Photoinduced cis-to-trans isomerization of poly(2-ethynylthiophene) prepared with a [Rh(norbornadiene)Cl]2 catalyst. 1H NMR, UV, and ESR studies

Article abstract of DOI:10.1021/ma0101198

Poly(2-ethynylthiophene) was stereoregularly prepared with a Rh complex catalyst, [Rh-(norbornadiene)Cl]₂, to selectively produce the cis-transoid isomer in high yields when triethylamine was used as the polymerization solvent at 20 °C. Photoinduced cis-to-trans isomerization was newly found to take place when the film of a pristine cis-transoid polymer was photoilluminated using a Xe lamp with light of wavelength, 320-500 nm under vacuum for 5 h. The cis and trans polymers obtained before and after the illumination were characterized in detail using ¹H NMR, UV-vis of solution and film, and electron spin resonance methods.

Full text of DOI:10.1021/ma0101198

2
000
Macromolecules 2002, 35, 2000-2004
Photoinduced Cis-to-Trans Isomerization of Poly(2-ethynylthiophene)
1
Prepared with a [Rh(norbornadiene)Cl]
ESR Studies
2
Catalyst. H NMR, UV, and
Min or u Na k a m u r a , Ma sa yosh i Ta ba ta ,* Ta k eyu k i Son e, Ya su ter u Ma w a ta r i, a n d
Atsu sh i Miya sa k a
Department of Molecular Chemistry, Graduate School of Engineering, Hokkaido University,
Sapporo 060-8628, J apan
Received J anuary 22, 2001; Revised Manuscript Received November 28, 2001
ABSTRACT: Poly(2-ethynylthiophene) was stereoregularly prepared with a Rh complex catalyst, [Rh-
2
(norbornadiene)Cl] , to selectively produce the cis-transoid isomer in high yields when triethylamine
was used as the polymerization solvent at 20 °C. Photoinduced cis-to-trans isomerization was newly found
to take place when the film of a pristine cis-transoid polymer was photoilluminated using a Xe lamp
with light of wavelength, 320-500 nm under vacuum for 5 h. The cis and trans polymers obtained before
1
and after the illumination were characterized in detail using H NMR, UV-vis of solution and film, and
electron spin resonance methods.
In tr od u ction
Sch em e 1. Syn th esis a n d P h otoin d u ced Cis-to-Tr a n s
Isom er iza tion of P oly(2-eth yn ylth iop h en e)
We previously have demonstrated1-8 that monosub-
stituted acetylenes such as phenylacetylene derivatives
and aliphatic acetylenes, i.e., propiolates called acetyl-
ene esters, can be stereoregularly polymerized to selec-
tively afford the corresponding polyacetylene polymers
bearing a cis-transoid structure in high yields under
mild conditions. We also showed that triethylamine
(
TEA) or alcohol used as the polymerization solvent
9
-11
works as the cocatalyst.
Further, the cis-transoid
polymer was shown to form a pseudohexagonal struc-
ture called a columnar or nanohole assembly as a
π-conjugated self-assembly whose diameter can be also
easily controlled by the length of the side chain in the
polyacetylenes, e.g., from ca.13 to ca. 65 Å.7 In the
case of polypropiolate columnar, interestingly, it was
evidenced that concentration of oxygen can be enriched
from ca. 21% to ca. 40% when the film was once passed
through air, irrespective of the fact that the polymer
,12
Sch em e 2. Syn th esis of 2-Eth yn ylth iop h en e
7
,12
possessed no trimethylsilyl moiety in the molecules.
