Direct Intramolecular Chemiexcitation Strategy Enables Sensitive Chemiluminescence Imaging of HOCl in Rheumatoid Arthritis

As a pivotal pathophysiological biomarker, hypochlorous acid (HOCl) necessitates sensitive detection technologies to resolve its spatiotemporal dynamics in biological systems. Excitation-free chemiluminescent probes circumvent tissue autofluorescence interference intrinsic to fluorescence imaging, thereby enabling high-contrast deep-tissue monitoring. However, current chemiluminescent probes often demand intricate modifications for HOCl recognition, resulting in compromised stability and sensitivity. Herein, employing intramolecular energy transfer, we engineered a HOCl-directly activated chemiluminescent probe for real-time visualization of oxidative stress in pathologically relevant models. This design leverages the carbon-carbon double bond as an intrinsic activation site, which enables efficient HOCl detection with rapid response while avoiding intermolecular energy dissipation. Crucially, electron-withdrawing group modification further enhanced sensitivity (LOD: 20 nM vs 179 nM), positioning <b>CL-2</b> competitively among state-of-the-art HOCl probes and offering a novel approach for future probe performance optimization. Mechanistic studies revealed that HOCl oxidizes the ethylene bridge to peroxide intermediates; their exothermic decomposition directly excites the intramolecular fluorophore. To validate its bioimaging potential, we validated <b>CL-2</b>'s in vivo responsiveness and applied it to a rheumatoid arthritis mouse model. The results demonstrated that <b>CL-2</b> selectively illuminated pathologically elevated HOCl levels in arthritic joints. This study pioneers a purely organic small-molecule chemiluminescent probe for HOCl detection utilizing direct intramolecular chemiexcitation (via π-conjugation), significantly advancing inflammatory disease imaging and chemiluminescent probe design strategies.