Synthesis and spectroscopy of anionic tridentate benzimidazole-pyridine carboxylate and tetrazolate chromophore ligands

•Seven new tridentate N^N^O carboxylate and N^N^N tetrazolate ligands.•New ligands are UV chromophores that sensitize the red luminescence of europium.•Synthesis of useful non-symmetric pyridines.

We report on seven new anionic benzimidazole-pyridine carboxylate and tetrazolate tridentate N^N^O and N^N^N ligands that are modified with chromophore (phenyl, biphenyl, naphthyl) and solubilizing groups. The ligands are UV chromophores with the lowest-energy absorption maxima at 312–335 nm and with the molar absorption coefficients of (20–25) × 103 M−1 cm−1 in DMSO solution. The ligands form neutral complexes with trivalent lanthanides and sensitize the red luminescence of europium. The triplet state energies of the deprotonated ligands, which were measured from the phosphorescence spectra of their lanthanum complexes at 77 K, are in the range of (18.8–21.1) × 103 cm−1. We also describe synthesis of non-symmetric pyridines that are 2,6- and 2,4,6-substituted with hydroxymethyl, carboxaldehyde, and carbonitrile groups.

Graphical abstractNew tridentate anionic benzimidazole-pyridine carboxylate and tetrazolate ligands sensitize the red luminescence of europium.Figure optionsDownload full-size imageDownload as PowerPoint slide