Binding of aromatic isocyanides on gold nanoparticle surfaces investigated by surface-enhanced Raman scattering

The adsorption structure and binding of phenyl isocyanide (PNC), 2,6-dimethyl phenyl isocyanide (DMPNC), and benzyl isocyanide (BZI) on gold nanoparticle surfaces have been studied by means of surface-enhanced Raman scattering (SERS). PNC, DMPNC, and BZI have been found to adsorb on gold assuming a standing geometry with respect to the surfaces. The presence of the v(CH) band in the SERS spectra denotes a vertical orientation of the phenyl ring of PNC, DMPNC, and BZI on An. The lack of a substantial red shift and significant band broadening of the ring breathing modes implied that a direct ring pi orbital interaction with metal substrates should be quite low. For PNC, the band ascribed to the C-NC stretching vibration was found to almost disappear after adsorption on An. On the other hand, the C-NC band remained quite strong for DMPNC after adsorption. This result suggests a rather bent angle of C-NdropC: for the nitrogen atom of the NC binding group on the surfaces, whereas a linear angle of C-NdropC: should be more favorable on gold surfaces due to an intramolecular steric hindrance of its two methyl groups. SERS of BZI on gold nano-paticles also supports a bent angle of :CdropN-CH2 for its nitrogen atom, suggesting a preference of sp(3) (or sp(2)) hybridization for the nitrogen atom.