A ruthenium(ii) polypyridyl complex as a luminescent chemodosimetric probe for selective and sensitive detection of phosgene and nerve agent simulant

Abstract

Chemical warfare agents (CWAs), including organophosphate nerve agents (e.g., sarin, tabun, soman, VX, etc.) and phosgene, are weapons of mass destruction (WMD) and agents of bioterrorism, posing a serious threat to public safety and national security. The current detection methods often lack a faster response, portability, and poor selectivity/sensitivity for specific biochemical threats. Therefore, developing reliable, direct, simpler, and sensitive optical sensors for such toxic biochemical hazards is critically important. Herein, we have rationally designed a Ru(II)-based emissive chemodosimeter possessing a reactive site in the peripheral ligand for the selective detection of a G-series CWA mimic (diethyl chlorophosphate, DCP) and phosgene (COCl₂) in the presence of relevant interferents. The Ru(II) complex, [Ru(phen)₂(phen-Nap-en)](PF₆)₂ [1], where phen is 1,10-phenanthroline and phen-Nap-en is 1,10-phenanthroline functionalized with a naphthalic anhydride conjugated 2-aminoethylamino group as the reactive site, was synthesized and characterized for the selective ‘turn-ON’ detection of a nerve agent mimic (DCP) and toxic phosgene at distinct excitation wavelengths. The structural integrity of the probe [1] was confirmed, and the solution chemistry and photophysical properties of the probe were studied using various spectroscopic techniques to evaluate its optical parameters. The probe functions as a highly effective chemodosimetric agent for the dual sensing of the CWA mimic (DCP) and phosgene. The probe exhibits a fast ‘turn-ON’ response (<10 s) and shows excellent selectivity over competing interferents with high sensitivity for phosgene [LOD = 126 nM] and DCP [LOD = 73 nM]. The appended 2-aminoethylamino group acts as the reactive site for the analyte-specific reaction. It reacts with phosgene or CWAs via nucleophilic or phosphorylation reactions to form cyclized or phosphorylated products, respectively. The final adducts, [1]-phos and [1]-DCP, containing 2-imidazolidinone or phosphorylated products, were identified using ESI-MS and ¹H, ¹³C and ³¹P NMR spectroscopy. This reaction mechanism was thoroughly investigated and supported by ESI-MS analysis, NMR spectroscopy, and theoretical calculations. The enhanced red luminescence of [1] upon reaction with phosgene or DCP is attributed to the perturbation of the ³MLCT state in the resulting products. Furthermore, a portable test kit utilizing [1] loaded on solid surface was developed for the real-time, selective, rapid, and highly sensitive visual monitoring of phosgene and nerve gases at the nM level.