Single-crystalline photochromism of a diarylethene dimer

Article abstract of DOI:10.1246/bcsj.77.945

A fluorene derivative having two diarylethene units at the 9,9′-positions was synthesized, and the photochromic behavior was examined in a single-crystalline phase as well as in solution. Upon irradiation with ultraviolet light (Λ = 313 nm), a hexane solu

Full text of DOI:10.1246/bcsj.77.945

Ó 2004 The Chemical Society of Japan
Bull. Chem. Soc. Jpn., 77, 945–951 (2004)
945
Single-Crystalline Photochromism of a Diarylethene Dimer
ꢀ
ꢀ
Seiya Kobatake, Shunpei Kuma, and Masahiro Irie
Department of Chemistry and Biochemistry, Graduate School of Engineering, Kyushu University,
Hakozaki 6-10-1, Higashi-ku, Fukuoka 812-8581
Received October 28, 2003; E-mail: irie@cstf.kyushu-u.ac.jp
A fluorene derivative having two diarylethene units at the 9,90-positions was synthesized, and the photochromic be-
havior was examined in a single-crystalline phase as well as in solution. Upon irradiation with ultraviolet light (ꢀ ¼ 313
nm), a hexane solution of the diarylethene dimer (1a) turned blue. The blue solution was found to contain the one closed-
ring form dimer (1b) and the two closed-ring form dimer (1c). Both 1b and 1c returned to 1a upon irradiation with visible
light (ꢀ > 500 nm). The photocyclization quantum yields of 1a to 1b and 1b to 1c were determined to be 0.46 and 0.29,
respectively. The photocycloreversion quantum yields of 1c to 1b and 1b to 1a were 5:8 ꢁ 10ꢂ3. The single crystal of the
dimer exhibited photochromism. The diarylethene chromophores were aligned almost perpendicular to each other in the
crystal, and one of the units in the dimer could be selectively isomerized by irradiation with linearly polarized light.
Photochromism is a reversible photoisomerization process of
a chemical species between two isomers that have different ab-
sorption spectra.1,2 Diarylethenes with heterocyclic aryl rings
belong to a class of thermally irreversible photochromic com-
pounds and are the most promising candidates for optoelectron-
ic devices, such as optical memory,3–5 photooptical switch-
ing,6–8 and displays,9–11 because of their fatigue-resistant prop-
erty.12,13 Recently, various types of diarylethene dimers con-
nected with a single bond,14 phenylene,15,16 ethynylene,17 or
diyne18 were synthesized. In most cases, only one of the diaryl-
ethene units can convert to the closed-ring form upon irradia-
tion with ultraviolet light. When the photogenerated dimers
having one open- and one closed-ring form units are irradiated
with ultraviolet light, the intramolecular excited energy transfer
from the open-ring form unit to the closed-ring form one pro-
hibits the formation of the two closed-ring form dimers. The di-
mers connected with a phenylene group can convert to the two
closed-ring form dimers.15,16
ethene molecules are packed in a herringbone structure, as ob-
served in a crystal of 1,2-bis(5-p-methoxyphenyl-2-methyl-3-
thienyl)perfluorocyclopentene, the polarized light can induce
a reaction of the molecules along the polarized direction, be-
cause the closed-ring isomers have an electronic transition mo-
ment in the direction of the long axis of the molecules. Crystal
engineering to control the alignment of molecules is useful not
only to endow various functions, but also to control the reaction
of the crystals.
We designed a diarylethene dimer (1a) as shown in
Scheme 1. Two diarylethene chromophores are connected to
fluorene, and there is no conjugation between the two diaryl-
ethene units in the dimer. In the present work, we examined
the photochromic reactivity of 1a in solution and in the sin-
gle-crystalline phase upon irradiation with linearly polarized
light.
