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This article is published as part of a themed issue of
Photochemical & Photobiological Sciences on
Synthetic and natural photoswitches
Guest edited by Dario Bassani, Johan Hofkens and
Jean Luc Pozzo
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Published on 13 January 2010 on http://pubs.rsc.org | doi:10.1039/B9PP00093C
Published in issue 2, 2010
Other articles in this issue include:
Photochromic dithienylethenes with extended π-systems
O. Tosic, K. Altenhöner and J. Mattay, Photochem. Photobiol. Sci., 2010, 9, 128
Hydrophilic and photochromic switches based on the opening and closing of [1,3]oxazine rings
M. Tomasulo, E. Deniz, S. Sortino and F. M. Raymo, Photochem. Photobiol. Sci., 2010, 9, 136
Efficient carrier separation from a photochromic diarylethene layer
T. Tsujioka, M. Yamamoto, K. Shoji and K. Tani, Photochem. Photobiol. Sci., 2010, 9, 157
Multiphoton-gated cycloreversion reactions of photochromic diarylethene derivatives with low
reaction yields upon one-photon visible excitation
Y. Ishibashi, K. Okuno, C. Ota et al., Photochem. Photobiol. Sci., 2010, 9, 172
Probing photochromic properties by correlation of UV-visible and infra-red absorption spectroscopy:
a case study with cis-1,2-dicyano-1,2-bis(2,4,5-trimethyl-3-thienyl)ethene
A. Spangenberg, J. A. Piedras Perez, A. Patra et al., Photochem. Photobiol. Sci., 2010, 9, 188
The DC gate in Channelrhodopsin-2: crucial hydrogen bonding interaction between C128 and D156
M. Nack, I. Radu, M. Gossing et al., Photochem. Photobiol. Sci., 2010, 9, 194
Quantitative investigations of cation complexation of photochromic 8-benzothiazole-substituted
benzopyran: towards metal-ion sensors
M. I. Zakharova, C. Coudret, V. Pimienta et al., Photochem. Photobiol. Sci., 2010, 9, 199
Spiropyrans as molecular optical switches
B. Seefeldt, R. Kasper, M. Beining et al., Photochem. Photobiol. Sci., 2010, 9, 213
Photoinduced shape changes of diarylethene single crystals: correlation between shape changes
and molecular packing
L. Kuroki, S. Takami, K. Yoza, M. Morimoto and M. Irie, Photochem. Photobiol. Sci., 2010, 9, 221
Functional interaction structures of the photochromic retinal protein rhodopsin
K. Kirchberg, T.-Y. Kim, S. Haase and U. Alexiev, Photochem. Photobiol. Sci., 2010, 9, 226
Facile synthesis and characterization of new photochromic trans-dithienylethenes functionalized
with pyridines and fluorenes
Q. Luo, Y. Liu, X. Li and H. Tian, Photochem. Photobiol. Sci., 2010, 9, 234
Higher resolution in localization microscopy by slower switching of a photochromic protein
H. Mizuno, P. Dedecker, R. Ando et al., Photochem. Photobiol. Sci., 2010, 9, 239
Optical control of quantum dot luminescence via photoisomerization of a surface-coordinated,
cationic dithienylethene
Z. Erno, I. Yildiz, B. Gorodetsky, F. M. Raymo and N. R. Branda, Photochem. Photobiol. Sci., 2010, 9, 249
Low-temperature switching by photoinduced protonation in photochromic fluorescent proteins
A. R. Faro, V. Adam, P. Carpentier et al., Photochem. Photobiol. Sci., 2010, 9, 254
PAPER
www.rsc.org/pps | Photochemical & Photobiological Sciences
Photoinduced shape changes of diarylethene single crystals: correlation
between shape changes and molecular packing†‡
Lumi Kuroki,a Shizuka Takami,b Kenji Yoza,c Masakazu Morimotod and Masahiro Irie*d
Downloaded by North Carolina State University on 27 September 2012
Published on 13 January 2010 on http://pubs.rsc.org | doi:10.1039/B9PP00093C
Received 4th September 2009, Accepted 30th October 2009
First published as an Advance Article on the web 13th January 2010
DOI: 10.1039/b9pp00093c
Correlation between the photoinduced shape changes of diarylethene single crystals and their
molecular packing in the crystals was studied. Crystals of 1,2-bis(5-ethyl-2-phenyl-4thiazolyl)perfluorocyclopentene (3a) and 1,2-bis(2-isopropyl-5-phenyl-3-thienyl)perfluorocyclopentene
(4a) showed similar photoinduced deformation from square to lozenge as that of 1,2-bis(2-ethyl-5-phenyl-3-thienyl)perfluorocyclopentene (1a). Although these three diarylethenes have
different electronic structures and exhibit different colours upon UV irradiation, the crystallographic
structures and molecular packing of the crystals are very similar to each other. The result indicates that
the deformation mode is determined by the packing mode of component molecules in the crystal.
