Single-crystalline photochromism of diarylethene dimers bridged by a spiro structure

Article abstract of DOI:10.1002/poc.1196

New types of diarylethene dimers bridged by a spiro structure were synthesized. One of their dimers formed three kinds of polymorphic forms by recrystallization from different solvents: hexane (1a-α), acetone (1a-β), and acetonitrile (la-γ). In crystals of 1a-α and 1a-β the molecules are packed in solvent-free crystal structures, whereas crystal 1a-γ includes acetonitrile molecules in the crystal. The difference of significant photochromic reactivities in their polymorphic crystals was observed for photocoloration reactions. Crystals 1a-β and 1a-γ showed photochromism in the single-crystal phase, but 1a-α did not do so. Their photochromic reactivity was found to depend on the distance between the reactive carbon atoms by X-ray crystallographic analysis. When the distance is less than 4.2 A in the antiparallel conformation, the molecule can undergo photochromism in the crystal. On the other hand, crystals of bromo-substituted diarylethene dimer (2a) cannot be suitable for X-ray crystallographic analysis when it was recrystallized from hexane, acetone, and acetonitrile. However, it formed single crystal by recrystallization from p-xylene, which showed photochromism in the crystalline phase. The edge-to-face aromatic interaction between p-xylene molecules assisted the crystal growth of the diarylethene dimer. Upon irradiation with ultraviolet light, two kinds of the enantiomers, (M,SS)- and (P,RR)-2b, are produced. Partial photobleaching reactions of either of the two enantiomers by irradiation with linearly polarized visible light were confirmed by polarized absorption spectroscopy. Copyright

Full text of DOI:10.1002/poc.1196

JOURNAL OF PHYSICAL ORGANIC CHEMISTRY
J. Phys. Org. Chem. 2007; 20: 960–967
Published online 9 May 2007 in Wiley InterScience
(www.interscience.wiley.com) DOI: 10.1002/poc.1196
Single-crystalline photochromism of diarylethene
dimers bridged by a spiro structure
1
2
*
2**
Seiya Kobatake, Shunpei Kuma and Masahiro Irie
1Department of Applied Chemistry, Graduate School of Engineering, Osaka City University and PRESTO, JST, Sugimoto 3-3-138,
Sumiyoshi-ku, Osaka 558-8585, Japan
2Department of Chemistry and Biochemistry, Graduate School of Engineering, Kyushu University, Hakozaki 6-10-1, Higashi-ku, Fukuoka
812-8581, Japan
Received 28 December 2006; revised 1 March 2007; accepted 16 March 2007
ABSTRACT: New types of diarylethene dimers bridged by a spiro structure were synthesized. One of their dimers
formed three kinds of polymorphic forms by recrystallization from different solvents: hexane (1a-a), acetone (1a-b),
and acetonitrile (1a-g). In crystals of 1a-a and 1a-b the molecules are packed in solvent-free crystal structures,
whereas crystal 1a-g includes acetonitrile molecules in the crystal. The difference of significant photochromic
reactivities in their polymorphic crystals was observed for photocoloration reactions. Crystals 1a-b and 1a-g showed
photochromism in the single-crystal phase, but 1a-a did not do so. Their photochromic reactivity was found to depend
on the distance between the reactive carbon atoms by X-ray crystallographic analysis. When the distance is less than
˚
4.2 A in the antiparallel conformation, the molecule can undergo photochromism in the crystal. On the other hand,
crystals of bromo-substituted diarylethene dimer (2a) cannot be suitable for X-ray crystallographic analysis when it
was recrystallized from hexane, acetone, and acetonitrile. However, it formed single crystal by recrystallization from
p-xylene, which showed photochromism in the crystalline phase. The edge-to-face aromatic interaction between
p-xylene molecules assisted the crystal growth of the diarylethene dimer. Upon irradiation with ultraviolet light, two
kinds of the enantiomers, (M,SS)- and (P,RR)-2b, are produced. Partial photobleaching reactions of either of the two
enantiomers by irradiation with linearly polarized visible light were confirmed by polarized absorption spectroscopy.
Copyright # 2007 John Wiley & Sons, Ltd.
