Polymorphism of 1,2-bis(2-methyl-5-p-methoxyphenyl-3-thienyl)perfluorocyclopentene and photochromic reactivity of the single crystals

Article abstract of DOI:10.1002/chem.200390066

Four polymorphic crystals were obtained by recrystallization of 1,2-bis(2-methyl-5-p-methoxyphenyl-3-thienyl)perfluorocyclopentene (1a) from hexane. All crystals underwent photochromic reactions upon alternate irradiation with ultraviolet (λ = 370 nm) and

Full text of DOI:10.1002/chem.200390066

FULL PAPER
Polymorphism of 1,2-Bis(2-methyl-5-p-methoxyphenyl-3-thienyl)perfluoro-
cyclopentene and Photochromic Reactivity of the Single Crystals
Masakazu Morimoto, Seiya Kobatake, and Masahiro Irie*[a]
Abstract: Four polymorphic crystals were obtained by recrystallization of 1,2-bis(2-
methyl-5-p-methoxyphenyl-3-thienyl)perfluorocyclopentene (1a) from hexane. All
crystals underwent photochromic reactions upon alternate irradiation with ultra-
violet (l ˆ 370 nm) and visible light (l > 500 nm). The photocyclization quantum
yields were found to be close to unity irrespective of the crystal types, while the
photocycloreversion quantum yields were different as much as four times depending
on the conformation of the closed-ring isomers in the crystals.
Keywords:
photochromism ¥ polymorphism ¥
quantum yield ¥ single crystal
diarylethene
¥
Introduction
photocyclization reaction takes place without any activation
energy, while the photocycloreversion reaction has to over-
come a small activation energy.[ iv) The activation energy of
the thermal cycloreversion reaction in crystal is smaller than
that in solution. The activation energy depends on the
conformation of the open- and closed-ring isomers in
crystal.[ Photochromic performance of diarylethene deriv-
atives in crystal strongly depends on the conformation of the
molecules.
22]
Photochromism is referred as a light-induced reversible
transformation between two isomers having different absorp-
Although a great number of photochromic
compounds have been reported so far, compounds which
exhibit the photochromic reactivity in the crystalline phase
tion spectra.[
1, 2]
24]
are very rare and in most cases photogenerated isomers are
thermally unstable.[
3±15]
Recently we found that some diaryl-
ethene derivatives undergo single-crystalline photochromism
During the course of study of single-crystalline photo-
chromism, we found that 1,2-bis(2-methyl-5-p-methoxyphen-
yl-3-thienyl)perfluorocyclopentene (1a) forms four polymor-
phic crystals when recrystallized from hexane (see Scheme 1).
Each molecule has a different conformation in the four types
of crystals. This enables us to study the effect of conformation
on the optical property and the reactivity. In this paper, we
report on the correlation between the conformation and the
optical property as well as the reactivity.
and both initial colorless and photogenerated colored isomers
are stable in the dark.[
16±2ꢀ]
The thermally irreversible and
fatigue resistant photochromic crystals can be potentially
applied to various optoelectronic devices, such as holographic
[26, 30±33]
and three-dimensional optical recording memories.
Single-crystalline photochromism of diarylethene deriva-
tives has following characteristics: i) The absorption spectrum
of the closed-ring form isomer exhibits a distinct dichroic
character and the maximum shifts to a longer wavelength in
comparison with that in solution. The spectrum shift is
ascribable to the difference in the conformation of the
molecules between in crystal and in solution. ii) The photo-
cyclization quantum yield in crystal is twice larger than that in
solution and is close to unity. On the other hand, the
photocycloreversion quantum yield in crystal varies depend-
ing on the molecules.[ The conformation of the closed-ring
isomer is considered to control the cycloreversion quantum
yield, but the details have not yet been clarified. iii) The
Results and Discussion
Photochromism in hexane: Figure 1 shows the absorption
spectral change of 1a by irradiation with 313 nm light in
hexane. Compound 1a has the absorption maximum at
28]
4
À1
À1
2
3
ꢀ3 nm (e ˆ 4.4  10 m cm ). Upon irradiation with
13 nm light, the colorless solution of 1a turned blue; a visible
absorption band was observed at 582 nm for this solution. The
blue color disappeared upon irradiation with visible light (l >
500 nm). The spectral change could be repeated many times.
