Ultralong aqueous organic room-temperature phosphorescent probes for in vivo time-resolved bioimaging

Long-lived emissive probes have evolved as promising visualized tools for monitoring complex biological processes because of their distinctive features of large Stokes shifts and long luminescence lifetimes, which can effectively circumvent the interference of autofluorescence from biological tissue and organs. Particularly, purely organic room-temperature phosphorescence (RTP), especially in aqueous media, is of great interest due to its ultralong lifetimes, high quantum yields, low production cost, and satisfactory biocompatibility, making them serve as excellent candidates for in vivo deep-tissue time-resolved bioimaging. This review systematically summarizes recent advances of organic RTP probes, principally focusing on their in vivo bioimaging application of subcutaneous tissue imaging, wound healing monitoring, sentinel lymph node detection, thermometry, primary tumor visualization, assessment of tumor hypoxia and metastatic imaging. Various chemical structures, such as carbazole, phenothiazine, phenylpyrrole, polycyclic aromatic hydrocarbon, triphenylamine, difluoroboron β-diketonate, naphthalimide, and others, have been explored for these probes. The review also highlights the current strategies employed to enhance the properties of organic RTP molecules. These strategies include the polymer-assisted top-down method, bottom-up nanoprecipitation method, supramolecular nanoassemblies, and silica-skeleton nanocomposites. These approaches offer benefits such as ultralong lifetime, excellent water dispersibility, and biocompatibility under physiological conditions, thereby enhancing the performance of organic RTP probes for various applications. Furthermore, the review outlines the existing challenges and presents future prospects in this field. The aim is to inspire the development of more advanced and intelligent organic RTP probes with potential biomedical and clinical applications. By addressing these challenges and exploring new directions, researchers aim to contribute to the evolution of this field and the realization of its full potential in diagnostic and therapeutic settings.