Photochromism of Diarylethenes Linked by Hydrogen Bonds in the Single-Crystalline Phase

Article abstract of DOI:10.1002/chem.200304947

Photochromic diarylethenes, which bear carboxyl groups at the ortho, meta, or para positions of both terminal phenyl groups, have been synthesized. The diarylethenes adopt linear chain structures as a result of hydrogen bonding in the crystalline phase, a

Full text of DOI:10.1002/chem.200304947

FULL PAPER
Photochromism of Diarylethenes Linked by Hydrogen Bonds
in the Single-Crystalline Phase
Satoshi Yamamoto, Kenji Matsuda, and Masahiro Irie*[a]
Abstract: Photochromic diarylethenes,
which bear carboxyl groups at the ortho,
meta, or para positions of both terminal
phenyl groups, have been synthesized.
The diarylethenes adopt linear chain
structures as a result of hydrogen bond-
ing in the crystalline phase, and the
crystals exhibit photochromic proper-
ties. The absorption maximum of the
photogenerated closed-ring isomer of
the para-substituted derivative shows
an 80 nm bathochromic shift in compar-
ison with that of the ortho-substituted
derivative. The maximum of the closed-
ring isomer of the meta-substituted de-
rivative is located in between those of
the para- and ortho-substituted deriva-
tives. The shifts can be attributed to the
differences in conformation among the
derivatives, arising from the restrictions
imposed by the hydrogen-bonded
chains.
Keywords:
diarylethene
¥
photochromism ¥ hydrogen bonding
¥ X-ray analysis
Hydrogen-bonded networks represent one of the most
convenient methods for constructing supramolecular archi-
tectures.[7] The direction-specific character of hydrogen-bond-
ing is successfully utilized to construct double helices, ring
structures, and nanotubes.[8, 9] The geometry of the photo-
generated closed-ring isomers in the crystals reflects the
crystal packing of the open-ring isomers.[3] Therefore, if
desired, crystal packing could be designed on the basis of
hydrogen-bonded supramolecular assemblies, and the spec-
troscopic properties of the photochromic crystal would be
controlled. Herein, we report on the synthesis and photo-
chromic performance of intermolecularly hydrogen-bonded
diarylethenes. The effect of the hydrogen bonding on the
photochromic performance has been studied in the crystalline
phase.
Introduction
Photochromic compounds inherently exhibit two different
chemical forms, which are reversibly interconverted upon
irradiation with light of appropriate wavelength.[1] Various
types of photochromic compounds, such as spirobenzopyrans,
azobenzenes, fulgides, and diarylethenes, have hitherto been
developed. Among such compounds, diarylethenes show
characteristic properties, including thermal stability of both
isomers and fatigue-resistant performance.[2] The open-ring
isomer of the diarylethene undergoes photocyclization to
produce the closed-ring isomer upon irradiation with UV
light, and the closed-ring isomer reverts to the open-ring
isomer upon irradiation with visible light.
Some diarylperfluorocyclopentene derivatives having thio-
phene or benzothiophene rings are known to undergo photo-
chromic reactions even in the single-crystalline phase.[3] An
antiparallel conformation of the aryl groups and a short
distance between the reactive carbons are essential for the
reaction to take place in the crystalline phase.[4] The color and
the photocycloreversion reactivity of the closed-ring isomers
are dependent on the conformation of the molecule in the
crystal.[5] The closed-ring isomer photogenerated in the crystal
generally shows a bathochromic shift with respect to the
closed-ring isomer in solution.[6]
Results and Discussion
Molecular design and synthesis: When molecules have two
carboxyl groups that cannot participate in intramolecular
hydrogen bonding, the formation of hydrogen-bonded linear
chain structures in aprotic solvents as well as in the crystal
may be anticipated. 1,2-Bis(2-methyl-5-phenyl-3-thienyl)hex-
afluorocyclopentene, which is known to undergo photochro-
mic reaction even in the crystalline phase,[3d] was chosen as the
photochromic core and carboxyl groups were introduced at
the ortho, meta, and para positions of both of the terminal
phenyl groups (Scheme 1). As reference compounds, diaryl-
ethenes 4a 6a bearing formyl substituents, which are similar
in size but have less hydrogen-bonding character as compared
to carboxyl groups, were also prepared.
[a] Prof. M. Irie, S. Yamamoto, Dr. K. Matsuda
Department of Chemistry and Biochemistry
Graduate School of Engineering, Kyushu University
Hakozaki 6-10-1, Higashi-ku, Fukuoka 812-8581 (Japan)
E-mail: irie@cstf.kyushu-u.ac.jp
Supporting information for this article is available on the WWW under
http://www.chemeurj.org or from the author.
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¹ 2003 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
DOI: 10.1002/chem.200304947
Chem. Eur. J. 2003, 9, 4878 4886

4878 4886
Compounds 1a 3a are an-
ticipated to form intermolecu-
lar hydrogen-bonded chains in
solution in aprotic solvents as
well as in the crystalline phase.
Intramolecular hydrogen-bond-
ing is essentially precluded be-
cause of the strained conforma-
tion.
Photochromic behavior of com-
pounds 1 6 in protic or aprotic
solvents: The photochromic re-
activity of diarylethenes 1
6
was examined in ethanol solu-
tion. Figure 1 shows the
changes in the absorption spec-
tra upon photoirradiation.
