Donor-Acceptor Fluorophores Emitting in the Second Near-Infrared Window for Biological Applications

Organic fluorophores are regarded as one of the most promising candidates for clinical applications owing to their adjustable chemical structures, tunable photophysical properties, and superior biocompatibility. Many scientific research has shown that organic fluorophores emitting in the second near-infrared window (NIR-II) have received great attention in fluorescence bioimaging since they provide outstanding spatiotemporal resolution and deep tissue penetration ability. Recently, NIR-II fluorophores with fantastic optoelectronic properties, constructed by directly linking separated electron donors and acceptors, have shown great potential in developing diagnostic and therapeutic applications. Herein, recent donor-acceptor (D-A) type NIR-II fluorophores for biological applications are reviewed. First, the design strategies of D-A type NIR-II fluorophores bearing distinct acceptors are outlined. Subsequently, various applications of D-A type NIR-II fluorophores in photothermal therapy, photodynamic therapy, in vivo fluorescence imaging, biosensing, and nanocarriers are systematically summarized. Eventually, existing challenges and research directions for future advancement of D-A type NIR-II fluorophores are presented.