Photochromism of 1,2-bis(2-methyl-5-phenyl-3-thienyl)perfluorocyclopentene in a single-crystalline phase

Article abstract of DOI:10.1021/ja993181h

1,2-Bis(2-methyl-5-phenyl-3-thienyl)perfluorocyclopentene (1a) and their derivatives, 1,2-bis(2-methyl-5-p-tolyl-3-thienyl)perfluorocyclopentene (2a) and 1,2-bis(2-methyl-5-p-tert-butylphenyl-3-thienyl)-perfluorocyclopentene (3a), were found to undergo re

Full text of DOI:10.1021/ja993181h

J. Am. Chem. Soc. 2000, 122, 4871-4876
4871
Photochromism of
1,2-Bis(2-methyl-5-phenyl-3-thienyl)perfluorocyclopentene in a
Single-Crystalline Phase
Masahiro Irie,*,† Thorsten Lifka,† Seiya Kobatake,† and Nobuo Kato‡
Contribution from the Department of Chemistry and Biochemistry, Graduate School of Engineering,
Kyushu UniVersity, and CREST, Japan Science and Technology Corporation, Hakozaki 6-10-1, Higashi-ku,
Fukuoka 812-8581, Japan, and Institute of AdVanced Material Study, Kyushu UniVersity, Kasugakoen 6-1,
Fukuoka 816-8580, Japan
ReceiVed September 2, 1999. ReVised Manuscript ReceiVed March 20, 2000
Abstract: 1,2-Bis(2-methyl-5-phenyl-3-thienyl)perfluorocyclopentene (1a) and their derivatives, 1,2-bis(2-
methyl-5-p-tolyl-3-thienyl)perfluorocyclopentene (2a) and 1,2-bis(2-methyl-5-p-tert-butylphenyl-3-thienyl)-
perfluorocyclopentene (3a), were found to undergo reversible photochromic reactions in the single-crystalline
phase. Upon irradiation with 366 nm light the single crystals turned blue. The blue colored crystals returned
to colorless by irradiation with visible light (λ > 480 nm). The substituents at para positions of the phenyl
groups did not affect the rates of photocyclization reactions both in the single-crystalline phase and in hexane.
Activation energies of the photocyclization reactions were almost zero. On the other hand, activation energies
as much as 5-10 kJ mol-1 were observed in the photocycloreversion reactions in the single-crystalline phase.
These values were smaller than those observed in solution, ca. 16 kJ mol-1. Slow thermal cycloreversion
reaction of the closed-ring isomer (1b) was observed above 150 °C. The activation energy was 139 kJ mol-1
.
Introduction
the crystalline phase.7-12 In the crystals the dithienylethenes
are fixed in a reactive antiparallel conformation and undergo
effective photocyclization reactions. The crystalline photochro-
mic materials show a fatigue resistant character13 and have
promising potential for optoelectronic devices.
In this paper we have carried out kinetic study of photo-
chromism of dithienylethenes 1, 2, and 3 in the single-crystalline
phase. The reactivities in crystals were examined at various
temperatures and compared with those in solution.
Photochromism is defined as a reversible transformation
between two isomers having different absorption spectra by
photoirradiation. Although many photochromic compounds have
been so far reported,1 compounds which show photochromic
reactivity in the crystalline phase are rare.2 Typical photochromic
compounds, such as azobenzenes, spirobenzopyrans, and spiroox-
azines, require large geometrical structural or molecular volume
changes in the photochromic reaction process. Therefore, the
reactivity is lost in the rigid crystalline lattice. Reversible radical
formations or hydrogen transfers are possible mechanisms for
the crystalline photochromism; the former plays a role in the
photochromism of triphenylimidazole dimers3 and the latter in
N-salicylideneanilines.4 In these systems, photogenerated iso-
mers are thermally unstable and return to the initial isomers in
the dark. Crystalline photochromic systems which undergo
thermally irreversible photochromic reactions are limited.5,6
Recently, we found that some dithienylperfluorocyclopentenes
undergo thermally irreversible photochromic reactions even in
Results and Discussion
† Graduate School of Engineering, Kyushu University and CREST, Japan
Science and Technology Corporation.
Photochromism in Solution. Figure 1 shows a typical
absorption spectral change of 1a in hexane upon ultraviolet light
irradiation. The spectrum of the isolated colored isomer is also
‡ Institute of Advanced Material Study, Kyushu University.
