Me
Solutiona)
Filmc)
Copolymer
b)
b)
ꢁmax,abs
ꢁmax,em
ꢁmax,abs
ꢁmax,em
H3C
Br
CH3
Br
N
P-2eh
P-Me
P-2Me
405
374
360
460
464
461
406
373
359
505
506
508
CH3 CH3
11
a) Measured in toluene. b) Excited at the absorption maxi-
mum. c) Measured for deposited thin film.
Scheme 2. Synthesis of precursor 11 for coupling reactions.
showing maxima at about 405, 374, and 360 nm, respectively,
which corresponds to ꢀ–ꢀ transitions. P-Me and P-2Me,
Thus, compared with BDT oligomers, the introduction of
triphenylamine moieties can result in partial suppression of
ꢀ-stacking/aggregation of conjugated copolymers in the solid
state.29 The PL spectra of all of the copolymers overlap fully,
which suggests that the emissions from these copolymers are
from the same excited states.
ꢀ
which contained methyl substituents at the TPA site, exhibited
distinct blue-shifts in their absorption maxima in comparison
with the unsubstituted P-2eh. Molecular structure calculations
of model compounds using WinMOPAC (Figure 2) suggest
that the presence of methyl substituents at ortho positions to
the BDT unit on the triphenylamine moiety limits conjugation
of the polymer backbones (Table 2).28
As shown in Figure 1a, the photoluminescence (PL) spectra
of P-2eh, P-Me, and P-2Me in dilute toluene solution were
almost the same, with emission maxima at about 460, 464,
and 461 nm, respectively. These results can be explained by
the stability of the excited states of the copolymers, which
is confirmed by the calculations shown in Figure 2. The PL
spectra of P-Me and P-2Me revealed broader emissions than
those of P-2eh because the methyl substituents in the former
two copolymers resulted in restricted rotation around the
C–C bond between BDT and the phenyl group. Figure 1b
shows the thin-film PL spectra. The fluorescence maxima of
these copolymers exhibited significant red-shifts of about
45 nm on changing from dilute solution to the solid state.
Based on consideration of the calculated structures shown in
Figure 2, these red-shifts can be explained by ꢀ-stacking/
aggregation arising from higher planarity in the excited states.
Electrochemical Properties. In order to evaluate the elec-
trochemical stability of the copolymers, cyclic voltammetry
measurements were carried out at a scan rate of 100 mV sꢁ1
in CH2Cl2, using tetrabutylammonium perchlorate as an
electrolyte. The cyclic voltammograms of P-2eh, P-Me, and
P-2Me are shown in Figure 3, and the electrochemical proper-
ties and HOMO–LUMO energy gaps (Eg) of the copolymers
are summarized in Table 3. The HOMO–LUMO energy gaps
were determined from the absorption edges for solutions of
P-2eh, P-Me, and P-2Me. Although P-Me and P-2Me exhibited
reversible oxidation waves, P-2eh showed an irreversible oxi-
dation process. This result indicates that the oxidation potential
(E1=2ox) increases in conjunction with the number of methyl
substituents on the triphenylamine site. From the cyclic vol-
tammetry measurements (10 cycles), all copolymers, with or
without methyl substituents, were shown to have electrochem-
ical stability. The HOMOs of P-2eh, P-Me, and P-2Me were
estimated to be ꢁ4:98, ꢁ5:18, and ꢁ5:22 eV, respectively.
These values are close to those of the HOMO of PEDOT/

Y. Nishide et al.
Bull. Chem. Soc. Jpn. Vol. 81, No. 10 (2008) 1325
2-ethylhexyl
Pd(PPh3)4,
CuO
N
15
+
4
toluene, reflux
S
S
Ph
Ph
n
P-2eh
Pd(PPh3)4,
CuO
15 + 7 and 8
toluene, reflux
n-hexyl
n-hexyl
n-hexyl
CH3
CH3
H3C
N
CH3
H3C
N
H3C
S
N
S
S
S
S
S
Ph
Ph
Ph
Ph
Ph
Ph
m
n
l
P-Me
n-hexyl
Pd(PPh3)4,
CuO
N
CH3
H3C
S
15
+
11
toluene, reflux
CH3 CH3
S
Ph
Ph
n
P-2Me
Scheme 4. Synthesis of P-2eh, P-Me, and P-2Me.
