Poly(silyleneethynylenephenylene) and poly(silylenephenyleneethynylenephenylene)s: Synthesis and photophysical properties related to charge transfer

Article abstract of DOI:10.1021/ma012140e

Novel poly(dimethylsilyleneethynylenephenylene) and poly(dimethyl (or diphenyl) silylenephenyleneethynylenephenylene)s without diyne defects were synthesized by using the Pd/Cu-catalyzed AB-type coupling reaction. 6's showed small but clear π-to-σ charge-transfer absorption bands at longer wavelengths (>340 nm) than those of π-π* absorption bands (<320 nm), whereas the charge-transfer absorption band was not found in 5. When 6's were excited at the π-π* absorption wavelengths, two type of emission were observed: One is the vibronically structured emission with a maximum around 325 nm due to the locally excited π* state, and the other is the intramolecular charge-transfer emission having a broad and structureless band (emission λ_max ca. 370 nm) with a large Stokes shift. On the other hand, when excited at the charge-transfer absorption wavelengths, 6's exhibited only the intramolecular charge-transfer emission with a maximum above 390 nm. This suggests that the indigo blue light emission of 6's is due to the charge-transfer phenomenon and not to the locally excited π* state. The charge-transfer character of 6's was clearly verified by the shift of emission in polar solvents.

Full text of DOI:10.1021/ma012140e

4138
Macromolecules 2002, 35, 4138-4142
Poly(silyleneethynylenephenylene) and
Poly(silylenephenyleneethynylenephenylene)s: Synthesis and
Photophysical Properties Related to Charge Transfer
Giseop Kw a k a n d Tosh io Ma su d a *
Department of Polymer Chemistry, Graduate School of Engineering, Kyoto University,
Kyoto 606-8501, J apan
Received December 10, 2001; Revised Manuscript Received February 22, 2002
ABSTRACT: Novel poly(dimethylsilyleneethynylenephenylene) [5] and poly(dimethyl (or diphenyl)
silylenephenyleneethynylenephenylene)s [6’s] without diyne defects were synthesized by using the Pd/
Cu-catalyzed AB-type coupling reaction. 6’s showed small but clear π-to-σ charge-transfer absorption
bands at longer wavelengths (>340 nm) than those of π-π* absorption bands (<320 nm), whereas the
charge-transfer absorption band was not found in 5. When 6’s were excited at the π-π* absorption
wavelengths, two type of emission were observed: One is the vibronically structured emission with a
maximum around 325 nm due to the locally excited π* state, and the other is the intramolecular charge-
transfer emission having a broad and structureless band (emission λmax ca. 370 nm) with a large Stokes
shift. On the other hand, when excited at the charge-transfer absorption wavelengths, 6’s exhibited only
the intramolecular charge-transfer emission with a maximum above 390 nm. This suggests that the indigo
blue light emission of 6’s is due to the charge-transfer phenomenon and not to the locally excited π*
state. The charge-transfer character of 6’s was clearly verified by the shift of emission in polar solvents.
Sch em e 1. (a ) Syn th esis a n d (b) P olym er iza tion of
(4-Br om op h en yl)d im eth yleth yn ylsila n e (2),
[4-{(4-Br om op h en yl)d im eth ylsilyl}]p h en yla cetylen e
(4a ), a n d
[4-{(4-Br om op h en yl)d im eth ylsilyl}]p h en yla cetylen e
(4b)
In tr od u ction
The σ-π conjugated polymers containing alternating
arrangements of silylene and π electron moieties possess
potential as semiconductors,1 photo- and electrolumi-
nescent materials,2 and ceramic precursors.3 The unique
electrical and optical propeties of these materials can
be attributed to through-space interaction between π
electrons bridged by silylene moiety and also the delo-
calization of electrons through the silylene linkages.
Some arylsilane compounds show intramolecular
charge-transfer absorption4 and, when photoexcited,
exhibit intramolecular charge-transfer emission.5 Thus,
in the molecular design of new types of silylene-arylene
σ-π conjugated polymers, it is important to estimate
the extent of intramolecular charge transfer in the
ground and excited states which affects their optical
properties. Although various σ-π conjugated polymers
have been synthesized so far, little attention has been
paid to the charge-transfer phenomenon. Recently, we
have synthesized highly regio- and stereoregular all-
trans and all-cis poly(silylenephenylenevinylene)s.6 These
polymers are very soluble and thermally stable. Inter-
estingly, their emission properties are affected by the
geometric structure; e.g., the cis-type polymer showed
charge-transfer emission, while the trans-type one
exhibited π-π* state emission.7 The ethynylene group
is more π-electron-rich than the vinylene group. Thus,
it is interesting to synthesize new types of σ-π conju-
gated organosilicon polymers containing ethynylene
moieties and study their absorption and emission
properties with respect to the charge-transfer phenom-
enon.
