Photochromism of diarylethenes with two nitronyl nitroxides: Photoswitching of an intramolecular magnetic interaction

Article abstract of DOI:10.1002/1521-3765(20010817)7:16<3466::AID-CHEM3466>3.0.CO;2-X

Photochromic diarylethenes that have p-phenylene-substituted benzothiophene aryl groups with and without nitronyl nitroxide radicals at both ends of the molecules were synthesized. The absorption maxima of the closed-ring isomers showed a hypsochromic shift with the increase in the π-conjugated chain length. The unique behavior was attributed to the stabilization by the resonant quinoid structures. Both photocyclization and photocycloreversion quantum yields of the diarylethene with nitronyl nitroxide radicals were found to increase with the increase in the π-conjugated chain length. Photoswitching of the magnetic interaction between two nitronyl nitroxide radicals was studied by means of ESR spectroscopy. The change in exchange interaction between open- and closed-ring isomers of 1,2-bis{6-{4-[4-(1-oxyl-3-oxide-4,4,5,5-tetramethylimidazolin-2-yl)phenyl] phenyl}-2-methyl-1-benzothiophen-3-yl}hexafluorocyclopentene was determined to be more than 30-fold.

Full text of DOI:10.1002/1521-3765(20010817)7:16<3466::AID-CHEM3466>3.0.CO;2-X

FULL PAPER
Photochromism of Diarylethenes with Two Nitronyl Nitroxides:
Photoswitching of an Intramolecular Magnetic Interaction
Kenji Matsuda* and Masahiro Irie*[a]
Abstract: Photochromic diarylethenes
that have p-phenylene-substituted ben-
zothiophene aryl groups with and with-
out nitronyl nitroxide radicals at both
ends of the molecules were synthesized.
The absorption maxima of the closed-
ring isomers showed a hypsochromic
shift with the increase in the p-conju-
gated chain length. The unique behavior
was attributed to the stabilization by the
resonant quinoid structures. Both pho-
tocyclization and photocycloreversion
quantum yields of the diarylethene with
nitronyl nitroxide radicals were found to
increase with the increase in the p-
conjugated chain length. Photoswitching
of the magnetic interaction between two
nitronyl nitroxide radicals was studied
by means of ESR spectroscopy. The
change in exchange interaction between
open- and closed-ring isomers of 1,2-
bis{6-{4-[4-(1-oxyl-3-oxide-4,4,5,5-tetra-
methylimidazolin-2-yl)phenyl]phenyl}-
2-methyl-1-benzothiophen-3-yl}hexa-
fluorocyclopentene was determined to
be more than 30-fold.
Keywords: EPR spectroscopy
´
magnetic properties ´ photochemis-
try ´ photochromism ´ pi-conjugat-
ed chain
interact magnetically.[3] If the p-conjugated chain length can
be switched by using a photochromic spin coupler, the
magnetic interaction can be controlled upon photoirradia-
tion.[4] For this purpose, diarylethenes are very effective
because the p-conjugated chain length is switched by the
photoirradiation (Figure 1). So far we have reported the
Introduction
Photochromic compounds reversibly change their molecular
properties upon photoirradiation, such as absorption and
fluorescence spectra, refractive indices, geometrical structures,
dielectric constants, oxidation/reduction potentials, and chirop-
tical properties. These property changes have been widely used
to switch the physical and chemical functions of molecular
systems that contain photochromic units.[1] Although various
types of photochromic compounds have been so far adopted as
the switching units, diarylethenes are among the most promising
compounds for molecular-scale memory and switch devices,
because of their fatigue-resistant and thermally irreversible pho-
tochromic performance.[2] The open- and closed-ring isomers
of the diarylethenes are substantially different in electronic
and geometrical structures. The most striking difference is
that while the p systems of the two aryl rings are separated in
the open-ring isomer, the closed-ring isomer has olefinic
electronic structure and the two p systems are connected to
each other and delocalize throughout the molecule.
Figure 1. Photoswitching of magnetic interaction.
photoswitching of intramolecular magnetic interaction using
diarylethene spin couplers evidenced by several methods, that
is, temperature dependence of the magnetic susceptibilities,[5]
temperature dependence of the ESR signal intensities at
cryogenic temperatures,[5] and ESR spectral change at room
temperature.[6] During the course of this study it was found
that the photochromic reactivity was affected by the intro-
duction of the radical moiety.[7] The cycloreversion reaction of
the diarylethenes with two nitronyl nitroxide radicals was
remarkably suppressed due to the contribution of the
resonant quinoid structure in the closed-ring isomer.
When two unpaired electrons are placed at both ends of a
p-conjugated chain, the two spins of the unpaired electrons
[a] Dr. K. Matsuda, Prof. Dr. M. Irie
In this work, we have synthesized several photochromic
diarylethenes that have different p-conjugated chain lengths
with and without nitronyl nitroxides and studied the photo-
switching of the magnetic interaction between two nitronyl
nitroxide radicals by an ESR method. Their photochromic
reactivity was also investigated.
