Two-Photon-Induced Fluorescence Study of Rhodamine-6G Dye in Different Sets of Binary Solvents

This study deals with the effects of different sets of binary solvents on the Two-Photon Induced Fluorescence (TPIF), a non-linear process, of the Rhodamine-6G (Rh6G) dye, which is a well-known xanthene dye. This work examines the importance of inter-molecular interactions, which results in the modulation of the TPIF of the Rh6G. In this work, we have investigated three binary solvent mixtures representing varying polarity and intermolecular interactions. Specific solvent mixtures used are methanol-water, methanol-dimethyl formamide, and methanol-chloroform. Since the solvent polarity across these binary solvents differs, there are significant intermolecular interactions in the binary mixture solvents, which modulate the two-photon process of Rh6G when irradiated with high-intensity laser light at 780 nm. In our studies, we find that Rh6G in the MeOH-H₂O binary solvent has maximum red-shift and minimum intensity as compared to other pairs of binary liquids when the volume fraction of methanol decreases due to more extensive hydrogen bonding between the two components. Additionally, at 1:1 ratio of binary mixtures, Rh6G is found to have the highest TPEACS value for methanol-chloroform binary solvent and reason for that is related to the formation of weak H-bond networks between proton donor chloroform and proton acceptor methanol.