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

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.

Two pairs of chiral YbIII enantiomers presenting distinct NIR luminescence and circularly polarized luminescence performances with giant differences in second-harmonic generation responses

“…The average distance of the six Yb–O bonds is 2.271(8) Å, slightly smaller than the value of 2.303(11) Å for the chiral eight-coordinated analogue Yb(tta) 3 ( 1 L R ) [ 1 L R = (−)-4,5-pinene-2,2′-bipyridine and tta − = 2-thenoyltrifluoroacetone]. 78 The average length of the two Yb–N bonds is 2.510(8) Å, almost the same as the corresponding value of 2.516(12) Å found in Yb(tta) 3 ( 1 L R ). The average lengths of the Yb–O and Yb–N bonds in D-1 are smaller than the corresponding values of 2.324(9) and 2.544(9) Å found in the chiral eight-coordinated Dy(btfa) 3 L R with the same btfa − and L R ligands as those of D-1 79 due to the lanthanide contraction effect.…”

“…We are interested in the synthesis of NCS complexes based on various chiral N-donor ligands due to their unique chirality-relevant properties, such as ferroelectricity, 9,73–77 CPL, 10,78 and SHG response. 79–81 Very recently we reported two eight- and nine-coordinated mononuclear Yb III enantiomeric pairs with the same β-diketonate but different chiral N-donor ligands, and the NIR photoluminescence (NIR-PL), NIR-CPL and SHG performances of eight-coordinated Yb III enantiomers are much better than those of the nine-coordinated ones.…”

“…79–81 Very recently we reported two eight- and nine-coordinated mononuclear Yb III enantiomeric pairs with the same β-diketonate but different chiral N-donor ligands, and the NIR photoluminescence (NIR-PL), NIR-CPL and SHG performances of eight-coordinated Yb III enantiomers are much better than those of the nine-coordinated ones. 78 This result encouraged us to explore Yb III complexes with NCS structures based on identical chiral N-donors but different β-diketonate ligands with distinct structural features to further probe their NIR-PL, NIR-CPL and NLO properties. In this work, by using the precursors Yb(btfa) 3 (H 2 O) 2 and Yb(dbm) 3 (H 2 O) to react with enantiomerically pure mono-bidentate N-donor ligands (L R /L S ), respectively, two chiral Yb III enantiomeric pairs, formulated as Yb(btfa) 3 L R /Yb(btfa) 3 L S ( D-1/L-1 ) and [Yb(dbm) 3 L R ]·[Yb(dbm) 3 (C 2 H 5 OH)]/[Yb(dbm) 3 L S ]·[Yb(dbm) 3 (C 2 H 5 OH)] ( D-2/L-2 ) were isolated, where L R /L S = (−)/(+)-4,5-pinenepyridyl-2-pyrazine (Scheme 1), btfa − = 4,4,4-trifluoro-1-phenyl-1,3-butanedionate with the –CF 3 group possessing a large polarity, and dbm − = dibenzoylmethanate bearing two benzene rings with a large π-conjugated system.…”

A pair of ionic 1D Cu(ii) chain enantiomers simultaneously displaying large second- and third-harmonic generation responses

“…As shown in Table 2, the THG intensities of D-1 and L-1 are much larger than those of some THG active CPs, such as the 2D Ag(I) enantiomer, 26 ninecoordinate Dy III enantiomer, 35 eight-coordinate Dy III enantiomer with large π-conjugated systems, 51 and Yb(tta) 3 (H 2 O) 2 with a centrosymmetric molecular structure. 30 In particular, the THG intensities of D-1 and L-1 are much larger than those of some metal iodates (traditional inorganic NLO materials). 55…”

“…25 However, the reported CPs with both SHG and THG responses are very scarce. [27][28][29][30] In particular, there has been no example of chiral CPs presenting simultaneously large THG and SHG responses.…”