Synthesis and properties of cyclopentadithiophene-based poly(silarylenesiloxane) derivatives

Article abstract of DOI:10.1016/j.polymer.2011.09.031

Poly(silarylenesiloxane) derivatives with 4,4-dimethylcyclopenta[2,1-b:3,4- b′]dithiophene moiety, bearing dimethyl- (P1), methylphenyl- (P2) and diphenyl- (P3) substituents on silyl moieties, were prepared via polycondensation of the corresponding disilanol monomers, that is, 2,6-bis(dimethylhydroxysilyl)-4,4-dimethylcyclopenta[2,1-b:3,4-b′] dithiophene (M1), 2,6-bis(methylphenylhydroxysilyl)-4,4-dimethylcyclopenta[2,1- b:3,4-b′]dithiophene (M2), and 2,6-bis(diphenylhydroxysilyl)-4,4- dimethylcyclopenta[2,1-b:3,4-b′]dithiophene (M3), respectively. P1-P3 exhibited the good solubility in common organic solvents, such as benzene, toluene, chloroform, dichloromethane, THF, and so on. The glass transition temperatures (T_gs) of P1, P2 and P3 were determined by differential scanning calorimetry to be 56, 97 and 137 °C, respectively, depending on the substituent on the silyl moieties. No melting temperatures (T_ms) of P1, P2 and P3 were observed, suggesting the obtained P1-P3 are amorphous polymers. The temperatures at 5% weight loss (T_d5s) of P1, P2 and P3 were 460, 459 and 479 °C, respectively, indicating that the larger number of phenyl group on the silyl moieties resulted in the better thermostability. Bathochromic and hyperchromic effects were observed in the absorption and fluorescence spectra by introducing silyl substituents onto 4,4- dimethylcyclopenta[2,1-b:3,4-b′]dithiophene moiety. In addition, the bathochromic shift of the maximum absorption (λ_abs) and the increase in the fluorescence quantum yield (Φ_F) were observed by the introduction of phenyl group onto the silyl moieties.

Full text of DOI:10.1016/j.polymer.2011.09.031

Polymer 52 (2011) 5282e5289
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Polymer
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Synthesis and properties of cyclopentadithiophene-based poly(silarylenesiloxane)
derivatives
*
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
Poly(silarylenesiloxane) derivatives with 4,4-dimethylcyclopenta[2,1-b:3,4-b0]dithiophene moiety,
bearing dimethyl- (P1), methylphenyl- (P2) and diphenyl- (P3) substituents on silyl moieties, were
prepared via polycondensation of the corresponding disilanol monomers, that is, 2,6-bis(dimethylhy-
droxysilyl)-4,4-dimethylcyclopenta[2,1-b:3,4-b0]dithiophene (M1), 2,6-bis(methylphenylhydroxysilyl)-
4,4-dimethylcyclopenta[2,1-b:3,4-b0]dithiophene (M2), and 2,6-bis(diphenylhydroxysilyl)-4,4-dime-
thylcyclopenta[2,1-b:3,4-b0]dithiophene (M3), respectively. P1eP3 exhibited the good solubility in
common organic solvents, such as benzene, toluene, chloroform, dichloromethane, THF, and so on. The
glass transition temperatures (Tgs) of P1, P2 and P3 were determined by differential scanning calorimetry
to be 56, 97 and 137 ꢀC, respectively, depending on the substituent on the silyl moieties. No melting
temperatures (Tms) of P1, P2 and P3 were observed, suggesting the obtained P1eP3 are amorphous
polymers. The temperatures at 5% weight loss (Td5s) of P1, P2 and P3 were 460, 459 and 479 ꢀC,
respectively, indicating that the larger number of phenyl group on the silyl moieties resulted in the better
thermostability. Bathochromic and hyperchromic effects were observed in the absorption and fluores-
cence spectra by introducing silyl substituents onto 4,4-dimethylcyclopenta[2,1-b:3,4-b0]dithiophene
moiety. In addition, the bathochromic shift of the maximum absorption (labs) and the increase in the
fluorescence quantum yield (FF) were observed by the introduction of phenyl group onto the silyl
moieties.
Article history:
Received 5 August 2011
Received in revised form
16 September 2011
Accepted 19 September 2011
Available online 22 September 2011
Keywords:
Cyclopentadithiophene
Polysiloxane
Photoluminescence
Ó 2011 Elsevier Ltd. All rights reserved.
