Morphology change of diarylethene derivatives having benzofuran derivatives - Photoinduced crystallization

Article abstract of DOI:10.1016/j.jphotochem.2010.05.013

We have synthesized three diarylethene derivatives - 1,2-bis(2-(4-n- alkylphenyl)benzofuran-3-yl)ethenes (1a-3a). We have observed the morphology changes of the melted diarylethenes after heating. The crystal of 2a melts at 102 °C. After heating at 130 °C, the liquid did not crystallize below 40 °C for more than 3 days because of the temperature above the eutectic point. When the liquid was irradiated with 365 nm light, the photoirradiated area crystallized, because of the generation of 2b. After the sample was irradiated with visible light, the crystals changed to a colorless liquid. Photoinduced crystallization was also observed for the 4-n-dodecyl derivative (3a).

Full text of DOI:10.1016/j.jphotochem.2010.05.013

Journal of Photochemistry and Photobiology A: Chemistry 213 (2010) 141–146
Contents lists available at ScienceDirect
Journal of Photochemistry and Photobiology A:
Chemistry
journal homepage: www.elsevier.com/locate/jphotochem
Morphology change of diarylethene derivatives having benzofuran
derivatives—Photoinduced crystallization
Tadatsugu Yamaguchia,∗, Koji Nanbaa, Toru Ozekia, Setsuko Irieb, Masahiro Iriec
a Hyogo University of Teacher Education, Shimokume 942-1, Kato, Hyogo 673-1494, Japan
b Osaka Prefecture University, Gakuen-cho, Naka-ku, Sakai, Osaka 599-8570, Japan
c Department of Chemistry, Rikkyo University, Nishi-Ikebukuro 3-34-1, Toshima-ku, Tokyo 171-8501, Japan
a r t i c l e i n f o
a b s t r a c t
Article history:
We have synthesized three diarylethene derivatives
— 1,2-bis(2-(4-n-alkylphenyl)benzofuran-3-
Received 2 February 2010
Received in revised form 22 April 2010
Accepted 25 May 2010
yl)ethenes (1a–3a). We have observed the morphology changes of the melted diarylethenes after heating.
The crystal of 2a melts at 102 ◦C. After heating at 130 ◦C, the liquid did not crystallize below 40 ◦C for more
than 3 days because of the temperature above the eutectic point. When the liquid was irradiated with
365 nm light, the photoirradiated area crystallized, because of the generation of 2b. After the sample was
irradiated with visible light, the crystals changed to a colorless liquid. Photoinduced crystallization was
also observed for the 4-n-dodecyl derivative (3a).
Available online 31 May 2010
Keywords:
Diarylethene
Photochromism
Benzofuran derivative
Morphology change
© 2010 Elsevier B.V. All rights reserved.
1. Introduction
connected to cyanobiphenyl groups, 1,2-bis(2-[11-{4-(4ꢀ-
cyanophenyl-4-yloxy)undecyl}]benzo[b]thiophene-3-yl)perflu-
Photochromism has attracted considerable attention because
of its potential applications to molecular devices such as optical
memories and switches [1,2]. Among various thermally irreversible
photochromic compounds, diarylethene derivatives are the most
promising compounds because of their fatigue resistance and ther-
mal irreversibility [3–24]. Benzofuran derivatives have the nature
of these properties.
