Photochromism of dithienylethenes included in cyclodextrins

Article abstract of DOI:10.1021/jo981199p

The effect of inclusion of diarylethenes in cyclodextrin cavities on cyclization quantum yields and on circular dichroism (CD) spectral changes by photoirradiation was studied. The addition of β-and γ-cyclodextrins to an aqueous solution of the open-ring form of 2,2'-dimethyl-3,3'-(perfluoro- cyclopentene-1,2-diyl)bis(benzo[b]thiophene-6-sulfonate) (1a) increased the ratio of the antiparallel conformation. The enrichment of antiparallel conformation caused an increase in the photocyclization quantum yield of 1a. The CD spectral intensity of the mixtures of 1a or 2,2'4,4'-tetramethyl- 3,3'-(perfluorocyclopentene-1,2-dyl)bis(thiophen-5-yl-(phenyl-4-sulfonate)) (2a) and cyclodextrins in aqueous solution increased with the increasing concentration of cyclodextrins. The induced CD spectrum of 1 in β- cyclodextrin reversibly changed from negative to positive by UV irradiation. The spectral change was attributed to the change in the direction of transition moment of 1 in the cavity.

Full text of DOI:10.1021/jo981199p

9306
J . Org. Chem. 1998, 63, 9306-9313
P h otoch r om ism of Dith ien yleth en es In clu d ed in Cyclod extr in s
Michinori Takeshita,*,† Nobuo Kato,‡ Susumu Kawauchi,§ Tatsuya Imase,§
J unji Watanabe,§ and Masahiro Irie*,†
Department of Chemistry and Biochemistry, Graduate School of Engineering, Kyushu University, and
CREST, J apan Science and Technology Corporation, Hakozaki 6-10-1, Higashi-ku, Fukuoka 812-8581,
J apan, Institute of Advanced Material Study, Kyushu University, Kasuga, Fukuoka 816-8580, J apan,
and Faculty of Engineering, Tokyo Institute of Technology, Ookayama 2-10-1,
Meguro-ku, Tokyo 152-8552, J apan
Received J une 22, 1998
The effect of inclusion of diarylethenes in cyclodextrin cavities on cyclization quantum yields and
on circular dichroism (CD) spectral changes by photoirradiation was studied. The addition of â-
and γ-cyclodextrins to an aqueous solution of the open-ring form of 2,2′-dimethyl-3,3′-(perfluoro-
cyclopentene-1,2-diyl)bis(benzo[b]thiophene-6-sulfonate) (1a ) increased the ratio of the antiparallel
conformation. The enrichment of antiparallel conformation caused an increase in the photocy-
clization quantum yield of 1a . The CD spectral intensity of the mixtures of 1a or 2,2′,4,4′-
tetramethyl-3,3′-(perfluorocyclopentene-1,2-diyl)bis(thiophen-5-yl-(phenyl-4-sulfonate)) (2a ) and
cyclodextrins in aqueous solution increased with the increasing concentration of cyclodextrins. The
induced CD spectrum of 1 in â-cyclodextrin reversibly changed from negative to positive by UV
irradiation. The spectral change was attributed to the change in the direction of transition moment
of 1 in the cavity.
Photochromic compounds are classified into two cat-
egories, thermally reversible and irreversible com-
pounds.1 Azobenzenes and spirobenzopyrans belong to
the former and furylfulgides and dithienylethenes to the
latter. The thermally irreversible photochromic com-
pounds are potentially applicable to various types of
optoelectronic devices, such as optical memory media2
and photooptical switching devices.3 Among the ther-
mally irreversible compounds, diarylethenes having het-
erocyclic aryl groups are promising candidates for the
practical applications because of their fatigue-resistant
characteristic.4 The photochromic reaction of diarylethenes
is based on the reversible hexatriene-cyclohexadiene-
type photocyclization as shown in Figure 1. The open-
ring form of the diarylethene has two conformations,
parallel and antiparallel. The photocyclization can pro-
ceed only from the antiparallel conformation, while the
parallel conformation is photochemically inactive.4 The
existence of the parallel conformation limits the quantum
yield for ring-closure reaction.5 One of the approaches
to increase the cyclization quantum yield is to increase
the ratio of the antiparallel conformation. Inclusion of
the diarylethene into a microcavity, such as cyclodextrins,
favors the antiparallel conformation.6
F igu r e 1. Reaction scheme of diarylethene with five-
membered heterocyclic aryl groups.