X-Ray crystallographic analysis of a micrometre-sized crystal 1a (20 ¥ 15 ¥ 8 mm) prepared by
sublimation revealed that the small-size crystal, which shows photoinduced deformation, has the same
crystal structure as that of the large bulk crystal.
Introduction
1,2-bis(5-methyl-2-phenyl-4-thiazolyl)perfluorocyclopentene (2a)
is ascribed to the changes of molecular packing in the crystal based
on the isomerization of the component molecules, as shown in the
ESI Fig. S1.† In this study, we have further examined two more
crystals and studied the correlation between the shape changes
and the molecular packing and tried to confirm the generality of
the proposed deformation mechanism.
It is of particular interest from both scientific as well as technological points of view to have molecules make mechanical motion
by chemical or physical stimuli and link the motion to macroscale mechanical work of bulk materials. One of such examples
is muscle. Conformational change of myosin upon release of
adenosine diphosphate (ADP) at the molecular level is used to
drive muscles and performs the macro-scale mechanical work.1 In
contrast, artificial molecular mechanical systems, which are based
on molecular-level shape changes, fail to be linked to macro-scale
mechanical motion of materials.2–4 Large scale mechanical motion
of molecular materials was observed only in nematic elastomers,
in which a photoinduced order–disorder phase transition is used
as the driving force.5,6
Recently, we have reported that some diarylethene molecular
crystals exhibit photoinduced reversible deformation.7 Similar
phenomena have also been found for anthracene carboxylates
and amino azobenzene crystals.8–11 In a recent report,7 we proposed that the anisotropic deformation of the single crystals of
1,2-bis(2-ethyl-5-phenyl-3-thienyl)perfluorocyclopentene (1a) and
Among various diarylethene crystals12 we chose the crystals of following two diarylethenes, 1,2-bis(5-ethyl-2-phenyl-4thiazolyl)perfluorocyclopentene (3a) and 1,2-bis(2-isopropyl-5phenyl-3-thienyl)perfluorocyclopentene (4a)13 (Scheme 1). The
photoinduced shape changes of micrometre-sized crystals 3a and
4a prepared by sublimation have been studied.
Unit cell parameters of crystals 3a and 4a are shown in Table 1.§
The data of 1a are also shown as a reference.7 As can be seen from
the table, crystals 3a and 4a have a similar unit cell to 1a, and
1a, 3a, and 4a have the same space group Pbcn. The molecular
structures and their packing are similar to those observed in 1a.
a
Department of Chemistry and Biochemistry, Graduate School of Engineering, Kyushu University, Motooka 744, Fukuoka, 819-0395, Japan
b
Niihama National College of Technology, Yakumo-cho 7-1, Niihama,
Ehime, 792-8580, Japan
c
Bruker AXS K.K., Moriya-cho 3-9, Kanagawa-ku, Yokohama, 221-0022,
Japan
d
Department of Chemistry and Research Center for Smart Molecules, Rikkyo
University, Nishi-Ikebukuro 3-34-1, Toshima-ku, Tokyo, 171-8501, Japan.
