Two Chiral EuIII Enantiomeric Pairs with Significantly Enhanced Photophysical and Third-Harmonic Generation Performances through the Coordination Roles of Enantiopure Bi- and Tridentate N-Donors

For inserting enantiopure bi- and tridentate N-donors (1LR/1LS and 2LR/2LS) into the precursor Eu(hfac)3(H2O)2 to replace two H2O molecules, respectively, two pairs of chiral eight- and nine-coordinate EuIII enantiomers Eu(hfac)3(1LR)/Eu(hfac)3(1LS) (D-1/L-1) and Eu(hfac)3(2LR)/Eu(hfac)3(2LS) (D-2/L-2) were isolated, in which hfac- = hexafluoroacetylacetonate, 1LR/1LS = (-)/(+)-4,5-pinene-2,2'-bipyridine, and 2LR/2LS = (-)/(+)-2,6-bis(4',5'-pinene-2'-pyridyl)pyridine. Compared with Eu(hfac)3(H2O)2, two chiral EuIII enantiomeric pairs not only show significant improvements in their photophysical performances but also display highly boosted third-harmonic generation (THG) effects, and the THG strengths of D-1/L-1 and D-2/L-2 are more than 14 and 27 times that of Eu(hfac)3(H2O)2, respectively. Especially, D-2 and L-2 with symmetric tridentate N-donors only have strong THG effects, while D-1 and L-1 with asymmetric bidentate N-donors simultaneously hold THG and SHG (second-harmonic generation) responses. More notably, from Eu(hfac)3(H2O)2 to eight-coordinate D-1 and L-1, and further to nine-coordinate D-2 and L-2, their THG strengths present successive considerable enhancements as degrees of π-electron conjugation of their ligands continue to rise. Furthermore, the circularly polarized luminescence (CPL) properties of two chiral EuIII enantiomeric pairs were also examined.