Stability against photodegradation of a photochromic spirooxazine dye embedded in amino-functionalized sol–gel hybrid coatings

Abstract

A photochromic spirooxazine derivative, 1-propyl-3,3,5,6-tetramethyl-spiro[indoline-2-3′-[quinolino]oxazine], was successfully embedded in sol–gel thin silica films functionalized with different amino groups. The resulting films show high transparency and exhibit a strong blue coloration upon irradiation with UV light. The composition of the embedding matrix has an important effect on the photostability of the photochromic molecules upon exposure to sunlight, and can therefore be used to design coatings in which the dye molecules have improved durability. In this sense, the incorporation of different amino groups (–PrNH₂, –PrNMe₂ and –PhNH₂) in the ormosil network, results in an enhanced stabilization of the photochromic dye, as compared with unfunctionalized matrices. In matrices modified with aminophenyl groups (–PhNH₂), the photostability of the dye has been increased, reaching a factor of 8, due to the formation of hydrogen bonds between the amino groups and the OH groups of the pore surface, limiting the availability of these groups to undergo side reactions with the dye during irradiation that lead to its degradation. Increasing the photostability of the photochromic dye is an important issue for the long term usage of photochromic materials in outdoors applications, limited, nowadays, by their low durability when exposed to sunlight.