E-mail: iriem@rikkyo.ac.jp
† Electronic supplementary information (ESI) available: Schematic illustration of photocontraction of a crystal and crystal data for 3a, 3a¢, 3b, 4a,
micro-crystal 1a and micro-crystal 1a¢. CCDC reference numbers 713390–
713395. For ESI and crystallographic data in CIF or other electronic
format see DOI: 10.1039/b9pp00093c
‡ This paper is part of a themed issue on synthetic and natural photoswitches.
§ Crystal data for 3a: C27 H20 F6 N2 S2 , M = 550.59, T = 123 K, orthorhombic
Pbcn, a = 21.5461(15), b = 10.8096(8), c = 10.8098(8) Å, V = 2517.7(3) Å3 ,
Z = 4, R1 (I > 2s(I)) = 0.0385. Crystal data for 3a¢: C27 H20 F6 N2 S2 , M =
550.59, T = 123 K, orthorhombic Pbcn, a = 21.586(2), b = 10.8692(11), c =
10.7268(11) Å, V = 2516.7(4) Å3 , Z = 4, R1 (I > 2s(I)) = 0.0332. Crystal
data for 3b: C27 H20 F6 N2 S2 , M = 550.59, T = 123 K, monoclinic P21 /c,
a = 9.5508(8), b = 19.4249(15), c = 13.5268(11) Å, b = 95.7430(10)◦ ,
V = 2496.9(3) Å3 , Z = 4, R1 (I > 2s(I)) = 0.0393. Crystal data for 4a:
C31 H26 F6 S2 , M = 576.66, T = 123 K, orthorhombic Pbcn, a = 21.307(6),
b = 12.193(4), c = 10.669(3) Å, V = 2771.8(14) Å3 , Z = 4, R1 (I > 2s(I)) =
0.0360. Crystal data for micro-crystal 1a: C29 H22 F6 S2 , M = 548.61, T =
100 K, orthorhombic Pbcn, a = 22.239(5), b = 10.971(3), c = 10.585(3)
Å, V = 2594.1(12) Å3 , Z = 4, R1 (I > 2s(I)) = 0.0627. Crystal data for
micro-crystal 1a¢: C29 H22 F6 S2 , M = 548.61, T = 100 K, orthorhombic
Pbcn, a = 22.30(3), b = 11.026(18), c = 10.542(18) Å, V = 2593(7) Å3 ,
Z = 4, R1 (I > 2s(I)) = 0.1009. The details of the crystal data are shown
in Tables S1 and S2 in the ESI.†
Results and discussion
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Table 1 Unit cell parameters of single crystals of 1a, 3a and 4a
Compound
Space group
a
b
c
1a7
3a§
4a§
Pbcn
Pbcn
Pbcn
22.33
21.55
21.31
10.99
10.81
12.19
10.60
10.81
10.67
The time dependence of the colour and shape changes upon
alternate irradiation with ultraviolet (UV) and visible light was
followed. Upon UV light irradiation the corner angle of crystal
3a initially remains unchanged and then decreases as much as 3◦
to 6◦ , as shown in Fig. 2. Any hysteresis between the forward and
reverse processes was not observed. The induction period of the
shape change is ascribed to the accumulation time of the adjacent
closed-ring isomers in the crystal.7 Crystal 4a changed its colour
from colourless to blue and the corner angles from 83◦ and 97◦ to
81◦ and 99◦ upon irradiation with UV light, respectively (Fig. 1b).
These deformation behaviour is the same as that observed for
microcrystal 1a.
Fig. 2 Relationship between the corner angle of micrometre-sized crystal
3a and the absorption intensity of the crystal measured at 550 nm upon
alternate irradiation with UV (l = 365 nm, open circles) and visible
(l > 480 nm, filled circles) light.
Scheme 1
When crystals 3a and 4a with the size of around 10 mm prepared
by sublimation were irradiated with 365 nm light, their colour and
shape changed. Crystal 3a changed its colour from colourless to
red and its corner angles from 90◦ and 90◦ to 86◦ and 94◦ , and
hence its shape from square to lozenge (Fig. 1a). The red colour is
ascribed to the colour of the photo-generated closed-ring isomer
3b. The deformed red crystal returned to the initial colourless and
square shape upon irradiation with visible light (l > 480 nm).
