Can p,p′-Dimercaptoazobisbenzene Be Produced from p-Aminothiophenol by Surface Photochemistry Reaction in the Junctions of a Ag Nanoparticle−Molecule−Ag (or Au) Film?

Abstract

In this study, we attempt to experimentally address the question of whether p,p′-dimercaptoazobisbenzene (DMAB) can be produced from p-aminothiophenol (PATP) by surface photochemistry reaction in the junctions of a Ag nanoparticle-molecule-Ag (or Au) film. First, utilizing surface-enhanced Raman scattering (SERS) spectra, we provide experimental and theoretical evidence that DMAB can be produced from PATP by surface photochemistry reaction in the junctions of a Ag nanoparticle-molecule-Ag film. Second, we investigate the SERS spectra utilizing both experimental and theoretical approaches, ultimately revealing that DMAB cannot be produced from PATP in the junctions of a Ag nanoparticle-molecule-Au film. The electromagnetic enhancements are estimated with three-dimensional finite-difference time domain methods, which are about 9 × 10 5 times in the junctions of Ag nanoparticle-PATP-Ag/Au films.

Activated vibrational modes and Fermi resonance in tip-enhanced Raman spectroscopy

“…Two series of typical measured spectra using the experimental conditions described the SERS and NRS studies. It is worthwhile to note that our previous report showed that the SERS peaks of PATP adsorbed on a bare Au film is very similar to the NRS of PATP [18], whereas the SERS peaks of PATP on Au colloidal nanoparticles is different from the corresponding NRS measurements.…”

“…Earlier explanations often attribute this phenomenon to selective enhancement of some b 2 modes of PATP due to charge transfer between the molecules and the metal substrates [10][11][12][13]. Recently, dimerization of PATP to dimercaptoazobenzene (DMAB) has been suggested to explain these unseen Raman modes [14][15][16][17][18]. Both theoretical simulations [14][15] and experimental observations [15][16] offer credible support to the explanation based on the dimerization mechanism; nevertheless, controversies remain regarding the dimerization explanation, due to the broadening and relatively few Raman modes in the SERS spectra [19][20][21].…”

Is 4‐nitrobenzenethiol converted to p,p′‐dimercaptoazobenzene or 4‐aminothiophenol by surface photochemistry reaction?

“…[6] All the Raman peaks were assigned as the symmetric ag vibrational modes, which are strongly enhanced by surface plasmons. [5,7] In this communication, we demonstrate that also a mixture of the nitro compounds related to PATP, i.e. 4-nitrobenzenethiol (4-NBT), yields very similar SERS spectra, which can be assigned to DMAB.…”

Nanowire-supported plasmonic waveguide for remote excitation of surface-enhanced Raman scattering

“…[38][39][40] One of the most promising applications of SPPs, especially localized SPPs, is surface-enhanced Raman scattering (SERS), which has been studied both theoretically and experimentally for many decades. [12][13][14][41][42][43][44][45][46][47][48][49][50][51][52][53][54][55][56][57] As an optical fingerprint, Raman spectra, which could be used to analyze chemical structures, are widely used in scientific investigations and material analysis. However, as a weak process, the small Raman scattering cross-section makes the detection of a small number of molecules a problem even after the laser power is increased.…”