Zhao_2026_Angew.Chem.Int.Ed.Engl__e3863987

Afterglow luminescence holds great promise for biomedical imaging by eliminating tissue autofluorescence. Unimolecular afterglow systems avoid the need for nanoencapsulation, providing enhanced simplicity and structure flexibility as well as in vivo stability over common nanoparticle-based designs. However, rational design remains challenging, and only a few unimolecular systems have been reported. These systems often exhibit low signal intensity, which restricts their biomedical applications. To resolve it, we design a hemicyanine-based unimolecular organic afterglow platform (CyIA) with high afterglow brightness and structural tunability for in vivo activatable imaging. CyIA displays anti-Kasha/Kasha dual-emission with bright afterglow signal in aqueous solution, up to 10(8) p/s/cm(2)/sr, which is nearly three orders of magnitude higher than previously reported unimolecular organic afterglow probes. Leveraging the structural flexibility, a butyrylcholinesterase (BChE)-activatable afterglow probe (CyIAB-T) is fabricated. This probe enables a specific and sensitive detection of BChE in Alzheimer's disease (AD) model mice with higher contrast relative to fluorescence imaging. Importantly, this probe permits dynamic tracking of the age-dependent upregulation of BChE during AD progression. Therefore, this study establishes a versatile unimolecular organic afterglow scaffold with high intensity and structural flexibility for developing activatable afterglow probes for high-contrast biomedical imaging.