Photoinduced topographical surface changes and photoresponse of the crystals of 7-methoxycoumarin

Abstract

Photoinduced topographical changes due to the dimerization reaction were observed on the surface of a single crystal of 7-methoxycoumarin, upon deep UV (254 nm) light irradiation. Upon 365 nm irradiation, a step or valley formation was observed on the crystalline surface depending on the surface index. As a function of UV light wavelength, the depth of dimerization thickness changes. After intensive UV irradiation, photosalient phenomena of the crystal were observed. As a result of sublimation from granular crystals of 7-methoxycoumarin, several kinds of shaped crystals, including thin rod-shaped crystals, hollow cone-shaped crystals, and crystalline capsules were formed. Photoinduced bending due to the dimerization reaction was observed in the thin rod-shaped crystals. The hollow crystals showed photosalient phenomena upon UV irradiation. The bending and photosalient phenomena, previously reported for several kinds of diarylethene crystals, were also observed for 7-methoxycoumarin crystals. Unlike the case of diarylethene crystals, however, we found photoinduced amorphization on a coumarin crystal surface as well as reverse bending with prolonged irradiation of 365 nm light.