Synthesis of poly(3-(2-benzotriazolovinyl)thiophene) (PBVT) copolymers containing the alkyl, electron-transporting, and hole-transporting groups

Article abstract of DOI:10.1002/bkcs.10238

(3-(2-Benzotriazolovinyl)thiophene (BVT) containing an electron-transporting moiety was polymerized through FeCl₃ oxidation. In addition, BVT was copolymerized with different functional groups: 3-octylthiophene (OT) containing alkyl groups for improving the solubility in common organic solvents; N-octylcarbazolylene (OcCz) containing hole-transporting groups for improving the optical property; and the alkyl groups for improving the solubility. Soluble π-conjugated poly(3-(2-benzotriazolovinyl)thiophene-co-3-(2-benzotriazoloethylthiophene)-co-N-octylcarbazolene) ([(BVT)_n-(BET)_m-OcCz₂)_y) copolymer was synthesized. ¹H NMR analysis was used to verify the structure of the polyBVT copolymers. Especially, the emission of the ([(BVT)_n-(BET)_m-OcCz₂]_y) copolymer (662 nm) was red-shifted by about 64 nm, compared to that of poly(3-(2-benzotriazolo-ethyl)thiophene) (polyBET, 598 nm).

Full text of DOI:10.1002/bkcs.10238

Article
DOI: 10.1002/bkcs.10238
BULLETIN OF THE
S.-Y. Jang et al.
KOREAN CHEMICAL SOCIETY
SynthesisofPoly(3-(2-benzotriazolovinyl)thiophene) (PBVT)Copolymers
Containing the Alkyl, Electron-transporting, and Hole-transporting
Groups
*
Suk-Yong Jang, Hyeok-Jin Hong, Sung-Kyu Ham, and Sien-Ho Han
Department of Chemical Engineering and Biotechnology, Korea Polytechnic University, Siheung-Si 429-793,
Korea. *E-mail: han@kpu.ac.kr
Received July 15, 2014, Accepted December 31, 2014, Published online March 26, 2015
(3-(2-Benzotriazolovinyl)thiophene (BVT) containing an electron-transporting moiety was polymerized
through FeCl3 oxidation. In addition, BVT was copolymerized with different functional groups: 3-
octylthiophene (OT) containing alkyl groups for improving the solubility in common organic solvents;
N-octylcarbazolylene (OcCz) containing hole-transporting groups for improving the optical property; and
the alkyl groups for improving the solubility. Soluble π-conjugated poly(3-(2-benzotriazolovinyl)thio-
phene-co-3-(2-benzotriazoloethylthiophene)-co-N-octylcarbazolene) ([(BVT)n-(BET)m-OcCz2)y) copolymer
was synthesized. 1H NMR analysis wasused toverify the structure of the polyBVT copolymers. Especially, the
emission of the ([(BVT)n-(BET)m-OcCz2]y) copolymer (662 nm) was red-shifted by about 64 nm, compared to
that of poly(3-(2-benzotriazolo-ethyl)thiophene) (polyBET, 598 nm).
Keywords: Poly(3-(2-benzotriazolovinyl)thiophene), OcCz, Hole-transporting, Electron-transporting
Introduction
of the rigid structure caused by the double bond between the
thiophene and benzotriazole segments.
Since polymer light-emitting diodes (PLEDs) based on poly
(p-phenylenvinylene) (PPV) were reported by Burroughes
et al. in 1990, a variety of π-conjugated polymers have been
found to exhibit luminescence.1–3 Especially, thiophene-
based conjugated copolymers have been attracting much
attention as light-emitting material for PLEDs because of their
advantages of easy functionalization and controllable
mechanical and thermal stability as well as electrical and opti-
cal properties.4–6 However, their poor solubility in common
organic solvents remains a serious problem for their applica-
tion in commercial PLEDs.7–9 Therefore, our laboratory
previously reported on the characterization of soluble poly-
thiophene (PT) derivatives containing an electron-
transporting moiety.10,11 The photoluminescence (PL)
intensities of the prepared poly(3-(2-benzotriazolo-ethyl)thio-
phene) (polyBET) and poly(3-(2-(5-chlorobenzotriazolo)
ethyl)thiophene) (polyCBET) were about 40 times higher than
that of poly(3-octylthiophene) (polyOT).10 However, their
emission was blue-shifted by about 70 nm. This finding led
us to develop a new kind of PT derivative for PLEDs.
