Thermal and spectral stability of electroluminescent hyperbranched copolymers containing tetraphenylthiophene-quinoline-triphenylamine moieties

Article abstract of DOI:10.1002/pola.25020

Fluorescent hyperbranched copolymers (HB-x, x = 1-4) with inherent tetraphenylthiophene, triphenylamine (TPA) and quinoline (Qu) moieties were prepared to study the influence of the TPA branching point on the thermal and the spectral stability. All the HB

Full text of DOI:10.1002/pola.25020

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Thermal and Spectral Stability of Electroluminescent Hyperbranched
Copolymers Containing Tetraphenylthiophene-Quinoline-Triphenylamine
Moieties
Ya-Ting Tsai,1 Chung-Tin Lai,1 Rong-Hong Chien,1 Jin-Long Hong,1 An-Chi Yeh2
1Department of Materials and Optoelectronic Science, National Sun Yat-Sen University, Kaohsiung 80424, Taiwan
2Department of Chemical Engineering, Chengshu Institute of Technology, Kaohsiung 80424, Taiwan
Correspondence to: J.-L. Hong (E-mail: jlhong@mail.nsysu.edu.tw) or A.-C. Yeh (E-mail: acyeh@csu.edu.tw)
Received 20 July 2011; accepted 30 August 2011; published online 14 October 2011
DOI: 10.1002/pola.25020
ABSTRACT: Fluorescent hyperbranched copolymers (HB-x, x ¼
1–4) with inherent tetraphenylthiophene, triphenylamine (TPA)
and quinoline (Qu) moieties were prepared to study the influ-
ence of the TPA branching point on the thermal and the spec-
tral stability. All the HB-x copolymers exhibited high glass
transition temperatures (Tgs ¼ 245–315 ꢀC) with the detected
values increasing with the increasing branching TPA content in
the HB-x. The solid HB-x films possess high emission efficiency
with the resulting quantum yields (UFs) in the ranges of 0.72–
0.74. More importantly, the HB-x copolymers and the derived
light-emitting devices exhibit high photoluminescence (PL) and
electroluminescence (EL) stability towards thermal annealing at
temperatures higher than 200 ꢀC. After annealing at 200 ꢀC (or
300 ꢀC), no change was observed in the respective PL and EL
spectra of HB-1 (or HB-4) copolymers. The spectral stability
was found to correlate with Tg and with the highest branching
density, HB-4 copolymer possesses the highest thermal stabil-
ity among all HB-xs and show no EL spectral change after
annealing at 300 ꢀC for 4 h. The results indicate that all the
branched HB-x copolymers are promising candidates for the
polymer light-emitting diodes due to their high quantum yield
C
V
and spectral stability.
2011 Wiley Periodicals, Inc. J Polym
Sci Part A: Polym Chem 50: 237–249, 2012
KEYWORDS: branching density; fluorescence; high temperature
materials; hyperbranched; hyperbranched copolymer, quino-
line; tetraphenylthiophene; thermal and spectral stability;
triphenylamine
INTRODUCTION Hyperbranched electroluminescent (EL)
polymers have attracted considerable interest over the past
decade due to their unique three-dimensional (3D) structure
in similarity to dendrimers, comparatively convenient one-
step preparation procedure, good solubility, low melt and
solution viscosity, and excellent physical and chemical prop-
erties in contrast to linear polymers.1 To demonstrate, a
number of hyperbranched conjugated polymers have been
synthesized and characterized to be good electron-transfer
and emitter materials.2 The 3D structures of hyperbranched
polymers also help in reducing the aggregation of the conju-
gated polymer chains and in some cases, it improves their
emission efficiency and thermal stability.3
photovoltaic devices9 and to bipolar charge transport materi-
als for light-emitting diodes (LEDs).10 As the widely-used elec-
tron-donating (e-donating) moieties, thiophene, oligothio-
phenes, and the derivatives4–7 had been incorporated with e-
deficient heterocyclic quinoxaline, anthrazoline, and quinoline
(Qu) rings7 to construct donor–acceptor conjugated polymers
for LED applications. To utilize this well-known property, we
prepared new donor–acceptor alternate copolymers11 with e-
donating tetraphenylthiophene (TP) connected to electro-
accepting Qu moieties recently. The construction unit of TP
moiety11 has the structural feature of alternate phenyl and
thiophene rings and with the rigid TP-Qu framework, the
alternate copolymer of poly 6-(3,4-diphenyl-5-(4-phenylquino-
lin-6-yl)thiophen-2-yl)-2,4-diphenylquinoline (PTPQu) (Fig. 1)
has high glass transition temperatures (Tg ¼ 245 ꢀC), good
solubility in common organic solvents, good film quantum
yield (UF ¼ 0.59) and most importantly, its photoluminescent
(PL) and EL spectra are quite stable without any emission
Conjugated polymers with donor–acceptor architectures are
interesting because that the inherent charge transfer can facil-
itate ready manipulation of the electronic structure (highest
occupied molecular orbital (HOMO)/lowest unoccupied molec-
ular orbital (LUMO) levels), leading to small band gap semi-
conducting polymers.4–8 Through design and synthesis of new
architectures, donor–acceptor conjugated polymers can be
applied to photoinduced charge transfer and separation for
ꢀ
reduction after annealed at a high temperatures of 250 C.
Encouraged by the good properties of the alternate PTPQu
copolymers, we further attempted to incorporate this
Additional Supporting Information may be found in the online version of this article.
C
V
2011 Wiley Periodicals, Inc.
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FIGURE 1 Chemical structures of PTPQu, HB-x copolymers and DTBD and TDA model compounds.
structural unit of PTPQu into hyperbranched framework. To
exercise this idea, triphenylamine-quinoline was used as the
branching point of the HB-x (x ¼ 1–4) copolymers (Fig. 1)
and with the designed archetecture, the e-donating triphenyl-
amine (TPA), TP units were separated by the e-accepting Qu
unit. Besides the study on the HB-x copolymers, small-mass
model compounds of DTBD and TDA with the respective TPA
and TP structural units were also prepared and character-
ized in this study. With the wholly aromatic-heterocyclic
structures, the resultant HB-x copolymers are rigid materials
with high thermal transitions and stabilities. In addition, the
multiple phenyl pendant rings originated from the TP moiety
inherited good solubility of the copolymers in common or-
ganic solvents, which is essential for the easy fabrication of
LED device. Polymer synthesis and identifications, property
characterizations, the PL and EL properties, and their corre-
sponding thermal and spectral stability were also investi-
gated in this study.
quinoline linkages in the model compounds of TDA and
DTBD compounds (Scheme 1) and in the hyperbranched
copolymers of HB-x (Scheme 2). Primarily, the TPA-Pm and
TP-Pm compounds with the built-in o-aminoketone function
attached to the respective TP and TPA units were synthe-
sized. Previously, Stille12 had pointed out that the most
versatile and useful method for synthesizing o-aminoketones
is a route via the generation of benzisoxazole from an aro-
matic nitro compound, followed by reductive cleavage of the
benzisoxazole. To conduct the Stille synthesis process, the
nitrated compounds of TP-NO2 and TPA-NO2 were primarily
prepared as the starting materials. The nitrated TP-NO2
(or TPA-NO2) compound was then reacted with benzyl nitrile
to generate TP-Bz (or TPA-Bz) with the inherent benzisoxa-
zole rings, which was then under reduction cleavage by iron
to obtain the desired TP-Pm (or TPA-Pm) monomer. As
shown in Scheme 1, the Friedla¨nder condensations between
TPA-Pm (or TP-Pm) and acetophenone generated the model
TDA (or DTBD) compound. Analogously, the desired HB-x
copolymers were obtained by the Friedla¨nder condensations
among TPA-Pm, TP-Pm, and 1,4-diacetylbenzene (DB) mono-
mers (Scheme 2). Altogether, four HB-x copolymers were
prepared according to the monomer molar fractions listed in
Table 1.