Department of Chemistry and Biochemistry
Graduate School of Engineering, Kyushu University
and CREST, Japan Science and Technology Corporation
6-10-1 Hakozaki, Higashi-ku, Fukuoka, 812-8581 (Japan)
Fax : (‡81)92-642-3568
E-mail: kmatsuda@cstf.kyushu-u.ac.jp
irie@cstf.kyushu-u.ac.jp
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3466±3473
1:2:3:2:1 and a 7.5 G spacing. When two nitronyl nitroxides
are magnetically coupled with an exchange interaction, the
diradical gives a nine-line ESR spectrum with relative
intensities 1:4:10:16:19:16:10:4:1 and a 3.7 G spacing. If the
exchange interaction is smaller than the hyperfine coupling in
the diradical, two nitroxide radicals are magnetically inde-
pendent and give the spectrum that is the same as the
independent monoradical. In intermediate situations the
spectrum becomes complex.[8]
Results and Discussion
Molecular design and synthesis: For the core photochromic
spin coupler we chose 1,2-bis(2-methyl-1-benzothiophen-3-
yl)perfluorocyclopentene, which is one of the most robust
photochromic units. One or two p-phenylene spacers were
introduced at the both ends. Nitronyl nitroxide was used as
the spin source because the radical is p-conjugative. The
molecules synthesized are listed in Scheme 1.
Nitronyl nitroxide itself has two identical nitrogen atoms to
give a five-line ESR spectrum with relative intensities
In a previous report we found that the antiferromagnetic
interaction between two nitronyl nitroxides remarkably
increased from 2J/kB ˆ 2.2 K
to 2J/kB ˆ 11.6 K upon photo-
irradiation when the nitronyl
nitroxides are introduced to
both ends of 2 (Scheme 1),
while any photoinduced ESR
spectral change was not ob-
served, because the exchange
interaction between the two
radicals was much stronger than
the hyperfine coupling con-
stant.[5b] To decrease the intra-
molecular magnetic interaction
it is effective to elongate the p-
conjugated chain.
Compounds 3a ± 6a were
synthesized
according
to
Scheme 2. The synthesis of 1a
and 2a has been described pre-
viously.[5b, 9] Diiodo compound
7 was used as a common inter-
Scheme 1. Photochromic diarylethenes with two nitronyl nitroxides.
Scheme 2. Reagents and conditions: a) I2, H5IO6, H2SO4, AcOH, H2O, 76%. b) [Pd(PPh3)4], phenylboronic acid, Na2CO3, THF, H2O, 29%. c) [Pd(PPh3)4],
4-biphenylboronic acid, Na2CO3, THF, H2O, 32%. d) [Pd(PPh3)4], 4-formylphenylboronic acid, Na2CO3, THF, H2O, 49%. e) 2,3-Dimethyl-2,3-
bis(hydroxyamino)butane sulfate, methanol then NaIO4, CH2Cl2, 13%. f) n-BuLi, B(OBu)3, [Pd(PPh3)4], 4-formyl-4'-iodobiphenyl, Na2CO3, THF, H2O,
60%. g) 2,3-Dimethyl-2,3-bis(hydroxyamino)butane, benzene/methanol, NaIO4, CH2Cl2, 15%.
Chem. Eur. J. 2001, 7, No. 16
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FULL PAPER
Table 1. Absorption maxima and coefficients of the open-ring isomers
1a ± 6a in ethyl acetate.
mediate for the syntheses of 3a ± 6a. Suzuki coupling of 7 with
phenylboronic acid, 4-biphenylboronic acid, and 4-formyl-
phenylboronic acid afforded 3a, 5a, and 8, respectively.
Transformation of 7 to diboronic acid followed by Suzuki
coupling with 4-formyl-4'-iodobiphenyl gave diformyl com-
pound 9. The diformyl compounds were transformed to the
bis(nitronyl nitroxide) derivatives. It should be noted that
diarylethene skeleton is so persistent that many chemical
transformations can be applied. This is an advantage of
diarylethenes as building blocks of functional molecules. For
all compounds, the structures were confirmed by NMR and
ESR spectroscopy, and elementary analysis or mass spec-
trometry.
lmax [nm] (e [m 1 cm 1])
1a
2a
3a
4a
5a
6a
258 (16000), 290 (6200), 299 (6800)
309 (34000), 377 (16000), 553 (sh), 598 (630), 646 (630), 706 (sh)
284 (48000)
313 (76000), 377 (22000), 555 (sh), 600 (790), 644 (740), 718 (sh)
298 (69000)
320 (104000), 375 (sh), 550 (sh), 601 (720), 647 (690), 720 (sh)
Table 2. Absorption maxima and coefficients of the closed-ring isomers
1b ± 6b in ethyl acetate.
lmax [nm] (e [m 1 cm 1])
1b
2b
3b
4b
5b
6b
276 (14000), 352 (12000), 523 (10000)
280 (17000), 348 (19000), 385 (sh), 400 (20000), 565 (15000)
307 (20000), 381 (27000), 543 (21000)
280 (43000), 367 (44000), 553 (26000)
313 (23000), 389 (33000), 549 (24000)
311 (58000), 374 (58000), 548 (28000)
Photochromic reaction: All synthesized diarylethenes 1a ± 6a
underwent reversible photochromic reactions in ethyl acetate
by alternative irradiation with 313 nm UV light and 578 nm
visible light with retention of isosbestic points. Figures 2 and 3
Figure 2. Absorption spectral changes of a) 3 (3.3 Â 10 6 m) and b) 5 (2.6 Â
10 6 m) in ethyl acetate solution by photoirradiation: (solid line) open-ring
isomer, (dashed line) closed-ring isomer, and (dotted line) in the photo-
stationary state under irradiation with 313 nm light.
