Photosalient Effect of a Diarylethene with a Perfluorocyclohexene Ring

Article abstract of DOI:10.1002/chem.201603020

Crystals of a diarylethene with a perfluorocyclohexene ring exhibit a remarkable photosalient effect upon UV light irradiation that is attributed to the structural changes that occur when going from open- to closed-ring isomers in the crystalline state, together with the existence of two conformers with different photoconversions compared with those of a perfluorocyclopentene derivative. Our current results give a design principle for molecular structures so as to achieve the photosalient effect for photochromic crystals.

Full text of DOI:10.1002/chem.201603020

A Journal of
Accepted Article
Title: Photosalient Effect of a Diarylethene Having Perfluorocyclohexene Ring
Authors: Eri Hatano; Masakazu Morimoto; Kengo Hyodo; Nobuhiro Yasuda; Satoshi
Yokojima; Shinichiro Nakamura; Kingo Uchida
This manuscript has been accepted after peer review and the authors have elected
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of the final Version of Record (VoR). This work is currently citable by using the Digital
Object Identifier (DOI) given below. The VoR will be published online in Early View as
soon as possible and may be different to this Accepted Article as a result of editing.
Readers should obtain the VoR from the journal website shown below when it is pu-
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To be cited as: Chem. Eur. J. 10.1002/chem.201603020
Link to VoR: http://dx.doi.org/10.1002/chem.201603020
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Photosalient Effect of a Diarylethene Having
Perfluorocyclohexene Ring
[a]
[b]
[a]
[c]
[d]
Eri Hatano, Masakazu Morimoto,* Kengo Hyodo, Nobuhiro Yasuda, Satoshi Yokojima,
[e]
[a]
Shinichiro Nakamura, and Kingo Uchida*
Abstract: Crystals of a diarylethene having perfluorocyclohexene
undergo crystal shape changes (elongation and shrinkage) as
[
9]
ring exhibit a remarkable photosalient effect upon UV light irradiation, well as photoinduced bending.
Irie et al. reported the
which is attributed to the larger structural changes from open- to
closed-ring isomers in the crystalline state together with the
existance of two conformers with different photo-conversion
compared with those of a perfluorocyclopentene derivative. Current
results will give a design principle for molecular structures to achieve
photosalient effect by the photochromic crystals.
photoinduced crystal jump of diarylethene microcrystals upon
[
10]
UV irradiation.
synthesized
perfluorocyclopentene ring.
The diarylethenes that have mainly been
previously have five-membered
On the other hand, a derivative
a
[
11]
having perfluorocyclohexene ring with two benzothiophene aryl
groups was reported in an effort to improve fatigue resistance
and physical properties, although no systematic study was
[
12]
performed.
It is well known that plants have a unique strategy to
increase their chances of successful reproduction. The
lightweight seeds move with the wind and spread out to far
distances, especially if they get caught on a bird or insect
moving about the region. Impatiens and squirting cucumber
Herein, we have newly synthesized a derivative having
phenylthiazole rings as aryl groups on both sides of the
perfluorocyclohexene ring 1o, based on previous papers
describing the synthesis of 1,2-bis(2-methylbenzothiophen-3-
yl)perfluorocyclohexene and 1,2-bis(5-methyl-2-phenylthiazo-4-
[
1]
have specific mechanism to scatter their seeds explosively.
[12,13]
yl)perfluorocyclopentene.
The photochromism in the
The first organic photosalient effect was reported by
crystalline state and the observed photosalient effect of 1o were
compared with those of 2o with perfluorocyclopentene ring.
Trommsdorff in 1834 on the “burst” of crystals of -santonin after
[
2]
the color turning yellow by exposing it to the sunlight. The
[
3]
photosalient effect was recently reinvestigated. Recently,
Naumov et al. intensively studied the crystal jump and breaking
due to a strong light stimulus and named it the photosalient
[
4-8]
effect.
They reported the following processes for
(NO )]Cl(NO ): (1) splitting
photoirradiated crystals of [Co(NH
3
)
5
2
3
of a crystal into two pieces of nearly equal size, (2) separation of
a small piece off the crystal, which propels the remaining part
into a spinning or linear motion, (3) crystal explosion, (4) minor
repositioning without lifting off the base and apparent splitting or
[
4]
separation of debris, and (5) rolling or flipping of the crystal.
The crystals of diarylethene derivatives were also reported to
[
a]
b]
E. Hatano, Dr. K. Hyodo, Prof. Dr. K. Uchida
Department of Materials Chemistry, Faculty of Science and
Technology, Ryukoku University
Seta, Otsu, Shiga 520-2194 (Japan)
E-mail; uchida@rins.ryukoku.ac.jp
Scheme 1. Molecular structures of the two isomers of diarylethene 1 and 2.
The absorption spectral changes of 1o in hexane solution
are shown in Figure 1. Open-ring isomer 1o shows the
[
M. Morimoto
Department of Chemistry and Research Center for Smart
Molecules, Rikkyo University
4
-1
-1
absorption maximum at 298 nm (: 3.1 × 10
13 nm irradiation, the solution turned to purple, and a band
attributed to the closed-ring isomer 1c appeared at 518 nm (:
M
cm ). Upon
3
3-34-1 Nishi-Ikebukuro, Toshima-ku, Tokyo 171-8501 (Japan)
[
c]
d]
N. Yasuda
4
-1
-1
Japan Synchrotron Radiation Research Institute, SPring-8
1.1 × 10 M cm ). Upon visible light (> 500 nm) irradiation,
the solution turned to colorless and the spectrum of 1o was
regenerated. Consequently, photochromism was observed. The
quantum yields of cyclization and cycloreversion reactions in
hexane were obtained to be 0.29 (oc at 313 nm) and 0.015 (co
at 492 nm), respectively. These values were very similar to
1-1-1 Kouto, Sayo-cho, Sayo-gun, Hyogo 679-5198 (Japan)
[
S. Yokojima
School of Pharmacy, Tokyo University of Pharmacy and Life
Sciences
1432-1 Horinouchi, Hachioji, Tokyo 192-0392 (Japan)
[e]
S. Nakamura
RIKEN Innovation Center, Nakamura Laboratory
those of perfluorocyclopentene derivatives 2o and 2c (2o: max
:
2-1 Hirosawa, Wako, Saitama 351-0198 (Japan)
4
-1
-1
4
-1
3
00 nm (: 3.4 × 10 M cm ), 2c:max: 525 nm (: 1.0 × 10 M
Supporting information for this article can be found under:
http://dx.doi.org/
-1
cm ), 0.32 (oc at 313 nm) and 0.02 (co at 492 nm)) in the