Results and Discussion
Recently, we have developed thermally irreversible and fati-
gue-resistant photochromic diarylethene crystals.4,10,11,19–30
The photoinduced coloration–decoloration cycles of the crys-
tals can be repeated more than 104 times while maintaining
the shape of the single crystals, and the photogenerated colored
states are stable even at 100 ꢃC. One of the characteristic prop-
erties of the single crystals is that the reaction of each molecule
can be controlled with linearly polarized light. When diaryl-
Photochromism in Hexane. Figure 1 shows the absorption
spectral change of dimer 1a in hexane. The open-ring form di-
mer 1a has an absorption maximum at 309 nm. Upon irradia-
tion with 313-nm light, the colorless hexane solution of 1a
turned blue, in which an absorption maximum was observed
at 595 nm. The blue color is due to the formation of the
closed-ring forms (1b and 1c). The blue-colored solution was
analyzed by high-performance liquid chromatography (HPLC)
Scheme 1. A diarylethene dimer linked by fluorene.
Published on the web May 6, 2004; DOI 10.1246/bcsj.77.945

946 Bull. Chem. Soc. Jpn., 77, No. 5 (2004)
Photochromic Diarylethene Dimer
Fig. 1. Absorption spectral change of dimer 1a (6:6 ꢁ 10ꢂ6
Fig. 3. Absorption spectra of 1a (– –), 1b (- - -), and 1c (—)
ꢄ
in hexane (4:9 ꢁ 10ꢂ6 M).
M) in hexane upon irradiation with 313-nm light.
Table 1. Absorption Maxima and Coefficients of 1a, 1b, and
1c in Hexane
ꢀ
max/nm ("/Mꢂ1 cmꢂ1
)
309 (98500)
1a
1b
1c
309 (74800), 595 (20600)
274 (52300), 320 (54600), 595 (40600)
dicates that the isomer has no open-ring form unit, and is as-
signed to 1c. In isomer 1c, both diarylethene units are converted
to the closed-ring form.
Figure 3 shows the absorption spectra of 1a, 1b, and 1c in
hexane. The absorption maxima and coefficients of 1a, 1b,
and 1c are given in Table 1. The absorption maximum of 1b
(595 nm) is the same as that of 1c. In addition, the absorption
coefficient of 1c (40600 Mꢂ1 cmꢂ1) is twice as large as that
of 1b (20600 Mꢂ1 cmꢂ1). This indicates that two diarylethene
units are independent, and that there is no intramolecular inter-
action between them. In the photostationary state upon irradia-
tion with 313-nm light, the ratio of 1a, 1b, and 1c was
0.1:3.5:96.4. The dimer having two closed-ring form units
was efficiently formed.
Quantum Yield. The photocyclization and cycloreversion
quantum yields of the dimer were measured in hexane at room
temperature. At first, the photocycloreversion reactions of 1c to
1b and 1b to 1a were examined. A hexane solution of 1c
(7:5 ꢁ 10ꢂ6 M) was irradiated with 595-nm light. The rates
of the photoreactions were followed by measuring the ratio
change of 1a, 1b, and 1c by HPLC. Figure 4 shows the time de-
pendence of the formation of 1b and 1a. Dimer 1b was first pro-
duced upon irradiation with visible light. Then, 1a was pro-
duced through 1b. The experimental data were analyzed using
the following equations:
Fig. 2. 1H NMR spectra of 1a (a), 1b (b), and 1c (c) in the
range of 1.8–2.3 ppm and 6.5–6.9 ppm.
with silica-gel column using hexane and ethyl acetate (9:1) as
the eluent. The absorption intensity change was monitored at
330 nm, which is the isosbestic point. The open-ring form di-
mer 1a was eluted at 60 min. Two colored isomers were eluted
at 41 and 50 min. Each peak was isolated and analyzed by
1H NMR spectroscopy.