Figure 3. Absorption spectral changes of a) 4 (2.8 Â 10 6 m) and b) 6 (2.9 Â
10 6 m) in ethyl acetate solution by photoirradiation: (solid line) open-ring
isomer, (dashed line) closed-ring isomer, and (dotted line) in the photo-
stationary state under irradiation with 313 nm light.
illustrate absorption spectra of the open- and closed-ring
isomers, and of the photostationary state under irradiation
with 313 nm light for 3 ± 6. The color of the solutions changed
from colorless (1a, 3a, and 5a) or pale blue (2a, 4a, and 6a) to
red-purple (1b ± 6b). Although nitronyl nitroxide has absorp-
tion around 550 ± 700 nm, it did not prohibit the photochromic
reactions. Absorption maxima and coefficients of the open-
and closed-ring isomers are summarized in Tables 1 and 2.
The absorption maxima of the diarylethenes without
radicals (1, 3, and 5) shifted to longer wavelengths with
increasing p-conjugated chain length in both open- and
closed-ring isomers. On the other hand, in the case of
diarylethenes with two nitronyl nitroxide radicals (2, 4, and
6) the visible absorption maxima of the closed-ring isomers
showed a hypsochromic shift with the increase in the chain
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Photoswitches
3466±3473
length. This phenomenon is attributed to the fact that the
contribution of the resonant quinoid structure becomes
smaller as the chain length becomes longer (Scheme 3). The
of 2a. More interestingly, it is clearly shown that the cyclo-
reversion quantum yield increased from 0.0010 to 0.062 with
increasing the p-conjugated chain length. In this case besides
the effect of the energy trans-
fer, the contribution of the
resonant quinoid structure of
2b' to the closed-ring isomer is
considered to suppress the cy-
cloreversion reaction.
The conversion in the pho-
tostationary state was also de-
pendent on the chain length.
In the case of diarylethenes
without radicals, the conver-
sions increased with the in-
crease in the chain length. In
contrast, in the case of diaryl-
ethenes with two nitronyl ni-
troxide radicals, the longer
chain length gave smaller con-
versions. Since the conversions
are related to the quantum
Scheme 3. The resonant stabilization of the closed-ring isomers with two nitronyl nitroxide radicals.
yields by Equation (1), the
difference in conversions orig-
inates from the difference in
absorption spectrum of the visible band of 6b is similar to that
of 5b. This indicates that the contribution of the resonant
quinoid structure 6b' shown in Scheme 3 is very small in the
closed-ring isomer.
the quantum yields. The calculated conversions agreed well
with the experimental values.
FO!CeO
conversionO!C
ˆ
(1)
FO!CeO ‡ FC!OeO
Switching of ESR spectra: The changes in the ESR spectra
along with the photochromism were examined in diaryl-
ethenes 4 and 6. A solution of 4a in benzene was irradiated
with UV or visible light in the ESR cavity and their ESR
spectral changes were measured at room temperature. Fig-
ure 4 shows the ESR spectra at different stages of the
Quantum-yield measurements: The quantum yields of cycli-
zation and cycloreversion reactions of 3 ± 6 were measured in
ethyl acetate by using 1 as a reference.[10] The conversions
under irradiation with 313 nm light were determined by
comparing the UV-visible spectra of the isolated closed-ring
isomers and the sample at the photostationary state. The
results are summarized in Table 3.
Table 3. The quantum yields and conversions of cyclization and cyclo-
reversion reactions in ethyl acetate.
Cyclization (313 nm)
Conversion
Cycloreversion[a] (517 nm)
F
F
1
2
3
4
5
6
0.31[b]
0.040[b]
0.31
0.10
0.49
0.43[b]
1.00[b]
0.74
0.99
0.91
0.28[b]
0.0010[b]
0.14
0.012
0.14
0.13
0.87
0.062
[a] For all compounds the conversions of the cycloreversion reaction were
1.00. [b] Taken from ref.[5b].
Figure 4. X-band ESR spectra measured at room temperature at different
stages of the photochromic reaction starting from open-ring isomer 4a
(1.1 Â 10 4 m benzene solution, 9.32 GHz). a) Initial, b) after irradiation
with 366 nm light for 1 min, c) 4 min, d) after irradiation with l > 520 nm
light for 20 min, e) 50 min.
The quantum yields of the cyclization reactions of the
diarylethenes with two nitronyl nitroxide radicals increased
from 0.040 to 0.13 with the increase in the p-conjugated chain
length. The energy transfer from the central diarylethene to
the radical moiety is considered to reduce the quantum yield
photochromic reaction. The ESR spectrum of 4a is complex
with 15 lines. This result suggests that the two spins of nitronyl
nitroxide radicals are coupled by the exchange interaction
that is comparable to the hyperfine coupling constant. Upon
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M. Irie and K. Matsuda
FULL PAPER
irradiation with 366 nm light, the signal of nine lines at the
center grew, and after four minutes the spectrum reached the
photostationary state. The nine-line spectrum corresponds to
the closed-ring isomer 4b. The spectrum indicates that the
exchange interaction between the two spins in 4b is much
larger than the hyperfine coupling constant.
