Photo-triggered phase transition of a crystal

Structural phase transitions induced by external stimuli such as temperature, pressure, electromagnetic fields, and light play crucial roles in controlling the functions of solid-state materials. Here we report a new phase transition, referred to as the photo-triggered phase transition, of a photochromic chiral salicylideneamine crystal. The crystal, which exhibits a thermal single-crystal-to-single-crystal phase transition which is reversible upon heating and cooling, transforms to the identical phase upon light irradiation at temperatures lower than the thermal transition temperature. The photo-triggered phase transition originates from the strain of trans -keto molecules produced by enol–keto photoisomerization owing to the small energy barrier associated with changes in the crystal structure. The photo-triggered phase is metastable and returns to the initial stable phase via back isomerization from the trans -keto to enol form.