New NIR-luminescent lanthanide complexes with tridentate oxybenzophenanthroline ligands

Abstract

Complexes of La (1), Sm (2), Gd (3), Er (4) and Yb (5) with benzophenanthroline-derivative ligands were synthesized under mild conditions through reactions of 8,10-di-tert-butylbenzo[b][1,10]phenanthrolin-11-ol (H(bphen)) with tris(trimethylsilyl)amide compounds of rare earth metals. The coordination arrangement of the ligand and complexes 2, 4 and 5 were established via single-crystal X-ray structural analyses. The La, Sm and Gd complexes in the solid state exhibited ligand emission of moderate intensity in the region from 600 to 850 nm. In the spectra of the Er and Yb complexes, there was no ligand emission, but f-f transition bands typical for the corresponding metal ions were observed. The complexes showed one reduction (ERed11/2 −2.04 V) and three oxidation events (EOx11/2 at −0.05 to 0.01 V, EOx21/2 at 0.22-0.26 V and EOx31/2 at 0.41-0.44 V vs. Fc+/Fc) via cyclic voltammetry, corresponding to successive one-electron oxidation events of the phenolate moieties to phenoxyl radicals.