At the photostationary state the 15-line spectrum originat-
ing from 4a disappeared; this is consistent with the high
conversion as observed in the UV-visible absorption spectral
changes upon UV irradiation. When the sample was irradi-
ated with l > 520 nm light, the spectrum returned to the
original one. The double integral values of the spectra at
initial and photostationary state were almost identical,
indicating that there is no gain or loss of the amount of the
spins during the photochromic reaction (Figure 5). This also
indicates that the closed-ring isomer maintains the biradical
character and so the contribution of the mesomeric form 4b' is
very small.
and after two minutes there were no additional signals. This
five-line spectrum corresponds to the open-ring isomer 6a.
This spectrum indicates that the exchange interaction be-
tween the two spins in 6a is much smaller than the hyperfine
coupling constant. Then the sample was irradiated with
366 nm light. After ten minutes the sample reached the
photostationary state. The spectrum in the photostationary
state was very similar but not identical to that of closed-ring
isomer 6b. This is because the cyclization conversion in the
photostationary state was 87%. The cycle could be repeated
several times. The open-ring isomer 6a, the closed-ring isomer
6b, and the sample in the photostationary state had same
signal intensity determined by the double integral of the
spectra, indicating the conservation of the total number of the
spins (Figure 7).
Figure 7. ESR spectra of a) 6 in the photostationary state under irradiation
with 366 nm light, b) open-ring isomer 6a, and c) closed-ring isomer 6b
with double integrals.
The simulation of the ESR spectra was performed by using
the BIRADG program written by Dr. B. Kirste[11] in order to
estimate the exchange interaction. The nine-line spectrum of
4b and five-line spectrum of 6a were reproduced as j2J/gmB j
> 300 G (j2J/kB j> 0.04 K) and j2J/gmB j< 2 G (j2J/kB j< 3 Â
10 4 K), respectively. The ESR spectra of 4a and 6b were
complicated because the exchange interactions were compa-
rable to the hyperfine coupling constants. Even in such cases,
the simulation of the spectra can afford the value of the
exchange interaction. Figure 8 shows the experimental and
simulated spectra of 4a and 6b. The ESR spectrum of 6b was
reproduced with an exchange interaction of j2J/gmB jˆ 76 G
(j2J/kB jˆ 0.010 K).
Figure 5. ESR spectra of a) closed-ring isomer 4b and b) open-ring isomer
4a with double integrals.
Figure 6 shows the ESR spectra of a solution of 6 in
benzene along with the photochromic cycle. The ESR
spectrum of 6b, which was isolated by HPLC, showed a
distorted nine-line spectrum. Upon irradiation with l >
520 nm light, the signal was converted into five-line spectrum
In the case of 4a, two kinds of exchange interaction were
required to reproduce the experimental spectrum. It is well
known that the open-ring isomer of 1,2-bis(2-methyl-1-
benzothiophen-3-yl)perfluorocyclopentene has two atrop-
isomers, which are parallel and antiparallel conformers, in
the NMR timescale (Figure 9).[12] The parallel and antiparallel
isomers should have different exchange interactions between
spins. The ratio between parallel and antiparallel conformers
was 35:65 for 1,2-bis(2-methyl-1-benzothiophen-3-yl)per-
fluorocyclopentene. By taking this ratio into account, the
exchange interaction was determined to be j2J/gmB jˆ 9.0 G
(j2J/kB jˆ 1.2  10 3 K) for the antiparallel conformer and
j2J/gmB j< 2 G (j2J/kB j< 3 Â 10 4 K) for the parallel con-
former.
Figure 6. X-band ESR spectra measured at room temperature at different
stages of the photochromic reaction starting from closed-ring isomer 6b
(1.9 Â 10 4 m benzene solution, 9.32 GHz). a) Initial, b) after irradiation
with l > 520 nm light for 1 min, c) 2 min, d) after irradiation with 366 nm
light for 1 min, e) 10 min.
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Photoswitches
3466±3473
Figure 8. a) ESR spectra of open-ring isomer 4a (1.1 Â 10 4 m benzene solution, 9.32 GHz). b) Simulated spectrum of 4a (see text). c) ESR spectra of open-
ring isomer 6b (1.9 Â 10 4 m benzene solution, 9.32 GHz). d) Simulated spectrum of 6b (see text).
diradicals closed-ring isomers have stronger interaction than
open-ring isomers. The exchange interaction change in 2 was
only fivefold, while more than 30-fold change was observed in
6. Although the SQUID measurement is not sensitive for the
weakly coupled diradicals, the value of the exchange inter-
action could be precisely determined by simulating the ESR
spectrum of the diradical, in which the exchange interactions
are comparable to the hyperfine coupling constants. The
intrinsic change between open- and closed-ring isomers was
estimated to be more than 30-fold. This result shows a very
large switching effect of diarylethenes and consolidates the
superiority of diarylethenes as molecular switching units.
Although the absolute value of the exchange interaction is
small, the information of the spins can be clearly transmitted
through the closed-ring isomer and the switching can be
detected by ESR spectroscopy.
Figure 9. Parallel and antiparallel conformations of an open-ring isomer of
1,2-bis(2-methyl-benzothiophen-3-yl)perfluorocyclopentene.