The blue colored solution in the photostationary state was
analyzed by HPLC. Two peaks were observed in the HPLC
[
a] Prof. Dr. M. Irie, M. Morimoto, Dr. S. Kobatake
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)
Fax : (‡81)ꢀ2-642-3568
(
silica gel column, hexane/ethyl acetate ꢀ:1) monitored at the
E-mail: irie@cstf.kyushu-u.ac.jp
isosbestic point of 316 nm. The elution time of the former
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M. Irie et al.
FULL PAPER
F2
F2
was determined to be 2.1 Â
F2
S
F2
4
À1
À1
F2
F2
10 m cm
at 582 nm. The
UV
Vis
conversion from 1a to 1b in
the photostationary state upon
irradiation with 313 nm light
was ꢀ6%. Upon irradiation
with visible light (l > 500 nm),
the solution turned colorless to
give the same spectrum as 1a.
Me
Me
Me
Me
S
S
S
MeO
OMe
MeO
OMe
1a
1b
Scheme 1. Photochromism of compound 1.
small peak was the same as that of 1a. The latter was isolated.
The structure of the compound was analyzed by H NMR
The quantum yields of photocyclization and photocyclo-
1
reversion reactions were determined in hexane to be 0.56 (by
irradiation with 2ꢀ3 nm light) and 0.0052 (with 582 nm light),
respectively. The photocyclization yield was similar to that of
1,2-bis(2-methyl-5-phenyl-3-thienyl)perfluorocyclopentene
having no methoxy substituents, while the photocyclorever-
sion yield was reduced to a half.[
spectrum, mass spectrum, elemental analysis, and X-ray
crystallography. X-ray crystallographic analysis data is shown
in Table 1. All data agreed with those of 1b. The absorption
spectrum of 1b is also shown in Figure 1. The spectrum was
almost the same as that of the photostationary solution,
indicating high conversion from 1a to 1b. The e value for 1b
22]
Polymorphism: Four kinds of crystals were obtained by slowly
evaporating hexane solutions of 1a at room temperature.
Figure 2a and b show the shapes of the four crystals, which are
named as 1a-a, b, g, and d, and color changes upon irradiation
with UV light. a-crystal had a well-developed surface with
angles of 74 and 1068. b- and g-crystals had surfaces with
angles of 77 and 1038. d-crystal was obtained as a needle. The
melting points were 14ꢀ ± 1508C (a), 136 ± 1388C (b), 148 ±
1
4ꢀ8C (g), and 135 ± 1378C (d), respectively. X-ray crystallo-
graphic analysis of the crystals was carried out to confirm the
polymorphic forms, and the resulting crystallographic data are
À5
shown in Table 1. The R values for the reflection with I >
2s(I) were less than 0.05 for all four crystals.
Figure 1. Absorption spectral change of 1 in hexane (1.1Â 10 m): 1a (±±±),
1
1
b (––), and 1 in the photostationary state (- - - -).
Table 1. Crystal data and structure refinement for 1a-a, 1a-b, 1a-g, 1a-d, and 1b.
