Photomechanical response of sulfonylhydrazone molecular crystals

Abstract

Sulfonylhydrazones are a novel hydrazone-based organic molecular photoswitch. The four derivatives with unsubstituted ando-,m- andp-nitro substituted sulfonylhydrazone (SH-1,SH-2,SH-3, andSH-4, respectively) derived fromp-toluenesulfonyl hydrazide and corresponding benzaldehydes were examined with respect to their solution state photoswitching and photomechanical response in the crystalline state. All the compounds displayed UV-inducedE→Zisomerization in the solution state, whereas the back conversion was slow. Single crystals ofSH-3displayed rapid and large photomechanical bending, whereasSH-1andSH-4crystals underwent slow bending to a comparatively lesser extent. On the contrary,SH-2crystals did not show any photomechanical effects. The photomechanical deflection of the crystal tip ofSH-1increased linearly; forSH-3, the deflection increased in a sub-linear manner for few seconds, after which it started to revert towards the light source. ForSH-4crystals, the photo-induced tip deflection initially increased in a sub-linear fashion, after which no motion was observed even after continuous exposure to UV light irradiation. The photomechanical behavior of the crystals was also inspected with the aid of velocity-time and acceleration-time plots that unravelled the instantaneous photomechanical motion at various time intervals.