The simulation of the ESR spectra does not afford the sign
of the exchange interaction, that is, whether the interaction is
ferromagnetic or antiferromagnetic. A spin polarization
model suggested that all the interactions in 2, 4, and 6 were
antiferromagnetic. The SQUID measurement of 2a and 2b
showed antiferromagnetic interaction between spins. Based
on these results we can infer all the interactions are
antiferromagnetic. In this photoswiching, the sign of the
interaction did not changed.
Conclusion
Table 4 lists the exchange interaction between two nitronyl
nitroxide radicals bridged by diarylethenes. The exchange
interaction decreases with increasing p-conjugated chain
length. By incorporating p-phenylene spacers, the interaction
could be detected by ESR spectroscopy. For all three
The diarylethenes with open-shell radical moieties were
synthesized and investigated photochemically and magneto-
chemically. It was proved that the photoreactivity was
perturbed by incorporating the open-shell moieties into the
diarylethenes. The photocycloreversion quantum yields of the
closed-ring isomers with two radicals was strongly suppressed
by the resonant quinoid structure. The considerably large
ESR spectral change, as large as 30-fold, upon photoirradia-
tion was observed due to the change in the exchange
interaction.
Table 4. The change of the ESR line shapes and exchange interactions
(j2J/kB K j ) between the open- and closed-ring isomers.
Open-ring isomer
Closed-ring isomer
ESR line shape j 2J/kB K j
ESR line shape
j 2J/kB K j
11.6[a,b]
> 0.04
0.010
2
4
6
9 lines[a]
15 lines
5 lines
2.2[a,b]
9 lines[a]
9 lines
distorted 9 lines
Experimental Section
1.2 Â 10 3, <3 Â 10
4
4
< 3 Â 10
Materials: 1H NMR spectra were recorded on a Varian Gemini 200 and
JEOL GSX400 instruments. UV-visible spectra were recorded on a Hitachi
U-3500 Spectrophotometer. Mass spectra were obtained by a JEOL JMS-
[a] Taken from ref. [5b]. [b] Determined by magnetic susceptibility measure-
ment.
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M. Irie and K. Matsuda
FULL PAPER
HX110A instrument. Melting points are not corrected. All reactions were
monitored by thin-layer chromatography carried out on 0.2 mm Merck
silica gel plates (60F-254). Column chromatography was performed on
silica gel (Merck, 70 ± 230 mesh).
Purification was performed by column chromatography (silica, chloroform/
Et2O 9:1) followed by GPC, and then recrystallization from CH2Cl2/hexane
by diffusion method in the dark. Compound 4a was obtained as a dark blue
solid (100 mg, 13%). M.p. 210.0 ± 211.08C (decomp); UV/Vis (AcOEt):
lmax (e) ˆ 313 (76000), 377 (22000), 555 (sh), 600 (790), 644 (740), 718 nm
(sh); ESR (benzene): complicated, 15 lines, g ˆ 2.007; FAB HRMS (m/z)
1,2-Bis(6-iodo-2-methyl-1-benzothiophen-3-yl)hexafluorocyclopentene
(7): Iodine (1.2 g, 4.0 mmol) and H5IO6 (0.39 g, 1.5 mmol) was added to a
stirred solution of 1a (2.0 g, 4.3 mmol) in acetic acid (150 mL), sulfuric acid
(3 mL), and water (7 mL), and the mixture was stirred for 3 h at 708C in the
open air. The reaction mixture was poured into 500 mL of ice-water. The
mixture was extracted with AcOEt, and the organic layer was washed with
water, an aqueous solution of NaHCO3, and an aqueous solution sodium
thiosulfate, and dried over MgSO4. The solvent was evaporated, and the
residue was purified by short-path column chromatography (silica, hexane)
and successively by digestion from hexane. Diiodo compound 7 (2.3 g,
76%) was obtained as a white solid. M.p. 194.5 ± 195.08C; 1H NMR
(CDCl3, 200 MHz) parallel conformer: d ˆ 2.46 (s, 6H), 7.22, (d, J ˆ 9 Hz,
2H), 7.48 (d, J ˆ 9 Hz, 2H), 7.96 (s, 2H); antiparallel conformer: d ˆ 2.18 (s,
6H), 7.36 (d, J ˆ 9 Hz, 2H), 7.65 (d, J ˆ 9 Hz, 2H), 8.03(s, 2H); parallel/
‡
[M‡H] calcd for C49H45F6N4O4S2: 931.2786; found 931.2739; elemental
analysis calcd (%) for C49H44F6N4O4S2: C 63.2, H 4.8, N, 6.0; found C 63.5,
H 5.2, N 5.7.
Closed-ring isomer 4b: UV/Vis (AcOEt): lmax (e) ˆ 280 (43000), 367
(44000), 553 (26000); ESR (benzene): 1:4:10:16:19:16:10:4:1, 9 lines, g ˆ
2.007, aN ˆ 3.7 G.