6
Recently, we found that not only pressure- but also
thermal-induced cis-to-trans isomerization takes place
for the stereoregular polyacetylenes (see Scheme 1),
although the trans isomer obtained by thermal treat-
ment of the cis polymer did not always have such planar
trans conjugation sequences but distorted trans se-
quences where the effective conjugation length is fairly
short. In this paper we show the first photoinduced cis-
to-trans isomerization regarding the film of the mono-
substituted polyacetylene, i.e., poly(2-ethynylthiophene),
P2ET, which was prepared with the Rh complex catalyst
Exp er im en ta l Section
Ma ter ia ls. 2-Ethynylthiophene (2ET) was prepared accord-
ing to the literature19 by the coupling reaction of trimethyl-
silylacetyelene (Aldrich) with 2-iodothiophene (Aldrich) cata-
lyzed by (Ph P) PdCl (Aldrich) and followed by deprotection
3 2 2
of the trimethylsilyl group (see Scheme 2, eq 2); yields 48%,
bp 50 °C/25 mmHg. The resulting monomer was distilled once
from CaH before use. [Rh(norbornadiene)Cl] (Aldrich) was
2 2
used without further purification. Triethylamine (TEA) was
distilled from sodium benzophenone ketyl. Ethanol was dis-
together with detailed characterization of the polymers
1
obtained before and after the illumination using
H
NMR, UV-vis, and electron spin resonance (ESR)
methods. No report on the polymerization of P2ET
polymer using [Rh(NBD)Cl]2 catalyst and TEA or alco-
hol solvent including the photoinduced cis-trans isomer-
ization of P2ET polymer has been published to date, to
the best of our knowledge, despite the potential impor-
tance of the materials from not only a scientific point
2
tilled once from Mg(OEt) and stored under nitrogen over
molecular sieve 3A (Merck).
P olym er iza tion . Polymerization was carried out using a
U-type glass ampule equipped with two inlets capped with a
septum rubber.8 A typical polymerization procedure is as
follows: [Rh(NBD)Cl] (13 mg, 0.028 mmol) and a monomer
2
1
3-18
of view but also possible industrial applications.
(0.3 g, 2.8 mmol) were placed in each side of the ampule, and
1
0.1021/ma0101198 CCC: $22.00 © 2002 American Chemical Society
Published on Web 02/09/2002

Macromolecules, Vol. 35, No. 6, 2002
Isomerization of Poly(2-ethynylthiophene) 2001
Ta ble 1. Resu lts of P olym er iza tion s of 2ET Mon om er
w ith th e Rh Com p lex Ca ta lysta
[
M], time, yield,
Mw/
Mn
run
solvent
TEA
mol/L
h
%
Mn
color
1
2
3
4
5
0.5
0.5
0.5
0.5
0.5
2
2
2
2
2
98
34
36
85
75
19 000
15 000
17 000
37 000
60 000
2.8 brown
2.1 yellow
2.3 yellow
3.6 yellow
4.4 yellow
EtOH
EtOH/TEA
toluene/TEA
THF/TEA
b
b
a
Polymerization temperature, 20 °C. b Bimodal distribution.
a solution of TEA (2.8 mL) or EtOH (2.8 mL) was also
introduced to both sides of the ampule. After standing the
solutions for 10 min, at 20 °C the monomer solution and the
catalyst solution were mixed in order to start the polymeri-
zation. After 2 h the resulting P2ET polymer was precipitated
into a large amount of methanol, obtained as a brown or yellow
powder, filtrated, and dried in vacuo at ca. 10-3 Torr for 24 h
at room temperature (see Table 1). Elemental analysis of no.
1
in Table 1 as a typical polymer: Calcd (%) for C
6 4 1
H S (MW
)
108.16): C, 66.6; H, 3.73; S, 29.65. Found: C, 63.67; H, 3.85;
S, 27.11.
F igu r e 1. 1H NMR spectrum of pristine poly(2-ethynylthio-
phene), P2ET, polymer (Table 1, run 1) observed in CDCl .
3
Ch a r a cter iza tion . Molecular weights and the molecular
weight dispersity of the resulting polymers were estimated by
J ASCO 900 gel permeation chromatography (GPC) equipped
with a refractive index detector using tetrahydrofuran (THF)
as the eluent at flow rate of 1.0 mL/min with a Shodex KF-
stituted acetylenes under mild conditions.1 It is clear
that the polymer yields of ca. 98-75% attained when
TEA or its mixed solvents (Table 1, runs 1, 3, 4, and 5)
were used for the polymerization solvent even at 20 °C
for 2 h where the molecular weight and its polydisper-
sity were estimated as Mn ) 15 000-60 000 and Mw/
Mn ) 2.1-4.4, respectively. It is suggested, however,
that in the cases of EtOH, runs 2 and 3 in Table 1, the
yield of the polymer was below that attained in the case
of the TEA and its mixed solvent, suggesting insufficient
dissociation of the Rh complex catalyst as the bidentate
complex to the monomeric species responsible for the
propagation species of the polymerization as has been
-8
8
06L column and calibrated with polystyrene standards (see
1
Table 1). H NMR spectra were recorded on a J EOL J NM-A
00 MHz using CDCl as solvent at room temperature. UV
4
3
spectra of solution and film of the polymers were recorded on
a J ASCO V550 equipped with ISV-469. ESR spectra were
observed on a J EOL FE1XG with 100 kHz field modulation
at room temperature and 77 K. The cis-to-trans isomerization
was performed by photoillumination using a Xe lamp with a
band-pass filter in order to pass visible light: 300-470 nm
under vacuum.
