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

Volume 58, Number 2 (Feb. 2004) Page 218-223

Joo, Sang-Woo; Kim, Wan-Joong; Yun, Wan Soo; Hwang, Sungu; Choi, Insung S.

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 ν(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.