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 ν(CH) band in the SERS spectra indicated a vertical orientation of the biphenyl ring of BPNC on Ag and Au. Neither a substantial red shift nor a significant band broadening of the ring breathing modes implied that a direct ring π 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 Au 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 ν(NC) band on gold increased by ∼10 cm -1 than that on silver surface. Such a higher blue shift of the ν(NC) stretching vibration in the gold sol SER spectrum may be due to a higher electronegativity of gold.

Binding property and structure of aromatic isocyanide self‐assembly monolayers on Ag and Au surfaces

“…The SERS spectral features appeared to be quite analogous to those in our previous report. 21 The prominent SERS bands at 3063, 1600, 1282, 1182, 1167, 1034, 993 and 401 cm 1 could be ascribed to (CH), 8a , 3 , 9a , 9b , 18a , 12 and 10b for the aromatic biphenyl ring of p-biphenyl isocyanide, along with the (NC) band at ¾2180 cm 1 . On increasing the temperature, the vibrational spectra became quite broadened, with the (CH) band at ¾3060 cm 1 indicating a vertical orientation and the (NC) band at ¾2180 cm 1 remaining quite observable with other vibrational bands of p-biphenyl isocyanide up to 453 K. Above ¾463 K the spectral features began to change, suggesting a desorption or structural change of the SAMs from the Au substrate.…”

Influence of the Anchor Group on Charge Transport through Single‐Molecule Junctions

“…Calculations based on density functional theory (DFT) yielded promising results [10,13,14] for isocyanide-linked molecules in terms of absolute conductance compared with thiol-linked ones. Previous experimental work reports on transport measurements through self-assembled monolayers (SAM), embedded between metallic electrodes [11,15,16,17] or contacted using scanning probe techniques. [18] Herein, we have systematically studied the influence of the chemical nature of the molecule-metal contact on the chargetransport properties of single-molecule junctions using two different anchor groups, namely, thiol (-SH) and isocyano (-NC) groups.…”

Characterization of self-assembled phenyl and benzyl isothiocyanate thin films on Au surfaces

“…This may be related to an electron donation from the NC group to the metals. 15 Also the broad doublet bands in the neat-liquid spectrum became a very symmetric feature.…”

“…The citrate-stabilized gold nanoparticles were synthesized by following the recipes in the literature. 15 A 133.5 mg portion of KAuCl 4 (from Aldrich) was initially dissolved in 250 ml of water, and the solution was brought to boiling. A solution of 1% sodium citrate (25 ml) was then added to the KAuCl 4 solution under vigorous stirring, and boiling was continued for ca 20 min.…”