Synthesis and optical properties of poly(tetramethylsilarylenesiloxane) derivative bearing diphenylcyclopentadithiophene moiety

Article abstract of DOI:10.1016/j.polymer.2014.10.048

The thermal and optical properties of a novel diphenylcyclopentadithiophene-based poly(tetramethylsilarylenesiloxane) derivative (P1), which was prepared via polycondensation of a novel disilanol monomer, i.e., 2,6-bis(dimethylhydroxysilyl)-4,4-diphenylcy

Full text of DOI:10.1016/j.polymer.2014.10.048

Polymer xxx (2014) 1e8
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Polymer
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Synthesis and optical properties of
poly(tetramethylsilarylenesiloxane) derivative bearing
diphenylcyclopentadithiophene moiety
Hitoshi Hanamura, Nobukatsu Nemoto*
Department of Chemical Biology and Applied Chemistry, College of Engineering, Nihon University, Tamura-machi, Koriyama, Fukushima 963-8642, Japan
a r t i c l e i n f o
a b s t r a c t
Article history:
The thermal and optical properties of
a novel diphenylcyclopentadithiophene-based poly(-
Received 21 August 2014
Received in revised form
15 October 2014
Accepted 20 October 2014
Available online xxx
tetramethylsilarylenesiloxane) derivative (P1), which was prepared via polycondensation of a novel
disilanol monomer, i.e., 2,6-bis(dimethylhydroxysilyl)-4,4-diphenylcyclopentadithiophene (M1), were
investigated. P1 exhibited good solubility in common organic solvents, such as benzene, toluene, chlo-
roform, dichloromethane and THF at ambient temperature. The glass transition temperature (Tg) of P1
was determined by differential scanning calorimetry to be 109 ꢀC. No melting temperature (Tm) of P1 was
observed, indicating the obtained P1 was an amorphous polymer. The temperature at 5% weight loss
(Td5) of P1 was 454 ꢀC, indicating the rather good thermostability of P1. Bathochromic and hyperchromic
effects were observed in the absorption and fluorescence spectra by introducing dimethylsilyl sub-
stituents onto 4,4-diphenylcyclopentadithiophene skeleton. The fluorescence quantum yields (FFs) of M1
and P1 in chloroform were determined to be 0.36 and 0.39, respectively. It was revealed that M1 and P1
exhibited the higher fluorescence intensity than diphenylcyclopentadithiophene owing to the cooper-
ative effects of the introduction of diphenyl groups onto spiro carbon of cyclopentadithiophene as well as
dimethylsilyl moieties onto 2- and 6-position of cyclopentadithiophene skeleton.
Keywords:
Cyclopentadithiophene
Poly(tetramethylsilarylenesiloxane)
Photoluminescence
© 2014 Elsevier Ltd. All rights reserved.
1. Introduction
aromatic species results in high fluorescence quantum yield [7e15].
From these points of view, we have reported the synthesis of
Polydimethylsiloxane (PDMS) has been well-known to be one of
the typical polymers which exhibit good thermostability based on the
high energy of siloxane bonding; however, PDMS has the low glass
transition temperature (Tg: e123 ꢀC) because of the flexible siloxane
bonding [1]. On the other hand, poly(tetramethylsilarylenesiloxane)
derivatives where aromatic moieties are introduced into the main
chain of PDMS have been reported to exhibit the excellent thermo-
stability as well as the high Tg. For example, the Tgs of a series of pol-
y(tetramethylsilarylenesiloxane)derivativeshavebeenreportedtobe
in the range from ꢁ52 ꢀC to 191 ꢀC depending on the arylene moiety
introduced [2e9]. Furthermore, poly(tetramethylsilarylenesiloxane)
derivatives have been also reported to show bathochromic and
hyperchromiceffectsintheabsorptionspectrabythealkylsilylgroups
diphenylfluorene-based poly(tetramethylsilarylenesiloxane) deriva-
tive which exhibited the high Tg as well as the good thermostability
and fluorescence property [8]. For example, poly(tetramethyl-9,9-
diphenyl-2,7-silfluorenylenesiloxane) (Pa as shown in Fig. 1) exhibi-
ted the rather high Tg of 125 ꢀC. In addition, the fluorescence quantum
yield of Pa in chloroform solution was determined to be 0.19, which
was five-fold value of 9,9-diphenylfluorene, indicating the introduc-
tion of dimethylsilyl moieties onto9,9-diphenylfluorene was effective
to improve the fluorescence quantum yield.
In the meantime, conjugated polymers [16,17] obtained by
polymerization of fused ring derivatives have emerged as attractive
materials for flexible, low cost and low power electro-optic devices.
Thiophene-based polymers and oligomers, such as dithienothio-
phene [18] derivatives, exhibit efficient charge transport in organic
field-effect transistors (OFETs) [19,20], while polyfluorene is one of
representative conjugated polymers suitable for use in optoelec-
tronic and electronic devices such as organic light emitting diode
(OLEDs) [21e23]. On the other hand, cyclopenta[2,1-b:3,4-b0]
dithiophene (CPDT) [24,25] is regarded as an analogous compound
of fluorene where the benzene rings are replaced by thiophene
introduced onto aromatic moieties owing to the s*ep* interaction
between alkylsilyl and aromatic moieties [7e12]. In addition, it has
been reported that incorporation of silyl substituents into the
* Corresponding author. Tel./fax: þ81 24 956 8812.
