Adsorption of 4,4′-biphenyl diisocyanide on gold nanoparticle surfaces investigated by surface-enhanced Raman scattering

We investigated the spectral features of the nu(NC) bands when 4,4'-biphenyl diisocyanide (BPDNC) is adsorbed on gold nanoparticle surfaces by surface-enhanced Raman scattering (SERS). The mode of adsorption of BPDNC on gold nanoparticles was found to change with the bulk concentration. At low concentrations of BPDNC, only the nu(NC)(bound) band was conspicuous at 2185 cm(-1) and the free NC stretching band was barely detected in,the SERS spectra. When the bulk concentration was increased, the nu(NC)(free) band became prominent at similar to2123 cm(-1). BPDNC was assumed to bridge two different gold particles at low concentrations, but as the concentration was increased, the bridge appeared to be broken and bonded to the gold particle only via one of the two isocyanide groups. On the basis of the electromagnetic surface selection rule, we attempted to explain the orientation of the adsorbate on Au surfaces by determining the relative enhancement factor of each vibrational band. Copyright (C) 2003 John Wiley Sons, Ltd.