title: Photoreduction of 4,4'-dimercaptoazobenzene on ag revealed by Raman scattering spectroscopy.
abstract: The surface-enhanced Raman scattering (SERS) of 4,4'-dimercaptoazobenzene (4,4'-DMAB) has recently seen a surge of interest, since it might be possible to form 4,4'-DMAB from 4-aminobenzenethiol (4-ABT) via a surface-induced photoreaction. We found in this study, however, that the reverse conversion of 4,4'-DMAB to 4-ABT on Ag is a more feasible process upon irradiation with a 514.5 nm (not 632.8 nm) laser under ambient conditions. First of all, the SERS spectral pattern of 4,4'-DMAB on Ag varied as a function of laser irradiation time, finally becoming the same as that of 4-ABT on Ag. Second, the coupling reaction with 4-cyanobenzoic acid to form amide bonds proceeded readily like 4-ABT once 4,4'-DMAB on Ag was exposed to 514.5 nm radiation. Third, the growth of a calcite crystal occurred on 4,4'-DMAB on Ag, also likely on 4-ABT, when it was exposed to 514.5 nm radiation beforehand. All of these results led us to conclude that the appearance of the so-called b(2)-type bands in the SERS of 4-ABT must be due to the involvement of the chemical enhancement mechanism, not due to the formation of 4,4'-DMAB.
authors.affiliation: Department of Chemistry, Seoul National University, Seoul 151-742, Korea. kwankim@snu.ac.kr
authors.forename: Kwan
authors.initials: K
authors.lastname: Kim
authors.forename: Kyung Lock
authors.initials: KL
authors.lastname: Kim
authors.forename: Kuan Soo
authors.initials: KS
authors.lastname: Shin