Polymerization of nitro compounds on silver surfaces during surface‐enhanced Raman scattering

Abstract

Abstract Surface‐enhanced Raman scattering (SERS) was observed from thin films formed by 1,4‐ and 1,3‐dinitrobenzene (DNB) spin‐coated onto silver island films from dilute solutions. During laser irradiation of 1,4‐DNB films on silver substrates at relatively high laser powers, new bands appeared near 1152, 1350, 1412 and 1460 cm −1 and bands near 1118, 1358 and 1372 cm −1 decreased in inensity. A band near 1598 cm −1 shifted to near 1605 cm −1 . The bands near 1152 and 1412 cm −1 were assigned to stretching modes of ϕN andNN bonds of azo compounds, respectively, indicating that polymerization of 1,4‐DNB had occurred. The extent of polymerization was greatest when the surface coverage of adsorbed 1,4‐DNB was greatest and when the SERS experiments were carried out in a nitrogen atmosphere, indicating that reducing conditions were required for the polymerization. No polymerization was observed for 1,3‐DNB under similar circumstances. The difference was attributed to orientation of the adsorbed species. It was concluded that 1,4‐DNB was adsorbed with a horizontal configuration in which the aromatic rings were parallel to the substrate surface and both nitro groups were in contact with the surface while 1,3‐DNB was adsorbed with a vertical configuration in which the rings were perpendicular to the surface and only one nitro group was in contact with the surface.