Resonant charge transfer on the nanoscale: studying doublet states of adsorbates by surface‐enhanced Raman scattering

Abstract

This paper summarizes a series of results where the main role of the charge-transfer (CT) mechanism in the surface-enhanced Raman scattering (SERS) of aromatic molecules is demonstrated. This mechanism consists on a photoinduced CT process between nanostructures of the metallic surface and the adsorbed molecules, giving rise to the transient formation of a radical anion of the adsorbate. A general methodology to detect the CT process in SERS is described. It is demonstrated that the SERS features are determined by the differences between the electronic properties of the neutral and the anionic molecular species. On the basis of these results, we propose to use SERS as a tool to characterize such doublet states.

Surface enhanced Raman scattering of p-aminothiophenol self-assembled monolayers in sandwich structure fabricated on glass

“…43 Oteral and co-workers have proposed that different relative intensities in the SERS spectra of aromatic molecules such as pyrazine on Ag, Au, Cu, and Ni depended on the nature of the metal. [49][50][51] Cao et al have also investigated the SERS of p-ATP on the Au͑core͒ /Cu͑shell͒ surface and proposed the difference in the relative intensity of the SERS spectra of p-ATP on the Au surface and Au͑core͒ /Cu͑shell͒ can be ascribed to the chemical effect. 18 But in our system, the substrate is the same metal of Ag, and then the nature of the metal cannot influence the chemical effect of the SERS spectra of p-ATP.…”

Surface-enhanced Raman scattering of hydroxybenzoic acids adsorbed on silver nanoparticles

“…According to this mechanism and from the point of view of the adsorbate, the relative enhancement observed in SERS-CT should be related to the differences between the geometries of the adsorbates and their respective radicals (A term in RR, Franck-Condon factors [13][14][15]). The nuclei are displaced from their original positions in the transient radical according to the shape of the LUMO orbital where the transferred electron is located in the CT-excited level.…”

“…In previous works [13][14][15] we have proposed a method to detect and to estimate the enhancement produced by the CT mechanism (SERS-CT) in a particular SERS on the basis of the particular behavior shown by the band assigned to the 8a;ν ring mode, which is representative of an active vibration in a resonant CT process. In …”

“…Consequently, the transient radical formed under photoexcitation is more stable if the molecule has an aromatic framework. Our studies dealing with several aromatic molecules have shown that the most striking feature of their CT-SERS spectra is the strong enhancement of vibration of the 8a;ν ring [13][14][15].…”

Surface‐enhanced Raman spectroscopy: advancements and applications

“…25 Otero and co-workers discuss the photo-induced chargetransfer process between metallic nanostructures and adsorbates and then briefly explain a general methodology to detect this process. 26 Polubotko presents his view on the dipole-quadrupole theory and uses it to explain the SERS spectra of some aromatic molecules adsorbed on transition metals. 27 Wu et al report a hybrid density functional theory study on the binding interaction and Raman spectral properties of pyridine-metal clusters by correlating its surface chemistry and the relative intensity of SERS spectra.…”