(a)
(b)
P-2eh
P-Me
P-2eh
P-Me
P-2Me
1
0.8
0.6
0.4
0.2
0
1
1
1
P-2Me
0.8
0.6
0.4
0.2
0
0.8
0.6
0.4
0.2
0
0.8
0.6
0.4
0.2
0
300
350
400
450
500
550
600
300 350 400 450 500 550 600 650
Wavelength / nm
Wavelength / nm
Figure 1. Absorption and photoluminescence spectra of P-2eh, P-Me, and P-2Me (a) in dilute toluene solution; (b) in thin films.

1326 Bull. Chem. Soc. Jpn. Vol. 81, No. 10 (2008)
Synthesis and Properties of Substituted Copolymers
Model Compounds
N
H3C
S
N
CH3
S
S
S
Ground State
(front view)
(front view)
(top view)
(top view)
Excited State
(front view)
(top view)
(front view)
(top view)
Figure 2. Molecular structures of model compounds calculated by WinMOPAC (PM5).
PSS (ꢁ5:0 eV), and thus hole injection from PEDOT/PSS to
these copolymers is expected to be comparatively easy.17
Electroluminescence Properties. Double-layer OLED
of analogous double-layer OLED devices, such as PDPF
(5.0 V).17 The maximum luminances of devices I–III were
213 (at 12.0 V), 1054 (at 8.5 V), and 936 cd mꢁ2 (at 10.5 V),
and their maximum EL efficiencies were 0.025, 0.078, and
0.071 cd Aꢁ1, respectively. The maximum EL efficiencies of
the devices based on P-Me and P-2Me, which contain methyl
substituents, were about 3 times higher than that of P-2eh,
which contains no methyl substituent. This difference is
thought to be due to restriction of ꢀ-stacking/aggregation in
the solid state and a resulting improvement in thermal and
electrochemical stability.
devices (type A) with the configuration ITO/PEDOT:PSS
(40 nm)/copolymer (35 nm)/Ca (30 nm)/Al (100 nm) were
fabricated using P-2eh, P-Me, and P-2Me (devices I–III, re-
spectively). The emission layer was fabricated by spin-coating
from toluene solution (1.0 wt %). The EL spectrum of each co-
polymer exhibited a similar emission to the corresponding
thin-film PL spectrum. The characteristics of the OLEDs are
summarized in Table 4. As shown in Figure 4, the turn-on
voltages of the OLEDs based on P-2eh, P-Me, and P-2Me were
7.0, 4.5, and 6.0 V, respectively, which are similar to those
The EL performances of type A devices I–III were poor,
probably due to a lack of electron-transporting ability. The in-

Y. Nishide et al.
Bull. Chem. Soc. Jpn. Vol. 81, No. 10 (2008) 1327
(a)
(b)
(c)
4.0
1.0
0.8
0.6
0.4
0.2
0
6
4
2
0
3.2
2.4
1.6
0.8
0
-0.8
-1.6
-2.4
-0.2
-0.4
-2
0.25 0.3 0.35 0.4 0.45 0.5 0.55 0.6
Potential / V vs Fc/Fc+
0.1
0.2
0.3
0.4
0.5
0.6
0.7
0.25
0.3
0.35
0.4
0.45
0.5
Potential / V vs Fc/Fc+
Potential / V vs Fc/Fc+
Figure 3. CV curves (10 cycles) of (a) P-2eh, (b) P-Me, and (c) P-2Me at a scan rate of 100 mV sꢁ1 in CH2Cl2 (1:0 ꢃ 10ꢁ4
mol dmꢁ3) with tetrabutylammonium perchlorate (0.1 mol dmꢁ3).
twice as high as that of device II (containing P-Me only).