Chemistry - A European Journal
10.1002/chem.201603020
COMMUNICATION
same hexane solution. Additionally, 1c showed much better
1
1
0
0
0
0
0
.2
.0
.8
.6
.4
.2
.0
[
14]
:
1c
: 1o
PSS
thermal stability compared with that of 2c.
The thermal
stability of 2c is reported to be reached at the half-life time of 30
h at 180 °C in degassed decalin. In contrast, the half-life time of
:
1c was almost 80 h at the same temperature in decalin under
the same condition (Figure S1 in the Supporting Information).
Compound 1o also showed the photochromism, even in the
crystalline state. In the single crystal, the two conformers of 1o
are located in a unit cell, and the distances between the reactive
carbon atoms were 3.476 Å (conformer A) and 3.582 Å
(
conformer B), respectively (Figure S2 in the Supporting
2
00
300
400
500
600
700
Information). These values are shorter than 4.2 Å, which
satisfies the condition for photo-reactivity in the crystalline
Wavelength / nm
[15]
state.
Figure 1. Absorption spectral changes of 1o in hexane solution (3.27 × 10-5
M); Absorption spectrum of 1o (solid line), Absorption spectrum of 1c (broken
line), and photostationary state upon 313 nm light irradiation (1o: 1c=12:88)
Upon UV irradiation to the thin crystals of 1o, the crystals
changed colour to purple, indicating the formation of 1c. Then
the crystals showed bending (Figure 2a), jumping (Figures 2b,
c (Movie I)), and explosive scattering into small pieces (Figure
(
dotted line).
2d (Movie II)), i.e. the photosalient effect appeared. As for the
photoinduced jumping, the use of lotus leaf is effective to
observe the event, because the adhesion force between the thin
crystals and the surface of lotus leaf is small compared to that
(a)
[
16]
between the thin crystals and the glass surface.
Their ratio
was nearly 6: 3: 1 for bending, jumping, and scattering.
Comparing to single crystals of 2o, which showed very fatigue-
(b)
(c)
(d)
Figure 3. Single crystal of 1o prepared by recrystallization from ethanol-
dichloromethane mixture and the polar plot figures. (a) (010) surface of single
crystal of 1o (scale bar: 200m), (b) polar plot of (010) surface monitored at
max of 540 nm after irradiation with UV light of 313 nm, (c) two separated
components of polar plots of (b) by waveform analysis, (d) unit cell consisting
of two conformers of 1o from (010) surface, (e) molecular packing of (d), (f)
side view of (a) surface indicating (001) surface (scale bar: 200 m), (g) polar
plot of (001) surface monitored at max of 537 nm after irradiation with UV light
of 313 nm, (h) unit cell consists of two conformers of 1o from the (001) surface,
and (i) molecular packing of (h), (j) bending direction to the incident light.
Figure 2. Photoresponsive phenomena of the thin film of 1o. (a) bending
scale bar: 100 m), (b) bending (I to II) followed by jumping (III to IV) (scale
(
bar: 50 m), (c) photoinduced jumping on a lotus leaf (scale bar: 100 m), (d)
photoinduced scattering (scale bar: 50m).

