Exploring the Effect of Intermolecular H-Bonding: A Study on Charge-Transfer Contribution to Surface-Enhanced Raman Scattering of p-Mercaptobenzoic Acid

We report the significant effect of intermolecular hydrogen bonding (H-bonding) on surface-enhanced Raman scattering (SERS) spectra in which the vibrational frequencies and intensities of some characteristic peaks of p-mercaptobenzoic acid (MBA) change with varying concentrations of aniline. These changes can be attributed to modifications in the electronic structure of the MBA molecule and the conjugation of the system under the influence of H-bonding. Of remarkable note is that the nontotally symmetric (b(2)) mode of MBA is dramatically enhanced, which can be considered as a manifestation of the charge-transfer (CT) transition process in the system. By comparing SERS spectra obtained under normal and basic conditions, the effect caused by H-bonding can be further understood. These results manifest that the CT resonance between MBA and Ag NPs through Herzberg-Teller contributions can be promoted by H-bonding. The current work may, therefore, be instructive for studying the influence of H-bonding on the electronic structure of molecules in a system via SERS technique.