Recent developments in Ru(II) and Ir(III) photosensitizers for anticancer therapeutics

Photodynamic Therapy (PDT) is an exciting alternative treatment strategy for certain cancers that is less invasive and toxic than traditional methods. It employs light-activated photosensitisers (PSs) to generate reactive oxygen species (ROS), that destroy cancer cells via electron transfer (Type I) or energy transfer (Type II). Transition metal complexes of Ru(II) and Ir(III) are highly effective PSs due to strong spin-orbital coupling (SOC) that facilitates intersystem crossing (ISC) and long-lived triplet excited states. Moreover, ligand design in these complexes improves photophysical properties and promotes selective accumulation in tumours, thereby improving both efficacy and selectivity. Together, these features make metal-based PSs promising candidates for the development of next-generation PDT, offering improved performance, precision targeting and biocompatibility. Building on a recent published review from 2020, which examined advanced strategies in the design of Ir(III) biscyclometalated complexes for PDT , Sanz-Villafruela et al. (2025) [1] this new review highlights Ir(III) and Ru(II) complexes that were published between 2020 and 2025. It considers these under two dominant design paradigms: triplet-state modulation, and biological vectorization. In so doing, it seeks to shed some light on how newly emerging photosensitisers with tuneable photophysical properties, are demonstrating further promise in the search for selective anticancer treatments. • Ir(III)/Ru(II) complexes show long-lived triplet states and efficient ISC for PDT. • Long-lived triplet states enable efficient ROS generation. • Ligand design tunes triplet energy and ROS selectively. • Hydrophilic ligands improve aqueous stability and delivery.