Radical Electroprecipitation from a Water|Oil|Electrode Interface Prolongs "Electro"Chemiluminescence of the Tris(2,2'-bipyridyl)Ruthenium(II) and Benzoyl Peroxide System by 10

Reactive intermediates, including radicals and other short-lived molecules, are ubiquitous in pure chemical processes and often highly difficult to isolate. Recently, we found that energetic, reactive radical species can be trapped through electroprecipitation, where the precipitate contains a reactive intermediate. The principle is straight-forward: If a solubility equilibrium can be exceeded before the reactive intermediate lifetime, the intermediate can be precipitated. Classically, electrochemiluminescence (ECL) is a process where electrical energy is transferred to chemical energy, and then the chemical energy is released in the form of light emission (often in the presence of an electroactive luminophore). The apparent luminescence lifetime, limited by radical lifetimes, of ECL reactions in solution is short (sub-microsecond), and thus can hinder the performance of the technique as light emission is confined to the electrode surface and occurs only when the electrical potential to the system is applied. Here, we show that with a high concentration (10-250 mM) of benzoyl peroxide (BPO) being co-reduced with a tris(2,2'-bipyridyl)ruthenium(II) complex, we can achieve an ECL emission that lasts for hundreds of seconds after potential arrest, corresponding to a thousand-fold (10