1. Introduction
precursors of polymeric semiconducting materials for the devel-
opment of organic photovoltaic devices [13e17].
Conjugated polymers [1,2] 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, including fused ring bithiophene deriva-
tives [3] such as dithienothiophene [4] derivatives, exhibit efficient
charge transport in organic field-effect transistors (OFETs) [5,6],
while polyfluorenes are representatives of conjugated polymers
which are suitable for applications in electronics and optoelec-
tronics, such as organic light emitting diodes (OLEDs) [7e9]. On the
other hand, cyclopenta[2,1-b:3,4-b0]dithiophene (CPDT) [10,11] is
regarded as an analogous compound of fluorene where the
benzene rings are replaced by thiophene rings and composed of
a fused ring bithiophene derivative. There have been few reports on
the fluorescent properties of CPDT derivatives or conjugated poly-
mers based on CPDT [12], while CPDT derivatives have been rigid
In the meantime, the incorporation of silyl substituents onto
aromatic species has been reported to result in high fluorescence
quantum yield [18e26]. The use of polysiloxane derivatives as
polymeric OLED materials seems to be inadequate because of their
low glass transition temperature (Tg) [27,28] allowing the formation
of aggregates and/or interchain excimers to induce the decline of
the color stability of light emission, even though the other prop-
erties of polysiloxanes such as good thermostability and stability
against atomic oxygen [27e29] seem to be appropriate for the
polymeric OLED materials. Raising Tg of polysiloxane derivatives
would be desirable to solve this problem. One of the methods for
raising Tg is incorporation of bulky and rigid moieties into the main
chain [30e36]. For example, the Tg of poly(dimethylsiloxane) has
been reported to be ꢁ123 ꢀC [27]; however, those of a series of poly
(tetramethylsilarylenesiloxane) derivatives to be in the range
from ꢁ52 ꢀC to 156 ꢀC depending on the arylene moiety introduced
[32e36]. From these points of view, we have reported the synthesis
of several poly(tetramethylsilarylenesiloxane) derivatives with
pyrene or dibenzosilole moieties which exhibited the high Tg as
* Corresponding author. Tel./fax: þ81 24 956 8812.
E-mail address: nemoto@chem.ce.nihon-u.ac.jp (N. Nemoto).
0032-3861/$ e see front matter Ó 2011 Elsevier Ltd. All rights reserved.
doi:10.1016/j.polymer.2011.09.031

H. Hanamura, N. Nemoto / Polymer 52 (2011) 5282e5289
5283
well as the good thermostability and fluorescence property [22,24].
In addition, it has been revealed that the introduction of phenyl silyl
substituents onto CPDT skeleton allowed CPDT to have good fluo-
rescent property [37].
In this article, we report the synthesis of novel
poly(silarylenesiloxane) derivatives with CPDT moieties, as shown
in Scheme 1. The effects of the introduction of CPDT moieties into
poly(silarylenesiloxane) derivatives as well as the substituent on
the silyl moieties on their thermal and optical properties will be
also discussed.
pair of Shodex GPC LF-804), eluted with THF using a calibration
curve of polystyrene standards. Gas chromatographyemass spec-
troscopy (GC/MS) was carried out using an Agilent 6890/5973
instrument. Absorption spectra were measured on a Shimadzu
UVe2450 spectrophotometer. 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) [22] 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) [38].
2. Experimental procedure
2.1. Materials
4,4-Dimethylcyclopenta[2,1-b:3,4-b0]dithiophene (1) [13,14,37]
was prepared by the method reported in the literature. Tetrahy-
drofuran (THF, Wako Pure Chemical Industries, Ltd.), diethyl ether
(Wako Pure Chemical Industries, Ltd.), and benzene (KANTO
KAGAKU) were used after distillation over sodium. N,N,N0,N0-Tet-
ramethylethylenediamine (TMEDA, Tokyo Kasei Kogyo Co., Inc.)
and N,N-dimethylformamide (DMF, Wako Pure Chemical Indus-
tries, Ltd.) 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.) [33e36]. N-Bro-
mosuccinimide (NBS, KANTO KAGAKU), 2.6 mol/L n-butyllithium in
hexane (KANTO KAGAKU), chlorodimethylsilane (Tokyo Kasei
Kogyo Co., Inc.), chloromethylphenylsilane (SigmaeAldrich, Inc.),
chlorodiphenylsilane (SigmaeAldrich, Inc.), 5% palladium on char-
coal (Wako Pure Chemical Industries, Ltd.) were commercially
available and used as received.
