Kingo Uchida

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.

Thermally irreversible photochromic systems. Reversible photocyclization of 1,2-bis(thiazolyl)perfluorocyclopentenes

Abstract Diarylethenes having thiazole rings, 1,2-bis(thiazol-4′-yl)perfluorocyclopentenes and 1,2-bis(thiazol-5′-yl)perfluorocyclopentenes, were synthesized. The binding positions of the thiazole rings to the perfluorocyclopentene moiety strongly affected the absorption spectra. The absorption maxima of the open- and closed-ring forms of 1,2-bis(5′-methyl-2′-phenylthiazol-4′-yl)perfluorocyclopentene were observed at 300 nm and 525 nm, respectively, while the maxima of 1,2-bis(4′-methyl-2′-phenylthiazol-5′-yl)perfluorocyclopentene shifted to 363 nm (open-ring form) and 406 nm (closed-ring form).

Photochromism of diarylethenes having thiophene oligomers as the aryl groups

Abstract Diarylperfluorocyclopentenes having thiophene oligomers as the aryl groups were synthesized and their photochromic reactivity was examined. The cylization quantum yields were scarcely affected by the oligomer chain length, while the ring-opening quantum yields dramatically decreased with the increasing number of the thiophene rings. The low quantum yield of a 1,2-bis(5″-cyano-2,4-dimethyl-5,2′: 5′,2″-terthiophen-3-yl)perfluoro-cyclopentene closed-ring form was increased as large as 34 times by raising the reaction temperature from 25°C to 150°C.

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.

One-color reversible control of photochromic reactions in a diarylethene derivative: three-photon cyclization and two-photon cycloreversion by a near-infrared femtosecond laser pulse at 1.28 μm.

One-color control of colorization/decolorization reactions of diarylethene molecules was attained by using nonresonant high-order multiphoton absorption processes with a near-infrared (NIR) femtosecond laser pulse at 1.28 μm with 35 fs full width at half-maximum (fwhm). The intensity of a rather weak laser pulse (<1 nJ/pulse) can induce the simultaneous three-photon absorption leading to the colorization, while much weaker intensity induces two-photon absorption resulting in the decolorization. The spatial patterning concomitant with higher-order multiphoton absorption processes was also demonstrated.

Selective metal deposition on photoswitchable molecular surfaces.

We report here a novel phenomenon: selective metal deposition on photoswitchable diarylethene (DAE) surfaces. Magnesium vapor was deposited by vacuum evaporation on the colored DAE but not on the uncolored surface. The selective deposition originates in the change of the glass transition temperature of the amorphous DAE film resulting from photoisomerization and therefore from changes of surface molecular motion. We clarified that Mg atoms on the uncolored surface actively migrated on the surface and were desorbed from the surface. The possibility of depositing other metals is also discussed. Light-controllable metal-integrated deposition was demonstrated as a new function of the photoswitchable molecular surfaces. This study reveals new features of the photoswitchable molecular surfaces, and their potential suggests bright prospects for future applications in organic electronics.

Photoresponsive dithienylethene-urea-based organogels with “reversed” behavior

Dithienylperhydrocyclopentene-bisurea-based low molecular weight gelators are described that function as photoresponsive organogels that show a remarkable gel-to-liquid transition upon irradiation. The two series of derivatives, with and without alkyl spacers between the urea hydrogen bonding groups and the photochromic unit, show different gelation behavior. Upon UV irradiation of the gels, a gel liquified at only 1.4% conversion of the photochromic unit. Transmission electron microscopy (TEM) shows that the gel fibres consist of thin ribbons. Semi-empirical (PM3) calculations indicate that the hydrogen bonding between the open-ring isomer (o) molecules is weak, and that formation of the closed-ring isomer (c) destabilises the hydrogen bonding further. The results indicate that a small amount of the closed-ring isomer will disrupt the intermolecular hydrogen-bonding, leading to disintegration of the gel fibre ribbons and hence reversible liquification.

Reversible Photocontrol of Surface Wettability between Hydrophilic and Superhydrophobic Surfaces on an Asymmetric Diarylethene Solid Surface

By alternate UV and visible light irradiation, reversible topographical changes were observed on a newly synthesized diarylethene microcrystalline surface between the rough crystalline surface of an open-ring isomer and flat eutectic surfaces. The contact angle changes of a water droplet between 80° and 150° and peak intensities changes of the open-ring isomer in XRD patterns within 2 h of repeating cycle were observed. The results indicated that reversibly photogenerated rod-shaped crystals on the surface were produced based on the lattice of the open-ring isomer crystals in the subphase.

Theoretical study of an intermediate, a factor determining the quantum yield in photochromism of diarylethene derivatives

Experimental and theoretical joint study on the photochemical reaction mechanism of photochromic diarylethenes is presented. An intermediate, suggesting an important role for the determination of the quantum yield, is proposed by ab initio multiconfiguration self-consistent (MCSCF) calculation.

Photochromism of dinaphthylethene derivatives. Stability of the closed-ring forms

Stability of various types of closed-ring forms of dinaphthylperfluorocyclopentenes was investigated from both experimental as well as theoretical points of view. The stability was dependent on the energy differences between the open-ring and the closed-ring forms. When the energy difference was small, the closed-ring form became stabler.