Designing photochromatic pigments based on clay minerals and spiropyran

Abstract

Inorganic-organic photochromic hybrid materials have attracted attention in different research fields, since they have a wide potential application in optical memories, sensors, filters, lenses, pigments, and decoration. In this work, the photochromism of the 1-(2-Hydroxyethyl)-3,3-dimethylindolino-6′-nitrobenzopyrylospiran dye was investigated through the preparation of hybrid pigments based on raw and pillared saponites at pH 2 and pH 13 at 25 °C. The second group of pigments was prepared at pH 2 and 25 °C by in-situ hydrolysis of TEOS in the presence of the same dye. All prepared solids were characterized by X-Ray diffraction, 13C CP/MAS NMR and thermogravimetry, and were submitted to irradiation under visible light. The results suggested both intercalation and/or adsorption of the dye onto clay mineral surface via hydrogen bonds for the saponite based pigments. Concerning the hybrids obtained from TEOS hydrolysis reaction, the dye acts as a template resulting in a higher photostability of the resulting pigment compared to those prepared with clay minerals. In general, all hybrid pigments presented photoreversible capacity after light exposure and subsequent time-out in the dark. The findings of this study proposed the multicolored prepared hybrids as promising materials to be applied in photochromic systems as smart pigments.