Raman spectra study of photochromic diarylethene in a single crystalline phase

The cyclization and cycloreversion of the photochromic single crystal 1,2-bis(2-methyl-3-thienyl)perfluorocyclopentene were investigated by Raman spectroscopy using an excitation wavelength of 785 nm. Polarized Raman spectra of the ring-open form using an excitation wavelength of 514 nm indicated that the ring-open isomers are regularly oriented in the crystal. The depolarization ratio of the Raman band at 740 cm−1 was 0.40 in scattered polarization of the Raman spectra when excited with a wavelength of 633 nm. Raman spectra of the ring-open and ring-closed isomers were calculated with the Gaussian 98 program at the B3LYP/6-31G* level, and the results were in good agreement with the recorded Raman spectra. The vibrations were assigned on the basis of the calculations and polarized Raman spectra.