2.3. Synthesis of 2,6-dibromo-4,4-dimethylcyclopenta[2,1-b:3,4-b0]
dithiophene (2)
Under a dry argon atmosphere with shielding light, 4,4-
dimethylcyclopenta[2,1-b:3,4-b0]dithiophene
(1)
(0.200
g,
0.97 mmol) and NBS (0.345 g, 1.94 mmol) in 7 mL of DMF were
stirred at ambient temperature for 1 h. The reaction mixture was
poured into 10 mL of saturated sodium thiosulfate aqueous solu-
tion, and the crude product was extracted with hexane. The
combined organic layers were washed with saturated sodium
chloride aqueous solution several times, dried over anhydrous
sodium sulfate and filtered. The filtrate was concentrated under
reduced pressure and purified by silica gel chromatography with
hexane eluent. The collected fraction with Rf value of 0.57 was
concentrated under reduced pressure and the residue was recrys-
tallized from hexane to afford 2 as colorless crystals with the yield
of 0.343 g (97%). 1H NMR (CDCl3, 400 MHz,
protons), 1.40 (s, 6H, eCH3). 13C NMR (CDCl3, 100 MHz,
d
): 6.99 (s, 2H, thienyl
): 158.3
d
(thienyl carbon),135.1 (thienyl carbon),124.0 (thienyl carbon), 111.4
2.2. Measurements
(thienyl carbon), 46.4 [>C(CH3)2], 24.8 (eCH3). M.p.: 106 ꢀC.
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 FTeIR 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 anal-
ysis (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 a SHOWA
DENKO Shodex GPC-101 system with polystyrene gel columns (a
2.4. Synthesis of 2,6-bis(diphenylsilyl)-4,4-dimethylcyclopenta[2,1-
b:3,4-b0]dithiophene (5)
Under a dry argon atmosphere, 2.6 mol/L n-butyllithium in
hexane (2.5 mL, 6.59 mmol) with TMEDA (0.767 g, 6.59 mmol) was
added dropwise to 2 (0.600 g, 1.65 mmol) in dry diethyl ether
(50 mL) at ꢁ78 ꢀC. The mixture was stirred for 30 min, and warmed
to ambient temperature. After the mixture was stirred for 1 h,
chlorodiphenylsilane (1.44 g, 6.59 mmol) was added to this solution
at 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
Scheme 1. Polycondensation of CPDT derivatives having hydroxysilyl substituents.

5284
H. Hanamura, N. Nemoto / Polymer 52 (2011) 5282e5289
washed with water several times, dried over anhydrous sodium
sulfate and filtered. The filtrate was concentrated under reduced
pressure and purified by silica gel chromatography using the mixed
solvent of hexane and chloroform (4/1 v/v) as eluent. The collected
fraction with Rf value of 0.60 was concentrated under reduced
pressure and the residue was recrystallized from a mixed solvent of
chloroform/methanol to afford 5 as colorless crystals with the yield
(phenyl carbon), 134.6(thienyl carbon), 134.4 (phenyl carbon), 130.6
(thienyl carbon), 130.2 (phenyl carbon), 128.4 (phenyl carbon), 44.1
[>C(CH3)2], 24.0 [>C(CH3)2], ꢁ4.3 [eSi(CH3)(Ph)eH]. IR (KBr,
cmꢁ1): 2135 (SieH). Mass (EI, m/z): 446 (Mþ). M.p.: 62 ꢀC.
2.6. Synthesis of 2,6-bis(diphenylhydroxysilyl)-4,4-
dimethylcyclopenta[2,1-b:3,4-b0]dithiophene (M3)
of 0.45 g (48%). 1H NMR (DMSO-d6, 400 MHz,
aromatic ring), 7.46 (m, 14H, aromatic ring), 5.50 [s, 2H,
eSi(Ph)2eH] 1.40 (s, 6H, eCH3). 13C NMR (DMSO-d6, 100 MHz,
):
d): 7.61 (m, 8H,
Under a dry argon atmosphere, 5 (0.55 g, 0.94 mmol) in dry THF
(6.5 mL) was added dropwise to 5%-Pd on C (5.0 mg) with H2O
(51 mg, 2.83 mmol) in THF (2.2 mL) at room temperature. The
reaction mixture was stirred for 14 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 M3 as
colorless crystals with the yield of 0.47 g (82%). 1H NMR (DMSO-d6,
d
164.4 (thienyl carbon), 141.9 (thienyl carbon), 135.3 (phenyl
carbon), 132.7 (thienyl carbon), 132.6 (phenyl carbon), 131.8
(thienyl carbon), 130.6 (phenyl carbon), 128.6 (phenyl carbon), 44.3
[>C(CH3)2], 24.9 (eCH3). IR (KBr, cmꢁ1): 2132 (SieH). Mass (EI, m/
z): 570 (Mþ). M.p.: 105 ꢀC.