(1) (a) Brown, G. H. Photochromism; Wiley-Interscience: New York,
1971. (b) Du¨rr, H.; Bouas-Laurent, H. Photochromism: Molecules and
Systems; Elsevier: Amsterdam, 1990.
(7) Irie, M.; Uchida, K.; Eriguchi, T.; Tsuzuki, H. Chem. Lett. 1995,
899.
(8) Irie, M.; Uchida. K. Bull Chem. Soc. Jpn. 1998, 71, 985.
(9) Kobatake, S.; Yamada, T.; Uchida, K.; Kato, N.; Irie, M. J. Am. Chem.
Soc. 1999, 121, 2380.
(10) Kobatake, S.; Yamada, M.; Yamada, T.; Irie, M. J. Am. Chem. Soc.
1999, 121, 8450.
(2) Scheffer, J. R.; Pokkuluri, P. R. In Photochemistry in Organized &
Constrained Media; Ramamurthy, V., Ed.; VCH Pub.: New York, 1990;
p 185.
(3) (a) Maeda, K.; Hayashi, T. Bull. Chem. Soc. Jpn. 1970, 43, 429. (b)
Kawano, M.; Sano, T.; Abe, J.; Ohashi, Y. J. Am. Chem. Soc. 1999, 121,
8106.
(4) (a) Hadjoudis, E.; Vittorakis, M.; Moustakali-Mavridis, I. Tetrahedron
1987, 43, 1345. (b) Harada, J.; Uekusa, H.; Ohashi, Y. J. Am. Chem. Soc.
1999, 121, 5809.
(5) Rieke, R. D.; Page, G. O.; Hudnall, P. M.; Arhart, R. W.; Bouldin,
T. W. J. Chem. Soc., Chem. Commun. 1990, 38.
(11) Kodani, T.; Matsuda, K.; Yamada, T.; Irie, M. Chem. Lett. 1999,
1003.
(12) Yamada, T.; Kobatake, S.; Muto, K.; Irie, M. J. Am. Chem. Soc.
2000, 122, 1589.
(13) Irie, M.; Lifka, T.; Uchida, K.; Kobatake, S.; Shindo, Y. Chem.
Commun. 1999, 747.
(6) Bradsher, C. K.; Beavers, L. E. J. Org. Chem. 1957, 22, 1740.
10.1021/ja993181h CCC: $19.00 © 2000 American Chemical Society
Published on Web 05/06/2000

4872 J. Am. Chem. Soc., Vol. 122, No. 20, 2000
Irie et al.
Table 1. Absorption Characteristics and Photoreactivity of
Dithienylethenes in Hexane
quantum yield
ꢀ/M-1 cm-1 a
cyclization cycloreversion
compd
a
b
(λmax
)
(492 nm)
convn/%b
97
1
35600
15600
0.59
0.53
0.56
0.013
(280 nm) (575 nm)
39900 18100
(285 nm) (580 nm)
38000 16800
(287 nm) (580 nm)
2
3
0.0097
0.011
98
99
a Absorption coefficient at the absorption maximum. b Conversion
from the open- to the closed-ring isomers in the photostationary state
under irradiation with 313 nm light.
Figure 1. Absorption spectral change of 1 in hexane (2.4 × 10-5 M)
upon irradiation with 313 nm light: 1a (- - -), 1 in the photostationary
state under irradiation with 313 nm light (- - -), and 1b (s).
shown in Figure 1. Upon irradiation with 313 nm light the
colorless hexane solution of 1a turned blue, in which absorption
maxima were observed at 306, 380, and 575 nm. The photo-
stationary spectrum is almost the same as that of the colored
isomer, indicating a high conversion from the colorless to the
colored isomers by irradiation with 313 nm light. The blue
colored solution returned colorless by irradiation with visible
light (λ > 450 nm). The colored isomer was stable and could
be isolated by HPLC (silica gel column, hexane). The molecular
characteristics of the isomer were examined by 1H NMR, mass
spectrum, elemental analysis, and X-ray crystallography. All
analysis data agreed with that of the closed-ring isomer 1b.
Similar spectral changes were observed for 2 and 3. The
absorption maxima and coefficients (ꢀ) of the open- and closed-
ring isomers for these three compounds are summarized in Table
1.
