Linear and Nonlinear Spectroscopic Insights Into the Synergistic Solvation of Rhodamine-6G in Methanol-Dichloromethane Binary Solvent Mixture

Rahul Kumar Gupta; Surya Kant; Debabrata Goswami

doi:10.1007/s10895-026-04796-3

Linear and Nonlinear Spectroscopic Insights Into the Synergistic Solvation of Rhodamine-6G in Methanol-Dichloromethane Binary Solvent Mixture

J Fluoresc. 2026 May;36(5):3633-3643. doi: 10.1007/s10895-026-04796-3. Epub 2026 May 14.

Authors

Rahul Kumar Gupta¹, Surya Kant², Debabrata Goswami^{3

4}

Affiliations

¹ Department of Chemistry, Hari Singh College, Munger University, Haveli Kharagpur, Munger, , Bihar, 811213, India.
² Department of Chemistry, Indian Institute of Technology Kanpur, Kanpur, 208016, India.
³ Department of Chemistry, Indian Institute of Technology Kanpur, Kanpur, 208016, India. dgoswami@iitk.ac.in.
⁴ Center for Bits and Atoms, Massachusetts Institute of Technology, Cambridge (Massachusetts), USA. dgoswami@iitk.ac.in.

PMID: 42133248
DOI: 10.1007/s10895-026-04796-3

Abstract

This study shows that intermolecular interactions in methanol-dichloromethane (MeOH-DCM) binary solvent mixtures play a crucial role in governing the solvation dynamics of the fluorescent probe rhodamine-6G (R6G). By employing both linear (UV-Vis absorption and steady-state fluorescence) and nonlinear (two-photon-induced fluorescence, TPIF) spectroscopic techniques, we demonstrate that the combined effects of solute-solvent and solvent-solvent interactions significantly modify the local environment around R6G. Methanol, a polar protic solvent, and dichloromethane, a polar aprotic solvent, interact through hydrogen bonding and dipole-dipole interactions, creating a microenvironment with an effective polarity higher than that of either pure solvent. As a result, the absorption spectrum exhibits a noticeable red shift, accompanied by enhanced TPIF intensity and a maximum two-photon excitation action cross-section in the mixed solvent system. These findings highlight that carefully choosing and tailoring the solvent provides a simple yet practical way to effectively tune two-photon absorption behavior. Such an approach offers promising opportunities for applications in high-sensitivity bioimaging, optical materials, and photonic devices, where strong nonlinear optical responses are essential.

Keywords: Binary solvent mixture; Molar electronic transition energy; Rhodamine-6G (R6G) dye; Solvation; Synergism; Two-photon induced fluorescence (TPIF).

Abstract

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