Preorganized helical chirality controlled homochiral self-assembly and circularly polarized luminescence in a quadruple-stranded Eu2L4 helicate
β-diketones are the ones of the most widely used ligands for lanthanide complexes luminescence due to their excellent sensitization abilities. However, the difficulties for introducing of the chiral groups to take part in the electron transitions of the conjugation systems limit their applications on lanthanide circularly polarized luminescence (CPL) materials. In view of the inherent chirality of the helical structure, herein, a pair of homochiral quadruple-stranded helicates, Eu2L4 are assembled based on the chiral bis-β-diketonate ligands, where the two point chirality centers in the spacer preorganize the helical conformation of the ligand (3S,4S)/(3R,4R)-3,4-bis(4,4'-bis(4,4,4-trifluoro-1,3-dioxobutyl)phenoxyl)-1-benzylpyrrolidine, LSS/LRR). X-ray crystallographic analyses reveal that the R,R configurations of the chirality carbons in the spacer induce the M helical sense of the ligand, whlile the S,S configurations induce a P helical sense. Through the comprehensive spectral characteristics in combination with semiempirical DFT calculation, it is confirmed that the preorganized ligands successfully control the homochirality of the helicates. Moreover, the mirror-image CD and CPL spectra and NMR measurements confirm the formations of the enantiomer pairs and their diastereopurities in solution. A detailed photophysical and chiroptical characterizations reveal that the helicates not only exhibit intense circularly polarized luminescence (CPL) with |glum| values reaching to 0.10, but also show high luminescence quantum yields of 34%. This study effectively marries the helical chirality of the helicate with the excellent sensitization ability of the β-diketone, providing an effective strategy for the syntheses of chiral lanthanide CPL materials.