Evaluation of Perylene Bisimide‐Based RuII and IrIII Complexes as Photosensitizers for Photodynamic Therapy

The synergistic action of a photosensitizer (PS), light, and oxygen is exploited in photodynamic therapy (PDT) to kill cancer cells with reduced side-effects compared with traditional chemotherapeutic treatments. In this regard, new PSs are still necessary to improve the efficacy and the outcomes of this medical technique. Over the past years, metal complexes have attracted interest as alternatives to traditional porphyrin and phthalocyanin-based PSs because of their tunable and thus tailor-made photophysical properties. Among others, RuII and IrIII derivatives have shown promising results. Here, we report on the investigation of [Ru(bpy)2(ab-PBI)][PF6]2 (1) and [Cp*Ir(ab-PBI)Cl]PF6 (2), where bpy = 2,2′-bipyridine, ab-PBI = azabenz-annulated perylene bisimide, and Cp* = pentamethylcyclopentadiene, as potential PDT PSs. These compounds display good photostability, as well as interesting singlet oxygen generation upon irradiation at 420 nm (in particular 2). Their biological activity was evaluated on four cell lines and, although the cytotoxicity of 1 did not improve significantly upon light irradiation, 2, which localizes in mitochondria of HeLa cells as indicated by ICP-MS measurements, reached nanomolar IC50 values on all the cell lines tested when activated with 420 nm light in low doses (9.27 J cm–2).