Chemical warfare agents (CWA) are some of the most nefarious weapons, and their possible use in terrorist attacks has led to growing interest in the development of reliable and accurate methods to detect these lethal chemicals. In this paper, we have prepared three nonfluorophores containing 2-(2-hydroxybenzylidene)-malononitrile with various 5-substituents as chemosensor probes for a nerve-agent simulant, diethylchlorophosphate (DCP). The phenolic group of the probes, as the active site, can be rapidly phosphorylated by DCP via nucleophilic substitution and then undergo a simultaneous intramolecular cyclization reaction within 45 s, which can respond to DCP in turn-on fluorescence mode. To the best of our knowledge, this is the first report on the utilization of non-fluorophoric small molecule species to generate a fluorogenic response from DCP along with an investigation of substituent effects on the sensing response. The detection process can be visualized by the naked eye and under a UV lamp the probe HNBM exhibits a strong green fluorescence upon interaction with DCP. Among the three chemosensors, probe HNBM displayed several beneficial attributes such as an extremely fast response time along with high selectivity, sensitivity and the lowest limit of detection (0.10 μM) with DCP in solution. TDDFT calculations were performed in order to demonstrate the electronic properties of the probe and the cyclized product. Furthermore, the probe was used to develop a low cost portable cellulose paper strip for real-time visual detection of DCP vapor. Also, the probe has been extensively used to detect DCP in live cells.