Synthesis and luminescent properties of novel europium(III) heterocyclic β-diketone complexes with Lewis bases:: Structural analysis using the Sparkle/AM1 model

Tris(beta-diketonato)europium(III) complexes of general formula [Eu(TPI)(3)-L], with chelating ligands such as 3-phenyl-4-(4-toluoyl)-5-isoxazolone (HTPI) and adduct-forming reagents [L = H2O, tri-n-octylphosphane oxide (TOPO), triphenylphosphane oxide (TPhPO), 1,10-phenanthroline], have been synthesized and characterized by elemental analysis and FT-IR, H-1 NMR, and photoluminescence spectroscopy. The coordination geometries of the complexes were calculated using the Sparkle/AM1 (Sparkle model for the calculation of lanthanide complexes within the Austin model 1) model. The ligand-Eu3+ energy-transfer rates were calculated using a model of intramolecular energy transfer in lanthanide coordination complexes reported in the literature. The room-temperature PL spectra of the europium(III) complexes are composed of the typical Eu (3+) red emission, assigned to transitions between the first excited state (5 DO) and the multiplet (F-7(0-4)). The results clearly show that the substitution of water molecules by TOPO leads to greatly enhanced quantum yields (i.e., 1.3% vs. 49.5%) and longer D-5(0) lifetimes (220 vs. 980 mu s). This can be ascribed to a more efficient ligand-to-metal energy transfer and a less efficient nonradiative D-5(0) relaxation process. The theoretical quantum yields are in good agreement with the experimental quantum yields, which highlights that the present theoretical approach can be a powerful tool for the a priori design of highly luminescent lanthanide complexes. ((c) Wiley-VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2005).