KEYWORDS: photochromism; crystal; diarylethene; dimer; enantiomer
INTRODUCTION
stable and fatigue-resistant photochromic reactions even
in the single-crystalline phase.17–33 The photochromic
diarylethene crystals have the following characteristic
properties and functions: (1) The photogenerated colored
crystals exhibit dichroism under polarized light;18,19 (2)
The conformations in the crystals strongly affect photo-
cyclization and photocycloreversion quantum yields;24–26
(3) Single-crystalline photochromism induces reversible
nano-scale surface morphological changes;22 and (4)
Photochromic diarylethene crystals have potential
applications to high-density three-dimensional optical
memory media,23,34 optical switches,35 and color dis-
plays.27,28,32
Diarylethenes have two stable conformations with the
two thiophene rings in mirror symmetry (parallel
conformation) and in C2 symmetry (antiparallel confor-
mation).17 They are in equilibrium each other in solution.
The photocyclization reaction can proceed only from the
antiparallel conformation. In crystals, their confor-
mations are fixed. In most cases, they are oriented in
the antiparallel or parallel conformation. Diarylethenes
fixed in the parallel conformation in crystal cannot exhibit
Photochromism is referred to as a photochemical
reversible transformation of a chemical species between
two isomers having different absorption spectra.1,2
Although many types of photochromic compounds have
been reported so far, crystals that show photochromic
reactions in the crystal are very rare.3 Typical examples of
photochromic crystals are paracyclophanes,4 triary-
limidazole dimer,5,6 diphenylmaleronitrile,7 aziridines,8
2-(2,4-dinitrobenzyl)pyridine,9–12N-salicylideneani-
lines,13–15 and triazenes.16 In the most cases of photo-
chromic crystals, the photogenerated isomers are ther-
mally unstable and return to the initial isomers even in the
dark. Some of diarylethene derivatives undergo thermally
*Correspondence to: S. Kobatake, Department of Applied Chemistry,
Graduate School of Engineering, Osaka City University, and PRESTO,
JST, Sugimoto 3-3-138, Sumiyoshi-ku, Osaka 558-8585, Japan.
E-mail: kobatake@a-chem.eng.osaka-cu.ac.jp
**Correspondence to: M. Irie, Department of Chemistry, Rikkyo
University Nishi-Ikebukuro 3-34-1, Toshima-Ku, Tokyo, 171-8501,
Japan. E-mail: iriem@rikkyo.ac.jp
Copyright # 2007 John Wiley & Sons, Ltd.
J. Phys. Org. Chem. 2007; 20: 960–967

SINGLE-CRYSTALLINE PHOTOCHROMISM
961
any photochromism. Even in the antiparallel confor-
mation diarylethenes cannot undergo photochromism in
crystal if the distance between the reacting carbons of the
diarylethene is longer than 4.2 A.25 Molecules which are
˚
packed in the antiparallel conformation with the distance
˚
shorter than 4.2 A can undergo photochromism. Some of
diarylethene dimers in which two diarylethenes are
combined with ethene parts are reported.36,37 However,
no research in the crystalline phase has been reported yet.
Here, we report on single-crystalline photochromism of
novel diarylethene dimers (1a and 2a, as shown in
Scheme 1). We found that 1a formed three kinds of
polymorphic forms recrystallized from different solvents.
Their polymorphic forms showed different photochromic
reactivity. Furthermore, the dimer molecules in crystal 2a
including p-xylene molecules were noticed that they were
packed in particular molecular structures.
RESULTS AND DISCUSSION
Photochromism in solution
Diarylethene dimers 1a and 2a undergo photochromic
reactions in hexane. Figure 1a shows absorption spectra
of 1a and the photostationary solution upon irradiation
with 313-nm light. The hexane solution of 1a was
colorless and the color changed to yellow upon irradiation
with 313-nm light. The colored solution has absorption
maximum at 452 nm and returned to the initial colorless
solution by irradiation with visible light. The low
absorption intensity at 452 nm in the photostationary
state indicates that the photocycloreversion quantum
yield is larger than the photocyclization quantum yield.
Dimer 2a also showed similar spectral changes.
