Fluorescent Chemosensors With Varying Degrees of Nucleophilicity for the Fast Detection of a Chemical Warfare Agent Mimic: Development of a Polymer Film Badge for On‐Site Detection

The detection of chemical warfare agents (CWAs) through simple and rapid methods with real‐sample applicability is crucial for reducing the risks they pose to living systems during unexpected terror attacks and armed conflicts. In response, there is growing demand for portable, wearable, and lightweight badge‐based kits that enable safe, user‐friendly, and on‐site detection of chemical warfare agents. For this purpose, we have developed a rhodamine‐based system incorporating a 2,6‐diaminopyridine probe (APX) with single X‐ray structure proof, enabling the visual detection of the Sarin simulant, diethyl chlorophosphate (DCP), in both solution and vapor phases. Three model compounds (MPX, AmPhX, and MeOPhX) were synthesized. Interestingly, upon reacting with DCP in acetonitrile, APX and MPX showed a distinct fluorescence turn‐on response at 582 nm, featuring an instantaneous reaction for probe APX (< 5 s) with a detection limit (2.5 nM), which is below the threshold level. The nucleophilicity of the pyridine‐N atom is influenced by the electron donating ability of 2‐amino group, which affects the intramolecular charge‐transfer (ICT) in the reaction site, resulting in a very fast reaction with DCP. The reaction‐based sensing mechanism was validated through high‐resolution mass spectrometry (HRMS) and nuclear magnetic resonance ( 1 H NMR and 31 P NMR) spectroscopy. Finally, the probe APX has been used to develop a test‐strip and badge‐based portable system for real‐time on‐site monitoring of DCP, enabling simple, safe, and selective detection.