P h otoillu m in a tion . The pristine cis polymer was cast from
a chloroform solvent on a quartz ampule, φ ) 3 mm, l ) 20
mm which was placed in a wider ESR ampule of φ ) 7 mm, l
9
-11
deduced by us.
)
200 mm for illumination. The wider ampule was evacuated
Polystyrenes and aromatic polyacetylenes have been
conjectured to have a random coil and rigid-rod-like
structure, respectively. Therefore, molecular weights of
the polyacetylenes estimated by GPC using the poly-
styrenes as standard may be larger compared with that
of the former polymer.
-3
at ca. 10 mmHg for 2 h at room temperature so as to prevent
oxidization of the film during the illuminations and was
shielded.
A thin film cast from the pristine cis polymer on a quartz
plate of 10 mm × 20 mm × 1.5 mm was used for UV
-
3
measurement after evacuation at ca. 10 mmHg for 2 h at
room, followed by illumination under nitrogen stream. The two
samples were photoilluminated using a USHIO SX-UI 500XQ
lamp together with the band filter in order to pass light of
1
Figure 1 shows the H NMR spectrum of the resulting
P2ET polymer (Table 1, run 1) observed in chloroform
solvent at ca. 30 °C. This spectrum featured a typical
cis-transoid structure because it is composed of very
sharp lines, indicating statistically a very narrow
distribution of the chemical shifts due to the highly
3
20-470 nm.
Resu lts a n d Discu ssion
P olym er iza tion . We previously showed1-10 that TEA
or alcohol is a notably preferred solvent to produce the
corresponding aromatic or aliphatic polyacetyelenes
bearing a cis-transoid structure as the major compo-
nent in high yields and worked as the cocatalyst of the
Rh complex catalyst, although such solvents have not
been used, to the best of our knowledge, to date. The
reason may be not only that the solvent is considered
unusual in an ordinary polymerization but also that it
can deactivate the catalysts such as the Ziegler-Natta
11
regular structure. This clearly evidenced that the ratio
of an integrated area due to the dC-H proton at 6.2
ppm and three thiophene protons observed at ca. 6.55-
6.99 ppm can be estimated rigorously as 1.0:3.0. It
seems that neither such a very sharp line width spectra
has been observed nor an accurate integration ratio
between the peaks of the relevant protons has been
obtained when other polymerization catalysts, e.g.,
metathesis catalyst, MoCl5, or WCl6, were used.21 Thus,
these results clearly indicate formation of a highly
stereoregular cis-transoid polymer. It should be also
noted, however, that even when such a heteroatom, i.e.,
sulfur having a d-orbital, is involved in the monomer
molecule, the polymerization is not retarded and/or
inhibited by the atom.
2
0
catalyst, Al(Et)3-Ti(On-alkyl)4, or metathesis catalyst,
e.g., WCl6 or MoCl5,21 as the so-called Lewis acids. In
this work we also used their solvents in order to
determine whether 2-ethynylthiophene, 2ET, monomer
containing even a sulfur atom can also be polymerized
to produce the cis polymer in high yields. Table 1 shows
the results of the polymerization of the thiophene
monomer, 2ET, using the Rh complex of the monosub-
Solu tion UV-vis Sp ectr a . Figure 2 shows the UV
spectrum of the brown and yellow polymers (Table 1,
runs 1 and 2) which were prepared with TEA and EtOH

2
002 Nakamura et al.
Macromolecules, Vol. 35, No. 6, 2002
F igu r e 2. UV spectra of the P2ET polymers (Table 1, runs 1
and 2) observed in CHCl solvent. Polymerization solvent: (a)
3
triethylamine (TEA) and (b) ethanol (EtOH).
