Thermal and spectral stability of fluorescent copolymers containing tetraphenylthiophene-quinoline unit

Article abstract of DOI:10.1002/pola.24635

Fluorescent alternative copolymers containing tetraphenylthiophene- quinoline (TP-Qu) moiety were synthesized from Friedlaender reaction between o-aminoketone and acetyl groups. With the wholly aromatic-quinoline chain structure, the alternative donor-acceptor copolymers of PTPQu and PTPTPQu are rigid materials with high glass transitions (T_g = 245 and 295 °C, respectively) and with high thermal stability (with a‰&2% weight loss at 500 °C). The multiple phenyl pendant rings inherited PTPQu and PTPTPQu copolymers with good solubility in common organic solvents, which facilitate the easy fabrications of light-emitting diode (LED) devices. CV study resulted in the reversible E;bsubesub & values of 0.78 and 0.75 V for the PTPQu and PTPTPQu copolymers, respectively. With high quantum yields (φ_Fs, = 0.59 for PTPQu and 0.74 for PTPTPQu) in the film states, the two copolymers and their devices exhibit stable photoluminescence (PL) and electroluminescence (EL) spectra, respectively, on change of annealing temperatures to at least higher than 250 °C. After annealing at 250 °C (or 300 °C), no change was observed in the respective PL and EL spectra of PTPQu (or PTPTPQu) copolymers. The results indicate that alternative copolymers containing donor-acceptor TP-Qu unit are promising candidates for LEDs with high efficiency and spectral stability.

Full text of DOI:10.1002/pola.24635

Thermal and Spectral Stability of Fluorescent Copolymers Containing
Tetraphenylthiophene-Quinoline Unit
CHUNG-TIN LAI, RONG-HONG CHIEN, CHI-WEI LIU, JIN-LONG HONG
Department of Materials and Optoelectronic Science, National Sun Yat-Sen University, Kaohsiung 80424, Taiwan
Received 13 January 2011; accepted 11 February 2011
DOI: 10.1002/pola.24635
Published online 9 March 2011 in Wiley Online Library (wileyonlinelibrary.com).
ABSTRACT: Fluorescent alternative copolymers containing tet-
PTPQu and 0.74 for PTPTPQu) in the film states, the two
copolymers and their devices exhibit stable photolumines-
cence (PL) and electroluminescence (EL) spectra, respectively,
on change of annealing temperatures to at least higher than
250 ꢀC. After annealing at 250 ꢀC (or 300 ꢀC), no change was
observed in the respective PL and EL spectra of PTPQu (or
PTPTPQu) copolymers. The results indicate that alternative
copolymers containing donor–acceptor TP-Qu unit are prom-
raphenylthiophene-quinoline (TP-Qu) moiety were synthe-
sized from Friedlander reaction between o-aminoketone and
¨
acetyl groups. With the wholly aromatic-quinoline chain
structure, the alternative donor–acceptor copolymers of
PTPQu and PTPTPQu are rigid materials with high glass tran-
sitions (Tg ¼ 245 and 295 ꢀC, respectively) and with high ther-
mal stability (with ꢁ2% weight loss at 500 ꢀC). The multiple
phenyl pendant rings inherited PTPQu and PTPTPQu copoly-
mers with good solubility in common organic solvents, which
facilitate the easy fabrications of light-emitting diode (LED)
devices. CV study resulted in the reversible Eox/onset values of
0.78 and 0.75 V for the PTPQu and PTPTPQu copolymers,
ising candidates for LEDs with high efficiency and spectral
C
V
stability.
2011 Wiley Periodicals, Inc. J Polym Sci Part A:
Polym Chem 49: 2059–2069, 2011
KEYWORDS: conjugated polymers; fluorescence; light-emitting
respectively. With high quantum yields (UFs,
¼
0.59 for
diodes (LED)
INTRODUCTION Conjugated polymers with donor–acceptor
architectures are interesting, because the inherent charge
transfer can facilitate ready manipulation of the electronic
structure (HOMO/LUMO levels), leading to small band gap
semiconducting polymers.1–5 Through design and synthesis
of new architectures, donor–acceptor conjugated polymers
can be applied to systems with photoinduced charge transfer
and separation for photovoltaic devices6 and to bipolar
charge transport materials for light-emitting diodes.7 As the
widely used electron-donating (e-donating) moieties, thio-
phene, oligothiophenes, and the derivatives1–4 had been
incorporated with e-deficient heterocyclic (such as quinoline,
anthrazoline, quinoxaline4) rings to construct donor–acceptor
conjugated polymers for light-emitting diode (LED) applica-
tions. Herein, we explored new donor–acceptor alternative
copolymers based on e-donating tetraphenylthiophene (TP)
and electron-accepting quinoline moieties in this study.
on the reactive site through proper substitution; therefore,
novel fluorene- and phenylene-based blue light-emitting
polymers with e-accepting sulphonate side group10
were developed. Further example is the use of
e-accepting dibenzothiophene-S,S-dioxide (DBS)11 moiety
with the e-donating fluorene rings, and the resultant copoly-
mers showed excellent spectral and thermal stabilities.
