Single-Atom Switching for Constructing a Full-Spectrum Hypochlorite-Responsive Probe Library: Screening Candidates for Water Analysis

Residual hypochlorite/hypochlorous acid (ClO–/HClO) is widely used in disinfection, yet simple assays integrating visual readout with quantitative fluorescence analysis remain limited. Herein, we report a single-atom-switching strategy for constructing a six-member, full-spectrum library of ClO–-responsive probes. Aqueous screening identified Scou, Scou-Ph, and Scou-CN as selected candidates based on pronounced spectral responses and visual contrast. HRMS supports the ClO–-triggered oxidative desulfurization of the thiocarbonyl moiety to the corresponding carbonyl fluorophore, while DFT calculations rationalize the associated spectral changes. Detailed evaluation of the three probes revealed distinguishable fluorescence responses over pH 2–10 and enabled determination of ClO– in tap water and lake water, affording recoveries of 98.3–111% with RSD values of 0.22–6.1%. This work expands the structural diversity of ClO– probes and offers a practical workflow for molecular-library screening and selected-probe evaluation.