a-a 1a-b
1
1a-g
1a-d
1b
formula
C
2ꢀ
H
22
F
6
O
2
S
2
C
2ꢀ
H
22
F
6
O
2
S
2
C
2ꢀ
H
22
F
6
O
2
S
2
C
2ꢀ
H
22
F
6
O
2
S
2
2ꢀ 22 6 2 2
C H F O S
formula weight
crystal size [mm ]
T [K]
crystal system
space group
a [ä]
b [ä]
c [ä]
a [8]
b [8]
580.5ꢀ
580.5ꢀ
580.5ꢀ
580.5ꢀ
580.5ꢀ
3
0.5 Â 0.3 Â 0.2
2ꢀ6(2)
monoclinic
C2/c
26.ꢀ87(6)
8.806(2)
11.4ꢀꢀ(2)
ꢀ0
ꢀ1.554(4)
ꢀ0
2731.7(10)
4
0.5 Â 0.3 Â 0.1
0.5 Â 0.5 Â 0.1
0.6 Â 0.2 Â 0.2
0.7 Â 0.4 Â 0.2
2ꢀ6(2)
2ꢀ6(2)
2ꢀ3(2)
2ꢀ8(2)
triclinic
monoclinic
monoclinic
triclinic
≈
≈
P1
P2
1
/c
P2
1
/c
P1
11.406(2)
13.758(3)
18.22ꢀ(4)
72.541(3)
82.208(3)
76.663(3)
2648.4(10)
4
26.157(5)
ꢀ.023(2)
11.2ꢀ6(4)
ꢀ0
ꢀ4.500(4)
ꢀ0
2657.ꢀ(ꢀ)
4
1.451
18.727(4)
6.643(1)
21.45ꢀ(4)
ꢀ0
101.035(3)
ꢀ0
2620.1(ꢀ)
4
1.472
11.085(3)
11.23ꢀ(3)
11.864(3)
83.276(4)
65.030(3)
88.1ꢀ8(5)
1330.5(6)
2
g [8]
V [ä ]
3
Z
À3
1
calcd [gcm
]
1.412
0.261
11ꢀ2
1.456
0.270
11ꢀ2
1.44ꢀ
0.268
5ꢀ6
À1
m [mm
F(000)
]
0.26ꢀ
11ꢀ2
0.273
11ꢀ2
q range [8]
1.51 ± 27.52
7757
2ꢀ34
206
0.ꢀ66
1.17 ± 27.64
2243ꢀ
112ꢀ3
833
0.ꢀ13
0.78 ± 27.52
15564
5808
438
0.ꢀ64
1.11 ± 27.51
14677
55ꢀ8
354
0.ꢀ62
1.82 ± 27.56
15001
5772
43ꢀ
1.022
reflections collected
independent reflections
parameters
goodness-of-fit on F2
final R indices [I > 2s(I)]
R
1
0.0462
0.1171
0.0411
0.0831
0.0410
0.1018
0.038ꢀ
0.0878
0.0530
0.1252
wR
R indices (all data)
2
R
1
0.0714
0.0ꢀ46
0.07ꢀ5
0.0810
0.088ꢀ
wR
largest diff. peak/hole [eä
2
0.1304
0.22ꢀ/ À 0.330
0.0ꢀ82
0.1ꢀ1/ À 0.27ꢀ
0.1244
0.213/ À 0.250
0.101ꢀ
0.218/ À 0.188
0.1456
0.242/ À 0.432
À3
]
622
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Chem. Eur. J. 2003, 9, No. 3

Photochromic Reactivity of the Single Crystals
621±627
Figure 2. Crystal shapes of 1a-a, 1a-b, 1a-g, and 1a-d (a), and
photographs of the crystals before and after UV irradiation (b).
The crystal system of 1a-a was monoclinic C2/c,
3
Z ˆ 4. The unit cell volume was 2731.7(10) ä . The
ORTEP drawing of 1a-a is shown in Figure 3a. Half
of the molecules were crystallographically inde-
pendent. The perfluorocyclopentene ring was dis-
ordered equally. The distance between the reactive
carbon atoms was 3.48 ä. The planes of two phenyl
rings were almost parallel to the perfluorocyclopen-
tene plane. The rotation angle between thiophene
and phenyl rings (C3-C4-Cꢀ-C10) was 23.ꢀ8.
The crystal system of 1a-b had a space group of
≈
triclinic P1 and Z ˆ 4. The unit cell volume was
3
2
648.4(10) ä . Two molecules were independently
packed, as indicated by molecules Aand B. The
distance between the reactive carbon atoms in the A
molecules was 3.55 ä. The rotation angles between
thiophene and phenyl rings (C3-C4-C16-C17 and
C12-C13-C22-C23) were À31.ꢀ and 33.28, respec-
tively. The distance between the reactive carbon
atoms in the B molecules was 3.70 ä. The rotation
angles between thiophene and phenyl rings (C41-
C42-C51-C52 and C32-C33-C45-C46) were 2.3 and
À14.48, respectively. The perfluorocyclopentene
rings were disordered in both Aand B molecules.
