Fractal aggregation in aqueous solutions of porphyrins

We have studied the aggregation of the porphyrin trans-bis(N-methylpyridinium-4-yl)-diphenylporphyrine (t−H2Pagg) in aqueous solutions by means of light scattering (elastic and quasielastic) and UV-visible absorption measurements. Elastic and dynamic light scattering indicate that the aggregation produces large monodisperse clusters having a fractal structure driven by diffusion limited aggregation (DLA). UV-visible absorption measurements have been applied to study the corresponding kinetics, obtaining the time dependence of the monomer concentration and of the mean cluster size. The obtained findings are in agreement with the picture proposed by current theoretical models and molecular dynamics (MD) simulations on DLA.