Fig. 1 Deformation of single crystals of (a) 3a and (b) 4a. The scale bars
are 10 mm.
222 | Photochem. Photobiol. Sci., 2010, 9, 221–225
It was reported that the melting point of micrometre-sized
crystal 1a prepared by sublimation is the same as that of the large
bulk crystal.7 For 3a, the melting point of the large crystals is
184 ◦ C and that of micrometre-sized crystals is also 184 ◦ C. The
result suggests that the microcrystals have the same crystal
structures as observed in the large bulk crystals. To confirm the
identical crystal structures, we carried out single-crystalline X-ray
analysis on micrometre-sized crystal 1a (20 ¥ 15 ¥ 8 mm) and
compared the crystal structure with that of the large bulk crystal.
We employed high-intensity X-ray system (Bruker APEX2
Ultra) for the measurement. With 300 s exposure for 1 frame,
we could observe high-angle reflection and succeeded in the
structural analysis. The crystallographic data of the micrometresized crystal are shown in Table S2.† Although the data quality
is poor, the analysis confirms that the micrometre-sized crystal
has the identical structure as the large crystal.¶ The microcrystal
was irradiated with UV light for 1 min (365 nm, 20 mW) and the
UV irradiated crystal 1a¢ was also analyzed by using the same
X-ray crystallographic system.† In the micrometre-sized crystal,
photoirradiation for 1 min was enough to induce the cyclization
reaction up to 12%. The photo-generated isomer was observed
as disorders of sulfur and reacting carbon atoms (S1B and C1B)
and formation of the closed-ring isomers was evidenced, as shown
in Fig. 3. The crystal again returned to the original one upon
irradiation with visible light.
¶ Because of the small size of the crystal, it was impossible to collect
enough number of reflection.
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Fig. 3 ORTEP drawings of 1a¢ (photo-irradiated micrometre-sized crystal 1a, conversion: 12%) showing 50% probability displacement ellipsoids.
The blue lines indicate photo-generated closed-ring isomer. Hydrogen
atoms and disordered structures which observed in 1a were omitted for
clarity.
Fig. 4a illustrates the crystal shape of crystal 3a and its face
indices. The edges of the largest surface are diagonals of the b
and c axes cell and the surface has square shape as shown in the
figure. This morphology is the same as that of the micrometresized crystal (Fig. 1a). Polarized absorption spectra and their
anisotropies of the coloured microcrystal are the same as those
observed on (100) surface of the large crystal.
Fig. 4
The face indices of crystal (a) 3a and (b) 4a.
Fig. 5a shows the molecular packing of crystals 3a. On (100)
surface, both long axis of 3a molecule and electronic transition
moment of photo-generated isomer are projected on the c axis.
It was found that the direction of contraction coincides with
the direction of strong polarized absorption. In other words, the
corner angles, which are perpendicular to the orientation of long
Fig. 5 Molecular packing of crystals of (a) 3a and (b) 4a before UV
irradiation viewed from (100) and (010) faces. The blue arrows show the
directions of contraction of the crystals.
axis of the molecules, become acute. The angle decrease upon
contraction of c axis is well explained by Fig. 4a.
We also carried on X-ray structural analysis of UV irradiated
crystal 3a (3a¢) and crystal 3b, as shown in Tables 2 and S1.†
Upon UV irradiation, the unit cell parameter of c axis showed
obvious contraction along with the photoirradiation time, while
the parameters of a and b axes exhibited expansion (Table 2). Fig. 6
shows side views of molecular structures of 3a, 3a¢, and 3b. The
thickness of molecule is reduced as the molecule converts from
the open- to the closed-ring isomer. This decrease of the thickness
upon UV irradiation is considered to cause contraction along the
c axis.
