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 (H 2 P 2 O 7 2- ) anions. The solution structure of 1[PF6] was fully characterized by 1D ( 1 H, 13 C) and 2D ( 1 H- 1 H COSY, 1 H- 13 C HSQC, and 1 H- 13 C HMBC) NMR spectroscopy, and ESI-HRMS. The 1[PF6] acted as a highly selective luminescent sensor for H 2 P 2 O 7 2- in CH 3 CN over other competitive ions, including H 2 PO 4 - , ATP, ADP and AMP. The PL titration of 1[PF6] with H 2 P 2 O 7 2- in CH 3 CN furnished the association constant K a = 8.6 × 10 7 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 H 2 P 2 O 7 2- ions. The PL enhancement with H 2 P 2 O 7 2- is due to the hydrogen bonding interaction of H 2 P 2 O 7 2- with the triazole C-H, imidazole N-H, methylene hydrogen and hydroxyl groups of the ligand that has been supported by 1 H NMR titration. Further, the PL enhancement of 1·H 2 P 2 O 7 2- adducts was supported by triplet-state TDDFT calculations. In 1·H 2 P 2 O 7 2- , the 3 MLCT- 3 MC energy gap is increased, and the 1·H 2 P 2 O 7 2- emits efficiently from the 3 MLCT and 3 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.