Bromopsoralens and bromocoumarins have been used to sensitize the inactivation of viruses. The bromine substituent increased the antiviral potency of the sensitizer, an effect attributed to cleavage of the C-Br bond of the aromatic radical anion produced by a light-induced electron transfer reaction with nucleic acids. This hypothesis was tested by a detailed mechanistic electrochemical investigation in acetonitrile and N,N-dimethylformamide of 5-bromo-8-methsxypsoralen, 8-methoxypsoralen, 3-bromocoumarin, and coumarin. A one-electron reduction process involves the formation of a radical anion, a step coupled with the cleavage of the carbon-bromine bond in the case of the brominated compounds, leading to the formation of an aryl radical moiety and a bromide anion. These experiments were further confirmed by radiolytic preparation coupled with UV-vis detection of the radical anions in glassy 2-methyltetrahydrofuran at 77 K and in ether, acetonitrile, and alcohol solutions at ambient temperature. This allows complete kinetic characterization of the ionic intermediates. The shorter lifetimes obtained with brominated radical anions relative to that of the parent structure are explained by scission of the carbon-halogen bond.