Affiliation:
1. Graduate School of Advanced Science and Engineering Waseda University 3-4-1 Okubo, Shinjuku-ku Tokyo 169-8555 Japan
2. Research Organization for Nano & Life Innovation Waseda University 513 Wasedatsurumaki-cho, Shinjuku-ku Tokyo 162-0041 Japan
Abstract
AbstractPhoto‐triggered phase transition is a new type of phase transition in which a photochromic crystal with a thermal phase transition transforms into an identical high‐temperature phase in a temperature region lower than the thermal phase transition temperature upon light irradiation. Here, we report a second crystal that exhibits a photo‐triggered phase transition, thereby demonstrating that the photo‐triggered phase transition is a general phenomenon that occurs in crystals. When the chiral salicylidenephenylethylamine crystal was irradiated with ultraviolet (UV) light, the photo‐triggered phase transition occurred in the temperature range −30 to −10 °C. The photo‐triggered phase transition is induced by local stress due to trans‐keto molecules produced by photoisomerization near the irradiated surface. Crystal cantilevers exhibited stepwise bending by the combination of the photo‐triggered phase transition and photoisomerization. Alternate irradiation with UV and visible light achieved locomotion of single crystals driven by repeated stepwise bending. Finally, a detailed comparison of photo‐triggered and non‐photo‐triggered phase transition crystals revealed that a sufficient molecular conformation change in affordable crystal voids, smooth photoisomerization, and most likely a chiral molecular arrangement are required for inducing the photo‐triggered phase transition.