RESULTS AND DISCUSSION
Synthesis and Basic Characterizations
The Friedla¨nder condensation between o-aminoketone and
acetyl functions is the main reaction used to construct the
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SCHEME 1 Syntheses of o-aminoketo monomers of TPA-Pm and TP-Pm and model compounds of TDA and DTBD.
Chemical structures of all organic intermediates were con-
firmed from the corresponding NMR (Fig. S1–S5, Supporting
Information), FTIR spectra and the elemental analysis
(included in Experimental section). The completeness of the
Friedla¨nder reaction is the key for the successful polymer
preparations. The 1H NMR spectra (Fig. S6–S9, Supporting
Information) suggest that the strong methyl resonances of
the acetyl (ACOCH3) group of DB at 2.5 ppm was absent in
the HB-x products. The completeness of the Friedla¨nder
reaction can be also confirmed from the FTIR spectra, that
is, the characteristic C¼¼O stretching (at 1,676 cmꢁ1) of DB
and the free and the hydrogen-bonded N-H stretchings (at
1
SCHEME 2 Friedlander condensations of TPA-Pm, TP-Pm with 1,4- diaceylbenzene (DB) to afford the HB-x copolymers.
¨
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TABLE 1 Feed Molar Ratio of the Monomers in Comparison to the Resultant Molar Ratios Found in the HB-x Copolymers and the
Molecular Weight Analysis from GPC and Mass Spectroscopy
nTPA
nTP
nDB
Mass Spectroscopyb
GPCc
a
a
a
Branched
Polymers
Feed
Found
Feed
Found
Feed
Found
Mn
Mw
MWD
Mn
Mw
PDI
HB-1
HB-2
HB-3
HB-4
a
0.024
0.031
0.035
0.041
0.024
0.033
0.038
0.045
0.471
0.462
0.456
0.449
0.454
0.450
0.449
0.441
0.505
0.507
0.509
0.510
0.522
0.517
0.513
0.512
c
13,320
11,894
12,903
10,984
13,800
12,493
13,384
11,650
1.036
1.050
1.037
1.061
9,600
7,700
4,600
4,000
22,000
16,000
7,100
2.1
1.5
1.5
2.2
5,800
nTPA, nTP, nDB refer to the respective molar fractions of TPA, TP and
DB units incorporated in the HB-x, calculated from elemental analysis.
Mn, Mw, and MWD were determined by gel permeation chromatogra-
phy using polystyrene standards and THF as eluent.
b
Number- (Mn) and Weight- (Mw) and molecular weight distribution
(MWD) were determined from the MALDI-TOF spectrometry.
3460 and 3343 cmꢁ1, respectively) of TPA-Pm and TP-Pm
were no longer observed in the spectra of HB-x (Fig. S10
and S11, Supporting Information). Results from 13C NMR
spectra give further support for the successful syntheses of
the polymers.
larger diameters, which can be clearly viewed from the
eluting curves shown in Figure 2.
With the wholly aromatic-quinoline structure, the hyper-
branched HB-x copolymers are supposed to have rigid chains
with limited segmental mobility and indeed, all HB-x copoly-
mers exhibit high glass transition temperature (Tg, lower
curves in Fig. 3) with the detected values closely correlated
to the density of the branching point. With the highest con-
tent of branching point, HB-4 has the highest Tg at 315 ꢀC,
which is 70 ꢀC higher than that of HB-1 with the lowest
branching density. The built-in branching unit thus imposes
restraint for segmental mobility and consequently elevates
the glass transition. Thermal stability of the polymers was
also evaluated by thermogravimetric analyses (TGA). All
four polymers have the initial wꢀeight-loss temperature at
Primary attempt to evaluate the composition of HB-x by the
1H NMR was unsuccessful due to the serious overlaps of the
aromatic resonance peaks at 6.9 ꢂ8.2 ppm. Nevertheless,
reliable results can be obtained from the elemental analysis
on the corresponding S, N, C, and H contents. The results
listed in Table 1 are correlated well with the feed ratios
used in the polymerization step: the molar ratios of
TPA:TP:DB units in HB-1, HB-2, HB-3, and HB-4 are esti-
mated to be (0.024:0.454:0.522), (0.033:0.45:0.517),
(0.038:0.449:0.513), and (0.045:0.441:0.512). The molar
fractions of aromatic triphenylamine (nTPA) branching point
in HB-1, 2, 3, and 4 can be thus evaluated to be 0.024,
0.033, 0.038, and 0.045, respectively. The estimated molar
percents are close to the feed ones (0.024–0.041%). The
results suggested that the branching density in HB-x progres-
sively increases from HB-1 to HB-4. The overall molecular
weight results determined from the MALDI/TOF mass spec-
trometry do not show much differences on the number- (Mn;
from 10,984 to 13,320) and the weight- (Mw; from 11,650 to
13,800) average molecular weights. Although there are little
difference (0.024–0.041) on the resultant molecular weight
and the branching density, the HB-x copolymers do show
large variations on the thermal transition and stability as we
will discuss later.
ꢀ
ꢂ520 C and after heating to 800 C, more than 60 wt % of
residues still remained. The higher the branching density,
ꢀ
the more the residues remained after heating to 800 C. The
high onset decomposition temperatures suggest that all the
HB-x copolymers are thermally stable.
Despite the inherent rigid aromatic-quinoline chain seg-
ments, the HB-x copolymers are readily soluble in common
organic solvents such as chloroform, toluene, tetrahydrofuran
(THF), and dimethylformamide (DMF). The multiple phenyl
The branching density of HB-x did affect the analysis results
from gel permeation chromatography (GPC). The Mn and Mw
of HB1-HB4 are in the ranges of 4000–9600 and 5800–
22,000 (Table 1), respectively, with polydispersity indexes
(PDI) lying in the ranges of 1.5 and 2.2. As we know, the
GPC analysis is actually based on polymer’s size in solution.
The molecular weights of all HB-x copolymers (see Table 1,
results from the MALDI/TOF mass spectrometry) are approx-
imately the same but the branching density determines the
polymer dimension in solution. With increasing branching
density, polymer chains are smaller in sizes when dispersed
in solution. With smaller dimensions, chains of HB-4 polymer
tend to be eluted at earlier time than the other samples with
FIGURE 2 GPC elution curves of the HB-x copolymers (eluting
rate ¼ 0.6 mL/min, eluent: THF).
