Abstract
We successfully realised plasmon-driven selective reduction reactions of 2-amino-5-nitrobenzenethiol (2A-5-NBT) to 3,3’-dimercapto-4,4’-diaminoazobenzene , an azobenzene derivative, using surface-enhanced Raman scattering (SERS) spectroscopy, and supported by the theoretical calculations. The SERS spectra demonstrated that two 5-nitro groups of 2A-5-NBTs were selectively reduced to the –N=N– chemical bond of 3,3’-dimercapto-4,4’-diaminoazobenzene, whereas the 2-amine group of 2A-5-NBT remained unchanged. Our experimental results revealed that aqueous environments were preferable to ambient atmospheric environments for this selective reduction reaction. The product is very stable in aqueous environments. However, in ambient atmosphere environments, the product is not stable and can revert back to 2A-5-NBT, where the –N=N– chemical bond can be broken by plasmon scissors. The plasmon-induced catalytic reactions in aqueous environments could be used for the efficient synthesis of aromatic azobenzene derivative compounds, which are valuable chemicals that are widely used in the chemical industry as dyes, food additives and drugs.
Highlights
2-amino-5-nitrobenzenethiol (2A-5-NBT, see Fig. 1a) is an interesting molecule that contains benzyl, amine, nitro and -SH groups
We used SERS spectroscopy in conjunction with theoretical calculations to investigate the plasmon-driven selective reduction reaction of 2A-5-NBT, which was chemically absorbed on a roughened Ag substrate and was dimerized to a new azobenzene derivative compound, 3,3’-dimercapto-4,4’diaminoazobenzene
2A-5-NBT contains an amine group (–NH2) and a nitro group (–NO2); it is difficult to ascertain which nitrogenous group participates in the selective formation of the azo bond
Summary
2-amino-5-nitrobenzenethiol (2A-5-NBT, see Fig. 1a) is an interesting molecule that contains benzyl, amine, nitro and -SH groups This molecule can be used to study the competition between plasmon-driven oxidation and reduction in different environments, e.g., aqueous or ambient atmospheric environments. We used SERS spectroscopy in conjunction with theoretical calculations to investigate the plasmon-driven selective reduction reaction of 2A-5-NBT, which was chemically absorbed on a roughened Ag substrate and was dimerized to a new azobenzene derivative compound, 3,3’-dimercapto-4,4’diaminoazobenzene. This selective reduction reaction proceeded via the nitro group of 2A-5-NBT, and oxidation via the amine group of 2A-5-NBT did not occur. Our findings provide a novel environmentally friendly synthetic method for forming azobenzene derivative compounds, which are important and valuable industrial dyes[28] and have potential applications as molecular wires and switches in molecular electronics[29,30,31]
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