Self-assembled nanoparticles based on cationic mono-/AIE tetra-nuclear Ir(III) complexes: long wavelength absorption/near-infrared emission photosensitizers for photodynamic therapy

Cyclometalated Ir(III) complexes as photosensitizers (PSs) have attracted widespread attention because of their good photostability and efficient 1O2 production ability. However, their strong absorption in the UV-vis region severely limits their applications in photodynamic therapy (PDT) because the short wavelength illuminating light can be easily absorbed by the skin and subcutaneous adipose tissue causing damage to the patient's normal tissue. Herein, mono- and tetra-nuclear Ir(III) complex-porphyrin conjugates are rationally designed and synthesized, especially [TPP-4Ir]4+ exhibits obvious aggregation-induced emission (AIE) characteristics. PSs comprising Ir(III) complex-porphyrin conjugates self-assembled as nanoparticles (NPs) are successfully achieved. The obtained [TPP-Ir]+ NPs and [TPP-4Ir]4+ NPs exhibit long wavelength absorption (500–700 nm) and near-infrared emission (635–750 nm), successfully overcoming the inherent defects of short wavelength absorption of traditional Ir(III) complexes. Moreover, [TPP-4Ir]4+ NPs exhibit good biocompatibility, high 1O2 generation ability, low half-maximal inhibitory concentration (IC50) (0.47 × 10−6 M), potent cytotoxicity toward cancer cells and superior cellular uptake under white light irradiation. This work extends the scope for transition metal complex PSs with promising clinical applications.