The crystal system of 1a-g had a space group of
monoclinic P2 /c and Z ˆ 4. The unit cell volume
1
3
was 2657.ꢀ(ꢀ) ä . The molecular packing was similar
to that of 1a-a. One of the phenyl ring planes was
almost parallel to the perfluorocyclopentene plane,
while the other tilted. The rotation angles between
thiophene and phenyl rings were À22.ꢀ and 25.08 for
C3-C4-C16-C17 and C12-C13-C22-C23, respectively. The
distance between the reactive carbon atoms was 3.52 ä. The
perfluorocyclopentene ring was disordered.
Figure 3. ORTEP drawings of 1a-a (a), 1a-b (b), 1a-g (c), and 1a-d (d).
planes of two phenyl rings were twist with the planes of
thienyl rings. The rotation angles between thiophene and
phenyl rings were 6.0 and À16.68 for C3-C4-C16-C17 and
C12-C13-C22-C23, respectively. The distance between the
reactive carbon atoms was 3.5ꢀ ä.
The crystal system of 1a-d had a space group of monoclinic
3
P2 /c and Z ˆ 4. The unit cell volume was 2620.1(ꢀ) ä . The
1
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M. Irie et al.
FULL PAPER
The four crystals have different space groups, unit cell
volumes, conformation of the molecules, and the distance
between the reactive carbon atoms. This indicates that the
four crystals are polymorphic forms. The necessary conditions
for the photocyclization reactions to take place in the single-
crystalline phase are that the diarylethenes should have an
antiparallel conformation and the distance between the
reactive carbon atoms is less than 4.2 ä.[ The thiophene
rings in all four crystals have the antiparallel conformation
and the distances between the reactive carbons are 3.48 ±
part of the closed-ring form. In the case of g-crystal the central
p-conjugation of the closed-ring form can extend to one of the
phenyl rings.
Figure 5 shows the molecular packing and the polar plots of
the absorbances. The order parameters ((A À A )/(A ‡2A ))
k
?
k
?
were estimated to be 0.60 (a), 0.66 (b), and 0.5ꢀ (g),
respectively. The relatively large order parameters indicate
that the diarylethenes undergo photochromism in the single-
crystalline lattice. In the case of d-crystal the absorption
anisotropy was not observed as shown in Figures 4d and 5d.
Molecules are packed in two different orientations, which are
almost perpendicular to each other.
3]
3.70 ä. This indicates that all four crystals have a possibility
to undergo photochromism in the crystalline phase.
Photochromism in a single-crystalline phase: All four single
crystals 1a turned blue upon irradiation with 370 nm, as
shown in Figure 2b. The photogenerated blue-colored crystals
were dissolved into hexane, and the absorption spectra were
measured in hexane. The visible absorption maxima of all
dissolved crystals were the same as that of 1b. The photo-
generated blue color of the crystals disappeared upon
irradiation with visible light (l > 500 nm).
To confirm the regular packing of the photogenerated
colored isomers, the dichroism of the crystals was measured
under linearly polarized light. The well-developed surfaces for
a, b, g, and d-crystals shown in Figure 2a were (100), (001),
(
100), and (100) faces, respectively. Figure 4 shows the
Figure 5. Packing diagrams of the open-ring isomers and polar plots of the
absorbance of the photogenerated colored isomers at the absorption
maximum. Right hand side shows typical molecule(s) in the crystal.
a) a-crystal, b) b-crystal, c) g-crystal, d) d-crystal.
Figure 4. Absorption spectra of the photogenerated colored crystals.
a) a-crystal, b) b-crystal, c) g-crystal, d) d-crystal.
Partially bleachingreaction : As described above, 1a mole-
cules in d-crystal are packed as shown in Figure 5d. The long
axes of the molecules are oriented perpendicularly to each
other. This suggests that linearly polarized light can selec-
tively bleach the closed-ring isomers. Figure 6 shows photo-
graphs of d-crystal under the polarized light. The colorless d-
crystal (Figure 6a) was irradiated with 370 nm non-polarized
light to give the blue colored crystal as shown in Figure 6b.