The combination of self-assembly and photochromic behavior
is very useful in opto electronic devices. It has been reported
that diarylethene derivatives control liquid-crystalline phases by
photochromism [20–24]. We report chiral photochromic dopants,
(1R,2R)-N,Nꢀ-bis(4-{3-[1-(2-methylbenzo[b]thiophene-3-yl)hexa-
fluorocyclopent-1-ene-2-yl]-2,4-dimethylthiophen-5-yl}benzili-
deneamino)cyclohexane [20] and (R)-1,1ꢀ-bis{3-[1-(2-methyl-
benzo[b]thiophene-3-yl)hexafluorocyclopent-1-ene-2-yl]-2,4-
dimethylthiophen-5-yl}-bi-2-naphthol [21], which control the
twisting power force in chiral nematic liquids by alternate irra-
diation with appropriate wavelengths of light. Polarization of a
ferroelectric liquid crystal can be modulated by a diarylethene
dopant, 1,2-bis(5-(4-n-(heptyloxy)phenyl)-2-methylthiophene-
3-yl)hexafluorocyclopentene [22]. Photochromic diarylethenes
orocyclopentene [23,24], show liquid-crystalline properties. The
diarylethene with a hexa(ethylene glycohol) side chains (S,S)-
1,2-bis[2-methyl-5-(4-(N-(2-{2-[2-(2-{2-[2-(2-methoxy-ethoxy)-
ethoxy]-ethoxy}-ethoxy)-ethoxy]-ethoxy}-1-methyl-ethyl))-
carbamoyl-phenyl)-thiophene-3-yl]hexafluorocyclopentene [25],
shows photoresponsive LCST (lower critical solution temperature)
change in water, and formed a chiral self-assembled structure.
Clouding is controlled by irradiation with the appropriate
wavelengths of light. On solubility there is
a large differ-
ence between benzo[b]thiophene and benzofuran derivatives.
Although the solubility of 1,2-bis(2-methylbenzo[b]thiophene-3-
yl)perfluorocyclopentene is 1 × 10−4 M in hexane, one of 1,2-bis
(2-methyl-benzofuran-3-yl)perfluorocyclopentene is 1 × 10−2 M
in hexane. The benzofuran derivatives undergo photochromism
under the high concentration in solution. And there might be a
difference between the open-ring and the closed-ring isomers
on solubility. The solubility changes controlled by photoirradi-
ation would make a novel category for functional materials. A
partial crystallization would make the physical changes — such
as transparency and polarization of the observed material. In this
work, we synthesized benzofuran derivatives — the 1,2-bis(2-(4-n-
alkylphenyl)benzofuran-3-yl)perfluorocyclopentene (1a–3a) and
investigated their morphological behavior by photoirradiation.
We attempted to construct a system in which crystallization can
be induced from liquid phase using UV and visible lights.
∗
Corresponding author. Tel.: +81 795 44 2200; fax: +81 795 44 2200.
E-mail address: tyamagu@hyogo-u.ac.jp (T. Yamaguchi).
1010-6030/$ – see front matter © 2010 Elsevier B.V. All rights reserved.
doi:10.1016/j.jphotochem.2010.05.013

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T. Yamaguchi et al. / Journal of Photochemistry and Photobiology A: Chemistry 213 (2010) 141–146
Scheme 1.
2.2. Synthesis of the diarylethene derivatives
2.2.1. 2-(4-n-Butylphenyl)-1-benzofuran (5)
1-Benzofuran-2-boronic acid (3.42 g, 21.2 mmol), tetrakistriph-
enylphosphine paradium (0) salt (763 mg, 0.96 mmol), sodium
bicarbonate (2.5 g) and water (30 ml) were added to a solution of
1-bromo-4-n-butylbenzene (4) (4.05 g, 19.0 mmol) in THF (70 ml).
The reaction mixture was heated for 3 h at 70 ◦C. The reaction mix-
ture was poured into water (30 ml) and extracted with diethyl
ether. The organic phase was dried over anhydrous magnesium
sulfate and evaporated in vacuo. The crude product was purified
by column chromatography on silica gel (hexane) to give 3.12 g of
5 in 66% yield.
2. Experimental methods
5: colorless liquid; 1H NMR (400 MHz, CDCl3) ı = 0.94 (t,
J = 7.6 Hz, 3H), 1.34–1.44 (m, 2H), 1.60–1.68 (m, 2H), 2.65 (t,
J = 8.0 Hz, 2H), 6.97 (s, 1H), 7.20–7.27 (m, 4H), 7.50–7.59 (m, 2H),
7.77–7.79 (m, 2H). Ms (EI) m/z: [M+] 250. Anal Calcd. for C18H18O:
C 86.36, H 7.25%. Found: C 86.37, H 7.10%.