Crystal 4a has similar unit cell parameters and the same space
group as those of 1a and 3a (Table 1). Furthermore, molecular
structure and packing in the crystal are similar to those of 1a
and 3a. Colourless microcrystal 4a turned to blue and the acute
corner angle further decreased upon irradiation with 365 nm light
(Fig. 1b). The blue colour and the angle returned to the initial
ones upon irradiation with visible light (l > 480 nm). Melting
points of the micrometre-sized crystal and the large crystal of 4a
were identical (171 ◦ C). Fig. 4b illustrated crystal shape of bulk
crystal 4a and its face indices. As shown in the figure, the shape of
Table 2 Unit cell parameters of 3a crystal before and after UV irradiation
Time of irradiation/h
a
b
c
0
2
4
21.546
21.568
21.586
10.810
10.850
10.869
10.810
10.752
10.727
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Fig. 6 ORTEP drawings of 3 oriented as in the Fig. 5a showing 50%
probability displacement ellipsoids. (a) 3a, (b) 3a¢ (3a crystal after UV
irradiation for 4 h) and (c) 3b. Reacting carbon and sulfur atoms of 3a¢
were disordered and only photo-generated structures (site occupancy ~
6%) are shown for clarity.
the largest surface, indexed (100), is diamond or hexagon. Fig. 5b
shows the molecular packing of crystal 4a. The shape change of
crystal 4a is similar to crystals 1a and 3a.
Conclusions
In conclusion, crystals of 3a and 4a showed similar deformation
mode as that of 1a. The crystallographic structures of these three
crystals are very similar each other. It is concluded that deformation mode is determined by the packing mode of component
molecules in the crystals.
Experimental
General
1
H NMR spectra were recorded with a Bruker AVANCE400 spectrometer (400 MHz). Mass spectra were recorded with a Shimadzu
GCMS-QP5050A gas chromatography-mass spectrometer. The
large bulk crystals of the diarylethene derivatives were prepared
by recrystallization. The micrometre-sized small single crystals
were prepared by sublimation of the compounds on glass plates.
Photographs were taken with a digital camera (NIKON Coolpix
4500 Microsystem, 4.0 megapixels) connected with a polarizing
microscopes (Leica DMLP). UV light irradiation was carried out
using an LED irradiation system (Keyence UV-400, l = 365 nm).
Visible light irradiation was carried out using a 200 W xenonmercury lamp (Moritex MUV-202U) as a light source. The light
longer than 480 nm was obtained by passing the light through a
cut-off filter (Asahi Techno glass Y-48).
Synthesis of 3a
3a was prepared according to the following synthesis route from
5-bromo-2-phenylthiazole, which was synthesized by the methods
reported previously (Scheme 2).14,15
4-Bromo-5-ethyl-2-phenylthiazole (5). To a dry THF solution
(60 cm3 ) containing a 2 M lithium diisopropylamide (LDA)
solution (5.0 cm3 , 10 mmol) was added 5-bromo-2-phenylthiazole
(2.0 g, 8.5 mmol) dissolved in dry THF (10 cm3 ) at -78 ◦ C
CF2 groups in each perfluorocyclopentene and ethyl groups of 3a and 3a¢
were disordered. Hydrogen atoms and minor structures of these disordered
parts are omitted for clarity.
224 | Photochem. Photobiol. Sci., 2010, 9, 221–225
Scheme 2
under an atmosphere of nitrogen and the solution was stirred
for 30 min at the low temperature. Iodoethane (1.0 cm3 , 12 mmol)
was added to the mixture and the stirring was continued for 1 h at
-40 ◦ C. After warming up the solution to the room temperature,
the reaction was stopped by the addition of water. The reaction
mixture was neutralized with HCl and then extracted with diethyl
ether. The organic layer was washed by brine, dried over MgSO4 ,
filtrated, and concentrated. The residue was purified by column
chromatography on silica gel (ethyl acetate–hexane, 1 : 9) to afford
5 (1.4 g, 61%); d H (400 MHz; CDCl3 ; Me4 Si) 1.31–1.35 (3 H, t,
CH3 ), 2.81–2.87 (2 H, q, CH2 ), 7.41–7.44 (3 H, m, Ph), 7.87–7.90
(2 H, m, Ph); m/z (EI) 267 (M+ ).
