Ruthenium(II) Polypyridine Complex-Based Aggregation-Induced Emission Luminogen for Rapid and Selective Detection of Phosgene in Solution and in the Gas Phase.

A bis-heteroleptic ruthenium(II) complex, , of 4,7-bis(2-aminoethylamino)-1,10-phenanthroline for selective "turn-on" detection of highly toxic chemical warfare agent phosgene is presented. Probe exhibits aggregation-induced emission (AIE), and the restricted intramolecular motion is responsible for the AIE activity. In a CHCl/CHCN [95:5 (v/v)] solvent mixture, a unique self-assembled vesicular structure was formed after aggregation, which was supported by transmission electron microscopy, field emission scanning electron microscopy, and atmoic force microscopy studies. Probe showed a rapid and highly selective luminescence turn-on response for phosgene over other competitive chemical warfare agents with a low detection limit (13.9 nM) in CHCN. The 2-aminoethylamino groups in act as a reacting site for nucleophilic addition to the carbonyl center of phosgene and undergo intramolecular cyclization. The final product of the phosgene-mediated reaction, , contains 2-imidazolidinone groups, which has been confirmed by electrospray ionization mass spectometry and H nuclear magnetic resonance (NMR) spectroscopy. H NMR titration of with phosgene supported the reaction mechanism and also pointed to the simultaneous reaction of phosgene at two 2-aminoethylamino sites. For the first time, the crystal structure of the phosgene reaction product, , containing the cyclized 2-imidazolidinone group was confirmed by single-crystal X-ray diffraction, which indubitably validates the reaction mechanism. Triplet state time-dependent density functional theory calculations showed that the weak luminescence of was mostly due to the population of the non-emissive MC state. The cyclization reaction with phosgene and the corresponding 2-imidazolidinone product formation populated the emissive MLCT state in and is the key reason for the enhanced luminescence. Furthermore, a low-cost portable test paper strip has been fabricated with for the real-time selective monitoring of phosgene gas at the nanomolar level.