Photochromism of dithienylethenes containing fluorinated thiophene rings

Bis(3-thienyl)perfluorocyclopentenes containing partially fluorinated thiophene rings were synthesized and their behaviors rings were also prepared as reference compounds. The absorption maxima of the closed-ring isomers, their thermal stabilities, and their quantum yields varied depending on the substitution position. The absorption maxima showed a red shift upon fluorine substitution at the 2- or 4-positions of the thiophene ring, whereas a blue shift was, observed upon substitution at the 5-position. This shift was explained by the shape of the HOMO and LUMO and was well reproduced by theoretical calculations using time-dependent density-functional theory (TD-DFT). The cycloreversion quantum yield of the dosed-ring isomer of 2-fluorine-substituted 1,2-bis(2-fluoro-3-thienyl)perfluorocyclopentene was about 130 times smaller than that of the closed-ring isomer of 5-fluorine-substituted 1,2-bis(5-fluoro-2-methyl-3-thienyl)-perfluorocyclopentene. This low quantum yield was attributed to the change of the pi-conjugation mode in the closed ring isomer. (C) Wiley-VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2005.