A protocol is presented for the synthesis of chromium(III) complexes of the type cis-[Cr(diimine)(2)(1-methylimidazole)(2)](3+). These compounds exhibit large excited state oxidizing powers and strong luminescence in solution. Emission is quenched by added guanine, yielding rate constants that track the driving force for guanine oxidation. The cis[Cr(TMP)(DPPZ)(1-MeImid)(2)](3+) species binds strongly to duplex DNA with a preference for AT base sites in the minor groove and may serve as a precursor for photoactivated DNA covalent adduct formation.