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and emission spectra of the model TDA, DTBD compounds
and the TDA/DTBD (in 1/1 molar ratio) mixtures. Solution of
model TDA compound absorbs at wavelength (peak at 405
nm) comparatively longer than that (at 368 nm) of the DTBD
solution [Fig. 4(B)]. Emission spectra of TDA and DTBD are
virtually different. In contrast to the two-band pattern
observed for the DTBD, TDA emitted with single band cen-
tered at the same position (ꢂ489 nm) with that of HB-x. With
its absorption well-overlapped with the emissions of DTBD,
TDA compound is supposed to be capable to re-absorb the
light emitted by DTBD; thus, the emission of the DTBD/TDA
solution mixtures is solely from the TDA component, leading
to the observed single emission band at the same position
(489 nm) with those of TDA and HB-x copolymers. Sugges-
tively, energy transfer from the TP- to the TPA-rich units pro-
ceeded efficiently, leading to the same emission spectra [Fig.
4(A)] for all HB-x copolymers of different branching densities.
FIGURE 3 TGA and DSC thermograms of HB-x copolymers
with a heating rate of 20 ꢀC/min.
The HB-x copolymers are materials with high emission effi-
ciency. The solution and film quantum yields (UFs) were
measured and summarized in Table 2. Solutions of HB-x in
THF (0.1 mg/mL) have high UF values of 0.73–0.74. The
efficient energy transfer from the TP- to the TPA-rich units
contributes to the same emission efficiency for all copoly-
mers. The efficient energy transfer process is also prevalent
in the solid films as judged by the close UF values (0.68–
0.72) of the film samples.
pendant groups of the TP moiety and the large interchain
space introduced by the branched framework render large
interchain volumes, which allow the easy penetrations of for-
eign solvent molecules when applied, resulting in the easy
dissolutions of the HB-x copolymers. With good solubility for
the copolymers, THF was selected as the solvent to prepare
and cast the film samples for spectroscopic study and for
devices application. The good solubility and the high thermal
stability of the HB-x copolymers make them ideal candidates
for LED devices.
The electrochemical behavior of the hyperbranched polymers
was investigated by cyclic voltammetry (CV) conducted by
film cast on an ITO substrate as the working electrode in
dry CH3CN containing 0.1 M of tetrabutylammonium hexa-
fluorophosphate (TBAH) as electrolyte under nitrogen
atmosphere. The typical cyclic voltammograms for all HB-x
are shown in Figure 5 for comparison. As illustrated by
the summarized data in Table 2, the reversible oxidation re-
dox of HB1-HB4 couples at Eox/onset values of 1.22–0.89 V.
The e-donating TPA branching point seems to be the struc-
tural units most susceptible to be electrochemically oxidized
as judged by the progressive decrease of the Eox/onset values
Optical and Electrochemical properties
The UV-vis absorption and the PL emission spectra of HB1-
HB4 in the dilute solution state (0.1 mg/mL) are compared in
Figure 4(A). All HB-x copolymers exhibited similar absorption
pattern with the peak maxima centered at the same position
of 392 nm. Despite the difference on the branching density,
the four HB-x copolymer solutions emitted at the same posi-
tion and with the same intensity. The same PL emission
behavior can be clarified by studying the solution absorption
FIGURE 4 Solution absorption and emission spectra of (A) HB-x copolymer and (B) TDA, DTBD model compounds and their equal
molar mixtures of TDA/DTBD (excited at 350 nm).
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TABLE 2 Optical and electrochemical properties of the hyperbranched HB-x colymers
Oxidation (V; vs Ag/Agþ
in CH3CN)
Solution k (nm)a
Film k (nm)
opt
Abs
PL
Maxb
Abs
Abs
PL
Maxb
Eg
Eox/onset
HOMO
(eV)f
LUMO
(eV)f
(eV)d
(V)
c
Polymer
Max
UF
Max
Onset
UF
HB-1
HB-2
HB-3
HB-4
a
392
392
392
392
497
497
497
497
0.73
0.74
0.74
0.74
392
392
392
392
453
452
449
445
498
498
498
498
e
0.68
0.71
0.72
0.72
2.74
2.74
2.76
2.79
1.22
1.04
0.97
0.89
ꢁ5.6
ꢁ2.86
ꢁ2.68
ꢁ2.59
ꢁ2.48
ꢁ5.42
ꢁ5.35
ꢁ5.27
Polymer solution in THF (concentration¼ 0.1 mg/mL).
The oxidation potential versus Ag/Agþ calculated from CV spectrum
b
c
Excited at 350 nm.
using ferrocene as internal standard.
f
Fluorescence quantum yields (UF) values of the samples in dilute THF
Calculated from the equation HOMO ¼ ꢁ(Eox/onset ꢁ EFc/onset) ꢁ 4.8,
solution were measured in an integrating sphere with a quinine sulfate
LUMO ¼ HOMO þ band gap.
standard (10ꢁ5 M in 0.1 N H2SO4, UF ¼ 0.55).
d
Calculated from UV absorption spectrum of polymer films by the
equation: band gap ¼ 1240/kabs (onset)
.
from 1.22 V for HB-1 to 1.04 V for HB-2, to 0.97 V for HB-3
and then to the lowest value of 0.89 V for HB-4.
Since all copolymers have the same on-set decomposition
temperature (cf. TGA in Fig. 3), the varied spectral stability
of HB1-HB4 should not be due to chemical decomposition
but rather, morphological variation during high-tempera-
ture annealing may be the plausible reason leading to the
observed emission reduction. To demonstrate, optical micros-
copy (OM) was used to evaluate the morphological variations
of the HB-1 and HB-4 films during thermal annealing at the
respective 270 and 320 ꢀC for 1 h (Fig. 7). Before anneal-
ing, both films [Fig. 7(A,B)] are homogenous in appearance
without noticeable unevenness on the surfaces; in con-
trast, lots of heterogeneous blocks formed after annealing
[Fig. 7(C,D)]. When heating at temperatures close to the
respective Tgs (245 and 315 ꢀC), polymer chains started to
flow and formed large aggregated domains to reduce their
unfavorable surface contact with the glass substrates. The
large aggregated blocks formed on the surface seriously scat-
tered the incident light and caused the observed emission
The energy of the HOMO and LUMO levels of the HB-x poly-
mers can be determined from the oxidation onset potentials
and the onset absorption wavelength of the polymer films,
and the results are summarized in Table 2, too. Taking HB-1
as example: as seen from Figure 5, the oxidation onset
potential for the HB-1 was determined to be 1.22 V versus
Ag/Agþ. The external ferrocene/ferrocenium (Fc/Fcþ) redox
standard Eonset (Fc/Fcþ) was 0.42 V versus Ag/Agþ in
CH3CN. Under the assumption that the HOMO energy for the
ferrocene standard was ꢁ4.80 eV with respect to the zero
vacuum level, the HOMO energy for the conjugated polymer
HB-1 was evaluated to be ꢁ5.6 eV. The resultant HOMO
energy listed in Table 2 indicates the progressive increase of
HOMO energy from HB-1 (ꢁ5.6 eV) to HB-2 (ꢁ5.42 eV), and
to HB-3 (ꢁ5.35 eV) and then to the highest value for HB-4
(ꢁ5.27 eV). The same trend was also observed in the LUMO
energy from HB-1 to HB-4.