F igu r e 4. 1H NMR spectra observed after the photoillumi-
nation using light of wavelength in the range of 320-470 nm
at room temperature under vacuum: (a) after 2 h and (b) after
6
h.
and main chains make a chromophore to show such a
peak absorption at ca. 420 nm as previously reported
1
-6
by us for aromatic polyacetylenes,
although the peak
at ca. 300 nm may be ascribed to that of the vinylthio-
phene moiety, suggesting that the plane of the thiophene
ring and the cis CdC bond plane are not planar but
6
decline to some extent. We found that the photoillu-
mination of the cis polymer using light of 320-470 nm
did dissipate the two absorption peaks completely and,
inversely, increased notably the intensity of the lower
wavelength absorption region from ca. 350 to ca. 275
nm. The difference spectrum obtained by subtraction
of spectra observed before and after the illumination for
5
h is shown in Figure 3b. This difference spectrum
clearly indicated that the photoillumination dissipates
the broad peak at ca. 420 nm which was assigned to
that of the cis isomer and, inversely, increased the
absorption peak intensity at the longer wavelength
region from 520 to 680 nm which can be ascribed to that
of fairly long trans conjugated sequences, although the
F igu r e 3. UV spectra of the P2ET polymer observed before
and after photoillumination using light of wavelength in the
range of 320-470 nm: (a) yellow polymer (Table 1, run 1) and
(b) subtraction spectrum.
solvents, respectively, and observed using highly puri-
fied spectrograde chloroform. These spectra are almost
the same as that of the yellow polymers in Table 1,
suggesting that the observed colors of their polymers
are not ascribed to that of the primary structure, such
as a repeated double-single structure, but rather to the
polymer molecular assembly, e.g., a pseudohexagonal
structure called columnar as has been proven by us
recently.7
6
intensity is not strong. We previously showed that the
thermal-induced cis-to-trans isomerization of poly(p-
nitro(phenyl)acetylene) takes place and generates so-
called relaxed trans-polyacetylenes which can be con-
sidered as distorted trans-polyacetylenes where the
effective conjugation length is shorter compared with
that of the trans sequences which was generated by
compression of the cis isomers. It is concluded, therefore,
that the trans isomer generated by the illumination has
a similar distorted trans conjugated sequence, i.e.,
shorter conjugation length without any clear absorption
peak as observed in Figure 3a.
,22,23
P h otoin d u ced Isom er iza tion . Figure 3a shows the
UV spectra of the film of the pristine P2ET polymer
(Table 1, run 1) observed before and after photoillumi-
nation using a Xe lamp with a band-pass filter in order
to pass wavelength light, 320-470 nm, under vacuum.
It is clear that the controlled polymer film shows two
peaks at ca. 420 and 300 nm, respectively. Such two
peaks are observed even in the solution UV-vis of the
pristine polymer. The longer wavelength absorption at
ca. 420 nm may be assigned to that of the cis isomer in
which a few monomer units containing the side chains
1
H NMR Sp ectr a a fter P h otoillu m in a tion . Figure
1
4 shows the H NMR spectra observed after the photo-
illumination of the P2ET polymer (Table 1, run 1) using
1
light of 320-470 nm. The H NMR spectrum of the
pristine P2ET polymer is already shown in Figure 1. It
is clear that the longer the illumination time, the wider
the line width of the spectra is, without large change

Macromolecules, Vol. 35, No. 6, 2002
Isomerization of Poly(2-ethynylthiophene) 2003
Ta ble 2. ESR P a r a m eter s of th e P 2ET P olym er s P r ep a r ed
Ta ble 3. Tim e Dep en d en cies of ESR P a r a m eter s of th e
P 2ET P olym er Obser ved d u r in g th e P h otoillu m in a tion
a
w ith th e Rh Com p lex Ca ta lyst
1
8
∆
Hmsl,
G
spins/
g × 10
2.1
2.1
2.3
2.3
spins/
unit
time, h
g value
∆Hmsl, G
spin concn × 10 spin/g
1
8
polymer solvent temp g value
0
1
2
3
4
2.0036
2.0035
2.0034
2.0034
2.0034
14.3
14.8
14.5
13.1
14.0
2.1
260
321
326
323
1
2
TEA
TEA
EtOH
EtOH
rt
77 K
rt
2.0035
2.0043
2.0031
2.0035
12.8
13.0
10.5
11.4
1/2700
1/2700
77 K
a
Polymerized at 20 °C for 2 h.