Figure 1b shows absorption spectra of 2a, 2b, and 2c
in hexane, which were isolated by HPLC. Photochromic
reaction of 2a in hexane proceeded to 2b in 16%
conversion and 2c in 0.6% conversion upon irradiation
with 313-nm light. The low conversion is ascribed to the
Figure 1. Absorption spectra of (a) 1a (4.3 ꢁ 10ꢀ5 M) and
the photostationary solution under irradiation with 313-nm
light and (b) 2a, 2b, and 2c (6.5 ꢁ 10ꢀ6 M) in hexane
fact that the photocycloreversion quantum yield is larger
than the photocyclization quantum yield. 2b and 2c have a
same absorption maximum at 465 nm. Absorption
coefficiency of 2c (e465 ¼ 15700 Mꢀ1 cmꢀ1) is twice as
Scheme 1. Photochromic reactions of diarylethene dimers, 1a and 2a
Copyright # 2007 John Wiley & Sons, Ltd.
J. Phys. Org. Chem. 2007; 20: 960–967
DOI: 10.1002/poc

962
S. KOBATAKE, S. KUMA AND M. IRIE
large as that of 2b (e465 ¼ 8300 Mꢀ1 cmꢀ1) at 465 nm.
There is no intramolecular interaction between two
diarylethene chromophores in the dimer molecule. This
indicates that two diarylethene chromophores indepen-
dently undergo the photocyclization reaction.
Polymorphism and single-crystalline
photochromism of 1a
Dimer 1a was recrystallized from hexane, acetone, and
acetonitrile solutions. Each crystal has different crystal
shapes, which are named as 1a-a, 1a-b, and 1a-g,
respectively. X-ray crystallographic analysis of the
crystals was carried out to confirm the polymorphic
forms, and the resulting crystallographic data are shown
in Table 1.
The crystal of 1a-a belongs to monoclinic C2, Z ¼ 2.
The density was 1.300 g cmꢀ3. The ORTEP drawing of
1a-a is shown in Fig. 2a. Half of the molecules were
crystallographically independent. Therefore, two diary-
lethene units are in the same conformation. They are
oriented in the parallel conformation, which indicates a
non-reactive conformation for the photochromic reaction.
The crystal of 1a-b had a crystal system of monoclinic,
a space group of C2/c, and Z ¼ 8. The density was
1.335 g/cm3. The molecules are packed denser than those
in 1a-a. Figure 2b shows the ORTEP drawing of 1a-b.
Two diarylethene units have different conformations. One
of them is in an antiparallel conformation with a distance
Figure 2. ORTEP drawings of (a) 1a-a, (b) 1a-b, and (c) 1a-g
showing 50% probability displacement ellipsoids. The bro-
ken lines showed the distance between the reacting carbons
(D). This figure is available in colour online at www.
interscience.wiley.com/journal/poc
˚
between the reactive carbons (D) of 3.47 A. This has a
possibility to undergo photochromic reaction in the
crystalline phase.25 On the other hand, the other
diarylethene unit has a parallel conformation, which
cannot undergo any photochromic reaction in the
crystalline phase. Therefore, only half of the diarylethene
Table 1. X-ray crystallographic data of 1a-a, 1a-b, 1a-g, and 2a
1a-a
1a-b
1a-g
2a
Recrystallization solvent
Fomula
T (K)
M
Hexane
C33H36O4S4
118 (2)
624.90
Monoclinic
C2
17.700 (6)
6.024 (2)
15.376 (5)
90
103.232 (5)
90
1595.9 (9)
2
1.300
0.0577
0.2329
0.09 (18)
Acetone
C33H36O4S4
123 (2)
624.90
Monoclinic
C2/c
39.982 (12)
10.129 (3)
15.373 (5)
90
92.684 (5)
90
6219 (3)
8
1.335
Acetonitrile
C33H36O4S4 ꢂ C2H3N
123 (2)
p-Xylene
C29H24Br4O4S4 ꢂ 2C8H10
148 (2)
665.95
Monoclinic
P21/c
9.720 (2)
11.047 (3)
32.017 (7)
90
94.271 (4)
90
3428.3 (14)
4
1.290
1096.68
Orthorhombic
Pna21
9.035 (4)
16.712 (8)
30.395 (15)
90
90
90
4589 (4)
4
1.587
0.0347
0.0725
0.013 (6)
Crystal system
Space group
˚
a (A)
˚
b (A)
˚
c (A)
a (8)
b (8)
g (8)
3
˚
Volume (A )
Z
Density (g cmꢀ3
R1 (I > 2s(I))
wR2 (all data)
)
0.0698
0.2220
—
0.0548
0.1804
—
Absolute structure parameter
Copyright # 2007 John Wiley & Sons, Ltd.