400 MHz,
protons), 7.31 [s, 2H, eSi(Ph)2eOH], 1.39 (s, 6H, eCH3). 13C NMR
(DMSO-d6, 100 MHz, ): 163.9 (thienyl carbon), 141.2 (thienyl
carbon),137.9 (phenyl carbon),136.4 (thienyl carbon),134.5 (phenyl
carbon), 130.5 (thienyl carbon), 130.2 (phenyl carbon), 128.1
(phenyl carbon), 44.1 [>C(CH3)2], 25.1 (eCH3). IR (KBr, cmꢁ1): 3293
(eOH). Mass (EI, m/z): 602 (Mþ). M.p.: 178 ꢀC.
d): 7.61 (m, 8H, aromatic protons), 7.42 (m, 14H, aromatic
2.5. Spectral data for 3 and 4
d
2,6-Bis(dimethylsilyl)-4,4-dimethylcyclopenta[2,1-b:3,4-b0]dithio-
phene (3) and 2,6-bis(methylphenylsilyl)-4,4-dimethylcyclopenta
[2,1-b:3,4-b0]dithiophene (4) were prepared by the similar method
as the preparation of 5 using chlorodimethylsilane and chloro-
methylphenylsilane as the raw material, respectively. The spectral
data for 3 and 4 are as shown below.
2.7. Spectral data for M1 and M2
3 was obtained as colorless liquid with the yield of 86%. 1H NMR
(DMSO-d6, 400 MHz,
eSi(CH3)2eH], 1.41 [s, 6H, >C(CH3)2], 0.38 [s, 12H, eSi(CH3)2eH].
13C NMR (DMSO-d6, 100 MHz,
): 163.6 (thienyl carbon), 140.1
d
): 7.38 (s, 2H, thienyl protons), 4.50 [m, 2H,
2,6-Bis(dimethylhydroxysilyl)-4,4-dimethylcyclopenta[2,1-b:
3,4-b0]dithiophene (M1) and 2,6-bis(methylphenylhydroxysilyl)-
d
4,4-dimethylcyclopenta[2,1-b:3,4-b0]dithiophene
(M2)
were
(thienyl carbon), 136.4 (thienyl carbon), 129.5 (thienyl carbon), 43.7
[>C(CH3)2], 24.8 [>C(CH3)2], ꢁ3.1 [eSi(CH3)2eH]. IR (KBr, cmꢁ1):
2134 (SieH). Mass (EI, m/z): 322 (Mþ).
prepared by the similar method as the preparation of M3 using 3
and 4 as the raw material, respectively. The spectral data for M1 and
M2 are as shown below.
4 was obtained as colorless crystals with the yield of 58%. 1H
M1 was obtained as colorless solids with the yield of 71%. 1H
NMR (DMSO-d6, 400 MHz,
d
): 7.60 (m, 4H, phenyl protons), 7.43 (m,
NMR (DMSO-d6, 400 MHz,
2H, eSi(CH3)2eOH], 1.41 [s, 6H, >C(CH3)2], 0.31 [s, 12H,
eSi(CH3)2eOH]. 13C NMR (DMSO-d6, 100 MHz,
): 163.6 (thienyl
carbon), 141.4 (thienyl carbon), 139.4 (thienyl carbon), 128.4
d): 7.30 (s, 2H, thienyl protons), 6.12 [s,
8H, aromatic protons), 4.98 [m, 2H, eSi(CH3)(Ph)eH], 1.40 [s, 6H,
>C(CH3)2], 0.42 [s, 6H, eSi(CH3)(Ph)eH]. 13C NMR (DMSO-d6,
d
100 MHz, d): 164.1 (thienyl carbon), 141.1 (thienyl carbon), 134.8
Scheme 2. Synthetic pathways for CPDT derivatives having hydroxysilyl substituents.

H. Hanamura, N. Nemoto / Polymer 52 (2011) 5282e5289
5285
Table 1
silcyclopentadithiophenylenesiloxane) (P2) were prepared by the
similar method as the preparation of P3 using M1 and M2 as
a monomer, respectively. The spectral data for P1 and P2 are as
shown below.
