Photochromism in Anils - A Review

This review describes in brief the historical perspective of photochromism and photochromic behaviour of ‘Anils’. This phenomenon among ‘Anils’ is exhibited due to the tautomerism between enol and keto form via six membered hydrogen transfer between the phenolic hydrogen and imine nitrogen and show the phenomenon of solid-state photochromism and thermochromism and photochromism in rigid glassy solutions as well. Photochromic property in ‘Anils’ is a characteristic of the molecule, but their chromo behaviour is not only influenced by the crystal structure of anils but also by the substituents in the salicylidene-aniline molecules by affecting the acidity of phenolic oxygen as well as the basicity of imine nitrogen that affects the enolic-character of anils. The growing interest in photochromic anils is due to the potential applications, more specifically due to the existence of anils in enolic- and keto- forms.