Newly synthesized 9,10-anthraquinone and acenaphthene-1,2-dione derivatives exhibited high potency for DNA scission under photolytic conditions at concentrations of 37 and 6.5 μM, respectively. Results from electron paramagnetic resonance (EPR) experiments reveal that the benzoyloxy radicals and their degraded aryl radical intermediates (rather than bis-iminyl radicals) were mostly responsible for the DNA cleavage.