ABSTRACT
Chemiluminescence (CL) is the emission of light by molecules that are electroni cally excited by virtue of their precursors’ participation in a highly exergonic chemical reaction, almost invariably an oxidation reaction. Such reactions occur in vitro and in vivo and in the latter case they are mediated by enzymes and the resulting chemiluminescence is called bioluminescence. Chemiluminescence is actually fluorescence (spin-allowed, radiative deactivation of the lowest excited singlet state) from the electronically excited product of the chemical reaction. It differs from the process normally called fluorescence (photofluorescence) only in that in fluorescence, the light-emitting molecules are electronically excited by the absorption of light whereas in CL, no external light source is employed. Al though, in principle, CL could arise from the lowest triplet state as a phosphores cent emission, the long inherent lifetimes of triplet states and their near-total quenching by photoreaction in fluid solutions has, to our knowledge, precluded such a phenomenon from ever having been observed.