1-(5-Ethyl-2-phenyl-4-thiazolyl)perfluorocyclopentene (6). To
a dry THF solution (20 cm3 ) containing 5 (0.47 g, 1.8 mmol)
was added n-BuLi (1.6 M in hexane, 1.4 cm3 , 2.2 mmol) at -78 ◦ C
under an atmosphere of argon, and the solution was stirred for
30 min at the low temperature. Octafluorocyclopentene (0.7 cm3 ,
5.2 mmol) was added to the reaction mixture at -78 ◦ C, and the
mixture was stirred for 3 h at that temperature. After warming up
the solution to the room temperature, the reaction was stopped by
the addition of methanol. The reaction mixture was extracted
with diethyl ether. The organic layer was dried over MgSO4 ,
filtrated, and concentrated. The residue was purified by column
chromatography on silica gel (chloroform–hexane, 3 : 1) to afford
6 (0.45 g, 65%); d H (400 MHz; CDCl3 ; Me4 Si) 1.37–1.41 (3 H, t, J
7.6, CH3 ), 2.84–2.90 (2 H, dq, J 7.6 and 2.0, CH2 ), 7.43–7.46 (3
H, m, Ph), 7.91–7.94 (2 H, m, Ph); m/z (EI) 381 (M+ ).
1,2-Bis(5-ethyl-2-phenyl-4-thiazolyl)perfluorocyclopentene (3a).
To a dry THF solution (15 cm3 ) containing 5 (0.27 g, 1.0 mmol)
was added n-BuLi (1.6M in hexane, 0.70 cm3 , 1.1 mmol) at -78 ◦ C
under an atmosphere of argon, and the solution was stirred for
30 min at the low temperature. 6 (0.45 g, 1.2 mmol) was added
to the reaction mixture at -78 ◦ C, and the mixture was stirred
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for 3 h at that temperature. After warming up the solution to
the room temperature, the reaction was stopped by the addition
of methanol. The reaction mixture was extracted with diethyl
ether. The organic layer was washed by brine, dried over MgSO4 ,
filtrated, and concentrated. The residue was purified by column
chromatography on silica gel (dichloromethane–hexane, 1 : 1) to
afford 3a (0.11 g, 20%). A small portion of this product was
recrystallized from hexane to give colourless blocks; mp 183–
184 ◦ C (from hexane); d H (400 MHz; CDCl3 ; Me4 Si) 0.96–1.01
(3 H, t, J 7.2, CH3 ), 2.44–2.52 (2 H, q, J 7.2, CH2 ), 7.42–7.46 (3
H, m, Ph), 7.88–7.94 (2 H, m, Ph); m/z (EI) 550 (M+ ).
Synthesis of 4a
4a was prepared according to the method reported previously.13
X-Ray crystallographic analysis
X-Ray crystallographic analysis was performed using a Bruker
APEX2 Ultra CCD-based diffractometer with Mo-Ka radiation
(0.71073 Å). The crystals were cooled with a cryostat. The data
were collected as a series of f- and w-scan frames. Data reduction
was performed using SAINT software, which corrects for Lorentz
and polarization effects, and decay. The cell constants were
determined by the global refinement. The structures were solved
by direct methods using SHELXS-9716 and refined by full leastsquares on F 2 using SHELXL-97.17 The positions of all hydrogen
atoms were calculated geometrically and refined by the riding
model. For disordered structures, occupancy factors were refined
under a constraint such that the sum is 1.
Acknowledgements
This work was partly supported by a Grant-In-Aid for Scientific
Research in Priority Areas “New Frontiers in Photochromism
(471)” (no. 19050008) from the Ministry of Education, Culture,
Sports, Science, and Technology (MEXT), Japan. L. K. also
acknowledges a Grant-In-Aid for JSPS Research Fellows.
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