Photochromism of cationic spiropyran-doped silica gels

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.