Strategic Design of Luminescent Rhenium(I), Ruthenium(II), and Iridium(III) Complexes as Activity-Based Probes for Bioimaging and Biosensing

The rapid development of responsive fluorescent probes has advanced optical imaging for biological research and biomedical applications. Among different sensing strategies, activity-based sensing, which exploits the unique reactivity of the target chemical species to achieve high chemoselectivity, has emerged as a promising paradigm for the development of responsive probes for selective molecular imaging. Luminescent transition metal complexes have received considerable attention for bioimaging and biosensing applications over the last decade due to their remarkable photophysical behavior including intense emission with large Stokes’ shifts, long emission lifetimes, strong two-photon absorption, and high photostability. In this Review, we summarize the design strategies and applications of luminescent complexes of rhenium(I), ruthenium(II), and iridium(III) polypyridines as activity-based probes for the detection of various chemical species and bioactive molecules in live cells and organisms. The current challenges and future prospects of these complexes as activatable reagents for disease diagnosis and treatment are also discussed.