A series of coumarin-enamine molecular probes have been synthesized. These low molecular weight fluorescence probes (LMFPs) show optical responses; UV-vis (naked eye detection) and fluorescence spectroscopy when bound to organophosphates (OPs)/nerve agents (diisopropylfluorophosphate (DFP), diisopropylchlorophosphate, omethoate, dimethoate, carbaryl and chlorfenvinphos). The three LMFPs (probes 1a-1c) are prepared in four steps with typical yield 80-85%. Quantum yield and photophysical properties also have been explored for three LMFPs. The ketoxime (1a), phosphorylates the analyte of interest (OPs/nerve agent) whereas methyloxime (1b) is model system and hydrazone (1c) is another potential nucleophile for phosphorylation. The ketoximate is formed upon the addition of a non-nucleophilic super base (P4-t-Bu), which is highly reactive towards nerve agents. The optical response is seen via UV-Vis. For example, the λabs for the ketoxime is observed at 410 nm (colored), whereas the ketoximate is seen at λabs 376 nm (colorless). Upon the addition of DFP the λabs shiftes to 408 nm (colored). Moreover, the fluorescence signal is PET quenched but is restored on upon phosphorylation. In the addition of nerve agents into the keoximate solution; UV-vis (colored) and fluorescence both back due to adduct of nerve agents/organophosphates to the ketoximate. Fluorescence lifetime experiment also carried out to confirm ketoximate formation and nerve agent adduct to ketoximate; lifetime ketoxime is 1.55 ns, whereas ketoximate is 3.69 ns and DFP adduct is 1.56 ns. Limit of detection (LoD) also calculated for DFP which found to be 1.1 ppm.

Design and synthesis of low molecular weight fluorescence probes for detection of organophosphates and nerve agents

ACS Fall 2021

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