Results of polycondensation and thermal properties of P1eP3.
Td5 (ꢀC)d
c
c
Polymer
Yield (%)
Mn
Mw/Mn
P1
P2
P3
40a
69a
30b
13000
17000
25000
1.34
1.78
1.49
460
459
479
P1 was obtained as colorless powder with the yield of 40%. 1H
NMR (CDCl3, 400 MHz,
d
): 7.08 (s, 2H, thienyl protons), 1.45 [s, 6H,
>C(CH3)2], 0.39 [s, 12H, eSi(CH3)2e]. 13C NMR (CDCl3, 100 MHz,
d
):
a
Insoluble part in methanol.
Insoluble part in acetone.
Estimated from SEC eluted with THF based on polystyrene standards.
Temperature at 5% weight loss determined by TG in N2.
b
c
163.3 (thienyl carbon), 141.2 (thienyl carbon), 140.2 (thienyl
carbon), 127.6 (thienyl carbon), 44.0 [>C(CH3)2], 25.3 [>C(CH3)2],
1.7 [eSi(CH3)2e]. IR (KBr, cmꢁ1): 1054 (SieO).
d
P2 was obtained as colorless powder with the yield of 69%. 1H
NMR (CDCl3, 400 MHz,
phenyl protons), 7.01 (s, 2H, thienyl protons), 1.33 [s, 6H, >C(CH3)2],
0.56 [s, 6H, eSi(CH3)(Ph)e]. 13C NMR (CDCl3, 100 MHz,
): 163.5
(thienyl carbon), 141.9 (thienyl carbon), 138.2 (phenyl carbon),
137.1(thienyl carbon), 133.9 (phenyl carbon), 129.9 (thienyl carbon),
129.1 (phenyl carbon), 127.8 (phenyl carbon), 44.0 [>C(CH3)2], 25.2
[>C(CH3)2], 0.5 [eSi(CH3)(Ph)e]. IR (KBr, cmꢁ1): 1053 (SieO).
d): 7.60 (m, 4H, phenyl protons), 7.34 (m, 6H,
(thienyl carbon), 43.9 [>C(CH3)2], 25.2 [>C(CH3)2], 1.6
[eSi(CH3)2eOH]. IR (KBr, cmꢁ1): 3170 (eOH). Mass (EI, m/z): 478
(Mþ). M.p.: >106 ꢀC (polymerization).
d
M2 was obtained as colorless solids with the yield of 76%. 1H
NMR (DMSO-d6, 400 MHz, d): 7.62 (m, 4H, phenyl protons), 7.39 (m,
6H, phenyl protons), 7.31 (s, 2H, thienyl protons), 6.75 [s, 2H,
eSi(CH3)(Ph)eOH], 1.39 [s, 6H, >C(CH3)2], 0.57 [s, 6H,
eSi(CH3)(Ph)eOH]. 13C NMR (DMSO-d6, 100 MHz,
d): 163.7 (thienyl
carbon),140.5 (thienyl carbon),139.8 (phenyl carbon),138.3(thienyl
carbon), 133.7 (phenyl carbon), 129.8 (thienyl carbon), 129.3
(phenyl carbon), 128.0 (phenyl carbon), 44.0 [>C(CH3)2], 25.1
[>C(CH3)2], 0.3 [eSi(CH3)(Ph)eOH]. IR (KBr, cmꢁ1): 3293 (eOH).
Mass (EI, m/z): 354 (Mþ). M.p.: >115 ꢀC (polymerization).
3. Results and discussion
3.1. Synthesis of monomer and polymer
Scheme 2 shows the synthetic pathways for disilanol mono-
mers, that is, M1, M2 and M3. M1eM3 were obtained by hydrolysis
reaction of 3e5, respectively, catalyzed by 5% palladium on char-
coal. 3e5 were obtained from 2,6-dibromo-4,4-dimethylcyclopenta
[2,1-b:3,4-b0]dithiophene (2) via the lithiation reaction and
successive reaction using chlorosilane reagents.
