In-depth theoretical understanding of the chemical interaction of aromatic compounds with a gold nanoparticle

Gold Nanoparticles (GNPs), owing to their unique properties and versatile preparation strategy, have been demonstrated to exhibit promising applications in diverse fields, which include bio-sensors, catalysts, nanomedicines and radiotherapy. Yet, the nature of the interfacial interaction of GNPs with their chemical environment remains elusive. Experimental vibrational spectroscopy can reveal different interactions of aromatic biological molecules absorbed on GNPs, that may result from changes in the orientation of the molecule. However, the presence of multiple functional groups and the aqueous solvent introduces competition, and complexifies the spectral interpretations. Therefore, our objective is to theoretically investigate the adsorption of aromatic molecules containing various functional groups on the surface of GNPs to comparatively study their preferred adsorption modes. The interaction between Au-32, as a model of GNPs, and a series of substituted aromatic compounds that includes benzene, aniline, phenol, toluene, benzoic acid, acetophenone, methyl benzoate, and thiophenol, is investigated. Our computed interaction energies highlight the preference of the aromatic ring to lie flat on the surface. The orientations of the molecules can be distinguished using infrared spectroscopy along with strong changes in intensity and significant shifts of some vibrational modes when the molecule interacts with the GNP. The interaction energy and the electron transfer between the nanoparticle and the aromatic molecule are not found to correlate, possibly because of significant back donation of electrons from GNPs to organic molecules as revealed by charge decomposition analysis. A thorough quantum topological analysis identifies multiple non-covalent interactions and assigns the nature of the interaction mostly to dative interactions between the aromatic ring and the GNP as well as dispersive interaction. Finally, energy decomposition analyses point out the role of the charge transfer energy contribution in the subtle balance of the different physical components.