Intramolecular and Metal-to-Molecule Charge Transfer Electronic Resonances in the Surface-Enhanced Raman Scattering of 1,4-Bis((E)-2-(pyridin-4-yl)vinyl)naphthalene

Abstract

Electrochemical surface-enhanced Raman scattering (SERS) of the cruciform system 1,4-bis((E)-2-(pyridin-4-yl)vinyl)naphthalene (bpyvn) was recorded on nanostructured silver surfaces at different electrode potentials by using excitation laser lines of 785 and 514.5 nm. SERS relative intensities were analyzed on the basis of the resonance Raman vibronic theory with the help of DFT calculations. The comparison between the experimental and the computed resonance Raman spectra calculated for the first five electronic states of the Ag2-bpyvn surface complex model points out that the selective enhancement of the SERS band recorded at about 1600 cm−1, under 785 nm excitation, is due to a resonant Raman process involving a photoexcited metal-to-molecule charge transfer state of the complex, while the enhancement of the 1570 cm−1 band using 514.5 nm excitation is due to an intramolecular π→π* electronic transition localized in the naphthalenyl framework, resulting in a case of surface-enhanced resonance Raman spectrum (SERRS). Thus, the enhancement of the SERS bands of bpyvn is controlled by a general chemical enhancement mechanism in which different resonance processes of the overall electronic structure of the metal-molecule system are involved.

Comparative Performance of Citrate, Borohydride, Hydroxylamine and β-Cyclodextrin Silver Sols for Detecting Ibuprofen and Caffeine Pollutants by Means of Surface-Enhanced Raman Spectroscopy

“…Alternatively, the two types of SERS could be consequences of the participation of physical and chemical enhancement mechanisms in the SERS signal. The physical plasmonic mechanism (also called electromagnetic) is the main mechanism responsible for the overall enhancement of SERS spectra, just as it happens in the case of Ag@HX NPs (Figure 5b), while the chemical mechanism could be responsible for the selective enhancement of particular bands [31,45]. The chemical contribution can involve changes in the relative intensities due to the subtle effect of the adsorption on the electronic structure of the molecule or to the presence of resonant processes up to new excited metal-to-molecule charge transfer (CT) states of the surface complex.…”

Recent Advances in Enhancement of Raman Scattering Intensity for Biological Applications

“…In recent years, surface-enhanced resonance Raman scattering (SERRS) based on the combination of SERS and RRS has shown a superstrong Raman signal enhancement, which is several orders of magnitude stronger than that of traditional SERS. It shows broad application prospects in the fields of materials science, biology, and biomedicine. − …”

Voltage Tuning of Photoinduced Charge Transfer Resonances between 2,2'-Bipyridine and a Nanostructured Silver Electrode

“…A closed shell Ag 2 silver cluster was chosen to model the metal substrate because, despite its simplicity, it has proved its powerfulness in previous studies [4,6] and allows to be bonded to one or both nitrogen atoms of 2,2′-bpy in trans-or cis-complexes, respectively. This Ag 2 -2,2′-bpy neutral system can be correlated with the surface complex formed in the interface at the potential of zero charge of a polycrystalline silver electrode which would be close to − 0.5 V [36].…”

“…SERS gives information about the adsorption process as the surface orientation of the adsorbate [2,3] and, very especially, the properties of the metal-adsorbate surface complex in the ground and excited electronic states. It is possible to detect resonance processes involving transient states of different nature [4][5][6] where photoexcited metal-molecule charge transfer (CT) states of the hybrid system are involved [7,8]. These CT transitions are related to the so-called chemical enhancement mechanism of SERS, being responsible of the selective enhancement of particular bands, unlike the plasmonic/ physical (PL) enhancement mechanism, which would provide an overall and more or less uniform enhancement of the intensities of all Raman bands.…”