Design and synthesis of phenothiazine-based D–A molecules with ICT characteristics as efficient fluorescent probes for detecting hypochlorite in water

Abstract

Phenylthiazide compounds are frequently utilized to construct electron donor–acceptor (D–A) dyes, exhibiting excellent fluorescence and colorimetric analysis performance due to their electron-rich properties. Three D-A type compounds 5a–c, featuring intramolecular charge transfer (ICT) characteristics, were designed and synthesized using phenothiazine as the donor and various aryl-substituted imidazoles as acceptors for the detection of hypochlorite. Additionally, the ICT properties of the compounds can be fine-tuned by introducing various substituents to achieve a more sensitive optical response to HClO/ClO⁻. Among these, compound 5c, which contains the electron-withdrawing group –CN, demonstrated high sensitivity (3.5 nM), high selectivity, and a rapid response to HClO/ClO⁻. Experimental results indicated that the strategy based on structural tuning presents a promising approach for optimizing fluorescent probes. To broaden practical applications, compound 5c was fabricated into paper test strips and thin-layer chromatography (TLC) plates for on-site analysis and detection of HClO/ClO⁻. The compound was capable of detecting HClO/ClO⁻ not only in actual water samples but also in complex environmental water samples, thereby providing a convenient tool for real-time HClO/ClO⁻ detection.