As analogous to the above DBS-fluorene systems, copolymer
with e-donating thiophene and e-accepting quinoline moi-
eties can be spectral and thermal stability. Therefore, we
attempted to incorporate novel type of e-donating tetra-
phenylthiophene (TP) group with e-accepting quinoline (Qu)
ring in this study. As illustrated in Scheme 1, two alternative
copolymers PTPQu and PTPTPQu with donor–acceptor TP-
Qu unit were prepared and characterized to be emitters with
good thermal and spectral stability at elevated temperatures.
The construction unit of TP moiety12 has the structural fea-
ture of alternative phenyl and thiophene rings and had been
used previously to prepare polymers with different linkages
(such as amide, imides, ester, or azomethines13). In addition,
fluorescent polymers14 with incorporated silyl14(c) or vinyl-
phenylene14(d) units were also prepared previously and were
characterized to be good emitters with high emission effi-
ciency. With the wholly aromatic-heterocyclic structures, the
For polymers used in LED devices, polyfluorenes (PFs) are
the widely studied blue-light emitters due to their high pho-
toluminescence (PL) efficiency and tunability of electrophysi-
cal properties.8 However, the LEDs fabricated from PFs
always suffered from oxidative degradation9 due to the fluo-
renone formation. Previous study indicated that oxidation of
fluorene can be prohibited by reducing the electron density
Additional Supporting Information may be found in the online version of this article. Correspondence to: J.-L. Hong (E-mail: jlhong@mail.nsysu.edu.
tw)
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Journal of Polymer Science Part A: Polymer Chemistry, Vol. 49, 2059–2069 (2011) 2011 Wiley Periodicals, Inc.
FLUORESCENT COPOLYMERS CONTAINING TP-QU, LAI ET AL.
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JOURNAL OF POLYMER SCIENCE PART A: POLYMER CHEMISTRY DOI 10.1002/POLA
SCHEME 1 Synthesis of PTPQu and PTPTPQu copolymers. [Color figure can be viewed in the online issue, which is available at
wileyonlinelibrary.com.]
resultant copolymers PTPQu and PTPTPQu are rigid materi-
als with high glass transition temperatures (Tgs ꢂ 245 ꢀC).
In addition, the multiple phenyl pendant rings originated
from the TP moiety inherited good solubility of the copoly-
mers in most of the organic solvents, which is an essential
property for the easy fabrication of LED device. In this study,
polymer synthesis and identifications, property characteriza-
tions, photo- and electro-luminescent (PL and EL) properties,
and thermal stability were investigated.
permeation chromatography (GPC, Fig. S9, Supporting Infor-
mation) using the polystyrene as the standard. The number-
average molecular weights of the prepared alternative
copolymers PTPQu and PTPTPQu are 24,000 and 8,900 with
polydispersity index of 2.77 and 2.3, respectively.
Chemical structures of all organic intermediates were con-
firmed from the corresponding 1NMR, FTIR spectral results,
and elemental analysis (included in Experimental section).
The completeness of the Friedla¨nder reaction is the key for
the successful copolymer preparations, which can be investi-
gated by the 13C, 1H NMR, and the FTIR spectra. The 1H
NMR spectra (Figs. S5 and S7, Supporting Information) sug-
gest that the strong resonances at 2.5 ppm due to the methyl
protons of the acetyl group (ACOCH3) in 1,4-diacetylbenzene
and TPAc have completely disappeared in the respective
spectrum of PTPQu and PTPTPQu. The complete conversion
of the Friedla¨nder reaction also can be evaluated from the
FTIR spectra (Fig. S10, Supporting Information) that the
characteristic C¼¼O stretching of 1,4-dicetylbenzene at 1676
cmꢃ1 was completely absent in spectrum of PTPQu. Similar
spectral variations were observed when the spectra of TPAc
are compared with PTPTPQu (Fig. S11, Supporting Informa-
tion). In addition, the free (3460 cmꢃ1) and hydrogen-
bonded (3343 cmꢃ1) ANH2 stretching bands of TPPm were
no longer observed in the spectra of PTPQu and PTPTPQu.
The 13C NMR spectra (Figs. S6 and S8, Supporting Informa-
tion) give further supports for the successful syntheses of
the copolymers. The UV–vis and photoluminescence spectra
of the two copolymers, to be presented and discussed later,
also provided additional evidence confirming their molecular
structures.
RESULTS AND DISCUSSION
Synthesis and Basic Characterizations
As illustrated in Scheme 1, Friedla¨nder reaction between o-
aminoketone and acetyl group was the main reaction to con-
struct the quinoline linkages in the resultant alternating
copolymers PTPQu and PTPTPQu. Primarily, TPPm monomer
with the built-in o-aminoketone group connected to the TP
framework was prepared. Stille15 pointed out that the most
versatile and useful method for synthesizing o-amino
ketones was a route via the generation of benzisoxazole
from an aromatic nitro compound, followed by reductive
cleavage of the benzisoxazole. Accordingly, TPNO2 with two
o-nitro groups was synthesized to undergo the Stille process,
in which TPNO2 was further reacted with benzyl nitrile to
generate TPBz with two benzisoxazole rings, followed by the
reduction with iron to obtain the desired TPPm. Another
monomer TPAc with two acetyl groups was prepared by
Friedel–Craft acetylation of TP compound in the presence of
acetyl chloride/AlCl3. Friedla¨nder condensation of TPPm
with either diacetylbenzene or TPAc resulted in the alterna-
tive copolymer of PTPQu or PTPTPQu. The molecular
weights of the conjugated polymers were determined by gel
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the copolymers, THF was used to prepare solution and film
samples for all spectroscopic studies and for devices. TGA
thermograms of PTPQuꢀand PTPTPQu showed less than 2%
weight loss before 500 C and major decompositions started
at 560 ꢀC (Fig. 1). More than 60% of residual weights still
remained in both copolymers after heated to 800 ꢀC. This
result suggests that the aromatic-quinoline backbones inherit
both good thermal stability of copolymers and with the mul-
tiple phenyl pendant groups, both rigid copolymers still have
good solubility toward different organic solvents.
