Carbon Nitride Quantum Dots Enhancing the Anodic Electrochemiluminescence of Ruthenium(II) Tris(2,2'-bipyridyl) via Inhibiting the Oxygen Evolution Reaction.

Although electrochemiluminescence (ECL) has been developed significantly in the past few decades, ECL efficiency in aqueous solutions remains quite low. Determination of the energy losses and development of new ECL-enhancing strategies are still of great value. In this work, we discovered a detrimental nonradiation relaxation pathway by a concurrent oxygen evolution reaction (OER) process in a well-known ruthenium(II) tris(2,2'-bipyridyl) (Ru(bpy)) aqueous ECL system due to similar surface-sensitive characteristics, and for the first time, a chemical strategy was developed by which carbon nitride quantum dots (CNQDs) could inhibit the surface OER process, alleviate the energy losses by nonradiation relaxation, and enhance the anodic ECL of Ru(bpy). In the Ru(bpy)/CNQD system, CNQDs could enhance the anodic ECL of Ru(bpy) in a nitrogen stream (10-fold) and ambient air (161-fold). The luminous and nitrogen-rich CNQDs were also confirmed not to serve as ECL luminophores, anodic coreactants, or donor/acceptors in ECL. The coreactant-free Ru(bpy)/CNQD system possesses several advantages over the common coreactant ECL system, such as low dosage (100 μg/mL CNQDs), favorable regeneration capacity, etc. As an example, ECL on-off detection of dopamine utilizing the Ru(bpy)/CNQD system was also developed to show prospects in ECL sensing. Besides, CNQDs were introduced into the classical Ru(bpy)/CO coreactant ECL system, leading to suppressed OER and improved ECL signal. Overall, the proposed new ECL-enhancing strategy is promising for applicable ECL sensing, could be extended to other ECL luminophores with high oxidation potential, and enables an in-depth understanding of the ECL process and mechanism.