The PL Spectral Stability
The PL spectral stability of the HB-x copolymers were stud-
ied by annealing the solid films in air at temperatures
ꢃ200 ꢀC for 1 h and then measuring the fluorescent spectra
after cooling down to room temperature. Figure 6(A–D)
shows the PL spectra of all HB-x films before and after
annealed at various temperatures for 1 h. Before annealing,
the solid film emission spectra are nearly the same with their
solution analogs [cf. Fig. 4(A)] and basically exhibit no differ-
ence among all four HB-x polymers. No spectral difference
was resolved if the annealing temperatures were kept below
ꢀ
200 C, indicating that all polymers have high thermal stabil-
ity. Obvious emission intensity reduction can be observed
ꢀ
when HB-1 copolymer was annealed at 250 C for 1 h but for
the HB-2, -3 and -4 copolymers, emission reductions can only
be observed when the annealing temperatures were reached
to high values of 270, 320, and 320 ꢀC, respectively. As the
one with the highest spectral stability, HB-4 can stand up at
FIGURE 5 Cyclic voltammograms of the HB-x copolymer films
on an ITO substrate in CH3CN solution containing 0.1 M TBAH.
The scanning rate is 50 mV/s.
ꢀ
300 C for 1 h without any spectral change.
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FIGURE 6 The fluorescence emission spectra of (A) HB-1, (B) HB-2, (C) HB-3, and (D) HB-4 after annealing at various temperatures
for 1 h. (excited at 350 nm).
reduction. It is therefore important for the fluorescent poly-
mers to have high thermal transitions to effectively elevate
their segmental inertia toward thermal agitation. With the
highest Tg, the HB-4 polymer possesses the best spectral sta-
bility among all samples.
1, the highest luminance can be achieved is 1,500 cd/m2 at
a bias voltage of 12 V. The branching density of the light-
emitting copolymer affected the performances of the devices:
the HB-4 copolymer with higher branching density yielded a
device with higher luminance compared to devices fabricated
form HB-1 with lower branching density. In any case, both
the HB-1 and the HB-4 copolymers can serve well as the
emitting layer in the LED devices.
Electroluminescent Properties
Preliminary EL devices were fabricated with a configuration
of ITO/PEDOT:PSS (100 nm)/HB-x copolymer (80–100 nm)/
Al (100 nm), and encapsulation was performed under nitro-
gen atmosphere. The EL spectra of HB-1 and HB-4 copoly-
mers are shown in Figure 8(A,B), respectively. Both spectra
basically consist of one emission band with peak maxima in
the vicinity of 550 and 560 nm. The current density (J, mA/
cm2)-voltage (V) and the luminance (L, cd/m2)-bias voltage
(V) for the devices from HB-1 and HB-4 were shown in Fig-
ure 8(A,B), respectively. The turn-on voltage is ꢂ5.5 V for
device fabricated from HB-1 and is ꢂ7.0 V for HB-4. With a
higher Tg, copolymer HB-4 can stand up to a higher voltage
of 16 V as compared with HB-1, whose maximum voltage
uptake is lower than 13 V. Copolymer HB-4 showed a high
luminance of 2815 cd/m2 at a bias voltage of 16 V. For HB-
To test the spectral stability, the dependence of EL spectra
on the annealing temperatures was also carried out. The EL
spectra of HB-1 [Fig. 9(A)] after annealing at 200 ꢀC for 2
and 4 h remained nearly identical with the EL spectrum
before heating. For HB-4 copolymer, annealing at a higher
temperature of 300 ꢀC resulted in no change on the corre-
sponding EL spectra [Fig. 9(B)]. Photos in Figure 10 clearly
demonstrated that the bright green yellow light emitted
from the devices derived from the HB-1 and HB-4 emitting
layers remained essentially the same despite the whole
assemblies had been annealed at the respective high temper-
atures of 200 and 300 ꢀC for 4 h. Therefore, it is confident
to conclude that the polymer light-emitting diodes (PLEDs)
based on the HB-1 and HB-4 copolymer are highly stable.
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FIGURE 7 Optical images of the HB-1 film: (A) before and (C) after annealed at 270 ꢀC for 1 h and the HB-4 film: (B) before and (D)
after annealed at 320 ꢀC for 1 h.
FIGURE 8 (A) EL spectra and L–J–V characteristics of the device based on the HB-1 copolymers. (B) EL spectra and L–J–V charac-
teristics of the device based on the HB-4 copolymers.
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FIGURE 9 EL spectra of (A) HB-1 and (B) HB-4 before and after annealing at the respective 200 and 300 ꢀC for 2 and 4 h.
EXPERIMENTAL
directly. TBAH was purchased from Fluka and purified by
recrystallization from ethyl acetate and dried in vacuo at
60 ꢀC. THF was refluxed over sodium and benzophenone
under nitrogen for more than 2 days before distillation for
use. Triethylamine and m-cresol was distilled from CaH2
under nitrogen before use.
Materials
Reagent grade nitric acid (>90%), benzyl cyanide, iron pow-
der, 1,4-diacetylbenzene (DB), TPA, acetophenone, acetoni-
trile (CH3CN), phosphorus pentoxide (P2O5), and ferrocene
were purchased from Sigma-Aldrich Chemical and were used
FIGURE 10 Photographic images of the devices with HB-1 emitting layer: (A) before and (B) after annealed at 200 ꢀC for 4 h and
with HB-4 emitting layer (C) before and (D) after annealed at 300 ꢀC for 4 h.
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Synthesis
acid (100 mL) at 95oC. The reaction mixture was heated for 1
h before cooled to room temperature. The resultant suspen-
sion was filtered to remove the un-reacted iron powder. The
filtrate was then poured into water (500 mL) and the result-
ant precipitate was collected (1.34 g, 94%).
TP, TP-NO2, TP-Bz, and TP-Pm compounds were prepared
according to the reported procedures.11 Compounds of TPA-
NO2, TPA-Bz, TPA-Pm, DTBD, and TDA and polymers of HB-x
were prepared according to the procedures illustrated in
Schemes 1 and 2 and details were given as follows:
Tris(4-nitrophenyl)amine (TPA-NO2)
A mixture of TPA (TPA, 5 g, 20 mmol) and glacial acetic acid
ꢀ
(10 mL) was vigorously stirred at 60 C to result in a homo-
geneous suspension, to which mixed liquids of glacial acetic
acid (30 mL) and concentrated nitric acid (5.34 mL) were
ꢀ
added quickly. After stirring at 100 C for 24 h, the precipi-
tate was filtered and washed with water to the extent of pH
¼ 7. Column chromatography with hexane eluent yielded the
final product (7 g; 92%).
Mp: 189 ꢀC; IR (KBr pellet, cmꢁ1) 3,107, 3,074, 1,581, 1,508,
1
1,340, 1,313, 1,272, 1,180, 1,111, 850, 750, 702; H NMR (500
MHz, (CD3)2SO) d 8.18 (d, 6H, Ha), 7.18 (d, 6H, Hb) (Fig. S1,
Supporting Information); MS m/e: calcd for C18H12N4O6, 380.08;
found, 379.04 (Mþ); Anal. Calcd for C18H12N4O6: C, 56.85; H,
3.18; N, 14.73; O, 25.24. C, 56.60; H, 3.42; N, 14.55; O, 25.27.