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resistant photoinduced bending, those of 1o showed
remarkable photosalient effect (“salient” means leaping).
a
[
5]
(a)
The largest surface of the thin crystals of 1o is estimated to
be a (010) surface from their XRD pattern (Figure S8 in the
Supporting Information). In order to clarify the reason why
crystals of 1o show the remarkable photosalient effect, we
[
17]
carried out the X-ray analysis of the crystal of 1o,
and
compared it with that of 2o. A crystal of 1o was prepared by
recrystallization from an ethanol-dichloromethane mixture, and
the polar plots of two faces of the crystals were observed as
shown in Figure 3. A CCD image of the (010) surface of a single
crystal of 1o is shown in Figure 3a. The crystal was irradiated
with UV light of 313 nm for 1 min, and the polar plot was
measured with a polarized microscope. In the measurement, a
polarizer and an analyzer were set parallel to each other. Then
the asymmetric polar plot (Figure 3b) was divided into two
components as an assumption that each polar pot should be
symmetric (Figure 3c). The intensity variation by rotation
depended on the perfluorocycloalkene rings. The dichroism
under polarized light clearly indicates that 1o underwent
photochromic reactions in the crystal lattice, and the existence of
two conformers with a tilt angle of about 60°, which is very close
to the twisting angle of 64° viewed from (001) face estimated
from X-ray analysis (Figure S6 in the Supporting Information).
Therefore, the face in Figure 3f is considered to be the (001)
surface. This is in good agreement with the XRD results of thin
crystals (Figure S8 in the Supporting Information). The distances
between two reactive carbons of the two conformers in a unit
cell were 3.476 Å (conformer A, blue) and 3.582 Å (conformer B,
green). These distances were shorter than 4.2 Å, indicating that
both conformers are photoreactive in the crystalline state.
Consequently, the crystalline surface shown in Figure 3a can be
attributed to the (010) surface.
(b)
Figure 4. Structural changes in the conformers of open-ring isomer 1o to the
closed-ring isomer 1c in the crystals (a) compared with 2o to 2c (b).
were 5.8 and 5.9%, respectively. These changes are far larger
than those of 2o to 2c.
The large molecular shape change in 1o upon cyclization
reaction is the direct consequence of the use of perfluorocyclo-
hexene instead of perfluorocyclopentene. The interior angle of 6
membered-ring (perfluorocyclohexene) is larger than that of 5
membered-ring (perfluorocyclopentene). Thus, the angles ()
related to the C-C bond between perfluorocyclohexene and
thiazole rings changed (Figure S9 in the Supporting Information)
and the distance between two thiazole rings becomes shorter in
1
o than in 2o. This results in the shorter horizontal axis and
longer longitudinal axis in 1o than in 2o. Similar tendency is
observed for the closed-ring isomer as well. However, the strong
framework of the closed-ring isomer suppresses the difference
in horizontal and longitudinal axes between the 1c and 2c.
The large geometrical change of the diarylethene molecule
induces the deformation of the crystal lattice as well as the
bending and salient phenomena. The photoinduced changes in
the cell parameters were directly observed by X-ray analysis on
a UV-irradiated crystal of 1o (1o-UV in Table S1 in the
Irie et al. demonstrated that the molecular shape changes
from an open- to closed-ring isomer of diarylethene in the
[
9]
crystals are the driving force of photoinduced crystal bending.
Therefore, larger shape changes of diarylethene are expected to
induce larger crystal deformation. Then the changes in
molecular structure from the open-ring isomer to the closed-ring
isomer of 1 and 2 are summarized and compared in Figure 4.
Upon UV irradiation to the crystals, 2o converted to 2c with
expansion of the longitudinal axis of the molecules from 5.930 to
[
17]
Supporting Information).
Upon UV irradiation, the a- and b-
axes were elongated from 13.3855(4) to 13.4391(6) Å (+0.40%)
and from 25.1206(9) to 25.2408(14) Å (+0.48%), respectively,
while the c-axis was contracted from 14.7089(5) to 14.6414(8) Å
6.086 Å. The expansion ratio was 2.6%. For the horizontal axis,
it expanded 0.6% from 2o to 2c, accompanied with a cyclization
reaction. The molecule also showed reduced thickness upon
cyclization. In the photoinduced bending of crystals of 2o,
cofacial packing of the photogenerated thinner closed-ring
isomers allows the molecules to be stacked one-by-one,
resulting in contraction along the long axis of the needle-like
(
−0.46%) accompanied with the 0.45% increment of angle.
The expansion of the horizontal axes of the diarylethene
molecule upon photocyclization contributes to the elongation of
the a-axis, which is parallel to the long axes of the thin plate
crystals of 1o. Therefore, the crystals bent in the direction away
from the UV light source (Figures 2a, b). The large shape
changes from 1o to 1c in the crystals, and the orientation of the
two conformers also gives rise to the effective photosalient effect.
By performing the crystrographic analysis on the electron
density peaks of the sulfur atoms for a UV-irradiated crystal as
[
9]
crystal and the bending phenomena. In contrast, 1o has two
types of conformers positioned in a twisted configuration to each
other as shown in Figure 3 (also in Figure 4a). Upon UV
irradiation, both conformers undergo cyclization reaction to form
1
c. The longitudinal axes of the blue- and green-coloured
conformers shrunk from 6.736 and 6.742 Å, respectively, to
.132 Å, at shrinkage ratios of 9.0 and 9.0%. The horizontal
axes of the conformers A (blue) and B (green) of 1o were
3.662 and 13.646 Å. They expanded to 14.456 Å when the
[
18]
has been done previously,
we obtained the ratio of
6
photocyclization for two conformers (Figure S5 in the Supporting
Information). After UV irradiation, the conformer A converted to
the closed-ring isomer of 6.9%, while the conformer B converted
1
[
17]
molecules were converted to 1c, and the expansion ratios

