A portable dual‐ratiometric fluorescent and colorimetric probe for ClO − sensing across environmental samples, smartphone platform and cabbage

A portable dual‐ratiometric fluorescent and colorimetric probe DBHN (( E )‐N′‐(4‐(diphenylamino)benzylidene)‐3‐hydroxy‐2‐naphthohydrazide) was designed for sensing ClO − . DBHN showed both a ratiometric fluorescence change from green to blue and a colorimetric change from pale yellow to colorless in the presence of ClO − . DBHN exhibited good limits of detection of 27.56 μM in fluorescence method and 4.46 μM in UV–vis method. DBHN enabled reliable ClO − detection over a pH range of 6–10 in fluorescence change and 4–9 in UV–vis change. DBHN effectively detected ClO − in real water samples, including drinking, tap, and river water, and was successfully applied to ClO − detection using test‐strip assays. In smartphone‐based analysis, DBHN enabled quantitative detection of ClO − with low limits of detection (27.38 μM in fluorescence and 13.30 μM in colorimetry) and reliably detected ClO − in real water samples. Furthermore, DBHN showed successful fluorescence imaging in Napa cabbage. The recognition mechanism of DBHN toward ClO − was proposed to be an imine bond cleavage reaction by electrospray ionization (ESI)‐mass spectrometry (MS) and density functional theory (DFT) calculations.