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. Scheme 1 Photochromic equilibrium for 2H-naphtho[1,2-b]pyran 1 and 3Hnaphtho[2,1-b]pyran 2.

Optical Properties of Hybrid Organic‐Inorganic Materials and their Applications

“…The rigid environment of a dye within the matrix can be beneficial, for instance, to avoid a non-desired photochromic transformation. This fact is detailed in aminealcohol-silicate hybrid materials doped with naphthopyran, [181] where the isomerization of one specific colored isomer (which is a space demanding reaction) is hindered, and films present fast and fully reversible coloration/transparent cycles upon irradiation/dark (Figure 14).…”

On‐Demand Control of the Photochromic Properties of Naphthopyrans

“…However, substitution at the 3‐phenyl ring typically causes significant changes in the color of the colored species. Although the speed of the thermal back‐reaction can be modulated by exploiting steric effects to destabilize the TC form and the long‐lived TT form, the synthetic procedures required to yield the desired products are not simple and moderate control of the thermal back‐reaction speed for photochromic lenses is difficult to achieve . In order to design appropriate naphthopyran derivatives showing on‐demand photochromic properties, the independent control of the thermal back‐reaction speed is an important challenge in the development of advanced photochromic materials.…”

A photochromic naphthopyran dye activated by the intramolecular hydrogen bond and its photodynamics in the ormosil matrix coating

“…Using organic silicone resins as host matrices can improve the decoloration speed of photochromic dyes [12]. Coelho et al [13] synthesized a novel organic-inorganic amine-alcohol-silicate hybrid gel in which the fused-naphthopyran has a fast and fully reversible photochromic performance. The photochromic performance of the organic-inorganic hybrid matrices could be enhanced by the additives including fluoroalkylsilane, bisphenol A and methyl-imidazole as well [14].…”