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DOI: 10.1002/poc

SINGLE-CRYSTALLINE PHOTOCHROMISM
963
units can participate in the photochromic reaction in the
crystal.
Table 2. Photochromic reactivity of the diarylethene dimers
a
Distance (L) /A
˚
Crystal
Photochromismb
lmaxc/nm
The crystal of 1a-g had a crystal system of monoclinic,
space group of P21/c, and Z ¼ 4. The density was
1.290 g cmꢀ3. Figure 2c shows the ORTEP drawing of
1a-g in which an acetonitrile molecule is included. The
two diarylethene units are in both antiparallel confor-
mations. The distances between the reactive carbons are
1a-a
1a-b
1a-g
2ad
4.11, 4.11
3.47, 4.34
3.62, 3.64
3.53, 3.68
No
—
Yes
Yes
Yes
470
480
480
a Distance between the reacting carbon atoms.
b Photochromism in crystal.
˚
3.62 and 3.64 A, which are short enough to undergo
c Absorption maxima of the photogenerated colored crystal.
d Recrystallized from p-xylene.
photochromic reactions.25 Crystals 1a-a, 1a-b, and 1a-g
were found to be polymorphic forms by X-ray crystal-
lographic analysis.
Single-crystalline photochromism of 1a-a, 1a-b, and
1a-g was examined using polarizing microscope upon
irradiation with UV light. Crystal 1a-a did not exhibit any
color change upon irradiation with 366-nm light. This is
ascribed to the parallel conformations for both diary-
lethene units. Crystals 1a-b and 1a-g exhibited color
change to orange upon irradiation with 366-nm light. The
polarized absorption spectra of the colored crystals were
measured using a polarizing microscopy under parallel
polarizer and analyzer. Figure 3 shows polarized
absorption spectra of the colored crystals. The absorption
intensity dramatically changed when the sample stage
was rotated as much as 908. This indicates that the
molecules are regularly oriented in the crystal. If the
cyclization reaction proceeded in an amorphous phase,
the color intensity change should not be observed by
rotating the sample stage of the microscope. The
absorption anisotropy was observed for both 1a-b and
1a-g. The dichroism under polarized light clearly
indicates that the photochromic reaction took place in
the crystal lattice.
Table 2 shows absorption maxima of the photogener-
ated colored crystals. The closed-ring isomer in crystal
1a-b has an absorption maximum at 470 nm. On the other
hand, the closed-ring isomer in crystal 1a-g has an
absorption maximum at 480 nm. The shift of the
absorption maximum between the two colored crystals
is ascribed to the difference of the strained structure of the
closed-ring forms arising from the different confor-
mations of the open-ring forms.26,38
Crystal growth assisted by p-xylene and
single-crystalline photochromism of the
crystal
Dimer 2a was recrystallized from hexane, acetone, and
acetnitrile solutions. However, well-developed single
crystal for X-ray analysis was not obtained. When 2a was
recrystallized from p-xylene, well-developed single
crystals were obtained. X-ray crystallographic analysis
of the crystal indicates that the crystal includes p-xylene
molecules, as shown in Fig. 4. Dimer 2a formed
co-crystals with p-xylene (1:2). The edge-to-face
aromatic interaction between p-xylene molecules led to
form a one-dimensional chain. The contact lengths of
˚
C . . . H in the interaction were 2.79 and 2.88 A. The chain
is arranged parallel to the a-axis. The molecules of 2a are
packed into the p-xylene chain to chain. The presence of
p-xylene assisted the crystal growth of 2a. The distances
between the reacting carbon atoms in the diarylethene
˚
parts were 3.53 and 3.68 A. It indicates that 2a can
undergo photochromism in the crystal. Two diarylethene
parts in the dimer have the same helical structures. In
other words, the molecules are fixed into either (M,M)-2a
or (P,P)-2a, which are oriented perpendicular each other.