To understand the origin of the ready dissolution of both
copolymers, theoretical calculations were carried out using
Gaussian package of Material Studio.16 Structural units rep-
resentative of the PTPQu and PTPTPQu copolymers are -TP-
phenylene-TP-phenylene-TP- (TPTPT) and TP-TP-TP-TP-TP
(TTTTT), respectively. The equilibrium conformers of the
TPTPT and TTTTT units were optimized using DFT with the
B3LYP functional and the 6-31G* basis set. It has been
shown that B3LYP/6-31G* gives proper ground state struc-
tures of conjugated polymers.17 The sketch map of the opti-
mized conformers of TPTPT and TTTTT are plotted in
Scheme 2. The energy levels of the highest- and the lowest-
occupied molecular orbitals (HOMO and LUMOs) and the
corresponding energy gaps of both conformers were formu-
lated. Both copolymers have similar values of energy levels
and band gaps, which are correlated with the experimental
results that both copolymers have similar absorption and PL
emission spectra as we will present later in this discussion.
Scheme 2 also illustrated a common feature that all the
resolved torsion angles (in Arabic number) intersected by
the phenyl and the connected thiophene (or quionoline)
rings are pretty large (>43ꢀ, Table 1) in values. Therefore,
the phenyl rings are largely tilted from the plane of the thio-
phene (or quinoline) rings and adopt noncoplanar geometry
with respect to the main chain segments. It is expected that
the multiple, tilted phenyl rings in the corresponding copoly-
mers will effectively prohibit the polymer chain from inter-
molecular approaches, which leave room for the incoming
small-mass solvents when added.
FIGURE 1 TGA and DSC thermograms of alternative copoly-
mers PTPQu and PTPTPQu with a heating rate of 20 ꢀC/min.
[Color figure can be viewed in the online issue, which is avail-
able at wileyonlinelibrary.com.]
In view of the wholly aromatic-quinoline backbones, both
copolymers are supposed to be rigid and may have limited
segmental mobility. Indeed, PTPQu and PTPTPQu have high
glass transition temperatures with the detected transition
mid-points located at 245 and 295 ꢀC (Fig. 1), respectively.
The rigid chain structures often rendered conjugated poly-
mers insoluble in common organic solvents, which became
problem because solubility is needed for easy preparation of
the diodes. However, with the rigid chain structure, the alter-
native copolymers are readily soluble in various common
organic solvents such as toluene, THF, and chloroform. This
implies that the multiple phenyl pendant groups of the
copolymers add steric hindrances for intermolecular chain
approach and result in more interchain spaces, which allow
penetrations and inter-reactions for the incoming small-mass
solvents when added. Nevertheless, the high aromaticity of
PTPQu and PTPTPQu copolymers make them less soluble in
polar solvents of DMF and DMSO. With good solubility for
SCHEME 2 Optimized confomers
of TPTPT (upper) and TTTTT
(bottom) model segments. [Color
figure can be viewed in the
online issue, which is available
at wileyonlinelibrary.com.]
FLUORESCENT COPOLYMERS CONTAINING TP-QU, LAI ET AL.
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JOURNAL OF POLYMER SCIENCE PART A: POLYMER CHEMISTRY DOI 10.1002/POLA
TABLE 1 The Resultant Torsion Angle (h) from the Simulated Conformers of TPTPT and TTTTT Model Segments
(as Illustrated in Scheme 2)
A. TPTPT segment
Sitea
1
2
3
4
5
6
7
8
9
10
11
12
hb
43.2 46.1 64.9 59.5 43.3 49.5 58.9 57.1 46.8 49.7 60.8 54.8
B. TTTTT segment
Sitea
1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
17
18
hb
58.2 60.1 57.1 56.2 61.5 59.6 46.2 43.8 57.6 59.2 47.1 43.9 61.7 57.8 47.3 45.5 60.1 59.6
a
b
The referred site indicated by the Arabic number in SCHEME 2.
Torsion angle in degree.
at 458 and 485 nm, respectively. With the same solution
concentration of 10ꢃ5 M (relative to mole of repeat unit),
PTPTPQu solution emits with higher intensity compared
with PTPQu sample. This result can be confirmed by the cor-
responding solution quantum yields (UPL) for PTPQu and
PTPTPQu (0.67 vs. 0.82). After solvent removal, both copoly-
mers still emit strongly with high UF values of 0.59 for
PTPQu and 0.74 for PTPTPQu.
The PL spectral stability of the copolymers PTPTPQu and
PTPQu were studied by annealing the solid films in air at
200, 250, 300, and 350 ꢀC for 1 h and then measuring the
fluorescent spectra after cooling down to room temperature.
