ACTIVATED OXYGEN: SINGLET MOLECULAR OXYGEN AND SUPEROXIDE ANION

Abstract

Abstract— Elusive processes associated with molecular oxygen in chemical and biological systems are interpreted in terms of two activated oxygen species, singlet molecular oxygen (1Σ+g/1Δg) and superoxide anion (X2πg). The generation and deactivation of singlet oxygen by interaction with organic triplet states are discussed within a comprehensive theoretical framework. Experimental results indicate the anomalous molecular oxygen enhanced luminescence from organic chromophores in polymer matrices results from the deactivation of singlet (1Δg) oxygen by energy transfer to electronically excited states of the chromophore, and three types of oxygen enhanced luminescence have been identified in these systems. Properties of the superoxide anion relevant to its solution chemistry are briefly discussed. Electron transfer theory is used to theoretically examine the generation of singlet oxygen in disproportionation reactions of the superoxide anion, predicting that, depending on the number of water molecules present, the disproportionation reaction is a proficient source of singlet oxygen. A competing quenching process imposes a limit to the steady state concentration of singlet oxygen in most chemical systems. Available experimental results on the quenching of singlet oxygen by superoxide anion are in good agreement with theoretical results obtained via application of electron transfer theory.