Synthesis And Characterization Of Metallo-Supramolecular Structures Based On Ortho-Modified Terpyridine Ligands

Nature has created many exquisite and complex structures such as the folding of protein and double helix structures of DNA by the way of supramolecular self-assembly.Among them,coordination-driven self-assembly has been developed as one of the most effective strategies for constructing complex supramolecular structures due to its good directionality and predictability.However,it is still in its infancy for the research on the synthesis and design of recognizable and highly selective coordination motifs.Terpyridine plays an important role in the coordination-driven self-assembly process and is widely used in catalysis,drug delivery and optical devices because they can form strong coordination bonds with different bare metals.In this paper,a series of highly selective narcissistic self-sorting and social self-sorting ligands are designed and synthesized based on the ortho-position(6,6")modification of terpyridine.Further,a variety of two-dimensional and three-dimensional supramolecular structures are precisely constructed through coordination-driven self-assembly.Both the ligands and assemblies are characterized by nuclear magnetic resonance spectroscopy(NMR),electrospray mass spectrometry(ESI-MS),ion mobility mass spectrometry(TWIM-MS)and X-ray diffraction,and the hierarchical self-assembly,crystal packing,and photophysical properties of assemblies are systematically investigated.The content of this study is divided into the following four parts:Chapter 1 A general introduction to the concepts of coordination-driven selfassembly and self-sorting,and we summarize the research development of the twodimensional and three-dimensional supramolecular structures based on the terpyridine in the past two decades.Combining with the research progress of narcissistic selfsorting and social self-sorting in coordination-driven self-assembly,we propose the topic of this thesis.Chapter 2 A series of bidentate ligands MA and MA-R with different substituents(R=-F,-OCH3,-OC6H13,-OC12H25,-CH3,-CH2CH3)are designed and synthesized based on the ortho-position(6,6")modification of terpyridine.The dimer structures 2n2(MA)2 and Zn2(MA-R)2 are obtained through the self-assemly of the ligands and Zn(II).The supramolecular structures are characterized by 1H NMR,ESI-MS,and TWIM-MS,and the single crystals of Zn2(MA)2,Zn2(MA-OCH3)2,Zn2(MAOC6H13)2,and Zn2(MA-F)2 are also obtained.The crystal analysis results show that two ligands formed a head-to-tail geometric coordination structure,sandwiching two Zn(II)ions in the center.Different substituents have an important influence on the configuration of the dimer structures and the stacking between complexes.The introduction of alkyl chains can form CH··? intermolecular interactions,thereby increasing the stacking between dimer structures.In addition,the fluorescence emission behaviors of different dimers are also studied,and the results show that the formation of dimer structures can enhance the fluorescence emission to a certain extent.Chapter 3 On the basis of Chapter 2,the higher-generation ligand MB is designed and synthesized based on the continuous ortho-modification(6,6")of terpyridine,and the dimer coordination compounds Zn3(MB)2 is assembled by the ligand and Zn(II).The single crystal structure show that two MB molecules form a helically head-to-tail geometric coordination mode due to the space constraints.Meanwhile,Zn(tpy)2,Zn2(MA)2,and Zn3(MB)2 exhibit excellent narcissistic self-sorting properties due to the principle of maximum coordination site occupation and space constraints.Subsequently,two dissymmetrical ligands LA and LB with narcissistic self-sorting moieties are designed and synthesized.Two complicated metal supramolecular hexagons Zn9(LA)6 and Zn12(LB)6 are assembled by the ligands LA and LB with Zn(II)ions,respectively.Furthermore,the rotation of the dimer is restricted due to the noncoaxial structure of the ortho-modified terpyridine complex,the single-layer hexagonal macrocycles Zn9(LA)6 and Zn12(LB)6 could form huge cyclic nanostructures and supramolecular gels by the stack of edge-to-edge.Chapter 4 Five tetraphenylethylene-based ligands,one host ligand L and four guest ligands LA-LD,with social self-sorting behavior are designed and synthesized based on the ortho-modified(6,6")terpyridine.Four tetraphenylethylene stacked supramolecular structures SA-SD with different stereoisomerism are obtained through the assembly of the ligands and Zn(II).The spatial configuration of SA is a doubledecker cage,while the changes of geometric angles of TPE-derivated isomers(LB-LD)enable controlled formation of assemblies with either "X-shaped" or "S-shaped" tripledecker stoichiometry(SB-SD).All the assemblies are fully characterized by 1H NMR,ESI-MS,TWIM-MS,and DFT calculations.Moreover,the rigid backbones of these assemblies imparts a strong emission in both dilute solution and solid states.More importantly,the photophysical properties of double-and triple-decker structures show distinct responses under hydrostatic pressure due to the different spatial arrangements and intermolecular stacking.