Role of molecular oxygen and its active forms in generation of electrochemiluminescence

A short review is dedicated to the role of molecular oxygen and its active forms in generation of electrochemiluminescence (ECL). It is shown at the example of such widely used luminogens as luminol, lucigenin, acridine esters, acridane, and indoles that the role of O 2 and its active forms, such as hydrogen peroxide, superoxide and hydroperoxide radicals in generation of ECL by organic compounds is largely reduced to oxidation of the initial luminogen or intermediates of its partial electrochemical preoxidation/prereduction. Such intermediates are most often particles in the doublet state (radical-cation, radical-anion, or free radicals) that form unstable emitter precursors of peroxide (dioxetanone) type under interaction with O 2 , hydrogen peroxide, or other active oxygen forms. It is also shown that the product of secondary transformations of active oxygen forms is singlet oxygen that may also be a radiation source as a result of cooperative transitions.