Revealing the mechanisms of p-aminothiophenol and p-nitrothiophenol dimerizing to p,p'-dimercaptoazobenzene on plasmonic metal surfaces by tip-/surface-enhanced Raman spectroscopy

Surface plasmon-mediated photocatalysis has attracted great interest. One model system is that p-aminothiophenol (PATP) could be dimerized into a new molecule of p,p′-dimercaptoazobenzene on noble metal surfaces under laser illumination. The mechanism of this catalytic reaction has caused wide discussion, but it is not fully understood yet. We performed a series of experiments for PATP and p-nitrothiophenol by tip-enhanced Raman spectroscopy and surface-enhanced Raman spectroscopy in a well-controlled gas environment (high vacuum, air, N2, and O2), and on different substrates (Au, Ag, Cu, Al, and corresponding oxides). The experimental results indicate that the electron acceptor or donor plays a decisive role in whether the reactions can occur or not.