2.1. General
The solvents used were spectrograde and were purified by distil-
lation before use. The solubility of the diarylethene was measured
in hexane (1 ml) at 25 ◦C. Absorption spectra were measured with a
spectrophotometer (Hitachi, U-3310). For solution measurements,
a mercury lamp (Ushio, 500 W) was used as the light source. Light
of appropriate wavelength was isolated by passing light through a
monochromator (RITSU MC-10N) or through Y-44 and UV-D33S
filters. The quantum yields were determined by comparing the
reaction rates of the diarylethene derivatives in hexane against that
of furylfulgide in toluene. The samples were not degassed. Differ-
ential scanning calorimetry (DSC) measurements were carried out
with a Pyris 1 apparatus (Perkin Elmer) with a liquid nitrogen cool-
ing system (Perkin Elmer Cryofill). XRD analysis was carried out on
a Mac Science MXP-18 (scan rate 4◦ min−1, CuK␣1, 40 kV, 100 mA).
Single crystals were observed using an OPTI-POL 2POL (Nikon)
polarizingmicroscope. Photoirradiationfor single-crystal measure-
ments was carried out using 100 W mercury lamp (Nikon, C-SHG1
and LH-M100CB-1) as a light source. 1H NMR were recorded on
a Bruker AVANCE 400 spectrometer (400 MHz) with CDCl3 as
solvent and tetramethylsilane as an internal standard at room
temperature. Good quality crystals (1a: 0.2 × 0.1 × 0.1 mm and 2a:
0.25 × 0.15 × 0.1 mm) were selected for the X-ray diffraction study.
These crystals were obtained from a solution of hexane and chlo-
roform. Data collection was performed on a Bruker SMART 1000
CCD-based diffractometer (55 kV, 35 mA) with MoK␣ irradiation.
We synthesized the 1,2-bis(2-(4-n-alkylphenyl)-1-benzofuran-3-
yl)ethenes (1a–3a) (Scheme 1).
2.2.2. 2-(4-n-Octylphenyl)-1-benzofuran (7)
Compound 7 was synthesized from 5.0 g (18.6 mmol) of 1-
bromo-4-n-octylbenzene (6) by the same procedure as used for 5.
After purification, 3.88 g of 7 was obtained in 68% yield.
7: colorless liquid; 1H NMR (400 MHz, CDCl3) ı = 0.88 (t,
J = 7.6 Hz, 3H), 1.26–1.38 (m, 2H), 1.60–1.68 (m, 2H), 2.64 (t,
J = 8.0 Hz, 2H), 6.97 (s, 1H), 7.20–7.27 (m, 4H), 7.50–7.58 (m, 2H),
7.77–7.79 (m, 2H). Ms (EI) m/z: [M+] 306. Anal Calcd. for C22H26O:
C 86.23, H 8.55%. Found: C 86.29, H 8.57%.
2.2.3. 2-(4-n-Dodecylphenyl)-1-benzofuran (9)
Compound 9 was synthesized from 6.5 g of 1-bromo-4-n-
dodecylbenzene (8) (20 mmol) by a same procedure as used for
5. After purification, 3.68 g of 9 was obtained in 51% yield.
9: colorless liquid; 1H NMR (400 MHz, CDCl3) ı = 0.94 (t,
J = 7.6 Hz, 3H), 1.34–1.44 (m, 18H), 1.60–1.68 (m, 2H), 2.65 (t,
J = 8.0 Hz, 2H), 6.97 (s, 1H), 7.20–7.27 (m, 4H), 7.50–7.59 (m, 2H),
7.77–7.79 (m, 2H). Ms (EI) m/z: [M+] 362. Anal Calcd. for C26H34O:
C 86.13, H 9.45%. Found: C 86.02, H 9.58%.
2.2.4. 3-Bromo-2-(4-n-butylphenyl)-1-benzofuran (10)
To
a
stirred THF solution (30 ml) containing 2-(4-n-
butylphenyl)-1-benzofuran (5) (3.12 g, 12.4 mmol), 2.66 g of
N-bromosuccinimide (14.9 mmol) was slowly added at 5 ◦C, The

T. Yamaguchi et al. / Journal of Photochemistry and Photobiology A: Chemistry 213 (2010) 141–146
143
Table 1
Absorption characteristics and photoreactivity of diarylethene derivatives 1–3 in
hexane.
