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A series of 1‘-substituted 6-nitro-3‘,3‘-dimethylspiro(2H-1-benzopyran-2,2‘-indoline) compounds (3−8) of different functionality were synthesized, and the rate of thermal decay was measured in polar and nonpolar solvents and in two organogels. A significant retardation of the decay rate was observed for spiropyrans substituted with a succinyl ester functionality in a gel derived from 4-tert-butyl-1-phenylcyclohexanol (BACO1). The gel network has been shown to consist of a three-dimensional network of bimolecular associations of the BACO1 molecules, and it is hypothesized that a unique mode of interaction exists between the succinyl group of the spiropyran and the gelling agent. The lifetime of the colored photomerocyanine was increased by over 300-fold in the organogel versus solution with a succinyl ester functionality present. Structurally similar spiropyrans without the succinyl ester functionality showed relatively little change in the lifetime of the photomerocyanine.
Shumburo et al. (Sat,) studied this question.