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 (HPO) anions. The solution structure of 1[PF6] was fully characterized by 1D (H, C) and 2D (H-H COSY, H-C HSQC, and H-C HMBC) NMR spectroscopy, and ESI-HRMS. The 1[PF6] acted as a highly selective luminescent sensor for HPO in CHCN over other competitive ions, including HPO, ATP, ADP and AMP. The PL titration of 1[PF6] with HPO in CHCN furnished the association constant = 8.6 × 10 M 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 HPO ions. The PL enhancement with HPO is due to the hydrogen bonding interaction of HPO with the triazole C-H, imidazole N-H, methylene hydrogen and hydroxyl groups of the ligand that has been supported by H NMR titration. Further, the PL enhancement of 1·HPO adducts was supported by triplet-state TDDFT calculations. In 1·HPO, the MLCT-MC energy gap is increased, and the 1·HPO emits efficiently from the MLCT and ILCT 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.