Photophysical and Chiroptical Properties of Europium(III) Enantiomers with Axially Chiral Ancillary Ligands

Chiral Eu(III) complexes with β-diketone 1,1,1-trifluoro-3-(2-thenoyl)acetonato and axially chiral ancillary ligands, R/S-[1,1′-binaphthalene]-2,2′-diylbis(diphenylphosphine oxide), R / S-(6,6′-dimethoxy-[1,1′-biphenyl]-2,2′-diyl)bis(diphenylphosphine oxide), and R/S-[4,4′-bibenzo[d][1,3]dioxole]-5,5′-diylbis(diphenylphosphine oxide) exhibit high photoluminescence efficiencies (0.49, 0.42, and 0.56, respectively) and strong circularly polarized luminescence with dissymmetry factor (|g _lum|) of up to 0.070, 0.131, and 0.147, respectively, demonstrating efficient ligand-to-metal energy transfer and tunable chiroptical properties.

Chiral lanthanide(III) complexes with superior circularly polarized luminescence (CPL) properties, especially for the efficient chiral europium(III) complexes with high dissymmetry factor (g _lum) obtained by rational design of coordination ligands, are important in the field of chiral functional materials. In this work, the β-diketone ligand 1,1,1-trifluoro-3-(2-thenoyl)acetonato (TTA) is used as the primary ligand and three axially chiral enantiomeric pairs, R/S-[1,1′-binaphthalene]-2,2′-diylbis(diphenylphosphine oxide) (R/S-BINAPO), R/S-(6,6′-dimethoxy-[1,1′-biphenyl]-2,2′-diyl)bis(diphenylphosphine oxide) (R/S-BINAPO), and R/S-[4,4′-bibenzo[d][1,3]dioxole]-5,5′-diylbis(diphenylphosphine oxide) (R/S-DiO-BIPHPO), are used as ancillary ligands for three pairs of chiral Eu(III) enantiomers. The photoluminescence efficiencies of Eu(TTA)₃(BINAPO), Eu(TTA)₃(MeO-BIPHPO), and Eu(TTA)₃(DiO-BIPHPO) are as high as 0.49, 0.42, and 0.56, respectively. Furthermore, Eu(TTA)₃(R/S-BINAPO), Eu(TTA)₃(R/S-MeO-BIPHPO), and Eu(TTA)₃(R/S-DiO-BIPHPO) enantiomers exhibit symmetric CPL spectra with g _lum factors at the magnetic-dipole transition (⁵D₀ → ⁷F₁) as high as 0.067/–0.070, 0.128/–0.131, and 0.138/–0.147, respectively. These results suggest that an effective ligand-to-metal energy transfer occurs, and the chiral ancillary ligands affect the chiroptical properties of the Eu(III) enantiomers effectively.

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