(M,P)-2a was not present in the crystal. When crystal 2a
was irradiated with 366-nm light, the color of the crystal
changed from colorless to yellow. The colored forms are
Figure 3. Absorption spectra of the colored crystals of (a)
1a-b and (b) 1a-g under polarized light. 08 denotes the
direction of maximum absorption intensity
Copyright # 2007 John Wiley & Sons, Ltd.
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DOI: 10.1002/poc

964
S. KOBATAKE, S. KUMA AND M. IRIE
Figure 5. Polarized absorption spectra of the colored crystal
of 2a on the (001) face (a) before and (b) after the partial
bleaching reaction upon irradiation with polarized visible
light at the angle of 308. 08 denotes the direction along
with a-axis
light can selectively isomerize the closed-ring forms to
the open-ring forms. A colorless dimer crystal was
irradiated with non-polarized 366-nm light to give a
yellow-colored crystal. When the crystal was irradiated
with linearly polarized light (l > 450 nm) in the direction
of 308, the colored forms along the polarized light were
preferentially bleached and the molecules oriented
perpendicularly to the irradiated polarized light remained.
The polarized absorption spectra and the polar plots after
partial bleaching are shown in Figs 5b and 6b. The polar
plots show the partial bleaching reactions took place
under the polarized light in the crystal. The order
parameter ((A ꢀ A )/(A þ 2A )) was determined to be
Figure 4. Molecular packing diagram of crystal 2a viewed
along (a) a-axis and (b) c-axis. a and b correspond to diagram
viewed normal to (100) and (001) faces, respectively. This
figure is available in colour online at www.interscience.
wiley.com/journal/poc
due to the production of (M,SS)-2b and (SS,SS)-2c from
(M,M)-2a or (P,RR)-2b and (RR,RR)-2c from (P,P)-2a.
Figure 5a shows absorption spectra of the colored crystal.
The absorption maximum of the closed-ring form in
crystal 2a was observed at 480 nm.
The molecular packing of the diarylethene dimer
viewed normal to the (001) face as shown in
Fig. 4b indicates that the long axes of the diarylethene
chromophores in the dimer are aligned at an angle of
ca. 608 to each other. This suggests that linearly polarized
jj
?
jj
?
0.37 after partial bleaching. The partial photobleaching
reactions are expected to produce selectively either of the
two enantiomers (M,SS)- or (P,RR)-2b at the low
conversion by irradiation with polarized light, as shown
in Scheme 2.
In conclusion, we synthesized novel two kinds of
diarylethene dimers bridged by a spiro structure. The
diarylethene dimers underwent photochromism in
solution and even in the single-crystalline phase. One
Copyright # 2007 John Wiley & Sons, Ltd.
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SINGLE-CRYSTALLINE PHOTOCHROMISM
965
Shimadzu GCMSQP5050A mass spectrometer. Absorp-
tion spectra in a solution were measured with a Hitachi
U-3410 absorption spectrophotometer. Absorption spec-
tra in a single-crystalline phase were measured using a
Leica DMLP polarizing microscope connected with a
Hamamatsu PMA-11 detector. The polarizer and analyzer
were set parallel to each other. Photoirradiation was
carried out using a USHIO 500-W high-pressure mercury
lamp or a xenon lamp attached to the microscope.
Monochromic light was obtained by passing the light
through a monochromator (Ritsu MV-10N) or a band pass
filter. X-ray crystallographic analysis was carried out
using a Bruker SMART CCD X-ray diffractometer.
