Aggregation kinetics of extended porphyrin and cyanine dye assemblies

The kinetics of J-aggregate formation has been Studied for two chromophores , tetrakis-4-sulfonatophenylporphine in an acid medium and pseudoisocyanine on a polyvinylsulfonate template. The assembly processes differ both in th eir sensitivity to initiation protocols and in the reaction profiles they p roduce. The porphyrin's assembly kinetics, for example, displays an inducti on period unlike that of the cyanine dye. Two kinetic models are presented. For the porphyrin, an autocatalytic pathway in which the formation of an a ggregation nucleus is rate-determining appears to be applicable; for the ps eudoisocyanine dye, an equation derived for diffusion-limited aggregation o f a fractal object satisfactorily fits the data. These models are shown to be useful for the analysis of kinetic data obtained for several biologicall y important aggregation processes.