CPL Research Of Chiral Lanthanide Supramolecular Assemblies Based On The β-Diketon

Chiral lanthanide supramolecular circularly polarized luminescent materials have found potential applications in three-dimensional（3D）displays,optical storage,fluorescent probes and chiral photoelectric devices.Luminescent dissymmetry factor(g_lum)is one of the most important parameters to evaluate the performance for CPL materials,and their values are closely related to their diastereomeric purities.However,the lacks of the coordination direction and the large coordination numbers for Ln³⁺ions often lead to the prescence of diastereoselective breaking in self-assembly process.Therefore,the reasonable ligand design is critical for the construction of enantiopure lanthanide supramolecules.In lanthanide-helicates and/or polyhedra,the helical twist of the ligand around the metal center would render the metal center theΔorΛconfigurations and a helical chirality for the assembly.The generation of helical chirality palys an important role for the chiral amplification and the improvement of g_lum value of CPL materials.However,the absence of an effective diastereoselective control would lead to the inversion ofΔandΛconformations and form an assembly without optical active.On the other hand,luminescence quantum yield（QY）is the other important parameter to evaluate the performance of CPL material,which mainly depends on the sensitization efficiency of the ligand.β-diketones are the most famous ligands due to their high efficiencies for sensitizing lanthanide luminescence;therefore,it is expected that the construction of the chiral helicates and tetrahedra withβ-diketones would combine the large g_lum value and high QYs for the CPL materials.Based on the above,we have carried out the following work:（1）Two bis-β-diketones L₁^R and L₁^S with the chiral（R/S）-1,2-propanediol containing a point chirality as spacer have been successfully designed and synthesized,and their self-assemblies with Ln³⁺ions in a 4:2 stoichiometric ratio form three pairs of chiral dinuclear lanthanide quadruple-stranded helicates（HNEt₃）₂⁺[Ln₂(L₁^R/S)₄]^2-（Ln=Eu,Gd,La）.Combination of spectral characterization and density functional theory（DFT）calculations,it is confirmed that the point chirality of the spacer has successfully controlled the formation of homochiral（ΔorΛ）dinuclear lanthanide quadruple-stranded helicates with P or M helical conformation.The photophysical experiments show that（HNEt₃）₂⁺[Ln₂(L₁^R/S)₄]^2-exhibits a high luminescence quantum yield of 69%and a large luminescence asymmetry factor(|g_lum|=0.146).（2）Two bis-β-diketones L₂^R and L₂^S with chiral（R/S）-binaphthol containing axial chirality as spacer have been successfully designed and synthesized,and their self-assemblies with Ln³⁺ions in a 4:2 stoichiometric ratio form three pairs of chiral dinuclear lanthanide quadruple-stranded helicates（HNEt₃）₂⁺[Ln₂(L₂^R/S)₄]^2-（Ln=Eu,Gd,La）.The comprehensive spectral characterization in combination with semi-empirical quantitative calculations confirm that axial chirality of spacer has successfully regulated the formation of binuclear lanthanide helicate with a single helical direction.Interestingly,the helicate exhibits a solvent dependent CPL activity,with the|g_lum|values varying from 0.72 to 1.58,which is attributed to the changes of helicate from the aggregation to the non-aggregation states.In addition,the luminescence quantum yields of（HNEt₃）₂⁺[Eu₂(L₂^R/S)₄]^2-reach up to 57%.（3）A pair of enantiopure chiral lanthanide tetrahedral cages Eu₄（L₃）₄（R/S-BINAPO）₄have been constructed with an achiral tris-β-diketone L₃ and Ln³⁺by chiral ancillary ligand induced strategy,where the chiral（R/S）-BINAPO successfully controlled the diastereoselectivity in self-assembly process.X-ray single crystal diffraction analyses confirm the stereochemistry of tetrahedral cage,that is the four metal vertices of the cage having the same configuration,ΛΛΛΛorΔΔΔΔ.The photophysical studies show that Eu₄L₄（R/S-BINAPO）₄ not only have strong CPL activities(|g_lum|=0.20),but also show the highest luminescence quantum yield（up to 81%）in the chiral lanthanide complexes.On this basis,we further employ the achiral bis[2-（diphenylphosphino）phenyl]ether oxide（DPEPO）to replace the chiral（R/S）-BINAPO to examine the stereochemistry memory effect of the Ln-cage.The result shows that the chirality of the original cage framework is retained,and thus another pair of enantiopure Eu（III）tetrahedral cages,Eu₄（L₃）₄（DPEPO）₄ have been isolated,which still show the high luminescence quantum yields（68%）and strong CPL activities(|g_lum|=0.11).