Adsorption of 4-biphenylisocyanide on gold and silver nanoparticle surfaces: Surface-enhanced Raman scattering study

Abstract

The adsorption behavior of 4-biphenylisocyanide (BPNC) has been studied by means of surface-enhanced Raman scattering (SERS). BPNC has been found to adsorb on silver and gold via the carbon lone pair electrons assuming a standing geometry with respect to the surfaces. The presence of the v(CH) band in the SERS spectra indicated a vertical orientation of the biphenyl ring of BPNC on Ag and An. Neither a substantial red shift nor a significant band broadening of the ring breathing modes implied that a direct ring 7 orbital interaction with metal substrates should be quite low. On the basis of the electromagnetic surface selection rule, we attempted to explain the orientation of the adsorbate on Ag and An surface by determining the relative enhancement factor of each vibrational band. The band analysis indicated that BPNC should have a slightly more vertical orientation on silver than on gold. The frequency of the v(NC) band on gold increased by similar to10 cm(-1) than that on silver surface. Such a higher blue shift of the v(NC) stretching vibration in the gold sol SER spectrum may be due to a higher electronegativity of gold.