Crossover in the kinetic growth process of porphyrin aggregation

By combining ultraviolet and visible absorption and elastic light scatterin g measurements we have studied the salt-induced aggregation kinetics of the porphyrin t-H2Pagg in aqueous solution, The temporal evolution of the spec tra, directly related to the time dependence of the monomer concentration a nd the mean cluster size, shows unambiguously the presence of an early stag e driven by a reaction limited aggregation. After a variable time (dependen t on the salt concentration) a crossover to a diffusion-limited aggregation regime is observed. Elastic light scattering data confirm such a result.