We synthesized poly(3-(2-benzotriazolovinyl)thiophene)
(polyBVT) as a π-conjugated polymer. Since the polyBVT
has a vinylene chain as a spacer to connect the thiophene
and benzotriazole with the electron-withdrawing groups, it
will lead to a decreased bandgap, a red-shifted emission wave-
length, and a stable planarization from the main chain by redu-
cing the torsional strain among side chains and extending the
effective conjugation chain. However, polyBVT was insolu-
bleinorganicsolventssuchasCHCl3, THF, andDMFbecause
To overcome this drawback, polyBVT was copolymerized
by introducing alkyl groups on the side chain in the BVT mon-
omer for improving the solubility. Furthermore, we synthe-
sized the PBVT copolymers containing hole-transporting
and electron-transporting groups for improving the optical
properties. The ultimate purpose of this work was to explore
therelationbetween the PTderivative with the vinylene spacer
and the introduction of the functional groups.
Experimental
Materials. 3-Thiophenecarboxaldehyde(96%)waspurchased
from Alfa Aesar Co., (Ward Hill, MA, USA). 1-Benzotriazole-
1-methanol (97%) was purchased from TCI Co., (Tokyo,
Japan). Prydine (99%), n-BuLi (1.6 M solution in hexane),
phosphorus tribromide (98%), triphenyl phosphine (99%),
3-(2-thienyl)ethanol (99%), benzotriazole (99%), potassium
carbonate (99%), sodium hydroxide (65%), carbazole (99%),
n-bromooctane (98%), and 3-octylthiophene (97%) were pur-
chased from Aldrich Chem. Co., (St. Louis, MO, USA) and
used without any further purification. Iron(III)chloride,
n-hexane(anhydrous),andtoluene(anhydrous)werepurchased
from Duksan Co., (Seoul, Korea). Chloroform, acetone, tetra-
hydrofuran (THF), and dimethylformamide (DMF) were pur-
chased from Tedia Co., (Fairfield, OH, USA).
1
Instruments. H-NMR spectra were obtained on an Advance
500 spectrometer. Infrared spectra were obtained on a Perkin-
Elmer instrument (GX1) (stamford, CT, USA). The molecular
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weights were determined by gel permeation chromatography
(GPC; YL Instrument Co.) (Anyang, Korea) with polystyrene
standard calibration. The UV–visible spectra were recorded
with a Mechasys spectrometer (Optizen 2120UV) (Daegue,
Korea). Cyclic voltammetry was carried out on a CH Instru-
ment Co., Instrument (CHI608D) (Austin, TX, USA). The
PL spectra were recorded on a fluorescent spectrometer (FS
2; Scinco Co.) (Anyang, Korea). The thermal properties were
obtained on a thermal analyzer (Q600; TA Instrument Co.)
(Dallas, TX, USA) at a heating rate of 1 ꢀC/min.
was added dropwise to the FeCl3 (0.572 g, 3.53 mmol)/CHCl3
(20 mL) solution at room temperature. The mixture was stirred
for 24 h. CHCl3 was removed from the reaction mixture using
anevaporator. Theresidualmonomer andFeCl3 wereSoxhlet-
extracted using a methanol/acetone solvent for 12 h. The red
([(BVT)n-OcCz2]y) copolymer was thus obtained (yield
0.085 g, 36.96%). The polymer was insoluble in organic sol-
vents such as CHCl3, THF, and DMF.
Copolymerization of ([(BVT)n-(BET)m-OcCz2]y) Copoly-
mer with Molar Ratio of BVT/BET/OcCz (1:1:1). The
BVT (0.20 g, 0.88 mmol)/BET (0.201 g, 0.88 mmol)/OcCz
(0.25 g, 0.88 mmol)/CHCl3(10 mL) mixture was added drop-
wise to the FeCl3 (1.64 g, 10.02 mmol)/CHCl3 (20 mL) solu-
tion at room temperature. The mixture was stirred for 24 h.
