Plasmonic Effects of Phenylenediisocyanides Linked at Interparticle Junctions of Metal Nanoparticles

Surface-enhanced Raman scattering (SERS) spectroscopy was employed in the present work to elucidate the adsorption of two diisocyanide molecules: 1,4-phenylenediisocyanide (PDI) and 1,4″-terphenylenediisocyanide (TPDI) on nanogaps of Ag and Au nanoparticles (NPs). The main goal of this work was the study of the adsorption of these molecules and more specifically the coordination mechanism and the orientation of these molecules on the metal surface as well as the study of the effect of the above adsorbates on the aggregation and formation of interparticle junctions. To get more insight into the above phenomena, we have investigated different experimental variables such as the numbers of phenylene rings (monophenylene vs terphenylene), the nature of the metal (Au and Ag), the excitation wavelength (532 and 785 nm), and the surface coverage provided by different adsorbate concentrations. The experiments carried out at these conditions revealed the existence concentration of critical values at 0.1 and 3 μM corresponding to changes in the coordination and a complete surface coverage of interparticle junctions. Finally, we have also deduced the great importance of charge-transfer processes occurring between the metal surface and diisocyanide molecules. This charge transfer exhibits a strong dependence on the surface coverage