Cyclometalated Iridium(III) Complexes with Optimally Allocated Excited-State Energy for Near-Infrared Photodynamic and Photothermal Therapy

Phosphorescent cyclometalated Ir(III) complexes can simultaneously generate reactive oxygen species and undergo photothermal conversion under light exposure, enabling synergistic photodynamic and photothermal therapy (PDT and PTT), and in vitro and in vivo bioimaging. However, how their light excitation properties and the distribution of excited-state (ES) energy across the photodynamic (energy or electron transfer), photothermal (nonradiative decay), and photoluminescent properties (radiative decay) determine their therapeutic and imaging efficacy are largely unclear. In this study, six Ir(III) complexes have been designed to explore the relationships between their structure and properties including ES energy level, population, and energy allocation. Through chemical, quantum chemical calculations, spectroscopic, and in vitro PDT/PTT for human malignant melanoma and cisplatin-resistant nonsmall-cell lung cancer, significant differences in activity and mechanisms were revealed among complexes with high structural similarity and the potential determining factors were systematically studied. In vivo, the selected complex Ir5 effectively inhibited the growth of cisplatin-resistant lung tumors by 96% and completely ablated 50% tumors in mice. This study provided not only single-molecule Ir(III) complexes for treatments of large, deep-seated, drug resistance tumors, but meaningful insights for the design of single molecules for synergistic PDT/PTT/bioimaging.