Rational Molecular Engineering of Organic Semiconducting Nanoplatforms for Advancing NIR‐II Fluorescence Theranostics

Second near-infrared window (NIR-II, 1000-1700 nm) fluorescence imaging (FI) in phototheranostics benefits from deep tissue penetration, negligible body spontaneous fluorescence, exceptional spatiotemporal resolution, and diversified imaging agents. Inorganic and metal nanomaterials with NIR-II emission are widely explored for NIR-II FI, however, the concern about their intrinsic long-term toxicity hampers further clinic applications. By contrast, whole organic NIR-II FI agents, in particular, organic semiconducting molecules derived from large pi-conjugated molecular architectures and biologically amicable ingredients, owning inert photophysical potencies, tunable optical properties, and favorable biocompatibility, have the potential to be degraded and excreted from the body in molecular level. In this review, the development of NIR-II fluorescence-emitting organic semiconducting nanoplatforms, with a focus on their theranostic applications in biomedicine is discussed. The recent advances in the molecular design of semiconducting NIR-II emitting agents for improving the properties of NIR-II photonics (e.g., emission intensity, quantum yield, emission wavelength, and activatable emission) and optimizing disease phototheranostics (the synergistic combination of NIR-II FI-based diagnosis and photo-related therapeutic methods) are highlighted. Finally, the challenges and perspectives to building high-powered new-generation organic semiconducting nanoplatforms for NIR-II phototheranostics of a variety of diseases are discussed.