Effect of aqueous and ambient atmospheric environments on plasmon-driven selective reduction reactions

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.