CHCl3 was removed from the reaction mixture using an evap-
orator. The residual monomer and FeCl3 were Soxhlet-
extracted using methanol/acetone solvent for 12 h. The red
([(BVT)n-(BET)m-OcCz2]y) copolymer was thus obtained
(yield 0.59 g, 92.32%). The resultant molar ratio of BVT/
BET/OcCz was 1.5:1.4:1. 1H-NMR (CDCl3, 500 MHz,
ppm): δ 8.16–7.42 (b, 11.39H), δ 7.26–7.00 (b, 6.29H), δ
2.8–2.56 (b, 8.95H), 1.70–0.85 (b, 128.43H). The synthetic
routes of the PBVT copolymers are shown in Scheme 2.
Film Fabrication. ThePBVT copolymerfilms wereprepared
by spin-coating on glass substrates at 3000 rpm for 30 s from
the copolymer/chloroform solution (0.01 g/mL). The films
were dried to remove the solvent in a N2 atmosphere at room
temperature.
SynthesisoftheBVTMonomerandPolyBVT. Thedetailed
synthetic procedure was given in our previous papers.10–12
The synthetic procedure of the BVT monomer is shown in
Scheme 1.
Synthesis of the BET and OcCz Monomers. The detailed
synthetic procedure was given in our previous papers.10–12
Copolymerization of ([(BVT)n-(OT)m]y) Copolymer with
Molar Ratio of BVT/OT (1:1). The BVT (0.30 g, 1.32
mmol)/OT (0.26 g, 1.32 mmol)/CHCl3 (10.0 mL) mixture
was added dropwise to the FeCl3 (1.72 g, 10.56 mmol)/CHCl3
(20 mL) solution at room temperature. The mixture was stirred
for 24 h. Then, the reaction mixture was placed in a rotary
evaporator and CHCl3 was removed. The residual monomer
and FeCl3 were Soxhlet-extracted using methanol/acetone
solvent. The copolymer was Soxhlet-extracted again in chlo-
roform. The red ([(BVT)n-(OT)m]y) copolymer was thus
obtained (yield 0.51 g, 89.9%/chloroform soluble fraction
0.24 g, 40.3%). The resultant molar ratio of BVT/OT was
1
1:1.8. H-NMR (CDCl3, 500 MHz, ppm): δ 8.16–7.42 (b,
Results and Discussion
11.39H), δ 7.26–7.00 (b, 6.29H), δ 2.8–2.56 (b, 8.95H),
1.70–0.85 (b, 128.43H).
Solubility and Molecular Weight. ([(BVT)n-(OT)m]y) and
([(BVT)n-(BET)m-OcCz2]y) copolymers were completely sol-
uble in common organic solvents such as CHCl3, THF, and
Copolymerization of ([(BVT)n-OcCz2]y) Copolymer with
Molar Ratio of BVT/OcCz (1:1). The BVT (0.1 g, 0.44
mmol)/OcCz (0.13 g, 0.44 mmol)/CHCl3(10 mL) mixture
Scheme 1. Synthetic procedure of the BVT monomer.
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Copolymerization of PBVTs Containing the Functional Groups
KOREAN CHEMICAL SOCIETY
Scheme 2. Synthetic routes of the PBVT copolymers.
DMF. The weight-average molecular weights (Mw) of
the ([(BVT)n-(OT)m]y) and ([(BVT)n-(BET)m-OcCz2]y) copo-
lymers were 29 500 and 32 100 with polydispersity index
(PDI) of 2.5 and 2.68. The number-average molecular weights
(Mn) were 11 400 and 12 000. However, the ([(BVT)n-
OcCz2]y) copolymer was only partially soluble in the common
organic solvents.
observed for the PBVT copolymers.16–19 The first mass deg-
radation of the PBVT copolymers in the temperature range
200–250 ꢀC is related to the destruction of the bond between
the two aromatics and aromatic. The second mass degradation
that occurred between 300 ꢀC and 400 ꢀC could be attributed
to the decomposition of the vinylene chains. The third mass
degradation of the two copolymers at about 430 ꢀC is due to
the decompositions of the main chain.
Optical Properties. Figure 3 shows the PL spectra and
UV–vis spectra of the PBVT copolymers and polyBET. The
PL spectrum of polyBET and ([(BVT)n-(OT)m]y) copolymer
showed that their maximum emission was at 598 and
620 nm, respectively. The emission of ([(BVT)n-(BET)m-
OcCz2]y) copolymer (662 nm) was red-shifted by about 64
nm compared to that of polyBET. This is probably because
the vinylene spacer in ([(BVT)n-(BET)m-OcCz2]y) played a
role in balancing the electron and hole transporters in the
light-emittinglayer.20
1H-NMR Analysis. Figure 1(a) shows the 1H-NMR spectrum
of BVT monomer. The strong peaks at around 7.3–8.1 ppm
were assigned. This was attributed to a new bond that was
formed between the two aromatic groups and an aromatic
group. It can be reasonably concluded that the polymerization
of vinylene occurs at positions a and b.13–15 Figure 1(b) shows
the 1H-NMR spectrum of ([(BVT)n-(OT)m]y) copolymer.