The quantum yields of cyclization and cycloreversion reac-
tions were measured in hexane at room temperature, and also
shown in Table 1. Any appreciable difference in the quantum
yields was not observed among the three compounds. The
cyclization quantum yield of 1a (Φ ) 0.59) was larger than
that of 1,2-bis(2,4-dimethyl-5-phenyl-3-thienyl)perfluorocyclo-
pentene (4a) (Φ ) 0.46), which has methyl substituents at 4
and 4′ positions of the thiophene rings, while the cycloreversion
quantum yields were similar (Φ ) 0.013 and 0.015, respec-
tively).14 The methyl groups at 4 and 4′ positions decreased
the cyclization quantum yield.
Figure 2. Crystal surface shape of 1a (a), 2a (b), and 3a (c). The
arrows show the maximum direction of absorption of the closed-ring
isomers under polarized light.
To confirm that the color is due to the closed-ring isomers,
the colored crystals were dissolved in hexane and the absorption
maxima were compared with each spectrum of 1b, 2b, and 3b
in hexane. In all cases the spectra of the solutions containing
the dissolved colored crystals were identical with those of the
closed-ring isomers. The blue colors of the crystals are due to
the closed-ring isomers.
The absorption spectra and intensities of the crystals were
measured by using a polarizing microscope to confirm that the
closed-ring isomers were produced in the crystal lattice. In the
measurement, polarizer and analyzer were set parallel to each
other. When the plane of the polarized light coincides with the
direction of the arrow shown in Figure 2, three crystals become
blue. Figure 3 shows the absorption spectra of the colored
crystals under the polarized light. The absorption maxima
slightly shifted to longer wavelengths from 589 (1) to 605 nm
(3) by introducing tert-butyl substituents at 4 and 4′ positions
of the phenyl groups. The methyl substituted compound had
the maximum at 595 nm. The absorbances at the absorption
maxima were plotted by rotating the crystals under polarized
light as shown in Figure 4. The absorption anisotropies were
observed for all crystals of 1, 2, and 3. The polar plots indicate
that at a certain angle the crystals are deep blue and the color
almost disappeared by rotating the crystals as much as 90°. The
intensity variation by rotation depended on the substituents. The
dichroism under polarized light clearly indicates that 1, 2, and
3 underwent the photochromic reactions in the crystal lattice.16
Photoreactivity in the Single-Crystalline Phase. The pho-
tocyclization reactivities of the crystals 1a, 2a, and 3a were
compared by measuring the absorbance changes of the colored
isomers in the single crystals upon 366 nm light irradiation.
The results are shown in Figure 5. The photoreactivities of 1a
Photochromism in the Single-Crystalline Phase. Single
crystals of 1a, 2a, and 3a were obtained by recrystallization
from hexane. The shape of the largest surface of each crystal is
illustrated in Figure 2. Upon irradiation with ultraviolet light
the single crystals turned blue while keeping the crystal shape.
The blue colored crystals returned to colorless by irradiation
with visible light (λ > 480 nm). During the coloration/
decoloration cycles the crystals neither shattered nor became
opaque. The crystals kept a clear transparent character.15
(15) The light could penetrate as deep as ∼0.5 mm and induce the
reaction. The degree of conversion of microcrystals was as large as 60-
70%.
(16) Powder X-ray diffraction analysis confirmed that the reactions
proceeded in the crystals. The X-ray crystallographic analysis of photoir-
radiated single crystal 1 is currently under way. The preliminary result
indicated that the photocyclization proceeded with keeping the single-crystal
structure up to 8% conversion.
(14) Irie, M.; Sakemura, K.; Okinaka, M.; Uchida, K. J. Org. Chem.
1995, 60, 8305.

1,2-Bis(2-methyl-5-phenyl-3-thienyl)perfluorocyclopentene
J. Am. Chem. Soc., Vol. 122, No. 20, 2000 4873
Figure 5. Coloration of single crystals of 1a (b), 2a (9), and 3a (2)
by irradiation with 366 nm light: (a) apparent absorption intensity
change and (b) corrected absorption intensity change by taking into
account ꢀ-values of the crystals. The 366 nm light was completely
absorbed by the crystals.
Figure 3. Absorption spectra of 1b (a), 2b (b), and 3b (c) in the
crystalline phases. The single crystals 1a, 2a, and 3a were irradiated
with 366 nm light.
