Excited-State Proton Transfer Dynamics in Betaine-Based Deep Eutectic Solvents: Is the Reaction Controlled by Solvent...

Area of Science:

• Physical Chemistry
• Photochemistry
• Materials Science

Background:

• Deep eutectic solvents (DESs) are gaining interest, but their excited-state photochemical dynamics remain underexplored.
• Understanding proton transfer in these novel solvent systems is crucial for their application in chemical processes.

Purpose of the Study:

• To investigate the excited-state proton transfer (ESPT) of a photoacid (HPTS) in betaine (BET)-based DESs.
• To analyze the influence of different hydrogen-bond donors (HBDs) on ESPT dynamics and solvation.
• To establish a correlation between solvent reorganization, solvation dynamics, and photochemical reactivity.

Main Methods:

• Utilized steady-state and time-resolved fluorescence spectroscopy to study HPTS in BET-based DESs with varying HBDs (ethylene glycol, 1,2-propanediol, glycerol).
• Analyzed multiexponential decay behavior, proton-transfer and dissociation times, and time-resolved emission spectra.
• Conducted temperature-dependent measurements to assess the impact on solvation and ESPT rates.

Main Results:

• Confirmed significant ESPT in BET-based DESs, with proton-transfer and dissociation times varying based on the HBD.
• Observed simultaneous ESPT and solvation occurring on comparable timescales, indicated by spectral shifts and lack of an iso-emissive point.
• Demonstrated that ESPT is governed by solvent reorganization, with temperature accelerating both solvation and ESPT rates, particularly in BET-Gly.

Conclusions:

• The photochemical reactivity of HPTS is modulated by solvation-shell dynamics in DESs.
• Tuning the hydrogen-bond donor component of DESs offers a rational approach to control proton transport.
• These findings provide insights into the photochemical behavior of solutes in DESs and their potential applications.