Synthesis And Circularly Polarized Luminescence Performance Study Of Alkynyl-Protected Silver And Copper Clusters

Circularly polarized luminescence materials have been attracting broad research interest due to the widespread potential applications in the field of 3D optical displays,encrypted transmission and information storage.Among many materials,metal clusters with excellent luminescence properties and unique chiral structures are expected to be a new class of CPL functional materials and their precise structure is helpful to understand the structure-chiral optical activity relationship at the atomic level.However,so far,due to the difficulty of chiral synthesis and separation of enantiomers and the low emission quantum efficiency of metal clusters,reported CPL-active metal clusters are very scarce.Therefore,it is necessary to develop a new synthesis strategy to effectively construct metal clusters with CPL properties.It was found that chiral ligand induction can effectively transfer chirality from the ligand to the metal core,thus inducing the synthesis of chiral metal clusters in a highly efficient and controllable manner.Compared with the commonly used chiral thiolate and phosphine ligands,chiral alkynyl ligands can anchor on a metal surface by both σ and π coordination modes,resulting in the structural diversity.Moreover,the richer coordination modes can effectively prevent the racemization during cluster assembly.In addition,the-C≡C bond of the alkynyl ligands may influence the electronic structures of the clusters,which leads to the changes in the optical properties.Therefore,combining the advantages of chiral ligand induction method and chiral alkynyl ligands,it is expected to efficiently construct chiral metal clusters with excellent CPL properties and further promote the development and application of metal cluster materials in the field of chiral optics.Based on the above analysis,this thesis mainly focuses on the construction of metal clusters with novel structures and chiral optical activities using different chiral alkynyl ligands,which further reveal the relationship between chiral structure and CPL properties at the atomic level.This thesis enriches the limited types of metal clusterbased CPL materials,further promotes the application of chiral luminescent clusters in the field of photoelectric materials.The main work is summarized as follows:1.For the first time,we used a pair of designed chiral alkynyl ligands,(R/S)-2diphenyl-2-hydroxylmethylpyrrolidine-1-propyne(R/S-DPM),to assemble an optically pure enantiomeric pair of copper(Ⅰ)clusters,[Cu14(R/S-DPM)8](PF6)6(R/SCu14),with atomically precise structures.The Cu14 metal framework could be considered as a distorted Cu66+ octahedron being encapsulated in a Cu88+ cube,which has never been previously reported in copper cluster systems.Isolated R/S-Cu14 monomers were nonemissive but showed mirror-image CD signals in solution.In addition,the aggregated state of R/S-Cu14 showed bright red luminescence stemming from aggregation-induced emission(AIE),which correspondingly triggered the CPL response of the clusters with the luminescence anisotropy factor(glum)up to 1.0 × 10-2.Finally,due to the excellent AIE characteristic and good biocompatibility,the R/S-Cu14 was further explored for biological imaging of HeLa and NG108-15 cells.This work opens a new avenue to chiral metal clusters by utilizing alkynyl ligands and provides the theoretical foundation and experimental basis for the application in the field of functional optics.2.Atomically precise enantiomeric pairs of[Cu8(R/S-TPI)6(CH3CN)6](PF6)8(R/S-Cu8)have been successfully constructed by the chiral alkynyl ligands.R/S-Cus exhibited an uncommon crystallization-induced emission enhancement(CIE)effect.The crystalline state of R/S-Cu8 displayed strong orange-red emission,in stark contrast to those of the amorphous and aqueous states.Interestingly,R/S-Cu8 showed also reversible thermochromism characteristic spanning from red-orange to yellow with a 90 nm blue-shift from 298 to 83 K,which can be recognized by the naked eye.The chiral structure and luminescent feature endow the crystalline state of R/S-Cus remarkable CPL response with luminescence anisotropy factor(glum)of 5.0 × 10-3.Furthermore,the enantiomeric pairs were studied for enantioselective catalysis of carbophilic addition of α-diazoesters,which provided desired product in 100%conversion with-14%ee.These results revealed the great potential of the atomically precise chiral metal clusters as asymmetric catalysts in the organic synthesis field.3.We prepared and structurally characterized for the first time an enantiomeric pair of superatomic silver clusters[Ag17(R/S-NYA)12](NO3)3(R/S-Ag17)having two free electrons by using designed chiral alkynyl ligands.The silver framework and the protecting ligand in R/S-Ag17 presented C3 symmetry and emitted bright near-infrared emission(NIR)in the solid state with a QY of 8%,resulting in an unprecedented nearinfrared emission CPL response.More importantly,the chirality transfer from the chiral protecting ligands to chiral superatomic states was definitively identified,and the fact that the CPL originated from transitions between superatomic S and P orbitals was clearly revealed by a combination of single-crystal X-ray structural analysis,optical experiments,and theoretical calculations.This work opens up new horizons for the construction of superatomic metal clusters with CPL response by using alkynyl ligands and provides new insight into the origin of NIR in metal clusters.