Figure 4. Polar plots of the absorbance for 1b (b), 2b (x), and 3b
(O) at the absorption maxima in the single-crystalline phases.
and 3a were almost similar. The photoreactivity of 2a was
apparently lower than those of 1a and 3a by a factor of about
10. This is in contrast with the solution reactivity. In hexane
solution all three compounds had similar reactivities.
Figure 6. Bleaching of 1b (b), 2b (9), and 3b (2) in the crystalline
phases by irradiation with 570 nm light: (a) apparent absorption
intensity change and (b) corrected absorption intensity change by taking
into account ꢀ-values of the crystals.
The absorption intensity in the single-crystalline phase
depends on the direction of electronic transition moments of
the packed molecules. In other words, the intensity depends on
the orientation of molecules in the crystal, therefore on the
measuring surface. When the transition moment vector coincides
with the electric field direction of the polarized light, strong
absorption is observed. When the vector deviates from the
polarized light direction, absorption becomes weaker. It is
necessary to determine the absorption coefficients (ꢀ) of the
packed molecules for the comparison of real reactivities.
ꢀ values of the closed-ring isomers, 1b, 2b, and 3b, in the
crystals were determined by comparing the absorption intensities
of the closed-ring isomers under polarized light and the number
of closed-ring isomer molecules, which was obtained by
dissolving the colored crystals in hexane. Figure 2 showed the
measuring surfaces. The ꢀ values of 1b, 2b, and 3b were
determined to be 1.4 × 104, 1.6 × 103, and 2.0 × 104 M-1
cm-1 at the absorption maxima, respectively. Figure 5b shows
the corrected photocyclization rates of 1a, 2a, and 3a. The
cyclization rates were similar among the three crystals.
Figure 6a shows apparent bleaching rates of the closed-ring
isomers 1b, 2b, and 3b in the crystalline phase upon 570 nm
light irradiation. The corrected bleaching rates are shown in
Figure 6b. The rates were dependent on the substituents. Among
the three crystals, the fastest bleaching was observed in crystal
2a and the slowest in crystal 3a. The bleaching rate of 1b in
crystal 1a was between crystals 2a and 3a. In solution the
bleaching rates were similar to each other as shown in Table 1.
This indicates that the crystal lattice controls the photocyclo-
reversion reactions.
Activation Energy. Temperature dependence of photocy-
clization/photocycloreversion reactions was measured in 3-me-

4874 J. Am. Chem. Soc., Vol. 122, No. 20, 2000
Irie et al.
Figure 8. Energy diagram of the photochromic reaction of 1 in crystals.
rate from 1b to 1a showed a linear relationship between ln k
and 1/T. The activation energy was determined from the slope
to be 139 kJ mol-1. Extrapolation of the temperature dependence
indicates that the half-life time of the colored closed-ring isomer
1b is 1900 years at 30 °C.
Figure 7. Temperature dependence of the rates of cyclization reactions
for 1a (b), 2a (9), and 3a (2) in 3-methylpentane (a) and in the single-
crystalline phases (b).
Table 2. Activation Energies of Cyclization and Cycloreversion in
From the above kinetic studies the energy diagram for the
reactions of 1 can be deduced as shown in Figure 8. The large
activation energy in the ground state practically prohibits the
thermal cycloreversion reaction. The absence of activation
energy in the photocyclization process indicates that the
molecules are in a favorable conformation for the reaction and
the crystal lattice does not disturb the rotation of the thiophene
rings. The very rapid photocyclization reaction of bis(2,5-
dimethyl-3-thienyl)perfluorocyclopentene in less than 10 ps
observed in crystal17 is ascribed to the absence of the activation
energy. The activation energy of the cycloreversion process was
also very low.
X-ray Crystallographic Analysis. X-ray crystallographic
analysis of the crystals of 1a, 2a, and 3a was carried out to
reveal the difference in the ꢀ values in the three crystals. Table
3 summarizes the results. The ꢀ values of the closed-ring isomers
depend on the direction of the long axis of the open-ring isomers.
Figure 9 shows vertical sectional views of packed molecules
taken on the arrows shown in Figure 2. The angles (θ) of the
long axes of the molecules to the crystal surface were measured
for the three crystals and are shown in Table 4 along with ꢀ
values. When the molecules were packed in parallel to the
surface (θ is low), the transition moment value increased. The
values are considered to be proportional to cos2 θ when the
molecule has C∞ symmetry. When the molecule has a plane
where π-electrons delocalize, the transition moment value also
depends on the angle between the molecular plane and the plane
of the polarizing light. The relatively low ꢀ value of 2b is
explained by the fact that the molecular plane is perpendicular
to the vertical plane.
