COMMUNICATION
Photoresponsive rolling and bending of thin crystals of chiral
diarylethenes{
Kingo Uchida,*ab Shin-ichiro Sukata,a Yuji Matsuzawa,a Masako Akazawa,a Jaap J. D. de Jong,b
Nathalie Katsonis,b Yuko Kojima,c Shinichiro Nakamura,c Jetsuda Areephong,b Auke Meetsmab and
Ben L. Feringa*b
Received (in Cambridge, UK) 4th October 2007, Accepted 21st November 2007
First published as an Advance Article on the web 4th December 2007
DOI: 10.1039/b715251e
controlled reversibly by light.7 In the present communication we
Dithienylhexafluorocyclopentene with (R)- or (S)-N-phenyl-
disclose the photoresponse of thin crystals of 1oRR, and 2oRR,
and show for the first time that reversible light-induced bending of
crystals in both a convex and a concave manner can be achieved.
Furthermore, we discovered that plate-like crystals of 1oRR can be
rolled up upon UV irradiation.
ethylamide substituents formed rod-like and 0.2–1.0 mm-thick
plate-like crystals by sublimation; upon UV irradiation, the
crystals bent concavely to the incident light and finally rolled
crystals were obtained; the bent crystals were reconverted to flat
crystals by visible light irradiation.
Diarylethenes 1oRR, 1oRS, 1oSS and 2oRR have been
synthesised using procedures adapted from previous reports.6
Upon UV and visible light irradiation, crystalline diarylethenes
1oRR, 1oRS, 1oSS and 2oRR showed the same photochromic
behaviour as 1oRR in acetonitrile. The crystalline powders of
1oRR, 1oSS, 1oRS and 2oRR were inserted into a demountable
optical cell having a thickness of 1 mm. This cell was placed
horizontally, and a glass plate was placed on top of it.{ The cell
was subsequently heated at a temperature 10 uC below the
compounds’ melting points. Maintaining this temperature, thin
crystal plates grew from the original crystalline powder of 1oRR
and 1oSS.
Photochromism is defined as the reversible transformation of a
single molecule between two states having different absorption
spectra. Hence photochromic molecules often hold considerable
potential for application as molecular switches and as control
elements in molecular devices.1 Diarylethenes are among the most
promising of photochromic compounds,2 not only as memory
materials but also as switching units for molecular devices and in
supramolecular systems.3 Recently changes in the surface mor-
phology of a diarylethene crystal were reported,4 as well as
modification of crystal shape. In particular, Irie and co-workers5
reported the reversible bending of a rod-like crystal of 1,2-bis(5-
methyl-2-phenyl-4-thiazolyl)perfluorocyclopentene upon UV and
visible light irradiation. The mechanism of bending was attributed
to differences in molecular stacking for the open- and the closed-
ring isomers, which resulted in macroscopic contraction of the
crystals along an axis. We have previously demonstrated that
dithienylperfluorocyclopentene derivatives like 1oRR (Fig. 1), with
chiral, (R)-N-phenylethylamide groups at both ends of the
molecule, undergo diastereoselective cyclisation in the crystalline
state under UV irradiation.6 We also demonstrated that chiral
N-phenylethylamide-based diarylethenes form organogels and that
the properties of the fibres as well as the transmission of chiral
information from the molecular to the supramolecular level can be
Fig. 2a schematically shows a side view of the thin crystals
growing on top of the crystal powder material of 1oRR (shown at
the bottom). The growing rate was around 0.1 mm min21. The
thickness of the film was observed by SEM to be 0.2–1.0 mm as
shown in Fig. 2b. Compound 1oSS formed similar thin crystalline
plates. As expected, these thin crystals of 1oRR and 1oSS had the
same melting point of 269.9–271.2 uC. 1oRR and 1oSS also
formed thin plate-like crystals from methanol, ethanol, 2-propanol,
and acetonitrile with mp 273.0–274.0 uC. The molecular packing of
1oRR in the crystal state has already been reported.6
aDepartment of Materials Chemistry, Faculty of Science and
Technology, Ryukoku University, CREST-JST, Seta, Otsu, Shiga 520-
2194, Japan. E-mail: uchida@chem.ryukoku.ac.jp;
Fax: +81-77-543-7483; Tel: +81-77-543-7462
bStratingh Institute for Chemistry, University of Groningen, Nijenborgh
4, 9747 AG Groningen, The Netherlands. E-mail: b.l.feringa@rug.nl;
Fax: +31-50-363-4296
cMitsubishi Chemical Group Science and Technology Research Center,
Inc. and CREST-JST, Japan Science and Technology Corporation, 1000
Kamoshida, Yokohama 227-8502, Japan
{ Electronic supplementary information (ESI) available: Absorption
spectra of the diarylethenes, X-ray analysis of 1oRR, description of
1oRR and 2oRR crystals and corresponding polar plots, IR spectra of
1oRR and 1cRR, ATR-IR spectra of the surface of the plate-like crystals
before and after irradiation, synthesis of the diarylethenes, and supporting
videos (growth of plate-like crystal of 1oRR, reversible bending of plate-
like crystal of 1oRR, bending of a needle-shaped crystal of 1oRR). See
DOI: 10.1039/b715251e
Fig. 1 Dithienylethene derivatives used in the study. o = open form, c =
closed form.
326 | Chem. Commun., 2008, 326–328
This journal is ß The Royal Society of Chemistry 2008