Upon irradiation with 313 nm
Scheme 1. Photochromic diarylethenes having intermolecular hydrogen-bonding sites.
light, the colorless solutions
containing 1a 6a turned blue
The synthetic procedure leading to 1a 6a is shown in
Scheme 2. Suzuki coupling of three isomeric bromobenzalde-
hydes with thiophene boronic acid gave formylphenylthio-
phene derivatives (8 10). After protection of compounds 8
10 with ethylene glycol, they were lithiated and then coupled
with octafluorocyclopentene to give diarylethene derivatives
(14 16). Deprotection gave formyl-substituted diarylethene
derivatives (4a 6a). Jones oxidation of the formyl-substitut-
ed derivatives (4a 6a) afforded carboxyl-substituted diaryl-
ethenes (1a 3a). The structures of 1a 6a were confirmed by
1H NMR spectroscopy, mass spectrometry, elemental analysis,
and UV/Vis spectroscopy.
or purple. These colors could be attributed to the formation of
the closed-ring isomers. Upon irradiation with 578 nm light,
the colored solutions reverted to their original colorless forms.
Table 1 shows the absorption maxima of the open- and closed-
ring isomers in ethanol. When the substituents are in the same
positions, the absorption maxima of diarylethenes bearing
carboxyl groups are similar to those of the derivatives bearing
formyl groups.
Table 1 also shows the maxima in aprotic cyclohexane. The
absorption maxima in ethanol and cyclohexane are similar. In
other words, Dlmax is small, except in the case of the ortho-
substituted derivative 3b, for which a considerable spectral
Scheme 2. Synthetic scheme used to obtain 1a 6a. Reagents and conditions: a) i) nBuLi, ii) tri-n-butyl borate, iii) Pd(PPh3)4, o-, m-, and p-
bromobenzaldehydes, Na2CO3, THF, H2O, 48 64%. b) ethylene glycol, p-toluenesulfonic acid monohydrate, benzene, 96%. c) i) nBuLi, ii) octafluor-
ocyclopentene, THF, 72 76%. d) PPTS, acetone, 96 98%. e) Jones× reagent, acetone, 70 87%.
Chem. Eur. J. 2003, 9, 4878 4886
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M. Irie
FULL PAPER
The packing diagrams of diary-
lethenes 1 3 in the crystalline
phase: Diarylethenes 1a 6a
formed clear colorless single
crystals upon recrystallization
from appropriate solvents.
Their molecular structures and
crystal packing were deter-
mined by X-ray crystallog-
raphic analysis. Table 2 shows
the X-ray crystallographic
data at 123 K. These single
crystals of the open-ring iso-
mers did not contain any sol-
vent.
Figure 2 shows the packing
diagrams of carboxyl-substitut-
ed diarylethenes 1a 3a. One-
dimensional hydrogen-bonded
chains were observed in their
single crystals. The distances
between carbonyl oxygen and
À
hydroxyl oxygen O ¥¥¥ H O in
1a 3a were 2.61 ä, 2.63 ä,
and 2.64 ä, respectively. These
sufficiently short distances in-
dicate that the carboxyl-substi-
tuted diarylethenes form hy-
drogen-bonded arrays with ad-
jacent molecules in the crystals.
The chains have twofold helical
symmetry and the position of
substitution changes the pitch.
The zigzag chain of ortho de-
rivative 3a shows the shortest
pitch.
Figure 1. Photochromic spectral changes of 1a 6a in ethanol solution before (dotted line) and after (solid line)
photoirradiation with light of wavelength 313 nm: a) 1a; b) 2a; c) 3a; d) 4a; e) 5a; f) 6a.
Figure 3 shows ORTEP
drawings of the molecular
structures of 1a 3a. The numbering of the atoms is the same
for all three molecules. Each of the compounds 1a 3a was
found to be packed in an antiparallel conformation in the
crystal. The distances between the reactive carbon atoms,
Table 1. Absorption maxima of the open- and closed-ring isomers in
ethanol and cyclohexane.
lmax (open)
lmax (closed)
lmax (closed)
in ethanol [nm]
in cyclohexane [nm]
in ethanol [nm]
1
2
3
4
5
6
312
278
273
330
289
270
598
584
567
605
585
553
600
580
546
601
581
549
À
C1 C10, are 3.49 ä (1a), 3.52 ä (2a), and 3.59 ä (3a), which
are short enough for the reaction to take place in the single-
crystalline phase (Table 3).[4] The angles between the planes of
the phenyl and thiophene rings are quite different among
these compounds. The angles C3-C4-C16-C17 were found to
be 32.58 (1a), 11.98 (2a), and À51.98 (3a), respectively. The
angles in 1a and 3a thus differ by more than 848. In meta-
substituted 2a, the phenyl and thiophene rings are co-
planar.
shift (Dlmax ˆ 21 nm) is observed between the protic and
aprotic solvents. When a small amount of ethanol was added
dropwise to a solution of 3b in cyclohexane, a bathochromic
shift of the maximum was observed. This finding suggests that
hydrogen bonding affects the conformation of the closed-ring
isomer of ortho derivative 3b. In the cases of the para and
meta derivatives 1b and 2b, no solvent dependence was
observed. This indicates that the contribution from intermo-
lecular hydrogen bonding is negligible for 1b and 2b in
solution.
