Phthalimide‐Based Off‐On‐Off Fluorosensor for Cascade Detection of Cyanide Ions and Picric Acid

<jats:title>Abstract</jats:title><jats:p>Novel methods that can be utilized to identify and detect harmful environmental pollutants still need to be proposed. This article describes the effective design and development of a turn‐on photoluminescence probe, <jats:bold>T1</jats:bold> [(E)‐5‐((2‐hydroxybenzylidene) amino) isoindoline‐1, 3‐dione], which is selective and sensitive towards CN<jats:sup>−</jats:sup> ions having detection limit nM to μM range. When exposed to CN<jats:sup>−</jats:sup> ions, Probe <jats:bold>T1</jats:bold> displays a strong fluorescence response under a 365 nm UV light irradiation with a noticeable low to high intense cyan color photoluminescence visible to the naked eye. For the practical utility of the present probe <jats:bold>T1</jats:bold>, a paper strips‐based test kit experiment has been demonstrated as a portable and displayable photonic device for on‐site detection of CN<jats:sup>−</jats:sup> ions. Furthermore, the <jats:bold>T1‐</jats:bold>CN<jats:sup>−</jats:sup> adduct has been applied for detecting explosive nitroaromatic compounds, especially PA, based on the photoluminescence quenching mechanism. Using CN<jats:sup>−</jats:sup> ions, and PA as chemically encoded inputs and corresponding optical output, a molecular logic gate has been constructed. Further, probe <jats:bold>T1</jats:bold> has been employed as a bio‐analytical tool to map intercellular CN<jats:sup>−</jats:sup> ions in live cells. This study invokes a novel approach for designing and developing efficient and selective sensors employing well‐known fluorescent probes as signaling units with prior photophysical knowledge.</jats:p>