E-mail address: nemoto.nobukatsu@nihon-u.ac.jp (N. Nemoto).
http://dx.doi.org/10.1016/j.polymer.2014.10.048
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Please cite this article in press as: Hanamura H, Nemoto N, Synthesis and optical properties of poly(tetramethylsilarylenesiloxane) derivative
bearing diphenylcyclopentadithiophene moiety, Polymer (2014), http://dx.doi.org/10.1016/j.polymer.2014.10.048

2
H. Hanamura, N. Nemoto / Polymer xxx (2014) 1e8
(KANTO KAGAKU) were used after distillation over calcium hydride.
1,1,3,3-Tetramethylguanidinium 2-ethylhexanoate was obtained
from the equimolar mixture of 1,1,3,3-tetramethylguanidine and 2-
ethylhexanoic acid (Tokyo Kasei Kogyo Co., Inc.) [3e9].
2.2. Measurements
1H and 13C NMR spectra were recorded on a Bruker AVANCE
400F spectrometer in deuterated chloroform (CDCl3) or dime-
thylsulfoxide [(CD3)2SO] at ambient temperature. IR spectra were
measured on a PerkineElmer Spectrum One FT-IR spectrometer.
Glass transition temperature (Tg) and melting temperature (Tm)
were determined by differential scanning calorimetry (DSC) on a
RIGAKU ThermoPlus DSC 8230 at a heating rate of 10 ꢀC/min under
a nitrogen flow rate of 10 mL/min. Thermogravimetry analysis
(TGA) was performed on a RIGAKU ThermoPlus TG8110 at a heating
rate of 10 ꢀC/min under a nitrogen atmosphere. Number-average
(Mn) and weight-average (Mw) molecular weights were estimated
by size-exclusion chromatography (SEC) on an SHOWA DENKO
Shodex GPC-101 system with polystyrene gel columns (a pair of
Shodex GPC LF-804), eluted with THF using a calibration curve of
polystyrene standards. Gas chromatography mass spectroscopy
(GC/MS) was carried out using an Agilent 6890/5973 instrument.
Absorption spectra were measured on a Shimadzu UV-2450 spec-
trophotometer. Emission spectra were measured on a Shimadzu
RF-5300PC spectrophotometer by use of the solution degassed by
argon bubbling for 30 min. Fluorescence quantum yields (FFs) were
determined by use of pyrene (FF: 0.19) [8] as a standard. The
optimized geometrical structures and the energies for the highest
occupied molecular orbital (HOMO) and the lowest unoccupied
molecular orbital (LUMO) were estimated by the density functional
theory (DFT) calculations at B3LYP/6-31G(d) level of theory using
Spartan ’08 for Windows (Wavefunction, Inc., Irvine, CA, USA) [34].
Fig. 1. Structure of poly(tetramethyl-9,9-diphenyl-2,7-silfluorenylenesiloxane) (Pa).
rings and composed of a fused bithiophene ring. There have been
few reports on the fluorescent properties of CPDT derivatives or
conjugated polymers based on CPDT [26,27], while CPDT de-
rivatives have been rigid precursors of polymeric semiconducting
materials for the development of organic photovoltaic devices
[28e32]. The effect of the introduction of dimethylsilyl moieties
onto 2- and 6-position of 4,4-dimethylCPDT skeleton on the optical
properties was investigated in our previous report [27], where the
introduction of dimethylsilyl moieties onto 2- and 6-position of
4,4-dimethylCPDT skeleton was not so effective to improve the
fluorescence quantum yield. Thus, we have kept the effect of the
introduction of dimethylsilyl moieties onto 9,9-diphenylfluorene as
mentioned above in mind and been interested in the substituent
effect on spiro carbon (4-position) of CPDT skeleton. Namely, we
expected the introduction of bulky substituent such as phenyl
moiety onto the spiro carbon of CPDT would inhibit the interaction
of CPDT moieties to result in the inhibition of non-radiative tran-
sition and the improvement of the fluorescence quantum yield.
In this work, we studied the synthesis of novel poly(-
tetramethylsilarylenesiloxane) derivative having 4,4-diphenylCPDT
moiety (P1), as shown in Scheme 1. The effects of the introduction of
4,4-diphenylCPDT moiety (P1) into poly(tetramethylsilaryl
enesiloxane) derivative on the thermal property will be discussed. In
addition, the cooperative effects of the introduction of diphenyl
groups onto spiro carbon of CPDT as well as dimethylsilyl moieties
onto 2- and 6-position of CPDT skeleton will be revealed to improve
the fluorescence quantum yield.
