Surface-enhanced Raman spectroscopy of bipyridines and phenylpyridines

Raman and SERS spectra in the region 700-3150 cm{sup {minus}1} are reported for 2,2{prime}-, 3,3{prime}-, 4,4{prime}-, 2,3{prime}-, and 2,4{prime}-bipyridines and for 2-, 3-, and 4-phenylpyridines. Spectra for 4,4{prime}-dimethyl-2,2{prime}-bipyridine, 1,10-phenanthroline, and N-methyl-4,4{prime}-bipyridinium are also reported. Comparison of the Raman and SERS spectra, and, in particular, analysis of the C-H stretching frequencies and intensities, indicates that in all cases except 2-phenylpyridine the molecules sit perpendicular to the sol surface consistent with {sigma} donation from the less sterically hindered nitrogen donor atom and an all-planar structure.