Investigations of the spiropyran-merocyanine photochemical switch

Few spiropyran-merocyanine photochemical switch systems based on 6-nitro-BIPS (SP.CH3) have exhibited the necessary requirements for practical information storage applications, namely bistability, fatigue resistance, and high yield for interconversion. In order to gain a broader understanding of these mechanisms, N-indolino derivatives of spiropyrans (the carboxylic acid SP.C₂COOH, and the novel cholesteryl ester SP.C₂COOCholesteryl) were investigated by molecular modeling, ultraviolet/visible (UV/Vis) spectroscopy, and nuclear magnetic resonance (NMR) spectroscopy. Properties of the spiropyran/merocyanine switch were shown to be sensitive to concentration, solvent, irradiation, acidification, metals, degradation and exchange of a labile proton. The existence of multiple merocyanine conformational isomers complicated the determination of the respective mechanisms, however kinetic descriptions of many of these reactions were presented.; The thermal equilibration rates of the spiropyrans were studied in a variety of solvents, showing negative solvatochromic trends, with hydrogen-bonding solvents stabilizing the merocyanine form substantially. The conformation of the merocyanine was investigated via ab initio and semi-empirical molecular modeling, suggesting either the trans-trans-trans- or trans-trans-cis-merocyanine as the most stable form. (Abstract shortened by UMI.)...