Circularly Polarized Luminescence of Eu(III) Complexes with Point- and Axis-Chiral Ligands Dependent on Coordination Structures

Circularly polarized luminescence (CPL) of Eu(III) complexes with point- and axis-chiral ligands, [Eu((R/S)-BINAPO)(D-facam)3] ((R/S)-BINAPO, (R/S)-2,2′-bis(diphenylphosphoryl)-1,1′-binaphthyl; D-facam, 3-trifluoroacetyl-d-camphor), [Eu(BIPHEPO)(D-facam)3] (BIPHEPO, 2,2′-bis(diphenylphosphoryl)-biphenyl), [Eu(TPPO)2(D-facam)3] (TPPO, triphenylphosphine oxide), and [Eu((R)-BINAPO)(hfa)3] (hfa, 1,1,1,5,5,5-hexafluoropentane-2,4-dione) are reported. The photophysical properties of chiral Eu(III) complexes were characterized by circular dichroism spectra, emission spectra, emission quantum yields, emission lifetimes, and CPL spectra. The dissymmetry factors of their CPL (|gCPL|) at the magnetic-dipole transition of [Eu((R)-BINAPO)(D-facam)3], [Eu((S)-BINAPO)(D-facam)3], [Eu(BIPHEPO)(D-facam)3], and [Eu(TPPO)2(D-facam)3] were as high as 0.44, 0.34, 0.24, and 0.47, respectively, while [Eu((R)-BINAPO)(hfa)3] exhibited a relatively smaller dissymmetry factor (|gCPL| = 0.03). Their coordination structures were determined by the X-ray single-crystal analyses with shape-measure estimations. The photophysical relationship between the CPL properties and the electric transition probabilities of the chiral Eu(III) complexes is elucidated in terms of the coordination structures.