2.3. Synthesis of 3,5,50-tribromo-2,20-bithiophene (2)
2,20-Bithiophene(1)(7.07g,0.0425mol)andN-bromosuccinimide
(22.7 g, 0.128 mol) were dissolved in chloroform/acetic acid (160 mL,
3:2, v/v). The reaction mixture was refluxed for 6 h under a dry argon
atmosphere. Then, the reaction mixture was poured into the stirred
mixtureofchloroform(100 mL)and water (100 mL). Theorganiclayer
was separated and dried over anhydrous magnesium sulfate and
filtered. The filtrate was concentrated under reduced pressure. The
residuewaspurified bysilica gel columnchromatographyeluted with
hexane. The fraction with an Rf value of 0.70 was collected and
concentrated under reduced pressure. The residue was recrystallized
fromthemixedsolventof chloroform and methanoltoafford2 aspale
yellow plates with the yield of 89% (15.3 g, 0.0380 mol). 1H NMR
2. Experimental procedure
2.1. Materials
2,20-Bithiophene (1) was prepared by the method reported in the
literature [33]. N-Bromosuccinimide (NBS), acetic acid, zinc, hydro-
chloric acid, tin(IV) chloride anhydrous (SnCl4), 1.6 mol/L n-butyl-
lithium in hexane, 2.6 mol/L n-butyllithium in hexane (KANTO
KAGAKU), benzophenone (nacalai tesque, inc.), chlorodimethylsilane
(Tokyo Kasei Kogyo Co., Inc.) and 5% palladium on charcoal (Wako
Pure Chemical Industries, Ltd.) were commerciallyavailableandused
as received. Tetrahydrofuran (THF, KANTO KAGAKU), diethyl ether
(KANTO KAGAKU) and cyclopentyl methyl ether (ZEON corporation)
were used after distillation over sodium. N,N,N0,N0-Tetramethyle-
thylenediamine(TMEDA, TokyoKaseiKogyoCo.,Inc.)andchloroform
(400 MHz, CDCl3, ppm):
d
7.05 (d, J ¼ 3.9 Hz,1H, thienyl proton), 7.01
(d, J ¼ 3.9 Hz,1H, thienyl proton), 6.89 (s,1H, thienyl proton).13C NMR
(100 MHz, CDCl3, ppm):
d 133.7 (thienyl carbon), 132.7 (thienyl car-
bon), 132.1 (thienyl carbon), 129.0 (thienyl carbon), 126.0 (thienyl
carbon), 112.7 (thienyl carbon),þ110.5 (thienyl carbon), 106.3 (thienyl
carbon). Mass (EI, m/z): 404 (M ). Tm: 80e82 ꢀC.
Scheme 1. Polycondensation of CPDT derivative having dimethylhydroxysilyl substituents.
Please cite this article in press as: Hanamura H, Nemoto N, Synthesis and optical properties of poly(tetramethylsilarylenesiloxane) derivative
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H. Hanamura, N. Nemoto / Polymer xxx (2014) 1e8
3
2.4. Synthesis of 3-bromo-2,20-bithiophene (3)
recrystallized from methanol to afford 5 as colorless crystals with
the yield of 73% (0.413 g, 1.25 mmol). 1H NMR (400 MHz, CDCl3,
Zn powder (10.8 g, 0.164 mol) was added in portions to a
vigorously stirred refluxing mixture of 2 (22.1 g, 0.0548 mol) in
140 mL of ethanol containing 13 mL of water, 34 mL of acetic acid,
and 3 mL of 3 mol/L HCl under a dry argon atmosphere. After
refluxing for 11 h, the mixture was extracted with hexane and the
combined organic layer was washed with saturated sodium
hydrogen carbonate aqueous solution. The organic layer was dried
over anhydrous magnesium sulfate and filtered. The filtrate was
concentrated under reduced pressure. The residue was purified by
silica gel column chromatography eluted with hexane. The fraction
with an Rf value of 0.50 was collected and concentrated under
reduced pressure to afford 3 as pale yellow liquid with the yield of
ppm): d 7.24e7.04 (m, 12H, thienyl protons and phenyl protons),
7.04 (d, J ¼ 1.8 Hz, 2H, thienyl protons). 13C NMR (100 MHz, CDCl3,
ppm): d 157.1 (thienyl carbon), 144.6 (thienyl carbon), 137.2 (phenyl
carbon), 129.0 (phenyl carbon), 128.3 (thienyl carbon), 127.5
(phenyl carbon), 126.2 (phenyl carbon), 124.1 (thienyl carbon), 62.7
(>C(Ph)2). Mass (EI, m/z): 330 (Mþ). Tm: 158e160 ꢀC.
2.7. Synthesis of 2,6-dibromo-4,4-diphenylcyclopentadithiophene (6)
N-Bromosuccinimide (0.634 g, 3.57 mmol) and 5 (0.589 g,
1.78 mmol) and in 30 mL of chloroform was stirred at ꢁ30 ꢀC for 3 h
under a dry argon atmosphere. The reaction mixture was poured
into 30 mL of saturated sodium thiosulfate aqueous solution, and
the crude product was extracted with chloroform. The combined
organic layer was washed with saturated sodium chloride aqueous
solution several times, dried over anhydrous sodium sulfate and
filtered. The filtrate was concentrated under reduced pressure and
the residue was recrystallized from methanol to afford 6 as yellow
crystals with the yield of 84% (0.730 g, 1.50 mmol). 1H NMR
94% (12.6 g, 0.0515 mol). 1H NMR (400 MHz, CDCl3, ppm):
d 7.35 (m,
2H, thienyl protons), 7.19 (d, J ¼ 5.4 Hz, 1H, thienyl proton), 7.08 (m,
1H, thienyl proton), 7.02 (d, J ¼ 5.4 Hz, 1H, thienyl proton). 13C NMR
(100 MHz, CDCl3, ppm):
d 134.3 (thienyl carbon), 131.8 (thienyl
carbon), 127.2 (thienyl carbon), 126.7 (thienyl carbon), 126.1
(thienyl carbon), 124.4 (thienyl carbon), 124.3 (thienyl carbon),
107.9 (thienyl carbon). Mass (EI, m/z): 246 (Mþ).
