Probe Dependent Solvation Dynamics Study in a Microscopically Immiscible Dimethyl Sulfoxide-Glycerol Binary Solvent

Area of Science:

• Photochemistry
• Physical Chemistry
• Chemical Physics

Background:

• Solvation dynamics are crucial for understanding excited-state processes in solutions.
• Binary solvent mixtures offer complex environments to study solute-solvent interactions.
• Coumarin dyes are widely used fluorescent probes for solvation studies.

Purpose of the Study:

• To investigate the excited state dipole solvation of coumarin dyes with varying hydrophobicities in a DMSO-glycerol binary solvent.
• To understand the influence of solvent composition and dye structure on solvation timescales.
• To explore the reasons behind probe-dependent solvation dynamics in binary solvent mixtures.

Main Methods:

• Time-resolved fluorescence spectroscopy was employed to measure solvation dynamics.
• Three coumarin dyes with distinct hydrophobicities (C343, C480, C153) were used as probes.
• The study was conducted in a binary solvent mixture of DMSO and glycerol.

Main Results:

• Solvation times varied significantly among the coumarin dyes, ranging from ~104 ps for the hydrophobic C153 to >12 ns for the hydrophilic C343.
• A moderately hydrophobic dye, C480, showed an intermediate solvation time of ~396 ps.
• Probe-dependent solvation was observed in DMSO-glycerol, unlike in DMSO-water or neat isopropanol.

Conclusions:

• The observed probe dependency in DMSO-glycerol is attributed to microscopic phase segregation and varying dye locations within the solvent mixture.
• Slow solvation of C343 likely involves slow solvent diffusion and hydrogen bond rearrangements.
• Fast solvation of C153 is possibly due to rapid reorganization of DMSO methyl groups or glycerol backbone around the solute.