Compound
ε (104 dm3 mol−1 cm−1
)
Quantum yield
Cyclization
a
b
Cycloreversion
1
2
3
3.81
(279 nm)
1.60
(482 nm)
0.43
(313 nm)
0.28
(500 nm)
4.02
(279 nm)
1.60
(482 nm)
0.46
(313 nm)
0.27
(500 nm)
4.25
1.56
0.47
0.27
(279 nm)
(482 nm)
(313 nm)
(500 nm)
reaction mixture was stirred for 15 h at room temperature. The
reaction mixture was poured into sodium thiosulfate solution and
extracted with diethyl ether. The organic layer was dried over
anhydrous magnesium sulfate, and the solution was evaporated in
vacuo. The crude product was purified by column chromatography
on silica gel (hexane) to give 3.53 g of 10 in 87% yield.
10: colorless liquid; 1H NMR (400 MHz, CDCl3) ı = 0.95 (t,
J = 7.8 Hz, 3H), 1.33–1.42 (m, 2H), 1.60–1.68 (m, 2H), 2.67 (t,
J = 7.8 Hz, 2H), 7.32–7.36 (m, 2H), 7.48–7.56 (m, 1H), 8.07–8.09 (m,
1H). Ms (EI) m/z: [M+] 328. Anal Calcd. for C18H17BrO: C 65.67, H
5.20%. Found: C 65.81, H 5.25%.
Fig. 1. Absorption spectra of 2a (solid line), 2b (dotted line) and at the pho-
tostationary state (dashed line) under irradiation with 313 nm light in hexane
(1.8 × 10−5 mol/l).
2.2.5. 3-Bromo-2-(4-n-octylphenyl)-1-benzofuran (11)
Bromination of 7 (6.88 g, 22.6 mmol) was carried out by a pro-
cedure similar to that used for 10. The crude product was purified
Fig. 2. ORTEP drawings of (a) 1a and (b) 2a. The ellipsoids represent 50% displacement of atoms. Hydrogen atoms are omitted for clarity.

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T. Yamaguchi et al. / Journal of Photochemistry and Photobiology A: Chemistry 213 (2010) 141–146
by column chromatography on silica gel (hexane) to give 7.16 g of
11 in 83%.
11: colorless liquid; 1H NMR (400 MHz, CDCl3) ı = 0.88 (t,
J = 7.2 Hz, 3H), 1.20–1.40 (m, 18H), 1.62–1.68 (m, 2H), 2.67 (t,
J = 7.2 Hz, 2H), 7.30–7.39 (m, 4H), 7.50–7.58 (m, 2H), 8.08–8.10 (m,
2H). Ms (EI) m/z: [M+] 384. Anal Calcd. for C22H25BrO: C 68.57, H
6.54%. Found: C 68.39, H 6.48%.
2.2.6. 3-Bromo-2-(4-n-dodecylphenyl)-1-benzofuran (12)
Bromination of 9 (3.67 g, 10.1 mmol) was carried out by a pro-
cedure similar to that used for 10. The crude product was purified
by column chromatography on silica gel (hexane) to give 3.25 g of
12 in 73%.
12: colorless liquid; 1H NMR (400 MHz, CDCl3) ı = 0.88 (t,
J = 7.2 Hz, 3H), 1.20–1.40 (m, 18H), 1.62–1.68 (m, 2H), 2.67 (t,
J = 7.2 Hz, 2H), 7.30–7.39 (m, 4H), 7.50–7.58 (m, 2H), 8.08–8.10 (m,
2H). Ms (EI) m/z: [M+] 440. Anal Calcd. for C26H33BrO: C 70.74, H
7.53%. Found: C 70.54, H 7.52%.
