Reference interaction site model study of self-aggregating cyanine dyes.

Using the reference interaction site model and supramolecular approach, we modeled the aggregation of thea-monomethinecyanine dyes in water. Various modifications of the hypernetted-closure expression for the excess free energy have been studied. We found that the partial wave approximation with semiempirical corrections for excluded volume and hydrogen bonding effects provides estimations of the binding and dimerization energies of the aggregates, which are in agreement with available experimental data. The hydrated H-dimers are obtained to be more stable than the hydrated J-dimers. However, the complexes consisting from more than four monomers change their arrangement while self-assembling in water and form ladderlike structures. We propose a model explaining this structural transition.