Solvent Polarity Dependence of Photochromic Reactions of a Diarylethene Derivative As Revealed by Steady-State and Transient Spectroscopies

Solvent polarity dependence of photochromic reactions such as cyclization and cycloreversion of a photochromic diarylethene derivative, 1,2-bis(2-methyl-3-benzothienyl)perfluorocyclopentene, was investigated by steady-state spectroscopic and femtosecond laser photolysis methods. For the cyclization reaction, it was revealed that the quantum yield decreased with an increase in solvent polarities, mainly due to the decrease in the fraction of the conformer with C2 symmetry favorable for the cyclization. This result indicated that the branching ratio for the cyclization and the deactivation to the open-ring isomer at the conical intersection was almost independent of the solvent polarity. On the other hand, it was found for the cycloreversion process that the closed-ring isomer in the S1 state rapidly deactivated into the ground state in competition with the activated process leading to the conical intersection providing a pathway toward both open- and closed-ring minima in the ground state. The cycloreversi...