Circular dichroism (CD) spectral changes accompany-
ing photochromic reactions have been reported7 for
dissymmetrical alkenes,8 bilirubin-IIIR,9 liquid crystals,10
[4n]annulenes,11 fulgides,12 spiropyranes,13 and dithie-
(6) Takeshita, M.; Choi, C.; Irie, M. J . Chem. Soc., Chem. Commun.
1997, 2265.
(7) For a review, see: Feringa, B. L.; J ager, W. F.; de Lange, B.
Tetrahedron 1993, 49, 8267.
† Graduate School of Engineering, Kyushu University, and CREST,
J apan Science and Technology Corporation.
(8) (a) Feringa, B. L.; J ager, W. F.; de Lange, B.; Meijer, E. W. J .
Am. Chem. Soc. 1991, 113, 5468. (b) Feringa, B. L.; J ager, W. F.; de
Lange, B. Tetrahedron Lett. 1992, 33, 2887. (c) Feringa, B. L.; J ager,
W. F.; de Lange, B. J . Chem. Soc., Chem. Commun. 1993, 288. (d)
J ager, W. F.; de J ong, J . C.; de Lange, B.; Huck, N. P. M.; Meetsma,
A.; Feringa, B. L. Angew. Chem., Int. Ed. Engl. 1995, 34, 348. (e) Huck,
N. P. M.; Feringa, B. L. J . Chem. Soc., Chem. Commun. 1995, 1095.
(f) Feringa, B. L.; Huck, N. P. M.; van Doren, H. A. J . Am. Chem. Soc.
1995, 117, 9929.
‡ Institute of Advanced Material Study, Kyushu University.
§ Tokyo Institute of Technology.
(1) For a review, see: Du¨rr, H.; Bouas-Laurent, H. Photochromism,
Molecules and Systems; Elsevier: Amsterdam, 1990.
(2) For example, see: (a) Irie, M. In Photoreactive Materials for
Ultrahigh-Density Optical Memory; Irie, M., Ed.; Elsevier: Amsterdam,
1994; p 1. (b) Tatezono, F.; Harada, T.; Shimizu, Y.; Ohara, M.; Irie,
M. J pn. J . Appl. Phys. 1993, 32, 3987.
(3) (a) Tanio, N.; Irie, M. J pn. J . Appl. Phys. 1994, 33, 1550. (b)
Tsujioka, T.; Kume, M.; Irie, M. Ibid. 1996, 35, 4353. (c) Hoshino, M.;
Ebisawa, F.; Yoshida, T.; Sukegawa, K. Ibid. 1997, 105, 75.
(4) For reviews, see: (a) Irie, M.; Uchida, K. Bull. Chem. Soc. J pn.
1998, 71, 985. (b) Reference 2a.
(5) Irie, M.; Miyatake, O.; Uchida, K.; Eriguchi, T. J . Am. Chem.
Soc. 1994, 116, 9894.
(9) Agati, G.; McDonagh, A. F. J . Am. Chem. Soc. 1995, 117, 4425.
(10) Suarez, M.; Schuster, G. B. J . Am. Chem. Soc. 1995, 117, 6732.
(11) Briquet, A. A. S.; Uebelhart, P.; Hansen, H.-J . Helv. Chim. Acta
1996, 79, 2282.
(12) Yokoyama, Y.; Uchida, S.; Yokoyama, Y.; Sugawara, Y.; Kurita,
Y. J . Am. Chem. Soc. 1996, 118, 3100.
(13) Eggers, L.; Buss, V. Angew. Chem., Int. Ed. Engl. 1997, 36, 881.
10.1021/jo981199p CCC: $15.00 © 1998 American Chemical Society
Published on Web 11/20/1998

Photochromism of Dithienylethenes
J . Org. Chem., Vol. 63, No. 25, 1998 9307
Sch em e 1
nylethenes.14 Such chiral property changes are useful
for optical display10 as well as photooptical switching.
When molecules are included in cyclodextrin cavities, the
asymmetric environment causes the induced CD spec-
tra.15,16 If the guest molecules undergo photochromism,
the CD spectra are expected to be changed by photoir-
radiation.17
In this paper, we examined the effect of inclusion of
thermally irreversible diarylethenes in cyclodextrin cavi-
ties on cyclization quantum yields and on CD spectral
changes by photoirradiation.
F igu r e 2. Absorption spectral change of 1 in aqueous solution
([1] ) 4.0 × 10-5 mol dm-3) upon irradiation with 313 nm light
(0-28 min). Dotted line showed the spectrum after irradiation
with >480 nm light (5 min).
Resu lts a n d Discu ssion
1. Syn th esis. Disulfonates 1a and 2a were synthe-
sized by treatment of the corresponding diarylethenes18,19
with chlorosulfonic acid and subsequent hydrolysis with
1% aqueous NaOH (Scheme 1).