1
Figure 2 shows the H NMR spectra in the range of methyl
dC1c=dt ¼ ꢂI1cꢀ1c!1b
dC1b=dt ¼ I1cꢀ1c!1b ꢂ I1bꢀ1b!1a
ð1Þ
ð2Þ
ð3Þ
protons and olefinic protons. The open-ring form dimer 1a
has two peaks at 1.94 and 1.96 ppm, which are due to the meth-
yl protons at the reactive carbons. The 1H NMR spectrum of an
isomer eluted at 50 min is shown in Fig. 2b. In addition to the
peaks at 1.94 and 1.96 ppm, new peaks appeared at 2.15, 6.63,
and 6.74. The peak intensity ratio at 1.94, 1.96, 2.15, 6.63, and
6.74 ppm was 3:3:6:1:1. This indicates that the isomer has one
open- and one closed-ring form units, and is assigned to 1b. An
isomer eluted at 41 min has no peak around 1.95 ppm. This in-
dC1a=dt ¼ I1bꢀ1b!1a
where I1c ¼ I0ð1 ꢂ 10ꢂA Þ and I1b ¼ I0ð1 ꢂ 10ꢂA Þ. In the
above equations, I0 is the intensity of light, and ꢀ1c!1b and
ꢀ1b!1a are the photoreaction quantum yields of 1c to 1b and
1b to 1a, respectively. A1c and A1b are the absorbances of 1c
and 1b, respectively, at the irradiation wavelength (595 nm).
1c
1b

S. Kobatake et al.
Bull. Chem. Soc. Jpn., 77, No. 5 (2004)
947
Fig. 4. Changes in the content of the isomers, 1a ( ), 1b
( ), and 1c ( ) in the photocycloreversion reaction of
1c upon irradiation with 595-nm light in hexane.
Fig. 5. Changes in the content of the isomers, 1a ( ), 1b
), and 1c ( ) in the photocyclization reaction of 1a upon
irradiation with 313-nm light in hexane.
(
C1c, C1b, and C1a are the concentrations of 1c, 1b, and 1a,
respectively.
the closed-ring form unit in 1b have a chance to isomerize 1b
to 1a. The result is shown as solid lines in Fig. 5. The light in-
tensity (I0) was calibrated by the photoreaction of furylfulgide
in hexane. The parameters used were as follows: I0 ¼
A numerical simulation according to differential equations
was carried out; the result is shown as solid lines in Fig. 4.
The light intensity (I0) was calibrated by the photoreaction
of furylfulgide in hexane. The parameters used were as
follows: I0 ¼ 5:91 ꢁ 10ꢂ8 einstein cmꢂ2 sꢂ1, "1b(595) ¼ 20600
5:64 ꢁ 10ꢂ10 einstein cmꢂ2 sꢂ1, "1a(313) ¼ 92600 Mꢂ1 cmꢂ1
,
"
¼ 71500 Mꢂ1 cmꢂ1, "1c(313) ¼ 54200 Mꢂ1 cmꢂ1
.
The photocyclization quantum yields of 1a to 1b and 1b to
1b(313)
M
ꢂ1 cmꢂ1, "1c(595) ¼ 40600 Mꢂ1 cmꢂ1
.
1c were determined to be 0.46 and 0.29, respectively. The dif-
ference of these quantum yields is attributed to an intramolec-
ular filter effect. The ratio of the absorption coefficients of the
open- and closed-ring form units in 1b at 313 nm is considered
to be the same as the ratio of those of 1a and 1c. The ratio is
1:0.54. 65% of the photons absorbed in 1b can be used for
the photocyclization reaction to 1c. Therefore, the actual photo-
cyclization quantum yield of 1b to 1c for the only open-ring
form unit in 1b is determined to be 0.45 (¼ 0:29=0:65). This
value is comparable with the photocyclization quantum yield
of 1a to 1b (0.46). It can be concluded that the reactivity of
the two diarylethene units is the same, even if one of the units
is in the closed-ring form and that the excited energy in the
open-ring form unit in 1b is not transferred to the closed-ring
form unit by an intramolecular excited energy transfer.
The quantum yields of 1c to 1b and 1b to 1a were almost the
same, which are both 5:8 ꢁ 10ꢂ3. This indicates that there is no
intramolecular interaction of the two diarylethene units.
