Shizuka Takami

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.

Photochromism of single crystals composed of dioxazolylethene and dithiazolylethene

Although dioxazolylethene 1a did not show any photocoloration in the single crystalline phase, 1a displayed photochromism in the mixed crystal containing both 1a and dithiazolylethene 2a ; the mixed crystal changed color from colorless to red, orange, and yellow upon irradiation with light of appropriate wavelengths.

Photochemically Stable Novel Yellow Developing Photochromic Compounds Having a Thiazole Group

ABSTRACT Diarylethene derivatives having a thiazole ring as the aryl group 1a , 2a , and 3a have been synthesized in an attempt to obtain photochromic compounds which change the color from colorless to yellow, and have low photocycloreversion quantum yields and high absorption coefficients of the colored isomers. Compounds 1 and 3 exhibited reversible photochromic reactions in hexane solution. The closed-ring isomers 1b and 3b showed orange and yellow colors, respectively. The ϵ value of 3b at the absorption maximum is 18400 M−1cm−1, which is much larger than those of 1b (ϵ = 10000 M−1cm−1) and 2b (ϵ = 11400 M−1cm−1). The photocyclization/cycloreversion quantum yields of 3 were determined to be 0.19 and 0.0014, respectively. The yellow color was sufficiently photochemically stable under room light.

Photochemical behavior of 2,5-di-tert-butyl-3H-azepine: Unexpected formation of a dicyclopenta[b,e]pyridine derivative and a cis,cis-cyclodeca- 1,6-diene derivative

Hitherto unknown photochemical behavior of 3H-azepine giving cyclopent[c]azete and a (4π + 4π) photodimer is reported on the basis of an unexpected formation of a tricyclic dicyclopenta[b,e]pyridine derivative and a ten-membered-ring dicarbaldehyde by irradiation of 2,5-di-tert-butyl-3H-azepine in hexane.