Seiya Kobatake

Photochromism of diarylethene molecules and crystals: Memories, switches, and actuators

Switches, and Actuators Masahiro Irie,*,† Tuyoshi Fukaminato,‡ Kenji Matsuda, and Seiya Kobatake †Research Center for Smart Molecules, Rikkyo University, Nishi-Ikebukuro 3-34-1, Toshima-ku, Tokyo 171-8501, Japan ‡Research Institute for Electronic Science, Hokkaido University, N20, W10, Kita-ku, Sapporo 001-0020, Japan Department of Synthetic Chemistry and Biological Chemistry, Graduate School of Engineering, Kyoto University, Katsura, Nishikyo-ku, Kyoto 615-8510, Japan Department of Applied Chemistry, Graduate School of Engineering, Osaka City University, Sugimoto 3-3-138, Sumiyoshi-ku, Osaka 558-8585, Japan

Rapid and reversible shape changes of molecular crystals on photoirradiation

The development of actuators based on materials that reversibly change shape and/or size in response to external stimuli has attracted interest for some time. A particularly intriguing possibility is offered by light-responsive materials, which allow remote operation without the need for direct contact to the actuator. The photo-response of these materials is based on the photoisomerization of constituent molecules (typically trans–cis isomerization of azobenzene chromophores), which gives rise to molecular motions and thereby deforms the bulk material. This effect has been used to create light-deformable polymer films and gels, but the response of these systems is relatively slow. Here we report that molecular crystals based on diarylethene chromophores and with sizes ranging from 10 to 100 micrometres exhibit rapid and reversible macroscopic changes in shape and size induced by ultraviolet and visible light. We find that on exposure to ultraviolet light, a single crystal of 1,2-bis(2-ethyl-5-phenyl-3-thienyl)perfluorocyclopentene changes from a square shape to a lozenge shape, whereas a rectangular single crystal of 1,2-bis(5-methyl-2-phenyl-4-thiazolyl)perfluorocyclopentene contracts by about 5–7 per cent. The deformed crystals are thermally stable, and switch back to their original state on irradiation with visible light. We find that our crystals respond in about 25 microseconds (that is, about five orders of magnitude faster than the response time of the azobenzene-based polymer systems) and that they can move microscopic objects, making them promising materials for possible light-driven actuator applications.

Single-crystalline photochromism of diarylethenes: reactivity–structure relationship

Photochromic reactivity of diarylethenes in the single-crystalline phase was found to be controlled by the distance between the reactive carbon atoms in the antiparallel conformation.

X-ray Crystallographic Study on Single-Crystalline Photochromism of Bis(2,5-dimethyl-3-thienyl)perfluorocyclopentene

The single-crystalline cycloreversion reaction of a photochromic diarylethene, bis(2,5-dimethyl-3-thienyl)perfluorocyclopentene, was studied by X-ray single-crystal structure analysis. The single crystal of the closed-ring form isomer was irradiated with 680 nm light and formation of the open-ring form isomer was followed. The crystal structure analysis revealed that the cycloreversion reaction proceeded in the single crystal in a conrotatory mode.

Substituent effect on the photochromic reactivity of bis(2-thienyl)perfluorocyclopentenes

Abstract Substituent effect on the photochromic reactivity of bis(2-thienyl)perfluorocyclopentenes was examined. Introduction of phenyl groups having electron-donating substituents on the para -position of the phenyl ring to the 5-position of the thiophene rings shifted the absorption bands of the open-ring isomers to longer wavelengths and reduced the quantum yield of the cyclization reactions. The substitution with p -( N , N -diethylamino)phenyl groups prohibited the cyclization reaction. The absorption spectra of the closed-ring isomers were not influenced by the substitution.

