Photochromic properties of diarylethenes having 2,4-diphenylphenyl substituents in the amorphous and PMMA films

1,2-Bis[5-methyl-2-(2,4-diphenyl)phenyl-4-thiazolyl]perfluorocyclopentene 1a and 1,2-bis-[2-methyl-5-(2,4-diphenyl)phenyl-3-thienyl]perfluorocyclopentene 2a were synthesized and their photochromic performance was examined in the bulk amorphous states. Compounds 1a and 2a formed stable amorphous bulk solid at room temperature and the glass transition temperatures (Tgs) of them were observed at 77 °C. The conversions in the photostationary states were evaluated to be 88% and 90% in the amorphous films prepared from the closed-ring isomers 1b and 2b. The values are higher than that of 1,2-bis[2,4-dimethyl-5-(2,4-diphenyl)phenyl-3-thienyl]perfluorocyclopentene 3 (74%). Photochromic reactions of these compounds were also examined in poly(methyl methacrylate) (PMMA) films. The conversion ratios of 1 and 2 (91% for both compounds) in the PMMA films are also higher than that observed in 3 (80%). The photocyclization quantum yields of 1a, 2a, and 3a are the same, while the photocycloreversion quantum yields of 1b and 2b are lower than that of 3b. The higher conversions of 1 and 2 are attributed to the lower photocycloreversion quantum yields, which were caused by the decrease in the steric hindrance between 4-position of the aryl groups and perfluorocyclopentene ring.