Mp: 276 C;IR (KBr pellet, cmꢁ1) 3,459, 3,342, 3,053, 1,620,
ꢀ
1,575, 1,492, 1,476, 1,442, 1,298, 1,246, 1,164, 826, 699,
1
656; H NMR (500 MHz, (CD3)2SO) d 7.47 (d, 6H, Ha), 7.32–
7.35 (m, 6H, Hb, Hc), 7.06 (m, 6H, Hd), 6.87 (d, 3H, He), 6.80
(d, 3H, Hf), 6.71(s, 3H, Hg) (Fig. S3, Supporting Information);
MS m/e: calcd for C39H30N4O3, 602.23; found, 602.20 (Mþ);
Anal. Calcd for C39H30N4O3: C, 77.72; H, 5.02; N, 9.30; O,
7.96. Found: C, 77.82; H, 5.03; N, 8.88; O, 7.69.
Tris(3-phenylbenzo[c]isoxazol-6-yl)amine (TPA-Bz)
To an ice-cooled mixture of sodium hydroxide (2 g, 50 mmol),
a mixture of benzyl nitrile (1.32 g, 11.23 mmol), methanol (15
mL) and THF (30 mL) was added slowly. After stirring for 5
min, TPA-NO2 (1.3 g, 3.42 mmol) was added and the mixture
was heated up to 80 ꢀC for 20 h. The resultant mixture was
then cooled in an ice bath and the precipitate was filtered and
exhaustively washed with cold methanol. The crude product
was purified by column chromatography (eluent: CH2Cl2) to
give the desired TPA-Bz (1.53 g; 75%).
Mp: 142 C; IR (KBr pellet, cmꢁ1) 3,059, 1,639, 1,555, 1,496,
ꢀ
1,479, 1,446, 1,438, 1,293, 1,242, 1,200, 1,126, 968, 816,
802, 767, 743, 685, 663, 631, 601; 1H NMR (500 MHz,
CDCl3) d 7.84 (d, 6H, Ha), 7.62 (m, 6H, Hb), 7.42–7.50 (m,
9H, Hc, Hd), 7.26–7.31 (m, 6H, He, Hf) (Fig. S2, Supporting In-
formation); MS m/e: calcd for C39H24N4O3, 596.18; found,
595.21 (Mþ); Anal. Calcd for C39H24N4O3: C, 78.51; H, 4.05;
N, 9.39; O, 8.04. Found: C, 78.53; H, 4.24; N, 9.01; O, 7.94.
Preparations of 6,60-(3,4-diphenylthiophene-2,5-diyl)-
bis(2,4-diphenylquinoline) (DTBD) and tris(2,4-diphenyl-
quinolin-6-yl)amine (TDA)
A solution of P2O5 ꢀ(10 g, 39.97 mmol) in m-cresol (10 mL)
was heated at 135 C for 2 h. After cooling to room tempera-
tures, TP-Pm (0.15 g, 0.24 mmol) (or TPA-Pm (0.15 g, 0.238
mmol)) and acetophenone (0.086 mL (0.72 mmol) for TP-Pm
and 0.129 mL (1.071 mmol) for TPA-Pm) were added and
the whole mixture was heated at 135 ꢀC for another 12 h.
The product after cooling to room temperature was precipi-
tated from a 10% triethylamine/ethanol (150 mL) solution
to give DTBD (94% yield) or TDA (95% yield).
(4,4’-(3-Amino-4-benzoylphenylazanediyl)
bis(6-aminocyclohexa-2,4-diene-4,1-diyl))
bis(phenylmethanone) (TPA-Pm)
Iron powder (4 g, 71.63 mmol) and water (4 mL) were added
to a stirred suspension of TPA-Bz (1.4 g, 2.35 mmol) in acetic
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DTBD, Mp: 290 C: IR (KBr, cmꢁ1) 3,058, 3,027, 1,584, 1,548,
1,491, 1,438, 1,356, 1,260, 1,097, 1,073, 1,026, 823, 784, 786,
tation procedures were repeated for three times before Soxh-
let extraction by 10% triethylamine/methanol solution for
24 h. The collected product was then dried at 40 ꢀC under
vacuum to give light yellow HB-x copolymers. Quantities of
reactants and characterization results for HB1-HB4 were
given below:
ꢀ
1
746, 693; H NMR (500 MHz, CDCl3 ) d 8.17–8.12 (m, 6H, Ha,
Hb), 7.75–7.73 (m, 6H, Hc, Hd), 7.52–7.38 (m, 10H, He, Hf, Hg),
7.19–7.09 (m, 8H, Hh, Hi, Hj), 6.91 (m, 2H, Hk) (Fig. S5, Sup-
porting Information); MS m/e: calcd for C57H40N2S, 794.28;
found, 794.19 (Mþ). Anal. Calcd for C57H40N2S: C, 87.63; H,
4.82; N, 3.52. Found: C, 88.35; H, 4.59; N, 3.35.
HB1. TP-Pm (0.150 g, 0.238 mmol), TPA-Pm (0.007 g, 0.012
mmol) and DB (0.042 g, 0.256 mmol) were used to give HB-
1 (yield: 92%). GPC (eluent: THF): Mn ¼ 9,600, Mw
¼
22,000, and PDI ¼ 2.2; Tg ¼ 245 ꢀC; IR (KBr, cmꢁ1) 3,054,
1,605, 1,585, 1,545, 1,485, 1,349, 1,262, 1,071, 1,011, 834,
772, 698, 622, 584; 1H NMR (500 MHz, CDCl3) d 8.28–8.37
(b, Ha, Hb), 8.04–8.17 (b, Hc, Hd, He), 7.70–7.83 (b, Hf, Hg, Hh,
Hi), 7.38–7.41 (b, Hj, Hk), 7.09–7.22 (b, Hl, Hm, Hn), 6.92 (b,
Ho) (Fig. S6A, supporting information); 13C NMR (500 MHz,
CDCl3) d 156.3 (C1), 149.1 (C2), 148.0 (C3), 140.3 (C4), 139.0
(C5), 137.8 (C6), 135.9 (C7), 132.2 (C8), 130.8 (C9), 130.3
(C10), 129.3 (C11), 129.1 (C12), 128.9 (C13), 128.8 (C14),
128.6 (C15), 128.2 (C16), 128.1 (C17), 127.9 (C18), 127.8
(C19), 127.6 (C20), 127.2 (C21), 126.7 (C22), 126.5 (C23),
125.5 (C24), 124.0 (C25), 119.6 (C26), 116.5 (C27), 114.8 (C28
)
TDA, Mp: 301 ꢀC: IR (KBr, cmꢁ1) 3,057, 3,026, 1,586, 1,546,
1,488, 1,438, 1,359, 1,261, 1,098, 1,069, 1,030, 827, 795,
785, 764, 697; 1H NMR (500 MHz, CDCl3 ) d 8.11 (d, 6H,
Ha), 8.14 (d, 3H, Hb), 7.77(s, 3H, Hc), 7.61–7.53(m, 21H, Hd,
He, Hf, Hg), 7.46 (m, 3H, Hh), 7.35–7.27(m, 6H, Hi, Hj) (Fig.
S4, Supporting Information); MS m/e: calcd for C63H42N4,
854.34; found, 854.24 (Mþ). Anal. Calcd for C63H42N4: C,
88.50; H, 4.95; N, 6.55. Found: C, 86.88; H, 5.43; N, 6.59.
(Fig. S6B, supporting information); MS m/e: 13,500 (Mþ);
Anal. Calcd for feed: C, 87.15; H, 4.50; N, 4.09; S, 4.25.
Found: C, 87.21; H, 4.54; N, 4.03; S, 4.21.