Figure 2 shows the absorption spectral change of 1 (4.0
× 10-5 mol dm-3) in an aqueous solution by irradiation
with 313 nm light. The initial colorless solution turned
red, and new absorption bands appeared at 358 and 529
nm. The red color is due to the closed ring form 1b, of
which the π-system is extended by the ring-closure
reaction.18 Upon visible (>480 nm) irradiation, the
spectrum returned to the initial one. A solution of 2 in
MeOH/water (1:4) also showed similar photochromism.
2. NMR Sp ectr a of Dia r yleth en es in Cyclod ex-
tr in s. Figure 3a shows the 1H NMR spectrum of methyl
groups of the open-ring form of 1a in D2O (3.0 × 10-3
mol dm-3, 20 °C, 200 MHz). The methyl signals in
parallel and antiparallel conformations are observed
separately. This indicates that the conformational change
takes place slowly relative to the NMR time scale (<56
Hz). The methyl protons at δ 2.27 (at higher magnetic
F igu r e 3. 1H NMR spectrum (200 MHz, 20 °C) of methyl
protons in D2O ([1a ] ) 3.0 × 10-3 mol dm-3): (a) 1a , (b) 1a +
â-cyclodextrin (1:5), and (c) 1a + â-cyclodextrin (1:10).
field) and δ 2.55 (at lower magnetic field) are assigned
to the antiparallel and the parallel conformations, re-
spectively.20 In this compound, the antiparallel confor-
mation is favored and the ratio of antiparallel and
parallel was 64:36. The absorption spectra of the two
conformations are very similar to each other.5 Therefore,
this ratio means that only 64% of 1a is photoreactive and
the rest is photochemically inactive when they are
photoexcited with 313 nm light. Upon addition of â-cy-
clodextrin to the solution, the ratio changed as shown in
Figure 3b,c. When 10 equiv of â-cyclodextrin was added
(14) Yamaguchi, T.; Uchida, K.; Irie, M. J . Am. Chem. Soc. 1997,
119, 6066.
(15) For example, see: Harata, K.; Uedaira, H. Bull. Chem. Soc.
J pn. 1975, 48, 375.
(16) (a) Kodaka, M. J . Phys. Chem. 1991, 95, 2111. (b) Kodaka, M.
J . Am. Chem. Soc. 1993, 115, 3702.
(17) (a) Ueno, A.; Saka, R.; Osa, T. Chem. Lett. 1979, 1007. (b)
Tamaki, T. Chem. Lett. 1984, 53. (c) Moriwaki, F.; Ueno, A.; Osa, T.;
Hamada, F.; Murai, K. Ibid. 1986, 1865. (d) Davidson, R. S.; Liu, J . J .
Photochem. Photobiol. A: Chem. 1993, 76, 121. (e) Costanzo, L. L.;
Giuffrida, S.; Sortino, S.; Chiacchio, U.; De Guidi, G. Ibid. 1993, 76,
127.
(18) Hanazawa, M.; Sumiya, R.; Horikawa, Y.; Irie, M. J . Chem. Soc.,
Chem. Commun. 1992, 206.
(19) Irie, M.; Sakemura, K.; Okinaka, M.; Uchida, K. J . Org. Chem.
1995, 60, 8305.
(20) Uchida, K.; Nakayama, Y.; Irie, M. Bull. Chem. Soc. J pn. 1990,
63, 1311.

9308 J . Org. Chem., Vol. 63, No. 25, 1998
Takeshita et al.
F igu r e 4. [CD]/[1a ] vs content of antiparallel conformation
determined by 1H NMR spectroscopy ([1a ] ) 3.0 × 10-3 mol
dm-3), with R-cyclodextrin (triangle), with â-cyclodextrin
(circle), and γ-cyclodextrin (square).
to the solution, the antiparallel conformer became domi-
nant as shown in Figure 3c.
Figure 4 shows cyclodextrin concentration dependence
of the ratio calculated from the NMR spectra. When 10
equiv of â-cyclodextrin is added, 94% of 1a converts to
the antiparallel conformation, while 80% converts to the
antiparallel conformation when γ-cyclodextrin is added.
The addition of R-cyclodextrin did not change the ratio
of the conformations. The result indicates that the cavity
of â-cyclodextrin is suitable for the antiparallel conforma-
tion of 1a , whereas that of R-cyclodextrin is too small to
include 1a . The methyl protons of both conformations
of 1a were found to split upon addition of â-cyclodextrin.