(400 MHz, CDCl3, ppm):
(m, 4H, phenyl protons), 7.03 (s, 2H, thienyl protons). 13C NMR
(100 MHz, CDCl3, ppm): 155.1 (thienyl carbon), 142.5 (thienyl
d 7.28e7.24 (m, 6H, phenyl protons), 7.16
2.5. Synthesis of 2,20-(bithiophenyl-3-yl)-diphenylmethanol (4)
d
Under a dry argon atmosphere, 1.6 mol/L n-butyllithium in
hexane (17 mL, 0.0272 mol) was added dropwise to 3 (6.67 g,
0.0272 mol) in dry diethyl ether (220 mL) at ꢁ78 ꢀC. The mixture
was stirred for 2 h, then, benzophenone (3.72 g, 0.0204 mol) in dry
diethyl ether (80 mL) was added to this solution at ꢁ78 ꢀC, and
warmed to ambient temperature. The reaction mixture was stirred
for 9 h at ambient temperature and poured into 150 mL of
ammonium chloride aqueous solution with stirring. The crude
product was extracted with ethyl acetate. The combined organic
layer was washed with water several times, dried over anhydrous
sodium sulfate and filtered. The filtrate was concentrated under
reduced pressure and purified by silica gel column chromatography
using the mixed solvent of hexane and ethyl acetate (8/1 v/v) as
eluant. The collected fraction with an Rf value of 0.33 was
concentrated under reduced pressure and the residue was recrys-
tallized from a mixed solvent of hexane/ethyl acetate to afford 4 as
black solid with the yield of 78% (5.55 g, 0.0159 mol). 1H NMR
carbon),136.1 (phenyl carbon),128.5 (phenyl carbon),127.3 (thienyl
carbon), 127.1 (phenyl carbon), 126.0 (phenyl carþbon), 112.1 (thienyl
carbon), 63.3 (>C(Ph)2). Mass (EI, m/z): 488 (M ). Tm: 289e291 ꢀC.
2.8. Synthesis of 2,6-bis(dimethylsilyl)-4,4-
diphenylcyclopentadithiophene (7)
Under a dry argon atmosphere, 2.6 mol/L n-butyllithium in
hexane (1.6 mL, 4.29 mmol) with TMEDA (0.498 g, 4.29 mmol) was
added dropwise to 6 (0.523 g, 1.07 mmol) in dry THF (44 mL)
at ꢁ78 ꢀC. After the mixture was stirred for
1 h, chlor-
odimethylsilane (0.405 g, 4.29 mmol) was added to this solution
at ꢁ78 ꢀC, and warmed to ambient temperature. The reaction
mixture was stirred for 24 h and poured into 50 mL of water with
stirring. The crude product was extracted with ethyl acetate. The
combined organic layer was washed with water several times,
dried over anhydrous sodium sulfate and filtered. The filtrate was
concentrated under reduced pressure and purified by silica gel
column chromatography using hexane as eluant. The collected
fraction with an Rf value of 0.40 was concentrated under reduced
pressure and the residue was recrystallized from methanol to
afford 7 as colorless crystals with the yield of 67% (0.318 g,
(400 MHz, CDCl3, ppm):
d 7.52e7.23 (m, 11H, thienyl protons and
phenyl protons), 7.12 (d, J ¼ 5.4 Hz, 1H, thienyl proton), 6.86 (m, 1H,
thienyl proton), 6.65 (m, 1H, thienyl proton), 6.37 (d, J ¼ 5.4 Hz, 1H,
thienyl proton), 3.40 (s, 1H, CeOH). 13C NMR (100 MHz, CDCl3,
ppm): d 147.4 (phenyl carbon), 145.4 (thienyl carbon), 135.0 (thienyl
carbon), 131.5 (thienyl carbon), 131.4(phenyl carbon), 128.7 (phenyl
carbon), 128.0 (thienyl carbon), 127.6 (phenyl carbon), 127.5
(thienyl carbon), 127.4 (thienyl carbon), 127.3 (thienyl carbon),
123.6 (thienyl carbon),þ80.6 (CeOH). IR (KBr, cmꢁ1): 3300 (eOH).
Mass (EI, m/z): 348 (M ). Tm: 121e123 ꢀC.
0.651 mmol). 1H NMR (400 MHz, (CD3)2SO, ppm):
d 7.45 (s, 2H,
thienyl protons), 7.29e7.18 (m, 10H, phenyl protons), 4.50 (m, 2H,
eSi(CH3)2eH), 0.39 (s, 12H, eSi(CH3)2e). 13C NMR (100 MHz,
(CD3)2SO, ppm):
d 160.3 (thienyl carbon), 144.0 (thienyl carbon),
141.8 (phenyl carbon), 138.2 (phenyl carbon), 132.8 (thienyl car-
bon), 129.0 (phenyl carbon), 127.9 (phenyl carbon), 127.3 (thienyl
carbon), 61.7 (>C(Ph)2), e2.5 (eSi(CH3)2e). IR (KBr, cmꢁ1): 2100
(eSieH). Mass (EI, m/z): 446 (Mþ). Tm: 128e130 ꢀC.
2.6. Synthesis of 4,4-diphenylcyclopentadithiophene (5)
SnCl4 (0.493 g,1.89 mmol) and 4 (0.599 g,1.72 mmol) in 60 mL of
chloroform was stirred at ambient temperature for 30 min under a
dry argon atmosphere. The reaction mixture was poured into 30 mL
of saturated sodium hydrogen carbonate aqueous solution, and the
crude product was extracted with chloroform. The combined
organic layer was washed with saturated sodium hydrogen car-
bonate aqueous solution several times, dried over anhydrous so-
dium sulfate and filtered. The filtrate was concentrated under
reduced pressure and purified by silica gel column chromatography
with hexane eluant. The collected fraction with an Rf value of 0.20
was concentrated under reduced pressure and the residue was
2.9. Synthesis of 2,6-bis(dimethylhydroxysilyl)-4,4-
diphenylcyclopenthadithiophene (M1)
To 5%-Pd on C (3.0 mg) with H2O (30 mg, 1.68 mmol) in THF
(3.0 mL), was added dropwise 7 (0.25 g, 0.560 mmol) in dry THF
(5.0 mL) at room temperature under a dry argon atmosphere. The
reaction mixture was stirred for 19 h and filtered. The filtrate was
concentrated under reduced pressure and the residue was recrys-
tallized from a mixed solvent of benzene/hexane to afford M1 as
colorless crystals with the yield of 86% (0.230 g, 0.480 mmol). 1
H
Please cite this article in press as: Hanamura H, Nemoto N, Synthesis and optical properties of poly(tetramethylsilarylenesiloxane) derivative
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H. Hanamura, N. Nemoto / Polymer xxx (2014) 1e8
NMR (400 MHz, (CD3)2SO, ppm):
d
7.33 (s, 2H, thienyl protons),
N-bromosuccinimide to generate 3,5,50-tribromo-2,20-bithiophene
(2) that was then selectively debrominated with Zn powder to give
3-dibromo-2,20-bithiophene (3). Compound 3 was lithiated using
n-butyllithium and then treated with benzophenone to afford (2,20-
bithiophenyl-3-yl)-diphenylmethanol (4), which was transformed
using SnCl4 to generate 4,4-diphenylcyclopentadithiophene (5).