HB-2. TP-Pm (0.150 g, 0.238 mmol), TPA-Pm (0.010 g,
0.016 mmol) and DB (0.042 g, 0.262 mmol) were used to
give HB-2 (yield: 95%). GPC (eluent: THF): Mn ¼ 7,700, Mw
¼ 16,000, and PDI ¼ 2.1; Tg ¼ 279 C; IR (KBr, cmꢁ1) 3,054,
ꢀ
1,605, 1,585, 1,545, 1,485, 1,349, 1,262, 1,071, 1,011, 834,
772, 698, 622, 584; 1H NMR (500 MHz, CDCl3) d 8.28–8.37
(b, Ha, Hb), 8.04–8.17 (b, Hc, Hd, He), 7.70–7.83 (b, Hf, Hg, Hh,
Hi), 7.38–7.41 (b, Hj, Hk), 7.09–7.22 (b, Hl, Hm, Hn), 6.92 (b,
Ho) (Fig. S7A, supporting information); 13C NMR (500
MHz, CDCl3) d 156.3 (C1), 149.1 (C2), 148.0 (C3), 140.3 (C4),
139.0 (C5), 137.8 (C6), 135.9 (C7), 132.2 (C8), 130.8 (C9),
130.3 (C10), 129.3 (C11), 129.1 (C12), 128.9 (C13),
128.8 (C14), 128.6 (C15), 128.2 (C16), 128.1 (C17), 127.9
(C18), 127.8 (C19), 127.6 (C20), 127.2 (C21), 126.7 (C22),
126.5 (C23), 125.5 (C24), 124.0 (C25), 119.6 (C26),
116.5 (C27), 114.8 (C28) (Fig. S7B, supporting information);
MS m/e: 14,600 (Mþ); Anal. Calcd form feed: C, 87.17; H,
4.49; N, 4.15; S, 4.18. Found: C, 87.20; H, 4.57; N, 4.08; S,
4.14.
HB-3. TP-Pm (0.150 g, 0.238 mmol), TPA-Pm (0.011 g,
0.018 mmol) and DB (0.043 g, 0.265 mmol) were used to
yield HB-3 (yield: 93%). GPC (eluent: THF): Mn ¼ 4,600, Mw
¼ 7,100, and PDI ¼ 1.5; Tg ¼ 310 C; IR (KBr, cmꢁ1) 3,054,
ꢀ
Preparation of hyperbranched polymer (HB1-HB4)
1,605, 1,585, 1,545, 1,485, 1,349, 1,262, 1,071, 1,011, 834,
772, 698, 622, 584; 1H NMR (500 MHz, CDCl3) d 8.28–8.37
(b, Ha, Hb), 8.04–8.17 (b, Hc, Hd, He), 7.70–7.83 (b, Hf, Hg, Hh,
Hi), 7.38–7.41 (b, Hj, Hk), 7.09–7.22 (b, Hl, Hm, Hn), 6.92 (b,
Ho) (Fig. S8A, supporting information); 13C NMR (500 MHz,
CDCl3) d 156.3 (C1), 149.1 (C2), 148.0 (C3), 140.3 (C4), 139.0
(C5), 137.8 (C6), 135.9 (C7), 132.2 (C8), 130.8 (C9), 130.3
(C10), 129.3 (C11), 129.1 (C12), 128.9 (C13), 128.8 (C14),
128.6 (C15), 128.2 (C16), 128.1 (C17), 127.9 (C18), 127.8
(C19), 127.6 (C20), 127.2 (C21), 126.7 (C22), 126.5 (C23),
A mixture of P2O5 (1 g, 7.05 mmol) in m-cresol (10 mL) was
ꢀ
heated at 135 C for 2 h. After cooling to room temperature,
calculated amounts of TP-Pm, TPA-Pm, and DB were then
added and the entire mixtures were reheated at 135 ꢀC for
another 12 h. The product after cooling to room temperature
was precipitated from a 10% triethylamine/ethanol (150
mL) solution. The collected polymer was then dissolved in
chloroform (10 mL) and re-precipitated from a 10% triethyl-
amine/methanol (300 mL) solution. The dissolution/precipi-
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125.5 (C24), 124.0 (C25), 119.6 (C26), 116.5 (C27), 114.8 (C28
)
the thermal transitions. The glass transition temperature (Tg)
is defined as the midpoint of the heat capacity transition
between the upper and lower points of deviation from the ex-
trapolated liquid and glass lines. TGA was performed under
air with use of a TA Q50 thermogravimetric analyzer operated
(Fig. S8B, supporting information); MS m/e: 15,300 (Mþ);
Anal. Calcd form feed: C, 87.17; H, 4.50; N, 4.18; S, 4.14.
Found: C, 87.19; H, 4.58; N, 4.11; S, 4.11.
HB-4. TP-Pm (0.150 g, 0.238 mmol), TPA-Pm (0.013 g,
0.022 mmol), DB (0.044 g, 0.270 mmol), m-cresol (10 mL)
and P2O5 (1 g, 7.05 mmol) were used to give HB-4 in
93%yield. GPV (eluent: THF): Mn ¼ 4,000, Mw ¼ 5,800, and
ꢀ
with a heating rate of 20 C/min under air flow (flow rate ¼
60 mL/min). FT-IR spectra were obtained from a Bruker Ten-
sor 27 spectrometer. Solution of organic compound or poly-
ꢀ
mer in THF was dropped on a KBr pellet and dried at 105 C
PDI ¼ 1.5; Tg ¼ 315 C; IR (KBr, cmꢁ1) 3,054, 1,605, 1,585,
ꢀ
under vacuum to prepare solid film for analysis.
1,545, 1,485, 1,349, 1,262, 1,071, 1,011, 834, 772, 698, 622,
584; 1H NMR (500 MHz, CDCl3) d 8.28–8.37 (b, Ha, Hb),
8.04–8.17 (b, Hc, Hd, He), 7.70–7.83 (b, Hf, Hg, Hh, Hi), 7.38–
7.41 (b, Hj, Hk), 7.09–7.22 (b, Hl, Hm, Hn), 6.92 (b, Ho) (Fig.
S9A, supporting information); 13C NMR (500 MHz, CDCl3) d
156.3 (C1), 149.1 (C2), 148.0 (C3), 140.3 (C4), 139.0 (C5),
137.8 (C6), 135.9 (C7), 132.2 (C8), 130.8 (C9), 130.3 (C10),
129.3 (C11), 129.1 (C12), 128.9 (C13), 128.8 (C14), 128.6
(C15), 128.2 (C16), 128.1 (C17), 127.9 (C18), 127.8 (C19),
127.6 (C20), 127.2 (C21), 126.7 (C22), 126.5 (C23), 125.5
(C24), 124.0 (C25), 119.6 (C26), 116.5 (C27), 114.8 (C28) (Fig.
S9B, supporting information); MS m/e: 14,200 (Mþ); Anal.
Calcd form feed: C, 87.18; H, 4.50; N, 4.22; S, 4.09. Found: C,
87.20; H, 4.58; N, 4.17; S, 4.04.