A photocyclization quantum yield measurement was carried
out as follows. Dimer 1a was dissolved in hexane and the solu-
tion was irradiated with ultraviolet light (ꢀ ¼ 313 nm). Upon
irradiation with 313-nm light, 1b was produced at first follow-
ing a decrease of 1a. During the early stage of the photoreac-
tion, the formation of 1c was negligible. 1c was gradually pro-
duced. The experimental data were analyzed by the following
equations:
dC1a=dt ¼ ꢂI1aꢀ1a!1b þ I1bꢀ1b!1a
dC1b=dt ¼ I1aꢀ1a!1b ꢂ I1bꢀ1b!1a
ꢂ I1bꢀ1b!1c þ I1cꢀ1c!1b
ð4Þ
Photochromism in Crystal. A single crystal with good
crystallinity was obtained by recrystallization from a ace-
tone/cyclohexane solution. The crystal was analyzed by X-
ray crystallography. The crystallographic data are given in
Table 2. The crystal has a triclinic system and a space group
ð5Þ
ð6Þ
¼
dC1c=dt ¼ I1bꢀ1b!1c ꢂ I1cꢀ1c!1b
where I1a ¼ I0ð1 ꢂ 10ꢂA Þ, I1b ¼ I0ð1 ꢂ 10ꢂA Þ, and I1c
1a
1b
I0ð1 ꢂ 10ꢂA Þ. In the above equations, I0 is the intensity of light
and ꢀ1a!1b, ꢀ1b!1c, ꢀ1c!1b, and ꢀ1b!1a are the reaction
quantum yields of 1a to 1b, 1b to 1c, 1c to 1b, and 1b to 1a,
respectively. A1a, A1b, and A1c are the absorbances at the irradi-
ation wavelength (313 nm). C1a, C1b, and C1c are the concentra-
tions of 1a, 1b, and 1c, respectively.
1c
ꢁ
of P1. Twelve cyclohexane molecules and four dimer mole-
cules were included in a unit cell. Figure 6 shows an ORTEP
drawing of the diarylethene dimer. The fluorene moieties are
stacked by the ꢁ–ꢁ intermolecular interaction. Two diaryl-
ethenes in the dimer are aligned almost perpendicular to each
other. The photochromic reactivity of diarylethene crystals de-
pends on the distance between the reactive carbon atoms.28 The
The differential equations in Eq. (4)–(6) were numerically
solved under the conditions that the photocycloreversion quan-
tum yield of 1c to 1b is 5:8 ꢁ 10ꢂ3, and the quantum yield of
ꢂ
dimer has distances of 3.41–3.52 A. This indicates that the
1b to 1a at 313 nm is 2:1 ꢁ 10ꢂ3 (¼ 5:8 ꢁ 10ꢂ3 ꢁ ð"1c(313)
=
dimer can undergo photochromism in the crystalline phase.
Upon irradiation with 366-nm light, the crystal turned blue,
as shown in Fig. 7a. The photogenerated blue color of the crys-
tals disappeared upon irradiation with visible light (ꢀ > 500
nm). The polarized absorption spectra of the crystal were meas-
ured under linearly polarized light. The crystal was irradiated
on the (ꢂ1 1 0) face with non-polarized 366-nm light. The
ð"1c(313) þ "1a(313ÞÞÞ). In the simulation, it was assumed that
the photocycloreversion quantum yield does not depend on the
irradiation wavelength. The intramolecular energy transfer of
the open- to the closed-ring forms in 1b was considered to be less
favorable because of non-ꢁ-conjugation and non-coplanarity
between the two diarylethene units. The photons absorbed in

948 Bull. Chem. Soc. Jpn., 77, No. 5 (2004)
Table 2. X-ray Crystallographic Data of 1a
Photochromic Diarylethene Dimer
Empirical formula
Formula weight
Temperature
Crystal system
C69H40F12N2S4 3C6H12
ꢄ
1505.78
123(2) K
Triclinic
ꢁ
P1
Space group
Unit cell dimensions
ꢂ
18.028(7) A
a
ꢂ
b
19.901(7) A
ꢂ
c
22.371(8) A
ꢂ
ꢃ
ꢄ
75.943(7)ꢃ
78.877(7)ꢃ
88.197(7)ꢃ
7639(5) A
4
ꢂ 3
V
Z
Density (calculated)
Goodness-of-fit on F2
Final R indices [I > 2ꢅðIÞ]
R indices (all data)
1.309 g cmꢂ3
0.850
R1 ¼ 0:0533
wR2 ¼ 0:1251
(ꢂ1 1 0) surface was prepared by cutting the crystal, as shown
in Fig. 7b. Figure 8 shows the polarized absorption spectra at
angles of 0, 45, and 90ꢃ. The absorption maximum was ob-
served at 615 nm. The absorbance at 615 nm was almost the
same as that at 0 and 45ꢃ. Polar plots of the absorbance at
615 nm are also shown in Fig. 8b. Well-defined absorption
anisotropy was not observed. The two diarylethene molecules
in the dimer are packed in two different directions, which are
almost perpendicular to each other. This is the reason why
absorption anisotropy was not observed.
