Circularly Polarized Photoluminescence and Electroluminescence of a Pair of Eu(III) Enantiomers Based on Chiral Phosphine-Oxide Ligands
Chiral europium(III) (Eu(III)) complexes, characterized by their f-f transitions and allowed magnetic dipole transitions, exhibit narrowband emission and superior circularly polarized luminescence (CPL) with high luminescence dissymmetry factors (g_lum), making them promising for circularly polarized organic light-emitting diodes (CP-OLEDs) and 3D displays. Here, we report a pair of R/S-Eu(TTA)3DFPO enantiomers, employing β-diketone 1,1,1-trifluoro-3-(2-thenoyl)acetone (TTA) as the main ligand and point-chiral R/S-tert-butyl(6-(diphenylphosphoryl)dibenzo[b,d]furan-4-yl)(phenyl)phosphine-oxide (R/S-DFPO) as ancillary ligands. In toluene, these enantiomers display characteristic narrowband red emission from the 5D0→7F2 transition of Eu(III), with a maximum emission wavelength of 617 nm, a full width at half maximum of 11 nm, a photoluminescence quantum yield of 43%, and pronounced chiroptical response, evidenced by |g_PL| values of 8.0 × 10^-3 around 590 nm (5D0→7F1 transition). Notably, CP-OLEDs fabricated via vacuum deposition achieve a maximum external quantum efficiency of 4.0% and exhibit obvious circularly polarized electroluminescence with |g_EL| values exceeding 1.0 × 10^-2. These results demonstrate that point-chiral phosphine-oxide ligands provide an effective strategy for achieving coordination-stable chiral Eu(III) complexes for high-performance CP-OLEDs.