DOI: 10.1002/chem.201406299
Communication
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Liquid Crystals
Photomobile Polymer Materials: Photoresponsive Behavior of
Cross-Linked Liquid-Crystalline Polymers with Mesomorphic
Diarylethenes
[a]
[a]
[a]
[a]
Jun-ichi Mamiya,* Akito Kuriyama, Naoki Yokota, Munenori Yamada, and
Tomiki Ikeda*
[b]
tion in response to light occurs in an isotropic way and the
degree of deformation is too small to be practically utilized.
A sophisticated way to amplify deformation of materials is
Abstract: Cross-linked liquid-crystalline (LC) polymers with
a mesomorphic diarylethene were prepared to demon-
strate a versatile strategy for cross-linked photochromic
LC polymers as photomobile materials. Upon exposure to
UV light to cause photocyclization of the diarylethene
chromophore, the cross-linked polymer films bend toward
an actinic light source. By irradiation with visible light to
cause a closed-ring to open-ring isomerization, the bent
films revert to the initial flat state. Without visible-light ir-
radiation, the bent films remain bent even at 1208C, indi-
cating high thermal stability of the cross-linked diaryle-
thene LC polymers.
[1]
to use cross-linked liquid-crystalline (LC) polymers (CLCPs),
which show anisotropic contraction resulting from the change
in alignment of mesogens by external stimuli, such as temper-
[6]
[7]
ature and light. In our previous work, we found that CLCP
films containing azobenzene moieties showed photoinduced
[8]
bending toward an actinic light source. A large and reversible
deformation of the azobenzene CLCPs is induced by reduction
of LC order by light. Deformation of these films can be con-
trolled by such factors as the cross-linking density, polarization
direction of actinic light and the initial alignment of meso-
[8,9]
gens.
We also have demonstrated new three-dimensional
movements of the CLCPs and their composite materials driven
only by light: a light-driven plastic motor, an inchworm walk,
[
10]
Recently, much attention has been paid to soft materials that
can convert light energy directly into mechanical work (photo-
mechanical effect) due to their advantages, such as miniaturi-
and a flexible robotic arm motion.
There have been many photochromic molecules developed
to date, such as azobenzenes, spiropyrans, fulgides, and diaryl-
ethenes, in an attempt to apply these materials to optoelec-
[
1,2]
zation, remote control, and quiet operation.
Polymers are
[
11]
one of the most promising candidates for soft actuator materi-
als because of their flexibility, lightweight, low costs, and
simple fabrication processes for devices. Many types of poly-
mers have been developed as actuator materials, such as
tronic devices, including optical memories and switches. Of
them, azobenzenes have been most widely used as a photores-
ponsive molecule in photomobile materials composed of
CLCPs, because 1) azobenzenes show a large change in shape
upon trans/cis photoisomerization, which could lead to a large
deformation of materials; and 2) many azobenzenes are meso-
morphic by themselves, which is very advantageous in view of
miscibility with many LC molecules, and high concentrations
of azobenzenes can be used in the LC mixtures, which could
[
2]
[3,4]
amorphous polymers, polymer gels,
and conducting poly-
[
5]
mers. Light as an external stimulus enables the remote con-
trol and rapid deformation of materials, and light-driven poly-
mer actuators have been extensively developed for the use of
a wide range of micro- and macroscale devices. These photo-
mobile polymer materials can convert light energy directly into
mechanical work without the aid of batteries, electric wires, or
gears. However, in amorphous polymer materials, the deforma-
[7–10]
lead to high sensitivity of photomobile materials.
However,
azobenzenes show drawbacks: their trans forms are very
stable, whereas cis isomers are thermally unstable, which
means that upon exposure to actinic light, CLCP films contain-
ing azobenzenes show deformation by trans/cis isomerization
of the azobenzenes, but the deformed films easily revert to
the initial state at high temperatures. To represent a more ver-
satile strategy for the photochromic CLCPs as photomobile
materials, we have been investigating the photomobile proper-
ties of CLCPs with various photochromic moieties.
[
a] Dr. J.-i. Mamiya, A. Kuriyama, N. Yokota, Dr. M. Yamada
Chemical Resources Laboratory, Tokyo Institute of Technology
R1-12, 4259 Nagatsuta, Midori-ku, Yokohama 226-8503 (Japan)
Fax: (+81)45-924-5275
E-mail: jmamiya@polymer.res.titech.ac.jp
[b] Prof. Dr. T. Ikeda
Research and Development Initiative, Chuo University
Diarylethenes undergo thermally irreversible and fatigue-re-
sistant photochromic reactions not only in solution, but also in
1
-13-27, Kasuga, Bunkyo-ku, Tokyo 112-8551 (Japan)
Fax: (+81)3-3817-1631
E-mail: tikeda@tamacc.chuo-u.ac.jp
Homepage: http://www.chem.chuo-u.ac.jp/~ikedalab/index_e.html
[12]
single crystals. The rod-like crystals of diarylethene deriva-
[13]
tives exhibit reversible bending upon photoirradiation. Fur-
thermore, fabrication of diarylethene crystals into various
shapes enables a variety of 3-dimensional movements of the
Supporting information for this article is available on the WWW under
http://dx.doi.org/10.1002/chem.201406299.
Chem. Eur. J. 2015, 21, 1 – 5
1
ꢀ 2015 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
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