Low Molecular Weight Fluorescent probes for the detection of organophosphates

Three Low Molecular Weight Fluorescent probes (LMFPs) coumarin-enamine (3a-c) have been synthesized, and their photophysical properties have been studied in different solvent systems (DMSO, CH3CN, DMF, MeOH, EtOH, Me2CO, MeCO2Et, CHCl3, C6H5Me, and C6H6). Dimethyl sulfoxide was chosen as the optimum solvent to investigate 3a for organophosphate detection. On deprotonation of the oxime, a significant spectroscopic shift is observed in the UV?Vis spectrum (? ?35 nm). The fluorescence spectrum shows a broad featureless band at 535 nm that shifts hypochromically. Both the UV?vis and fluorescence spectra undergo drastic optical responses when the OP-adduct is formed. Diisopropyl chlorophosphate was found to have the most extensive changes among the phosphorus (V) center OPs investigated (diisopropyl chlorophosphate, diisopropyl fluorophosphate (DFP), dimethoate, omethoate, chlorfenvinphos, and carbaryl). The fluorescence turn ?off-on? response is a consequence of the PET mechanism, supported by the molecular modeling calculations. A limit of detection was calculated to be 1.1 ppm for DFP (a nerve agent simulant). Fluorescence lifetime studies were carried out, which showed significant decay times for 3a, its oximate, and its DCP-adduct of ? = 1.56, 3.23, and 1.55 ns, respectively, to aid in our understanding of selectivity.

Automated summary

Three low molecular weight fluorescent probes have been synthesized and their photophysical properties studied in various solvent systems. Significant optical responses were observed, particularly in the detection of organophosphates, shedding light on the mechanism of selectivity.