Investigation of strong photoluminescence and highly soluble Eu(III) complexes with phosphine oxides and β-diketonates

Abstract

Several Eu(III) complexes with two phosphine oxide ligands and three β-diketonate ligands were prepared and their properties were investigated to realize strong photoluminescence and highly soluble Eu(III) complexes.Comparison of photoluminescence properties of Eu(III) (tfnb)3(TPPO)2 (5) (tfnb = 4,​4,​4-​trifluoro-​1-​(2-​naphthyl)​-​1,​3-​butanedionato and TPPO = triphenyl phosphine oxide), Eu(III)(tfpb)3(TPPO)2 (6) (tfpb = 4,4,4-trifluoro-1-phenyl-1,3-butanedionato), Eu(III) (hfnh)3(TPPO)2 (8) (hfnh = 4,4,5,5,6,6,6-heptafluoro-1-(2-naphthyl)-1,3-hexanedionato) and Eu(III)(tfdh)3(TPPO)2 (9) (tfdh = 6,6,6-trifluoro-2,2-dimethyl-3,5-hexanedionato), which have the same phosphine oxide, reveals that photoluminescence intensities are in the descending order 8, 5, 6, 9. “hfnh” and “tfnb” are found to be preferable for molecular structures of β-diketonates.Next, effects of molecular structures of phosphine oxide- ligands on photoluminescence intensities of Eu(III) complexes were investigated.Comparison of photoluminescence spectra of Eu(III) (hfnh)3(TBPO)2 (7) (TBPO = tributyl phosphine oxide), Eu(III) (hfnh)3(TPPO)2 (8) and Eu(III) (hfnh)3(TPPO)(TBPO) (12), which have the same β-diketonate (hfnh), reveals that photoluminescence intensities are in the descending order 12, 7, 8. Likewise, comparison of photoluminescence spectra of Eu(III) (tfnb)3(TBPO)2 (3), Eu(III) (tfnb)3(TPPO)2 (5) and Eu(III) (tfnb)3(TPPO)(TOPO) (11), which have the same β-diketonate (tfnb), reveals that photoluminescence intensities are in the descending order 11, 5, 3.On the other hand, solubilities of Eu(III) (tfnb)3(TPPO)(TBPO) (11) and Eu(III) (hfnh)3(TPPO)(TBPO) (12) with two different phosphine oxides in 2,3-dihydrodecafluoropentane are much larger than those of other complexes.These results indicate that the optimum β-diketonate is “hfnh” and coordination of two different phosphine oxides with one Eu(III) ion has a remarkable effect in enlarging both photoluminescence intensity and solubility of Eu(III) complexes.Eu(III) complex 12 satisfies these conditions and quantum yield is very high (= 0.6). It is a promising candidate for many applications by virtue of its strong photoluminescence and high solubility.