Table 3. Electrochemical Properties of P-2eh, P-Me, and
This difference is probably due to improvement of the carrier
P-2Me
balance by enhancement of electron-transporting ability.2b
ox a)
1=2
b)
c)
d)
While the addition of an electron-transporting material leads
to enhancement of EL efficiency, it is still probable that in de-
vices I–IV, the injected holes and electrons (mainly the holes)
partially pass through without recombination at the emitting
layer.31 Therefore, a type B multi-layer OLED device with
the configuration ITO/PEDOT:PSS (40 nm)/P-Me (35 nm)/
BCP (30 nm)/Alq3 (30 nm)/LiF (0.5 nm)/Al (100 nm) was
fabricated (device V). The characteristics of this type B OLED
are shown in Table 4. As expected, the introduction of the
hole-blocking BCP layer and the electron-transporting Alq3
layer resulted in improved EL performance. The EL efficiency
of device V was 5 times higher than that of device IV. These
results indicate that the EL efficiency of type B devices is
enhanced by suppression of the carrier passage due to the in-
troduction of a hole-blocking BCP layer and by improvement
of the carrier balance due to the introduction of an electron-
transporting Alq3 layer.
E
EHOMO
/eV
ELUMO
/eV
Eg
/eV
Copolymer
vs. (Fcþ/Fc)/V
P-2eh
P-Me
P-2Me
ox
0.18e)
0.38
ꢁ4:98
ꢁ5:18
ꢁ5:22
ꢁ2:30
ꢁ2:51
ꢁ2:58
2.68
2.67
2.64
0.42
a) E potentials (vs. Fc/Fcþ couple) were determined by cy-
1=2
clic voltammetry in CH2Cl2 (1:0 ꢃ 10ꢁ4 mol dmꢁ3) containing
tetrabutylammonium perchlorate (0.1 mol dmꢁ3) as a support-
ox
1=2
ing electrolyte. b) EHOMO was estimated from E using Fe/
Feþ couple (E ¼ 0:54) as an internal standard. EHOMO
¼
ox
1=2
ox
1=2
ꢁ4:8 ꢁ E . c) ELUMO was calculated approximately by
subtracting Eg from EHOMO. d) Eg was determined from the
optical absorption edge in toluene solution. Eg = 1240/
ox
onset
(wavelength of the absorption edge) (eV). e) E
¼ 0:44).
potential
ox
onset
vs. Fc/Fcþ couple (E
troduction of a triphenylamine moiety enhanced only hole-
transporting ability, and the balance of hole and electron injec-
tion/transport was poor. Therefore, we replaced the emission
layer of the OLED with P-Me containing 10% 2-(4-biphenyl-
yl)-5-(4-t-butylphenyl)-1,3,4-oxadiazole (PBD,2b used as an
electron-transporting material), which was fabricated by spin-
coating from toluene solution (1.0 wt %). The structure of the
resulting double-layer OLED (device IV) was ITO/PEDOT:
PSS (40 nm)/P-Me:PBD (9:1) (35 nm)/Ca (30 nm)/Al (100
nm). The characteristics of this OLED are shown in Table 4.
