Oxygen singlet state donor

In the third major type of aromatic photosubstitution, which is designated as Stf+vl Ar, a radical cation of the arene is the reactive species, interacting with the nucleophile. The radical cation may be solvated by the medium or it may be part of an excited donor-acceptor complex. The reactive excited state may be singlet or triplet. The electron expelled by excited ArX may be taken up by the solvent, by ground-state ArX, by oxygen or by an... 

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