High-Luminescence Efficiency NIR-II Nanocrystals via Hierarchical Confinements for Imaging-Guided Surgery of Acute Intestinal Ischemia.

Among the diverse challenges encountered by fluorescence imaging in the second near-infrared region (NIR-II, 1000-1700 nm), achieving high quantum yields (QYs) for contrast agents is critical yet rarely addressed. Herein, we demonstrate an approach to overcoming this issue through rational structural design that leverages hierarchical confinements at both molecular and aggregate levels. Through an alteration of methyl substituents, the rotational freedom of aromatic rings is effectively reduced, facilitating the formation of rigid mortise-and-tenon joints within the crystal lattice. As a result, an absolute QY of 9.7% is achieved in the crystal state. Moreover, the abundant intermolecular noncovalent interactions endow B-ToMeT with crystallization ability, enabling the assembly of nanocrystals (NCs) formed in aqueous solution, whose emission peak is 970 nm with an exceptionally high relative QY of 28.2%. This underscores the remarkable advantage of the hierarchical confinement strategy. By using the ultrabright NCs for real-time monitoring of intestinal vessels in the living system, early diagnosis and surgical treatment of acute intestinal ischemia can be realized, indicating the great potential of this molecular design for high-performance NIR-II materials in in vivo imaging and surgery navigation.