PHOTOCHROMISM, THERMOCHROMISM AND SOLVATOCHROMISM OF SOME SPIRO[INDOLINOXAZINE]-PHOTOMEROCYANINE SYSTEMS - EFFECTS OF STRUCTURE AND SOLVENT

Three spiro[indoline-naphthoxazines] and a spiro[indoline-phenanthroxa zine], which exhibit photochromic and thermochromic properties, have b een investigated. Solvent and structure effects on the absorption spec tra of the merocyanines produced under UV irradiation and kinetic para meters for the ring-closure and ring-opening reactions were studied. P ositive solvatochromism was found, indicating that the opened form is a weakly polar species. Equilibrium constants and rate constants for t he forward and back reactions spiroxazine reversible arrow merocyanine increase with increasing the solvent polarity and with electron-donat ing groups in the oxazine moiety. The reaction is endothermic by 10-20 kJ mol(-1) and almost isoentropic. The activation entropy is generall y negative, while the activation Gibbs energy is approximately indepen dent of solvent and structure.