- Role of the ancillary ligand N,N-dimethylaminoethanol in the sensitization of EuIII and TbIII luminescence in dimeric β-diketonates
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Two types of dimeric complexes [Ln2(hfa) 6(μ2-O(CH2)2NHMe 2)2] and [Ln(thd)2(μ2, η2O(CH2)2NMe2)]2 (Ln = YIII EuIII, GdIII, TbIII, Tm III, LuIII; hfa- = hexafluoroacetylacetonato, thd- = dipivaloylmethanato) are obtained by reacting [Ln(hfa) 3(H2O)2] and [Ln(thd)3], respectively, with N,N-dimethylaminoethanol in toluene and are fully characterized. X-ray single crystal analysis performed for the TbIII compounds confirms their dimeric structure. The coordination mode of N,N-dimethylaminoethanol depends on the nature of the β-diketonate. In [Tb2(hfa)6(μ2-O(CH2) 2NHMe2)2], eight-coordinate TbIII ions adopt distorted square antiprismatic coordination environments and are O-bridged by two zwitterionic N,N-dimethylaminoethanol ligands with a Tb1...Tb2 separation of 3.684(1) A. In [Tb(thd) 2(μ2,η2-O(CH2) 2NMe2)]2, the N,N-dimethyIaminoethanol acts as chelating-bridging O,N-donor anion and the TbIII ions are seven-coordinate; the Tb1...Tb1A separation amounts to 3.735(2) A within centrosymmetric dimers. The dimeric complexes are thermally stable up to 180°C, as shown by thermogravimetric analysis, and their volatility is sufficient for quantitative sublimation under reduced pressure. The Eu III and TbIII dimers display metal-centered luminescence, particularly [Eu2(hfa)6(O(CH2) 2NHMe2)2] (quantum yield QLn L = 58%) and [Tb(thd)2(O(CH2) 2NMe2)]2 (32%). Consideration of energy migration paths within the dimers, based on the study of both pure and Eu III- or TbIII-doped (0.01-0.1 mol %) LuIII analogues, leads to the conclusion that both the β-diketone and N,N-dimethylaminoethanol ligands contribute significantly to the sensitization process of the EuIII luminescence. The ancillary ligand increases considerably the luminescence of [Eu2(hfa)6(O(CH 2)2NHMe2)2], compared to [Ln(hfa)3(H2O)2], through the formation of intra-ligand states while it is detrimental to TbIII luminescence in both β-diketonates. Thin films of the most luminescent compound [Eu 2(hfa)6(O(CH2)2NHMe 2)2] obtained by vacuum sublimation display photophysical properties analogous to those of the solid-state sample, thus opening perspectives for applications in electroluminescent devices.
- Eliseeva, Svetlana V.,Kotova, Oxana V.,Gumy, Frederic,Semenov, Sergey N.,Kessler, Vadim G.,Lepnev, Leonid S.,Buenzli, Jean-Claude G.,Kuzmina, Natalia P.
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