Near-infrared luminescence in different conjugate ancillary ligands erbium(III) complexes with via ligand and metal centred excitation

Four mononuclear β-diketone compounds with near-infrared (NIR) luminescence characteristics were synthesized and characterized by changing the ancillary ligand of different conjugated structures. The central erbium(III) ion coordinates with three β-diketone (1-(1-ethyl-1H-indol-3-yl)-4,4,4-trifluorobutane-1,3-dione (EIFD)) ligands and one acetone (1), one 1,10-phenanthroline (phen) (2), one dipyrazine [2,3-f: 2′,3′-h] quinoxaline (dpq) (3), one dipyrido [3,2-a:2′,3′-c] phenazine (dppz) (4), respectively. The crystal structures of compounds 1–4 with the erbium(III) ions of seven (1)/eight (2–4) coordinated configuration are determined by single-crystal X-ray diffraction. The NIR luminescence properties of compounds 1–4 were experimentally investigated by replacing the solvent acetone with nitrogen-containing ancillary ligands such as phen, dpq and dppz. This study investigates the emission lifetimes of the central Er(III) ions in these compounds.