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

Abstract

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 K_a = 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.