The obtained M1, M2 and M3 underwent polycondensation
using 1,1,3,3-tetramethylguanidinium 2-ethylhexanoate as a cata-
lyst to afford the corresponding poly(silarylenesiloxane) deriva-
tives P1, P2 and P3, respectively, as shown in Scheme 1. As reported
previously [33e36], any solvents forming azeotropic mixtures with
water and dissolving both monomer and the resulting polymer,
such as benzene and toluene, can be used for the present poly-
condensation. The 1H and 13C NMR and IR spectroscopy confirmed
the structures of P1eP3. The results of the polycondensation of M1,
M2 and M3 are summarized in Table 1.
2.8. Synthesis of poly(tetraphenyl-4,4-dimethyl-2,6-silcyclopenta
[2,1-b:3,4-b0]dithiophenylenesiloxane) (P3)
Under a dry atmosphere, 1,1,3,3-tetramethylguanidinium 2-
ethylhexanoate (0.02 g) was added to M3 (0.27 g, 0.45 mmol) dis-
solved in benzene (15.5 mL), and the reaction mixture was refluxed
for 12 h. The reaction mixture was poured into acetone (100 mL) to
isolate P3 as white precipitates with the yield of 0.08 g (30%). 1H
NMR (CDCl3, 400 MHz,
12H, phenyl protons), 6.91 (s, 2H, thienyl protons), 1.20 (s, 6H,
eCH3). 13C NMR (CDCl3, 100 MHz,
): 164.2 (thienyl carbon), 143.3
d): 7.56 (m, 8H, phenyl protons), 7.30 (m,
d
(thienyl carbon), 136.8 (phenyl carbon), 135.8 (thienyl carbon),
135.6 (phenyl carbon), 131.4 (thienyl carbon), 130.7 (phenyl
carbon), 128.3 (phenyl carbon), 44.6 [>C(CH3)2], 25.7 (eCH3). IR
(KBr, cmꢁ1): 1067 (SieO).
P1eP3 were soluble in common organic solvents such as THF,
chloroform, dichloromethane, toluene, and so on. The formation of
P1eP3 was confirmed by SEC measurement and NMR spectros-
copy. The SEC profiles of P1eP3 indicated that the obtained poly-
mers were unimodal and that the low-molecular weight species
such as a cyclic dimer or trimer were almost completely removed
2.9. Spectral data for P1 and P2
Poly(tetramethyl-4,4-dimethyl-2,6-silcyclopentadithiophenyle-
nesiloxane) (P1) and poly(dimethyldiphenyl-4,4-dimethyl-2,6-
Fig. 1. (a) 1H NMR (solvent: DMSO-d6, 400 MHz) and (b) 13C NMR spectra (solvent: DMSO-d6, 100 MHz) of M3 at ambient temperature.

5286
H. Hanamura, N. Nemoto / Polymer 52 (2011) 5282e5289
Fig. 2. (a) 1H NMR (solvent: CDCl3, 400 MHz) and (b) 13C NMR spectra (solvent: CDCl3, 100 MHz) of P3 at ambient temperature.
by reprecipitation in methanol or acetone. The 1H and 13C NMR
spectra of M3 and P3 are shown in Figs. 1 and 2, respectively, where
each signal was consistently assigned. The 1H and 13C NMR spectra
of P3 were almost similar to those of M3 except the disappearance
of a signal of 7.31 ppm based on hydroxy groups as observed in the
1H NMR spectrum of M3. The integrated ratio of each 1H NMR
signal and the assignment of 13C NMR signals were consistent with
the structure of P3 as described in Fig. 2. These results would
support that no side-reactions occurred during the poly-
condensation of M3. It was confirmed that the similar results were
obtained in the polycondensation of M1 and M2.
It has been known that the bathochromic effects are induced by
lowering the energy gap between the highest occupied molecular
orbital (HOMO) and lowest unoccupied molecular orbital (LUMO)
states because of both destabilization of the HOMO state through
se
p
conjugation and stabilization of the LUMO state through
s*e
p* conjugation. The hyperchromic effects would be caused by
the enhancement of the transition moment based on the increase
in the dipole moments of the HOMO and LUMO states owing to the
se
p
conjugation in the HOMO and the
s*ep* conjugation in the
LUMO [18e26].
In addition, the bathochromic shift of the maximum absorption
(labs) and the increase of the molar extinction coefficient (ε) were
observed by the introduction of phenyl group onto the silyl moie-
ties. Namely, the introduction of phenyl group onto silyl moieties
was also revealed to induce the bathochromic and hyperchromic
effects.
In the meantime, we calculated the HOMO and LUMO energy
levels of M1, M2 and M3 with the DFT method at the B3LYP/6-
31G(d) level of theory for the confirmation of the effects of the
introduction of silyl moieties on the absorption spectra.