Formyl-substituted diarylethenes (4a 6a) are also packed
in an antiparallel conformation in their single crystals. The
distances between the reactive carbon atoms were found to be
3.65 ä (4a), 3.54 ä (5a), and 3.66 ä (6a). In these derivatives,
intermolecular hydrogen bonding was not discerned. The
angles between the planes of the phenyl and thiophene rings,
C3-C4-C16-C17, were found to be similar, at 258 (4a), 33.98
(5a), and 33.78 (6a).
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Photochromism of Diarylethenes
4878 4886
Table 2. Crystallographic data of 1a 6a.
1a (para)
2a (meta)
3a (ortho)
4a (para)
5a (meta)
6a (ortho)
recrystallization solvent
empirical formula
formula weight
temperature [K]
crystal system
space group
a [ä]
b [ä]
c [ä]
a [8]
2-propanol/THF
methanol
C29H18F6S2O4
608.55
123
monoclinic
C2/c
23.694
8.488
13.483
90
acetonitrile/THF
C29H18F6S2O4
608.55
123
triclinic
P-1
8.379
11.003
14.809
91.154
acetonitrile
C29H18F6S2O2
576.55
123
monoclinic
C2/c
25.936
9.198
10.368
90
acetonitrile
C29H18F6S2O2
576.55
123
monoclinic
P21
8.3543(18)
13.106(3)
11.347(3)
90
acetonitrile
C29H18F6S2O2
576.55
123
monoclinic
C2/c
17.057
8.4761
18.152
90
C29H18F6S2O4
608.55
123
monoclinic
P21/c
15.561
12.833
14.501
90
b [8]
g [8]
volume [ä3]
Z
116.235
90
2597.5(5)
4
100.279
90
2668(3)
4
95.179
100.825
90
2429.4(12)
4
93.389(4)
90
1240.3(5)
2
104.260
90
2543.5(8)
4
110.575
1271.0(8)
2
goodness-of-fit on F 2
data/restraints/parameters
R1 [I > 2s(I)]
wR2 (all data)
0.910
1.127
0.986
5270/0/372
0.0706
1.065
1.098
3536/1/354
0.0488
1.008
5551/0/380
0.0448
0.1250
2862/0/219
0.0659
0.1903
2531/0/167
0.0777
0.2373
2674/0/204
0.0392
0.1071
0.1976
0.1293
Figure 2. X-ray structures of one-dimensional linear chains of carboxyl-substituted diarylethenes: a) 1a; b) 2a; c) 3a.
Photochromism of diarylethenes 1a 6a in the single-crystal-
line phase: Compounds 1a 3a were found to undergo
photochromic reactions in the single-crystalline phase. Upon
irradiation with 366 nm light, the single crystals turned blue or
reddish purple. These color changes are due to the generation
of the closed-ring isomers 1b 3b. The colors disappeared
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M. Irie
FULL PAPER
Figure 4. Absorption anisotropy of 3a: a) the crystal shape and the direction of the
polarizer, b) polarized absorption spectra of the (001) face, c) polar plot at 610 nm,
d) packing diagrams of crystal 3a projected onto the (001) face.
changed to a deep reddish-purple color. At a certain angle
(q ˆ 878), the crystal showed strong absorption, and the
absorption maximum was observed at 560 nm. When the
crystal was rotated as much as 908, the absorption intensity
decreased but the position of the maximum was unchanged.
The deep reddish-purple color reappeared upon rotation
through 1808. The change in color intensity seen upon rotating
the crystal sample indicates that the closed-ring isomers are
regularly oriented in the crystal and that photochromic
reaction had taken place in the crystal lattice. Upon irradi-
ation with visible light (l > 500 nm), the color disappeared.
The direction of the transition moment, which was deter-
mined from the polarized absorption spectrum, is shown in
Figure 4d, along with the crystal structure. The direction of
the transition moment coincides with the long axis of the
open-ring isomer of 3a.
Figure 5 shows the polarized absorption spectra of photo-
generated closed-ring isomers 1b 3b (Figure 5a) and 4b 6b
(Figure 5b) at the angles of maximum color intensity.[10] The
positions of the absorption maxima are listed in Table 3. It is
inferred from the spectra that the substitution position
strongly affects the position of the maximum in the case of
carboxyl-substituted derivatives, while the effect is negligible
in the case of formyl-substituted derivatives. The maximum of
para-substituted 1a (640 nm) shows an 80 nm bathochromic
shift in comparison with that of ortho-substituted 3a (560 nm).
The fairly large spectral shift in the carboxyl-substituted
derivatives is considered to reflect the difference in the angles
between the planes of the phenyl and thiophene rings, as
observed for the spectra of 1,2-bis(2-methyl-5-(4-methoxy-
phenyl)-3-thienyl)perfluorocyclopentene in the single-crys-
talline phase.[5]
Figure 3. ORTEP drawings of a) 1a, b) 2a, and c) 3a. The hexafluorocy-
clopentene unit is located below the plane of the paper, away from the
viewer. The red circles indicate the positions of the sulfur atoms that appear
in the UV-irradiated crystal.
Table 3. Distances between the reactive carbons and torsion angles
between the planes of the thiophene and phenyl rings, as obtained from
X-ray data, along with the absorption maxima of the photogenerated
closed-ring isomers in the single-crystalline phase.
