Crystalline photochromism of N-salicylidene-2,6-dialkylanilines: advantage of 2,6-dialkyl substituents of aniline for preparation of photochromic Schiff base crystals.

N-(3,5-Dihalosalicylidene)-2,6-dialkylaniline derivatives were prepared and their structure and photochromic properties were investigated. From the X-ray crystallography, it was revealed that steric repulsion between the azomethine hydrogen atom and the alkyl groups at the 2,6-positions of the aniline ring lead to non-planar molecular structure, which was effective for the crystals to exhibit photochromism. The relationship between photochromicity and crystal packing of N-(3,5-dichlorosalicylidene)-2,6-dialkylanilines series was also discussed.

Deuterium isotope effect on the solid-state thermal isomerization of photo-coloured cis-keto species of N-salicylideneaniline.

Deuterium isotope kinetic effect in the solid state was observed by using thermal fading reaction of photo-coloured species derived from N-salicylideneaniline deuterohydroxyl derivative; thus, the existence of a cis-keto form in the photo-coloured Schiff base crystals was suggested experimentally along with 6-methyl-substitution effect on the stability of the photoproduct.