Photoinduced Crystal-to-Liquid Transition of Acylhydrazone-Based Photoswitching Molecules.

A photoinduced crystal-to-liquid transition (PCLT) behavior of new acylhydrazone derivatives (NCs) is reported. The photoswitching of the NCs was identified as a negative photochromism with a high E -to- Z conversion yield (>98%). A kinetic analysis shows a half-life of almost one month. Owing to these high photoswitching performances, we successfully isolated both E - and Z -forms, evaluated their crystal structures, and observed distinct thermal behaviors. The Z -form melts at a lower temperature than the E -form by several tens of degrees. The PCLT occurs at even lower temperatures. UV irradiation induces the E -to- Z conversion in the crystalline state, thereby inducing a eutectic melting. In addition to the PCLT, we observed a photomechanical behavior of the crystals, which suggests that the presented acylhydrazones can be new members of the photoresponsive crystalline materials.