1,2-Bis{6-[4-(4-formylphenyl)phenyl]-2-methyl-1-benzothiophen-3-yl}hexa-
fluorocyclopentene (9): n-Butyllithium in hexane (1.6m, 1.0 mL, 1.6 mmol)
was added to a solution of 7 (510 mg, 0.71 mmol) in THF (10 mL) at
788C. After the mixture was stirred for 1 h at 788C, tri-n-butylborate
(0.8 mL, 3.0 mmol) was added. The solution was allowed to warm to 108C
with stirring. Water (3 mL) was added to the reaction mixture followed by
addition of [Pd(PPh3)4] (80 mg, 0.07 mmol), Na2CO3 (2.4 g), water (10 mL),
and 4-formyl-4'-iodobiphenyl (1.1 g, 3.5 mmol). The reaction mixture was
heated under reflux 12 h. The reaction mixture was poured into water,
extracted with AcOEt, washed with water, dried over magnesium sulfate,
and concentrated. Column chromatography (dichloromethane) gave com-
pound 9 (350 mg, 60%) as a white powder. M.p. 263.0 ± 264.08C; 1H NMR
(CDCl3, 400 MHz): d ˆ 2.29 (s, 3.9H), 2.55 (s, 2.1H), 7.50 ± 8.00 (m, 22H),
‡
antiparallel ˆ 35:65; FAB HRMS (m/z) [M] calcd for C23H12F6I2S2:
719.8374; found 719.8376.
1,2-Bis(6-phenyl-2-methyl-1-benzothiophen-3-yl)hexafluorocyclopentene
(3a): [Pd(PPh3)4] (175 mg, 0.15 mmol), Na2CO3 (2.5 g), water (10 mL), and
phenylboronic acid (600 mg, 4.0 mmol) was added to a solution of 7 (1.2 g,
1.1 mmol) in THF (10 mL). The reaction mixture was heated under reflux
24 h. The reaction mixture was poured into water, extracted with Et2O,
washed with water, dried over magnesium sulfate, and concentrated.
Column chromatography (hexane/dichloromethane 3:1) gave 3a (290 mg,
29%) as a white solid. 1H NMR (CDCl3, 400 MHz): d ˆ 2.25 (s, 3.9H), 2.50
(s, 2.1H), 7.3 ± 7.9 (m, 16H); UV/Vis (AcOEt): lmax (e) ˆ 284 nm (48000);
‡
10.05 (s, 0.35H), 10.08 (s, 0.65H); FAB HRMS (m/z) [M‡H] calcd for
C49H30F6O2S2: 828.1591; found 828.1594.
1,2-Bis{6-{4-[4-(1-oxyl-3-oxide-4,4,5,5-tetramethylimidazolin-2-yl)phenyl]-
phenyl}-2-methyl-1-benzothiophen-3-yl}exafluorocyclopentene (6a):
A
‡
FAB HRMS (m/z) [M] calcd for C35H22F6S2: 620.1067; found 620.1059.
solution of 9 (100 mg, 0.12 mmol), 2,3-bis(hydroxyamino)-2,3-dimethylbu-
tane sulfate (300 mg, 1.2 mmol), and potassium carbonate (170 mg,
1.2 mmol) in benzene (10 mL) and methanol (3 mL) was heated under
reflux for 15 h. The reaction mixture was poured into water, extracted with
ethyl acetate, washed with water, dried over magnesium sulfate,and
concentrated to give tetrahydroxylamine as yellow oil. Purification was
not performed. A solution of sodium periodate (120 mg, 0.57 mmol) in
water (30 mL) was added to a solution of tetrahydroxylamine in dichloro-
methane (30 mL), and the reaction mixture was stirred for 30 min in the
open air. The organic layer was separated, washed with water, dried over
magnesium sulfate, and concentrated. Purification was performed by
column chromatography (silica, chloroform/Et2O 1:1). Compound 6a was
obtained as a dark blue solid (20 mg, 15%). UV/Vis (AcOEt): lmax (e) ˆ
320 (104000), 375 (sh), 550 (sh), 601 (720), 647 (690), 720 nm (sh); ESR
Closed-ring isomer 3b: 1H NMR (CDCl3, 400 MHz): d ˆ 2.08 (s, 6H), 7.3 ±
8.0 (m, 16H); UV/Vis (AcOEt): lmax (e) ˆ 307 (20000), 381 (27000),
543 nm (21000).
1,2-Bis[6-(4-biphenyl)-2-methyl-1-benzothiophen-3-yl]hexafluorocyclo-
pentene (5a): [Pd(PPh3)4] (80 mg, 0.07 mmol), Na2CO3 (1.2 g), water
(5 mL), and 4-biphenylboronic acid (550 mg, 2.78 mmol) was added to a
solution of 7 (500 mg, 0.69 mmol) in THF (5 mL). The reaction mixture was
heated under reflux 24 h. The reaction mixture was poured into water,
extracted with ethyl acetate, washed with water, dried over magnesium
sulfate, and concentrated. Column chromatography (hexane/dichlorome-
thane 4:1) gave 5a (170 mg, 32%) as a white solid. M.p. 278.5 ± 279.58C;
1H NMR (CDCl3, 400 MHz): d ˆ 2.28 (s, 3.9H), 2.54 (s, 2.1H), 7.3 ± 8.0 (m,
24H); UV/Vis (AcOEt): lmax (e) ˆ 298 nm (69000); FAB HRMS (m/z)
‡
(benzene): 1:2:3:2:1, 5 lines, g ˆ 2.007, aN ˆ 7.5 G; FAB MS (m/z) [M‡H]
‡
[M] calcd for C47H30F6S2: 772.1693; found 772.1690.
calcd for C61H53F6N4O4S2: 1083; found 1083.
