SERS spectroscopy and quantum-chemical calculations of stilbene amino derivatives in conditions of adsorption on silver nanoparticles

In this paper, the DFT calculations for three stilbene derivatives, of 4-aminostilbene, 4,4'-diaminostilbene and 4-amino-4'-(N,N-diethylamino)stilbene, are proposed enabling to assign the SERS spectra reliably, including in the "hot spots" conditions. The choice of the best model is made based on more than 50 calculations of molecule*Ag-n clusters. We studied, how the cluster size (4, 6 and 14 silver atoms), charge (positive localized, non-localized and neutral) and solvent accounting affect on the results of calculation. The obtained theoretical data is compared with the SERS experimental results and with the similar systems from literature. The best correspondence is obtained for the systems with Ag-14 complexes (both, in the "bridge way" and "single-end" absorption). Accounting for the solvent brings the calculated data substantially closer to the experimental as well. Charge localization affects on the calculated results for asymmetric complexes only at a given level of theory.