2,6-Dibromo-4,4-diphenylcyclopentadithiophene (6) was synthe-
sized by bromination reaction of 5 using N-bromosuccinimide. 2,6-
Bis(dimethylsilyl)-4,4-diphenylcyclopentadithiophene (7) was
7.25e7.16 (m, 10H, phenyl protons), 6.16 (s, 2H, eSi(CH3)2eOH),
0.29 (s, 12H, eSi(CH3)2e). 13C NMR (100 MHz, (CD3)2SO, ppm):
d
160.0 (thienyl carbon), 144.2 (thienyl carbon), 142.8 (phenyl car-
bon), 141.4 (phenyl carbon), 130.8 (thienyl carbon), 129.1 (phenyl
carbon), 127.9 (phenyl carbon), 127.3 (thienyl carbon), 61.6
(>C(Ph)2), 2.0 (eSi(CH3)2e). IR (KBr, cmꢁ1): 3300 (eOH). Mass (EI,
m/z): 478 (Mþ). Tm: 171e173 ꢀC.
synthesized by lithiation reaction of
6 using n-butyllithium
2.10. Synthesis of polymer (P1)
at ꢁ78 ꢀC and successive reaction with chlorodimethylsilane. M1
was synthesized by the hydrolysis reaction of 7 using 5 %-Pd on C.
The obtained M1 underwent polycondensation using 1,1,3,3-
tetramethylguanidinium 2-ethylhexanoate as a catalyst to afford
the corresponding poly(tetramethylsilarylenesiloxane) derivative
P1 as shown in Scheme 1. As reported previously [3e9], any sol-
vents forming azeotropic mixtures with water and dissolving both
monomer and the resulting polymer, such as benzene and toluene,
can be used for the present polycondensation; however, the use of
cyclopentyl methyl ether as solvent resulted in high molecular
weight of the obtained polymer probably because of the good
solubility of both M1 and P1. The result of the polycondensation of
M1 is summarized in Table 1.
To M1 (0.250 g, 0.522 mmol) dissolved in cyclopentyl methyl
ether (1.7 mL), was added 1,1,3,3-tetramethylguanidinium 2-
ethylhexanoate (0.20 g). After the reaction mixture was refluxed
for 12 h, it was filtered and poured into 100 mL of methanol to
isolate the corresponding polymer (P1) as white precipitates with
the yield of 62% (0.158 g). 1H NMR (400 MHz, CDCl3, ppm):
d
7.21e7.18 (m, 10H, phenyl protons), 7.13 (s, 2H, thienyl protons),
0.32 (s, 12H, eSi(CH3)2e). 13C NMR (100 MHz, CDCl3, ppm):
d
160.1
(thienyl carbon), 144.1 (thienyl carbon), 142.3 (phenyl carbon), 141.1
(phenyl carbon),130.1 (thienyl carbon),128.4 (phenyl carbon),127.8
(phenyl carbon), 126.8 (thienyl carbon), 61.5 (>C(Ph)2), 1.7
(eSi(CH3)2e). IR (KBr, cmꢁ1): 1100 (SieOeSi).
P1 was soluble in common organic solvents such as THF, chlo-
roform, dichloromethane, toluene, and so on. The formation of P1
was confirmed by SEC measurement and NMR spectroscopy. The 1H
and 13C NMR spectra of M1 and P1 are shown in Figs. 2 and 3,
respectively. The 1H and 13C NMR spectra of P1 were almost similar
to those of M1; however, the progress of polycondensation of M1 to
afford P1 was confirmed by the disappearance of a signal at
3. Results and discussion
3.1. Synthesis of monomer and polymer
Scheme 2 shows the synthetic pathways for disilanol monomer
(M1). In the first step, 2,20-bithiophene (1) was brominated using
Scheme 2. Synthetic pathways for CPDT derivative having dimethylhydroxysilyl substituents.
Please cite this article in press as: Hanamura H, Nemoto N, Synthesis and optical properties of poly(tetramethylsilarylenesiloxane) derivative
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H. Hanamura, N. Nemoto / Polymer xxx (2014) 1e8
5
Table 1
unimodal and that the low-molecular weight species such as a
cyclic dimer or trimer were almost completely removed by repre-
cipitation in methanol as depicted in Fig. S1. It would be speculated
that the ratio of the cyclic oligomers in the reaction mixture was
below 38% because the yield of linear polymer was 62%. These re-
sults would support that no side-reactions occurred during the
polycondensation.
Results of polycondensation and thermal properties of P1.
Yield (%)a
62
Mn
18000
Mw/Mn
Tg (ꢀC)c
Tm (ꢀC)d
Td5 (ꢀC)e
b
b
Polymer
P1
1.41
109
ef
454
a
Insoluble part in methanol.
