Multinuclear Ru(ii) and Ir(iii) decorated tetraphenylporphyrins as efficient PDT agents

Two novel porphyrin-core systems were prepared by Sonogashira cross-coupling of the terminal alkyne groups of meso-tetra(4-ethynylphenyl)porphyrin-Zn(ii) (P-1) with halogenated Ru(ii)- or Ir(iii)-phenanthroline complexes. The resulting compounds (P-Ru and P-Ir) were spectroscopically characterised and their photophysical properties were investigated (λ_em 625, 665 nm; τ_T 339.6 μs (P-Ru) and λ_em 530, 612, 664 nm; τ_T 396.6 μs (P-Ir)). Nanosecond time-resolved transient absorption studies were used to explore the ³MLCT nature of the triplet excited states, and the singlet oxygen quantum yields were determined (Φ_Δ 44.8 (P-Ru), 33.2 (P-Ir)%). The subcellular uptake of P-Ru and P-Ir and their application as photosensitisers (PS) in photodynamic therapy (PDT) were explored due to their solution photophysics and absence of dark toxicity. Upon irradiation (λ_exc = 620-630 nm; 10 min; 33 J cm^-2), both P-Ru and P-Ir killed 90% of SKBR-3 cells at 1 μM. Notably P-Ru induced a 77% decrease in cell viability at only 0.25 μM.