Point Chirality Controlled Diastereoselective Self-Assembly and Circularly Polarized Luminescence in Quadruple-Stranded Europium(III) Helicates

摘要

Aromatic beta-diketones have been extensively employed as highly effective sensitizers in luminescent lanthanide complexes. However, the difficulties to make the chiral modified groups effectively participate in the frontier molecular orbital (FMO) distributions limit their applications on lanthanide circularly polarized luminescence (CPL) fields. Considering the inherent chirality of the helical structure, a pair of enantiopure dinuclear europium quadruple-stranded helicates, Delta Delta/Lambda Lambda-(HNEt3)(2)(Eu2L4) (Delta Delta/Lambda Lambda)-1; L = R/S-1,2-bis(4,4'-bis(4,4,4-trifluoro-1,3-dioxobutyl)phenoxyl)propane are assembled via a point chirality induced strategy. The comprehensive spectral characteristics combined with density functional theory (DFT) calculations demonstrate that the one point chirality at the spacer of the ligand successfully controls the Delta or Lambda configuration around the Eu(III) ion center and the P or M helical patterns of the helicates. The mirror-image CPL and CD spectra further confirm the formation of the enantiomer pairs. As expected, the helicate presents a higher luminescence quantum yield (QY) of 68% and a large vertical bar(glum)vertical bar value (0.146). This study effectively combines the excellent sensitization capability of beta-diketone and the helical chirality of helicates. This strategy provides an effective path for the synthesis of lanthanide material with excellent CPL performance.