Photochromic behavior of diarylbenzene nanoparticles prepared by top-down and bottom-up approaches

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Abstract

Different fabrication methods of nanoparticles resulted in different photochromic behaviors.

Abstract

The use of photochromic molecules as active elements in aggregates is very important for developing advanced materials in the next generation. The nanoparticle is one of the aggregate forms and has been attracting much attention due to not only the ease of preparation but also the characteristic photoswitching properties. In this work, we fabricated nanoparticles composed of a photochromic diarylbenzene by both ball-milling and reprecipitation methods and investigated their photochromic behaviors. The nanoparticles made by the ball-milling method had crystallinity, while those made by the reprecipitation method were amorphous. Both nanoparticles exhibited reversible T-type photochromic behavior, but the kinetics of the thermal back reaction depended on the state of the nanoparticles. The results in this study provide a convenient and useful way to prepare nanoparticles with different thermal back reactivity from one molecule.

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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.