When near-infrared fluorescence meets supramolecular coordination complexes: Challenges and opportunities of metallacycles/metallacages in precision biomedicine

In the past decade, the metallacycles/metallacages have attracted unremitting interest in biomedical fields, yet visual tracking of their in vivo delivery, targeting ability, biodistribution and therapeutic evaluation are still hampered by their short emission wavelengths. More recently, the near-infrared biochannel (NIR, 0.7-1.7 & mu;m) especially the NIR-II region (1.0-1.7 & mu;m) provides deeper tissue penetration and higher contrast than traditional UV-Vis region for in vivo imaging. In this context, we provide a comprehensive and systematic insight into the development of NIR metallacycles/metallacages for biomedical applications. Finally, we also discuss the challenges and prospects of NIR metallacycles/metallacages for future biomedical research and clinical translation.