When the crystal was irradiated with linearly polarized light
(l > 570 nm) in the direction of 458, the colored isomers along
the polarized light were preferentially bleached and the
molecules oriented perpendicularly to the irradiated polar-
ized light were hardly bleached, as shown in Figure 6c. On the
other hand, when the direction of the irradiated polarized
light was rotated as much as ꢀ08, the molecules in other
polarized absorption spectra of the four colored crystals. The
absorption maxima at the highest intensity angle (k) were
different among the four crystals. a-, b-, g-, and d-crystals gave
the maxima at 630, 600, 615, and 600 nm, respectively. The
absorption maxima shifted to longer wavelengths with the
following order: b and d < g < a. This order is considered to
reflect the p-conjugation length of the closed-ring isomers. As
can be seen from the structures shown in Figure 3, two phenyl
groups in a-crystal become to almost parallel to the perfluor-
ocyclopentene ring by photocyclization. On the other hand, in
the case of b- and d-crystals the planes of phenyl rings tilted to
the plane of perfluorocyclopentene. This means that the
phenyl rings scarcely enter the p-conjugation of the central
624
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Chem. Eur. J. 2003, 9, No. 3

Photochromic Reactivity of the Single Crystals
621±627
6
18 nm light. The quantum yields are also shown in Table 2.
The yields of a- and g-crystals were almost similar and slightly
larger than the yield in hexane. On the other hand, the yields
of b- and d-crystals were much larger than the yield in solution
by a factor of 5. The difference of the cycloreversion quantum
yield between a- and g-crystals and b- and d-crystals
correlates well with the absorption maxima of the closed-ring
isomers. The closed-ring isomers with the absorption maxima
of 600 nm (b- and d-crystals) were efficiently bleached, while
the isomers with the absorption maxima at longer wavelengths
(
a- and g-crystals) kept the photostability as in solution.
The correlation suggests that the p-conjugation length, or
the conformation of the phenyl and thiophene rings, of the
closed-ring isomer controls the quantum yields. When the p-
conjugation extension is limited to the thiophene rings, the
absorption maximum is expected to appear at a shorter
wavelength region and cycloreversion quantum yield increas-
es. On the other hand, when the p-conjugation extends to the
p-methoxyphenyl rings, the absorption maximum shifts to a
longer wavelength region and the quantum yield decreases.
The correlation between the conformation of the closed-ring
isomer and the absorption maximum was further examined
using semi-empirical molecular orbital calculations.
Figure 6. Photographs of d-crystal observed under polarized light: a) d-
crystal, b) after non-polarized UV light irradiation, c and d) after partial
bleaching by linearly polarized light in the direction of 458 and À458.
Simulation of the structure of the closed-ringisomer : The
molecular structures of the closed-ring isomers in a- and d-
crystals were simulated based on the X-ray crystallographic
data for 1,2-bis(2,5-dimethyl-3-thienyl)perfluorocyclopen-
tene; the structure of the photogenerated closed-ring isomer
in the open-ring isomer crystal was precisely determined.[
The closed-ring isomer was constructed by replacing the
methyl groups of 1,2-bis(2,5-dimethyl-3-thienyl)perfluorocy-
clopentene with p-methoxyphenyl groups. The angle between
the thiophene and the phenyl rings was determined by
assuming that only the thiophene rings rotate as much as
direction were preferentially bleached as shown in Figure 6d.
The order parameter of 0.75 was obtained after the partial
bleaching.
Quantum yields in crystal: In crystal, the conformation of
individual molecule is fixed in the crystal lattice. In general,
the photoreactivity depends on the conformation. Therefore,
the reactivity in crystal is influenced by the packing of
molecules in crystal. The cyclization and cycloreversion
quantum yields in the four polymorphic crystals were
23]
measured according to the method described in the litera-
2
2.28 and the phenyl rings do not follow the rotation during
ture.[
27, 28]
The photocyclization reaction was carried out by
[34]
the photocyclization.
