Unprecedented sensitization of visible and near-infrared lanthanide luminescence by using a tetrathiafulvalene-based chromophore

Abstract

Ligand L was synthesized and then coordinated to [Ln-(hfac) 3 ]·2H 2 O (Ln III = Tb, Dy, Er; hfac - = 1,1,1,5,5,5-hexafluoroacetylacetonate anion) and [Ln(tta) 3 ]·2H 2 O (Ln III = Eu, Gd, Tb, Dy, Er, Yb; tta - = 2-thenoyltrifluoroacetonate) to give two families of dinuclear complexes [Ln 2 (hfac) 6 (L)]·C 6 H 14 and [Ln 2 (tta) 6 (L )]·2CH 2 Cl 2. Irradiation of the ligand at 37 040 cm -1 and 29 410 cm -1 leads to tetrathiafulvalene-centered and 2,6-di(pyrazol-1-yl)-4-pyridine-centered fluorescence, respectively. The ligand acts as an organic chromophore for the sensitization of the infrared Er III (6535 cm -1) and Yb III (10200 cm -1) luminescence. The energies of the singlet and triplet states of L are high enough to guarantee an efficient sensitization of the visible Eu III luminescence (17 300-14 100 cm -1). The Eu III luminescence decay can be nicely fitted by a monoexponential function that allows a lifetime estimation of (0.49 ± 0.01) ms. Finally, the magnetic and luminescence properties of [Yb 2 (hfac) 6 (L)]·C 6 H 14 were correlated, which allowed the determination of the crystal field splitting of the 2 F 7/2 multiplet state with M J = ± 1/2 as ground states.