Photochromic reaction of 1,2-bis(3-methyl-2-thienyl)perfluorocyclopentene has been studied by FT-Raman spectroscopy. The Raman bands in the 1300-1700 cm(-1) region of the open-ring isomer of 1,2-bis(3-methyl-2-thienyl)perfluorocyclopentene are clearly distinguished from those of the closed-ring isomer. The vibrational assignment has been made by measuring the polarized Raman spectrum and density functional theory calculations at the B3LYP/6-31G** level. (C) 2002 Published by Elsevier Science B.V.