(Scheme 1). Polymers 6a and 6b exhibited unusual
absorption and emission based on intramolecular charge-
transfer ground and excited states. This result agrees
with the idea that the indigo blue light emission of these
polymers is due to the charge-transfer phenomenon but
not to locally excited π* state. Furthermore, quantum
yields of the charge-transfer emissions were fairly high.
The AB-type polycondensation does not require
stoichiometrical consideration unlike the AA-BB-type
one. In this study, we synthesized novel poly(silylene-
ethynylenephenylene) [5] and poly(silylenephenylene-
ethynylenephenylene)s [6a , 6b] without diyne defects
by using the Pd/Cu-catalyzed AB-type coupling reaction
Exp er im en ta l Section
Syn th esis of Mon om er s [Sch em e 1a ]. (4-Bromophenyl)-
chlorodimethylsilane (1): A 300 mL round-bottomed flask was
equipped with a dropping funnel, a three-way stopcock, and a
10.1021/ma012140e CCC: $22.00 © 2002 American Chemical Society
Published on Web 04/05/2002

Macromolecules, Vol. 35, No. 10, 2002
Poly(silyleneethynylene)s 4139
magnetic stirring bar and flushed with dry nitrogen. After
p-dibromobenzene (12.7 g, 53.5 mmol) and diethyl ether (200
mL) were placed in the flask at 0 °C, a hexane solution of
n-butyllithium (34 mL, 1.59 M, 53.5 mmol) was added drop-
wise, and the reaction mixture was stirred for 2 h. Then, this
reaction mixture was added slowly into a 1 L round-bottomed
flask in which diethyl ether (300 mL) and dichlorodimethyl-
silane (6.9 g, 53.5 mmol) had been placed beforehand. After
completion of addition, stirring was continued at 0 °C and then
gradually warmed to room temperature overnight. The salts
were removed by filtration of the reaction mixture through a
sintered glass (G3) filled with Celite. Diethyl ether was
evaporated at room temperature. The crude product was
purified by distillation to give the desired product (yield 9.4
g, 70%) as colorless liquid; bp 80 °C/1.0 mmHg (250 °C/760
mmHg). 1H NMR (CDCl3, δ): 7.48-7.60 (m, 4H, aromatic) and
0.68 ppm (s, 6H, (SiCH3)2).
(4-Bromophenyl)dimethylethynylsilane (2): A 300 mL round-
bottomed flask was equipped with a dropping funnel, a three-
way stopcock, and a magnetic stirring bar and flushed with
dry nitrogen. After compound 1 (9.4 g, 37.4 mmol) and diethyl
ether (100 mL) were placed in the flask at 0 °C, a THF solution
of ethynylmagnesium bromide (75 mL, 0.5 M, 37.4 mmol) was
added dropwise and then gradually warmed to room temper-
ature for 2 h. After treatment with cold aqueous ammonium
chloride, the product was extracted with diethyl ether, washed
with water, and dried over anhydrous sodium sulfate. Diethyl
ether was evaporated, and the crude product was purified by
flash column chromatography (Nakarai Tesque Co., silica gel
60; eluent, hexane) to give the desired product (yield 5.8 g,
65%) as a colorless liquid. 1H NMR (CDCl3, δ): 7.47-7.53 (m,
4H, aromatic), 2.53 (s, 1H, CH), and 0.42 ppm (s, 6H, (SiCH3)2).
13C NMR (CDCl3, δ): 135.2, 131.0 (d), 124.5, 95.3, 95.1, 87.5,
-1.2 (d) ppm. Anal. Calcd for BrC10H11Si: Br, 33.42; C, 50.23;
H, 4.60. Found: Br, 33.55; C, 50.28; H, 4.71.
138.7, 136.5, 135.7, 133.9, 131.3, 131.0, 124.2, 122.9, 83.6, 77.9,
-2.6 ppm (d). Anal. Calcd for BrC16H15Si: Br, 25.35; C, 60.98;
H, 4.76. Found: Br, 25.52; C, 60.72; H, 4.74.