ESR spectroscopic studies of radical polymerization

Abstract Radical polymerization, a typical chain reaction involving a short-lived and highly reactive propagating radical as the chain carrier, has been studied by various ESR spectroscopic techniques. Not all systems can be studied, as the steady state concentration of propagating radicals is not always above the limit of detection of ESR. This review deals with recent advances in the ESR spectroscopic studies of radical polymerization involving detection of a variety of radical species, such as primary radicals from initiators, primary propagating radicals, and propagating radicals. Furthermore, spin trapping techniques can be applied where direct detection of the radical species fails, and can be used to obtain structural information about radical species. Propagating radicals from a variety of monomers have been quantified during polymerizations in homogeneous systems. The absolute values of the rate coefficients of propagation and termination have been determined from ESR quantification of the propagating radical for conventional monomers, sterically congested monomers, and macromonomers. ESR techniques have been used to determine the rate coefficients from low to high conversion in bulk polymerizations of methyl methacrylate and styrene. The values of the propagation rate coefficients for some copolymerizations have been determined by ESR methods, and the validity of the penultimate model has been supported by the dependence of the apparent values on comonomer composition. ESR spectroscopic study of emulsion polymerization has also been employed to quantify the propagating radicals and to determine the corresponding rate coefficients.

X-Ray Crystallographic Study on Single-Crystalline Photochromism of 1,2-Bis(2,5-dimethyl-3-thienyl)perfluorocyclopentene.

Single-crystalline photochromism of 1,2-bis(2,5-dimethyl-3-thienyl)perfluorocyclopentene was studied by X-ray crystallography. The crystal was irradiated with linearly polarized monochromatic 360 nm light and analyzed with an X-ray diffractometer. The X-Ray crystallographic analysis showed that the conversion from the open-ring to the closed-ring isomers was as much as 8% and that the reaction proceeded in a conrotatory mode. Two sulfur atoms and reactive carbon atoms in the thiophene rings clearly changed their positions. The photogenerated closed-ring isomers completely returned to the initial open-ring isomers in the crystal by irradiation with 650 nm light.

REFRACTIVE INDEX CHANGE OF DITHIENYLETHENE IN BULK AMORPHOUS SOLID PHASE

A diarylethene derivative, 1,2-bis(5-(4-tert-butylphenyl)-2,4-dimethylthiophen-3-yl)- 3,3,4,4,5,5-hexafluorocyclopentene, forms stable amorphous solid with Tg of 68°C. Reversible photochromism in the amorphous solid film is observed upon alternate irradiation with UV (e.g. 313 nm) light and visible (580 nm) light. The refractive index of the solid film changed by as much as 3.8×10-2 along with the photoisomerization.

Picosecond and femtosecond laser photolysis studies of a photochromic diarylethene derivative: multiphoton gated reaction

Cycloreversion (ring-opening) process of one of the photochromic diarylethene derivatives, 1,2-bis(2-methyl-3-benzothienyl)perfluorocyclopentene (BPFC), was investigated by means of picosecond and femtosecond laser photolysis methods. The drastic enhancement of the reaction yield was observed by the picosecond laser exposure. On the other hand, the cycloreversion reaction yield under femtosecond laser exposure was consistent with the steady-state light irradiation. The excitation intensity effect of the reaction profiles revealed that the successive multiphoton absorption process leading to higher excited states opened the efficient cycloreversion process.

Photochromic polymers bearing various diarylethene chromophores as the pendant: synthesis, optical properties, and multicolor photochromism

Photochromic polymers with various diarylethene derivatives were synthesized by a conventional radical polymerization of styrene derivatives having diarylethene chromophores as the pendant. All the polymers exhibited reversible photochromism in the film as well as in solution, while the photocyclization conversion in the film decreased in comparison with that in solution because of a restriction of the conformational structure in the solid state. Although the photocyclization and photocycloreversion quantum yields at the initial stage of the reactions in the film were comparable to those in solution, the apparent cycloreversion quantum yield decreased along with the reaction, which is derived from a distribution of the quantum yields in the solid state. Finally, the photochromic terpolymers consisting of three diarylethene monomers which show photochromism changing color to cyan, magenta, and yellow were synthesized. The terpolymers were demonstrated to show bright colors including black, green, red, and blue both in solution and in the solid state by selective bleaching processes. Such multicolor photochromic polymers composed of diarylethene derivatives have a potential for rewritable photochromic display devices.