Surface-Enhanced Raman Scattering of 4-Cyanobiphenyl on Gold and Silver Nanoparticle Surfaces

The adsorption behavior of 4-cyanobiphenyl (CNBP) has been investigated by means of surface-enhanced Raman scattering (SERS). CNBP appeared to assume a tilted orientation on silver and gold. The presence of the ring C−H band denoted a rather vertical orientation of the biphenyl ring on Ag and Au. On the other hand, considerable red shifts of the ring-breathing modes with the increase in their bandwidths indicated a substantial π-type interaction between the benzene rings and metal substrates. On gold, the concentration-dependent SERS experiment showed CNBP to have a slightly perpendicular stance at its high surface coverage. The presence of the BH4 - ion in sols was found to affect the adsorption reaction and surface orientation of CNBP. The spectral band analysis based on electromagnetic selection rule indicated that CNBP should have a slightly more vertical orientation on gold than on silver at the concentration of ∼10-4 M.