The maximum luminance was 1848 cd mꢁ2 (at 8.0 V), and
the maximum EL efficiency was 0.14 cd Aꢁ1, which was about
Summary
Benzodithiophene/triphenylamine copolymers P-2eh (with
no methyl substituent) and P-Me and P-2Me (containing
methyl substituents at triphenylamine sites) were synthesized
by Stille coupling reactions. The thermal stability was en-
hanced as the number of methyl groups on the triphenylamine
moiety increased. The absorption spectra in toluene solution
and in thin film suggests that the presence of methyl substitu-
ents at ortho positions to the BDT unit on the triphenylamine
moiety limits conjugation in the polymer backbone, leading to
Table 4. Electroluminescence Properties of Type A and Type B Devices
a)
b)
d)
EL ꢁmax
/nm
Von
/V
Lmax
/cd mꢁ2
Efficiencyc)
/cd Aꢁ1
ꢂex
Device
Copolymer
/%
I (Type A)
II (Type A)
III (Type A)
IV (Type A)
V (Type B)
P-2eh
P-Me
P-2Me
P-Me:PBD (9:1)
P-Me
505
500
500
500
515
7.0
4.5
6.0
5.5
7.5
213 (at 12.0 V)
1054 (at 8.5 V)
936 (at 10.5 V)
1848 (at 8.0 V)
1861 (at 17.0 V)
0.025 (at 9.0 V)
0.078 (at 8.5 V)
0.071 (at 10.0 V)
0.14 (at 8.0 V)
0.71 (at 11.0 V)
0.081
0.027
0.025
0.047
0.20
a) Turn-on voltage: the voltage required for a device to reach a luminance of about 1 cd mꢁ1. b) Luminance at
maximum bias voltage. c) Maximum EL efficiency. d) Maximum external quantum efficiency.30

1328 Bull. Chem. Soc. Jpn. Vol. 81, No. 10 (2008)
Synthesis and Properties of Substituted Copolymers
(a)
(b)
80
1200
1000
800
600
400
200
0
device I
70
device I
device II
device III
device II
device III
60
50
40
30
20
10
0
0
2
4
6
8
10
12
14
0
2
4
6
8
10
12
14
Voltage / V
Voltage / V
Figure 4. (a) Current density–voltage and (b) luminance–voltage characteristics of devices I–III.
a HSV-100 instrumenꢁt (Hokuto Denko) in dichloromethane con-
a blue shift in the absorption maximum. The PL spectra of all
three copolymers in toluene solution and in thin film overlap-
ped fully, which indicated that the emissions from these co-
polymers were from the same excited states. Although P-Me
and P-2Me exhibited reversible oxidation waves in cyclic
voltammetry measurements, P-2eh showed an irreversible
oxidation process. The maximum EL efficiencies of devices
based on P-Me and P-2Me were about 3 times higher than that
of P-2eh, because the presence of methyl substituents resulted
in restriction of ꢀ-stacking/aggregation of the conjugated
copolymers in the solid state and improvement of the thermal
and electrochemical stability.
taining n-Bu4NþClO4 (0.1 mol dmꢁ3) as a supporting electrolyte
at a scan rate of 100 mV sꢁ1. The counter and working electrodes
were made from Pt, and the reference electrode was Ag/AgCl.
The organic layers of the EL devices were prepared by spin
coating from toluene. The devices were tested in air under ambi-
ent conditions with no encapsulation. EL spectra, device luminan-
ces, and current–voltage characteristics were recorded by combin-
ing a BM-9 luminance meter (Topcon) and a Photal MCPD-7000
(Otsuka Electronics).
4-Bromotriphenylamine (2). To a stirred solution of triphen-
ylamine (5.00 g, 20.4 mmol) in dry CH2Cl2 (80 mL) was added
NBS (3.63 g, 20.4 mmol) and the mixture was stirred at room
temperature for 2 h. Aqueous Na2S2O3 and NaHCO3 were then
added and the organic layer was separated. The crude product
was purified by silica gel column chromatography (hexane), and
the resulting material was recrystallized from ethanol to give 2
(4.59 g, 69%) as a white solid. Mp 115–116 ꢂC; 1H NMR (300
MHz, CDCl3): ꢃ 6.94 (2H, d, J ¼ 8:7 Hz), 7.03 (2H, t, J ¼
7:5 Hz), 7.06 (4H, d, J ¼ 7:8 Hz), 7.25 (4H, dt, J ¼ 1:5, 7.8 Hz),
7.31 (2H, d, J ¼ 8:7 Hz); 13C NMR (75 MHz, CDCl3): ꢃ 114.7,
123.2, 124.4, 125.1, 129.3, 132.1, 147.4; IR (KBr) 1486, 1334,
1284, 1073, 1003, 824 cmꢁ1; Anal. Found: C, 66.48; H, 4.56; N,
4.31%. Calcd for C18H14BrN: C, 66.68; H, 4.35; N, 4.32%.
