Synthesis and Luminescent Properties of Novel Europium( III ) Heterocyclic β‐Diketone Complexes with Lewis Bases: Structural Analysis Using the Sparkle/AM1 Model

Tris(β‐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 = H 2 O, tri‐ n ‐octylphosphane oxide (TOPO), triphenylphosphane oxide (TPhPO), 1,10‐phenanthroline], have been synthesized and characterized by elemental analysis and FT‐IR, 1 H 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–Eu 3+ 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 D 0 ) and the multiplet ( 7 F 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 5 D 0 lifetimes (220 vs. 980 μs). This can be ascribed to a more efficient ligand‐to‐metal energy transfer and a less efficient nonradiative 5 D 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. (© Wiley‐VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2005)