Influence of surfactants on the aggregation behavior of water-soluble dendritic phthalocyanines

The interactions of a series of water-soluble dendritic: phthalocyanines containing terminal carboxylate functionality with a range of surfactants in aqueous media have been investigated. Cationic surfactants, as compared with neutral and anionic counterparts, are much more effective to disrupt the molecular aggregation of phthalocyanines, in particular for the first generation macrocycle, as demonstrated by the absorption and fluorescence spectroscopy. The interactions are mainly electrostatic in nature, arising from the cationic head of the surfactant and the anionic surface of the dendrimers which has been supported by the fluorescence quenching experiments using the cationic porphyrin (TMePyP)(4+) as the quencher. The complex formation between the first generation dendritic phthalocyanine and the cationic surfactant CTAB has also been monitored by dynamic laser light scattering in 0.01 mol dm(-3) NaBr aqueous media. As the concentration of CTAB increases, the apparent average hydrodynamic radius of the aggregates decreases significantly from 14.1 to 3.2 nm, showing that the aggregation of phthalocyanines is greatly relieved by CTAB and eventually the anionic macrocycles, mainly in monomeric form, are adsorbed onto the cationic micelle surfaces in a sideways manner.