Morphology Changes of Photochromic Single Crystals

在本项目中，我们从分子结构的变化到单晶表面形貌的变化及其动力学，研究了单晶光致变色的机理，特别是激发能在晶体中的迁移和放大机制。主要研究结果如下：(1)为了制备具有黄色、红色和蓝色的单晶，在紫外光和可见光的照射下，我们合成了三种结构相似的二芳基乙烯衍生物1，2-bis(2-methyl-5-phenylthiophen-3-yl)perfluorocyclopentene，1，2-bis(5-methyl-2-phenylthiazol-4-yl)-perfluorocyclopentene，和1，2-bis(5-methyl-2-pehnyloxazol-4-yl)perfluorocyclopentene.。这三种二芳基乙烯的含量几乎相等，在适当波长的光照射下，单晶的颜色从无色变为黄色、红色和蓝色。结果表明，长程激发能在晶体中的迁移效率不高。(2)利用原子力显微镜研究了二芳基乙烯单晶的表面形貌变化。表面的分子尺度图像表明，表面甲基在紫外光照射下发生位置变化，在可见光照射下恢复到原来的位置。结果清楚地表明，分子结构的变化导致了单晶表面形态的变化。

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.