Closed-ring isomer 5b: 1H NMR (CDCl3, 400 MHz): d ˆ 2.10 (s, 6H), 7.3 ±
8.1 (m, 24H); UV/Vis (AcOEt): lmax (e) ˆ 313 (23000), 389 (33000),
549 nm (24000).
Closed-ring isomer 6b: UV/Vis (AcOEt): lmax (e) ˆ 311 (58000), 374
(58000), 553 nm (28000); ESR (benzene): 1:4:10:16:19:16:10:4:1, 9 lines,
g ˆ 2.007, aN ˆ 3.9 G.
Photochemical measurements: Absorption spectra were measured on a
spectrophotometer (Hitachi U-3500). Photoirradiation was carried out by
using a USHIO 500 W super high-pressure mercury lamp or a USHIO
500 W xenon lamp. Mercury lines of 313 and 578 nm were isolated by
passing the light through a combination of Toshiba band-pass filter (UV-
D33S) or sharp-cut filter (Y-52) and monochrometer (Ritsu MC-20L).
Photoirradiation in the ESR cavity was performed by using a 200 W fiber
mercury-Xe lamp with band-pass filter or sharp-cut filter.
1,2-Bis[6-(4-formylphenyl)-2-methyl-1-benzothiophen-3-yl]hexafluorocy-
clopentene (8): [Pd(PPh3)4] (175 mg, 0.15 mmol), Na2CO3 (2.5 g), water
(10 mL), and 4-formylphenylboronic acid (600 mg, 4.0 mmol) was added to
a solution of 7 (1.2 g, 1.1 mmol) in THF (10 mL). The reaction mixture was
heated under reflux for 24 h. The reaction mixture was poured into water,
extracted with Et2O, washed with water, dried over magnesium sulfate, and
concentrated. Column chromatography (silica, dichloromethane/Et2O 3:1)
gave diformyl compound 8 (540 mg, 49%) as a white solid. 1H NMR
(CDCl3, 400 MHz): d ˆ 2.28 (s, 3.9H), 2.55 (s, 2.1H), 7.48 ± 7.99 (m, 14H),
ESR spectroscopy: A Bruker ESP300E spectrometer was used to obtain
X-band ESR Spectra. The sample was dissolved in benzene and degassed
with Ar bubbling for 5 min.
‡
10.03 (s, 0.35H), 10.07 (s, 0.65H); FAB HRMS (m/z) [M‡H] calcd for
C37H23F6O2S2: 677.1044; found 677.1074.
1,2-Bis{6-[4-(1-oxyl-3-oxide-4,4,5,5-tetramethylimidazolin-2-yl)phenyl]-2-
methyl-1-benzothiophen-3-yl}hexafluorocyclopentene (4a): A solution of 8
(540 mg, 0.80 mmol), 2,3-bis(hydroxyamino)-2,3-dimethylbutane sulfate
(2 g, 8.0 mmol), and potassium carbonate (1.1 g, 8 mmol) in methanol
(60 mL) was heated under reflux for 24 h. The reaction mixture was poured
into water, extracted with ethyl acetate, washed with water, dried over
magnesium sulfate, and concentrated to give tetrahydroxylamine as yellow
oil. Purification was not performed. A solution of sodium periodate
Acknowledgement
We thank Professor Paul M. Lahti and Professor B. Kirste for the program
BIRADG, which they made available to us. This work was supported by
CREST of Japan Science and Technology Corporation and by a Grant in
Aid for Scientific Research on Priority Area ªCreation of Delocalized
Electronic Systemsº (No. 12020244) from the Ministry of Education,
Science, Culture, and Sports (Japan).
(520 mg, 2.4 mmol) in water (100 mL) was added to
a solution of
tetrahydroxylamine in dichloromethane (60 mL), and the reaction mixture
was stirred for 30 min in the open air. The organic layer was separated,
washed with water, dried over magnesium sulfate, and concentrated.
3472
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Chem. Eur. J. 2001, 7, No. 16

Photoswitches
3466±3473
[1] Photocontrol of physical properties by photochromic molecules:
a) ªPhotochromism: Memories and Switchesº: Chem. Rev. 2000, 100,
whole of issue 5; b) G. H. Brown, Photochromism, Wiley-Inter-
science, New York, 1971; c) H. Dürr, H. Bouas-Laurent, Photo-
chromism: Molecules and Systems, Elsevier, Amsterdam, 1990; d) J.-P.
Desvergne, H. Bouas-Laurent, J. Chem. Soc. Chem. Commun. 1978,
403; e) M. Blank, L. M. Soo, N. H. Wasserman, B. F. Erlanger, Science
1981, 214, 70; f) M. Irie, Y. Hirano, S. Hashimoto, K. Hayashi,
Macromolecules 1981, 14, 262; g) M. Irie, M. Kato, J. Am. Chem. Soc.
1985, 107, 1024; h) S. Shinkai, Pure Appl. Chem. 1987, 59, 425; i) K.
Ichimura, Y. Suzuki, T. Seki, A. Hosoki, K. Aoki, Langmuir 1988, 4,
1214; j) M. Irie, Adv. Polym. Sci. 1990, 94, 27; k) M. Irie, Adv. Polym.
Sci. 1993, 110, 49; l) T. Ikeda, T. Sasaki, K. Ichimura, Nature 1993, 361,
428; m) S. L. Gilat, S. H. Kawai, J.-M. Lehn, J. Chem. Soc. Chem.
