Surface‐enhanced Raman scattering of 4‐aminobenzenethiol on silver: confirmation of the origin of b₂‐type bands

Abstract

In order to resolve the dispute on the origin of the b 2 -type bands in the surface-enhanced Raman scattering (SERS) of 4-aminobenzenethiol (4-ABT), we have measured its SERS spectra under a variety of conditions, including variable temperature and rotation, electrochemistry, and pH, as well as in the presence of a reducing agent. For comparison, the SERS spectra of 4-nitrobenzenethiol (4-NBT) and methyl orange (MO), a prototype azo compound, were also measured. First, we found that 4-ABT on Ag is not subjected to photoreaction, although 4-NBT is highly photoreactive on a silver surface. In the electrochemical environment, b 2 -type bands of 4-ABT lost their intensity at very negative potentials, but the intensity recovered immediately upon raising the potential. In addition, b 2 -type bands were observed under rotation even after lowering the potential. The disappearance and reappearance of the b 2 -type bands could also be observed by bringing the sample of 4-ABT on Ag into contact consecutively with a borohydride solution and water. This is because the surface potential of Ag is lowered by contact with a borohydride solution. Besides, we found that not only the normal Raman but also the SERS spectral features of 4-ABT are hardly affected by pH variation, while the spectral features of MO are greatly affected, especially in the region of the N N stretching vibration, suggesting that the possibility of a photoconversion of 4-ABT to an azo compound is low. Altogether, the b 2 -type bands were attributed to 4-ABT, appearing in conjunction with the chemical enhancement mechanism in SERS.

Spectroelectrochemical Study of the Photoinduced Catalytic Formation of 4,4′-Dimercaptoazobenzene from 4-Aminobenzenethiol Adsorbed on Nanostructured Copper

“…Since then, many papers have been published, and the three strongly enhanced Raman peaks have been widely considered as an experimental evidence of a chemical mechanism of SERS. [20][21][28][29][30][31] Alternatively, it has been also proposed, based on the spectral similarity of 4-ABT and 4,4'-dimercaptoazobenzene (4,4'-DMAB) adsorbed on Ag, that these bands correspond to N=N stretching (a g symmetric vibrational modes) of 4,4'-DMAB produced from 4-ABT via a photocatalytic coupling reaction. 24,32 Recently, similar SERS spectra have been obtained when 4-ABT was adsorbed on nanostructured Pt substrates.…”

Intense Raman scattering on hybrid Au/Ag nanoplatforms for the distinction of MMP-9-digested collagen type-I fiber detection

“…CV peak at 1618 cm À 1 was used as index for relation of relative Raman intensities with respect to Au or Ag NCs on fibAu_NR. chemistry of Ag (relatively dark) caused by 4-ABT (Kim et al, 2011a(Kim et al, , 2011b. In Fig.…”

Direct observation of p,p′‐dimercaptoazobenzene produced from p‐aminothiophenol and p‐nitrothiophenol on Cu2O nanoparticles by surface‐enhanced Raman spectroscopy

“…[12] Since then, the identification of surface species during SERS measurement became widely concerned. [13] Although arguing existed, [14][15][16][17][18] the novel surface-catalytic reaction from PATP to DMAB still drew great interests with investigations on this power-, wavelength-, substrate-, pH-, and time-dependent process. [19][20][21][22][23][24][25][26][27][28][29] Surface mass spectrometry, electrochemistry, and theoretical calculations were introduced into this field as well as remote-excitation technique that could rule out disruptive effects such as laser heating.…”