Kinetics of a photochromic reaction in a dibenzoazo crown ether in solution and in polymer matrices

The kinetics of thermal cis-trans isomerisation of photochromic dibenzoazo 16-crown-4 ether was studied in several matrices (isooctane, polystyrene an d pMMA samples fabricated in various ways) using UV-vis spectroscopy. The r ate constants were found to be almost independent of the nature of the matr ix and the method of its fabrication. The average activation energy of the isomerisation amounts to 93 +/- 5 kJ mol(-1), the pre-exponential factor be ing of the order of 10(10) s(-1). The independence of activation energy on the matrix can be explained by taking into account the relatively small dif ference in the molecular volumes of the two isomers, In polymerised pMMA sa mples the decays were non-exponential, probably owing to a distribution of rate constants associated with a distribution of microenvironments of photo active molecules. Copyright (C) 2000 John Wiley a Sons, Ltd.