Estimated from SEC eluted with THF based on polystyrene standards.
Glass transition temperature determined by DSC on a second heating scan at a
b
c
rate of 10 ꢀC/min in N2.
d
Melting temperature determined by DSC at a heating rate of 10 ꢀC/min under a
3.2. Thermal characterization of polymer
nitrogen atmosphere.
e
Temperature at 5% weight loss determined by TG in N2.
Not detected from ꢁ50 ꢀC to 400 ꢀC.
f
Fig. 4 shows the DSC trace of P1 on a second heating scan under
a nitrogen atmosphere at a heating rate of 10 ꢀC/min. The glass
transition temperature (Tg) of P1 was determined by DSC to be
109 ꢀC as summarized in Table 1. No melting temperature (Tm) was
observed in the DSC thermogram of P1. This result would indicate
that P1 was a noncrystalline polymer as observed in the other
poly(tetramethylsilarylenesiloxane) derivatives [3,4,6,8]. 9,9-
6.16 p.p.m. based on eOH groups as observed in the 1H NMR
spectrum of M1. The structure of P1 as described in Fig. 3 was also
confirmed by the consistent integrated ratio of each 1H NMR signal.
The SEC profile of P1 indicated that the obtained polymer was
Fig. 2. (a) 1H NMR (solvent: DMSO-d6, 400 MHz) and (b) 13C NMR spectra (solvent: DMSO-d6, 100 MHz) of M1 at ambient temperature.
Fig. 3. (a) 1H NMR (solvent: CDCl3, 400 MHz) and (b) 13C NMR spectra (solvent: CDCl3, 100 MHz) of P1 at ambient temperature.
Please cite this article in press as: Hanamura H, Nemoto N, Synthesis and optical properties of poly(tetramethylsilarylenesiloxane) derivative
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6
H. Hanamura, N. Nemoto / Polymer xxx (2014) 1e8
454 ꢀC, which was somewhat lower than that of Pa, plausibly owing
to the increase in molecular mobility of the main chain of P1 as
deduced from the relatively low Tg of P1.
3.3. Optical properties
The optical properties of the obtained CPDT derivatives,
including monomers and polymers, were also studied. Fig. 5 shows
the absorption and fluorescence spectra of CPDT derivatives and
the optical properties of CPDT derivatives are summarized in
Table 2. The introduction of dimethylsilyl groups onto CPDT skel-
eton induced the bathochromic and hyperchromic effects in the
absorption spectra of CPDT derivatives as shown in Fig. 5(a)
through
s*ep* conjugations between the dimethylsilyl groups
and aromatic moieties [7e13]. It has been reported [8,9,27] that
lowering the energy gap between the highest occupied molecular
orbital (HOMO) and the lowest unoccupied molecular orbital
(LUMO) causes the bathochromic effects by stabilization of the
Fig. 4. DSC thermogram of P1 on a second heating scans under a N2 flow rate of 10 mL/
LUMO state through
the dipole moments of the HOMO and LUMO states owing to the
conjugation in the HOMO and the *e * conjugation in the
s*ep* conjugation. In addition, the increase in
min and a cooling or heating rate of 10 ꢀC/min.
se
p
s
p
LUMO [7e13] would cause the enhancement of the transition
moment to result in the hyperchromic effects.
Diphenylfluorene-based poly(tetramethylsilarylenesiloxane) has
the structural correlation with P1, and it bears the same sub-
stituents on the spiro-carbon moiety such as 9-position of fluorene
and 4-position of CPDT. The Tg of 9,9-diphenylfluorene-based pol-
y(tetramethylsilarylenesiloxane) (Pa as shown in Fig. 1) has been
reported to be 125 ꢀC [8] and somewhat higher than that of P1
(109 ꢀC). In addition, Pa has been reported to exhibit the crystal-
lizing temperature (Tc) and Tm at 194 ꢀC and 276 ꢀC during a heating
scan, respectively; however, CPDT-based P1 showed neither Tc nor
Tm during a heating scan, indicating the introduction of CPDT
moieties instead of fluorenylene ones in the main chain decreased
the crystallization tendency of polymer chain. The temperature at
5% weight loss (Td5) of the present P1 was determined by TGA to be
Table 3 summarizes the HOMO and LUMO energy levels as well
as the energy gap between LUMO and HOMO for M1 and 5 calcu-
lated by the DFT method at the B3LYP/6-31G(d) level of theory for
the confirmation of the effects of the introduction of dimethylsilyl
moieties on the absorption spectra. The introduction of dime-
thylsilyl moieties onto CPDT skeleton was confirmed to lower the
LUMO energy level by comparison of the LUMO energy level of M1
(ꢁ1.47 eV) with that of 5 (ꢁ1.15 eV), probably owing to the stabi-
lization of LUMO state through
s*ep* conjugation. Thus, the
introduction of dimethylsilyl moieties caused the decrease in the
energy gap between LUMO and HOMO, resulting in the bath-
ochromic shift of the maximum absorption.
Fig. 5. Absorption (a) and fluorescence (b) spectra of CPDT derivatives in CHCl3 at ambient temperature (conc.: 2.0 ꢂ 10ꢁ6 mol/L, lex: 317 nm).
Fig. 6. Structure of 4,4-dimethylcyclopentadithiophene derivatives. 4,4-dimethylCPDT; CPDT1, 2,6-bis(dimethylsilyl)-4,4-dimethylcyclopentadithiophene; CPDT2, 2,6-
bis(dimethylhydroxysilyl)-4,4-dimethylcyclopentadithiophene; Pb, 4,4-dimethylCPDT based poly(tetramethylsilarylenesiloxane).
