Photo-cyclization, photo-ring opening and thermo-ring opening reaction of cationic diarylethene adsorbed on the clay nanosheet surface

Abstract

The effect of the clay nanosheet surface on the photo-cyclization, photo-ring opening and thermo-ring opening reaction of 1,2-bis(2′-methyl-5′-(N-methylpyrid-4"-yl)-thien-3′-yl)perfluorocyclopentene dichloride (DAE2+) were investigated. The quantum yield of photo-cyclization on the clay surface was smaller than that in water. The decrease in quantum yield could be explained by the change in the existence ratio of two conformers of the open-ring isomer. The thermo-ring opening rate of DAE2+ was accelerated by the adsorption onto the surface, while the quantum yield of the photo-ring opening was suppressed by the adsorption. A temperature effect experiment on the thermo-ring opening reaction was carried out and the thermodynamic parameters were calculated from the Arrhenius plot to discuss the opposite effect of the surface on photo- and thermo-ring opening. Both activation energy (Ea) and the frequency factor (A) for thermo-ring opening reaction decreased by the adsorption on the surface, compared to those in water. Thus, the acceleration of the thermo-ring opening was derived from the change of Ea and could be interpreted as the reactive CC single bond elongation due to the molecular distortion by the adsorption. Moreover, the cause of the suppression of the photo-ring opening reaction was considered as the frequency reduction of the active vibration mode for the C-C cleavage that was brought by the immobilization on the clay surface. While both the closed-ring isomer of DAE2+ and the clay surface have flat structures, the open-ring isomer of DAE2+ is distorted. Several effects on the closed- and open-ring isomers of DAE2+ could be crucial factor to determine the reaction efficiency on the nanosheet surface.