Nanosized porphyrin J-aggregates in water/AOT/decane microemulsions

Water/decane/AOT microemulsions have been used to obtain J-aggregates of the anionic water soluble porphyrin tetrakis(4-sulfonatophenyl)porphyrin (TPPS4), having sizes that are controlled by the dimension of the water pool. The kinetics of aggregation have been investigated on changing pH, ionic strength and size of the microemulsions and treated by a model derived for self-assembling processes and based on the catalytic role of a critical size nucleus. The analysis of the present data evidences the role of dimer or trimer in the rate determining step. The J-aggregates exhibit resonance light scattering (RLS) signals whose intensities follow a behavior that is predicted from the quantum mechanical theory developed for RLS. Depolarized light scattering together with quasielastic light scattering experiments allow for an estimation of the geometrical arrangement of the porphyrin linear arrays inside the microemulsions and the corresponding aggregation number. The ratio between the coherence length and the hydrodynamic radius of the aggregates decreases on increasing the size of the water pool, being close to the unity for the smaller nanoaggregates.