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

Abstract

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.

Near infrared light emission quenching in organolanthanide complexes

“…We have performed this analysis in Er-quinoline complexes, for which detailed x-ray studies have been reported. 7,13 The comparative study confirms that Eq. ͑4͒ just leads to a negligible underestimation, ϳ10%, of the exact dipole-induced transfer rate, calculated using Eq.…”

“…A further elegant proof of this scaling law is provided by Van Deun's experimental results in solutions of complexes synthesized with the same mononuclear molecular structure, namely, Er-8-quinoline ͑ErQ͒, Er-5-chloro-Q ͑Er5ClQ͒, and Er-5,7-dichloro-Q ͑Er57ClQ͒. 7 In these systems, the Cl contribution to ͗␣ A ͘ Er is negligible, owing to the heavy mass of the halogen atom. 6 Neglecting the contribution of the solvent, ͗␣ A ͘ Er is proportional to the density of CH groups, and, hence, to the number N H of hydrogen per each quinoline.…”

“…Investigations on halogenated systems show an unambiguous improvement of the NIR light emission. 7,8 The best performances have been obtained in perfluorinated ͑PF͒ systems, which show nonradiative decay times in the submillisecond timescale. 9 NIR emission quantum yield has been drastically enhanced, but remains, however, rather low, around a few percent.…”

Near-infrared photoluminescence of erbium tris(8-hydroxyquinoline) spin-coated thin films induced by low coherence light sources

“…1 show an absorption peak centered at 380 nm, corresponding to one of the → * absorption transitions of the quinoline ligand. 21,28,29 Comparing these spectra to the ones related to ErQ 3 evaporated thin films and ErQ 3 solution, a similar behavior can be observed, suggesting that the light sensitization scheme of the material is preserved by HTSC deposition. Laser-induced photoluminescence ͑PL͒ spectra of spincoated thin films ͑see Fig.…”

Field-induced single-ion magnetic behaviour in a highly luminescent Er3+ complex

“…A possible strategy to overcome such drawback is the substitution of the H atoms with heavier halogen atoms in the ligands. Successful examples showing the improvement of the NIR light emission have been reported in the literature [1][2][3].…”