Thermo- and acid-responsive photochromic spironaphthoxazine-containing organogelators

A series of photochromic spironaphthoxazine derivatives has been designed, synthesized, and characterized by using (1)H NMR spectroscopy, FAB mass spectrometry, and elemental analysis. Their photophysical and photochromic behavior have been investigated. Two of the compounds (G(12)-en-SA-SO and G(16)-en-SA-SO) have been shown to be capable of forming stable thermoreversible organogels in organic solvents, tested by the "stable-to-inversion of a test tube" method. Addition of p-toluenesulfonic acid was found to induce the formation of stable organogels at concentrations below that of the critical gelation concentration (c.g.c.), with a concomitant change in color from colorless to purple. Transmission electron microscopy and scanning electron microscopy of the xerogels showed typical fibrous structures in the micrometer scale. The activation parameters for the bleaching reaction of G(8)-en-SA-SO in the solution state and G(16)-en-SA-SO in the gel state have been determined in ethanol through kinetic studies at various temperatures. The results showed that the rate of the bleaching reaction in the gel state was much slower than that in the solution state.