due to the mobile unpaired electrons is induced in such
2
6,27
in the chemical shifts when spectra of Figures 1 and 4
were compared. The spectra observed after the il-
lumination is explained in terms of photoinduced cis-
to-trans isomerization, i.e., spectra of Figure 4a,b are
superposed with sharp components due to cis structure
and broad components due to the resulting trans
structure. Such similar spectra have been observed in
the case of monosubstituted polyacetylenes which were
prepared with the so-called metathesis catalysts or
thermal-treated polyacetylenes.21 The observed line
broadening may be interpreted by the so-called dipole-
dipole magnetic interaction between the unpaired elec-
trons produced by the rotational scission of the cis
double bonds and the protons in the cis and trans
isomers, associated with slowing of the molecular mo-
tion of their isomers in the chloroform solution.
a cis isomer,
because of narrow and restricted
conjugation ranges compared with that of the trans
isomer bearing longer planar conjugation sequences.
Thus, the ESR parameters strongly evidenced that the
resulting polymer has a typical cis-transoid structure
shown in Scheme 1.
The ESR parameters observed before and after the
illumination using the band filter in order to pass the
light of 320-470 nm at 20 °C are shown in Table 3.
The line widths of the powder and its film for the
brown cis polymer (Table 1, run 1) were estimated as
12.8 and 14.3 G, respectively (see Tables 2 and 3). This
difference may be ascribed to the conformation and/or
morphology of the powder and film polymers.
The photoillumination did not induce appreciably
increase of the line width in the ESR spectra but rather
slightly decreased the line width as shown in Table 3.
This strongly indicates that the illumination never
induces the so-called cross-linking between the intra-
and/or intermolecular chains during the photoinduced
cis-to-trans isomerization. This result was also sup-
ported by an important experimental fact that the
photoillumination never increased the molecular weight
but rather decreased, i.e., from Mn ) 19,000 to Mn )
9800 for only 2 h at room temperature. This photoin-
duced cis-to-trans isomerization through the rotational
scission of the cis double bonds was also supported by
the fact that during the illumination the spin concen-
tration is not decreased but increased with irradiation
ESR Sp ectr a . ESR spectra were observed in order
to determine the geometrical structures of the pristine
brown polymer (Table 1, run 1). Table 2 shows the ESR
spectral parameters of the brown polymer in the case
of the TEA solvent. The ESR parameters of the brown
polymer were determined as g ) 2.0035 and line width,
∆
Hmsl ) 12.8 G at room temperature and g ) 2.0043
and ∆Hmsl ) 13.0 G at 77 K. On the other hand, in the
case of the EtOH solvent (Table 1, run 2), the param-
eters of the pristine yellow polymer were also estimated
as g ) 2.0031 and ∆Hmsl ) 10.5 G at room temperature
and g ) 2.0035 and ∆Hmsl ) 11.4 G at 77 K. These data
strongly support that the resulting P2ET polymer was
stereoregularly prepared to selectively produce the cis-
transoid polymers, because the observed g values agreed
with those of the typical cis isomers containing such a
heteroatom, i.e., O or N in the poly(n-alkoxyphenyl)-
1
8
20
26
time from ca. 2.1 × 10 to ca. 1.37 × 10 spins/g.
Thus, the observed increase of the spin concentration
strongly proves formation of trans conjugation lengths
as mentioned above.
1
-6
6
acetylene or poly(p-nitrophenyl)acetylene whose spin-
The slight decrease observed in the line width may
be explained by the increase of motional narrowing rate
of the resulting mobile unpaired electrons, which are
created by rotational scission of the original cis CdC
double bonds. This means that the resulting trans
sequences are not completely planar but bent and/or
distorted structures where effective trans sequence
length is shorter compared with that of the extended
orbit coupling constant: δ is fairly large compared with
that of a carbon atom.1
-6,24,25
The observed g value and
temperature dependency of the line width observed at
room temperature and 77 K did not allow us to assign
the pristine P2ET polymer to the corresponding trans
isomer but to the cis polymer, because usually the g
value in the trans isomer is similar to that of a free
electron, i.e., 2.0023-4, which is fairly different from
the g values shown in Table 2. The π conjugation
between the cis double bonds in the main chain and the
thiophene moiety plane operates fairly; i.e., the main
chain plane is nearly in-plane to that of the thiophene
ring plane to give such a larger g value compared with
that of the planar trans isomer as previously reported
6
planar trans sequences. This distortion is supported
by the UV-vis spectrum of the polymer film which was
photoilluminated for 5 h as shown in Figure 3. The UV-
vis spectrum has no sharp absorption peak in the range
from 275 to 850 nm, irrespective of trans polyacetylene
2
8
polymers. Further, the observed increment of the spin
concentration proves that the photoilluminated cis-to-
trans isomerization resulted in not direct but rotational
breakage of the cis CdC bonds in the main chain of the
polymer.