4-[(4-Bromophenyl)diphenylsilyl]phenylacetylene (4b): This
compound was prepared similarly to 4a using compound 3b.
3b was sparely soluble in triethylamine unlike 3a , so that
piperidine was used instead of triethylamine. The crude
product was purified by flash column chromatography (eluent,
hexane:benzene ) 10:1) to give the desired product (yield 24%)
as white solid; mp 158-159 °C. 1H NMR (CDCl3, δ): 7.60-
7.35 (m, 18H, aromatic) and 3.13 ppm (s, 1H, CH). 13C NMR
(CDCl3, δ): 137.8, 136.2, 136.1, 134.9, 133.0, 132.7, 131.4,
131.2, 130.0, 128.0, 124.9, 123.5, 83.5, 78.3 ppm. Anal. Calcd
for BrC26H19Si: Br, 18.19; C, 71.09; H, 4.32. Found: Br, 18.71;
C, 71.01; H, 4.23.
P olym er iza tion [Sch em e 1b]. The following polymeriza-
tion procedures are exemplary: Triethylamine (20 mL), THF
(20 mL), (Ph3P)2PdCl2 (21.0 mg, 3.0 µmol), CuI (5.7 mg, 3.0
µmol), PPh3 (15.7 mg, 6.0 µmol), and 2 (0.48 g, 2.0 mmol) were
placed in the flask, and the mixture was stirred at 50 °C for 2
days. The resulting solution was filtered. Then the solution
was concentrated and poured into a large amount of methanol
under stirring to precipitate the formed polymer. The polymer
was purified by reprecipitation from dichloromethane into
methanol (1:10).
Mea su r em en ts. NMR spectra were measured in CDCl3
solution at 25 °C on a J EOL EX-400 spectrometer. The weight-
and number-average molecular weights (Mw and Mn, respec-
tively) of polymers were determined by gel permeation chro-
matography (GPC); eluent CHCl3, Shodex K-805, K-804, and
K-803 polystyrene gel columns (Showa Denco, Co., J apan),
polystyrene calibration. The measurements of thermogravi-
metric analysis (TGA) were conducted with a Perkin-Elmer
TGA-7 analyzer in N2 at a heating rate of 10 °C/min. IR, UV,
and emission spectra were measured on Shimadzu FTIR-8100
(KBr pellet), Shimadzu UV-2200, and J ASCO FP-750 spec-
trophotometers, respectively. Emission quantum yields were
determined relative to quinine sulfate in 1 N H2SO4 assuming
a quantum yield of 0.546 at an excitation wavelength of 365
nm.
Bis(4-bromophenyl)dimethylsilane (3a ): A 1 L round-bot-
tomed flask was equipped with a dropping funnel, a three-
way stopcock, and a magnetic stirring bar and flushed with
dry nitrogen. Diethyl ether (500 mL) and p-dibromobenzene
(38.0 g, 160 mmol) were placed in the flask. The solution was
cooled at 0 °C, to which a hexane solution of n-butyllithium
(102 mL, 1.56 M, 160 mmol) was added dropwise, and the
reaction mixture was stirred for 2 h. A solution of dichlorodi-
methylsilane (9.6 mL, 80 mmol) in diethyl ether (20 mL) was
added dropwise, and stirring was continued for 4 h. After
removal of insoluble salts by filtration, the product was
extracted with diethyl ether, washed with water, and dried
over anhydrous sodium sulfate. Diethyl ether was evaporated,
and the crude product was recrystallized from hexane to give
Resu lts a n d Discu ssion
In this study, we employed Pd/Cu-catalyzed coupling
reaction under the Heck condition. The polymerization
of the present monomers (2, 4a , and 4b) with (Ph3P)2-
PdCl2 and CuI in THF and triethylamine (volume ratio
1:1) quantitatively provided light-yellow polymers
[Scheme 1b; poly(silyleneethynylenephenylene) (5) and
poly(silylenephenyleneethynylenephenylene)s (6a and
6b)]. The molecular weights (Mw) of 5, 6a , and 6b were
33 × 103 (Mw/Mn 3.5), 30 × 103 (Mw/Mn 4.5), and 50 ×
103 (Mw/Mn 2.9), respectively. All the present polymers
were soluble in common organic solvents such as
toluene, THF, cyclohexane, and CHCl3.