The rotation angles between the
irradiation with 370 nm polarized light. The quantum yields
are summarized in Table 2. The cyclization quantum yields of
thiophene and the phenyl rings became 1.78 for a-crystal,
and À16.28 and À38.88 for d-crystal. The structures are shown
in Figure 7. As can be seen from the structures in a-crystal, the
two phenyl rings are in the same plane as the thiophene rings
and the molecule has high planarity. On the other hand, they
are twisted in the d-crystal. Employing these structures, the
absorption spectra of the photogenerated closed-ring isomers
in a- and d-crystals were calculated using the program MOS-F
with CNDO/S method (Fujitsu). The lowest energy absorp-
tion peaks were calculated at 477.21 and 454.45 nm for a- and
d-crystals, respectively. The closed-ring isomer in a-crystal,
which has higher planarity, gave the absorption peak at longer
wavelength than that in d-crystal.[ This simulation supports
the conclusion that the differences in the absorption maxima
and the photocycloreversion quantum yields among the four
crystals are due to the difference in the conformation of the
molecules in crystal.
1
a-a, b, g, and d were very similar and close to unity. This
indicates that the cyclization reaction took place in almost
00% efficiency, that is, all photon energy absorbed by the
1
crystal is used for the chemical reaction. This extremely high
efficiency is ascribed to that the distance between the reacting
carbon atoms of the open-ring isomers in the four polymor-
phic crystals are short enough for the photocyclization
reaction.[
3, 22, 28]
The cycloreversion quantum yields were determined for the
photogenerated blue colored crystals by irradiation with
35]
Table 2. Photocyclization/cycloreversion quantum yields.
in hexane
in crystal
a
b
g
d
[
a]
l
max [nm]
582
21000
0.56
630
4700
0.ꢀ8
600
24000
1.00
615
4600
0.ꢀ7
600
e[a,b] [m cm
cyclization
cycloreversion
À1
À1
]
6400
0.ꢀ5
0.027
0.0052
0.0064
0.026
0.0061
Conclusion
[
a] lmax and e value at the longest wavelength of the photogenerated closed-
1,2-Bis(2-methyl-5-p-methoxyphenyl-3-thienyl)perfluorocy-
ring isomer. [b] The e values were estimated at the strongest absorption
direction under polarized light.
clopentene (1a) formed four polymorphic crystals. All of the
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M. Irie et al.
FULL PAPER
reaction mixture were added 20 wt% Na
2
CO
3
aq (135 mL), 4-iodoanisole
(
15 g, 0.066 mol), and Pd(PPh ) (2.2 g, 0.001ꢀ mol). The mixture was
3 4
heated under reflux for 11 h at 708C. The mixture was neutralized with
HCl, and then was extracted with diethyl ether. The organic layer was dried
over MgSO , filtrated, and concentrated. The residue was purified by silica
4
gel column chromatography using hexane as the eluent and recrystalliza-
tion from methanol to give 2 (11 g, 61%) as crystals. M.p. 108 ± 10ꢀ8C;
1
H NMR (200 MHz, CDCl
3
, 258C, TMS): d ˆ 2.40 (s, 3H; CH
3
), 3.83 (s,
3
H; OCH
3
), 6.ꢀ0 (d, J ˆ 8.7 Hz, 2H; phenyl protons), 6.ꢀ8 (s, 1H; thienyl
‡
proton), 7.43 (d, J ˆ 8.7 Hz, 2H; phenyl protons); MS: m/z: 282, 284 [M ];
elemental analysis calcd (%) for C12
H11BrOS (283.1ꢀ): C 50.ꢀ0, H 3.ꢀ2;
found: C 50.ꢀ1, H 3.83.
1,2-Bis(2-methyl-5-p-methoxyphenyl-3-thienyl)perfluorocyclopentene
(
1a): A15% nBuLi hexane solution (17 mL, 0.028 mol) was added at
À788C under nitrogen atmosphere to a dry THF solution (370 mL)
containing 2 (7.3 g, 0.026 mol), and the solution was stirred for 3 h at the low
temperature. Octafluorocyclopentene (1.7 mL, 0.013 mol; Nippon Zeon)
was slowly added to the reaction mixture at À788C, and the mixture was
stirred for 4.5 h at the temperature. The reaction was stopped by the
addition of methanol. The product was extracted with diethyl ether. The
4
organic layer was dried over MgSO , filtrated, and concentrated. The
residue was purified by column chromatography on silica gel using hexane/
ethyl acetate (4:1) as the eluent and by recrystallization from ethanol to
1
give 1a (5.5 g, 72%) as colorless crystals. H NMR (200 MHz, CDCl
3
,
2
2
58C, TMS): d ˆ 1.ꢀ4 (s, 3H; CH
3
), 3.84 (s, 3H; OCH
3
), 6.ꢀ1 (d, J ˆ 8.6 Hz,
H; phenyl protons), 7.16 (s, 1H; thienyl proton), 7.47 (d, J ˆ 8.6 Hz, 2H;
Figure 7. Simulated structures of the photogenerated closed-ring isomers
in a-crystal (a) and d-crystal (b).
