Surface enhanced Raman scattering of 2,2 ' biquinoline adsorbed on colloidal silver particles

Surface enhanced Raman scattering (SERS) in silver sol and normal Raman spe ctra in the bulk and in solution of 2,2' biquinoline (BQ) molecule have bee n investigated. The observed Raman bands along with their corresponding FTI R bands have been assigned based on the established assignments of the vibr ational bands of the parent napthalene and quinoline molecules. Existence o f both the cis and trans form of the BQ molecule in solution and in the bul k are inferred from the normal Raman and FTIR spectra, whereas SERS study r eveal that in the surface adsorbed state the molecule exists in the cis for m. Definite evidence of the charge transfer interaction to the overall cont ribution in the SER enhancement have been reported. The excitation profile also supports the CT interaction; Estimated enhancement factor of the princ ipal SERS bands indicate that the molecule is adsorbed on the silver surfac e through both the nitrogen atoms with the molecular plane almost perpendic ular to the surface. This preferred orientation of the molecule is in confo rmity with its existence in the cis form in the surface adsorbed state. (C) 2000 Elsevier Science B.V. All rights reserved.