Red-Shifted Photochromism of Diarylethenes Induced by Shear Stress

The solid-state photochromism of two diarylethenes, 1,2-bis(2,4-dimethyl-5-phenyl-3-thienyl)perfluorocyclopentene (la) and 1,2-bis(2-methylbenzothiophen-3-yl)perfluorocyclopentene (2a), under shear stress has been investigated. It was found that la and 2a exhibited photochromic behavior, transforming from their open-ring isomers to closed-ring isomers during irradiation with visible light while under shear stress. This phenomenon was similar to that observed for cis-1,2-dicyano-1,2-bis (2,4,5-trimethyl-3-thienyl)ethene (CMTE). These phenomena in la, 2a, and CMTE are intriguing because, ordinarily, photochromism in diarylethenes requires irradiation with ultraviolet (UV) light. The application of shear stress allowed non-photochromic crystal 2a to undergo photochromism. Visible absorption spectra for the three diarylethenes indicated that shear stress induced a red shift in the absorption, spanning from the UV region to the visible region. As a result, the diarylethenes in the solid state were able to absorb visible light around 400 nm for 1a and 2a, and 500 nm for CMTE, with photochromism confirmed by the appearance of a new absorption. Herein, we explore the comparative effects of shear stress and hydrostatic pressure.