‡
phenyl protons); MS: m/z: 580 [M ]; elemental analysis calcd (%) for
C H F O S (580.61): C 5ꢀ.ꢀꢀ, H 3.82; found: C 60.08, H 3.87.
2ꢀ 22 6 2 2
Closed-ringisomer of 1a (1b) : Compound 1b was isolated by passing a
photostationary solution containing 1a and 1b through a HPLC (Hitachi
L-6250 pump system equipped with Hitachi L-7400 detector, and silica gel
column (Kanto, MightySil Si 60), using hexane/ethyl acetate ꢀ:1 as the eluent.
four crystals underwent photochromism in the single-crystal-
line phase. The photocyclization quantum yields were found
to be close to unity for all crystals. On the other hand, the
photocycloreversion quantum yields depended on the con-
formation of the closed-ring isomers in the crystals and well
correlated with the absorption maxima of the closed-ring
isomers.
1
Retention time was 37 (1a) and 48 min (1b). M.p. 181±1828C; H NMR
(
200 MHz, CDCl
3
, 258C, TMS): dˆ 2.14 (s, 3H; CH
3 3
), 3.87 (s, 3H; OCH ),
6.58 (s, 1H; olefinic proton), 6.ꢀ3 (d, Jˆ 8.8 Hz, 2H; phenyl protons), 7.53 (d,
‡
Jˆ 8.8 Hz, 2H; phenyl protons); MS: m/z: 580 [M ]; elemental analysis calcd
(
22 6 2 2
%) for C2ꢀH F O S (580.61): C 5ꢀ.ꢀꢀ, H 3.82; found: C 60.0ꢀ, H 3.80.
X-ray diffraction: X-ray crystallographic analysis was carried out with a
Bruker SMART1000 CCD-based diffractometer (50 kV, 40 mA) with
MoKa radiation (l ˆ 0.71073 ä). The data were collected as a series of w-
scan frames, each with a width of 0.38 per frame. The crystal-to-detector
distance was 5.118 cm. Crystal decay was monitored by repeating the 50
initial frames at the end data collection and analyzing the duplicate
reflections. Data reduction was performed using SAINT software, which
corrects for Lorentz and polarization effects, and decay. The cell constants
were calculated by the global refinement. The structure was solved by
Experimental Section
General: Solvents used were spectroscopic grade and purified by distil-
lation before use. H NMR spectra were recorded on a Varian Gemini 200
1
spectrometer (200 MHz). Tetramethylsilane was used as an internal
standard. Mass spectra were taken with a Shimadzu GCMS-QP5050A
gas chromatography coupled mass spectrometer. Absorption spectra in
solution were measured with a Hitachi U-3410 absorption spectropho-
tometer. Photoirradiation was carried out using an Ushio 500 W super
high-pressure mercury lamp or an Ushio 500 W xenon lamp as the light
sources. Monochromic light was obtained by passing the light through a
monochrometer (Ritsu MV-10N). Absorption spectra in a single-crystalline
phase were measured by using a Leica DMLP polarizing microscope
connected with a Hamamatsu PMA-11 photodetector. Polarizer and
[36]
2
direct methods using SHELXS-86 and refined by full least-squares on F
[37]
using SHELXL-ꢀ7. The positions of all hydrogen atoms were calculated
geometrically and refined by the riding model. CCDC-185ꢀ42 (1a-a),
CCDC-185ꢀ43 (1a-b), CCDC-185ꢀ44 (1a-g), CCDC-185ꢀ45 (1a-d),
CCDC-185ꢀ46 (1b) contain the supplementary crystallographic data for
this paper. These data can be obtained free of charge via www.ccdc.ac.uk/
conts/retrieving.html (or from the Cambridge Crystallographic Data
Centre, 12 Union Road, Cambridge CB2 1EZ, UK; fax: (‡44)1223-336-
0
33; or e-mail: deposit@ccdc.cam.ac.uk).