Diarylethene dimers (1a and 2a) were synthesized
according to the routes shown in Scheme 3. 3-Acetyl-
2,5-dimethylthiophene (4) was prepared by a reaction of
2,5-dimethylthiophene (15 g; 0.13 mol) with acetic
anhydride (14 ml; 0.15 mol) in the presence of Tin(IV)
chloride (21 ml; 0.18 mol) in benzene (130 ml) for 2 h at
room temperature in 85% yield.36,44 (2,5-Dimethyl-3-
thienyl)oxoacetoaldehyde (5) was prepared by a reaction
of selenium dioxide (5.0 g; 45 mmol) in dioxane (30 ml)
and water (1.4 ml) with 4 (5.0 g; 32 mmol) for 5 h at
1058C in 42% yield.36,44 1,2-Bis(2,5-dimethyl-3-thienyl)-
2-hydroxyethanone (6) was prepared by a reaction of
2,5-dimethylthiophene (3.2 g; 29 mmol) with 5 (4.0 g;
24 mmol) in the presence of Tin(IV) chloride (6.0 ml;
51 mmol) in benzene for 12 h at room temperature in 62%
yield.36,44 Dimer 1a was synthesized by reaction of 6
(1.0 g; 3.6 mmol) with pentaerythritol (160 mg;
1.2 mmol) in the presence of p-toluenesulfonic acid
(20 mg) in benzene refluxing using Dean–Stark condenser
for 22 h. The product was carefully purified by column
chromatography (hexane/ethyl acetate ¼ 9/1) and separa-
tive high performance liquid chromatography, and was
Figure 6. Polar plots of absorbance at 480 nm in Fig. 5 (a)
before and (b) after the partial bleaching reaction upon
irradiation with polarized visible light at the angle of 308.
08 denotes the direction along with a-axis
1
obtained in 2.5% yield. H-NMR (200 MHz, CDCl3):
d ¼ 1.96 (s, 12H, CH3), 2.31 (s, 12H, CH3), 4.22 (s,
8H, CH2O), 6.39 (s, 4H, Ar); m/z ¼ 624 (Mþ); Anal. Calc.
for C33H36O4S4: C, 63.43; H, 5.81. Found: C, 63.40; H,
5.85%.
of their dimers formed polymorphic forms. The photo-
chromic reactivity in the polymorphic crystals depended
on the conformation of the diarylethene units. Either of
the two enantiomers ((M,SS)- or (P,RR)-2b) was produced
by partial bleaching reactions of the colored crystal
including both enantiomers by irradiation with linearly
polarized visible light. Although the formation of
diastereomers and enantiomers of diarylethene clo-
sed-ring isomers in the crystal has been so far
reported,39–43 our present work can selectively produce
either of the two enantiomers by partial bleaching
reactions using linearly polarized visible light.
3-Acetyl-2-bromo-5-methylthiophene (8) was pre-
pared by a reaction of 2-bromo-5-methylthiophene
(2.0 g; 11 mmol) with acetic anhydride (1 ml; 11 mmol)
in the presence of Tin(IV) chloride (1.8 ml; 15 mmol) in
benzene (12 ml) for 3 h at room temperature in 51%
yield. (200 MHz, CDCl3) d ¼ 2.46 (s, 3H, CH3), 2.66
(s, 3H, CH3), 7.29 (s, 1H, Ar); MS m/z ¼ 218 (Mþ).
(5-Bromo-2-methyl-3-thienyl)oxoaceto-aldehyde (9) was
prepared by a reaction of selenium dioxide (1.3 g;
12 mmol) in dioxane (10 ml) and water (0.3 ml) with 8
(1.0 g; 4.6 mmol) for 5 h at 1058C in 83% yield. 1H-NMR
(200 MHz, CDCl3): d ¼ 2.75 (s, 3H, CH3), 7.81 (s, 1H,
Ar), 9.47 (s, 1H, CHO); MS m/z ¼ 232 (Mþ).
1,2-Bis(5-bromo-2-methyl-3-thienyl)-2-hydroxyethanone
(10) was prepared by a reaction of 2-bromo-5-
methylthiophene (0.73 g; 4.1 mmol) with 9 (0.6 g;
2.6 mmol) in the presence of Tin(IV) chloride (0.48 ml;
EXPERIMENTAL
General
1H NMR spectra were recorded on a Varian Gemini 200
spectrometer (200 MHz). Tetramethylsilane was used as
an internal standard. Mass spectra were taken with a
Copyright # 2007 John Wiley & Sons, Ltd.
J. Phys. Org. Chem. 2007; 20: 960–967
DOI: 10.1002/poc

966
S. KOBATAKE, S. KUMA AND M. IRIE
Scheme 2. Photochromic reaction scheme of M-helical 2a ((M,M)-2a) and P-helical-2a ((P,P)-2a), and their photogenerated
isomers
Scheme 3. Synthetic routes of 1a and 2a
Copyright # 2007 John Wiley & Sons, Ltd.
