Merocyanine-Spiropyran Photochemical Transformation in Polymers, Probing Effects of Random Matrices

Isomerization kinetics of the merocyanine-spiropyran transformation in several poly(alkyl acrylates) are detected by time-resolved absorption spectroscopy. The decay of the colored merocyanine exhibits significant deviations from first-order patterns. The energy of activation can be separated into a stabilization energy for the isomer and an activation inherent to the amorphous matrix by observing the decoloration patterns for the corresponding photoisomerization. These observations can be explained by matrix effects in the isomerization modeled by statistics and fluctuations of matrix-site energies. Quantification of matrix effects is based on the concept of transport theories in random media applied to reflect the dynamics of potential energies. The gradual decrease of dispersion of reaction rates with rising temperature is correlated to the time a chromophore remembers its initial matrix cage, thereby extending the kinetic model to the range above the glass transition.