Probe dependence on polar solvation dynamics from fs broadband fluorescence

Area of Science:

• Physical Chemistry
• Photochemistry
• Spectroscopy

Background:

• Understanding solvation dynamics is crucial for chemical reactions and material properties.
• 7-aminocoumarins and 4-aminophthalimide (4AP) are fluorescent probes sensitive to their environment.

Purpose of the Study:

• To investigate and compare the polar solvation dynamics of six 7-aminocoumarins and 4-aminophthalimide (4AP).
• To elucidate the role of specific solute-solvent interactions in solvation dynamics.

Main Methods:

• Broadband Fluorescence UP-conversion Spectroscopy (FLUPS).
• Global analysis using time-dependent band-shape functions.
• Investigation across different polar solvents: ethanol, dimethyl sulfoxide, and benzonitrile.

Main Results:

• Solvation dynamics of coumarins in ethanol showed minor differences, distinct from 4AP.
• Band-shape parameters (width, asymmetry) varied significantly with excitation energy.
• Differences in solvation dynamics between 4AP and C151 in dimethyl sulfoxide highlight solute-specific effects.
• Nearly identical solvation dynamics for 4AP and C151 in benzonitrile suggest weak solute-solvent interaction.

Conclusions:

• Solvation dynamics are molecularly specific, depending on solute structure and solute-solvent interactions (e.g., hydrogen bonding).
• Specific interactions, particularly hydrogen bonding, play a significant role in modulating solvation dynamics.
• Solvation is not solely determined by the bulk dynamic properties of the solvent.