Helicene-Based Ligands Enable Strong Magneto-Chiral Dichroism in a Chiral Ytterbium Complex

Here we report the first experimental observation of magneto-chiral dichroism (MChD) detected through light absorption in an enantiopure lanthanide complex. The P and M enantiomers of [Yb^III((X)-L)(hfac)₃] (X = P, M; L = 3-(2-pyridyl)-4-aza[6]-helicene; hfac = 1,1,1,5,5,5-hexafluoroacetylacetonate), where the chirality is held by the helicene-based ligand, were studied in the near-infrared spectral window. When irradiated with unpolarized light in a magnetic field, these chiral complexes exhibit a strong MChD signal (g_MChD ca. 0.12 T^-1) associated with the ²F_5/2 ← ²F_7/2 electronic transition of Yb^III. The low temperature absorption and MChD spectra reveal a fine structure associated with crystal field splitting and vibronic coupling. The temperature dependence of the main dichroic signal detected up to 150 K allowed, for the first time, the disentanglement of the two main microscopic contributions to the dichroic signal predicted by the MChD theory. These findings pave the way toward probing MChD in chiral lanthanide-based single-molecule magnets.