Rare-Earth Quinolinates:  Infrared-Emitting Molecular Materials with a Rich Structural Chemistry

• Published in: Inorganic chemistry Vol. 43; no. 26; pp. 8461 - 8469
• Main Authors: Van Deun, Rik, Fias, Pascal, Nockemann, Peter, Schepers, An, Parac-Vogt, Tatjana N, Van Hecke, Kristof, Van Meervelt, Luc, Binnemans, Koen
• Format: Journal Article
• Language: English
• Published: United States American Chemical Society 27.12.2004
• ISSN: 0020-1669; 1520-510X
• DOI: 10.1021/ic048736a

Near-infrared-emitting rare-earth chelates based on 8-hydroxyquinoline have appeared frequently in recent literature, because they are promising candidates for active components in near-infrared-luminescent optical devices, such as optical amplifiers, organic light-emitting diodes, ... Unfortunately, the absence of a full structural investigation of these rare-earth quinolinates is hampering the further development of rare-earth quinolinate based materials, because the luminescence output cannot be related to the structural properties. After an elaborate structural elucidation of the rare-earth quinolinate chemistry we can conclude that basically three types of structures can be formed, depending on the reaction conditions:  tris complexes, corresponding to a 1:3 metal-to-ligand ratio, tetrakis complexes, corresponding to a 1:4 metal-to-ligand ratio, and trimeric complexes, with a 3:8 metal-to-ligand ratio. The intensity of the emitted near-infrared luminescence of the erbium(III) complexes is highest for the tetrakis complexes of the dihalogenated 8-hydroxyquinolinates.