2.2.7. 1,2-bis(2-(4-n-Butylphenyl)-1-benzofuran-3-
yl)perfluorocyclopentene
(1a)
To a stirred THF solution (30 ml) containing 3-bromo-2-(4-
n-butylphenyl)-1-benzofuran (10) (2.78 g, 8.47 mmol), 8.47 ml of
1.6 M n-butyllithium hexane solution (9.31 mmol) was slowly
added at −78 ◦C, and the solution was stirred for 15 min at
−78 ◦C. Then the octafluorocycylpentene (0.561 ml, 0.424 mmol)
was added slowly to the reactionmixture at −78 ◦C and left to stand
with stirring at −78 ◦C to 30 ◦C for 12 h. The reaction mixture was
poured into concentrated sodium chloride solution and extracted
with diethyl ether. The organic phase was dried over anhydrous
magnesium sulfate and evaporated in vacuo. The crude product
was purified by column chromatography on silica gel (hexane) to
give 0.569 g of 1a in 40% yield.
Fig. 3. DSC profiles of 2a: (a) the first run and (b) the second run (heating rate:
4
◦C/min, cooling rate: 4 ◦C/min).
1a: yellow crystals; 1H NMR (400 MHz, CDCl3) ı = 0.93 (t,
J = 7.2 Hz, 6H), 1.26–1.34 (m, 4H), 1.40–1.48 (m, 4H), 2.32 (t,
J = 7.2 Hz, 4H), 6.77–6.79 (m, 4H), 7.00–7.07 (m, 6H), 7.14–7.16
(m, 4H), 7.25–7.27 (m, 2H). Ms (EI) m/z: [M+] 672. Anal Calcd. for
C41H34F6O2: C 73.20, H 5.09%. Found: C 73.31, H 5.21%. CCDC depo-
sition number: 724436.
3a: yellow crystals; 1H NMR (400 MHz, CDCl3) ı = 0.88 (t,
J = 7.2 Hz, 6H), 1.26–1.33 (m, 36H), 1.40–1.48 (m, 4H), 2.32 (t,
J = 7.2 Hz, 4H), 6.76–6.78 (m, 4H), 6.98–7.05 (m, 6H), 7.12–7.16
(m, 4H), 7.24–7.26 (m, 2H). Ms (EI) m/z: [M+] 897. Anal Calcd. for
C
57H66F6O2: C 76.31, H 7.42%. Found: C 76.32, H 7.47%.
2.2.8. 1,2-bis(2-(4-n-Octylphenyl)-1-benzofuran-3-
yl)perfluorocyclopentene
3. Results and discussion
(2a)
3.1. Synthesis of diarylethenes 1a–3a
The
reaction
of
3-bromo-2-(4-n-octylphenyl)-1-
benzothiophene (11) (2.00 g, 5.19 mmol), 1.6 M n-butyllithium
in hexane (3.57 ml, 5.70 mmol), and octafluorocyclopentene
(0.343 ml, 2.59 mmol) was carried out as described for compound
1a. The crude product was purified by column chromatography on
silica gel (hexane) to give 0.680 g of 2a in 33% yield.
Diarylethenes 1a–3a were prepared from 2-(4-n-alkylphenyl)-
3-bromo-1-benzofuran with octafluorocyclopentene. The detailed
strategy was shown in Scheme 1. Their structures were con-
firmed by 1H NMR, mass spectrometry, and elemental analysis.
Diarylethenes 1a and 2a were confirmed by X-ray crystallography.
2a: yellow crystals; 1H NMR (400 MHz, CDCl3) ı = 0.90 (t,
J = 7.2 Hz, 6H), 1.27–1.35 (m, 20H), 1.40–1.48 (m, 4H), 2.30 (t,
J = 7.2 Hz, 4H), 6.77–6.79 (m, 4H), 6.98–7.05 (m, 6H), 7.12–7.15
(m, 4H), 7.25–7.27 (m, 2H). Ms (EI) m/z: [M+] 784. Anal Calcd. for
C49H50F6O2: C 74.98, H 6.42%. Found: C 75.07, H 6.39%. CCDC depo-
sition number: 724437.
3.2. Photochromism of 1a–3a in hexane and in the crystalline
phase
Diarylethenes 1a–3a show photochromism in hexane solution.
