Selecting the Mechanism of Surface-Enhanced Raman Scattering Effect using Shell Isolated Nanoparticles and an Oxo-Triruthenium Acetate Cluster Complex.

Abstract

After more than 40 years, surface-enhanced Raman spectroscopy (SERS) stills attract much attention from chemists, not only because of the synthesis of plasmonic nanostructures but also due to the several simultaneous mechanisms which still remain unclear. One of the possibilities for a better understanding of the SERS mechanisms is the utilization of suitable inorganic complexes. The use of inorganic complexes makes it possible to observe the two main SERS mechanisms (electromagnetic and chemical) and to observe the intensification of Raman scattering due to the resonance Raman effect. In this publication, the observation of these mechanisms was possible utilizing an unpublished and very interesting complex with two oxo-triruthenium acetate clusters and an iron bis(terpyridine) in its structure (seven metals) and which interacted with bare gold nanoparticles and shell-isolated gold nanoparticles (SHIN), with a 1 nm silica shell. The utilization of SHIN allowed to quench the SERS chemical mechanism and led to a spectrum where iron-terpyridine peaks are absent and only the modes related to [Ru3O] center were observed (due to enhancement by resonance Raman, SERRS); it can be said that the the shell-isolated nanoparticles enhanced resonance Raman spectroscopy (SHINERRS) is observed. This approach led to a perfect selection of SERS mechanisms never seen before with any other molecule/complex. As can be seen in the UV-vis spectrum, this complex has a strong band around 700 nm, which suggests that silica shell enhances only surface-enhanced resonance Raman scattering, a long-distance phenomenon, different from chemical enhancement (a short-distance phenomenon). Additionally, along with the Raman spectroscopy results, cyclic voltammetry, UV-vis spectroelectrochemistry, resonance Raman (using 568 and 676 nm lasers), and density functional theory calculations of this new ruthenium cluster are presented.