Cucurbit[8]Uril Driven Upconversion Near‐Infrared Delayed Fluorescence for Targeted Cell Imaging

Abstract Pure organic upconversion systems have opened new possibilities for deep‐tissue bioimaging based on efficient two or three‐photon excitation. Herein, a pure organic room‐temperature phosphorescence (RTP) upconversion supramolecular assembly is reported that exhibits near‐infrared (NIR) delayed fluorescence by upconverted excitation at 940 nm. This system is constructed by co‐assembling cucurbit[8]uril (CB[8])‐confined indole‐bridged xanthene derivative (CyBr) with the complex of CB[8] encapsulated two sulfonated bromophenylpyridinium (PySO 3 ⊂CB[8]), guided by β ‐cyclodextrin‐grafted hyaluronic acid (HACD). First, the spatial confinement of CB[8] 10‐fold enhances the fluorescence of CyBr. Subsequently, as the tumor‐targeting agent, HACD realizes cascade fluorescence enhancement, boosting the quantum yield (QY) of CyBr by 22 times. Moreover, the cavities of β ‐CDs in HACD provide assembly sites for multivalent interactions with the sulfonic acid group of PySO 3 ⊂CB[8], achieving highly efficient phosphorescence resonance energy transfer (PERT) with an efficiency of 84.49%. This leads to NIR delayed fluorescence at 710 nm with a lifetime of 99.16 µs. Notably, this system exhibits exceptional upconversion capability under 940 nm three‐photon excitation, enabling targeted A549 cancer cell imaging with deep‐tissue penetration and long‐lived NIR emission for low‐background detection.