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

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.

Automated summary

Photoinduced topographical changes were observed on the surface of a single crystal of 7-methoxycoumarin upon UV light irradiation, with different reactions and crystal formations depending on the wavelength of UV light. Additionally, photoinduced amorphization was found on the coumarin crystal surface, along with reverse bending after prolonged irradiation.