Visual and ratiometric fluorescent probe via an intramolecular charge transfer for detection of a nerve agent simulant in solutions and in the gas phase

The development of fluorescent probes for rapid and accurate detection of hazardous nerve agents (NA) has been a main focus of research because of their use as chemical warfare agents (CWA) for mass destruction in war and terrorist attacks, and lethal toxicity for human beings. In this paper, a probe (PPID) based on the phenanthrene-imidazole unit and the 4-phenyl pyridine group was synthesized and characterized by single crystal X-ray diffraction, and could visually detect and quantify a nerve-agent simulant diethylchlorophosphate (DCP) with excellent sensing properties in solution and in the vapor phase. The probe with the nucleophilic pyridine-N atom as the active site reacts with the electrophilic central phosphorous atom of DCP and after that catalytic hydrolysis by moisture in the DMSO solution occurs to form a protonated sensor. Interestingly, the protonated chemosensor PPIDH showed an apparent intramolecular charge transfer (ICT), leading to a large red-shifted fluorescence "turn-on" response. The effects of the ICT character on the sensing properties displayed a ratiometric fluorescence response to DCP and a low limit of detection (1.4 nM). The sensing process was also verified by test strips by loading probe PPID with DCP vapor, response time, theoretical calculations, and live cell imaging.