Enhancing Circularly Polarized Luminescence of Tb(III) Complexes via Remote Substitutions on...

Chiral trivalent lanthanide complexes are of interest since their parity-allowed magnetic dipole transition generally shows large luminescence dissymmetry (g_lum) factors. However, the luminescence intensity is normally weak, which is yet another challenge. Herein, we introduce electron-withdrawing and -donating moieties (F and methyl, respectively) at the para-positions of phenyl on N,N'-bis (1-phenylethyl)-2,6-pyridinediamide. We found that this approach, for example, modifying the remote positions of ligands, enables decreasing the triplet state energy levels of ligands from 27060 cm^-1 (H) to 24154 cm^-1 (F) and 24390 cm^-1 (methyl) and enhancing the ligand-to-ion sensitization from 0.35 to 0.41 and 0.47 and photoluminescent quantum yields (PLQYs) from 17% to 23% and 25%. The g_lum-factors are ±0.1 for the three Tb(III) complexes coordinated with the synthesized ligands in their ethanol solutions, yielding circularly polarized luminescence (CPL) brightness (B) values of 0.017, 0.023, and 0.025, respectively. Single crystal structures reveal the chirality transfer from the chiral ligands to the complex and then to supramolecular chiral packing of complexes and also effective modulations on the supramolecular chiral packing. Collectively, these findings establish remote ligand engineering as a robust and versatile strategy for fine-tuning CPL brightness.