J. Phys. Org. Chem. 2007; 20: 960–967
DOI: 10.1002/poc

SINGLE-CRYSTALLINE PHOTOCHROMISM
967
4.1 mmol) in benzene for 12 h at room temperature in
37% yield. 1H-NMR (200 MHz, CDCl3): d ¼ 2.52
(s, 3H, CH3), 2.73 (s, 3H, CH3), 4.34 (d, J ¼ 5.7 Hz,
1H, CH—OH), 5.51 (d, J ¼ 5.7 Hz, 1H, CH—OH), 6.61
(s, 1H, Ar), 6.94(s, 1H, Ar). Dimer 2a was synthesized by
reaction of 10 (0.39 g; 0.95 mmol) with pentaerythritol
(40 mg; 0.29 mmol) in the presence of p-toluenesulfonic
acid (10 mg) in benzene refluxing using Dean-Stark
condenser for 26 h. The product was carefully purified by
column chromatography (hexane/ethyl acetate ¼ 9/1) and
separative high performance liquid chromatography, and
was obtained in 3.0% yield. 1H-NMR (200 MHz, CDCl3):
d ¼ 2.00 (s, 12H, CH3), 4.21 (s, 8H, CH2O), 6.70 (s, 4H,
Ar); MS m/z ¼ 880 (Mþ); Anal. Calc. for C33H36O4S4: C,
39.38; H, 2.74. Found: C, 39.48; H, 2.72%. Dimers 2b and
2c were isolated by passing a photostationary solution
containing 2a, 2b, and 2c through a HPLC (Hitachi
L-6250 HPLC system, silica gel column, hexane/ethyl
10. Eichen Y, Lehn JM, Scherl M, Haarer D, Fischer J, DeCian A,
Corval A, Trommsdor HP. Angew. Chem., Int. Ed. Engl. 1995; 34:
2530–2533.
11. Schmidt A, Kababya S, Appel M, Khatib S, Botoshansky M,
Eichen Y. J. Am. Chem. Soc. 1999; 121: 11291–11299.
12. Naumov P, Sekine A, Uekusa H, Ohashi Y. J. Am. Chem. Soc.
2002; 124: 8540–8541.
13. Hadjoudis E, Vittorakis M, Moustakali-Mavridis I. Tetrahedron
1987; 43: 1345–1360.
14. Harada J, Uekusa H, Ohashi Y. J. Am. Chem. Soc. 1999; 121:
5809–5810.
15. Akimoto K, Kanatomi H, Nagakari A, Fukuda H, Koyama H,
Kawato T. Chem. Commun. 2003; 870–871.
16. Mori Y, Ohashi Y, Maeda K. Bull. Chem. Soc. Jpn. 1989; 62:
3171–3176.
17. Irie M. Chem. Rev. 2000; 100: 1685–1716.
18. Kobatake S, Yamada T, Uchida K, Kato N, Irie M. J. Am. Chem.
Soc. 1999; 121: 2380–2386.
19. Kobatake S, Yamada M, Yamada T, Irie M. J. Am. Chem. Soc.
1999; 121: 8450–8456.
20. Irie M, Lifka T, Kobatake S, Kato N. J. Am. Chem. Soc. 2000; 122:
4871–4876.
21. Kobatake S, Shibata K, Uchida K, Irie M. J. Am. Chem. Soc. 2000;
122: 12135–12141.
22. Irie M, Kobatake S, Horichi M. Science 2001; 291: 1769–1772.
23. Fukaminato T, Kobatake S, Kawai T, Irie M. Proc. Japan Acad.,
Ser. B 2001; 77: 30–35.
24. Shibata K, Muto K, Kobatake S, Irie M. J. Phys. Chem. A 2002;
106: 209–214.
25. Kobatake S, Uchida K, Tsuchida E, Irie M. Chem. Commun. 2002:
2804–2805.
1
acetate (97:3) as the eluent). 2b: H-NMR (200 MHz,
CDCl3): d ¼ 1.99 (s, 6H, CH3), 2.12 (s, 6H, CH3),
3.80–4.30 (m, 8H, CH2O), 6.21 (s, 2H, Ar), 6.70 (s, 2H,
Ar). 2c: 1H-NMR (200 MHz, CDCl3): d ¼ 2.11
(s, 12H, CH3), 3.95 (s, 4H, CH2O), 4.01 (s,
4H, CH2O), 6.22 (s, 4H, Ar).