3-Methylpentane and in the Crystalline Phase
cyclization (kJ mol-1
compd 3-methylpentane crystal
)
cycloreversion (kJ mol-1
)
3-methylpentane
crystal
1
2
3
0
0
0
0
3.8
0
15.9
16.1
6.9
4.8
9.8
thylpentane solution as well as in the crystalline phase. Figure
7a,b shows the temperature dependence of the cyclization rates
in 3-methylpentane and in the single-crystalline phase, respec-
tively. In both solutions and crystals appreciable temperature
dependence of the cyclization rates was not observed. The
reaction rates of crystals 1a and 3a were the same even if the
reaction temperature was changed from 70 to -50 °C. In the
case of crystal 2a there exists an activation energy, though it is
very small (<4 kJ mol-1).
The photocycloreversion reactions of 1b, 2b, and 3b were
also measured at various temperatures in 3-methylpentane and
in the single-crystalline phase. The activation energies of 1b
and 2b in 3-methylpentane were determined to be 16 kJ mol-1
.
The activation energies in the single-crystalline phase were
smaller than those in solution. They were less than 10 kJ mol-1
and dependent on the substituents. The lower activation energies
in crystals indicate that the photogenerated colored isomers have
different stability between solution and crystals. The conforma-
tion of the photogenerated closed-ring isomers in crystals
contains some strain energy,12 which possibly decreases the
activation energy. The activation energies are summarized in
Table 2.
Thermal stability of the colored closed-ring isomers is one
of the main advantages of diarylethene photochromic perfor-
mance. The blue color of the crystals remains stable even at
100 °C. To determine the stability at elevated temperatures, the
decay of the absorption band at 580 nm of the crystal 1b (or
melt) was measured at 150, 170, 190, and 211 °C in the dark.
The absorbance of 1b gradually started to decrease at 150 °C.
The half-life time at 150 °C was 3.3 h. The colorless product
produced by heating above 200 °C was confirmed to be the
Conclusions
It has been demonstrated that 1,2-bis(2-methyl-5-phenyl-3-
thienyl)perfluorocyclopentene (1a) and its derivatives, 1,2-bis-
(2-methyl-5-p-tolyl-3-thienyl)perfluorocyclopentene (2a) and
1,2-bis(2-methyl-5-p-tert-butylphenyl-3-thienyl)perfluorocyclo-
pentene (3a), undergo photochromic reactions in the single-
crystalline phase. Upon irradiation with 366 nm light the
1
open-ring isomer 1a by H NMR and mass spectroscopy. The
temperature dependence of the thermal cycloreversion reaction
(17) Miyasaka, H.; Nobuto, T.; Itaya, A.; Tamai, N.; Irie, M. Chem. Phys.
Lett. 1997, 269, 281.

1,2-Bis(2-methyl-5-phenyl-3-thienyl)perfluorocyclopentene
J. Am. Chem. Soc., Vol. 122, No. 20, 2000 4875
Table 3. Crystal Data and Structure Refinements for 1a, 1b, 2a, and 3a
1a
1b
2a
3a
formula
formula weight
temp/K
crystal system
space group
unit cell dimensions
a/Å
C27H18F6S2
520.53
C27H18F6S2
520.53
296(2)
triclinic
P1h
C29H22F6S2
548.59
C35H34F6S2
632.74
296(2)
296(2)
296(2)
monoclinic
P21/c
monoclinic
C2/c
monoclinic
P21/n
18.786(2)
11.762(1)
21.675(3)
90
96.323(2)
90
4759.9(10)
8
1.453
11.770(4)
12.023(5)
9.626(3)
94.45(3)
95.89(3)
60.07(3)
1173.7(7)
2
25.978(4)
9.251(2)
10.714(2)
90
102.708(3)
90
2511.7(7)
4
1.451
14.953(1)
14.160(1)
16.028(2)
90
103.550(2)
90
3299.1(6)
4
1.274
b/Å
c/Å
R/deg
â/deg
γ/deg
vol/Å3
Z
D
calcd/(g/cm3)
1.473
final R indices [I > 2σ(I)]
R1
wR2
R indices (all data)
R1
wR2
0.0485
0.1328
0.0504
0.1263
0.0504
0.1365
0.0655
0.1854
0.0806
0.1516
0.0905
0.1538
0.0668
0.1492
0.0822
0.2017
Scheme 1
a Varian Gemini 200 spectrometer using deuteriochloroform and
tetramethylsilane as the solvent and the internal standard, respectively.
