Photo-Induced or Plasmon-Induced Reaction: Investigation of the Light-Induced Azo-Coupling of Amino Groups

The plasmon-mediated azo-coupling of p-aminothiophenol (PATP) and p-nitrothiophenol (pNTP) was recently achieved using gold and silver nanostructures with the help of hot electrons. To further investigate the underlying mechanisms the azo-coupling of dibenzo-1,2-dithiine-3,8-diamine (D3ATP) was investigated under distinct environmental conditions. Depending on the presence or absence of oxygen, either a plasmon-mediated or a photochemical reaction can be inferred. O-2 plays an active role in the case of photoinduced azo-coupling of D3ATP but is not required under plasmonic conditions. Consequently, two different reaction channels are proposed. In the photoreaction, NH2 needs to react with oxygen to finally form the coupling-molecule and H2O, while under the plasmonic conditions the -NH2 groups can directly couple to form the azo compound and H-2. This study suggests that plasmon-induced hot electrons provide the necessary activation energy for the azo-coupling of D3ATP without the need for O-2.