The Pd/Cu-catalyzed polymerizaton of diethynylare-
nes and dihaloarenes occasionally forms minor amounts
of 1,3-diyne moiety as defect in the polymer backbone.8
As a result, the polymers gradually become insoluble
when stored in the solid state. The structure of the
present polymers was characterized by IR, 1H NMR, and
13C NMR spectra. These spectral data supported the
selective formation of polymers with the expected
structures. The IR spectra of the present polymers
exhibited absorptions around 2200 cm-1, which indi-
cates the presence of the ethynylene group. Figure 1
1
the desired product (yield 19.0 g, 64%) as a colorless solid. H
NMR (CDCl3, δ): 7.51-7.32 (t, 8H, aromatic) and 0.56 ppm
(s, 6H, (SiCH3)2).
Bis(4-bromophenyl)diphenylsilane (3b): This compound was
prepared similarly to 3a using dichlorodiphenylsilane; yield
66%, white solid. 1H NMR (CDCl3, δ): 7.61-7.35 ppm (m, 18H,
aromatic).
4-[(4-Bromophenyl)dimethylsilyl]phenylacetylene (4a ):
A
500 mL round-bottomed flask was equipped with a reflux
condenser, a three-way stopcock, and a magnetic stirring bar
and flushed with dry nitrogen. Triethylamine (300 mL),
(Ph3P)2PdCl2 (100 mg, 0.10 mmol), CuI (200 mg, 1.07 mmol),
PPh3 (200 mg, 0.71 mmol), and 3a (19.0 g, 51.3 mmol) were
placed in the flask, and the mixture was stirred for 4 h at 80
°C. After the completion of reaction had been confirmed by
TLC, the resulting solution was filtered, and then the solution
was evaporated. Methanol (ca. 200 mL), THF (ca. 200 mL),
and NaOH (ca. 2 g) were added to the crude product and
stirred for 1 h. After the volatiles had been evaporated, the
product was extracted with diethyl ether, washed with water,
and dried over anhydrous sodium sulfate. Diethyl ether was
evaporated, and the crude product was purified by flash
column chromatography (eluent, hexane) to give the desired
product (yield 7.3 g, 45%) as white solid; mp 49-50 °C. 1H
NMR (CDCl3, δ): 7.58-7.30 (m, 8H, aromatic), 3.12 (s, 1H,
CH), and 0.51 ppm (s, 6H, (SiCH3)2). 13C NMR (CDCl3, δ):
1
1
shows the H and 13C NMR spectra of 5 and 6a . The H
NMR spectra of 5 and 6a clearly show a singlet peak
due to methyl protons and multiple peaks due to
phenylene protons. In the 13C NMR spectrum of 5,
signal b at 92 ppm is due to the ethynyl carbon adjacent
to the silicon atom, and signal c at 107 ppm is assigned

4140 Kwak and Masuda
Macromolecules, Vol. 35, No. 10, 2002
F igu r e 1. 1H and 13C NMR spectra of 5 and 6a (in CDCl3, 25 °C).
F igu r e 2. TGA curves of 5, 6a , and 6b (heating rate 10 °C/
min, in N2).
to the ethynyl carbon bonded to the phenylene group.
6a exhibits signal f ′ due to the ethynyl carbons at 90
ppm. No diyne carbon signal, which should appear
around 75 and 80 ppm,8 was found. Similarly, 6b
showed a signal due to the ethynylene carbons at 91
ppm but no diyne carbon signal. Thus, the present
polymers have no diyne defect in the backbone. Accord-
ingly, when kept under ambient conditions for a month,
the present polymers remained completely soluble.
Organosilicon polymers containing unsaturated func-
tional groups such as ethynylene and vinylene groups
tend to retain weight up to high temperature. For
instance, poly(silyleneethynylene)s3a cross-link at rela-
tively low temperature to be converted to silicon car-
bides in high char yields. The thermal stability of the
present polymers was examined by thermogravimetric
analysis (Figure 2). The weight residues of 5, 6a , and
6b at 900 °C in N2 were 83, 61, and 64%, respectively.
Thus, these polymers kept weight up to high tempera-
ture owing to cross-linking of ethynylene groups. Espe-
cially, the high char yield of 5 indicates that this
polymer possesses potential usefulness as a precursor
for ceramic fiber.
