Phenothiazine-based fluorescent probe with microenvironment-regulated cascade emission for Zn2+ and HClO detection

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Zinc ions (Zn 2+ ) and hypochlorous acid (HClO) play critical roles in chemical, environmental, and biological systems, yet their different reactivities make their selective detection in complex matrices highly challenging. Herein, we report a cascade-activated fluorescent probe (PTZ-TH ) rationally constructed by integrating a salicylaldehyde acylhydrazone coordination unit with a phenothiazine-based donor-acceptor chromophore. PTZ-TH exhibits distinct microenvironment-dependent fluorescence behavior, displaying strong intramolecular charge transfer (ICT) emission in organic solvents, significant aggregation-caused quenching (ACQ) in mixed aqueous media, and fluorescence recovery at high water fractions driven by aggregation-induced emission (AIE). This intrinsic fluorescence suppression in mixed aqueous environments provides a controllable “off” state for programmed signal activation. Upon coordination with Zn 2+ , conformational rigidification suppresses non-radiative decay and produces a distinct yellow “turn-on” emission. Subsequent exposure to HClO induces selective oxidative transformation of the phenothiazine unit, leading to electronic reconstruction and a blue-shifted emission. This cascade process enables temporally and spectrally resolved fluorescence outputs on a single molecular platform. PTZ-TH demonstrates high selectivity, rapid response kinetics, and visually discernible color changes. Its practical application was validated by successful monitoring of Zn 2+ and HClO in representative environmental water, beverage, food, and plant samples. This work establishes a microenvironment-regulated cascade strategy for constructing multi-stimuli-responsive fluorescent probes with programmable optical outputs, paving the way for the rational design of advanced logic-controlled fluorescent systems with broad potential in chemical sensing, environmental monitoring, and biological imaging.