The typical peaks of the OT were observed at 7–7.2 and
0.8–2.8 ppm. The characteristic peaks of the BVT monomer
were also assigned at 7.3–8.1 ppm. This shows that
([(BVT)n-(OT)m]y) copolymer was successfully polymerized.
Figure 1(c) shows the 1H-NMR spectrum of ([(BVT)n-
(BET)m-OcCz2]y) copolymer. The characteristic peaks of
the BVT, BET, and OcCz monomers were observed at
7.3–8.1 ppm, 3.5–5.0 ppm, and 0.8–1.9 ppm, respectively.
Thermal Properties. Figure 2 shows the results of thermo-
gravimetry(TGA) analysisofthePBVTcopolymers andpoly-
BET. Three consecutive mass degradation steps were
Also, solid-state UV–vis spectra gave further insight
into the extent of polymer conjugation and structure, as
well as the electronic effects of the polymeric materials
in the solid state. As shown in Figure 3, the π–π∗ transition
of ([(BVT)n-(OT)m]y) and ([(BVT)n-(BET)n-OcCz2]y) copo-
lymers and polyBET were characterized by absorption max-
ima (λmax) at around 453, 462, and 440 nm, respectively.21–24
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Copolymerization of PBVTs Containing the Functional Groups
KOREAN CHEMICAL SOCIETY
(a)
(b)
OT
(c)
BET
OcCz
Figure 1. 1H-NMR spectrum of (a) BVT (b) ([(BVT)n-(OT)m]y), and (c) ([(BVT)n-(BET)m-OcCz2]y).
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Copolymerization of PBVTs Containing the Functional Groups
KOREAN CHEMICAL SOCIETY
Figure 2. TGA analysis of the PBVT copolymers and polyBET.
Figure 4. Cyclic voltammogram of the PBVT copolymers and
polyBET.
voltammograms of these can be calculated by the following
equation:
À
Á
HOMO ðeVÞ = −4:8− Eonset − E1=2ðFerroceneÞ
The highest occupied molecular orbital (HOMO) levels of
the ([(BVT)n-(OT)m]y) and ([(BVT)n-(BET)m-OcCz2]y) copo-
lymers and polyBET were −5.25, −5.27, and −5.36 eV,
respectively.25–28 The lowest unoccupied molecular orbital
(LUMO) levels were calculated from the optical bandgaps
estimated from UV–vis spectra and the HOMO levels. The
LUMO levels of ([(BVT)n-(OT)m]y) and ([(BVT)n-(BET)m-
OcCz2]y) copolymers and polyBET were −3.14, −3.21 and
−3.12 eV, respectively.
Conclusion
For improving their solubility and optical properties, PBVT
copolymers containing alkyl, electron-transporting, and
hole-transporting groups were copolymerized. Especially,
([(BVT)n-(BET)m-OcCz2)y) copolymer containing both elec-
tron- and hole-transporting groups and ([(BVT)n-(OT)m]y)
copolymer containing the alkyl groups were very well soluble
in common organic solvents. The emission of ([(BVT)n-
(BET)m-OcCz2]y) and ([(BVT)n-(OT)m]y) copolymers was
red-shifted by about 64 and 22 nm, respectively, compared
to that of the polyBET. Their HOMO and LUMO levels were
−5.27, −5.25 and −3.21, −3.14 eV, respectively. The optical
bandgaps were 2.06 and 2.11 eV, respectively.
Figure 3. Optical properties of the PBVT copolymers and polyBET.
The optical bandgaps calculated from UV band edge were
2.11, 2.06, and 2.24 eV for the ([(BVT)n-(OT)m]y), ([(BVT)n-
(BET)m-OcCz2]y) copolymer and polyBET.
Cyclic Voltammogram. Figure 4 shows the cyclic voltam-
mograms of the PBVT copolymers and polyBET. The cyclic
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