Photochromism of 1,2-Bis(2-thienyl)perfluorocyclopentene Derivatives: Substituent Effect on the Reactive Carbon Atoms

Abstract

In this work, we prepared a new 1,2-bis(3-cyanothiophen-2-yl)perfluorocyclopentene with electro-withdrawing cyano groups at both reactive carbon atoms. Furthermore, we studied the substituent effects of the reactive carbon atoms on the photochromic properties of 1,2-bis(3-R-substituted thiophen-2-yl)perfluorocyclopentene derivatives by comparing the absorption wavelengths and quantum yields of the derivatives having R = cyano, methyl, and methoxy groups. The absorption bands of the closed-ring isomers generated by UV irradiation shifted to longer wavelengths with an increase in the electron-donating characteristic of the substituents. The closed-ring isomer having cyano groups at both reactive carbon atoms has an absorption band at 427 nm (λ(max)), whereas those of methyl and methoxy derivatives have bands at 432 and 481 nm, respectively. The derivative with cyano groups shows the largest cycloreversion quantum yield (0.45), and this yield decreased with an increase in the substituents' donating characteristic. Theoretical calculation explains that the excited state of the closed-ring isomer with cyano groups has the highest energy, because there is no barrier to ring-opening on the excited potential surface.