Distance between the
reactive carbons [ä][a]
Torsion angle [8][b]
Absorption
maxima [nm]
1a
2a
3a
4a
5a
6a
3.49
3.52
3.59
3.65
3.54
3.66
32.5[c]
11.9
640
600
560
605
610
605
À 51.9[c]
25
33.9[c]
33.7
À
[a] The distance C1 C10. [b] The angle C3-C4-C16-C17. [c] The two angles
in the molecules are different in these compounds. The other torsion angles
are 23.78 (1a), À40.58 (3a), and 33.68 (5b).
upon irradiation with visible light (l > 500 nm). The colora-
tion/decoloration cycles could be repeated many times with-
out loss of integrity of the crystals.
To establish the precise structures of the colored closed-ring
isomers photogenerated in the crystals, in situ X-ray crystallo-
graphic analyses were carried out. The red circles shown in
The colors of the crystals were analyzed under polarized
light. Figure 4 shows polar plots of the (001) surface of a
crystal of 3a. Upon irradiation with 366 nm light the crystal
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Chem. Eur. J. 2003, 9, 4878 4886

Photochromism of Diarylethenes
4878 4886
Figure 5. Photochromism in the single-crystalline phase: a) carboxyl-
substituted diarylethene crystals 1b 3b; b) formyl-substituted diaryle-
thene crystals 4b 6b.
Figure 6. The calculated structures of the closed-ring isomers of a) 1b,
b) 2b, and c) 3b in the crystal. The coordinates of the sulfur atoms (red
line) that appeared in the difference Fourier electron density maps of the
UV-irradiated crystals were used for the calculations. Partial MM2
calculations were carried out on the thiophene and methyl moieties (blue
line) with the rest of the structures being fixed. The open-ring isomers are
overlaid. Hydrogen atoms have been omitted for clarity.
Figure 3 indicate the positions of the photogenerated sulfur
atoms, as ascertained from the difference Fourier electron
density map.[11] The sulfur atoms moved from upper or lower
positions to central ones. It is possible to estimate the
structures of the photogenerated closed-ring isomers from
the positions of the sulfur atoms. The structural optimizations
were carried out by means of partial MM2 calculations of the
thiophene and methyl moieties (C1, C2, C3, C4, C10, C11,
C12, C13, C14, and C15 in Figure 3), with the assumption
that the positions of the hexafluorocyclopentene ring, the
carboxyphenyl groups, and the photogenerated sulfur atoms
(S1' and S2') are fixed. The calculated structures are shown in
Figure 6.
As can be seen from Figure 6, para-substituted derivative
1b has the greatest coplanarity between the planes of the
phenyl and thiophene rings, and p-conjugation is considered
to extend throughout the molecule. In the case of the ortho
derivative 3b, the two rings are almost perpendicular. The
shift in the absorption maximum from 560 nm (ortho-sub-
stituted derivative 3b) to 640 nm (para-substituted derivative
1b) can thus be ascribed to the difference in coplanarity
between the phenyl and thiophene rings.
Table 4. Calculated torsion angles of the photogenerated closed-ring
isomers and calculated absorption maxima of photogenerated closed-ring
isomers 1a 3b.
Calculated
torsion angle [8][a]
Calculated
absorption maxima [nm]
1b
2b
3b
À 14.7[b]
À 25.8
492
461
383
À 93.5[b]
[a] The angle C3-C4-C16-C17. [b] The two angles in the molecules are
different in these compounds. The other calculated torsion angles are
À16.48 (1a) and À84.78 (3a).
result verified that the differences in position of the absorp-
tion maxima between the three derivatives are due to
different conformations of the closed-ring isomers in the
crystals.
To confirm this assumption, theoretical calculations
(INDO/S method) of the spectra were carried out, based
on the estimated structures. The lowest-energy absorption
peaks were calculated to appear at 492, 461, and 383 nm
for 1b, 2b, and 3b, respectively (Table 4). A coplanar
configuration of the planes of the phenyl and thiophene rings
gave rise to a longer wavelength absorption maximum. The
Conclusion
Photochromic diarylethenes bearing carboxyl groups at the
ortho, meta, and para positions of both terminal phenyl groups
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M. Irie
FULL PAPER
hydrogen carbonate solution, extracted with diethyl ether, and the
combined extracts were washed with aqueous sodium hydrogen carbonate
solution and water, dried (MgSO4), and concentrated. Dioxolane 11 (9.1 g,
96%) was obtained as a white solid. M.p. 117.5 119.68C; 1H NMR
(CDCl3, 200 MHz): d ˆ 2.42 (s, 3H), 4.04 4.15 (m, 4H), 5.82 (s, 1H), 7.12
have been synthesized. These derivatives have been found to
form various types of linear polymers linked by hydrogen
bonds in their crystals. The diarylethenes show photochrom-
ism in the crystalline state upon irradiation with light of
appropriate wavelengths, and the absorption maxima of the
closed-ring isomers show large differences, as much as 80 nm
between the para- and ortho-substituted compounds. The
large bathochromic shift of the para-substituted diarylethene
can be ascribed to the coplanar conformation between the
thiophene and phenyl rings that affects the p-conjugation length.
‡
(s, 1H), 7.35 7.55 ppm (m, 4H); EI-MS: m/z: [M] 326; elemental analysis
calcd (%) for C14H13BrO2S: C 51.70, H 4.03; found: C 51.83, H 4.03.