The split suggests that two methyl protons exist in
different environments in the chiral cyclodextrin cavity.
Any appreciable NMR spectral change was not ob-
F igu r e 5. NOESY spectrum (in part, 600 MHz, 20 °C) of a
mixture of 1a (3.0 × 10-3 mol dm-3) and â-cyclodextrin (3.0 ×
10-2 mol dm-3) in D2O.
served for 2a in MeOH/water (1:4) (3.0 × 10-3 mol dm-3
,
20 °C, 200 MHz) even in the presence of 10 equiv of
â-cyclodextrin. This is due to low concentration of the
inclusion complex. CD spectral titration revealed that
only 10% of 2a is included in the cavity (see below).
The NOESY experiments are useful to determine the
structure of the complex.21 The packing structure of the
inclusion complex was examined using a NOESY spec-
trum. Figure 5 shows the NOESY spectrum (600 MHz,
mixing time 500 ms) of a mixture of 1a (3.0 × 10-3 mol
dm-3) and â-cyclodextrin (3.0 × 10-2 mol dm-3) in D2O
solution at 20 °C. A strong and a weak NOE signals were
observed between protons at the 7- and 5-positions of a
benzothiophene ring of 1a and the methylene protons at
the 6-position of â-cyclodextrin, respectively. When a
guest 1a is included in the cyclodextrin cavity from the
secondary hydroxy group side, which is wider than the
primary hydroxy group side,22 the structure of a complex
of 1a and â-cyclodextrin is depicted as shown in Figure
6.
F igu r e 6. Conceivable structure of a complex of 1a and
â-cyclodextrin.
Ta ble 1. Cycliza tion Qu a n tu m Yield s of 1a Ir r a d ia ted
w ith 313 n m Ligh t in th e P r esen ce of CDx in Aqu eou s
Solu tion a
system
1a
1a b 1a + R-CD 1a + â-CD 1a + γ-CD
quantum yield 0.32 0.32
0.31
0.49
0.45
a
[1a ] ) 4.0 × 10-5 mol dm-3, [CD] ) 8.0 × 10-3 mol dm-3, 20
b
3. Qu a n t u m Yield Ch a n ge b y t h e Ad d it ion of
Cyclod extr in s. As described above, the diarylethene in
the parallel conformation is not photoreactive. Therefore,
the increase in the ratio of antiparallel to parallel
conformations is expected to result in the increase in the
cyclization quantum yield. Table 1 shows the cyclization
quantum yields of 1a by irradiation with 313 nm light.
°C. In MeOH.
The cyclization quantum yield of 1a in the presence of
200 times excess â-cyclodextrin is about 1.5 times larger
than that of 1a in an aqueous solution. NMR measure-
ment indicated that 97% of 1a is in the antiparallel
conformation in the presence of excess â-cyclodextrin. The
increase in the quantum yield is due to the increase in
the population of the antiparallel conformation.
(21) For example, see: Anderson, S.; Claridge; T. D. W.; Anderson,
H. L. Angew. Chem., Int. Ed. Engl. 1997, 36, 1310.
(22) For a review, see: Bender, M. L.; Komiyama, M. Cyclodextrin
Chemistry; Springer-Verlag: Heidelberg, 1978.
The cyclization quantum yield of 1a in the presence of
200 times excess γ-cyclodextrin is also increased due to

Photochromism of Dithienylethenes
J . Org. Chem., Vol. 63, No. 25, 1998 9309
in cyclodextrin concentration. On the other hand, no
remarkable CD spectral change was observed by the
addition of γ-cyclodextrin, whose cavity is larger than for
â-cyclodextrin, to an aqueous solution of 1a . This
indicates that the cavity of the γ-cyclodextrin is too large
to fix the guest molecule 1a in the cavity.
The addition of â-cyclodextrin to a solution of 2a ([2a ]
) 1.0 × 10-4 mol dm-3, [â-cyclodextrin] ) 0-1.0 × 10-2
mol dm-3, 20 °C) in MeOH-water (1:4) increased the
intensity of the CD spectrum, and the positive cotton
effect was observed at 298 nm as shown in Figure 7b.
The intensity of the spectrum is increased with an
increase in the concentration of â-cyclodextrin. Figure
7c shows the CD spectral change by addition of γ-cyclo-
dextrin to a solution of 2a (1.0 × 10-4 mol dm-3) in
MeOH-water (1:4). The negative cotton effect was
observed around 288 nm. The different behavior of the
CD spectral change indicates that the structure of the
complex is different between 2a and â-cyclodextrin and
2a and γ-cyclodextrin.
