Strongly circularly polarized luminescence from dinuclear Eu(III) helicates prepared through a BINOLbased bis-diketone ligands

Abstract

C lanthanide helicates have potential applications in biology and material science as chiral probes and circularly polarized luminescence (CPL) materials. However, the preparation of homochiral helicates through coordination-directed self-assembly strategy is challenging due to the greatly labile coordination geometries of lanthanides, which raised the higher requirement for ligand designs. Herein, a BINOL-based bis-β-diketone ligand is developed, which give rise to preorganized helical conformation and induced the formation of homochiral helical structure. X-ray crystallographic analysis reveals that the ligand assemble with Ln(III) ions to give homochiral either P or M quadrupleand triple-stranded helicates, [HNEt3]2+•[Eu2(BTTB)4]2and Eu2(BTTB)3(R/ S-BINAPO)2 {(R/S)-BINAPO=(R/S)-2,2 -bis(diphenylphosphoryl)-1,1 -binaphthyl; BTTB=bis[4-(4,4,4-trifluoro-1,3-dioxobutyl) (2,3,5,6-tetrafluorophenoxyl)]-1,1 -binaphthalene}. The 1H, 31P NMR and CD measurements confirm the diastereo purity of the assemblies in solution. A detailed optical and chiroptical characterization reveals that the luminescent enantiopure helicates not only exhibit intense circularly polarized luminescence (CPL) with |glum| values reaching 0.80 but also show high luminescence quantum yields of 72.8%. Our results provide a feasible strategy for designing homochiral helical lanthanide supramolecular architecture and synthesizing excellent CPL materials.