STOCHASTIC EFFECTS ON THE TIME-DEPENDENT RATE-CONSTANT OF PHOTODIMERIZATION OF 12-(9-ANTHROYLOXY)STEARIC ACID IN MICELLES

We present a detailed study of the kinetics of photodimerization of 12 -(9-anthroyloxy)stearic acid, 12-AS, in cetyltrimethylammonium chlorid e and polyoxyethylene(10) lauryl ether micelles. The primary objective of this study is to analyze the consequences of the distribution of r eactant by the micelles on the reaction kinetics. It was found that th e influence of stochastic effects on the photodimerization cannot, by itself, account for the deviation from a homogeneous media kinetics, a nd interchange of 12-AS molecules between micelles has to be invoked t o explain the experimental data. Further, besides the stable head-to-t ail dimer a non-negligible amount of a thermally unstable head-to-head photodimer is observed. It is concluded that the inhibition of photoc hemical bimolecular reactions, such as photodimerization, in compartme ntalized media results from two factors: shortness of reactants within the mean displacement distance of the excited species and, in a more pronounced manner, the depletion of available reactants as reaction pr oceeds in the non-homogeneous media.