Photodynamic therapy (PDT) is a slightly invasive modality of chemotherapy that is arising as a new alternative for the clinical treatment of cancer and other illnesses. This therapy is based on the use of a photosensitiser (PS) which can be activated locally and specifically upon light irradiation to generate reactive oxygen species (ROS) which damage key biomolecules, leading to cancer cell death and tumour regression. This control in the cytotoxicity thanks to the activation of the PS, benefits from a reduction of the undesirable side-effects of the common chemotherapeutics. Among the wide variety of photosensitisers, Ir(III) complexes stand out due to their exceptional photophysical properties and high photostability. In the last years, there have been substantial advances in the development of new Ir(III) scaffolds that have allowed to overcome some of the limitations of PDT and might contribute to a wider clinical development. In this review, we feature the latest and cutting-edge strategies that have been recently employed in the design of new Ir(III) complexes to increase both their light harvesting ability in the therapeutic window and their photodynamic efficiency, to achieve a better biocompatibility, to increase the selectivity towards cancer cells or specific organelles and the possibility of using a combination of PDT with other advanced therapies to enhance the therapeutic effect.