Fig. 6. ORTEP drawing of 1a showing the 50% probability
displacement ellipsoids.
Partially Bleaching Reaction in Crystal. Figure 9 shows
the molecular packing of the diarylethenes viewed normal to
Fig. 7. Photographs of crystal 1a before and after photoirradiation with 366-nm light (a) and the crystal shape of 1a (b).

S. Kobatake et al.
Bull. Chem. Soc. Jpn., 77, No. 5 (2004)
949
Fig. 9. Molecular packing of 1a viewed from the (ꢂ1 1 0)
face. Red and blue arrows show long axes of the diaryl-
ethene chromophores.
Fig. 8. Polarized absorption spectra (a) and the polar plots
of the absorbance at 615 nm (b) after irradiation with non-
polarized 366-nm light.
the (ꢂ1 1 0) face. The long axes of the diarylethene chromo-
phores in the dimer are aligned at an angle of 75ꢃ to each other,
as shown by the blue and red arrows, when the crystal is
viewed from the (ꢂ1 1 0) face. This suggests that linearly po-
larized light can selectively isomerize the closed-ring isomers
to the open-ring isomers. A colorless dimer crystal was irradi-
ated with non-polarized 366-nm light to give a blue-colored
crystal. When the crystal was irradiated with linearly polarized
light (ꢀ > 570 nm) in the direction of 45ꢃ, the colored isomers
along the polarized light were preferentially bleached, and the
molecules oriented perpendicularly to the irradiated polarized
light remained. In other words, the diarylethene molecules
shown by the red arrows in Fig. 9 were preferentially bleached
under polarized light in the direction of 45ꢃ. The polarized ab-
sorption spectra and the polar plots are shown in Fig. 10. The
order parameter ((A ꢂ A )/(A þ 2A )) was determined to
k
?
k
?
be 0.51 after partial bleaching, though the value was less than
0.1 before bleaching. The increase in the order parameter up
to 0.51 suggests that the partially bleaching reaction took place
under the polarized light.
Conclusions
A fluorene derivative having two diarylethene units at the
9,90-positions underwent photochromism in solution as well
as in the single-crystalline phase. The two diarylethene units
in the dimer are almost perpendicular to each other. Photoirra-
Fig. 10. Polarized absorption spectra (a) and the polar plots
of the absorbance at 615 nm (b) after partially photobleach-
ing upon irradiation with polarized 570-nm light.

950 Bull. Chem. Soc. Jpn., 77, No. 5 (2004)
Photochromic Diarylethene Dimer
124.8–125.4 ꢃC; 1H NMR (200 MHz, CDCl3, 25 ꢃC, TMS) ꢆ 2.45
(s, 3H, CH3), 7.23 (s, 1H, thienyl proton), 7.5–7.7 (m, 4H, Ar). MS
m/z 277, 279 (Mþ). Anal. Calcd for C12H8BrNS: C, 51.81; H,
2.90%. found: C, 51.87; H, 2.86%.
diation with linearly polarized light induced partial bleaching
of one of the two closed-ring forms. Such a crystal can be ap-
plied to optoelectronic devices, such as photoswitchable polar-
izers and multi-recording materials.
