Fractal structures in homo- and heteroaggregated water soluble porphyrins

Depending on the experimental conditions, various charged water soluble por phyrins can aggregate, leading to large supramolecular assemblies whose bas ic building blocks are constituted by J-type aggregates or heteroaggregated species made up by oppositely charged molecules. The mesoscopic structures resulting on (i) the self-aggregation of the anionic porphyrin tetrakis(4- sulfonatophenyl)porphine (H2TPPS44-) and (ii) its heteroaggregates with the cationic tetrakis(4-N-methylpyridinium)porphine (H(2)TMpyP(4)(4+)) or some of its metal derivatives, under various experimental conditions, have been investigated through elastic light-scattering technique. The experimental results suggest the presence of large clusters that can be described in ter ms of fractal geometry. The corresponding d(f) values depend strongly on th e growth mechanisms, which can be modulated by changing pH and/or ionic str ength.