Please cite this article in press as: Hanamura H, Nemoto N, Synthesis and optical properties of poly(tetramethylsilarylenesiloxane) derivative
bearing diphenylcyclopentadithiophene moiety, Polymer (2014), http://dx.doi.org/10.1016/j.polymer.2014.10.048

H. Hanamura, N. Nemoto / Polymer xxx (2014) 1e8
7
Table 2
diphenylCPDT. It would be remarkable that the cooperative ef-
fects of the introduction of diphenyl groups onto spiro carbon of
CPDT as well as dimethylsilyl moieties onto 2- and 6-position of
Optical properties of CPDT derivatives.
labs/nm (ε/L molꢁ1 cmꢁ1
)
lem/nm
FF
a
Compound
CPDT skeleton appears and improves the FF
.
5
7
M1
P1
323 (12700) 332 (10500)
340 (23700) 351 (19400)
338 (21000) 351 (17900)
340 (22200) 352 (19200)
317 (15000) 329 (11800)
336 (24500) 348 (19200)
335 (24300) 346 (19200)
336 (23700) 348 (19200)
373
387
385
387
382
382
381
381
0.03
0.41
0.36
0.39
0.01
0.09
0.09
0.09
4. Conclusions
4,4-dimethylCPDTb
CPDT1c
We achieved the synthesis of poly(tetramethylsilary
lenesiloxane) derivative with diphenylcyclopentadithiophene
moiety (P1). P1 exhibited the good solubility in common organic
solvents such as benzene, toluene, chloroform, dichloromethane
and THF. The Tg of P1 was determined by DSC to be 109 ꢀC. The Td5
of P1 was 454 ꢀC, indicating the relatively good thermostability of
P1. As for the optical properties of the obtained 4,4-diphenylCPDT
derivatives, the bathochromic and hyperchromic effects were
observed by introducing dimethylsilyl moieties onto 4,4-
diphenylCPDT. The bathochromic shifts of wavelength at the
maximum absorption and fluorescence were induced by stabiliza-
CPDT2d
Pbe
a
Fluorescence quantum yield (FF) was determined by using pyrene (FF: 0.19) [8]
as a standard in CHCl3.
b
4,4-Dimethylcyclopentadithiophene (as shown in Fig. 6) [27].
2,6-Bis(dimethylsilyl)-4,4-dimethylcyclopentadithiophene (as shown in Fig. 6)
c
[27].
d
2,6-Bis(dimethylhydroxysilyl)-4,4-dimethylcyclopentadithiophene (as shown
in Fig. 6) [27].
e
4,4-DimethylCPDT based poly(tetramethylsilarylenesiloxane) (as shown in
Fig. 6) [27].
tion of LUMO state through s*ep* conjugation. It was remarkable
that the cooperative effects of the introduction of diphenyl groups
onto spiro carbon of CPDT as well as dimethylsilyl moieties onto 2-
and 6-position of CPDT skeleton are revealed to be much effective
for the increase in fluorescence quantum yield, as deduced from the
low fluorescence quantum yields of both unsubstituted 4,4-
diphenylCPDT and 2,6-bis(dimethylsilyl)substituted-4,4-dimethy
lCPDT.
Table 3
Results of DFT calculation for CPDT derivatives.
Compound
LUMO/eVa
HOMO/eVa
LUMOꢁHOMO gap/eV
5
M1
ꢁ1.15
ꢁ1.47
ꢁ5.25
ꢁ5.36
4.10
3.89
a
Calculated with density-functional theory (DFT) method at the B3LYP/6-31G(d)
level.
Acknowledgments
Table 2 also provides the wavelength at maximum emission
lem) and fluorescence quantum yields (FFs) of CPDT derivatives.
The authors would like to appreciate Ms. Satoko Tokiwa and Ms.
Nami Sugashima, Nihon University College of Engineering World-
wide Research Center for Advanced Engineering and Technology
(NEWCAT), for performing NMR measurements.
(
The introduction of dimethylsilyl groups onto 4,4-diphenylCPDT
skeleton was revealed to induce bathochromic effects also in the
fluorescence spectra of CPDT derivatives as well as the improve-
ment of the FF. The FFs of unsubstituted 4,4-diphenylCPDT (5) and
dimethylsilylated adducts (7, M1, P1) were 0.03, 0.41, 0.36, and 0.39,
respectively, indicating that the introduction of dimethylsilyl moi-
eties onto 4,4-diphenylCPDT skeleton rather increased FF. 9,9-
Diphenylfluorene-based poly(tetramethylsilarylenesiloxane) (Pa
as shown in Fig. 1) is regarded as the analogous polymer of P1
where the thiophene rings are replaced by phenyl rings. The FF of
Pa has been reported to be 0.19 [8] and smaller than that of P1
(0.39) in chloroform solution, indicating a decrease in the tendency
to aggregate by use of a CPDT skeleton. This result may also be
supported by the observation that the introduction of CPDT moiety
in the main chain decreases the crystallization tendency of polymer
chains. The use of CPDT skeletons was confirmed to be effective in
the inhibition of aggregate formation and to result in improved
emission intensity.
