Visible-Light Response of 4-Aminobenzenethiol and 4,4 '-Dimercaptoazobenzene Silver Salts

초록

Silver thiolate, which is an organic-inorganic heterostructured material, converts into thiol-derivatized Ag nanoparticles after irradiation with a visible laser. In this study, the visible-laser responses of 4-aminobenzenethiol (4-ABT) and 4,4'-dimercaptoazobenzene (4,4'-DMAB) silver salts were examined to verify that 4,4'-DMAB on Ag converts to 4-ABT on Ag because of the irradiation of light with a wavelength of 514.5 nm, to resolve the issues that result from the surface-enhanced Raman scattering (SEAS) characteristics of 4-ABT. Due to the appearance of unpredicted, non-a(1)-type bands, the SERS spectrum of 4-ABT is very similar to that of 4,4'-DMAB. One explanation for the non-a(1)-type bands is that they are associated with the charge-transfer chemical-enhancement mechanism of SERS, but a few researchers have attributed them to photoinduced catalytic conversion of 4-ABT on Ag to 4,4'-DMAB. Using 514.5 nm radiation, we recently reported the successful conversion of 4,4'-DMAB on Ag to 4-ABT; however, the reverse reaction from 4-ABT to 4,4'-DMAB did not occur. Similarly, in this study, 4,4'-DMAB Ag salts first converted to 4,4'-DMAB-adsorbed Ag nanoparticles and then to 4-ABT on Ag nanoparticles after prolonged 514.5 nm irradiation. According to the results of a laser-power dependence study, the photoinduced reduction of 4,4'-DMAB on Ag to 4-ABT is a single-photon process. The photoinduced conversion of 4,4'-DMAB to 4-ABT was more facile as Ag salts than as being assembled on Ag films, which implies that fresh Ag nanoparticles produced in situ are more efficient photoelectron emitters than are aged ones. The non-a(1)-type bands that appear in the SERS of 4-ABT are thus attributed to the chemical-enhancement mechanism rather than to photoconversion.

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