In Situ SERS Study of Azobenzene Derivative Formation from 4‑Aminobenzenethiol on Gold, Silver, and Copper Nanostructured Surfaces: What Is the Role of Applied Potential and Used Metal?

The aromatic mercapto derivative 4-aminobenzenethiol (4-ABT) is a substance that can be easily adsorbed on Au, Ag, and Cu surfaces, but in some studies, formation of 4,4′-dimercaptoazobenzene (4,4′-DMAB) on Ag and Au is described. We have studied 4-ABT on all three SERS-active metals in a spectroelectrochemical cell aiming at the role of the metal and electrode potential on formation of 4,4′-DMAB at 785-nm excitation. In the case of Au, intense bands of 4,4′-DMAB are observed in a potential range from +0.2 to −0.8 V. Only at very negative potentials do these bands almost disappear and only spectral features of 4-ABT are observed. In the case of Ag, a similar spectral behavior is observed, but relative bands intensities are weaker than on Au. In the case of Cu, there is no spectral evidence of 4,4′-DMAB at any potential value. Only characteristic bands of 4-ABT are observed in the whole potential range; the highest signals are obtained at potentials around −0.6 V. Experimental results are supported by DFT calculations. We can conclude that the crucial aspect of surface photocatalytic formation of 4,4′-DMAB from 4-ABT is the metal. The reaction is very effective on Au, and it is inhibited on Cu

In Situ SERS Study of Azobenzene Derivative Formation from 4‑Aminobenzenethiol on Gold, Silver, and Copper Nanostructured Surfaces: What Is the Role of Applied Potential and Used Metal?

The aromatic mercapto derivative 4-aminobenzenethiol (4-ABT) is a substance that can be easily adsorbed on Au, Ag, and Cu surfaces, but in some studies, formation of 4,4′-dimercaptoazobenzene (4,4′-DMAB) on Ag and Au is described. We have studied 4-ABT on all three SERS-active metals in a spectroelectrochemical cell aiming at the role of the metal and electrode potential on formation of 4,4′-DMAB at 785-nm excitation. In the case of Au, intense bands of 4,4′-DMAB are observed in a potential range from +0.2 to −0.8 V. Only at very negative potentials do these bands almost disappear and only spectral features of 4-ABT are observed. In the case of Ag, a similar spectral behavior is observed, but relative bands intensities are weaker than on Au. In the case of Cu, there is no spectral evidence of 4,4′-DMAB at any potential value. Only characteristic bands of 4-ABT are observed in the whole potential range; the highest signals are obtained at potentials around −0.6 V. Experimental results are supported by DFT calculations. We can conclude that the crucial aspect of surface photocatalytic formation of 4,4′-DMAB from 4-ABT is the metal. The reaction is very effective on Au, and it is inhibited on Cu

Explanation of Surface-Enhanced Raman Scattering Intensities of <i>p</i>‑Aminobenzenethiol by Density Functional Computations

<i>p</i>-Aminobenzenethiol (ABT) is a popular molecule for surface-enhanced Raman scattering experiments (SERS), providing large signal enhancements on a range of metal surfaces. However, SERS intensities vary very much according to experimental conditions, and the interplay between ABT protonation, polymer state, and electronic structure/Raman cross section is still not completely clear. To understand main factors affecting Raman intensities, density functional theory (DFT) and matrix polarization theory (MPT) models were used to generate the spectra and compare to the experiment. The simulations showed that ABT protonation as well as its binding to the metal surface shift the absorption threshold, which invokes resonance or preresonance conditions favorable to the signal enhancement. The MPT approximation enabled modeling of the effect of the metal bulk and orientation of the dye on the metal surface on the enhancement and relative band intensities. The simulations can be done relatively easily and reveal chemical changes and system geometry important in rational design of SERS molecular sensors

In Situ SERS Study of Azobenzene Derivative Formation from 4‑Aminobenzenethiol on Gold, Silver, and Copper Nanostructured Surfaces: What Is the Role of Applied Potential and Used Metal?

The aromatic mercapto derivative 4-aminobenzenethiol (4-ABT) is a substance that can be easily adsorbed on Au, Ag, and Cu surfaces, but in some studies, formation of 4,4′-dimercaptoazobenzene (4,4′-DMAB) on Ag and Au is described. We have studied 4-ABT on all three SERS-active metals in a spectroelectrochemical cell aiming at the role of the metal and electrode potential on formation of 4,4′-DMAB at 785-nm excitation. In the case of Au, intense bands of 4,4′-DMAB are observed in a potential range from +0.2 to −0.8 V. Only at very negative potentials do these bands almost disappear and only spectral features of 4-ABT are observed. In the case of Ag, a similar spectral behavior is observed, but relative bands intensities are weaker than on Au. In the case of Cu, there is no spectral evidence of 4,4′-DMAB at any potential value. Only characteristic bands of 4-ABT are observed in the whole potential range; the highest signals are obtained at potentials around −0.6 V. Experimental results are supported by DFT calculations. We can conclude that the crucial aspect of surface photocatalytic formation of 4,4′-DMAB from 4-ABT is the metal. The reaction is very effective on Au, and it is inhibited on Cu

Laser-Induced Reactions of 4‑Aminobenzenthiol Species Adsorbed on Ag, Au, and Cu Plasmonic Structures Followed by SERS Spectroscopy. The Role of Substrate and Excitation Energy – Surface-Complex Photochemistry and Plasmonic Catalysis

This study focuses on investigating the laser-induced reactions of various surface complexes of 4-aminobenzenethiol on Ag, Au, and Cu surfaces. By utilizing different excitation wavelengths, the distinct behavior of the molecule species on the plasmonic substrates was observed. Density functional theory (DFT) calculations were employed to establish the significant role of chemical enhancement mechanisms in determining the observed behavior. The interaction between 4-aminobenzenethiol (4-ABT) molecules and plasmonic surfaces led to the formation of surface complexes with absorption bands red-shifted into the visible and near-infrared regions. Photochemical transformations were induced by excitation wavelengths from these regions, with the nature of the transformations varying based on the excitation wavelength and the plasmonic metal. Resonance with the electronic absorption transitions of these complexes amplifies surface-enhanced Raman scattering (SERS), enabling the detailed examination of ongoing processes. A kinetic study on the Ag surface revealed processes governed by both first- and second-order kinetics, attributed to the dimerization process and transformation processes of individual molecules interacting with photons or plasmons. The behavior of the molecules was found to be primarily determined by the position and variability of the band between 1170 and 1190 cm–1, with the former corresponding to molecules in the monomer state and the latter to dimerized molecules. Notably, laser-induced dimerization occurred most rapidly on the Cu surface, followed by Ag, and least on Au. These findings highlight the influence of plasmonic surfaces on molecular behavior and provide insights into the potential applications of laser-induced reactions for surface analysis and manipulation