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Visible light response of silver 4-aminobenzenethiolate and silver 4-dimethylaminobenzenethiolate probed by Raman scattering spectroscopy


Correspondence to: Kwan Kim, Department of Chemistry, Seoul National University, Seoul 151-742, Korea.


Kuan Soo Shin, Department of Chemistry, Soongsil University, Seoul 156-743, Korea.



Silver thiolate is a layered compound with a Raman spectrum that is known to change with time, becoming the same as the surface-enhanced Raman scattering (SERS) spectrum of the parent thiol molecule adsorbed on Ag nanoparticles. On this basis, the Raman scattering characteristics of silver 4-aminobenzenethiolate (Ag-4ABT) compounds were investigated to determine whether certain peaks that are identifiable in the SERS spectrum of 4-aminobenzenethiol (4-ABT) but absent in its normal Raman spectrum were also apparent in the Ag salt spectrum. For comparative purposes, the Raman scattering characteristics of silver 4-dimethylaminobenzenethiolate (Ag-4MABT) were also examined. Raman spectra acquired while spinning the sample were typified by only a1-type vibrational bands of Ag-4ABT and Ag-4MABT, whereas in the static condition, several non-a1-type bands were identified. The spectral patterns acquired in the static condition were similar to the intrinsic SERS spectra of 4-ABT or 4-dimethylaminobenzenethiol (4-MABT) adsorbed on pure Ag nanoparticles. Notably, the CH3 group vibrational bands were observable for Ag-4MABT irrespective of the sample rotation. In addition, no decrease in intensity during irradiation with a visible laser was observed for any of the bands, suggesting that no chemical conversion actually took place in either 4-ABT or 4-MABT. The preponderance of evidence led to the conclusion that the non-a1-type bands observable in the SERS spectra must be associated with the chemical enhancement mechanism acting on the Ag nanoparticles. The chemical enhancement effect was more profound at 514.5 nm than at 632.8 nm, and was more favorable for 4-ABT than 4-MABT at both wavelengths. Copyright © 2012 John Wiley & Sons, Ltd.