Figure 3 shows the PL spectra of the polymers PTPTPQu
and PTPQu before and after annealed at various tempera-
tures. Compared with the two emission bands observed in
the solution spectra shown in Figure 2, the PL spectra of
solid films contain only the long-wavelength emission band.
It can be seen from Figure 3 that the PL spectra of boꢀth
copolymers remain nearly identical after annealing at 250 C
for 1 h, indicating that both copolymers have high thermal
stability at elevated temperatures. Obvious emission intensity
reduction can be observed when PTPQu copolymers was
FIGURE 2 Solution UV–vis absorption and PL emission spectra
of PTPQu and PTPTPQu in THF (10ꢃ5 M). (Emission spectra
was excited at their respective absorption maximum value).
[Color figure can be viewed in the online issue, which is avail-
able at wileyonlinelibrary.com.]
Optical and Electrochemical Properties
ꢀ
The UV–vis absorption and the PL emission spectra of
PTPQu and PTPTPQu in the dilute solution state (10ꢃ5 M)
are compared in Figure 2. The absorption band of PTPQu is
slightly red-shifted relative to the absorption band of
PTPTPQu. Despite the slight absorption difference, the two
emission bands observed for both sample solutions are
located at the same positions with the resolved peak maxima
annealed at 300 C for 1 h but for PTPTPQu, higher anneal-
ing temperature of 350 ꢀC was required to cause significant
emission reduction. For PTPTPQu copolymer, annealing at
300 ꢀC only resulted in the extra long-wavelength emission
tail but without any intensity reduction, which indicates the
higher thermal stability of copolymer PTPTPQu in compari-
son with PTPQu. The emission reductions occurred when the
FIGURE 3 PL emission spectra of (A) PTPQu and (B) PTPTPQu films after annealing at different temperatures for 1 h. [Color figure
can be viewed in the online issue, which is available at wileyonlinelibrary.com.]
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in Table 2. For instance (Fig. 4), the oxidation onset potential
for the copolymer PTPTPQu was determined to be 0.75 V
versus Ag/Agþ. The external ferrocene/ferrocenium (Fc/Fcþ)
redox standard Eox/onset (Fc/Fcþ) was 0.42 V versus Ag/Agþ
in CH3CN. Under the assumption that the HOMO energy for
the ferrocene standard was ꢃ4.80 eV with respect to the
zero vacuum level, the HOMO energy for the conjugated
polymer PTPTPQu was evaluated to be ꢃ5.13 eV.
Electroluminescent Properties
Preliminary EL devices were fabricated with a configuration
of ITO/PEDOT:PSS (100 nm)/copolymer (80–100 nm)/Al
(100 nm), and encapsulation was performed under a nitro-
gen atmosphere. EL spectra of PTPQu and PTPTPQu copoly-
mers are shown in Figures 5(A) and 6(A), respectively. Both
spectra basically consist of one emission band with peak
maxima in the vicinity of 500 nm, which approximately
locate at the same positions with the solid state PL spectra
(cf. Fig. 3). Preliminary device performances are encouraging.
The current density (J, mA/cm2)-voltage (V) and the lumi-
nance (L, cd/m2)-bias voltage (V) for the devices from
PTPQu and PTPTPQu were shown in Figures 5(B) and 6(B),
respectively. The turn-on voltage is ꢄ8.5 V for device fabri-
cated from PTPQu and is ꢄ10 V for PTPTPQu. Copolymer
PTPTQu shows a high luminance of 2192 cd/m2 at a
bias voltage of 15 V. For PTPTPQu, the highest luminance of
1269 cd/m2 can be achieved at a bias voltage of 16 V. The
resultant properties suggest that both PTPQu and PTPTPQu
copolymers can serve well as the emitting layer in the LED
devices.
FIGURE 4 Cyclic voltammograms of the alternative copolymers
PTPQu and PTPTPQu films on an ITO substrate in CH3CN solu-
tion containing 0.1 M TBAH. The scanning rate is 50 mV/s.
[Color figure can be viewed in the online issue, which is avail-
able at wileyonlinelibrary.com.]
anneꢀaling temperatures exceeded copolymer’s Tgs (245 and
295 C), which indicates the important role of thermal tran-
sitions on spectral stability.
The electrochemical behavior of the alternative polymers
was investigated by cyclic voltammetry conducted by film
cast on an ITO substrate as the working electrode in dry
CH3CN containing 0.1 M of TBAH as electrolyte under nitro-
gen atmosphere. The typical cyclic voltammograms for the
copolymer PTPQu and PTPTPQu are shown in Figure 4 for
comparison. The reversible oxidation redox of the copoly-
mers PTPQu and PTPTPQu couples at Eox/onset values of 0.78
and 0.75 V, respectively. With higher fraction of electron-
donating TP moiety, copolymer PTPTPQu thus has lower oxi-
dation potential compared with copolymer PTPQu.
To testify the spectral stability, the experiments concerning
the dependence of EL spectra on annealing temperatures
were carried out. ꢀThe EL spectra of PTPQu [Fig. 7(A)] after
annealing at 250 C for 2 and 4 h remained nearly identical
with the spectrum from the pristine device without heating.