F igu r e 3. (a) UV and (b) emission spectra of 5, 6a , and 6b
(in CHCl3, 7.9 × 10-6 mol/L).
acetylene [λmax (ꢀmax) 287 nm (22 200 M-1 cm-1) and 295
nm (27 300 M-1 cm-1), in methanol9] suggests that the
absorption bands of 6a at 298 and 318 nm correspond
to π-π* transition involving only the phenyleneethy-
nylenephenylene moiety. Similarly, the absorption
maxima of 6b due to π-π* transition appeared at 300
and 320 nm. 5 exhibited an absorption maximum at 272
nm due to π-π* transition. The π-π* absorption bands
of 6a and 6b shifted to longer wavelengths by ca. 20
nm or more as compared to that of 5. Thus, the insertion
of a phenylene moiety into 5 is effective to extend π
character conjugation in the main chain. The absorption
of 6b is slightly red-shifted compared to that of 6a ,
despite the main-chain phenylene and side-chain phenyl
groups through silicon. Diarylsilanes (e.g., 4,4′-substi-
tuted dimethyldiphenylsilane4a and dimethyldithienyl-
silane4c) show a small π-to-σ charge-transfer absorption
band at a longer wavelength than that of the absorption
band due to the π-π* transition. As seen in Figure 3a,
6a and 6b possess a small but clear absorption at longer
Figure 3a shows UV spectra of the present polymers.
The comparison with the UV spectrum of diphenyl-

Macromolecules, Vol. 35, No. 10, 2002
Poly(silyleneethynylene)s 4141
F igu r e 4. UV spectra of a model compound, 1-[p-(trimethyl-
silyl)phenyl]-2-phenylacetylene, and 6a (in CHCl3, 7.9 × 10-6
mol/L).
wavelengths (342 and 345 nm, respectively), whereas
no absorption band was found around the same UV
region in 5. This suggests that intramolecular charge
transfer occurs between phenyleneethynylenephenylene
π unit and the silylene σ unit at the ground state, but
it hardly takes place between the ethynylenephenylene
π unit and the silylene σ unit. When 5, 6a , and 6b were
excited at 272, 342, and 345 nm, repectively, these
polymers exhibited emission maxima at 307, 394, and
395 nm, respectively (Figure 3b). In accordance with
these emission spectra, 6a and 6b emitted visible indigo
blue light in dilute solution, whereas 5 emitted no
visible lights. The quantum yields of these emission of
5, 6a , and 6b were 0.24, 0.26, and 0.82, respectively.
As mentioned above, 6a and 6b exhibited very clear
intramolecular charge-transfer absorption bands. To
confirm this finding, we synthesized a model compound,
1-[p-(trimethylsilyl)phenyl]-2-phenylacetylene, whose
structure is close to that of the repeating unit of 6a ,
according to the literature method.10 Figure 4 compares
UV spectra of 6a and the model compound. The model
compound shows a small but obvious charge-transfer
absorption band at a longer wavelength (λmax 329 nm)
besides the π-π* absorption band (λmax 287 and 305
nm). This means that the σ-π combination between the
silylene and phenyleneethynylenephenylene units is
effective to give rise to the intramolecular charge
transfer in the ground state. The charge-transfer ab-
sorption of 6a is much stronger than that of the model
compound, which is explicable in terms of the idea that
the π-to-σ charge transfer is amplified in polymers by a
high-density through-space interaction between π elec-
trons of phenylene groups bridged by silylene moiety.
Some of silyl-substituted aromtic compounds form
intramolecular charge transfer in the excited state.
Consequently, both a shorter wavelength emission with
vibronically structured band ascribed to the locally
excited π* state and a longer wavelength emission with
structureless broad band due to the charge-transfer
excited state are observed simultaneously.2a,5 Very
interestingly, the emission spectra of 6a and 6b ap-
preciably changed with excitation wavelengths. As
shown in Figure 5, when 6a is excited at a π-π*
absorption wavelength (298 or 318 nm), two types of
emission are observed: one is the vibronically struc-
tured emission with a maximum at 325 nm and shoul-
ders at 338 and 349 nm due to the locally excited π*
state, and the other is the intramolecular charge-
transfer emission having a broad and structureless band
(emission λmax values are 369 and 377 nm when excited
at 298 and 318 nm, respectively) with a large Stokes
shift. On the other hand, when excited at the charge-
transfer absorption wavelength (342 nm), this polymer
exhibits only the intramolecular charge-transfer emis-
sion with a maximum at 394 nm. This means that the
F igu r e 5. Variation of emission spectra of 5, 6a , and 6b on
excitation wavelength (in CHCl3, 7.9 × 10-6 mol/L).
