NIR electrochemiluminescence from Au-25(-) nanoclusters facilitated by highly oxidizing and reducing co-reactant radicals

The well-defined electrochemical features and optical properties of the negatively charged Au-25 clusters (Au-25(-)) provide opportunities for a photoelectrochemical study by means of electrochemiluminescence (ECL) technique. Under annihilation conditions where the Au-25(-) is electrochemically pumped to its various oxidized and reduced forms showed no appreciable ECL light emission, due presumably to the short lifetime of the electrogenerated intermediates and their reactivity. Interestingly, in either Au-25(-)/tri-n-propylamine (TPrA) or Au-25(-)/benzoyl peroxide (BPO) co-reactant systems, the correspondingly highly reducing and oxidizing intermediates electrogenerated from TPrA and BPO lead to light emission at 950 and 890 nm in near-infrared (NIR) region. The ECL in the presence of various concentrations of TPrA (6.3, 12.5, 25, 50, 100 and 200 mM) and BPO (2.5, 5, 25 and 50 mM) was explicitly investigated. Along with the concentration dependence study, spooling ECL spectroscopy provided insight into the ECL mechanisms. Notably, while the Au-25(-)* is the main light emission source with BPO, ECL in the presence of TPrA is attributed to emissions from the Au-25(-)*, Au-25(0)* and Au-25(+)* that are tuneable by means of the applied potential and TPrA concentration.