Photochromism of cationic spiropyran-doped silica gels

Abstract

New cationic spiropyrans (SP–R)⁺X⁻ (R = Me, Ph, Hex, C₂H₄OH; X = I, Cl, NO₃) have been synthesised and embedded in a silica gel prepared from the gelation of TMOS (tetramethyloxysilane). The influence of the substituent R and of the anion on the gelation time has been studied. Spectroscopic studies of these new spiropyran-doped gels provide evidence for negative solvatochromism and for a competition between normal and reverse photochromism.