4-(2-Ethylhexyl)triphenylamine (3). To a stirred solution of
2 (3.00 g, 9.25 mmol) and NiCl2(dppp) (0.10 g, 0.19 mmol) in
ether (70 mL) was added a stirred suspension of 2-ethylhexylmag-
nesium bromide [9.25 mmol, prepared from Mg (0.47 g, 19.4
mmol) and 1-bromo-2-ethylhexane (3.29 mL, 0.19 mmol) in 30
mL of ether] at 0 ꢂC. The reaction mixture was allowed to warm
to room temperature over 1.5 h, followed by refluxing for 3 h. The
crude product was purified by silica gel column chromatography
(hexane) to give 3 (1.52 g, 46%) as a colorless oil. 1H NMR
(300 MHz, CDCl3): ꢃ 0.88 (6H, t, J ¼ 7:3 Hz), 1.25–1.35 (9H,
m), 2.48 (2H, d, J ¼ 6:9 Hz), 6.96 (2H, d, J ¼ 7:3 Hz), 7.01
(2H, t, J ¼ 6:9 Hz), 7.06 (4H, dd, J ¼ 1:2, 8.4 Hz), 7.22 (4H, dt,
J ¼ 1:2, 8.4 Hz), 7.26 (2H, d, J ¼ 7:3 Hz); 13C NMR (75 MHz,
CDCl3): ꢃ 10.8, 14.1, 23.1, 25.5, 28.9, 32.3, 39.5, 41.1, 122.2,
123.7, 124.5, 129.1, 129.9, 136.7, 145.3, 148.1; IR (Si) 3031,
2923, 2861, 1589, 1496, 1280, 836, 752, 698 cmꢁ1; Anal. Found:
C, 87.51; H, 8.78; N, 4.07%. Calcd for C26H31N: C, 87.34; H,
8.74; N, 3.92%.
Experimental
All reactions were carried out under an atmosphere of argon
unless otherwise noted. Anhydrous THF was purchased from
Kanto Chemical Co. and used without further purification. Di-
chloromethane was distilled from calcium hydride and stored over
˚
4 A molecular sieves. Toluene was distilled from sodium and stor-
˚
ed over 4 A molecular sieves. A hexane solution of butyllithium
(Kanto Chemical Co.) was titrated using diphenylacetic acid.
Melting points were determined using a Yanako MP-S3 hot stage
apparatus and were not corrected. Thin layer chromatography was
performed using Merck precoated silica gel sheets 60 F254. Silica
gel (Fuji Silysia PSQ100B) was used for column chromatography.
NMR spectra were obtained using a JNM-AL 300 FT NMR
(300 MHz) or JNM-ECA 400 FT NMR (400 MHz) spectrometer
in CDCl3 solution with tetramethylsilane as an internal standard.
The molecular weights and polydispersity indices of the copoly-
mers were determined by gel permeation chromatography
(GPC) analysis relative to a polystyrene standard using GPC col-
umns (TSKgel MultiporeHXL-M, TOSOH) using THF as an eluent
at 40 ꢂC. The 5% weight loss temperatures were determined using
a TG/DTA6200 instrument (SII NanoTechnology), and the glass-
transition temperatures were determined using a DSC6200 instru-
ment (SII NanoTechnology). IR spectra were recorded on a
FT/IR-420 Fourier transform infrared spectrometer (JASCO).
