Two single-bond conformational isomers (all-trans and trans-cis) of 1,4-bis[2-(4-pyridyl) ethenyl]-benzene (BPENB) have been studied using density functional theory (DFT) methods. The Fourier transform infrared (FTIR), Fourier transform Raman spectra (FT-Raman) and surface-enhanced Raman scattering (SERS) spectra of BPENB on new Ag substrates at different concentrations have been recorded. All FTIR, FT-Raman and SERS bands were assigned on the basis of the B3LYP/6-31+G(d,p) method. Our calculated vibrational frequencies are in good agreement with experimental wavenumbers. Surface selection rules derived from the electromagnetic enhancement model were employed to infer BPENB orientations on a silver substrate surface at different concentrations. (c) 2005 Elsevier B.V. All rights reserved.