Intermolecular Hydrogen Bonding Structural Dynamics in Ethylene Glycol by Femtosecond Nonlinear Infrared Spectroscopy

In this work, we examined the structural and -OH stretching vibrational dynamics of ethylene glycol (EG) solvated in acetonitrile (MeCN), acetone (AC), tetrahydrofuran (THF), and dimethylsulfoxide (DMSO) using steady-state linear infrared (IR) spectroscopy and ultrafast pump-probe IR spectroscopy. The results suggested that the frequency position, bandwidth, and vibrational relaxation of the -OH stretching vibration that participate in the formation of intermolecular hydrogen bonds (IHBs) were strongly influenced by the type of solvent. At least two types of IHBs were detected in the EG solution including clustered solute-solute IHBs and solute-solvent IHBs. Quantum chemical calculations predicted a similar solvent dependence of the -OH stretching vibrational frequency to that observed in the IR experiments. Furthermore, we found that the IHB-involved -OH stretching mode in the case of solute-solvent clusters displayed the slowest population relaxation dynamics in the case of EG in MeCN. The relaxation became slightly faster in AC and even faster in THF. The fastest dynamics was observed in the case of EG in DMSO. However, in each solvent environment examined, the IHB-involved -OH stretching mode in the solute-solute cluster displayed the fastest population relaxation. The results obtained in this study provide further insights into different IHB structural dynamics in co-existing solute-solute and solute-solvent clusters.