For PTPTPQu copolymer, annealing at a higher temperature
of 300 ꢀC resulted in no change on the corresponding EL
spectra [Fig. 7(B)]. Photos in Figure 8 clearly demonstrated
that the bright blue-green light emitted from devices with
the PTPQu and PTPTPQu emitting layers remained essen-
tially unaltered despite the whole assemblies had been
The energy of the highest occupied molecular orbital
(HOMO) and lowest unoccupied molecular orbital (LUMO)
levels of the alternative copolymers could be determined
from the oxidation onset potentials and the onset absorption
wavelength of polymer films, and the results are summarized
TABLE 2 Optical and Electrochemical Properties of the Conjugated Polymers
Oxidation (V; vs.
Ag/Agþ in CH3CN)
Solution k (nm)a
Film k (nm)
abs
abs
abs
Eogpt
(eV)d
Eox/onset
(V)e
HOMO
(eV)f
LUMO
(eV)f
c
Polymer
max
PL maxb
UF
max
onset
PL maxb
UF
PTPQu
PTPTPQu
a
391
393
457, 486
457, 487
0.67
0.82
397
399
458
447
503
504
e
0.59
0.74
2.71
2.78
0.78
0.75
ꢃ5.16
ꢃ5.13
ꢃ2.38
ꢃ2.42
Polymer solution in THF (ca. 1 ꢅ 10ꢃ5 M solution).
The oxidation potential versus Ag/Agþ calculated from CV spectrum
b
c
Excited at the abs max for both the solution and solid states.
using ferrocene as internal standard.
f
Fluorescence quantum yields (UF) values of the samples in dilute THF
Calculated from the equation HOMO ¼ ꢃ(Eox/onset ꢃ EFc/onset) ꢃ 4.8,
solution were measured in an integrating sphere with a quinine sulfate
LUMO ¼ HOMO þ band gap.
standard (10ꢃ5 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
.
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JOURNAL OF POLYMER SCIENCE PART A: POLYMER CHEMISTRY DOI 10.1002/POLA
FIGURE 5 (A) EL spectra and (B) L-J-V characteristics of the device based on the PTPQu copolymers. [Color figure can be viewed
in the online issue, which is available at wileyonlinelibrary.com.]
annealed at the respective high temperatures of 250 and
300 ꢀC for 4 h. Therefore, it is safe to conclude that the EL
spectra of the PLEDs based on the PTPQu and PTPTPQu
copolymers are highly stable.
gen. TP compound was prepared according to the reported
procedures.14
Synthesis
2,5-Bis(4-nitrophenyl)-3,4-diphenylthiophene (TPNO2)
A mixture of TP (10 g, 25.74 mmol) and glacial acetic acid
(200 mL) was vigorously stirred at 60 C to result in a homo-
EXPERIMENTAL
ꢀ
Materials
geneous suspension, to which mixed liquids of glacial acetic
acid (20 mL) and concentrated nitric acid (10 mL) were
added quickly. After stirring at 100 ꢀC for another 3 h, the
yellow suspension was filtered to obtain the crude product.
Continuous washing of the crude product with water was per-
formed until pH ¼ 7 reached. Column chromatography with
hexane eluent yielded the final product (11.21 g; 90 %).
Reagent grade benzyl chloride, sulfur powder, glacial acetic
acid, nitric acid (>90%), sodium hydroxide, methanol, benzyl
cyanide, tetrahydrofuran (THF), iron powder, 1,4-diacetylben-
zene, aluminum chloride, acetyl chloride, acetonitrile
(CH3CN), dichloromethane (DCM), m-cresol, phosphorus
pentoxide (P2O5), ammonium hydroxide solution (28% in
H2O), triethylamine, and ferrocene were purchased from
Sigma-Aldrich Chemical and were used directly. Tetrabuty-
lammonium hexafluorophosphate (TBAH) was purchased
from Fluka and purified by reꢀcrystallization from ethyl ace-
tate and dried in vacuo at 60 C. THF was refluxed over so-
dium/benzophenone under nitrogen for more than 2ꢄ3 days
and were distilled before use. Dichloromethane, triethyl-
amine, and m-cresol were distilled from CaH2 under nitro-
Mp: 220 ꢀC; IR (KBr pellet, cmꢃ1) 3061, 1591, 1515, 1346,
1115, 853, 700; 1H NMR (500 MHz, CDCl3) d 6.85 (d, 2H,
He) 7.05–7.13 (m, 8H, Hc, Hd), 7.16 (d, 4H, Hb), 7.95 (d, 4H,
Ha) (Fig. S1, Supporting Information); MS m/e: calcd for
C
28H18N2O4S, 478.1; found, 478.9 (Mþ); Anal. Calcd for
C28H18N2O4S: C, 70.28; H, 3.79; N, 5.85; O, 13.37; S, 6.7.
Found: C, 70.56; H, 3.11; N, 5.76; O, 13.67; S, 6.9.
FIGURE 6 (A) EL spectra and (B) L-J-V characteristics of the device based on the PTPTPQu copolymers. [Color figure can be
viewed in the online issue, which is available at wileyonlinelibrary.com.]
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FIGURE 7 EL spectra of (A) PTPQu after annealed at 250 ꢀC and (B) PTPTPQu after annealed at 300 ꢀC for 2 and 4 h. [Color figure
can be viewed in the online issue, which is available at wileyonlinelibrary.com.]
isolated by filtration and washed with cold methanol exhaus-
tively. The crude product was purified by column chromatog-
raphy (CH2Cl2) to give TPBz (2.18 g; 67%).