intramolecular charge-transfer absorption causes the
charge-transfer emission selectively. Similarly, 6b ex-
hibited two types of emissions, i.e., π-π* emission
(emission λmax 328 nm; shoulders appear at 341 and 351
nm) and charge-transfer emission (emission λmax 369
nm) when excited at 300 or 320 nm. Further, 6b showed
only intramolecular charge-transfer emission (emission
λmax 395 nm) when excited at 345 nm. It suggests that
the indigo blue light emission of 6a and 6b is due to
the charge-transfer phenomenon but not to locally
excited π* state. It is noteworthy that, when the
excitation wavelength is shifted up to the charge-
transfer region in these polymers, the two kinds of
excited species reduce into one, i.e., only the charge-
transfer species. On the other hand, 5 showed no shift
of emission wavelength at all upon the modulation of
excitation wavelength.
The excitation spectrum of 5 is essentially the same
as its absorption spectrum (see Figures 3a and 6); i.e.,
when the emission wavelength was fixed at 307 nm, the
excitation spectrum exhibited a maximum at 275 nm.
The shape of excitation spectrum hardly changed even
though the emission wavelength was shifted in the
range of 270-400 nm. This means that the excitation
of 5 is based on the simple π and π* states. In contrast,
the shape of excitation spectra of 6a and 6b appreciably
changed when the emission wavelength was shifted
(Figure 6); e.g., when the emission was fixed at 394 nm,
the excitation spectrum of 6a showed two excitation
maxima around 320 and 340 nm. The excitation band
around 340 nm, however, disappeared when the emis-
sion was fixed at 325, 338, or 349 nm. 6b showed the
same tendency. This means that the excitation band
around 320 nm is related to the π-π* excited state,
while the band around 340 nm is related to the charge-
transfer excited state. This interpretation agrees well
with the results that the proportion of the excited states
in 6a and 6b depends on the excitation wavelength and
that the short wavelength emission does not occur from
the charge-transfer excited state.
In general, the intramolecular charge-transfer emis-
sion band red-shifts with increasing solvent polarity.5c,f

4142 Kwak and Masuda
Macromolecules, Vol. 35, No. 10, 2002
excited states and that the indigo blue light emission
of these polymers originates from the charge transfer.
The charge-transfer character of these polymers was
clearly verified by the shift of emission in polar solvents.
The present study on charge-transfer phenomenon will
be helpful to design new σ-π conjugated organosilicon
polymers for light-emitting diode materials.
Ack n ow led gm en t . We thank Professor S. Ito for
helpful discussion. This research was supported by a
Grant-in-Aid for Scientific Research from the Ministry
of Education, Science, Culture and Sports, J apan. The
authors thank Shin-Etsu Chemical Co., Ltd., J apan, for
the donation of trimethylsilylacetylene.
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F igu r e 7. Emission spectra of 6b in various solvents [benzo-
nitrile (- - -), CHCl3 (s), cyclohexane (- - -), 7.9 × 10-6 mol/
L].
To gain definitive evidence for the existence of intra-
molecular charge transfer in poly(silylenephenylene-
ethynylenephenylene)s, we examined solvent effects on
the emission property. The dielectric constant (D) values
of cyclohexane, CHCl3, and benzonitrile are 2.05 (at 25
°C),11 4.9 (at 20 °C),11 and 25.2 (at 25 °C),12 respectively.
As estimated from these D values, the solvent polarity
is in the order benzonitrile . CHCl3 > cyclohexane. As
shown in Figure 7, the emission intensity of 6b was
smaller in benzonitrile than in cyclohexane and CHCl3.
This is explained in terms of the increase of nonradia-
tive transition in more polar solvents. Further, the
emission spectrum in benzonitrile was more structure-
less and broader than in cyclohexane or CHCl3, and the
emission band shifted toward longer wavelengths in
polar solvents; e.g., emission λmax 387 nm in cyclohex-
ane, emission λmax 395 nm in CHCl3, and emission λmax
405 nm in benzonitrile. Thus, this solvent shift of
emission of 6b indicates that the emitting state is polar.
The same tendency was observed in 6a as well.
In conclusion, we successfully synthesized novel poly-
(silyleneethynylenephenylene) and poly(silylenephe-
nyleneethynylenephenylene)s without diyne defects by
using the Pd/Cu-catalyzed AB-type coupling reaction.
We found that the σ-π combination between the si-
lylene and phenyleneethynylenephenylene units in poly-
(silylenephenyleneethynylene-phenylene)s is effective to
form intramolecular charge transfer in both ground and
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MA012140E