Fast and fully reversible photochromic performance of hybrid sol–gel films doped with a fused-naphthopyran

Abstract

A new type of photochromic naphthopyran with a fused structure was embedded in an organic–inorganic amine–alcohol–silicate hybrid gel producing colourless, transparent and flexible photochromic films. Under UV-vis light these materials developed, in less than 30 s, intense yellow-orange colours that faded completely in the dark in 3 min. This behaviour contrasts with the usual performance of common naphthopyrans that always generate two coloured species which fade with different kinetics, leading to the formation of a residual colour that persists for several minutes/hours. The structural design of this new naphthopyran prevents the formation of the long-lived coloured species and therefore fully reversible photo-switchable materials can be easily obtained.