Absorption spectra in solution were measured with a Hitachi U-3410
absorption spectrophotometer. Absorption spectra in single-crystalline
phases were measured by using a Leica DMLP polarizing microscope
connected with a Hamamatsu PMA-11 detector. Polarizer and analyzer
were set in parallel to each other. A Mettler FP82 hot stage was used
to maintain constant temperature of the crystal. Photoirradiation was
carried out using a USHIO 500 W high-pressure mercury lamp or a
USHIO 500 W xenon lamp as the light source. Monochromic light
was obtained by passing the light through a monochromator (Ritsu MV-
10N) or a band-pass filter (∆λ1/2 ) 15 nm). X-ray crystallographic
analysis was carried out with a Bruker SMART CCD diffractometer
or a Enraf-Nonius FR250 diffractometer.
Figure 9. Vertical sectional views of packed molecules in crystals
1a, 2a, and 3a along with the arrows shown in Figure 2: (a) crystal
surface shapes, (b) vertical sectional views, and (c) the packed
molecules.
Table 4. ꢀ Values of 1b, 2b, and 3b in the Crystalline Phase
compd
ꢀ/M-1 cm-1
θ/deg
cos2 θ
1b
2b
3b
1.4 × 104
1.6 × 103
2.0 × 104
41
55
3
0.57
0.33
1.0
Determination of ꢀ Values in Crystal. Absorbance (A) is defined
as the following equation:
A ) log(I0/I) ) ꢀn/S
colorless open-ring form crystals turned blue, and the blue color
disappeared by irradiation with visible light (λ > 480 nm). The
rates of photocyclization reactions were not affected by the
substituents at para positions of the phenyl groups and their
activation energies were almost zero in both solution and
crystals. The photocycloreversion rates were dependent on the
substituents and the fastest bleaching of the blue color was
observed in crystal 2a, which has methyl substituents at the
para positions. The activation energies of the photocyclorever-
sion reactions in crystals (<10 kJ mol-1) were lower than those
in solution (16 kJ mol-1).
where I0 and I are the light intensity before and after passing through
the sample, respectively. n and S represent the molar number of closed-
ring isomer molecules presented in the light path and the irradiated
area, respectively. A ()log(I0/I)) in the crystal was determined using
polarized light. n was determined by dissolving the colored crystal in
hexane and measuring the absorption spectrum (ꢀ values in hexane
solution are known, see Table 1). The ꢀ values were calculated from
the values of A, n, and S.
3-Bromo-2-methyl-5-phenylthiophene (6). 6 was prepared by
reacting 3-bromo-2-methyl-5-thienylboronic acid (5)18 (1.33 g; 6.0
mmol) with iodobenzene (1.22 g; 6.0 mmol) in the presence of Pd-
(PPh3)4 (208 mg; 0.18 mmol) and Na2CO3 (1.59 g; 15 mmol) in
tetrahydrofuran (THF) (50 mL containing 10% water) for 6 h at 70
Experimental Section
General. Solvents used were spectroscopic grade and purified by
1
distillation before use. H NMR spectra (200 MHz) were recorded on
(18) Gilat, S. L.; Kawai, S. H.; Lehn, J.-M. Chem. Eur. J. 1995, 1, 275.

4876 J. Am. Chem. Soc., Vol. 122, No. 20, 2000
Irie et al.
°C. 6 was purified by column chromatography on SiO2 using hexane
Closed-Ring Isomer of 1a (1b). 1b was isolated by passing a
photostationary solution containing 1a and 1b through a HPLC (Hitachi
L-6250 HPLC system, silica gel column, hexane as the eluent): mp
as the eluent and 1.1 g obtained as colorless crystals in 50% yield:
1
mp 72-73 °C; H NMR (200 MHz, CDCl3) δ 2.41 (s, 3H), 7.10 (s,
1H), 7.33-7.51 (m, 5H); MS m/z (M+) 252, 254. Anal. Calcd for C11H9-
BrS: C, 52.19; H, 3.58. Found: C, 52.04; H, 3.70.
