Binding of Aromatic Isocyanides on Gold Nanoparticle Surfaces Investigated by Surface-Enhanced Raman Scattering

Abstract

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 Au. The lack of a substantial red shift and significant band broadening of the ring breathing modes implied that a direct ring π 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 Au. On the other hand, the C–NC band remained quite strong for DMPNC after adsorption. This result suggests a rather bent angle of C–N≡C: for the nitrogen atom of the NC binding group on the surfaces, whereas a linear angle of C–N≡C: should be more favorable on gold surfaces due to an intramolecular steric hindrance of its two methyl groups. SERS of BZI on gold nanopaticles also supports a bent angle of: C≡N–CH₂ for its nitrogen atom, suggesting a preference of sp³ (or sp²) hybridization for the nitrogen atom.