A dual-phase luminescent phosgene sensor based on an AIE-active ruthenium(II) polypyridine complex

Herein, we report a bis-heteroleptic ruthenium(II) complex 1[PF6]2 carrying two o-phenylenediamine groups (OPD) connected to the 4,7-positions of a 1,10-phenanthroline ligand. Compound 1[PF6]2 shows aggregation-induced emission enhancement (AIEE) properties through the restriction of intramolecular motion (RIM), which is a known phenomenon where the luminescence intensity of compounds is enhanced in the aggregated state. 1[PF6]2 was used as a highly sensitive (<2 min) luminescent turn-on phosgene-responsive probe and showed high selectivity over other competitive reactive toxic analytes with a low detection limit (72 nM). The -NH- and -NH₂ groups in the OPD group provide two active reaction sites for coupling with electrophilic phosgene. It was anticipated that phosgene would generate a five-membered imidazolone ring by concurrently coupling with the -NH₂ and -NH- groups in the chemosensor. FTIR, ESI-HRMS analysis, and extensive ¹H NMR titration established the detailed reaction mechanism. The probe 1[PF6]2 is non-luminescent due to the OPD group present in the analyte targeting σ-donor ligand L1, and nonradiative decay occurs from ³MC excited states. Following its reaction with phosgene, the cyclized ligand became a strong π-acceptor; additionally, the steric hindrance of ligand L1 restricted intramolecular rotation around the C-N bond. Consequently, the ³MLCT_{Ru(d)→L(π*)} state becomes responsible for the bright red emission of the phosgene-reacted product through a shift in population from the ³MC to the ³MLCT state. Finally, the 1[PF6]2 coated solid-state paper strip was utilized for practical applications to detect different concentrations of phosgene vapor without any interference from other competitive analytes.