MiS Preprint Repository

We performed a modeling study of the effects of aqueous solvent on the structure of of supramolecular nanoaggregates formed by cyanine dyes. Using a supermolecule approach and the reference interaction site model we calculated optimal structures of hydrated monomer-ion, dimer, and tetramer complexes formed by thea-monomethinecyanine dyes and $I^{-}$ counter-ions. We calculated the binding and the dimerization energies of the aggregates in vacuum and in water. We found that the most stable structure of all investigated aggregates in vacuum is similar to that of the so-called H-aggregates. However, we observed that the structure of the complexes changes while self-assembling in water. The structure of the most stable dimer in water is found to be also similar to that of the H-aggregates, whereas the tetramer complex shows a structure typical for another structural form of the complexes - J-aggregates. We proposed an explanation of this cross-over transformation. The obtained results correlate well with available experimental data.