Deep eutectic solvents, promising green alternativesto conventionalsolvents, consist of a hydrogen bond donor and a hydrogen bond acceptor.The hydrogen bonding components in deep eutectic solvents form anextended hydrogen bonding network, which can be tuned to specificapplications by changing the hydrogen bond donors. In this work, wehave changed the hydrogen bond donor from a diol to a dicarboxylicacid by systematically replacing a hydroxyl group with an acid groupone at a time to investigate the solvation structure and dynamicsof the deep eutectic systems. Using a combination of ultrafast vibrationalspectroscopy and molecular dynamics simulations, we compared the spectraldiffusion and orientational relaxation dynamics of three deep eutecticsystems using the vibrational responses of a dissolved anion. Ourresults indicate that although the solvation structures are marginallydifferent across the systems, distinct differences are present inthe solvent fluctuation and solute reorientation dynamics. This workprovides a detailed molecular understanding of carboxylic-acid-baseddeep eutectic systems and how they differ from alcohol-based deepeutectic systems.

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