1-(5-p-Cyanophenyl-2-methyl-3-thienyl)heptafluorocyclo-
pentene (3). To a dry THF solution (600 mL) containing 2 (10 g,
0.036 mol) was added a 15% n-BuLi hexane solution (24 mL,
0.038 mol) at ꢂ78 ꢃC under an argon atmosphere, and the reaction
mixture was stirred for 1 h at that low temperature. Octafluorocy-
clopentene (13 mL, 0.040 mol; Nippon Zeon) was added to the re-
action mixture at ꢂ78 ꢃC, and the mixture was stirred for 2.5 h at
this temperature. The reaction was stopped by the addition of wa-
ter. The product was extracted with diethyl ether. The organic layer
was dried over MgSO4, filtrated, and concentrated. The residue
was purified by column chromatography on silica gel using hex-
ane/ethyl acetate (95:5) as the eluent and by recrystallization from
hexane to give 1a (3.3 g, 24%) as coꢃlorless crystals. mp = 92–93
Experimental
General. The solvents used were of spectroscopic grade and
purified by distillation before use. 1H NMR spectra were recorded
on a Varian Gemini 200 spectrometer (200 MHz). Tetramethyl-
silane was used as an internal standard. Mass spectra were taken
with a Shimadzu GCMS-QP5050A gas chromatography–mass
spectrometer. Absorption spectra in solution were measured with
a Hitachi U-3410 absorption spectrophotometer. Photoirradiation
was carried out using an Ushio 500 W super high-pressure mercury
lamp or an Ushio 500 W xenon lamp as the light source. Mono-
chromic light was obtained by passing the light through a mono-
chrometer (Ritsu MV-10N). Absorption spectra in a single-crystal-
line phase were measured using a Leica DMLP polarizing micro-
scope connected with a Hamamatsu PMA-11 photodetector. The
polarizer and analyzer were set in parallel to each other. Photoirra-
diation was carried out using a 75 W xenon lamp. The wavelength
of the light was selected by passing the light through a band-pass
filter. Diarylethene dimer 1a was synthesized according to
Scheme 2.
3-Bromo-5-p-cyanophenyl-2-methylthiophene (2). To a dry
THF solution (300 mL) containing 3,5-dibromo-2-methylthio-
phene (30 g, 0.12 mol) was added a 15% n-BuLi hexane solution
(77 mL, 0.12 mol) at ꢂ78 ꢃC under an argon atmosphere, and
the reaction mixture was stirred for 2 h at that low temperature.
Tributyl borate (47 mL, 0.18 mol) was slowly added to the reaction
mixture at ꢂ78 ꢃC, and the mixture was stirred for 2 h at this tem-
perature. A small amount of water was added to the mixture. To the
reaction mixture were added 20 wt % Na2CO3aq (280 mL), 4-bro-
mobenzonitrile (21 g, 0.12 mol), and [Pd(PPh3)4] (2.0 g, 1.3
1
ꢃC; H NMR (200 MHz, CDCl3, 25 C, TMS) ꢆ 2.51 (d, J ¼ 3:0
Hz, 3H, CH3), 7.36 (s, 1H, thienyl proton), 7.6–7.8 (m, 4H, Ar).
MS m/z 391 (Mþ). Anal. Calcd for C17H8F7BrNS: C, 52.18; H,
2.06; N, 3.58%. Found: C, 52.37; H, 2.05; N, 3.62%.
9,90-Bis[4-(4-bromo-5-methyl-2-thienyl)phenyl]fluorene (4).
4-Bromo-5-methylthienylboronic acid (4.9 g, 0.022 mol) was add-
ed into a flask containing THF (120 mL), 20 wt % Na2CO3aq (50
mL), 9,90-bis(4-bromophenyl)fluorene (3.5 g, 0.0074 mol), and
[Pd(PPh3)4] (1.3 g, 1.1 mmol). The mixture was refluxed for 12
ꢃ
h at 80 C, neutralized with HCl, and then extracted with diethyl
ether. The organic layer was dried over MgSO4, filtrated, and con-
centrated. The residue was purified by silica-gel column chroma-
tography using hexane/ethyl acetate (10:1) as the eluent and by
HPLC on polystyrene-gel using chloroform as the eluent to give
1
ꢃ
4 (2.3 g, 48%). H NMR (200 MHz, CDCl3, 25 C, TMS) ꢆ 2.39
(s, 6H, CH3), 7.03 (s, 2H, thienyl proton), 7.1–7.5 (m, 14H, Ar),
7.78 (d, J ¼ 7:2 Hz, 2H, Ar). MS m/z 666, 668, 670 (1:2:1)
(Mþ). Anal. Calcd for C35H24Br2S2: C, 62.88; H, 3.62%. Found:
C, 62.95; H, 3.62%.