3-Bromo-5-(2-(2,5-dioxolanyl)phenyl)-2-methylthiophene (ortho 13):
A
solution of 10 (8.2 g, 29 mmol), ethylene glycol (19.7 g, 310 mmol), and p-
toluenesulfonic acid monohydrate (73 mg, 0.29 mmol) in benzene (300 mL)
was refluxed for 7 h in an apparatus fitted with a Dean Stark condenser.
The reaction mixture was subsequently poured into aqueous sodium
hydrogen carbonate solution, extracted with diethyl ether, and the
combined extracts were washed with aqueous sodium hydrogen carbonate
solution and water, dried (MgSO4), and concentrated. Dioxolane 13 (9.1 g,
96%) was obtained as a colorless oil. 1H NMR (CDCl3, 200 MHz): d ˆ 2.43
(s, 3H), 3.99 4.23 (m, 4H), 5.87 (s, 1H), 7.06 (s, 1H), 7.36 7.43 (m, 3H),
Experimental Section
‡
General: 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 (Kanto Chemical, 63
210 mesh). 1H NMR spectra were recorded on a Varian Gemini 200
instrument. Mass spectra were obtained on Shimadzu GCMS-QP5050A
(EI) and JEOL JMS-GCmateII (FAB) mass spectrometers. Melting points
were measured using a Laboratory Devices MEL-TEMP II apparatus and
are uncorrected. Jones× reagent (1.94m) was prepared as follows: H2SO4
(6.1 mL, 110 mmol) was added dropwise to an aqueous solution (10 mL) of
CrO3 (7.0 mg, 70 mmol) at 08C, and then distilled water (20 mL) was added.
The synthesis of 5a has been reported previously.[3n]
7.70 7.75 (m, 1H); EI-MS: [M] m/z: 326; elemental analysis calcd (%) for
C14H13BrO2S: C 51.70, H 4.03; found: C 51.83, H 4.03.
1,2-Bis(2-methyl-5-(4-(2,5-dioxolanyl)phenyl)thiophen-3-yl)hexafluorocy-
clopentene (para 14): A solution of n-butyllithium in hexane (1.6m, 6.1 mL,
9.7 mmol) was added dropwise to a well-stirred solution of monobromo
compound 11 (3.0 g, 9.3 mmol) in anhydrous THF (100 mL) under Ar at
À788C, and stirring was continued at this temperature for 1 h. Then, a
solution of octafluorocyclopentene (0.6 mL, 4.6 mmol) in anhydrous THF
(5 mL) was added dropwise. The mixture was stirred for 6 h and allowed to
warm to room temperature, whereupon saturated aqueous NH4Cl solution
was slowly added. The resultant mixture was then extracted with diethyl
ether and the combined organic extracts were washed with brine and dried
(MgSO4). After removal of the solvent, column chromatography (silica gel;
CH2Cl2/hexane, 1:1) of the residue afforded diarylethene 14 (2.36 g, 76%)
as white crystals. M.p. 128.4 129.48C; 1H NMR (CDCl3, 200 MHz): d ˆ
1.96 (s, 6H), 4.01 4.19 (m, 8H), 5.83 (s, 2H), 7.29 (s, 2H), 7.47 7.58 ppm
3-Bromo-5-(4-formylphenyl)-2-methylthiophene (para 8): A solution of n-
butyllithium in hexane (1.6m, 64.0 mL, 102 mmol) was added dropwise to a
well-stirred solution of dibromo compound
7 (25.0 g, 98 mmol) in
anhydrous THF (250 mL) under Ar at À788C, and stirring was continued
at this temperature for 1 h. Tri-n-butyl borate (39.3 mL, 102 mol) was
slowly added to the reaction mixture at À788C, and the mixture was stirred
for 2 h at this temperature. Then, 4-bromobenzaldehyde (18.1 g, 98 mmol),
Pd(PPh3)4 (3.2 g, 2.8 mmol), and a suspension of Na2CO3 (40 g) in water
(160 mL) were successively added to the reaction mixture at room
temperature. The mixture was stirred under reflux for 4.5 h, and then
allowed to cool to room temperature. Diethyl ether was added, the organic
layer was collected, and the aqueous layer was further extracted with
diethyl ether. The combined organic layers were dried over MgSO4, and the
solvents were evaporated. Purification of the crude product by column
chromatography (silica gel, CHCl3) afforded phenylthiophene derivative 8
(13.3 g, 48%) as a white solid. M.p. 114.1 114.78C; 1H NMR (CDCl3,
200 MHz): d ˆ 2.44 (s, 3H), 7.26 (s, 1H), 7.66 (d, J ˆ 8 Hz, 4H), 7.88 (d, J ˆ
‡
(m, 8H); FAB-MS: m/z: [M‡H] 665; elemental analysis calcd (%) for
C33H26F6O4S2: C 59.63, H 3.94; found: C 59.63, H 3.98.
