Selective Sensitization of Eu(III) and Tb(III) Emission with Triarylboron-Functionalized Dipicolinic Acids

Three triarylboron-
(Mes2BAr-) functionalized dipicolinic acids, namely, 4-(4-(dimesitylboranyl)-2,3,5,6-tetramethylphenyl)­pyridine-2,6-dicarboxylic
acid (H2L1), 4-(4-(4-dimesitylboranyl)-2,3,5,6-tetramethylphenyl)-1H-1,2,3-triazol-1-yl)­pyridine-2,6-dicarboxylic acid (H2L2), and 4-(4-(4-dimesitylboranyl) phenyl)-1H-1,2,3-triazol-1-yl)­pyridine-2,6-dicarboxylic acid (H2L3), have been designed and synthesized. Lanthanide­(III)
complexes with the general formula of [NBu4]3[LnL3] (Ln = Eu or Tb; L = L1, L2, or L3) were obtained. The new triarylboron-functionalized
ligands were found to be effective in the selective sensitization
of the emissions of Eu­(III) and Tb­(III) ions with a high quantum efficiency
(e.g., 0.54 for [NBu4]3[TbL13] in the solid state) upon excitation at ∼330 nm. An
intraligand charge-transfer (ILCT) transition from the mesityl or
aryl group to the boron or boron-aryl unit was found to play a key
role in the activation of the Eu­(III) and Tb­(III) emissions, based
on TD-DFT computational data and luminescence titration experiments
performed using fluoride and cyanide ions.