Mp: 285 ꢀC; IR (KBr pellet, cmꢃ1) 3059, 1634, 1597, 1558,
1490, 1435, 1343, 1206, 1069, 1030, 796, 766, 727, 688,
1
600; H NMR (500 MHz, CDCl3) d 7.72 (d, 4H, Ha), 7.45–7.48
(m, 4H, Hb, Hc), 7.21–7.27 (m, 12H, Hd, He), 7.07–7.09 (m,
6H, Hf, Hg) (Fig. S2, Supporting Information); MS m/e: calcd
for C42H26N2O2S, 622.17; found, 622.28 (Mþ); Anal. Calcd
for C42H26N2O2S: C, 81.01; H, 4.21; N, 4.5; O, 5.14; S, 5.15.
Found: C, 80.95; H, 4.54; N, 4.2; O, 5.15; S, 5.16.
5,50-(3,4-Diphenylthiophene-2,5-diyl)bis
(3-phenylbenzo[c]isoxazole) (TPBz)
To an ice-cooled mixture of sodium hydroxide (5 g, 125
mmol), methanol (30 mL), and THF (20 mL), benzyl nitrile
(1.32 g, 11.23 mmol) was added slowly. After stirring for 5
min, TPNO2 (2.5 g, 5.22 mmol) was added, and the mixture
ꢀ
was then heated at 80 C for 20 h. The reaction mixture was
then cooled in an ice bath, and the resulting precipitate was
(5,50-(3,4-Diphenylthiophene-2,5-diyl)bis(2-amino-
5,1-phenylene))bis(phenylmethanone) (TPPm)
Iron powder (4 g, 71.63 mmol) and water (4 mL) were
added to a stirred suspension of TPBz (1.5 g, 2.41 mmol) in
acetic acid (100 mL) at 95 ꢀC. The reaction mixture was
heated for 1 h before being cooled to room temperature to
remove the iron powder by filtration. The filtrate was
poured into water (500 mL), and the resulting precipitate
was collected and purified by column chromatography
FIGURE 8 Photographic images of the devices with the PTPQu
(EtOAc/hexane ¼ 1:5) to give TPPm (1.43 g, 94%).
emitting layer and (A) before and (B) after annealed at 250 ꢀC
Mp: 258 ꢀC; IR (KBr, cmꢃ1) 3463, 3350, 3047, 1633, 1579,
1490, 1423, 1299, 1255, 1164, 758, 694, 659; H NMR (500
for 4 h and with the PTPTPQu emitting layer and (C) before
and (D) after annealed at 300 ꢀC for 4 h.
1
FLUORESCENT COPOLYMERS CONTAINING TP-QU, LAI ET AL.
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JOURNAL OF POLYMER SCIENCE PART A: POLYMER CHEMISTRY DOI 10.1002/POLA
MHz, CDCl3) d7.39 (t, 2H, Ha), 7.23–7.29 (m, 10H, Hb, Hc, Hd),
7.17 (d, 8H, He), 7.06 (d, 2H, Hf), 6.81 (d, 2H, Hg), 6.60 (d, 2H,
Hh), 6.2 (s, 4H, Hi) (Fig. S3, Supporting Information); MS m/e:
calcd for C42H30N2O2S, 626.20; found, 626.28 (Mþ); Anal.
Calcd for C42H30N2O2S: C, 80.48; H, 4.82; N, 4.47; O, 5.11; S,
5.12. Found: C, 80.54; H, 4.73; N, 4.49; O, 5.13; S, 5.11.
Preparation of PTPQu
A mixture of Pꢀ2O5 (1 g, 7.05 mmol) in m-cresol (10 mL) was
heated at 135 C for 2 h. After cooling the whole mixtures to
room temperature, TPPm (0.5 g, 0.79 mmol) and 1,4-diace-
tylbenzene (0.13 g, 0.79 mmol) were then added, and the
ꢀ
entire system was reheated to 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 redissolved in chloroform and precipi-
tated from a 10% triethylamine/methanol (330 mL) solution.
This procedure was repeated for three times before Soxhlet
extraction by 10% triethylamine/methanol solution for 24 h.
ꢀ
The resulting product was then dried at 40 C under vacuum
to give PTPQu (0.54 g, 95%).
GPC (eluent: THF): Mn ¼ 24,000, Mw ¼ 66,000, and PDI ¼
2.77; Tg ¼ 245 ꢀC; IR (KBr pellet, cmꢃ1) 3065, 3024, 2922,
2854, 1579, 1539, 1484, 1349, 1078, 839, 704; 1H NMR
(500 MHz, CDCl3) d7.65–7.86 (b, 8H, Ha, Hb, Hc), 7.33–7.45
(b, 6H, Hd, He), 7.07–7.22 (b, 14H, Hf, Hg, Hh, Hi), 6.86–6.92
(b, 4H, Hj, Hk) (Fig. S5, Supporting Information); 13C NMR
(500 MHz, CDCl3) d102.5 (C1), 120.0 (C2), 126.8 (C3), 127.4
(C4), 127.5 (C5), 128.1 (C6), 128.4 (C7), 128.8 (C8), 129.3
(C9), 129.5 (C10), 133.5 (C11), 134.3 (C12), 134.9 (C13), 136.4
(C14), 136.9 (C15), 138.0 (C16), 147.5 (C17), 150.6 (C18),
156.8 (C19) (Fig. S6, Supporting Information).