1,2-Bis(2-methyl-5-(2-(2,5-dioxolanyl)phenyl)thiophen-3-yl)hexafluorocy-
clopentene (ortho 16): A solution of n-butyllithium in hexane (1.6m,
5.1 mL, 8.1 mmol) was added dropwise to a well-stirred solution of
monobromo compound 13 (2.5 g, 7.7 mmol) in anhydrous THF (50 mL)
under Ar at À788C, and stirring was continued at this temperature for
0.5 h. Then, a solution of octafluorocyclopentene (0.5 mL, 3.9 mmol) in
anhydrous THF (3 mL) was added dropwise. The mixture was stirred for
5 h and allowed to warm to room temperature, whereupon saturated
aqueous NH4Cl solution was slowly added. The resultant mixture was then
extracted with diethyl ether and the combined organic extracts were
washed with brine and dried (MgSO4). After removal of the solvent,
column chromatography (silica gel; CH2Cl2/hexane, 1:1) of the residue
afforded diarylethene 16 (1.85 g, 72%) as yellow crystals. M.p. 189.5
190.08C; 1H NMR (CDCl3, 200 MHz): d ˆ 2.00 (s, 3H), 3.97 4.20 (m,
8H), 5.80 (s, 2H), 7.26 (s, 2H), 7.30 7.45 (m, 6H), 7.75 7.77 ppm (m, 2H);
‡
8 Hz, 4H), 10.0 ppm (s, 1H); EI-MS: m/z: 280 [M] ; elemental analysis
calcd (%) for C12H9BrOS: C 51.26, H 3.23; found: C 51.36, H 3.23.
3-Bromo-5-(2-formylphenyl)-2-methylthiophene (ortho 10): A solution of
n-butyllithium in hexane (1.6m, 137 mL, 218 mmol) was added dropwise to
a well-stirred solution of dibromo compound 7 (54.4 g, 213 mmol) in
anhydrous THF (250 mL) under Ar at À788C, and stirring was continued
at this temperature for 0.5 h. Tri-n-butyl borate (84 mL, 218 mol) was
slowly added to the reaction mixture at À788C, and the mixture was stirred
for 2 h at this temperature. Then, 2-bromobenzaldehyde (6.3 g, 218 mmol),
Pd(PPh3)4 (1.2 g, 1.0 mmol), and a suspension of Na2CO3 (20 g) in water
(80 mL) were successively added to the reaction mixture at room temper-
ature. The mixture was stirred under reflux for 4.5 h, and then allowed to
cool to room temperature. Diethyl ether was added, the organic layer was
collected, and the aqueous layer was further extracted with diethyl ether.
The combined organic layers were dried over MgSO4, and the solvents
were evaporated. Purification of the crude product by column chromatog-
raphy (silica gel, CHCl3) afforded phenylthiophene derivative 10 (4.1 g,
68%) as a white solid. M.p. 69.5 70.28C; 1H NMR (CDCl3, 200 MHz): d ˆ
2.47 (s, 3H), 6.90 (s, 1H), 7.66 (t, J ˆ 7 Hz, 2H), 7.59 7.67 (m, 1H), 7.98
‡
FAB-MS: m/z: [M‡H] 665; elemental analysis calcd (%) for
C33H26F6O4S2: C 59.63, H 3.94; found: C 59.58, H 3.92.
1,2-Bis(2-methyl-5-(4-formylphenyl)-thiophen-3-yl)hexafluorocyclopen-
tene (para 4a): A solution of diarylethene 14 (2.3 g, 2.7 mmol) in wet
acetone (50 mL) containing pyridinium tosylate (3.9 g, 9.0 mmol) was
refluxed for 16 h. The mixture was cooled to room temperature and water
was added. The resultant mixture was then extracted with diethyl ether and
the combined organic extracts were washed with brine and dried (MgSO4).
After removal of the solvent in vacuo, purification of the crude product by
recrystallization afforded slightly yellow crystals of diarylethene 4a (2.6 g,
98%). M.p. 199.1 200.58C; 1H NMR (CDCl3, 200 MHz): d ˆ 2.01 (s, 6H),
7.45 (s, 1H), 7.71 (d, J ˆ 8 Hz, 4H), 7.91 (d, J ˆ 8 Hz, 4H), 10.02 ppm (s,
‡
2H); FAB-MS: m/z: [M‡H] 577; elemental analysis calcd (%) for
‡
C29H18F6O2S2: C 60.41, H 3.15; found: C 60.45, H 3.18.
8.02 (m, 1H), 10.22 ppm (s, 1H); EI-MS: m/z: [M] 280; elemental analysis
calcd (%) for C12H9BrOS: C 51.26, H 3.23; found: C 51.34, H 3.20.
1,2-Bis(2-methyl-5-(2-formylphenyl)-thiophen-3-yl)hexafluorocyclopen-
tene (ortho 6a): A solution of diarylethene 16 (900 mg, 1.4 mmol) in wet
acetone (50 mL) containing pyridinium tosylate (1.36 g, 5.41 mmol) was
refluxed for 24 h. The mixture was cooled to room temperature and water
was added. The resultant mixture was then extracted with diethyl ether and
the combined organic extracts were washed with brine and dried (MgSO4).
3-Bromo-5-(4-(2,5-dioxolanyl)phenyl)-2-methylthiophene (para 11):
A
solution of 8 (8.2 g, 29 mmol), ethylene glycol (19.7 g, 310 mmol), and p-
toluenesulfonic acid monohydrate (73 mg, 0.29 mmol) in benzene (300 mL)
was refluxed for 7 h in an apparatus fitted with a Dean Stark condenser.
