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 (H-1, C-13) and 2D (H-1-H-1 COSY, H-1-C-13 HSQC, and H-1-C-13 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 K-a = 8.6 x 10(7) M-1 and a low detection limit of similar to 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 H-1 NMR titration. Further, the PL enhancement of 1 center dot H2P2O72- adducts was supported by triplet-state TDDFT calculations. In 1 center dot H2P2O72-, the (MLCT)-M-3-(MC)-M-3 energy gap is increased, and the 1 center dot H2P2O72- emits efficiently from the (MLCT)-M-3 and (ILCT)-I-3 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.