ꢃ
mmol). The mixture was refluxed for 12 h at 80 C. The mixture
was neutralized with HCl, and then extracted with diethyl ether.
The organic layer was dried over MgSO4, filtrated, and concentrat-
ed. The residue was purified by silica-gel column chromatography
using hexane/chloroform (1:1) as the eluent, and recrystallize from
hexane/chloroform (10:1) to give 2 (13 g, 39%) as crystals. mp =
Diarylethene Dimer (1a). To a dry THF solution (10 mL) con-
taining 4 (0.50 g, 0.75 mmol) was added a 15% n-BuLi hexane so-
lution (1.0 mL, 1.6 mmol) at ꢂ78 ꢃC under an argon atmosphere,
and the reaction mixture was stirred for 30 min at the low temper-
ature. Compound 3 (0.73 g, 1.9 mmol) in dry THF (3 mL) was add-
Scheme 2. Synthetic route of diarylethene dimer 1a.

S. Kobatake et al.
Bull. Chem. Soc. Jpn., 77, No. 5 (2004)
951
ed to the reaction mixture at ꢂ78 ꢃC, and the resulting mixture was
stirred for 1.5 h at this temperature. The reaction was stopped by
the addition of water. The product was extracted with chloroform.
The organic layer was dried over MgSO4, filtrated, and concentrat-
ed. The residue was purified by column chromatography on silica
gel using hexane/ethyl acetate (95:5) as the eluent to give 1a (0.76
g, 81%). 1H NMR (200 MHz, CDCl3, 25 ꢃC, TMS) ꢆ 1.94 (s, 6H,
CH3), 1.96 (s, 6H, CH3), 7.2–7.5 (m, 18H, Ar), 7.6–7.7 (m, 8H,
Ar), 7.80 (dd, J ¼ 1:2, 8.0 Hz, 2H, Ar). MS m/z 1252 (Mþ). Anal.
Calcd for C69H40F12N2S4: C, 66.12; H, 3.22; N, 2.24%. Found: C,
66.10; H, 3.24; N, 2.18%.
4
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10 M. Morimoto, S. Kobatake, and M. Irie, Adv. Mater., 14,
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11 M. Morimoto, S. Kobatake, and M. Irie, J. Am. Chem. Soc.,
125, 11080 (2003).
12 M. Irie and K. Uchida, Bull. Chem. Soc. Jpn., 71, 985
(1998).
13 M. Irie, Chem. Rev., 100, 1685 (2000).
14 A. Peters and N. R. Branda, Adv. Mater. Opt. Electron., 10,
245 (2000).
15 K. Matsuda and M. Irie, J. Am. Chem. Soc., 123, 9896
(2001).
16 S. Kobatake and M. Irie, Tetrahedron, 59, 8359 (2003).
17 T. Kaieda, S. Kobatake, H. Miyasaka, M. Murakami, N.
Iwai, Y. Nagata, A. Itaya, and M. Irie, J. Am. Chem. Soc., 124,
2015 (2002).
18 K. Yagi and M. Irie, Chem. Lett., 32, 848 (2003).
19 M. Irie, K. Uchida, T. Eriguchi, and H. Tsuzuki, Chem.
Lett., 1995, 899.
20 K. Uchida and M. Irie, Chem. Lett., 1995, 969.
21 a) S. Kobatake, T. Yamada, K. Uchida, N. Kato, and M.
Irie, J. Am. Chem. Soc., 121, 2380 (1999). b) T. Yamada, S.
Kobatake, K. Muto, and M. Irie, J. Am. Chem. Soc., 122, 1589
(2000). c) T. Yamada, S. Kobatake, and M. Irie, Bull. Chem.
Soc. Jpn., 73, 2179 (2000).
