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 ³

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 (10³) increase in apparent afterglow chemiluminescence lifetimes. This electroprecipitation process occurs at an aqueous|organic multiphase boundary, which are present all through nature and are arguably more representative of natural chemical processes. Furthermore, experimental parameters, including BPO concentration, applied potential, and electrode material, were investigated. Competitive and parasitic processes, such as the hydrogen evolution reaction and decarboxylation, diminish the electroprecipitation of reactive intermediates, and we detail mitigation and optimization efforts. Overall, this work reveals that multiphase interfaces can be used to electroprecipitate reactive radicals, separating their use in space and time.