Grey colouring thermally reversible photochromic 1-vinylidene-naphthofurans

Abstract

A set of new 1-vinylidene-naphthofurans substituted by styryl groups were synthetized. These compounds show photochromic properties when adsorbed in silica gel, or in acidified THF solutions, developing intense colours after exposure to the UV light and returning to the uncoloured state, in the dark, in several minutes. The introduction of the styryl chain extends the conjugation of the photoproducts and shifts their absorption bathochromically relative to the parent unsubstituted naphthofuran. For styryl-naphthofuran 5a, in an acidified THF solution, an intense grey colouration can be achieved after 1 min of UV exposure (or direct sunlight) and the decolouration, in the dark, occurs in less than 10 min at room temperature.