Fig. 1 shows absorption spectra of 2a, 2b, and photostationary state
under irradiation with 313 nm light in hexane. Upon irradiation
with 313 nm light, the open-ring isomers of 1a, 2a, and 3a transform
to the closed-ring isomers 1b, 2b, and 3b, respectively. Upon irra-
diation with >440 nm light, 1b, 2b, and 3b convert to 1a, 2a, and 3a,
respectively. Absorption characteristics and photoreactivity of 1–3
are summarized in Table 1. The cyclization quantum yields were
increased with the increasing of chain length, but the cyclorever-
sion quantum yield did not affect by the increasing of the chain
length.
2.2.9. 1,2-bis(2-(4-n-Dodecylphenyl)-1-benzofuran-3-
yl)perfluorocyclopentene
(3a)
The
reaction
of
3-bromo-2-(4-n-dodecylphenyl)-1-
benzothiophene (12) (1.8 g, 4.07 mmol), 1.6 M n-butyllithium
hexane solution (2.80 ml, 4.48 mmol), and octafluorocyclopentene
(0.269 ml, 2.03 mmol) was carried out as described for compound
1a. The crude product was purified by column chromatography on
silica gel (hexane) to give 0.247 g of 3a in 14% yield.

T. Yamaguchi et al. / Journal of Photochemistry and Photobiology A: Chemistry 213 (2010) 141–146
145
Fig. 4. Photographs of 2: (a) a single crystal, (b) after being heated at 130 ◦C (observed at 40 ◦C), (c) after 3 h at 30 ◦C, (d) second heating at 80 ◦C, (e) after 3 days at 40 ◦C, and
(f) upon irradiation with 365 nm light at 40 ◦C for 3 min.
Single crystals of 1a and 2a were obtained from hexane solu-
tion. The single crystals of 1a and 2a underwent photochromism in
a single-crystalline phase. These crystals were analyzed by X-ray
crystallography (Fig. 2) [26]. The aryl groups are in an anti-parallel
conformation, and the distances between the reactive carbons are
0.382 and 0.399 nm, respectively. The distances are sufficient for
the molecules to undergo photochromism in the single-crystalline
phase [27]. The crystals 3a did not analyze by X-ray crystallography
because the suitable crystals did not obtained. The crystals showed
photochromism in the crystalline phase upon alternate irradiation
with 365 nm light and >440 nm light.
of 2a is square, and the molecules are packed in an anti-parallel con-
formation. After heating at 130 ◦C, the single crystals of 2a melted
(Fig. 4(b)). During the liquid was cooled to 30 ◦C after 3 h, the liquid
changed into the crystals (Fig. 4(c)). During the second heating, part
of the crystals melts at 80 ◦C, and only square crystals are observed
(Fig. 4(d)). The square crystals melt at 86 ◦C, and the phase changes
to the liquid, as indicated in Fig. 4(b). We confirmed that the sample
did not decompose after heating at 130 ◦C by HPLC measurements.
These results suggest that two (or more) conformations exist after
heating at 130 ◦C. The existence of two kinds of crystals produces
the liquid state of 2a at 40 ◦C, because the temperature is above the
eutectic point. The state is stable after more than 3 days at 40 ◦C
(Fig. 4(e)).
3.3. DSC profiles and morphology changes of 1a–3a
The existence of two (or more) kinds of crystals was observed by
XRD analysis. A series of phase transfer changes was also observed
in the XRD pattern (Fig. 5). The sample in Fig. 5(a) is the same as
that in Fig. 4(a), which is initially a square crystal. After the crystal
of 2a melts, the XRD spectrum is changed to the shallow pattern
(Fig. 5(b)), which indicates that the state is liquid. The XRD pat-
tern of 2a after recrystallization sample is shown in Fig. 5(c). The
spectrum indicates that two (or more) kinds of crystals are con-
tained in the sample. The two states between Fig. 5(a) and (c) are
not identical.