193 °C; H NMR (200 MHz, CDCl3) δ 2.18 (s, 6H), 6.68 (s, 2H),
1
7.3-7.7 (m, 10 H); MS m/z (M+) 520. Anal. Calcd for C27H18F6S2: C,
3-Bromo-2-methyl-5-p-tolylthiophene (7). 7 was prepared by a
method similar to that used for 6 and obtained as colorless crystals:
62.30, H, 3.49. Found: C, 62.39; H, 3.50.
1,2-Bis(2-methyl-5-p-tolyl-3-thienyl)perfluorocyclopentene (2a).
2a was prepared by a method similar to that used for 1a and obtained
1
mp 96 °C; H NMR (200 MHz, CDCl3) δ 2.36 (s, 3H), 2.41 (s, 3H),
7.06 (s, 1H), 7.17-7.40 (m, 4H); MS m/z (M+) 266, 268. Anal. Calcd
for C12H11BrS: C, 53.94; H, 4.15. Found: C, 53.61; H, 4.32.
1
as colorless prisms: mp 160 °C; H NMR (200 MHz, CDCl3) δ 1.96
(s, 6H), 2.35 (s, 6H), 7.24 (s, 2H), 7.23-7.47 (m, 8H); MS m/z (M+)
548. Anal. Calcd for C29H22F6S2: C, 63.49; H, 4.04. Found: C, 63.77;
H, 4.31.
3-Bromo-2-methyl-5-(p-tert-butylphenyl)thiophene (8). 8 was
prepared by a method similar to that used for 6 and obtained as colorless
crystals: mp 65 °C; 1H NMR (200 MHz, CDCl3) δ 1.32 (s, 9H), 2.39
(s, 3H), 7.05 (s, 1H), 7.25-7.55 (m, 4H); MS m/z (M+) 308, 310. Anal.
Calcd for C15H17BrS: C, 58.25; H, 5.54. Found: C, 58.38; H, 5.86.
1,2-Bis(2-methyl-5-phenyl-3-thienyl)perfluorocyclopentene (1a).
To a stirred solution of 6 (1.01 g; 4.0 mmol) in THF was added
dropwise a 15% n-BuLi/hexane solution (2.6 mL; 4.3 mmol) at -78
°C under nitrogen atmosphere. Stirring was continued for 20 min at
the low temperature. Perfluorocyclopentene (0.42 g; 2.0 mmol, Nippon
Zeon) was slowly added to the reaction mixture at -78 °C, and the
mixture was stirred for 3 h at that temperature. The reaction was stopped
by the addition of methanol. The product was extracted with ether.
The organic layer was washed with 1 N HCl aqueous solution and
water. The organic layer was dried over MgSO4, filtrated, and
evaporated. The crude product was purified by column chromatography
on SiO2 using toluene/hexane (1:3) as the eluent and by recrystallization
from hexane to give 0.85 g of 1a in 81% yield as colorless cubes: mp
1,2-Bis(2-methyl-5-p-tert-butylphenyl-3-thienyl)perfluorocyclo-
pentene (3a). 3a was prepared by a method similar to that used for 1a
1
and obtained as colorless prisms: mp 195 °C; H NMR (200 MHz,
CDCl3) δ 1.32 (s, 18H), 1.98 (s, 6H), 7.23 (s, 2H), 7.39-7.47 (m,
8H); MS m/z (M+) 632. Anal. Calcd for C35H34F6S2: C, 66.44; H, 5.42.
Found: C, 66.18; H, 5.69.
Acknowledgment. This work was supported by CREST
(Core Research for Evolutional Science and Technology) of
Japan Science and Technology Corp. (JST). We also thank
NIPPON ZEON CO., Ltd. for their supply of chemicals.
Supporting Information Available: X-ray structural infor-
mation on 1a, 1b, 2a, and 3a (PDF) and an X-ray crystal-
lographic file (CIF). This material is available free of charge
via the Internet at http://pubs.acs.org.
1
139-140 °C; H NMR (200 MHz, CDCl3) δ 1.97, (s, 6H), 7.28 (s,
2H), 7.2-7.6 (m, 10 H); MS m/z (M+) 520. Anal. Calcd for
C27H18F6S2: C, 62.30, H, 3.49. Found: C, 62.66; H, 3.72.
JA993181H