Chromo-Fluorogenic Detection of Nerve-Agent Mimics Using Triggered Cyclization Reactions in Push-Pull Dyes

A family of azo and stilbene derivatives (1-9) are synthesized, and their chromo-fluorogenic behavior in the presence of nerve-agent simulants, di-ethylchlorophosphate (DCP), diisopropylfluorophosphate (DFP), and di-ethylcyanophosphate (DCNP) in acetonitrile and mixed solution of water/acetonitrile (3:1 v/v) buffered at pH 5.6 with MES, is investigated. The prepared compounds contain 2-(2-N,N-dimethylaminophenyl)ethanol or 2-[(2N,N-dimethylamino)phenoxy]ethanol reactive groups, which are part of the conjugated a-system of the dyes and are able to give acylation reactions with phosphonate substrates followed by a rapid intramolecular N-alkylation. The nerve-agent mimic-triggered cyclization reaction transforms a dimethylamino group into a quaternary ammonium, inducing a change of the electronic properties of the delocalized systems that results in a hypsochromic shift of the absorption band of the dyes. Similar reactivity studies are also carried out with other "non-toxic" organophosphorus compounds, but no changes in the UV/Vis spectra were observed. The emission behaviour of the reagents in acetonitrile and water acetonitrile 3:1 v/v mixtures is also studied in the presence of nerve-agent simulants and other organophosphorous derivatives. The reactivity between 1-9 and DCP, DCNP, or DFP in buffered water acetonitrile 3:1 v/v solutions under pseudo first-order kinetic conditions, using an excess of the corresponding simulant, are studied in order to determine the rate constants (k) and the half-life times (t(1/2)=ln2/k) for the reaction. The detection limits in water/acetonitrile 3:1 v/v are also determined for 1-9 and DCP, DCNP, and DFP. Finally, the chromogenic detection of nerve agent simulants both in solution and in gas phase are tested using silica gel containing adsorbed compounds 1, 2, 3, 4, or 5 with fine results.