Organorhenium complexes as theranostic agents: Bridging anticancer activity and molecular sensing

Organometallic complexes are highly explored in the field of cancer theranostics as well as in biomedical sensor applications, based on their unparalleled photophysical as well as bioimaging features. Among all of them, rhenium(I) Re(I) complexes are special in that they contain superior photostability, huge Stokes shifts, as well as long-lived excited states - features that are ideal for applications in luminescence-mediated imaging as well as therapeutic applications. However, compared to other transition metal-based systems, Re(I) complexes are still less explored. Here, we give an exhaustive survey of the latest developments in the designing as well as applications of luminescent Re(I) complexes, with a special emphasis on the highlighting of the potential in using them for biomedical sensing, imaging, as well as anticancer therapies. Particular focus has been given to mechanistic aspects and future prospects for designing multi-functional Re(I) complexes for biomedical imaging. A discussion was presented about various mechanistic interpretations of their cellular uptake, localization, and cytotoxicity pathways in an attempt to conceptualize their behaviour in biological settings. Addition of Re(I) centres within biologically compatible ligands has also improved the specificity as well as the efficacy of the systems, providing improved pharmacokinetics with a sharp reduction in systemic toxicity. Furthermore, through the provision of activation within specific physiological conditions such as oxidative pressure or hypoxia, the assembly of redox-switchable Re(I) complexes has built new avenues for clinical imagery as well as therapy. Re(I) based luminescent assemblies contain immense potential as next-generation agents that contain new avenues for early detection, real-time imagery, as well as efficient cancer therapy by virtue of cumulative efforts as well as coherent molecular design. Each of the advances reflects how transformative Re(I) complexes can be in next-generation biological applications. • Rhenium (Re) complexes, due to their outstanding photophysical properties, are highly suitable for applications in bioimaging and sensing. • Despite their promising potential in biomedical fields, Re(I) luminescent complexes remain underexplored • This review provides a comprehensive overview of recent progress in the development of Re(I)-based complexes for applications in sensing, imaging, and anticancer therapy. • An additional focus is given to mechanistic insights and future design strategies for creating multifunctional Re(I) complexes engineered for use in biomedical fields.