Sensitizing Tb(III) and Eu(III) Emission with Triarylboron Functionalized 1,3-Diketonato Ligands

Four BMes2Ar (Mes = mesityl, Ar = phenyl or duryl) functionalized 1,3-diketonato ligands have been investigated

for use in selective sensitization of Tb(III) and Eu(III) emission. These ligands have the general formula of

[R1C(O)CR2C(O)R3]? (R1 = Ph, R2 = H, R3 = p-Ph-BMes2, L1; R1 = R3 = p-Ph-BMes2, R2 = H, L2; R1 = R3 = Me, R2 =

p-Ph-BMes2, L3; R1 = R3 = Me, R2 = p-duryl-BMes2, L4) and belong to class I (L1 and L2) and class II (L3 and L4), respectively. In class I, the boron unit is conjugated with the phenyl linker and the diketone backbone, while in class II, the boron unit, the linker unit, and the diketone unit are nonconjugated with a mutually orthogonal arrangement. To understand the impact of the location of the BMes2Ar unit on the electronic properties of the 1,3-diketone molecules and their ability in activating lanthanide emission, the difluoroboron chelate compounds (1-BF2 to 4-BF2) of ligands L1?L4 were synthesized and examined. The class I ligands were effective in activating Eu(III) emission, while the class II ligands were effective in activating Tb(III) emission. FourLn(III) complexes, 1Eu, 2Eu, 3Tb, and 4Tb, based on the L1?L4 ligands, respectively, were prepared and examined. Theemission quantum efficiency of 1Eu and 2Eu is low (?Eu ? 0.01 in THF, 0.07?0.13 in the solid state), but can be greatlyenhanced by the addition of fluoride ions. In contrast, the complex 4Tb has a moderate emission efficiency (?Tb = 0.14 in THF,0.47 in the solid state) and experiences a distinct emission quenching upon the addition of fluoride. The selective sensitization ofEu(III) and Tb(III) by L1?L4 and the distinct luminescent response of their Ln(III) complexes toward fluoride ions are causedby the distinct intraligand charge transfer transitions of the two different classes of ligands involving the BMes2 unit.