Liquid Structure and Dynamics of TetraalkylammoniumBromide-Based Deep Eutectic Solvents: Effect of Cation Chain Length

Deep eutectic solvents (DESs) have emerged in recent years as environmentally sustainable media across several fields. However, knowledge of the liquid structure, dynamics and solute-solvent interactions in many DESs that is essential for exploiting their potential, is still lacking. In this work, we make an attempt to obtain some insight into these aspects of a set of less-explored DESs comprising tetraalkylammonium bromide salts and ethylene glycol by monitoring the fluorescence response of some carefully chosen dipolar (C153 and 4-AP) and nonpolar (9-PA) solutes in these media. Specifically, we have studied the translational and rotational diffusion dynamics of these molecular systems using single-molecule based fluorescence correlation spectroscopy technique and ensemble-based time-resolved fluorescence anisotropy measurements. These results point to spatial and dynamic heterogeneity of these DESs, which becomes prominent in systems comprising cation with a longer alkyl chain length. This study reveal...