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Both the fluorescence yield and the yield of singlet oxygen generated from the quenching of the triplet state of two water-soluble hybrid molecules ‘zinc porphyrin-ellipticine’, (1) and (2), are low compared to those of simple zinc porphyrin complexes; both these photochemical properties are dramatically enhanced by addition of calf thymus DNA to solutions of (1) or (2), as a result of the conformation change of these hybrid molecules upon interaction with double-stranded nucleic acids.

Hybrid molecules ‘cationic metalloporphyrin–intercalators’ have been synthesized which have a high affinity for double-stranded DNA and are able to cleave it at low concentrations; compound (2), an efficient bleomycin model based on a cationic metalloporphyrin, is cytotoxic towards murine leukaemia cells L1210 in vitro; iron and zinc analogues of (2) are less active, despite having the same affinity for nucleic acids.