Hill plots of the complexation of 1a with â-cyclodextrin
in aqueous solution based on ∆ꢀ change at 212 nm gave
stoichiometry and an association constant (Kassoc). From
the slope, the stoichiometry of the complexation was
determined to be 1:1 and from the intercept the associa-
tion constant (Kassoc) was calculated to be 2190 mol-1 dm3
at 20 °C. The stoichiometry and Kassoc of the complex-
ation of 2a with â-cyclodextrin in MeOH-water (1:4)
were determined from the spectral change at 298 nm to
be 1:1 and 260 mol-1 dm3 at 20 °C, respectively. The
stoichiometry and the association constant for the com-
plexation of 2a with γ-cyclodextrin could not be deter-
mined because of the complex CD spectral change by the
addition of γ-cyclodextrin.
5. CD Sp ectr a l Ch a n ge by P h otoir r a d ia tion . It
has been reported that the direction of the Cotton effect
in induced CD spectrum of cyclodextrin inclusion complex
is dependent on the direction of the transition moment
of the chromophore in the cyclodextrin cavity.16 It is
reported that when the direction of the transition mo-
ment of the chromophore included in the cavity is
polarized perpendicular to the axis of cyclodextrin, the
complex shows negative ICD for the transition. If the
direction of the transition moment is parallel to the axis,
the ICD is positive. The cotton effect can give informa-
tion concerning the direction of the transition moment
or packing structure of the chromophore.
F igu r e 7. CD spectral change (20 °C) of (a) 1a (4.0 × 10-5
mol dm-3) in aqueous solution upon addition of â-cyclodextrin,
(b) 2a (1.0 × 10-4 mol dm-3) in MeOH/water (1:4) solution upon
addition of â-cyclodextrin, and (c) 2a (1.0 × 10-4 mol dm-3) in
MeOH/water (1:4) solution upon addition of γ-cyclodextrin.
Figure 8a shows the CD spectral change of a mixture
of 1 (4.0 × 10-5 mol dm-3) and â-cyclodextrin (8.0 × 10-3
mol dm-3) in aqueous solution by irradiation with 313
nm light. 1H NMR and absorption spectral studies
revealed that in the photostationary state the conversion
of 1a to the closed-ring form 1b by irradiation with 313
nm light is 68%. Upon 313 nm irradiation, the troughs
at 300, 276, and 212 nm disappear and the new peaks
appear near 294 and 225 nm. These peaks increase with
irradiation time. Irradiation with visible light (>480 nm)
restores the original CD spectrum of the open-ring form
as shown by the dotted line in Figure 8a. The CD
spectral change suggests16 that the transition moment
of 1a included in the â-cyclodextrin cavity at 212 nm is
perpendicular to the cyclodextrin axis, whereas that of
1b at 225 nm is parallel to the axis.
the enrichment of antiparallel conformation. On the
other hand, no change was observed in either the 1H
NMR spectrum or the quantum yield for cyclization of
1a in the presence of R-cyclodextrin. The enhancement
of quantum yields in the presence of â- and γ-cyclodextrin
is ascribed to the favorable antiparallel conformation of
1a in the cyclodextrins’ cavities.
4. CD Sp ectr a l Ch a n ge by th e Ad d ition of Cyclo-
d extr in s. Figure 7a shows the CD spectral change of
1a by the addition of â-cyclodextrin in an aqueous
solution ([1a ] ) 4.0 × 10-5 mol dm-3, [â-cyclodextrin] )
0-8.0 × 10-3 mol dm-3, 20 °C). The negative cotton effect
appeared at 300, 276, and 212 nm, and the spectral
intensity increased with the increasing concentration of
â-cyclodextrin. The intensity increase indicates that
â-cyclodextrin includes 1a in the cavity, and the concen-
tration of inclusion complex increases with an increase
The CD spectral change of a mixture of 2 (1.0 × 10-4
mol dm-3) and â-cyclodextrin (1.0 × 10-2 mol dm-3) in
MeOH/water (1:4) is shown in Figure 8b. Upon irradia-

9310 J . Org. Chem., Vol. 63, No. 25, 1998
Takeshita et al.
Ta ble 2. AM1-RP A Resu lts for Op en -Rin g F or m 3a
(f > 0.1)
λ (nm)
TrX
TrY
TrZ
f
381
297
280
278
274
266
254
244
241
238
220
-0.296
0.676
0.463
-0.600
0.000
0.225
-0.158
0.000
0.001
-0.001
0.001
-0.002
0.844
0.002
-0.002
1.054
-0.452
0.276
-0.956
0.833
0.002
-0.874
0.700
0.195
0.356
0.751
0.703
0.475
0.543
0.343
0.741
0.865
0.491
0.283
0.002
-0.467
-0.318
-0.622
0.002
0.002
0.000
-1.039
-0.797
0.193
tion with 313 nm light, a peak at 298 nm decreases and
a peak at 248 nm increases. Under the experimental
conditions, the conversion of 2 is 91% in the photosta-
tionary state (313 nm).
