Photocytotoxicity of a New Rh₂(II,II) Complex: Increase in Cytotoxicity upon Irradiation Similar to That of PDT Agent Hematoporphyrin

A new type of heteroleptic dirhodium complex cis-[Rh2(μ-O2CCH3)2(bpy)(dppz)]2+ (3) was synthesized and its potential as a photodynamic therapy (PDT) agent was investigated. Although 27% hypochromicity of the absorption of 3 in the near-UV and visible regions is observed in the presence of duplex DNA, relative viscosity measurements reveal that the complex does not intercalate between the DNA bases. The DNA photocleavage with visible light by 3 proceeds via both oxygen dependent and independent mechanisms, and it is more efficient than that of related complexes. The increase in the cytotoxicity of 3 towards human skin cells is similar to that of hematoporphyrin, a key ingredient in a PDT drug currently in use. This feature makes this complex a useful candidate for further PDT studies.