The Roles of Solute-Solute and Solute-Solvent Interactions on the Nonlinearity of Aqueous Solutions of Ionic Dyes

In this paper, the roles of intermolecular interactions and probability of aggregates formation on the nonlinear optical properties of thiazine dyes are investigated. Our results show that saturable and reverse saturable absorption properties of these dyes depend strongly on the molecular surrounding media characteristics and their collective properties that tend to form aggregated species at high concentrations. Depending on molecular surrounding media characteristics, by increasing the concentration of dye solutions and formation of aggregates, the strong solute-solute interactions can modify the nonlinear responses of dye solutions. The experimental results indicate that by increasing the contribution of J aggregates, the third-order nonlinear responses of binary mixtures of water and ethanol are increased at room temperature. Therefore, the intermolecular interactions and the presence of J aggregates can be considered as simple techniques for improving the nonlinear responses of selected ionic dyes.