On the other hand, the FFs of 4,4-diphenylCPDT with dime-
thylsilyl groups (7, M1, P1) are higher than those of 4,4-
dimethylCPDT with dimethylsilyl groups (CPDT1, CPDT2, Pb) as
shown in Table 2 [27]. The introduction of dimethylsilyl moieties
onto 2- and 6-position of 4,4-dimethylCPDT skeleton was not so
effective to improve the FF, that is, the FF of 4,4-dimethylCPDT was
0.01 and those of CPDT1, CPDT2 and Pb were the almost constant
values of 0.09 [27]. On the other hand, the introduction of dime-
thylsilyl moieties onto 4,4-diphenylCPDT skeleton effectively
improve the FF, that is, the FF of 4,4-diphenylCPDT was 0.03 and
those of 7, M1 and P1 were 0.41, 0.36 and 0.39, respectively, as
mentioned above. It would be probably because the interaction and
molecular mobility of 4,4-diphenylCPDT would be inhibited by
bulky diphenyl moieties on spiro carbon and result in the inhibition
of non-radiative transition that the improvement of FF was
observed by the introduction of dimethylsilyl moieties onto 4,4-
Appendix A. Supplementary data
Supplementary data related to this article can be found at http://
dx.doi.org/10.1016/j.polymer.2014.10.048.
References
[1] Brook MA. Silicon in organic, organometallic, and polymer chemistry. New
York: John Wiley and Sons, Inc.; 2000 [chapter 9].
[2] Zhang R, Pinhas AR, Mark JE. Macromolecules 1997;30:2513.
[3] Otomo Y, Nagase Y, Nemoto N. Polymer 2005;46:9714.
[4] Sato I, Takeda S, Arai Y, Miwa H, Nagase Y, Nemoto N. Polym Bull 2007;59:607.
[5] Hattori Y, Miyajima T, Sakai M, Nagase Y, Nemoto N. Polymer 2008;49:2825.
[6] Nemoto N, Yamaguchi T, Ozawa Y, Nigorikawa M, Yanai Y, Nagase Y. Polym
Bull 2008;61:165.
[7] Imai K, Sasaki T, Abe J, Kimoto A, Tamai Y, Nemoto N. Polym J 2009;41:584.
[8] Imai K, Kihara Y, Kimoto A, Abe J, Tamai Y, Nemoto N. Polym J 2011;43:58.
[9] Imai K, Sasaki T, Abe J, Nemoto N. Polym Bull 2012;68:1589.
[10] Shizuka H, Sato Y, Ueki Y, Ishikawa M, Kumada M. J Chem Soc Faraday Trans
1984;80:341.
[11] Karatsu T. J Photochem Photobiol C Photochem Rev 2008;9:111.
[12] Kyushin S, Ikarugi M, Goto M, Hiratsuka H, Matsumoto H. Organometallics
1996;15:1067.
[13] Declercq D, Delbeke P, De Schryver FC, Van Meervelt L, Miller RD. J Am Chem
Soc 1993;115:5702.
[14] Maeda H, Inoue Y, Ishida H, Mizuno K. Chem Lett 2001;30:1224.
[15] Ponomarenko SA, Kirchmeyer S. Adv Polym Sci 2011;235:33.
[16] Grimsdale AC, Müllen K. Adv Polym Sci 2006;199:1.
[17] Grimsdale AC, Chan KL, Martin RE, Jokisz PG, Holmes AB. Chem Rev 2009;109:
897.
[18] Ozturk T, Ertas E, Mert O. Tetrahedron 2005;61:11055.
[19] Shirota Y, Kageyama H. Chem Rev 2007;107:953.
[20] Zhang X, Zhu D. Polym Chem 2010;1:409.
[21] Leclerc M. J Polym Sci Part A Polym Chem 2001;39:2867.
[22] Neher D. Macromol Rapid Commun 2001;22:1365.
[23] Scherf U, List EJW. Adv Mater 2002;14:477.
[24] Kraak A, Wiersema AK, Jordens P, Wynberg H. Tetrahedron 1968;24:3381.
[25] Coppo P, Turner ML. J Mater Chem 2005;15:1123.
Please cite this article in press as: Hanamura H, Nemoto N, Synthesis and optical properties of poly(tetramethylsilarylenesiloxane) derivative
bearing diphenylcyclopentadithiophene moiety, Polymer (2014), http://dx.doi.org/10.1016/j.polymer.2014.10.048

8
H. Hanamura, N. Nemoto / Polymer xxx (2014) 1e8
[26] Pal B, Yen WC, Yang JS, Chao CY, Hung YC, Lin ST, et al. Macromolecules
2008;41:6664.
[31] Chen CH, Hsieh CH, Dubosc M, Cheng YJ, Hsu CS. Macromolecules 2010;43:
697.
[27] Hanamura H, Nemoto N. Polymer 2011;52:5282.
[28] Beyer R, Kalaji M, Kingscote-Burton G, Merphy PJ, Pereria VMSC, Taylor DM,
et al. Synth Met 1998;92:25.
[29] Chochos CL, Economopoulos SP, Deimede V, Gregoriou VG, Lloyd MT,
Malliaras GG, et al. J Phys Chem C 2007;111:10732.
[30] Li KC, Huang JH, Hsu YC, Huang PJ, Chu CW, Lin JT, et al. Macromolecules
2009;42:3681.
[32] Ko S, Mondal R, Risko C, Lee JK, Hong S, McGehee MD, et al. Macromolecules
2010;43:6685.
[33] Washino T, Yoshikura M, Obata S. Agric Biol Chem 1986;50:565.
[34] Calculated using Spartan '08 for Windows (Wavefunction, Inc, Irvine, CA, USA)
Shao Y, Molnar LF, Jung Y, Kussmann J, Ochsenfeld C, et al. Phys Chem Chem
Phys 2006;8:3172.
Please cite this article in press as: Hanamura H, Nemoto N, Synthesis and optical properties of poly(tetramethylsilarylenesiloxane) derivative
bearing diphenylcyclopentadithiophene moiety, Polymer (2014), http://dx.doi.org/10.1016/j.polymer.2014.10.048