3.2. Thermal characterization of polymer
Glass transition temperatures (Tgs) of P1eP3 were determined
by DSC. Fig. 3 shows the DSC traces of P1eP3 on a second heating
scan under a nitrogen atmosphere at a heating rate of 10 ꢀC/min.
The Tgs of P1, P2 and P3 were determined to be 56, 97 and 137 ꢀC,
respectively. The difference in the Tgs among P1eP3 depended on
the substituents on the silyl moieties. The introduction of bulky
phenyl group onto the silyl moieties caused the raising of Tg,
because bulky phenyl groups would restrict the motion of the main
chain. No melting temperatures (Tms) were observed in the DSC
thermogram of P1, P2 and P3. This result would indicate that
P1eP3 are noncrystalline polymers as observed in the other pol-
y(silarylenesiloxane) derivatives [24,36].
The temperatures at 5% weight loss (Td5s) of the present P1eP3
were determined by TGA to be 460, 459 and 479 ꢀC, respectively, as
summarized in Table 1. It was revealed that the introduction of
phenyl groups onto silyl moieties improved the thermostability,
plausibly because of the restriction of the main chain motion by the
bulky phenyl groups.
3.3. Optical properties
We investigated the optical properties of the obtained CPDT
derivatives, including monomers and polymers. The absorption and
fluorescence spectra of CPDT derivatives are shown in Fig. 4. Table 2
summarizes the optical properties of CPDT derivatives.
In the absorption spectra of CPDT derivatives, bathochromic and
hyperchromic effects were observed by the introduction of silyl
groups onto CPDT skeleton, presumably because of sep and s*ep*
conjugations between the silyl groups and aromatic moieties
[18e26].
Fig. 3. DSC thermograms of (a) P1, (b) P2, and (c) P3 on a second heating scans under
a N2 flow rate of 10 mL/min and a cooling or heating rate of 10 ꢀC/min.

H. Hanamura, N. Nemoto / Polymer 52 (2011) 5282e5289
5287
Fig. 4. Absorption [(a)e(c)] and fluorescence [(d)e(f), lex: 317 nm] spectra of CPDT derivatives in CHCl3 at ambient temperature (conc.: 2.0 ꢂ 10ꢁ6 mol/L); (a) and (d): 1, 3, M1, P1;
(b) and (e): 1, 4, M2, P2; (c) and (f) 1, 5, M3, P3.
Fig. 5 depicts the energy diagrams for the HOMO and LUMO
energy levels as well as the energy gap between LUMO and HOMO.
The difference in the LUMO energy level between 1 (ꢁ1.01 eV) and
M1 (ꢁ1.28 eV) and that in the HOMO energy level between 1
(ꢁ5.18 eV) and M1 (ꢁ5.22 eV) means that stabilization of LUMO
increase in the number of phenyl group on silyl moieties, inducing
the rather bathochromic shift of the maximum absorption with
increase in the number of phenyl group on silyl moieties.
The wavelength at maximum emission (lem) and fluorescence
quantum yield (FF) of CPDT derivatives are also summarized in
Table 2. In the fluorescence spectra of CPDT derivatives, bath-
ochromic effects were observed by the introduction of silyl groups
onto CPDT skeleton. In addition, the bathochromic shifts of the
maximum emission were observed by the introduction of phenyl
group onto the silyl moieties.
state through
state through
s
*e
p* conjugation and destabilization of HOMO
sep conjugation are induced by the introduction of
dimethylsilyl moieties. Thus, the introduction of dimethylsilyl
moieties caused the decrease in the energy gap between LUMO and
HOMO, resulting in the bathochromic shift of the maximum
absorption. The replacement of methyl group by phenyl one on silyl
moieties was found to decrease both HOMO and LUMO energy
levels as shown in Fig. 5. The degree of decrease in LUMO energy
level was rather higher than that in HOMO energy level with the
The FFs were improved by the introduction of silyl groups onto
CPDT skeleton. The FFs of unsubstituted cyclopenta[2,1-b:3,4-b0]
dithiophene (1) and dimethylsilylated adducts (3, M1, P1) were
0.01, 0.09, 0.09, and 0.09, respectively, indicating that the

5288
H. Hanamura, N. Nemoto / Polymer 52 (2011) 5282e5289
Table 2
increase in FF; however, the plausible reasons for the increase in FF
Optical properties of CPDT derivatives.