Figure 8c shows the CD spectral change of a mixture
of 1 (4.0 × 10-5 mol dm-3) and γ-cyclodextrin (2.0 × 10-2
mol dm-3) in aqueous solution by irradiation with 313
nm light. CPK molecular modeling study suggests that
the increase in CD spectrum of a mixture of 1 and
γ-cyclodextrin at 224 nm by 313 nm irradiation is
ascribed to the rigid structure of 1b in γ-cyclodextrin
cavity, while in the case of 1a and γ-cyclodextrin, there
are various structures of complex and the CD spectral
intensity is weak. A peak at 224 nm in 1b and γ-cyclo-
dextrin indicates that transition moment of 1b at 224
nm is parallel to the cyclodextrin axis. In the case of 2
and γ-cyclodextrin (Figure 8d), a trough at 295 nm in
CD spectrum of a mixture of 2a and γ-cyclodextrin
disappears and peaks around 280 and 570 nm appear.
The CD spectral change to positive in Figure 8a,c,d
indicates that the transition moments of the closed-ring
forms, which are rigid and rodlike structures, are parallel
to the cyclodextrin axis.
The CD spectra changed by UV irradiation returned
to the initial spectra upon irradiation with visible light
(>480 nm).
The closed ring form of diarylethene 1b and 2b have
C2 symmetry.14 Therefore, formation of one of the
enantiomers in the CD cavity is anticipated. However,
there was no remarkable difference between CD spectra
of the two samples, which were formed in the presence
of â-cyclodextrin and mixed with â-cyclodextrin later.
This result indicates that CD spectra observed here are
induced CD spectra and not the enrichment of an
enantiomer of the closed-ring forms.
6. Ca lcu la tion of Tr a n sition Mom en ts. As de-
scribed above, the photoreversible CD spectral changes
are considered due to the transition moment changes of
diarylethenes in the cyclodextrin cavity. To clarify the
CD spectral changes by irradiation, the transition mo-
ments of the open- and closed-ring forms of a diarylethene
were calculated. The transition moments of diarylethene
3 were calculated as a model for simplifying the calcula-
tion. Tables 2 and 3 show the list of electronic transitions
of the open-ring form 3a and the closed-ring form 3b,
whose f values are larger than 0.1. The calculations were
carried out by the AM1-RPA method.23,24 The coordinates
of 3a and 3b for calculations are shown in Figure 9.
F igu r e 8. CD spectral change (20 °C) of mixtures of (a) 1 (4.0
× 10-5 mol dm-3) and â-cyclodextrin (8.0 × 10-3 mol dm-3) in
aqueous solution, (b) 2 (1.0 × 10-4 mol dm-3) and â-cyclodex-
trin (1.0 × 10-2 mol dm-3) in MeOH/water (1:4) solution, (c) 1
in aqueous solution, and (d) 2 (1.0 × 10-4 mol dm-3) and
γ-cyclodextrin (5.0 × 10-2 mol dm-3) in MeOH/water (1:4)
solution upon irradiation with 313 nm light. Dotted line in (a)
showed the spectrum after irradiation with >480 nm light.
(4.0 × 10-5 mol dm-3) and γ-cyclodextrin (2.0 × 10-2 mol dm-3
)
(23) (a) Sasagane, K.; Mori, K.; Ichihara, A.; Itoh, R. J . Chem. Phys.
1990, 92, 3619 and see also references therein. (b) Kawauchi, S.; Muta,
H.; Imase, T.; Watanabe, J .; Satoh, M.; Komiyama, J .; Sasagane, K.;
Suzuki, K.; Mori, K. Manuscript in preparation.

Photochromism of Dithienylethenes
J . Org. Chem., Vol. 63, No. 25, 1998 9311
Ta ble 3. AM1-RP A Resu lts for Closed -Rin g F or m 3b
Con clu sion s
(f > 0.1)
The addition of â- and γ-cyclodextrins to 1 or 2 in
aqueous solution increases the quantum yield of the ring-
closure reaction by favorable inclusion of the photoreac-
tive antiparallel conformations. The induced CD spectra
were observed in the mixture of diarylethenes and
cyclodextrins. The CD spectrum of a mixture of 1 and
â-cyclodextrin changed from negative to positive by
irradiation with 313 nm light. The CD spectral change
is ascribed to the transition moment change of di-
arylethene in the cavity by photoirradiation. The calcu-
lation of the transition moments of 3 confirmed the
photoreversible CD spectral change is due to the change
in the direction of the transition moments of diarylethene
by photoirradiation.