The reaction mixture was subsequently poured into aqueous sodium
4884
¹ 2003 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
www.chemeurj.org
Chem. Eur. J. 2003, 9, 4878 4886

Photochromism of Diarylethenes
4878 4886
After removal of the solvent in vacuo, purification of the crude product by
recrystallization afforded colorless crystals of diarylethene 6a (750 g,
96%). M.p. 178.5 180.08C; 1H NMR (CDCl3, 200 MHz): d ˆ 1.98 (s, 3H),
and CCDC-204753 (6a) contain the supplementary crystallographic data
for this paper. These data can be obtained free of charge via www.ccdc.a-
c.uk/conts/retrieving.html (or from the Cambridge Crystallographic Data
Centre, 12 Union Road, Cambridge CB2 1EZ, UK; fax: (‡44)1223-
336033; or e-mail: deposit@ccdc.cam.ac.uk).
‡
2.00 (s, 3H), 7.26 7.92 (m, 10H), 10.01 ppm (s, 2H); EI-MS: m/z: [M] 576;
elemental analysis calcd (%) for C29H18F6O2S2: C 60.41, H 3.15; found: C
60.51, H 3.25.
Simulation of the photogenerated closed-ring isomers: CS Chem3D
(Cambridge Software) was used for partial MM2 optimizations. The
structural optimizations were carried out by means of partial MM2
calculations of the thiophene and methyl moieties (C1, C2, C3, C4, C10,
C11, C12, C13, C14, and C15), with fixed positions of the hexafluorocy-
clopentene and carboxyphenyl moieties and the photogenerated sulfur
atoms (S1' and S2').
1,2-Bis(2-methyl-5-(4-carboxylphenyl)thiophen-3-yl)hexafluorocyclopen-
tene (para 1a): Jones× reagent (5.7 mL, 10.8 mmol) was added dropwise to
a well-stirred solution of 4a (1.5 g, 2.6 mmol) in acetone (120 mL) at room
temperature, and stirring was continued for 5 h. 2-Propanol was then slowly
added, the resultant mixture was extracted with diethyl ether, and the
combined organic extracts were dried (MgSO4). After removal of the
solvent, column chromatography (silica gel; ethyl acetate) of the residue
afforded diarylethene 1a (2.4 g, 76%) as a white powder. M.p. 2908C
(dec.); 1H NMR (CDCl3, 200 MHz): d ˆ 2.00 (s, 6H), 7.70 (s, 2H), 7.78 (d,
Calculation of absorption spectra: The INDO/S method as implemented in
MOS-F (Fujitsu) was used for these calculations. Twenty molecular orbitals
were taken into account in the calculations (default value). Coordination of
the photogenerated closed-ring isomers obtained by MM2 calculation was
assumed for this INDO/S calculation.
‡
J ˆ 8 Hz, 4H), 7.97 ppm (d, J ˆ 8 Hz, 4H); FAB-MS: m/z: [M] 608;
elemental analysis calcd (%) for C29H18F6O4S2: C 57.23, H 2.98; found: C
57.60, H 3.19.
1,2-Bis(2-methyl-5-(3-carboxylphenyl)thiophen-3-yl)hexafluorocyclopen-
tene (meta 2a): Jones× reagent (6.0 mL, 12 mmol) was added dropwise to a
well-stirred solution of 5a (1.0 g, 1.8 mmol) in acetone (100 mL) at room
temperature, and stirring was continued for 5 h. 2-Propanol was then slowly
added, the resultant mixture was extracted with diethyl ether, and the
combined organic extracts were dried (MgSO4). After removal of the
solvent, column chromatography (silica gel; ethyl acetate) of the residue
afforded diarylethene 2a (900 mg, 87%) as a white powder. M.p. 2908C
(decomp); 1H NMR (CDCl3, 200 MHz): d ˆ 2.02 (s, 6H), 7.52 7.61 (m,
Acknowledgement
This work was partly supported by CREST of Japan Science and
Technology Corporation and Grant-in-Aids for Scientific Research (S)
and (15105006) and for the 21st Century COE Program from the Ministry
of Education, Culture, Sports, Science and Technology of Japan.
‡
4H), 7.89 (d, J ˆ 8 Hz, 4H), 8.11 ppm (s, 2H); FAB-MS: m/z: [M] 608;
elemental analysis calcd (%) for C29H18F6O4S2: C 57.23, H 2.98; found: C
57.41, H 3.15.
[1] a) G. H. Brown, Photochromism, Wiley-Interscience, New York, 1971;
b) H. D¸rr, H. Bouas-Laurent, Photochromism: Molecules and
Systems, Elsevier, Amsterdam, 1990.
[2] a) M. Irie, Chem. Rev. 2000, 100, 1685 1716; b) K. Uchida, M. Irie,
Bull. Chem. Soc. Jpn. 1998, 71, 985 996.
1,2-Bis(2-methyl-5-(2-carboxylphenyl)thiophen-3-yl)hexafluorocyclopen-
tene (ortho 3a): Jones× reagent (2.0 mL, 4.0 mmol) was added dropwise to a
well-stirred solution of 6a (580 mg, 1.0 mmol) in acetone (50 mL) at room
temperature, and stirring was continued for 14 h. 2-Propanol was then
slowly added, the resultant mixture was extracted with diethyl ether, and
the combined organic extracts were dried (MgSO4). The solvent was
removed and the resultant powder was washed with ethyl acetate.
Diarylethene 3a (425 mg, 70%) was obtained as a white powder. M.p.
