Surface enhanced Raman scattering of 2,2′-biphenyl dicarboxylic acid on silver surfaces: Structure and orientation upon adsorption

The SERS spectrum of 2,2′-biphenyl dicarboxylic acid (22-BPDC) adsorbed on Ag nanoparticles has been measured and the observed bands are identified and assigned referred to the ordinary Raman spectrum and to the previously measured SERS spectrum of 4,4′-biphenyl dicarboxylic acid (44-BPDC). [J. Mol. Struct. 1050, 2013, 128] As in the case of 44-BPDC, quantum chemical density functional theory calculations have also been performed to figure out structures and to calculate vibrational wavenumbers and eigenvectors in 22-BPDC. The observed SERS spectra could successfully be simulated from the models for adsorption of 22-BPDC to Ag and three Ag atom clusters. As opposed to 44-BPDC adsorbed flat on the Ag surfaces through both the COO–Ag and phenyl π-electron-metal interactions, the two phenyl rings remain twisted in 22-BPDC upon adsorption on the Ag surfaces with less π-electron-metal interaction because of small space allowances for the two closely located carboxyl groups compared to 44-BPDC. [Display omitted] •SERS and DFT study of 2,2′-biphenyl dicarboxylic acid on silver surfaces.•Upon adsorption on the Ag surfaces, two phenyl rings remain twisted in 22-BPDC.•Calculation of the molecule attached to one or 3 Ag atoms to model the SERS spectra.