A Eu-III Tetrakis(beta-diketonate) Dimeric Complex: Photophysical Properties, Structural Elucidation by Sparkle/AM1 Calculations, and Doping into PMMA Films and Nanowires

Abstract

Reaction of Ln(III) with a tetrakis(diketone) ligand H4L [1,1'-(4,4'-(2,2-bis((4-(4,4,4-trifluoro-3-oxobutanoyl) phenoxy)methyl)propane-1,3-diyl)bis(oxy)bis(4,1-phenylene))bis(4,4,4-trifluorobutane-1,3-dione)] gives new podates which, according to mass spectral data and Sparkle/AM1 calculations, can be described as dimers, (NBu4[LnL])(2) (Ln = Eu, Tb, Gd:Eu), in both solid-state and dimethylformamide (DMF) solution. The photophysical properties of the Eu-III podate are compared with those of the mononuclear diketonate (NBu4[Eu(BTFA)(4)], BTFA = benzoyltrifluoroacetonate), the crystal structure of which is also reported. The new Eu-III dimeric complex displays bright red luminescence upon irradiation at the ligand-centered band in the range of 250-400 nm, irrespective of the medium. The emission quantum yields and the luminescence lifetimes of (NBu4[EuL])(2) (solid state: 51% +/- 896 and 710 +/- 2 mu s; DMF: 31% +/- 596 and 717 +/- 1 mu s) at room temperature are comparable to those obtained for NBu4[Eu(BTFA)4] (solid state: 60 +/- 996 and 730 +/- 5 mu s; DMF: 30 +/- 5% and 636 +/- 1 mu s). Sparkle/AM1 calculations were utilized for predicting the ground-state geometries of the Eu-III dimer. Theoretical Judd Ofelt and photoluminescence parameters, including quantum yields, predicted from this model are in good agreement with the experimental values, proving the efficiency of this theoretical approach implemented in the LUMPAC software (http://lumpac.pro.br). The kinetic scheme for modeling energy transfer processes show that the main donor state is the ligand triplet state and that energy transfer occurs on both the D-5(1), (44.2%) and D-5(0) (55.8%) levels. Furthermore, the newly obtained Eu-III complex was doped into a PMMA matrix to form highly luminescent films and one-dimensional nanowires having emission quantum yield as high as 67%-69% (doping concentration = 4% by weight); these materials display bright red luminescence even under sunlight, so that interesting photonic applications can be foreseen.