PL emission spectra were obtained from a LabGuide X350
fluorescence spectrophotometer using a 450W Xe lamp as
the continuous light source. UV-vis absorption spectra were
recorded with an Ocean Optics DT 1000 CE 376 spectropho-
tometer. Small quartz cell with dimensions of 0.2 ꢄ 1.0 ꢄ
4.5 cm3 was used for the UV-vis absorption spectra measure-
ments. For reliable results, UV-vis and PL emission spectra
were immediately undertaken once the samples were pre-
pared. For polymer films, quantum yield (UF) was deter-
mined from integrating sphere. CV was conducted on Auto-
lab PGSTAT302N model with a three-electrode cell, in which
ITO substrate was used as working electrode and platinum
wire as an auxiliary electrode at a scan rate of 50 mV/s
against a Ag/Agþ reference electrode in a solution of 0.1 M
TBAH/CH3CN.
The EL devices with copolymers as emitting layers were fab-
ricated with a configuration of ITO/PEDOT: PSS (100 nm)/
HB-x (100 nm)/Al (100 nm). The encapsulation was
performed under nitrogen atmosphere and further tests
under ambient conditions were operated without protection.
First, the hole injecting poly(3,4-ethylene-dioxythiophene)
(PEDOT:PSS) layer was spin-coated onto indium tin oxide
(ITO) glass and treated at 120 ꢀC for 30 min. Continuously,
the emissive layer followed with spin-coating onto the
PEDOT-coated ITO from a polymer solution and baked.
Finally, the aluminum was successively deposited onto the
polymer film via vacuum evaporation under 10ꢁ5 torr.
The film thicknesses of emissive layers were measured by
the a-Step surface profiler (AMBIO XP-1). The EL spectra and
current-voltage-luminance (L-J-V) characteristics of devices
were obtained using a Keithley 2400 Source meter.
Instrumentation
The 1H- and 13C- NMR spectra were recorded with a Varian
Unity Inova-500 instrument operating at 500 MHz for proton
and 125 MHz for carbon in CDCl3 solution. A VG Quattro GC/
MS/MS/DS instrument was used to determine the molar
mass of the organic molecules. Elemental analyses were per-
formed on an Elementary Vario EL-III (Germany) C, H, N, O,
and S analyzer. Molecular weight and molecular weight dis-
tribution of copolymers were determined from GPC using a
Waters 510 HPLC model equipped with a 410 differential re-
fractometer, a UV detector, and three Ultrastyragel columns
(100, 500, and 1000 Å) connected in series. Polymer solu-
tion was eluted by THF with a flow rate of 0.6 mL/min. The
molecular weight calibration curve was obtained from poly-
styrene standards. A mass spectrum was obtained using a
Bruker Daltonics Autoflex III MALDI-TOF mass spectrometer.
Melting point (Tm) of organic compound and glass transition
temperature (Tg) of copolymer were determined from a TA
Q-20 differential scanning calorimeter (DSC) calorimeter
with a scan rate of 20 ꢀC/min under nitrogen. The polymer
CONCLUSIONS
Alternate TP-Qu-TPA hyperbranched copolymers of HB-x and
model compounds of TDA and DTBD were successfully pre-
pared through the facile Friedla¨nder condensations between
the corresponding o-aminoketo and acetyl monomers. Solution
absorption and emission study on model compounds suggest
that energy transfer from the TP to the TPA units occurred in
the HB-x copolymers, which led to the identical emission spec-
tra for all copolymers. The resultant copolymers are all fluo-
rescent materials with high quantum efficiency (0.68–0.74 for
HB-x) in the solution and in the solid film states.
The wholly aromatic-qunoline chain structures render the HB-
x copolymers rigid backbones and high glass transition tem-
peratures (Tgs ¼ 245–315 ꢀC) with the Tg values increased
ꢀ
samples (5–10 mg) were primꢀarily held at 400 C for 1 min
and then cooled rapidly to 25 C before re-scanned to obtain
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mun 2010, 31, 834–839; (f) Chen, J.; Peng, H.; Law, C. C. W.;
Dong, Y.; Lam, J. W. Y.; Williams, I. D.; Tang, B. Z. Macromole-
cules 2003, 36, 319–4327; (g) Lam, J. W. Y.; Chen, J.; Law, C. C.
W.; Peng, H.; Xie, Z.; Cheuk, K. K. L.; Kwok, H. S.; Tang, B. Z.
Macromol Symp 2003, 196, 289–300; (h) Xie, Z.; Peng, H.; Lam,
J. W. Y.; Chen, J.; Zheng, Y.; Qiu, C.; Kwok, H. S.; Tang, B. Z.;
Macromol Symp 2003, 195, 179–184.
with the increasing branching density from HB-1 to HB-4
copolymers. The high Tgs of the HB-x copolymers enhance
their corresponding thermal and spectral stability during
ꢀ
annealing at temperatures below Tg. With a high Tg of 315 C,
the film PL spectrum of HB-4 remained nearly identical after
thermal annealing at 300 ꢀC for 1 h. OM investigation sug-
gested that the emission reduction after annealing at tempera-
tures close to Tg is due to the chain flow and the formation of
large aggregates, which seriously scattered the incident light to
cause the reduced absorption and emission. The resultant EL
spectrum after heating HB-4-derived device at 300 ꢀC for 4 h
remained essentially the same with the pristine one before
heating. The resultant properties suggest that the branching
points in the HB-x copolymers help to enhance both the ther-
mal and spectral stabilities of the hyperbranched copolymers.
All HB-x copolymers in this study can serve well as the emit-
ting layer in the PLED devices.
4 (a) Agrawal, A. K.; Jenekhe, S. A. Macromolecules 1991, 24,
6806–6808; (b) Agrawal, A. K.; Jenekhe, S. A. Macromolecules
1993, 26, 895–905; (c) Agrawal, A. K.; Jenekhe, S. A. Chem
Mater 1993, 5, 633–640; (d) Cui, Y.; Zhang, X.; Jenekhe, S. A.
Macromolecules 1999, 32, 3824–3826; (e) Agrawal, A. K.;
Jenekhe, S. A. Chem Mater 1996, 8, 579–589; (f) Shetty, A. S.;
Liu, E. B.; Lachicotte, R. J.; Jenekhe, S. A. Chem Mater 1999,
11, 2292–2299; (g) Xin, H.; Guo, X.; Kim, F. S.; Ren, G.; Watson,
M. D.; Jenekhe, S. A. J Mater Chem 2009, 19, 5303–5310; (h)
Kim, J. L.; Kim, J. K.; Cho, H. N.; Kim, D. Y.; Kim, C. Y.; Hong,
S. I. Macromolecules 2000, 33, 5880–5885; (i) Kim, J. L.; Kim, J.
K.; Hong, S. I. Polym Bull 1999, 42, 511–517.
5 (a) Zhang, Q. T.; Tour, J. M. J Am Chem Soc 1998, 120,
5355–5362; (b) Zhang, Q. T.; Tour, J. M. J Am Chem Soc 1997,
119, 5065–5066; (c) Devasagayaraj, A.; Tour, J. M. Macromole-
cules 1999, 32, 6425–6430.
We appreciate the financial support from the National Science
Council, Taiwan, under Contract No. NSC 100–2221-E-110–
045-.
6 (a) Lee, B.-L.; Yamamoto, T. Macromolecules 1999, 32,
1375–1382; (b) Yamamoto, T.; Zhou, Z. H.; Kanbara, T.; Shi-
mura, M.; Kizu, K.; Maruyama, T.; Nakamura, Y.; Fukuda, T.;
Lee, B. L.; Ooba, N.; Tomaru, S.; Kurihara, T.; Kaino, T.; Kubota,
K.; Sasaki, S. J Am Chem Soc 1996, 118, 10389–10399; (c) Hay,
C.; Vilain, D. L.; Deborde, V.; Toupet, L.; Reau, R. Chem Com-
mun 1999, 4, 345–346; (d) Ferraris, J. P.; Bravo, A.; Kim, W.;
Hrncir, D. C. J Chem Soc Chem Commun 1994, 991–992.
