Sensitization of Lanthanide Ions by Triarylboron Functionalized B-Diketones
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This work concerns the development of two classes of triarylboron functionalized β-diketone ligands. In the first class, the boron unit is conjugated with a phenyl linker and the diketone backbone. In the second class, the boron unit, the aryl linker, and the diketone backbone are non-conjugated with a mutual orthogonal arrangement. To understand the impact of the location of the triarylboron unit on the electronic and photophysical properties of the β-diketone ligands, difluoroboron chelate complexes were synthesized and characterized. The complexes were studied computationally to determine the singlet and triplet transitions, along with their major contributing orbitals. They were then studied for their photophysical properties. The first class of ligands displayed a concentration dependent excimer emission. Finally, they were studied for their ability to sense fluoride and the binding constants of the fluoride-boron interaction were estimated. The four ligands were also investigated for their use in selective sensitization of Tb(III) and Eu(III). The four Ln(III) complexes were characterized and their photophysical properties were investigated. The first class of ligands were found to be effective in activating Eu(III) emission while the second class is effective in activating Tb(III) emission. The Eu(III) complexes were found to have a low quantum efficiency, but can it can be greatly enhanced by the addition of fluoride ions. In contrast, the Tb(III) complexes have moderate quantum efficiencies that are quenched upon the addition of fluoride. The selective sensitization of Eu(III) and Tb(III) and the luminescent response towards fluoride is caused by the distinct intra-ligand charge transfer transitions of the two classes of ligands and the triarylboron unit.