A Convenient and Portable Turn‐On Fluorescent Probe for Reliable Detection of Hypochlorite: Smartphone‐Based Application

A convenient and portable turn‐on fluorescent probe, MITC (( E )‐N′‐((1‐methyl‐1H‐indol‐3‐yl)methylene)thiophene‐2‐carbohydrazide), was synthesized for selective and practical detection of ClO − . MITC selectively detected ClO − in water‐containing environments through a response that exhibited distinct blue fluorescence. The limit of detection of MITC to ClO − was 7.94 μM, which was significantly below the World Health Organization (WHO) standard (5 mg/L; 70.5 μM) for free chlorine in water. MITC exhibited effective detection ability over a wide pH range of 6–11. Test strip and smartphone‐based detection tools using MITC offered the advantage of easy and convenient detection. Notably, MITC showed reliable recoveries for the quantification of ClO − in real water samples (tap, drinking, river, and sea water) using the smartphone‐based detection method. The mechanism for ClO − detection by MITC was presumed to be a cleavage process through ESI‐MS, NMR titrations, and density functional theory (DFT) calculations.