Closed-Ring Isomers of 1a (1b and 1c). 1b and 1c were iso-
lated by passing a photoirradiated solution containing 1a, 1b, and
1c through a HPLC (Hitachi L-7100 pump system equipped with a
Hitachi L-7400 detector, a silica-gel column (Kanto, MightySil Si
60), and hexane/ethyl acetate (9:1) as the eluent). The retention
times for 1a, 1b, and 1c were 60, 50, and 41 min, respectively.
1b: 1H NMR (200 MHz, CDCl3, 25 ꢃC, TMS) ꢆ 1.94 (s, 3H,
CH3), 1.97 (s, 3H, CH3), 2.15 (s, 6H, CH3), 6.63 (s, 1H, olefinic
proton), 6.74 (s, 1H, olefinic proton), 7.2–7.5 (m, 16H, Ar), 7.6–
1
7.7 (m, 8H, Ar), 7.81 (d, J ¼ 7:4 Hz, 2H, Ar). 1c: H NMR (200
MHz, CDCl3, 25 ꢃC, TMS) ꢆ 2.16 (s, 12H, CH3), 6.64 (s, 2H, ole-
finic proton), 6.74 (s, 2H, olefinic proton), 7.2–7.5 (m, 14H, Ar),
7.6–7.7 (m, 8H, Ar), 7.81 (d, J ¼ 7:4 Hz, 2H, Ar).
General Procedure of X-ray Crystallographic Analysis. An
X-ray crystallographic analysis was performed using a Bruker
SMART1000 CCD-based diffractometer (50 kV, 40 mA) with
Mo Kꢂ radiation. The crystals were cooled at 123 K by a cryostat
(Rigaku GN2). The data were collected as a series of !-scan
frames, each with a width of 0.3ꢃ/frame. The crystal-to-detector
distance was 5.124 cm. Crystal decay was monitored by repeating
the 50 initial frames at the end of data collection and analyzing the
duplicate reflections. Data reduction was performed using SAINT
software, which corrects for Lorentz and polarization effects, as
well as decay. The cell constants were determined by a global re-
finement. The structures were solved by direct methods using
SHELXS-86,31 and refined by full least-squares on F2 using
SHELXL-97.32 The positions of all hydrogen atoms were calculat-
ed geometrically and refined by the riding model. Crystallographic
data have been deposited at the CCDC, 12 Union Road, Cambridge
CB2 1EZ, UK and copies can be obtained on request, free of
charge, by quoting the publication citation and the deposition num-
ber CCDC-230686.
22 S. Kobatake, M. Yamada, T. Yamada, and M. Irie, J. Am.
Chem. Soc., 121, 8450 (1999).
23 a) M. Irie, T. Lifka, S. Kobatake, and N. Kato, J. Am. Chem.
Soc., 122, 4871 (2000). b) T. Yamada, K. Muto, S. Kobatake, and
M. Irie, J. Org. Chem., 66, 6164 (2000).
24 T. Kodani, K. Matsuda, T. Yamada, S. Kobatake, and M.
Irie, J. Am. Chem. Soc., 122, 9631 (2000).
25 S. Yamamoto, K. Matsuda, and M. Irie, Angew. Chem., Int.
Ed., 42, 1936 (2003).
26 K. Matsuda, K. Takayama, and M. Irie, Chem. Commun.,
2001, 363.
27 M. Irie, S. Kobatake, and M. Horichi, Science, 291, 1769
(2001).
28 a) K. Shibata, K. Muto, S. Kobatake, and M. Irie, J. Phys.
Chem. A, 106, 209 (2002). b) S. Kobatake, K. Uchida, E. Tsuchida,
and M. Irie, Chem. Commun., 2002, 2804.
29 T. Yamada, S. Kobatake, and M. Irie, Bull Chem. Soc. Jpn.,
75, 167 (2002).
This work was partly supported by the Grants-in-Aid for
Scientific Research (S) (No. 15105006), Scientific Research
on Priority Areas (Nos. 15033252 and 12131211), and the
21st century COE program from the Ministry of Education,
Culture, Sports, Science and Technology. We thank Nippon
Zeon Co., Ltd. for their supply of octafluorocyclopentene.
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¨ ¨ ¨