A Readily Available Red‐Emitting Methylthio‐Substituted Salicylaldehyde Azine with AIE Feature for Ratiometric Detection of HClO

Abstract Developing a simple, selective, and rapid reliable method to monitor hypochlorous acid (HClO) in vivo is very meaningful due to its important physiological and pathological functions. In this research, a novel AIE based fluorescent probe for ratiometric detection of HClO was fabricated by a simple one‐step synthesis, in which the methyl sulfide group and salicylaldehyde azine serve as the recognition unit and fluorophore, respectively. This probe was visible‐light‐excitable, and showed a palpable aggregation‐induced emission into the red region with high stability to Cu 2+ and pH. Oxidation of the methyl sulfide group can be achieved rapidly and specifically by HClO in physiological condition, which enables it to display a rapid, ratiometric fluorescent response to HClO with high selectivity over other biologically pertinent species. By exploiting the probe‐based tool, we successfully validated its practical utility in selectively recognizing HClO in living cells via ratiometric fluorescence signals, thereby providing a potential method for investigating the relevant functions of HClO in biosystems.