Aggregation-Induced Emission Phosphorescence Featured Au–Ag Coordination Polymer with a Diphosphine N-Heterocyclic Carbene Ligand for Highly Sensitive Detection of Cr(VI)

Luminescent materials with aggregation-induced emission (AIE) characteristics have been recognized as highly selective and sensitive probes for the detection of toxic metal ions in recent years. In this paper, a Au-Ag cluster-based coordination polymer [Au₃Ag₃(L)₂(CN)₆(H₂O)₂]_n [1, L = 1,3-bis((diphenylphosphanyl)methyl)-4,5-dihydro-imidazolylidene] was prepared by in situ generation of the diphosphine N-heterocyclic carbene (PC^NHCP)-type ligand L in the presence of the corresponding metal salts. Compound 1 exhibited 530 nm phosphorescence under 380 nm excitation with a QY of 6.30% and a lifetime (τ) of 7.14 μs in the solid state. 1 showed good AIE behavior in the mixture of MeOH/H₂O while the best aggregation state (f_water = 90%, QY = 6.79%, τ = 6.70 μs) exhibited selective and sensitive emission quenching toward Cr(VI) ions. Ultralow detection limits of 9.7 ppb (w/w) for Cr₂O₇^2- and 17.9 ppb (w/w) for CrO₄^2- were achieved.