SURFACE-ENHANCED RAMAN-SPECTROSCOPIC STUDY OF ISOMERIC FORMYLTHIOPHENES IN SILVER COLLOID

Surface enhanced Raman (SER) spectra of 2- and 3-formyltiophenes (2FT and 3FT) in silver colloids are compared with their normal Raman spect ra in bulk and in acetonitrile solution. Experimental results indicate adsorption of 2FT on metal surface through the sulfur and the oxygen atoms with the ring plane vertical to the metal surface, whereas the r ing plane of the 3FT molecule is inclined to the surface, Moreover, th e SER spectrum of 2FT molecule predicts the existence of syn-form of t his molecule in the adsorbed state because of large enhancement of the carbonyl stretching mode. Concentration dependence of relative enhanc ement infers the monolayer formation on metal surface at a specific co ncentration, implying strong evidence of chemisorption of the adsorbat es, The excitation profile of C=C symmetric stretching mode of 2FT sug gests classical plasmon resonance as the main contributor to surface e nhancement. (C) 1997 Academic Press.