Recent advances in biomedical applications of organic fluorescence materials with reduced singlet–triplet energy gaps

Purely organic, thermally activated delayed fluorescence (TADF) materials have recently emerged as novel and attractive organic luminescent materials for use in many research fields. Motivated by the unique features of TADF fluorophores, most notably their long-lived delayed fluorescence and high triplet formation, many organic TADF fluorophores have been developed for biomedical applications. In this review, we briefly summarize recent progress in the development of intelligent TADF probes, ranging from single molecules to delicate nanomaterials, for time-resolved fluorescence imaging and biosensing in biology and medicine. Moreover, recent strategies for designing novel photosensitizers (PSs) based on donor–acceptor systems with reduced singlet–triplet energy gaps (ΔE_ST) for photodynamic therapy of cancer are also introduced. Finally, the main challenges of and prospects for organic molecules with reduced ΔE_ST for biomedical applications are discussed.