Journal
PHYSICAL CHEMISTRY CHEMICAL PHYSICS
Volume 14, Issue 12, Pages 4095-4100Publisher
ROYAL SOC CHEMISTRY
DOI: 10.1039/c2cp24135h
Keywords
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Funding
- National Research Foundation (NRF) of Korea
- Korean Government (MEST) [2011-0001218, 2011-0006737, 2011-0019157, 2009-0072467]
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The surface-enhanced Raman scattering (SERS) of 4,4'-dimercaptoazobenzene (4,4'-DMAB), an alpha, omega-dithiol possessing also an azo moiety, has seen a surge of interest recently, since 4,4'-DMAB might be able to form from 4'-aminobenzenethiol (4-ABT) via a surface-induced photoreaction. An understanding of the intrinsic SERS characteristics of 4,4'-DMAB is thus very important to evaluate the possibility of such a photoreaction. We found in this work that 4,4'-DMAB should adsorb on a flame-annealed Au substrate via one of its two thiol groups such that Au nanoparticles could adsorb further on the pendent thiol group, forming a SERS hot site. The most distinctive feature in the SERS of 4,4'-DMAB was the appearance of a(g) bands, which were quite similar to the b(2)-type bands occurring in the SERS of 4-ABT. In an electrochemical environment, the a(g) bands of 4,4'-DMAB at 1431, 1387, and 1138 cm(-1) became weakened at lower potentials, completely disappearing at -1.0 V, but the bands were restored upon increasing the electrode potential, implying that neither electro- nor photo-chemical reaction to break the azo group took place, in agreement with data from a cyclic voltammogram. The appearance and disappearance of these a(g) bands are thus concluded to be associated with the charge transfer phenomenon: 4,4'-DMAB must then be one of a unique group of compounds exhibiting chemical enhancement when subjected to a SERS environment.
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