λ (nm)
TrX
TrY
TrZ
f
528
430
418
378
339
302
284
265
254
245
226
-0.257
0.333
-0.428
-0.277
0.546
-0.228
-0.362
-0.516
0.616
-0.404
-0.190
0.245
-0.445
0.913
-0.387
0.206
0.295
1.085
0.262
0.119
0.073
-0.094
0.102
-0.110
0.031
-0.078
-0.114
0.014
0.162
0.101
0.168
0.190
0.763
0.135
0.120
0.244
1.037
0.192
0.119
-0.457
-0.210
-0.101
0.004
-0.366
Exp er im en ta l Section
Gen er a l Rem a r k s. 1H NMR spectra were recorded at 200
MHz unless otherwise noted, and a 600 MHz instrument was
used only for NOESY spectra. TSP was used as reference.
Circular dichroism spectra were measured with a CD spec-
tropolarimeter. A mercury lamp (1 kW) was used as a light
source. Monochromic light was obtained by passing light
through a monochromator.
Ma ter ia ls. 1,2-Bis(2-methylbenzo[b]thiophen-3-yl)hexaflu-
orocyclopentene (3)18 and 1,2-bis(2,4-dimethyl-5-phenylthien-
3-yl)hexafluorocyclopentene (4)19 were synthesized according
to the literature.
Sod iu m 2,2′-Dim eth yl-3,3′-(p er flu or ocyclop en ten e-1,2-
d iyl)bis(ben zo[b]th iop h en e-6-su lfon a te) (1a ). To a stir-
ring solution of 1.5 g of 3 (3.2 mmol) in 6 mL of CHCl3 was
added 0.6 mL of chlorosulfonic acid dropwise at room temper-
ature, and the reaction mixture was stirred for 1 h. The lower
layer was withdrawn and was poured into 100 mL of NaOH
aqueous solution. Saturated NaCl aqueous solution (100 mL)
was poured into the mixture, and the formed white precipitate
was collected by filtration. Recrystallization of the precipitate
from methanol afforded 1.68 g of 1a in 78% yield as white
powder: mp >400 °C; 1H NMR (D2O, 20 °C) δ 2.27 (s, 3.84 H,
ap), 2.55 (s, 2.16 H, p), 7.58-7.96 (m, 4H, ap and p), 8.14 (s,
0.72 H, p), 8.26 (s, 1.28 H, ap); although the spectrum shows
parallel (p) and antiparallel (ap) conformation separately,
these conformations exchange slowly relative to the NMR time
scale;19 MS m/z 673 (M+). Anal. Calcd for C23H12F6O6S4Na2‚
H2O: C, 40.00; H, 2.04. Found: C, 39.56; H, 2.27.
Sod iu m 2,2′,4,4′-Tetr a m eth yl-3,3′-(p er flu or ocyclop en -
ten e-1,2-d iyl)bis(th iop h en -5-yl(p h en yl-4-su lfon a te)) (2a ).
Compound 2a was synthesized from 4 in 66% yield in a
manner similar to that described for 1a . 2a : white powder;
mp >400 °C; 1H NMR (CD3OD, 20 °C) δ 2.12 (s, 3 H, ap), 2.18
(s, 3 H, p), 2.36 (s, 3 H, p), 2.41 (s, 3 H, ap), 7.47 (d, 4 H, J )
9 Hz), 7.87 (d, 4 H, J ) 9 Hz); although the spectrum shows
parallel (p) and antiparallel (ap) conformations separately,
these conformations exchange slowly relative to the NMR time
scale; MS m/z ) 753 (M + 1)+. Anal. Calcd for C29H20F6O6S4-
Na2‚2H2O: C, 44.20; H, 3.07. Found: C, 44.02; H, 3.25.
Qu a n tu m Yield Mea su r em en t. A water solution contain-
ing 1a was divided into four cells, and then R, â, and
γ-cyclodextrins were each added into the three cells. All four
solutions have the same absorption (∼0.3) at 313 nm. Upon
irradiation with 313 nm light, the absorption at 529 nm
increased. By comparing the relative rates of the initial
increases, we determined the relative quantum yields (the
experimental error included in the relative quantum yields was
less than 10%). The absolute quantum yields were determined
by using furylfulgide (Aberchrome-540) as a reference.25,26 We
F igu r e 9. Coordinates of 3a ((a) front view and (b) side view)
and 3b ((c) front view and (d) side view) for calculation.