REFERENCES AND NOTES
1 (a) Liu, X. M.; He, C. B.; Hao, X. T.; Tan, L. W.; Li, Y. Q.; Ong,
K. S. Macromolecules 2004, 37, 5965–5970; (b) Wang, H. L.; Li,
Z.; Jiang, Z. Q.; Liang, Y. K.; Wang, H.; Qin, J. G.; Yu, G.; Liu,
Y. Q. J Polym Sci Part A: Polym Chem 2005, 43, 493–504; (c)
Tao, X. T.; Zhang, Y. D.; Wada, T.; Sasabe, H.; Suzuki, H.; Wata-
nabe, T.; Miyata, S. Adv Mater 1998, 10, 226–230; (d) Fre´chet,
J. M. J. Science 1994, 263, 1710–1712; (e) Thompson, D. S.;
Markoski, L. J.; Moore, J. S. Macromolecules 1999, 32,
4764–4798; (f) Kuo, P. L.; Ni, S. C. J Polym Sci Part A: Polym
Chem 2004, 42, 5504–5513; (g) Kuo, P. L.; Liang, W. J.; Wang,
F. Y. J Polym Sci Part A: Polym Chem 2003, 41, 1360–1370; (h)
Yamaguchi, N.; Wang, J. S.; Hewitt, J. M.; Lenhart, W. C.;
Mourey, T. H. J Polym Sci Part A: Polym Chem 2002, 40,
2855–2867; (i) Keul, H. Macromol Chem Phys 2005, 206,
1154–1154.
7 (a) Jenekhe, S. A.; Lu, L.; Alam, M. M. Macromolecules 2001,
34, 7315–7324; (b) Tonzola, C. J.; Alam, M. M.; Bean, B. A.;
Jenekhe, S. A. Macromolecules 2004, 37, 3554–3563.
8 (a) Jenekhe, S. A. Nature 1986, 322, 345–347; (b) Chen, W. C.;
Jenekhe, S. A. Macromolecules 1995, 28, 465–480.
9 (a) Chang, Y. T.; Hsu, S. L.; Su, M. H.; Wei, K. H. Adv Mater
2009, 21, 2093–2097; (b) Wang, H. S.; Su, M. S.; Wei, K. H. J
Polym Sci Part A: Polym Chem 2010, 48, 3331–3339; (c)
Koyuncu, S.; Zafer, C.; Koyuncu, F. B.; Aydin, B.; Can, M.; Sefer,
E.; Ozdemir, E.; Icli, S. J Polym Sci Part A: Polym Chem 2009,
47, 6280–6291; (d) Zhan, X. W.; Tan, Z. A.; Domercq, B.; An, Z.
S.; Zhang, X.; Barlow, S.; Li, Y. F.; Zhu, D. B.; Kippelen, B.;
Marder, S. R. J Am Chem Soc 2007, 129, 7246–7247; (e) Steck-
ler, T. T.; Zhang, X.; Hwang, J.; Honeyager, R.; Ohira, S.;
Zhang, X. H.; Grant, A.; Ellinger, S.; Odom, S. A.; Sweat, D.;
Tanner, D. B.; Rinzler, A. G.; Barlow, S.; Bre´das, J.-J.; Kippelen,
B.; Marde, S. R.; Reynolds, J. R. J Am Chem Soc 2009, 131,
2824–2826.
2 (a) Tsai, L. R.; Chen, Y. J Polym Sci Part A: Polym Chem
2007, 45, 5541–5551; (b) Tang, D. F.; Wen, G. A.; Wei, W.;
Huang, W. Polym Int 2008, 57, 1235–1241; (c) Ding, L.; Bo, Z.;
Chu, Q.; Li, J.; Dai, L.; Pang, Y.; Karasz, F. E.; Durstock, M. F.
Macromol Chem Phys 2006, 207, 870–878; (d) Xu, M. H.; Pu, L.
Tetrahedron Lett 2002, 43, 6347–6350; (e) Palei, A. K.; Mishra,
S. P.; Kumar, A.; Srivastava, R.; Kamalasanan, M. N.; Patri, M.
J Polym Sci Part A: Polym Chem 2011, 49, 832–841; (f) Yu, J.
M.; Sakamoto, T.; Watanabe, K.; Furumi, S.; Tamaoki, N.; Chen,
Y.; Nakano, T. Chem Commun 2011, 47, 3799–3801; (g) Yu, J.
M.; Chen, Y. Polymer 2010, 51, 4484–4492; (h) Li, Z. A.; Jiang,
Z. Q.; Qiu, G.; Wu, W. B.; Yu, G.; Liu, Y. Q.; Qin, J. G.; Li, Z.
Macromol Chem Phys 2010, 211, 1820–1825; (i) Li, C.; Bo, Z.
Polymer 2010, 51, 4273–4294.
10 (a) Kraft, A.; Grimsdale, A. C.; Holmes, A. B. Angew
Chem Int Ed 1998, 37, 402–428; (b) Sokolik, I.; Yang, Z.; Kar-
asz, F. E.; Morton, D. C. J Appl Phys 1993, 74, 3584–3586;
(c) Tarkka, R. M.; Zhang, X.; Jenekhe, S. A. J Am Chem
Soc 1996, 118, 9438–9439; (d) Jenekhe, S. A.; Zhang, X.;
Chen, X. L.; Choong, V.-E.; Gao, Y.; Hsieh, B. R. Chem
Mater 1997, 9, 409–412; (e) Zhang, X.; Shetty, A. S.;
Jenekhe, S. A. Acta Polym 1998, 49, 52–55; (f) Zhang, X.;
Shetty, A. S.; Jenekhe, S. A. Macromolecules 1999, 32,
7422–7429; (g) Zhang, X.; Jenekhe, S. A. Macromolecules
2000, 33, 2069–2082.
3 (a) Che, P.; He, Y.; Wang, X. Macromolecules 2005, 38,
8657–8663; (b) Tsai, L. R.; Chen, Y. Macromolecules 2007, 40,
2984–2992; (c) Xin, Y.; Wen, G. A.; Zeng, W. J.; Zhao, L.; Zhu,
X. R.; Fan, Q. L.; Feng, J. C.; Wang, L. H.; Wei, W.; Peng, B.;
Cao, Y.; Huang, W. Macromolecules 2005, 38, 6755–6758; (d)
Haussler, M.; Liu, J.; Zheng, R.; Lam, J. W. Y.; Qin, A.; Tang, B.
¨
11 Lai, C. T.; Chen, R. H.; Liu, C. W.; Hong, J. L. J Polym Sci
Part A: Polym Chem 2011, 49, 2059–2069.
Z. Macromolecules 2007, 40, 1914–1925; (e) Lu, P.; Lam, J. W.
Y.; Liu, J.; Jim, C. K. W.; Yuan, W.; Xie, N.; Zhong, Y.; Hu, Q.;
Wong, K. S.; Cheuk, K. K. L.; Tang, B. Z. Macromol Rapid Com-
12 Stille, J. K. Macromolecules 1981, 14, 870–880.
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