are as follows [18,20,26]. In the case of the present CPDT deriva-
tives, the larger number of phenyl groups on the silyl moieties
resulted in the larger molar extinction coefficient (ε) as mentioned
above. It would be likely that the increase in FF was induced by the
increase in ε because the radiative rate constant has linear relation
with ε. Another reason for the increase in FF would be that the
intersystem crossing rate constant becomes negligible owing to the
energy stabilization of the first singlet excited state (S1) by silyl
substitution to result in the change of the relative energy position
against the second triplet excited state (T2) as observed in the case
of silyl substituted certain aromatic compounds [18,20,26]. It would
be also likely that the increase in FF was induced by the energy
stabilization of the first singlet excited state (S1) by the introduction
of phenyl groups on the silyl moieties.
a
Compound
labs/nm (ε/L molꢁ1 cmꢁ1
)
lem/nm
FF
1
3
317 (15000) 329 (11800)
336 (24500) 348 (19200)
335 (24300) 346 (19200)
336 (23700) 348 (19200)
338 (30500) 349 (25000)
337 (23700) 349 (22000)
338 (27000) 350 (22000)
342 (32500) 354 (27500)
341 (30000) 354 (25000)
342 (31000) 354 (26500)
382
382
381
381
385
383
385
389
387
389
0.01
0.09
0.09
0.09
0.24
0.21
0.26
0.85
0.81
0.78
M1
P1
4
M2
P2
5
M3
P3
a
Fluorescence quantum yields (FFs) were determined by using pyrene (FF: 0.19)
[22] as a standard in CHCl3.
introduction of dimethylsilyl moieties onto CPDT skeleton rather
increased FF. In addition, the FFs of methylphenylsilylated adducts
(4, M2, P2) were 0.24, 0.21, and 0.26, respectively, and 2.7 times as
large as that of dimethylsilylated adducts, indicating that the
introduction of a phenyl group onto a silyl moiety drastically
increases FF. It should be still remarkable that the increase in the
number of phenyl group on silyl moieties enhances the fluorescent
efficiency, as observed that the FFs of diphenylsilylated adducts (5,
M3, P3) were 0.85, 0.81, and 0.78, respectively. The optical prop-
4. Conclusions
We achieved the synthesis of three poly(silarylenesiloxane)
derivatives with CPDT moieties (P1eP3). P1eP3 exhibited the good
solubility in common organic solvents such as benzene, toluene,
chloroform, dichloromethane and THF. The Td5s of P1, P2 and P3
were determined to be 460, 459 and 479 ꢀC, respectively, indicating
the introduction of phenyl group onto silyl moieties improved
thermostability. As for the optical properties of the obtained CPDT
derivatives, the bathochromic and hyperchromic effects were
observed by introducing silyl moieties onto CPDT. The bath-
ochromic shifts of wavelength at the maximum absorption and
fluorescence were induced by both destabilization of HOMO state
erties
of
9,9-diphenylfluorene-based
poly(tetramethyl-
silarylenesiloxane) have been reported [24]. 9,9-Diphenylfluorene-
based poly(tetramethylsilarylenesiloxane) has the structural
correlation with P1, though it bears the different substituents on
the spiro-carbon moiety such as 9-position of fluorene and 4-
position
of
cyclopentadithiophene.
The
FF
of
9,9-
through
sep conjugation and stabilization of LUMO state through
diphenylfluorene-based poly(tetramethylsilarylenesiloxane) in
chloroform solution has been reported to be 0.19 [24] and larger
than that of P1 (0.09) in chloroform solution; however, it would be
much interesting that the substitution of the methyl groups on the
silyl moieties with phenyl groups enlarges the FF. Namely, it would
be remarkable that the phenyl substituents on the silyl moieties
provide the fluorescent ability to CPDT derivatives having essen-
tially little fluorescent ability, indicating that the CPDT-based
poly(silarylenesiloxane) with diphenyl substituent on the silyl
moieties such as P3 would be one of promising candidates for the
fluorescent materials.
s
*e * conjugation. It should be remarkable that the increase in the
p
number of phenyl group on silyl moieties enhances the fluorescent
efficiency.
Acknowledgments
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.
Further detailed analysis of photochemical processes including
the determination of the rate constants as radiative rate constant,
intersystem crossing rate constant, and non-radiative rate constant
would be necessary for the clarification of the reason for the
Appendix. Supplementary material
Supplementary data related to this article can be found online at
doi:10.1016/j.polymer.2011.09.031.
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