AIE-active Ir() complexes functionalised with a cationic Schiff base ligand: synthesis, photophysical properties and applications in photodynamic therapy

Photodynamic therapy (PDT) is a promising cancer treatment method. Traditional small-molecule photosensitizers (PSs) suffer from low intersystem crossing (ISC) ability and aggregation-caused quenching (ACQ), which adversely affects the luminous efficiency and singlet oxygen ( 1 O 2 ) yield of PSs in the aggregated state. Ir( iii ) complexes are promising PSs with long excited-state lifetime, good photophysical and photochemical properties and large Stokes shifts. Aggregation-induced emission (AIE) characteristics could reduce the nonradiative recombination and improve the ISC ability of excited states through the restriction of the intramolecular motions in aggregated states. Accordingly, two AIE-active Ir( iii ) complexes Ir-1-N + and Ir-2-N + were successfully designed and obtained based on Schiff base ligands. Experimental results showed that Ir-1-N + and Ir-2-N + have good photophysical properties and the corresponding nanoparticles (NPs) have good water solubility and 1 O 2 generation ability. Notably, Ir-2-N + NPs can be efficiently taken up by mouse breast cancer cells (4T1 cells) with good biocompatibility, low dark toxicity and excellent phototoxicity. This work demonstrates a versatile strategy for exploiting efficient transition metal PSs with a cationic ligand in PDT. Two AIE-active Ir( iii ) cationic complexes containing Schiff base ligands were synthesised. Ir-2-N + NPs are shown to be good PSs in vitro for PDT.