Differences in intermolecular interactions between 4-hydroxycoumarin and 7-hydroxycoumarin studied by terahertz spectroscopy and density functional theory

Abstract

Herein, differences in intermolecular interactions between the two positional hetero-substituents-aromatic isomers i.e. 4-hydroxycoumarin (4-HC) and 7-hydroxycoumarin (7-HC) are studied by terahertz (THz) spectroscopy and density functional theory (DFT) calculations. Combining the THz spectra with potential energy distribution (PED) results to analyze characteristic absorption peaks and vibrational modes, we found that the characteristic absorption peaks of 4-HC and 7-HC are dominated by intermolecular interactions, including electrostatic interactions and van der Waals (vdW) interactions. Comparing the electrostatic potential (ESP) and vdW potential distribution between 4-HC and 7-HC, we deduced that the differences in the THz spectra can be possibly attributed to the difference in vibrational modes and intermolecular hydrogen bonds between 4-HC and 7-HC due to the different position of hydroxyl group. Results demonstrate that THz spectroscopy combined with the above analysis methods is an effective way to analyse intermolecular interactions and identify biomolecules with similar structures.