Photoinduced topographical changes on microcrystalline surfaces of diarylethenes

By alternate irradiation with UV and visible light, reversible topographical changes were observed on the microcrystalline surfaces of diarylethene derivatives above the glass transition temperatures (T-g) of their open-ring isomers. For the photogenerated closed-ring isomers, the crystal growth proceeded at the surface softened by molecular movement. This is the self-aggregation of the closed-ring isomers. The photogenerated surface topographies appear depending on the crystal habits of the closed-ring isomers. Reflecting the properties (crystal habits) of diarylethene derivatives, we obtained cubic, needle, and plate-shaped crystals of the closed-ring isomers on the microcrystalline surfaces of the open-ring isomers by irradiation with UV light. Even a derivative having one isopropyl group at a reactive carbon atom, whose closed-ring isomer is thermally unstable, showed photoinduced topographical changes, because the Tg of the open-ring isomer is around ambient temperature.