Elemental analysis was performed using a JM10 Micro Corder
(J-Science Lab). UV spectra were recorded on a V-530 instrument
(JASCO). Photoluminescence spectra were recorded on a FP-6200
instrument (JASCO). Cyclic voltammograms were recorded using

Y. Nishide et al.
Bull. Chem. Soc. Jpn. Vol. 81, No. 10 (2008) 1329
4,40-Dibromo-400-(2-ethylhexyl)triphenylamine (4). To a
stirred solution of 3 (0.33 g, 0.93 mmol) in dry CH2Cl2 (20 mL)
was added NBS (0.36 g, 2.05 mmol) and the mixture was stirred
at room temperature for 3 h. The crude product was purified by
silica gel column chromatography (hexane) to give 4 (0.47 g,
99%) as a colorless oil. 1H NMR (300 MHz, CDCl3): ꢃ 0.88
(6H, t, J ¼ 7:2 Hz), 1.25–1.35 (9H, m), 2.48 (2H, d, J ¼ 6:9
Hz), 6.90 (4H, d, J ¼ 9:0 Hz), 6.95 (2H, d, J ¼ 8:7 Hz), 7.04
(2H, d, J ¼ 8:7 Hz), 7.30 (4H, d, J ¼ 9:0 Hz); 13C NMR (75
MHz, CDCl3): ꢃ 10.8, 14.1, 23.0, 25.5, 28.8, 32.3, 39.5, 41.0,
114.9, 124.8, 125.0, 130.3, 132.2, 137.9, 144.3, 146.7; IR (Si)
2959, 2925, 2857, 1485, 1310, 1284, 1071, 1007, 820 cmꢁ1; Anal.
Found: C, 60.77; H, 5.95; N, 2.60%. Calcd for C26H29Br2N: C,
60.60; H, 5.67; N, 2.72%.
(hexane) to give 14 (3.42 g, 70%) as white crystals. Mp 177–
178 ꢂC; 1H NMR (300 MHz, CDCl3): ꢃ 7.25–7.37 (m, 10H),
7.55 (2H, d, J ¼ 5:6 Hz), 7.79 (2H, d, J ¼ 5:6 Hz); 13C NMR
(75 MHz, CDCl3): ꢃ 122.1, 127.2, 127.3, 128.1, 130.2, 131.3,
133.65, 139.2, 139.4; IR (KBr) 3056, 1758, 1442, 849,
666 cmꢁ1; Anal. Found: C, 77.10; H, 4.08%. Calcd for C22H14S2:
C, 77.15; H, 4.12%.
4,5-Diphenyl-2,7-bis(tributylstannyl)benzo[1,2-b:4,3-b0]dithio-
phene (15). To a stirred solution of 14 (0.20 g, 0.58 mmol) in
THF (4 mL) was added butyllithium (1.45 mmol, 0.96 mL of 1.5
mol dmꢁ3 hexane solution) at 0 ꢂC, and the mixture was
stirred for 1.5 h. To the resulting brown solution was added tri-
butylstannyl chloride (0.44 mL, 1.62 mmol) at 0 ꢂC, and the reac-
tion mixture was stirred for 3 h. The mixture was filtered through
a celite pad, the filtrate was concentrated, and the residue was
dried in vacuo to give 15 (crude) as light yellow oil. The crude
product 15 was used for the subsequent reaction without further
purification.
P-2eh. To a stirred solution of dibromide 4 (0.10 g, 0.19
mmol) and stannyl compound 15 (0.26 g, 0.28 mmol) in toluene
(3 mL) were added Pd(PPh3)4 (13.2 mg, 0.0114 mmol) and CuO
(33.2 mg, 0.42 mmol), and the mixture was refluxed for 24 h. After
cooling, the reaction was filtrated through a celite pad. The crude
product was dissolved in a small amount of chloroform and pour-
ed into 500 mL of methanol. The resulting precipitate was collect-
ed by filtration, washed with methanol, and dried in vacuo to give
P-2eh as a yellow solid. 1H NMR (300 MHz, CDCl3): ꢃ 0.79–0.92
(6H, m), 1.15–1.38 (9H, m), 2.43–2.55 (2H, m), 7.00–7.14 (8H,
m), 7.19–7.38 (14H, m), 7.55–7.64 (1H, m), 7.84–7.92 (1H, m);
IR (KBr) 3028, 2923, 1599, 1492, 1321, 1286, 1182, 1119,
699 cmꢁ1; Anal. Found: C, 80.79; H, 6.02; N, 1.82%.
