Morphology Changes of Photochromic Single Crystals

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In this project, we investigate the mechanism of the single-crystalline photochromism, especially excited energy migration in the crystal and amplification mechanism from the molecular structure changes to the surface morphology changes of the single crystals and their dynamics. The results are as follows.(1) In order to prepare a single crystal, which exhibits multi-colors, yellow, red and blue, upon irradiation with UV and visible light, we synthesized three diarylethene derivatives with similar structures, 1,2-bis(2-methyl-5-phenylthiophen-3-yl)perfluorocyclopentene, 1,2-bis(5-methyl-2-phenylthiazol-4-yl)-perfluorocyclopentene, and 1,2-bis(5-methyl-2-pehnyloxazol-4-yl)perfluorocyclopentene. The single crystal, which contains the above three diarylethenes in almost equal amounts, showed the color change from colorless to yellow, red and blue upon irradiation with light of appropriate wavelength. The result suggests that long-range excited energy migration is not efficient in the crystal.(2) Surface morphology changes of diarylethene single crystals were examined using AFM. The molecular scale images of the surface indicated that surface methyl groups change the position upon UV irradiation and return to the original positions upon visible light irradiation. The result clearly indicated that the molecular structure changes induce the surface morphology changes of the single crystal.