Commun. 1993, 1439; n) Y. Atassi, J. A. Delaire, K. Nakatani, J. Phys.
Chem. 1995, 99, 16320; o) S. L. Gilat, S. H. Kawai, J.-M. Lehn, Chem.
Eur. J. 1995, 1, 275; p) M. Takeshita, M. Irie, J. Org. Chem. 1998, 63,
6643; q) T. Kawai, T. Kunitake, M. Irie, Chem. Lett. 1999, 905.
[2] a) M. Irie, Chem. Rev. 2000, 100, 1685; b) M. Irie, K. Uchida, Bull.
Chem. Soc. Jpn. 1998, 71, 985.
35, 3975; k) W. Fujita, K. Awaga, J. Am. Chem. Soc. 1997, 119, 4563;
l) K. Hamachi, K. Matsuda, T. Itoh, H. Iwamura, Bull. Chem. Soc. Jpn.
Â
1998, 71, 2937; m) J.-F. Letard, P. Guionneau, L. Rabardel, J. A. K.
Howard, A. E. Goeta, D. Chasseau, O. Kahn, Inorg Chem. 1998, 37,
4432; n) M.-L. Boillot, S. Chantraine, J. Zarembowitch, J.-Y. Lalle-
Â
mand, J. Prunet, New J. Chem. 1999, 179; o) J.-F. Letard, J. A. Real, N.
Moliner, A. B. Gaspar, L. Capes, O. Cador, O. Kahn, 1999, 121, 10630;
p) T. Ojima, H. Akutsu, J.-i. Yamada, S. Nakatsuji, Chem. Lett. 2000,
918; q) S. Nakatsuji, Y. Ogawa, S. Takeuchi, H. Akutsu, J.-i. Yamada,
A. Naito, K. Sudo, N. Yasuoka, J. Chem. Soc. Perkin Trans. 2 2000,
1969; r) S. Hayami, Z.-Z. Gu, M. Shiro, Y. Einaga, A. Fujishima, O.
Sato, J. Am. Chem. Soc. 2000, 122, 7126; s) E. Breuning, M. Ruben, J.-
M. Lehn, F. Renz, Y. Garcia, V. Ksenofontov, P. Gütlich, E. K.
Wegelius, K. Rissanen, Angew. Chem. 2000, 112, 2563; Angew. Chem.
Int. Ed. 2000, 39, 2504.
[5] a) K. Matsuda, M. Irie, Chem. Lett. 2000, 16; b) K. Matsuda, M. Irie, J.
Am. Chem. Soc. 2000, 122, 7195.
[6] K. Matsuda, M. Irie, J. Am. Chem. Soc. 2000, 122, 8309.
[7] K. Matsuda, M. Irie, Tetrahedron Lett. 2000, 41, 2577.
Á
[8] a) R. Briere, R.-M. Dupeyre, H. Lemaire, C. Morat, A. Rassat, P. Rey,
[3] O. Kahn, Molecular Magnetism, VCH, New York, 1993.
Bull. Soc. Chim. France 1965, 11, 3290; b) S. H. Glarum, J. H.
Marshall, J. Chem. Phys. 1967, 47, 1374.
[9] M. Hanazawa, R. Sumiya, Y. Horikawa, M. Irie, J. Chem. Soc. Chem.
Commun. 1992, 206.
[10] K. Uchida, E. Tsuchida, Y. Aoi, S. Nakamura, M. Irie, Chem. Lett.
1999, 63.
[11] B. Kriste, Anal. Chim. Acta 1992, 265, 191.
[12] a) M. Irie, O. Miyatake, K. Uchida, T. Eriguchi, J. Am. Chem. Soc.
1994, 116, 9894; b) M. Takeshita, N. Kato, S. Kawauchi, T. Imase, J.
Watanabe, M. Irie, J. Org. Chem. 1998, 63, 9306.
[4] Photocontrol of magnetic properties: a) S. Decurtins, P. Gütlich, C. P.
Köhler, H. Spiering, A. Hauser, Chem. Phys. Lett. 1984, 105, 1; b) S.
Decurtins, P. Gütlich, K. M. Hasselbach, A. Hauser, H. Spiering,
Inorg. Chem. 1985, 24, 2174; c) A. Hauser, Chem. Phys. Lett. 1986,
124, 543; d) A. Hauser, J. Chem. Phys. 1991, 94, 2741; e) A. Hauser, A.
Vef, P. Adler, J. Chem. Phys. 1991, 95, 8710; f) T. Buchen, P. Gütlich,
H. A. Goodwin, Inorg. Chem. 1994, 33, 4573; g) P. Gütlich, A. Hauser,
H. Spiering, Angew. Chem. 1994, 106, 2109; Angew. Chem. Int. Ed.
Engl. 1994, 33, 2024; h) O. Sato, T. Iyoda, A. Fujishima, K. Hashimoto,
Science 1996, 272, 704; i) Z.-Z. Gu, O. Sato, T. Iyoda, T. K. Hashimoto,
A. Fujishima, J. Phys. Chem. 1996, 100, 18289; j) M.-L. Boillot, C.
Á
Roux, J.-P. Audiere, A. Dausse, J. Zarembowitch, Inorg. Chem. 1996,
Received: January 22, 2001 [F3013]
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