The negative CD spectrum of the open-ring form at 212
nm corresponds to the calculated electric transitions
around 240 nm with large f values such as 244 and 241
nm. The transition at 244 nm is parallel to the C2
symmetry axis of 3a as shown in Figure 10a,b. The
NOESY spectrum of the complex of the open-ring form
1a and â-cyclodextrin indicates that the C2 symmetry
axis of 1a is perpendicular to the axis of â-cyclodextrin
when 1a is included in the cavity. Therefore, the CD
spectrum at around 212 nm shows negative.
On the other hand, the positive CD spectrum of the
closed-ring form at around 230 nm corresponds to the
calculated transition at 254 nm, which is the only
transition moment with a large f value as shown in Table
3. The transition moment is perpendicular to the C2
symmetry axis as shown in Figure 10c,d. Therefore, the
transition moment of 1b is parallel to the axis of
â-cyclodextrin, and the CD spectrum at 230 nm shows
positive. Figure 11 shows the schematic representation
of the transition moment change by photoirradiation. The
CD spectral change from negative to positive is due to
the transition moment change by the cyclization reaction
of the diarylethene.
As described above, the ring-opening and the ring-
closure reactions of diarylethenes are photoreversible.
The reversible CD change of a mixture of 1 and â-cyclo-
dextrin in aqueous solution by alternate irradiation with
313 nm (5 min) and >480 nm light (2 min) was demon-
strated as shown in Figure 12.
(24) We thank the Computer Center of Tokyo Institute of Technology
and the Institute for Molecular Science for their generous permission
to use IBM SP2 computers, DEC AlphaServer8400, and Cray C916/
12256 computers, respectively.
(25) Heller, H.G.; Langan, J . R. J . Chem. Soc., Perkin Trans. 2 1981,
341.
(26) Wintgens, V.; J ohnston, L. J .; Scaiano, J . C. J . Am. Chem. Soc.
1988, 110, 511.

9312 J . Org. Chem., Vol. 63, No. 25, 1998
Takeshita et al.
F igu r e 10. Calculated transition moment of the open-ring form of 3a at 244 nm ((a) front view and (b) side view) and the closed-
ring form of 3b at 254 nm ((c) front view and (d) side view) calculated with AM1-RPA.
F igu r e 11. Schematic representation of the transition mo-
ment change of a 1 and â-cyclodextrin complex by photoirra-
diation.
F igu r e 12. CD spectral change at 216 nm by alternate
compared the rates of increases at 494 nm (Aberchrome-540)
irradiation of a mixture of 1 (4.0 × 10-5 mol dm-3) and
and at 529 nm (1a ) by irradiation with 313 nm. By the use of
â-cyclodextrin (8.0 × 10-3 mol dm-3) in aqueous solution with
ꢀ values of both compounds (8200 and 9600 M-1cm-1, respec-
313 nm (5 min) and >480 nm light (2 min).
tively) the absolute quantum yields were determined.
Ca lcu la tion s. The structures were optimized by the AM1
phase approximation (RPA),23a using the AM1-RPA program.23b
The RPA calculations included the lowest 1000 single-excita-
tion configurations of the AM1 MOs. The RPA is particularly
well suited to calculating electronic transition moments and
oscillator strengths.23a The AM1-RPA method well reproduces
the experimental transition energies and oscillator strengths
of dyes and pigments.23b All the calculations were carried out
method27 of the MOPAC program package.28 The low-lying
singlet electronic excitations were calculated in the random-
(27) Dewar, M. J . S.; Zoebisch, E. G.; Healy, E. F.; Stewart, J . J . P.
J . Am. Chem. Soc. 1985, 107, 3902.
(28) Stewart, J . J . P. MOPAC Version 6.0, QCPE Program 455,
Department of Chemistry, Indiana University, Bloomington, IN 47405.

Photochromism of Dithienylethenes
J . Org. Chem., Vol. 63, No. 25, 1998 9313
using a Cray C90 computer at the computer center of Tokyo
Institute of Technology.
ported by a Grant-in-Aid for Encouragement of Young
Scientists (No. 09750956) from the Ministry of Educa-
tion, Science and Culture, J apan, and CREST of J apan
Science and Technology Corporation (J ST).
Ack n ow led gm en t. The authors are grateful to
Professor S. Mataka and co-workers at the Institute of
Advanced Material Study, Kyushu University, for mea-
surement of mass spectra. This work was partly sup-
J O981199P