More interestingly, crystallization by UV light illumination was
observed. Fig. 4(f) shows the photoinduced crystallization of 2
upon irradiation with 365 nm light for 3 min at 40 ◦C. The crystal
color generated was red, and the crystal contained the closed-ring
isomer. The crystal generated in the liquid dissolved upon irradi-
Fig. 3(a) shows DSC curve of 2a on the first cycle. The cycle pro-
ceeds as follows: (1) heat from 30 to 130 ◦C at 4 ◦C/min, (2) hold
for 2 min at 130 ◦C, and (3) cool from 130 to 30 ◦C at 4 ◦C/min. From
the DSC measurement, sample 2a melts at 102 ◦C When the sample
was cooled to 30 ◦C, the crystallization of 2a did not occur immedi-
ately, but occurred after 90 min. Fig. 3(b) shows DSC curves on the
second cycle for recrystallized 2a after standing for 1 day at 30 ◦C.
In the cycle, two clear endotherms occur at 72 and 86 ◦C upon heat-
ing. A single crystal of 1a melts at 164 ◦C. DSC measurements show
that there is no change in the melting point between the first and
second scans (see supplementary data).
In order to elucidate this phase change, we observed single crys-
tals of 2a under a polarized microscope under crossed nicol prisms.
Fig. 4(a) shows a photograph of the single crystal of 2a. The crystal

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T. Yamaguchi et al. / Journal of Photochemistry and Photobiology A: Chemistry 213 (2010) 141–146
photo-generated crystal was identical with 2b. After the sample
was irradiated with visible light, the crystals changed to a col-
orless liquid. Photoinduced crystallization was also observed for
the 4-n-dodecyl derivative (3a) at 40 ◦C. We have constructed a
photoinduced crystallization system based on this photochromic
reaction.
Acknowledgements
This work was partially supported by Grant-in-Aids for Scientific
Research on Priority Areas (471) (No. 21021016) and for Funda-
mental Research Program (C) (No. 19550152) from the Ministry of
Education, Culture, Sports, Science and Technology (MEXT) of the
Japanese Government.
Appendix A. Supplementary data
Supplementary data associated with this article can be found, in
the online version, at doi:10.1016/j.jphotochem.2010.05.013.
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ation with 440 nm light for 1 min at 40 ◦C. The crystallization by
photoirradiation was reversed 10 times by alternating irradiation
between 365 and 440 nm light. Crystallization by photoirradiation
was observed at temperature between 40 and 70 ◦C. The photoin-
duced crystallization was also observed by XRD (Fig. 5(d)). The
peaks of the XRD spectrum represent the crystals of 2b, because the
XRD pattern is consistent with one of the pure 2b crystals (recrys-
tallization solvent: diethyl ether). The solubility of 2a is 0.1 M in
hexane at 25 ◦C, but that of 2b is 0.002 M in hexane at 25 ◦C. The
poor solubility of 2b induces crystallization in the bulk liquid of 2a.
A similar photoinduced crystallization was observed for 3a. The
melting point of 3a was 68 ◦C from DSC measurements. After heat-
ing at 80 ◦C, the single crystal 3a melted, but the liquid did not
change into the crystals at 30 ◦C. The crystallization by photoirradi-
ation was reversed several times by alternating irradiation between
365 and 440 nm light at 30 or 40 ◦C.
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4. Conclusions
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[26] CCDC 724436 and 724437 (compounds 1a and 2a) contain the sup-
plementary crystallographic data for this paper. These data can be
obtained free of charge via www.ccdc.cam.ac.uk/data request/cif, by emailing
data request@ccdc.cam.ac.uk, or by contacting The Cambridge Crystallo-
graphic Data Centre, 12, Union Road, Cambridge CB2 1EZ, UK; fax: +44 1223
336033.
We have synthesized 1,2-bis(2-(4-n-alkylphenyl)benzofuran-
3-yl)ethene derivatives. A single crystal of 1a melted at 164 ◦C. DSC
measurements show that there is no change in the melting point
between the first and second scans. The crystal of 2a melted at
102 ◦C. After heating at 130 ◦C, the liquid did not crystallize below
40 ◦C for more than 3 days because of the temperature above the
eutectic point. When the liquid was irradiated with 365 nm light,
the photoirradiated area crystallized. From the XRD analysis, the
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