Surface‐enhanced Raman scattering of 4,4′‐dicyanobiphenyl on gold and silver nanoparticle surfaces

The adsorption behavior of 4,4′‐dicyanobiphenyl (DCBP) on Ag and Au nanoparticle surfaces was studied by surface‐enhanced Raman scattering (SERS). The absence of the ring CH band denoted a flat orientation of the biphenyl ring on Ag and Au. The red shift of the ν 8a band indicated a direct ring π‐orbital interaction with the surfaces. The two benzene rings of DCBP appeared to lie on the same plane with a π‐type interaction upon adsorption on the surfaces. The ν(CN) bands were blue shifted in the Ag and Au SERS spectra by 2 and 22 cm −1 , respectively from the ordinary Raman spectrum. The orientation of DCBP on the Ag and Au surfaces was analyzed by the relative enhancement factors of the vibrational bands based on the electromagnetic SERS selection rule.