NIR‐II Fluorescent Brightness Promoted by “Ring Fusion” for the Detection of Intestinal Inflammation

Abstract Fluorophores with emission in the second near‐infrared window (NIR‐II) have displayed salient advantages for biomedical applications. However, the common strategy of reducing the energy bandgap of fluorophores so as to achieve red‐shifted wavelengths always leads to compromised fluorescent brightness. Herein, we propose a molecular design concept of “ring‐fusion” to modify the acceptor of AIEgen that can extend the luminous wavelength from NIR‐I to NIR‐II. The fused‐acceptor‐containing fluorophore yielded, TTQP, has an enhanced absorption coefficient with a higher brightness in nanoparticle formation compared to its NIR‐I emissive counterpart (TTQ‐DP) with a non‐fused acceptor. Theoretical calculation further confirms that the ring fusion can efficiently promote the rigidity and planarity of the electron‐deficient core, leading to a lower reorganization energy and nonradiative decay. The TTQP NPs yielded thus allow sensitive NIR‐II fluorescence imaging of vasculature and intestinal inflammation in mice models. Therefore, we anticipate that our work will provide a promising molecular‐engineering strategy to enrich the library and broaden the application scope of NIR‐II fluorophores.