analyzer were set in parallel to each other. The quantum yields were
measured according to a method described in the literature.[27, 28] Photo-
Simulation of the structure of the closed-ringisomer : For the central part
consisting of the thiophene and the perfluorocyclopentene rings, the
irradiation was carried out using a 75 W xenon lamp or a 100 W halogen
lamp as the light sources attached with the microscope. The wavelength of
the light used for the photocyclization and photocycloreversion reactions in
a single-crystalline phase was selected by passing the light through a band
pass filter. The selected wavelengths were 370 nm (Dl1/2 ˆ 20 nm) for
cyclization reactions and 618 nm (Dl1/2 ˆ 14 nm) for cycloreversion reac-
tions.
structure of the photogenerated closed-ring isomer in crystal of 1,2-bis(2,5-
dimethyl-3-thienyl)perfluorocyclopentene was employed.[
23]
From the
X-ray crystallographic data, the thiophene rings rotate by 22.28 during
the photocyclization reaction. In the software winMOPAC (Fujitsu), two
methyl groups were replaced with p-methoxy phenyl groups, and its
conformation was set under the assumption that the thiophene rings rotate
and the p-methoxy phenyl rings keep its conformation during the photo-
cyclization reaction.
3
-Bromo-2-methyl-5-(p-methoxyphenyl)thiophene (2): A15%
nBuLi
hexane solution (44 mL, 0.072 mol) was added at À788C under nitrogen
atmosphere to a dry THF solution (170 mL) containing 3,5-dibromo-2-
methylthiophene (17 g, 0.066 mol), and the solution was stirred for 3 h at
the low temperature. Tri-n-butylborate (27 mL, 0.10 mol) was slowly added
to the reaction mixture at À788C, and the mixture was stirred for 2 h at the
temperature. Asmall amount of water was added to the mixture. To the
Calculation of absorption spectra: MOS-F (Fujitsu) with CNDO/S method
was used for these calculations. Twenty molecular orbitals were taken into
account for calculation (default value). Coordinates of the closed-ring
isomers in a- and d-crystals, which obtained by the above simulations, were
used for the model structure.
626
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Chem. Eur. J. 2003, 9, No. 3

Photochromic Reactivity of the Single Crystals
621±627
[
21] T. Yamada, S. Kobatake, K. Muto, M. Irie, J. Am. Chem. Soc. 2000,
Acknowledgement
1
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[
This work was supported by CREST (Core Research for Evolutional
Science and Technology) of Japan Science and Technology Corporation
JST). We thank Nippon Zeon Co., Ltd. for their supply of octafluorocy-
4
[
[
23] T. Yamada, S. Kobatake, M. Irie, Bull. Chem. Soc. Jpn. 2000, 73, 217ꢀ.
24] S. Kobatake, K. Shibata, K. Uchida, M. Irie, J. Am. Chem. Soc. 2000,
(
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reaction.
[35] In fact, the exact structure of the photogenerated closed-ring isomer in
the open-ring isomer crystal is not known. However, it is safe to say
that the structure of the closed-ring isomer is in between the two
limiting structures. One is a structure obtained under the assumption
that phenyl rings do not rotate during the photocyclization reaction
(demonstrated in the text), and the other is a structure obtained under
the assumption that the phenyl rings rotate together with the
thiophene rings keeping the rotation angles in the open-ring isomer.
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rings of the simulated closed-ring isomers were calculated to be 23.ꢀ8
for a-crystal, and 6.0 and À16.68 for d-crystal. Then, the lowest energy
absorption peaks located at 473.73 and 473.32 nm for a- and d-
crystals, respectively.
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Received: June 6, 2002 [F4160]
Chem. Eur. J. 2003, 9, No. 3
¹ 2003 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim
0ꢀ47-653ꢀ/03/0ꢀ03-0627 $ 20.00+.50/0
627