255 2568C; 1H NMR (CDCl3, 200 MHz): d ˆ 1.93 (s, 6H), 7.14 (s, 2H),
[3] a) M. Irie, K. Uchida, T. Eriguchi, H. Tsuzuki, Chem. Lett. 1995, 899
900; b) S. Kobatake, T. Yamada, K. Uchida, N. Kato, M. Irie, J. Am.
Chem. Soc. 1999, 121, 2380; c) S. Kobatake, M. Yamada, T. Yamada,
M. Irie, J. Am. Chem. Soc. 1999, 121, 8450; d) M. Irie, T. Lifka, S.
Kobatake, N. Kato, J. Am. Chem. Soc. 2000, 122, 4871; e) T. Yamada,
S. Kobatake, K. Muto, M. Irie, J. Am. Chem. Soc. 2000, 122, 1589; f) T.
Yamada, S. Kobatake, M. Irie, Bull. Chem. Soc. Jpn. 2000, 122, 4871;
g) T. Kodani, K. Matsuda, T. Yamada, M. Irie, Chem. Lett. 1999, 1003;
h) T. Kodani, K. Matsuda, T. Yamada, S. Kobatake, M. Irie, J. Am.
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Chem. Int. Ed. 2003, 14, 1636 1639.
‡
7.48 7.59 (m, 6H), 7.70 ppm (d, J ˆ 7 Hz, 2H); EI-MS: [M] m/z: 608;
elemental analysis calcd (%) for C29H18F6O4S2: C 57.23, H 2.98; found: C
57.23, H 3.18.
Photochemical measurements: Absorption spectra were measured on a
Hitachi U-3500 spectrophotometer. Photoirradiation was carried out using
a USHIO 500 W super high-pressure mercury lamp or a USHIO 500 W
xenon lamp. Mercury lines of 313 nm and 578 nm were selected by passing
the light through a combination of either a band-pass filter (UV-D33S) or a
sharp-cut filter (Y-52) and a monochromator (Ritsu MC-20L). Single
crystals were irradiated with light of wavelength 400 nm, obtained by
passing the light from a xenon lamp through a combination of a UV-D33S
band pass filter and a UV29 or a UV35 sharp-cut filter and monochro-
mator. Changes in the absorption spectra in the single-crystalline phase
were measured with a Leica DMLP polarizing microscope connected to a
Hamamatsu PMA-11 photodetector. The polarizer and analyzer were set in
parallel to each other. Photoirradiation was carried out using a 75 W xenon
lamp or a 100 W halogen lamp as the light source, which was attached to the
microscope.
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2804 2805.
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[7] J.-M. Lehn, Supramolecular Chemistry: Concepts andPerspectives ,
VCH, Weinheim, 1995.
X-ray crystallographic analysis: X-ray crystallographic analysis was carried
out on a Bruker SMART1000 CCD-based diffractometer (50 kV, 40 mA)
using Mo-Ka radiation. The data were collected as a series of w-scan frames,
each with a width of 0.38/frame. The crystal-to-detector distance was
5.118 cm. Crystal decay was monitored by repeating the 50 initial frames at
the end of the data collection and analyzing the duplicate reflections. Data
reduction was performed using SAINTPLUS software,[12] which corrects
for Lorentz and polarization effects, as well as for decay. The cell constants
were calculated by global refinement. The structure was solved by direct
methods and refined by full-matrix least-squares on F 2 using SHELXL
software.[13] The positions of all hydrogen atoms were calculated geometri-
cally and they were refined as a riding model. CCDC-204750 (1a), CCDC-
204751 (2a), CCDC-200319 (3a), CCDC-204752 (4a), CCDC-194694 (5a),
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Ranganathan, M. P. Samant, I. L. Karle, J. Am. Chem. Soc. 2001, 123,
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Chem. Soc. 1999, 121, 2115 2122. f) S. Hanessian, R. Saladino, R.
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[10] Absorption anisotropy and photochromic behavior in the single-
crystalline phases of diarylethenes 1a, 2a, 4a, 5a, 6a is shown in the
Supporting Information.
Chem. Eur. J. 2003, 9, 4878 4886
www.chemeurj.org
¹ 2003 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
4885

M. Irie
FULL PAPER
[11] a) J. Harada, H. Uekusa, Y. Ohashi, J. Am. Chem. Soc. 1999, 121,
5809 5810; b) M. Kawano, T. Sano, J. Abe, Y. Ohashi, J. Am. Chem.
Soc. 1999, 121, 8106 8107; c) M. Kawano, T. Sano, J. Abe, Y. Ohashi,
Chem. Lett. 2000, 1372 1373; d) S. Kobatake, K. Shibata, K. Uchida,
M. Irie, J. Am. Chem. Soc. 2000, 122, 12135 12141; e) T. Yamada, K.
Muto, S. Kobatake, M. Irie, J. Org. Chem. 2001, 66, 6164 6168; f) T.
Yamada, S. Kobatake, K. Muto, M. Irie, J. Am. Chem. Soc. 2000, 122,
1589 1592; g) T. Yamada, S. Kobatake, M. Irie, Bull. Chem. Soc. Jpn.
2000, 73, 2179 2184.
[12] SAINTPLUS Software Package, Bruker AXS, Madison, WI, USA,
2001.
[13] SHELXTL Software Package, Bruker AXS, Madison, WI, USA, 2001.
Received: March 12, 2003 [F4947]
4886
¹ 2003 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
www.chemeurj.org
Chem. Eur. J. 2003, 9, 4878 4886