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

Abstract

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 312–335nm and with the molar absorption coefficients of (20–25)×103M−1cm−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 77K, are in the range of (18.8–21.1)×103cm−1. We also describe synthesis of non-symmetric pyridines that are 2,6- and 2,4,6-substituted with hydroxymethyl, carboxaldehyde, and carbonitrile groups.