Diarylethene 1 shows reversible transformation between the open-ring isomer (1o) and the closed-ring isomer (1c) by alternate UV and visible light irradiation, accompanied with reversible melting and crystallization of the microcrystalline film of 1 at 67 degrees C, which is the eutectic temperature of 10 and 1c. The reversible epitaxial crystal growth of an 1o of a diarylethene derivative was observed on a 110 surface of a strontium titanate (SrTiO3) single crystal by maintaining a constant temperature and monitoring six reversible intensity changes (within 2 h of repeating cycles) of the reflection of 004 of 1o on XRD measurements.