Near Infrared Electrochemiluminescence of Rod-Shape 25-Atom AuAg Nanoclusters That Is Hundreds-Fold Stronger Than That of Ru(bpy) Standard.

Near infrared (near-IR) electrogenerated chemiluminescence (ECL) from rod-shape bimetallic AuAg nanoclusters is reported. With ECL standard tris(bipyridine)ruthenium(II) complex (Ru(bpy)) as reference, the self-annihilation ECL of the AuAg nanoclusters is about 10 times higher. The coreactant ECL of AuAg is about 400 times stronger than that of Ru(bpy) with 1 mM tripropylamine as coreactants. Voltammetric analysis reveals both oxidative and reductive ECLs under scanning electrode potentials. Transient ECL signals (tens of milliseconds) and decay profiles are captured by potential step experiments. An extremely strong and transient self-annihilation ECL is detected by activating LUMO and HOMO states sequentially via electrode reactions. The ECL generation pathways and mechanism are proposed based on the key anodic and cathodic activities arising from the energetics of this unique atomic-precision bimetallic nanocluster. Successes in the generation of the unprecedented strong near-IR ECL strongly support our prediction and choice of this nanocluster based on its record-high 40% quantum efficiency of near-IR photoluminescence. Correlation of the properties to the atomic/electronic structures has been a long-pursued goal particularly in the fast growing atomic-precision nanoclusters field. The mechanistic insights provided in this fundamental study could guide the design and syntheses of other nanoclusters or materials in general to achieve improved properties and further affirm the structure-function correlations. The high ECL signal in the less interfered near-infrared spectrum window offers combined merits of high-signal-low-noise/interference or high contrast for broad analytical sensing and immunoassays and other relevant applications.