Solvent effects on the crystal photochromism of 4,4′-methylenebis{(N-3,5-di-tert-butylsalicylidene)-2,6-dimethylaniline}

Abstract

4,4 0 -methylenebis{N-(3,5-di-tert-butylsalicylidene)-2,6-dimethylaniline} formed a definite acetone-inclusion crystal by recrystallization with acetone. Through crystal-to-crystal solvent exchange of the crystal, various types of crystals were obtained. All resulting crystals exhibited photochromism. Rate constants of thermal fading of photochromes were found to depend on the number of solvent molecules included in the crystal unit. The thermal stability of photochrome is discussed in connection with molecular mobility in the crystal lattice.

Solid state photochromism and thermochromism of two related N-salicylidene anilines

“…Kawato et al reported a similar fading process in the case of thermal relaxation of N-salicylidene aniline itself and of its deuterated derivative [16], and also for N-(3-tert-butylsalicylidene)-3-nitro-aniline [16] and 4,4 0 -methylenebis(N-salicylidene-2,6-diisopropylaniline) [17], or 4,4 0 -methylenebis{(N-3,5-di-tert-butylsalicylidene)-2,6-dimethylaniline} [18]. Since we monitored the relaxation process at 564 nm, one could ascribe the two stages of back-isomerisation to two different kinds of trans-keto species.…”