Cyclometalated iridium() 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[PF 6 ] 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[PF 6 ] 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[PF 6 ] 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. A cyclometalated iridium( iii ) complex of a benzimidazole-substituted methylene-bridged 1,2,3-triazole-based ligand has been developed for highly selective luminescent 'light-up' sensing of pyrophosphate ions.