6
,24,25
by us.
In the planar trans isomer the trans
conjugation sequence plane is nearly perpendicular to
that of the thiophene ring in the polymer where no
stronger magnetic interaction between the unpaired
electrons in the main chain and the sulfur atom in the
thiophene should be expected to give a rather large g
value as mentioned below (see Scheme 1). This is also
supported by small temperature dependencies of the line
widths observed in the pristine polymers (see Table 2),
indicating that no significant motional narrowing effect
It is noteworthy, however, that the observed spin
1
8
concentration, ∼2.0 × 10 spins/g, in the P2ET polymer
is fairly high, around 2 orders of magnitude compared
1
6
with that, ca. 10 spins/g, of ordinary nonsubstituted
2
7
cis-polyacetylenes. This value is rather comparable to
that of trans polyacetylene which was prepared using
the Ziegler-Natta catalyst at room temperature where

2
004 Nakamura et al.
Macromolecules, Vol. 35, No. 6, 2002
one unpaired electron is stabilized in ca. 3000 carbons
in the trans-polyacetylene, although, inversely, one
electron is stabilized in ca. 30 000 carbons in the cis-
(4) Tabata, M.; Sone, T.; Sadahiro, Y.; Yokota, K.; Nozaki, Y. J .
Polym. Sci., Part A: Polym. Chem. 1998, 36, 217.
(5) Tabata, M.; Sone, T.; Sadahiro, Y.; Yokota, K. Macromol.
Chem. Phys. 1998, 199, 1161.
2
6
polyacetylene. This indicates that the spin concentra-
tions of the P2ET polymer observed before and after the
illumination are clearly comparable not to that of cis
but that of trans in the nonsubstituted polyacetylene.
Thus, the ESR data clearly evidenced that the initial
and irradiated P2ET polymer can be ascribed to the cis-
transoid and trans-transoid polymers, respectively,
although the reason why the cis P2ET polymer can
stabilize such large amount of radical spins remains to
be examined.
(6) D’Amato, R.; Sone, T.; Tabata, M.; Sadahiro, Y.; Russo, M.
V.; Furlani, A. Macromolecules 1998, 31, 8660.
(7) Tabata, M.; Sadahiro, Y.; Nozaki, Y.; Inaba, Y.; Yokota, K.
Macromolecules 1996, 29, 6673.
(8) Tabata, M.; Inaba, Y.; Yokota, K.; Nozaki, Y. J . Macromol.
Sci., Pure Appl. Chem. 1994, A31, 465.
(9) Tabata, M.; Yang, W.; Yokota, K. Polym. J . 1990, 22, 1105.
(
10) Yang, W.; Tabata, M.; Kobayashi, S.; Yokota, K.; Shimizu,
A. Polym. J . 1991, 23, 1135.
(11) Tabata, M.; Yang, W.; Yokota, K. J . Polym. Sci., Polym. Chem.
Ed. 1994, 32, 1113.
(
(
(
12) Tabata, M.; Sadahiro, Y.; Sone, T.; Inaba, Y.; Yokota, K.
Koubunshi Ronbunsyuu (in J apanese) 1999, 56, 330.
13) Masuda, T.; Isobe, E.; Higashimura, T.; Takada, K. J . Am.
Chem. Soc. 1983, 105, 7473.
14) (a) Stockheim, T. A., Ed. Handbook of Conducting Polymers;
Dekker: New York, 1986; Vols. 1 and 2. (b) Ferraro, J . R.,
Williams, J . M., Eds. Introduction to Synthetic Electrical
Conductors; Academic Press: New York, 1987. (c) Salomone,
J . C., Ed.Polymeric Materials; CRC Press: New York, 1996;
Vol. 8, p 6481.
