Adsorption characteristics of arylisocyanide on Au and Pt electrode surfaces: surface-enhanced Raman scattering study

It is very important to understand metal-molecule interface characteristics for the development of efficient molecular wires in molecular electronics. Because isocyanide is potentially a good alligator clip, we have investigated in this work the adsorption characteristics of 2,6-dimethylphenylisocyanide (DMPI) on Au and Pt electrodes by recording the potential-dependent surface-enhanced Raman scattering (SERS) spectra. First of all, we confirmed that Pt nanoaggregate films were efficient SERS-active substrates, not only in ambient conditions, but also in electrochemical environments. Second, we confirmed that aryl isocyanide should adsorb on Au and Pt by forming exclusively metal-CN bonds, via a pure sigma type interaction in the case of gold compared with a sigma/pi synergistic interaction on Pt. This implies that DMPI should adsorb on Au only via the on-top site, whereas not only the on-top site, but also the 2-fold bridge and 3-fold hollow sites, could be used in the surface adsorption of DMPI on Pt. Despite these differences, DMPI was assumed to possess a vertical orientation with respect to the Au and Pt substrates, irrespective of the potential variation between +0.2 and -0.6 V relative to the Ag/AgCl reference electrode. The latter characteristics of the Au-CN and Pt-CN combinations are presumed to be useful in designing molecular-scale wires.