1,10-(4,40-(3,4-Diphenylthiophene-2,5-diyl)bis
(4,1-phenylene))diethanone (TPAc)
TP (3.5 g, 9.01 mmol), anhydrous DCM (50 mL), and AlCl3
(2.5 g, 18.75 mmol) were added to a three-neck flask under
nitrogen atmosphere. The whole mixtures were then cooled
to 0 ꢀC by ice-water bath. Acetyl chloride (1.47 g, 18.75
mmol) was then added dropwise to the stirred reaction mix-
ture at 0 ꢀC. The reaction was allowed to warm to room
temperature and continued for overnight. The resulting mix-
ture was poured into ice water (300 mL), and the organic
layer was collected, concentrated, and poured into a large
amount of ethanol. The white powder precipitates were
collected and purified by column chromatography (EtOAc/
hexane ¼ 1:9) to give TPAc (4.1 g, 96%).
Mp: 259 ꢀC; IR (KBr, cmꢃ1) 3063, 3031, 3000, 1674, 1598,
1404, 1354, 1269, 1179, 958, 841, 696 cmꢃ1 1H NMR (500
;
MHz, CDCl3) d7.76 (d, 4H, Ha), 7.27 (d, 4H, Hb), 7.19 (d, 4H,
Hc), 7.10 (d, 4H, Hd), 6.93 (d, 2H, He) 2.54 (s, 6H, Hf)
(Fig. S4, Supporting Information); MS m/e: calcd for
Preparation of PTPTPQu
A solution of P2O5 (1 g, 7.05 mmol) in m-cresol (10 mL) was
ꢀ
heated at 135 C for 2 h. After cooling to room temperatures,
C
32H24O2S, 472.15; found, 472.11 (Mþ); Anal. Calcd for
TPPm (0.5 g, 0.79 mmol) and TPAc (0.37 g, 0.79 mmol)
were added before reheating at 135 C for another 12 h. The
C32H24O2S: C, 81.33; H, 5.12; O, 6.77; S, 6.78. Found: C,
ꢀ
81.54; H, 4.79; O, 6.72; S, 6.95.
product after cooling to room temperature was precipitated
from a 10% triethylamine/ethanol (100 mL) solution. The
collected product was then dissolved in chloroform and
precipitated from a 10% triethylamine/methanol (200 mL)
solution for three times. The resultant polymer was Soxhlet
extracted by a 10% triethylamine/methanol solution for
24 h. The resulting polymer was then dried at 40 ꢀC under
vacuum to give the final PTPTPQu polymer (0.76 g, 94%).
GPC (eluent: THF): Mn ¼ 8,900, Mw ¼ 20,500, and PDI ¼
2.3; Tg ¼ 295 ꢀC; IR (KBr pellet, cmꢃ1) 3055, 3027, 2918,
1598, 1584, 1538, 1479, 1437, 1355, 1263, 1180, 1152,
1070, 1019, 955; 1H NMR (500 MHz, CDCl3) d7.64ꢃ7.87 (b,
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8H, Hi, Hj, Hh, Hg), 7.33ꢃ7.46 (b, 6H, Hd, Hf), 7.08ꢃ7.22 (b,
14H, Hc, He), 6.85ꢃ6.91 (b, 4H, Ha, Hb) (broad, aromatic Hs)
(Fig. S7, Supporting Information); 13C NMR (500 MHz,
CDCl3) d102.5 (C1), 120.0 (C2), 126.8 (C3), 127.4 (C4), 127.5
(C5), 128.0 (C6), 128.1 (C7), 128.4 (C8), 128.8 (C9), 129.3
(C10), 129.5 (C11), 132.4 (C12), 133.5 (C13), 134.3 (C14),
136.3 (C15), 136.4 (C16), 136.9 (C17), 138.0 (C18), 147.5
tometer. Small quartz cell with dimensions of 0.2 ꢅ 1.0 ꢅ
4.5 cm3 was used for the UV–vis absorption spectra meas-
urements. All excitation wavelengths for fluorescent spectra
measurement were chosen to their respective absorption
maximum value. For reliable results, UV–vis and PL emission
spectra were immediately undertaken once the samples
were prepared. Quantum yields (UF) for solutions of PTPQu
and PTPTPQu in THF (10ꢃ5 M) were determined in relative
to the quinine sulfate standard (10ꢃ5 M in 0.1 N H2SO4, UF
¼ 0.55). For polymer films, UF was determined from
integrating sphere. The ground state optimization was for-
mulated from the Gaussian Tools of Materials Studio (MS)
commercial software of Accelrys. The calculation of density
functional theory (DFT) at B3LYP/6-31G level was
performed.
(C19), 150.6 (C20), 156.8 (C21
)
(Fig. S8, Supporting
Information).
Cyclic voltammetry (CV) was conducted on Autolab
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 tetrabuty-
lammonium hexafluorophosphate (TBAH)/CH3CN.
The EL devices with copolymers as emitting layers were fab-
ricated with a configuration of ITO/PEDOT: PSS (100 nm)/
PTPQu (100 nm)/Al (120 nm) and ITO/PEDOT: PSS (100
nm)/PTPTPQu (80 nm)/Al (120 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 10ꢃ5 torr.
