Effect of the chemical environment on the light-induced degradation of a photochromic dye in ormosil thin films

The naphthopyran (NP) derivative (3-(2,4-dimethoxyphenyl)-3-(4-methoxyphenyl)-3H-naphtho[2,1-b]pyran) exhibits photochromism in solution or embedded in solid matrices. The molecule suffers a progressive photodegradation upon prolonged irradiation with UV-light, which depends strongly on the solvent or the embedding matrix. The photodegradation of the dye molecules in THF or benzene solutions is much faster than that of the molecules embedded in solid matrices (polymer or ormosil). The organic functional groups incorporated in the network of the ormosil matrix play an important role in the photostability of the dye, as they determine the chemical environment of the dye molecules in the matrix. In this way, the dye embedded in matrices whose inner pore surface is functionalized with phenyl groups exhibits a photostability nine times higher than in unmodified matrices, being their degradation half-life (t(1/2(deg)) 181 h and 21 h, respectively. The photostability of the photochromic dye in the ormosil matrices was also measured as a function of the dye loading, showing higher stability as the amount of dye is increased. The photostability of the dye in photochromic materials is an important issue in sight of the possible applications of these materials, as the performance of the devices involves repeated exposure to UV radiation. (C) 2008 Elsevier B.V. All rights reserved.