Rational design of photochromic diarylbenzene with both high photoreactivity and fast thermal back reactivity

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Abstract

Utilizing the intramolecular CH–N hydrogen bonding and the bulky substituents at the reactive carbons resulted in the development of photochromic diarylbenzene with both high photoreactivity and fast thermal back reactivity.

Abstract

Recently, diarylbenzenes (DABs) have been developed as a new family of T-type photochromic molecules. In this work, we newly designed and synthesized DABs for the creation of molecules with both high photoreactivity and fast thermal back reactivity. Utilizing the intramolecular CH–N hydrogen bonding and the bulky substituents at the reactive carbons resulted in the enhancement of photoreactivity and the acceleration of the thermal back reaction rate. Furthermore, we demonstrated that the high photoreactivity resulted in much better coloration compared with that of the previously reported DAB even at a lower concentration. These results would not only provide a strategy for molecular design but also be useful for the development of materials with less environmental load.

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Photochromism of diarylethene molecules and crystals: memories, switches, and actuators.

Masahiro Irie, Tuyoshi Fukaminato, Kenji Matsuda … (2014)

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Rapid and reversible shape changes of molecular crystals on photoirradiation.

Seiya Kobatake, Shizuka Takami, Hiroaki Muto … (2007)

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.