The film thicknesses of emissive layers were measured by a
a-Step surface profiler (AMBIO XP-1). The EL spectra and
luminance-current-voltage (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 Bruker
DRX-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 performed
on Perkin-Elmer 2400 C, H, N, O, and S analyzer. Molecular
weight and molecular weight distribution of copolymers
were determined from GPC using a Waters 510 HPLC model
equipped with a 410 differential refractometer, a UV detector,
and three Ultrastyragel columns (100, 500, and 1000 Å) con-
nected in series. Polymer solution was eluted by THF with a
flow rate of 0.6 mL/min. The molecular weight calibration
curve was obtained from polystyrene standards. Melting
point (Tm) of organic compound and glass transition temper-
ature (Tg) of copolymer were determined from a TA Q-20
DSC calorimeter with a scan rate of 20 ꢀC/min under nitro-
gen atmosphere. The samples (5–10 mg) were primarily
CONCLUSIONS
Alternative tetraphenylthiophene-quinoline (TP-Qu) copoly-
mers with high efficiency, thermal and spectral stability were
prepared. Both PTPQu and PTPTPQu copolymers exhibit sim-
ilar UV–vis absorption and PL emission spectra with the
resolved peak maxima located at approximately the same
wavelength, which is correlated with theoretical calculation
results that the model TPTPT and TTTTT conformers possess
similar energy levels. The multiple phenyl pendant rings
inherited by the TP and Qu moieties of PTPQu and PTPTPQu
copolymers prohibit compact chain packing and result in
interchain space for easy dissolution in small-mass organic
solvents. In addition, the wholly aromatic-qunoline chain
structures render the copolymers rigid backbones and high
glass transition temperatures (Tg ¼ 245 ꢀC for PTPQu and
295 ꢀC for PTPTPTQu). The high glass transition tempera-
tures of both copolymers enhance their corresponding ther-
mal and spectral stability at temperatures in the vicinity of
ꢀ
ꢀ
held at 320 C for 3 min and then cooled rapidly to ꢃ50 C
before rescanned to obtain 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 extrapolated liquid and glass lines.
Thermogravimetric analyses (TGA) was performed under air
with use of a TA Q50 thermogravimetric analyzer operated
ꢀ
with a heating rate of 20 C/min under air flow (flow rate ¼
60 mL/min). FTIR spectra were obtained from a Nicolet IR-
200 spectrometer. Solution of organic compound or polymer
in THF was dropped on a KBr pellet and dried at 105 ꢀC
under vacuum to prepare solid film for analysis.
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-
FLUORESCENT COPOLYMERS CONTAINING TP-QU, LAI ET AL.
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JOURNAL OF POLYMER SCIENCE PART A: POLYMER CHEMISTRY DOI 10.1002/POLA
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,
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Tg. The electrochemical behavior studied by cyclic voltamme-
try revealed that the reversible oxidation redox of the
copolymers PTPQu and PTPTPQu couples at Eox/onset value
of 0.78 and 0.75 V, respectively.
7 (a) Kraft, A.; Grimsdale, A. C.; Holmes, A. B. Angew Chem Int
Ed 1998, 37, 402–428; (b) Sokolik, I.; Yang, Z.; Karasz, 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. Macromole-
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molecules 2000, 33, 2069–2082.
The PTPQu and PTPTPQu films have high quantum yields of
0.59 and 0.74, respectively. The PL spectra of both copoly-
mers remain nearly identical ifꢀthe thermal annealingꢀ tem-
peratures were kept below 250 C for PTPQu and 300 C for
PTPTPQu. Devices fabricated from the copolymers also show
EL spectral stability toward thermal annealing. The resultant
EL spectrum after heating PTPQu-derived device at 250 ꢀC
for 4 h remained essentially the same with the pristine one
without heating. For device fabricated from PTPTPQu, heat-
8 (a) Scherf, U.; List, E. J. W. Adv Mater 2002, 14, 477–487;
(b) Sainova, D.; Miteva, T.; Nothofer, H. G.; Scherf, U.;
Glowacki, I.; Ulanski, J.; Fujikawa, H.; Neher, D. Appl Phys
Lett 2002, 76, 1810–1812; (c) Buckley, A. R.; Rahn, M. D.; Hill,
J.; Cabanillas-Gonzalez, J.; Fox, A. M.; Bradley, D. D. C. Chem
Phys Lett 2001, 393, 331–336; (d) Leelerc, M. J Polym Sci Part
A: Polym Chem 2001, 39, 2867–2873; (e) Gong, X.; Iyer, P. K.;
Bazan, G. C.; Moses, D.; Heeger, A. J.; Xiao, S. S. Adv Funct
Matter 2003, 13, 325–330.
ꢀ
ing at 300 C for 4 h resulted in no change on the EL spec-
trum. The resultant properties suggest that both PTPQu and
PTPTPQu copolymers can serve well as the emitting layer in
the LED devices.
The authors appreciate the financial support from the National
Science Council, Taiwan, under Contract No. NSC 98-2221-E-
110-005-MY2.
9 (a) Montiilla, F.; Mallavia, R. Adv Funct Mater 2007, 17,
71–78; (b) List, E. J. W.; Guentner, R.; de Freitas, P. S.; Scherf,
U. Adv Mater 2002, 14, 374–378; (c) Kappaun, S.; Slugovc, C.;
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Jo, J. Y.; Lee, S. Y.; Keivanidis, P. E.; Wegner, G.; Yoon, D. Y.
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