26. Morimoto M, Kobatake S, Irie M. Chem. Eur. J. 2003; 9: 621–627.
27. Morimoto M, Kobatake S, Irie M. Adv. Mater. 2002; 14:
1027–1029.
Acknowledgements
28. Morimoto M, Kobatake S, Irie M. J. Am. Chem. Soc. 2003; 125:
11080–11087.
29. Kobatake S, Irie M. Bull. Chem. Soc. Jpn. 2004; 77: 195–210.
30. Kobatake S, Matsumoto Y, Irie M. Angew. Chem. Int. Ed. 2005; 44:
1248–1251.
31. Morimoto M, Irie M. Chem. Commun. 2005: 3895–3905.
32. Kuroki L, Takami S, Shibata K, Irie M. Chem. Commun. 2005:
6005–6007.
This work was partly supported by the Grants-in-Aid for
Scientific Research (KAKENHI) on Priority Areas ‘Mol-
ecular Nano Dynamics’ (No. 16072214 and No.
17034055) and Young Scientists (A) (No. 16685014)
from the Ministry of Education, Culture, Sports, Science
and Technology, Japan.
´
´
33. Giraud M, Leaustic A, Charlot MF, Yu P, Cesario M, Philouze C,
Pansu R, Nakatani K, Ishow E. New. J. Chem. 2005; 29: 439–446.
34. Kawata S, Kawata Y. Chem. Rev. 2000; 100: 1777–1788.
35. Delaire JA, Nakatani K. Chem. Rev. 2000; 100: 1817–1845.
36. Uchida K, Masuda G, Aoi Y, Nakayama K, Irie M. Chem. Lett.
1999: 1071–1072.
REFERENCES
37. Tian H, Chen B, Liu PH. Chem. Lett. 2001: 990–991.
38. Kobatake S, Morimoto M, Asano Y, Murakami A, Nakamura S,
Irie M. Chem. Lett. 2002: 1224–1225.
39. Kodani T, Matsuda K, Yamada T, Kobatake S, Irie M. J. Am. Chem.
Soc. 2000; 122: 9631–9637.
1. Brown GH. Photochromism. Wiley-Interscience: New York, 1971.
2. Du¨rr H, Bouas-Laurent H. Photochromism. Molecules and Sys-
tems. Elsevier: Amsterdam, 1990.
3. Scheffer JR, Pokkuluri PR. In Photochemistry in Organized &
Constrained Media, Ramamurthy V (ed.). VCH Publ: New York,
1990.
40. Matsuda K, Yamamoto S, Irie M. Tetrahedron Lett. 2001; 42:
7291–7293.
4. Golden JH. J. Chem. Soc. 1961: 3741–3748.
5. Maeda K, Hayashi T. Bull. Chem. Soc. Jpn. 1970; 43: 429–438.
6. Kawano M, Sano T, Abe J, Ohashi Y. J. Am. Chem. Soc. 1999; 121:
8106–8107.
7. Ichimura K, Watanabe S. Bull. Chem. Soc. Jpn. 1976; 49:
2220–2223.
41. Yamamoto S, Matsuda K, Irie M. Angew. Chem. Int. Ed. 2003; 42:
1636–1639.
42. Yamamoto S, Matsuda K, Irie M. Org. Lett. 2003; 5: 1769–1772.
43. Uchida K, Walko M, de Jong JJD, Sukata S, Kobatake S, Meetsma
A, van Esch J, Feringa BL. Org. Biomol. Chem. 2006; 4:
1002–1006.
8. Trozzolo AM, Leslie TM, Sarpotdar AS, Small RD, Ferraudi GJ,
DoMinh T, Hartless RL. Pure Appl. Chem. 1979; 51: 261–270.
9. Sixl H, Warta R. Chem. Phys. 1985; 94: 147–155.
44. Ivanov SN, Lichitskii BV, Dudinov AA, Martynkin AY, Krayush-
kin MM. Chemistry of Heterocyclic Compounds 2001; 37: 85–
90.
Copyright # 2007 John Wiley & Sons, Ltd.
J. Phys. Org. Chem. 2007; 20: 960–967
DOI: 10.1002/poc