An Organoiridium(III) Complex-Based Bifunctional Probe for Light-Up Detection of Phosgene and Nerve Agent Mimic Diethyl Chlorophosphate by Accessing the Suitable ³MLCT Excited State

A cyclometalated iridium(III) complex-based bifunctional luminescent probe, Ir1, with o-phenylenediamine (OPD) (L) as a recognition site, is developed for the discriminative detection of phosgene and nerve agent mimic diethyl chlorophosphate (DCP) in photoluminescent (PL) spectroscopic channels. Ir1 exhibits instant red emission (<1 min) and PL enhancement at 593 nm toward phosgene with high selectivity and a low detection limit (44 nM). Probe Ir1 displays an obvious quick PL turn-on response at 512 nm and green luminescence with DCP due to the phosphorylation of L with a low detection limit (0.6 μM). Extensive ¹H NMR titration and ESI-HRMS analysis established a detailed reaction mechanism. Probe Ir1 is nonluminescent due to the OPD group present in the analyte targeting ligand L, and nonradiative decay occurs from ³MLCT excited states. The benzimidazolone group is formed after the reaction with phosgene, and the ³MLCT_{Ir(d)→L(π*)} state is responsible for the bright red emission of phosgene-reacted product Ir2. The bright green emission of phosphorylated product Ir1-DCP is readily explained by the radiative decay from the ³MLCT_{Ir(d)→ppy(π*)} excited state. Moreover, the probe exhibits stronger binding affinity for phosgene compared to its likely competitor DCP, enabling quantification of phosgene in samples containing DCP without interference. The excited-state time-dependent DFT calculation fully supported the luminescence switching behavior. Furthermore, a portable Ir1-loaded paper strip was fabricated for the efficient discriminative detection of trace amounts of gaseous phosgene and DCP vapor for real-time practical applications.