Thermodynamic and kinetic properties of the tautomerism of an indoline spiropyran in compressed CO2-ethanol and cyclohexane-ethanol mixtures were studied at different temperatures by using UV-Vis spectroscopy. The thermodynamic and kinetic properties of the reaction in CO2-ethanol mixtures can be adjusted by the pressure of CO2. The rate constant of the reaction depends on the polarity and viscosity of the solvent. The rate constant of the reaction in the CO2-ethanol mixture is higher than that in the cyclohexane-ethanol mixture at the same equilibrium constant (K-e). (C) 2000 Elsevier Science B.V. All rights reserved.