P-Me. To a stirred solution of dibromides 7 and 8 (0.10 g,
0.19 mmol) and stannyl compound 15 (0.26 g, 0.28 mmol) in
toluene (2 mL) were added Pd(PPh3)4 (13.2 mg, 0.0114 mmol)
and CuO (33.2 mg, 0.42 mmol), and the mixture was refluxed
for 24 h. After cooling, the reaction was filtered through a
celite pad. The crude product was dissolved in a small amount
of chloroform and poured into 500 mL of methanol. The resulting
precipitate was collected by filtration, washed with methanol, and
dried in vacuo to give P-Me as a yellow solid. 1H NMR (300 MHz,
CDCl3): ꢃ 0.86–0.92 (3H, m), 1.24–1.39 (6H, m), 1.58–1.67 (2H,
m), 2.08 (1H, s), 2.41–2.46 (5H, m), 2.53–2.62 (2H, m), 6.93–7.12
(6H, m), 7.23–7.40 (14H, m), 7.53–7.81 (2H, m); IR (KBr) 3022,
2923, 1598, 1483, 1320, 1259, 1119, 1031, 698 cmꢁ1; Anal.
Found: C, 81.07; H, 5.40; N, 1.13%.
Triarylamine Mixture 7 and 8. To a stirred solution of
Pd2(dba)3 (54.9 mg, 0.06 mmol) and DPPF (55.5 mg, 0.10 mmol)
in toluene (6 mL) was added 2,5-dibromotoluene (0.58 mL, 4.20
mmol) at room temperature, and the resulting mixture was stirred
for 10 min. NaO-t-Bu (0.48 g, 5.00 mmol) and 4-hexylaniline
(0.39 mL, 2.0 mmol) were then added to the solution and the
mixture was stirred at 90 ꢂC for 24 h. The crude product was
purified by alumina column chromatography (40:1 hexane–ethyl
1
acetate) to give 7 and 8 (0.48 g, 47%, 1.5:1 from H NMR) as a
colorless oil. IR (Si) 3023, 2923, 2857, 1589, 1477, 1311, 1261,
1025, 813 cmꢁ1; Anal. Found: C, 60.51; H, 5.91; N, 2.75%. Calcd
for C26H29Br2N: C, 60.60; H, 5.67; N, 2.72%.
N-(4-Bromo-2,5-dimethylphenyl)-4-hexylaniline (10). To a
stirred solution of Pd2(dba)3 (65 mg, 0.07 mmol) and DPPF
(66 mg, 0.12 mmol) in toluene (8 mL) was added 2,5-dibromo-p-
xylene (1.5 g, 5.7 mmol) at room temperature, and the resulting
mixture was stirred for 10 min. NaO-t-Bu (0.57 g, 5.9 mmol)
and 4-hexylaniline (0.46 mL, 2.4 mmol) were then added to the
solution and the mixture was stirred at 90 ꢂC for 24 h. The crude
product was purified by silica gel column chromatography
(20:1, hexane–ethyl acetate) to give 10 (0.71 g, 83%) as a
wine-red oil. 1H NMR (300 MHz, CDCl3): ꢃ 0.89 (3H, t, J ¼
6:9 Hz), 1.26–1.37 (6H, m), 1.55–1.64 (2H, m), 2.18 (3H, s),
2.28 (3H, s), 2.55 (2H, t, J ¼ 7:9 Hz), 5.21 (1H, s), 6.90 (2H, d,
J ¼ 8:4 Hz), 7.03 (1H, s), 7.09 (2H, d, J ¼ 8:4 Hz), 7.30 (1H,
s); IR (Si) 2926, 2855, 1607, 1562, 1515, 1389, 1312, 1265,
971 cmꢁ1
.