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to that of 4.4%. The different conversion of open-ring isomers
with different orientation in the crystal will also work for
photosalient effect (Figure S5 in the Supporting Information).
The photosalient phenomena were observed mainly after
bending. To induce photosalient effect, much more conversion
and difference of the conversions to their closed-ring isomers of
the two conformers of open-ring isomers are necessary. The
explosive scattering (Figure 2d) can be attributed to the
significant deformation in the ac-plane, which corresponds to the
large (010) face of the thin plate crystal. The diarylethene
molecules are stacked along the c-axis. The shrinkage of the
thickness of the diarylethene molecule upon photocyclization
results in contraction along the c-axis. The accumulated strain
produced by the elongating and contracting deformation in the
ac-plane induces the scattering phenomenon. The photoinduced
jump of the 1o crystal on the surface of a lotus leaf (Figure 2c)
and the photoinduced breaking of the crystal 1o are included in
the Supporting Information as movies.
A diarylethene having perfluorocyclohexene 1o undergoes a
cyclization reaction to form 1c even in the crystalline state. Due
to the large geometrical changes in the molecules during the
reaction, the thin crystals broke into their pieces explosively.
This is in very clear contrast to changes in the corresponding
thiazole-based diarylethene having perfluorocyclopentene 2o,
which shows reversible bending upon UV irradiation. The
diarylethene 1o, having the size of a six-membered ethene
moiety, showed larger changes in the size of the molecule
during a cyclization reaction in the crystalline state and induced
remarkable photosalient phenomena. In general terms,
modification of the molecular structure of diarylethenes will
induce the more remarkable photosalient effect and will be the
experiments were performed at the BL02B1 and BL40XU of
SPring-8 with the approval of the Japan Synchrotron Radiation
Research Institute (JASRI) (Proposal No. 2013A1219,
2014A1048, 2014B1098, and 2014B1082).
Keywords: Photosalient effect • Photochromism • Diarylethene •
Perfluorocyclohexene
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Acknowledgements
2
[
[
This work was supported by JSPS KAKENHI Grant Numbers
JP26107012 and JP15H01096 in Scientific Research on
Innovative Areas “Photosynergetics”, and the Ministry of
Education, Culture, Sports, Science and Technology, Japan
17]
CCDC 1453359 (1o), 1476101 (1o-UV), and 1453360 (1c) contain the
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1
(
MEXT) as a Supported Program for the Strategic Research
Foundation at Private Universities. The synchrotron radiation

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[
a]
[b]
Upon UV irradiation to the single
crystal of 1o, the crystal suddenly
broke into their spices explosively
like as seed dispersal of impatient.
Eri Hatano, Masakazu Morimoto,*
[
a]
[c]
Kengo Hyodo, Nobuhiro Yasuda,
[
d]
Satoshi Yokojima, Shinichiro
[
e]
[a]
Nakamura, and Kingo Uchida*
Page No. – Page No.
Photosalient Effect of a Diarylethene
having Perfluorocyclohexene Ring
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