Two Chiral Yb^III Enantiomeric Pairs with Distinct Enantiomerically Pure N-Donor Ligands Presenting Significant Differences in Photoluminescence, Circularly Polarized Luminescence, and Second-Harmonic Generation

Abstract

Using enantiomerically pure bidentate and tridentate N-donor ligands ( 1 L R / 1 L S and 2 L R / 2 L S ) to replace two coordinated H 2 O molecules of Yb(tta) 3 (H 2 O) 2, respectively, two eight- and nine-coordinated Yb III enantiomeric pairs, namely, Yb(tta) 3 1 L R /Yb(tta) 3 1 L S ( Yb- R -1 / Yb- S -1 ) and [Yb(tta) 3 2 L R ]·CH 3 CN/[Yb(tta) 3 2 L S ]·CH 3 CN ( Yb- R -2 / Yb- S -2 ), were isolated, in which Htta = 2-thenoyltrifluoroacetone, 1 L R / 1 L S = (−)/(+)-4,5-pinene-2,2′-bipyridine, and 2 L R / 2 L S = (−)/(+)-2,6-bis(4′,5′-pinene-2′-pyridyl)pyridine. Interestingly, they not only present distinct degrees of chirality but also show large differences in near-infrared (NIR) photoluminescence (PL), circularly polarized luminescence (CPL), and second-harmonic generation (SHG). Eight-coordinated Yb- R -1 with an asymmetric bidentate 1 L R ligand has a high NIR-PL quantum yield (1.26%) and a long decay lifetime (20 μs) at room temperature, being more than two times those (0.48%, 8 μs) of nine-coordinated Yb- R -2 with a C 2 -symmetric tridentate 2 L R ligand. In addition, Yb- R -1 displays an efficient CPL with a luminescence dissymmetry factor g lum = 0.077, being 4 × Yb- R -2 (0.018). In particular, Yb- R -1 presents a strong SHG response (0.8 × KDP), which is 8 × Yb- R -2 (0.1 × KDP). More remarkably, the precursor Yb(tta) 3 (H 2 O) 2 exhibits a strong third-harmonic generation (THG) response (41 × α-SiO 2 ), while the introduction of chiral N-donors results in the switching of THG to SHG. Our interesting findings provide new insights into both the functional regulation and switching in multifunctional lanthanide molecular materials.