15) Korshak, Y. V.; Medvedeva, T. V.; Ovchinnikov, A. A.; Spector,
V. Nature (London) 1987, 32, 370.
16) Tabata, M.; Nozaki, Y.; Yang, W.; Yokota, K.; Tazuke, Y. Proc.
J pn. Acad. 1995, Ser. B71, 219.
(17) (a) Tabata, M.; Sone, T.; Yokota, K.; Wada, T.; Sasabe, H.
Nonlinear Opt. 1999, 22, 341. (b) Tada, K.; Sawada, H.;
Kyokane, J .; Yoshino, K. J pn. J . Appl. Phys. 1995, 34, L1083.
18) Furlani, A.; Iucci, G.; Russo, M. V.; Bearzotti, A.; D’Amico,
A. Sens. Actuators B 1992, 13, 447.
(19) Takahashi, S.; Kuroyama, Y.; Sonogashira, K.; Hagihara, N.
Con clu sion
2
-Ethynylthiophene was successfully polymerized us-
ing a [Rh(norbornadiene)Cl]2 catalyst in the presence
of triethylamine or ethanol as the polymerization sol-
vent to produce the poly(2-ethynylthiophene), P2ET,
polymers. The resulting polyacetylenes were character-
1
ized in detail using H NMR, solution and film UV-
(
vis, and ESR methods. The difference in the color of
their polymers prepared using TEA or EtOH solvent
was suggested in terms of the difference in the degree
of the aggregation of the polymer chains. Photoinduced
cis-to-trans isomerization of the pristine polymer was
newly found to occur when the polymer was irradiated
using light of 320-470 nm under vacuum for 5 h.
The obtained trans isomer was also studied in detail
using ESR and UV-vis spectra. The data showed that
the distorted trans conjugation sequences were formed
in the solid phase where a large number of radicals
produced by the rotational scission of the cis CdC bonds
is stabilized.
(
(
Synthesis 1980, 627.
20) Natta, G.; Mazzanti, G.; Corradini, P. J . Rend. Accad. Naz.
Lincei 1958, 25, 3.
21) Kunzler, J .; Percec, V. J . Polym. Sci., Polym. Chem. Ed. 1990,
(
(
(
2
8 1221 and reference cited therein.
22) Tabata, M.; Kobayashi, S.; Sadahiro, Y.; Nozaki, Y.; Yokota,
Studies on the reason why the P2ET polymer can
stabilize such large amount of π radicals is in progress
in our laboratory at present together with another
ethynylthiophene polymer, and the results will be
published elsewhere soon.
K.; Yang, W. J . Macromol. Sci., Pure Appl. Chem. 1997, A34,
6
41.
(
23) Tabata, M.; Sadahiro, Y.; Yokota, K.; Kobayashi, S. J pn. J .
Appl. Phys. 1996, 35, 5411.
24) Pshezhetskii, S. Y.; Kotov, A. G.; Milincuk, V. A.; Rozinskii,
V. I.; Tupikov, V. I. ESR of Free Radicals in Radiation
Chemistry; Wiley: New York, 1972; p 22.
(
Refer en ces a n d Notes
(25) Tabata, M.; Lund, A. Chem. Phys. 1983, 75, 379.
(
(
(
26) Shirakawa, H.; Ito, T.; Ikeda, S. Macromol. Chem. 1978, 179,
(
1) Tabata, M.; Sone, T.; Sadahiro, Y. Macromol. Chem. Phys.
999, 200, 265.
1565.
1
27) Su, W. P.; Schrefer, J . R.; Heeger, A. J . Phys. Rev. Lett. 1979,
(
2) Tabata, M.; Takamura, H.; Yokota, K.; Nozaki, Y.; Hoshina,
4
2, 1698.
28) Harada, I.; Tasumi, M.; Shirakawa, H.; Ikeda, S. Chem. Lett.
978, 1411.
T.; Minakawa, H.; Kodaira, K. Macromolecules 1994, 27,
6
234.
1
(
3) Tabata, M.; Tanaka, Y.; Sadahiro, Y.; Sone, T.; Yokota, K.;
Miura, I. Macromolecules 1997, 30, 5200.
MA0101198