Cyclometalated iridium(iii) complex of a 1,2,3-triazole-based ligand for highly selective sensing of pyrophosphate ion

A new cyclometalated Ir(III) complex of a methylene-bridged benzimidazole-substituted 1,2,3-triazole methanol ligand has been synthesized for the photoluminescent detection of pyrophosphate (H2P2O72-) anions. The solution structure of 1[PF6] was fully characterized by 1D (1H, 13C) and 2D (1H-1H COSY, 1H-13C HSQC, and 1H-13C HMBC) NMR spectroscopy, and ESI-HRMS. The 1[PF6] acted as a highly selective luminescent sensor for H2P2O72- in CH3CN over other competitive ions, including H2PO4-, ATP, ADP and AMP. The PL titration of 1[PF6] with H2P2O72- in CH3CN furnished the association constant Ka = 8.6 × 107 M-1 and a low detection limit of ∼127 nM. The structure of the analyte interacting ligand renders the Ir(III) complex-based probe highly selective for H2P2O72- ions. The PL enhancement with H2P2O72- is due to the hydrogen bonding interaction of H2P2O72- with the triazole C-H, imidazole N-H, methylene hydrogen and hydroxyl groups of the ligand that has been supported by 1H NMR titration. Further, the PL enhancement of 1·H2P2O72- adducts was supported by triplet-state TDDFT calculations. In 1·H2P2O72-, the 3MLCT-3MC energy gap is increased, and the 1·H2P2O72- emits efficiently from the 3MLCT and 3ILCT excited states. Finally, a cytotoxicity study and live-cell imaging were performed. The probe showed low cytotoxicity against HeLa cells and was suitable for intracellular pyrophosphate imaging.