N,N-Bis(4-bromo-2,5-dimethylphenyl)-4-hexylaniline (11).
To a stirred solution of Pd2(dba)3 (54 mg, 0.06 mmol) and DPPF
(55 mg, 0.10 mmol) in toluene (5 mL) was added 2,5-dibromo-p-
xylene (2.1 g, 7.9 mmol) at room temperature, and the resulting
mixture was stirred for 10 min. NaO-t-Bu (0.38 g, 3.9 mmol)
and 10 (0.71 g, 2.0 mmol) were then added to the solution and
the mixture was stirred at 90 ꢂC for 3 days. The crude product
was purified by silica gel column chromatography (hexane) to
give 11 (0.25 g, 23%) as a colorless oil. 1H NMR (300 MHz,
CDCl3): ꢃ 0.85–0.90 (3H, m), 1.27–1.34 (6H, m), 1.55–1.63
(2H, m), 1.89 (6H, s), 2.25 (6H, s), 2.52 (2H, t, J ¼ 7:5 Hz),
6.58 (2H, d, J ¼ 8:4 Hz), 6.76 (2H, s), 6.96 (2H, d, J ¼ 8:4 Hz),
P-2Me. To a stirred solution of dibromide 11 (70 mg, 0.13
mmol) and stannyl compound 15 (0.15 mmol) in toluene
(1.5 mL) were added Pd(PPh3)4 (9.0 mg, 0.0077 mmol) and CuO
(23 mg, 0.28 mmol), and the mixture was refluxed for 2 d. After
cooling, the reaction was filtrated through a celite pad. The
crude product was dissolved in a small amount of chloroform and
poured into 500 mL of methanol. The resulting precipitate was
collected by filtration, washed with methanol, and dried in vacuo
to give P-2Me as a yellow solid. 1H NMR (400 MHz, CDCl3):
ꢃ 0.84–0.91 (3H, m), 1.26–1.36 (6H, m), 1.55–1.64 (2H, m),
1.96 (6H, s), 2.41 (6H, s), 2.49–2.57 (2H, m), 6.70 (2H, d, J ¼
7:5 Hz), 6.87 (2H, s), 7.00 (2H, d, J ¼ 7:5 Hz), 7.22–7.42 (12H,
m), 7.69–7.78 (2H, m); IR (KBr) 3022, 2923, 1601, 1493, 1320,
1119, 699 cmꢁ1; Anal. Found: C, 82.16; H, 5.84; N, 1.36%.
7.33 (2H, s); IR (Si) 2924, 2856, 1718, 1363, 1222, 977 cmꢁ1
.
4,5-Diphenylbenzo[1,2-b:4,3-b0]dithiophene (14). A stirred
solution of 13 (5.00 g, 14.52 mmol) and iodine (0.07 g, 0.28 mmol)
in benzene (1600 mL) was irradiated with a high-pressure mercury
lamp under air for 12 h at room temperature. The reaction mixture
was then washed with aqueous Na2S2O3, concentrated, and fil-
tered through a celite pad. The filtrate was washed with water
and brine, dried over Na2SO4, and concentrated. The crude prod-
uct was purified by alumina and silica gel column chromatography
This work was partly supported by the Wakayama City Area
Program.

1330 Bull. Chem. Soc. Jpn. Vol. 81, No. 10 (2008)
Synthesis and Properties of Substituted Copolymers
14 Y. Shirota, Y. Kuwabara, H. Inada, T. Wakimoto, H.
Nakada, Y. Yonemoto, S. Kawami, K. Imai, Appl. Phys. Lett.
1994, 65, 807.
15 N. Tamoto, C. Adachi, K. Nagai, Chem. Mater. 1997, 9,
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