Effect of donor-π-acceptor structure on photochromism of dithienylethene-based dyes

Dithienylethene-based donor-π-acceptor photochromic dyes were synthesized to investigate the effect of the structure on photo-switching properties. Specifically, 3,5-dimethoxyphenyl and 4,4′-tert-butyltriphenylamino groups (donors) and benzoic and cyanoacetic acid groups (acceptors) were attached to an oxazole-based dithienylethene core in a horizontal or vertical fashion. The photochromic properties of these dyes were probed by UV–visible absorption spectroscopy upon exposure to UV (365 nm) and visible (>400 nm) light. The dye bearing 3,5-dimethoxyphenyl and carboxylic acid groups showed the best photochromic behavior in terms of quantum yield, and response time, which confirmed that strong electron-withdrawing substituents can hinder photo-induced cyclization by decreasing electron density at thiophene ring carbons 2 and 2’. Moreover, the introduction of an electron-withdrawing group onto the cycloethene moiety of vertical-type dyes led to a lower photochromic quantum yield than the introduction of an electron-withdrawing group at thiophene ring positions 5 and 5’.