Evidence for Charge Transfer and Impact of Solvent Polar Properties on Aminobenzonitrile Adsorption on Silver Nanostructures

Aminobenzonitrile adsorption on silver nanoparticles (SNPs) was studied with SERS, SEIRA, and DFT. It was found that 4-aminobenzonitrile (4ABN) and 2-aminobenzonitirle (2ABN) could resonantly distribute an amino group charge so that the cyano group could strongly interact with the SNPs in the mono/multilayer. Cyano stretching frequency shifts in SEIRA spectra showed that a 4ABN multilayer interacted strongly with the SNPs when deposited using an alkane solvent with nonpolar bonds. 2ABN could interact with the SNPs even when deposition occurred using a solvent with polar bonds because intramolecular hydrogen-bonding in 2ABN limited solvation. 3-Aminobenzonitrile (3ABN) never interacted strongly with the SNPs in the multilayer because it could not resonantly distribute the amino group charge. 2ABN also formed C–H hydrogen-bonds with n-heptane, which could interact with both the amino and cyano groups of 2ABN. Charge transfer between adsorbed ABN isomers and the SNPs is evidenced in SERS spectra by the presence of nontotally symmetric vibrational bands that do not appear intense in Raman spectra of the ABN powders. It is anticipated that this work will affect applications where interactions of benzonitrile compounds with metal nanoparticles is important.