A strategy for the design of photochromic naphthopyrans with large optical density at photosteady state and fast fading speed at ambient temperature in the dark

A photochromic naphthopyran system in which both optical density and fading speed of colored forms are significantly increased has been described. 3-Aryl-3-(α-naphthalene)-3H-naphtho[2,1-b]pyrans showed thermal stability, and a large optical density of colored forms was obtained at ambient temperature. By attachment of an alkoxyl group to the α-naphthalene group, the fading speed of colored forms was dramatically increased, and the fading speed was increased with increase of the length of alkoxyl chain. The generic nature of the system is beneficial for both the design of naphthopyran molecules with large optical density and fast fading speed at ambient temperature and applications.