Construction Of Metal-organic Supramolecular System Based On Saddle-shaped Cyclooctatetrathiophene As Building Blocks

Metal-organic supramolecule is one type of the supramolecular frameworks formed via the self-assembly of the metal ions and structure-matched monodentate or multidentate ligands utilization the coordination bonds.A variety of weak interactions result in unique optical,electrical and magnetic properties for metal-organic supramolecular system,which provides potential application in biocatalysis,drug design,MOF materials,molecular devices and so on.Whereas,the diversity of the assembly motifs and the geometric configuration of metal coordination are the main factors which would greatly influence the final supramolecular structures,so it becomes especially important for the development of new ligands.Cyclohexylenethiophene as a typical nonplanar oligothiophene,bearing a three-dimensional"saddle-shape"structure,has displayed interesting optical properties,good stability and chiral characteristics.In this thesis,the“saddle-shape”cyclooctathiophene is selected as building block and different metal ions are utilized for the supramolecular complex construction,which present helical,gel-type,macrocyclic configurations.The detailed study related to the structure-property relationship have been carried out as in the following two parts:1.Cyclooctatetrathiophene-based double helicates:syn-locked strategy for chiral self-sorting by using S···N interactionWith cyclooctathiophene as building block and 2-pyridyl substituent as binding sites,ligands L1 and L2 were designed and synthesized.The single crystal structure and ¹H-¹H NOESY confirm that the thiophene and pyridine favor the near-plane and syn-locked configurations in ligands L1 and L2 due to the intramolecular N···S interaction.Benefiting from the N···S intramolecular interactions,chiral self-sorting and assembly occurs induced by the silver ions.Therefore,ligands possessing the same configurations are favoring in coordinating together to give homochiral complex L1₂Ag₂ and L2₂Ag.Through the crystal study,it's clear that a pair of double helical racemates?R,R,R,R,R,R?-L1₂Ag₂ and?S,S,S,S,S,S?-L1₂Ag₂could be detected in the crystal lattice and it has been also confirmed by the ¹H-¹H NOESY that the thiophene and pyridine are cis-locked in the final structures.The resolution of L1 has been carried out on the HPLC eluting and the corresponding chiral isomers?+?-L1 and?-?-L1 are obtained,respectively.Finally,AgBF₄ was utilized for the self-assembly study and two duplexes?+?-L1₂Ag₂ and?-?-L1₂Ag₂ were obtained,which have been confirmed by circular dichroism.2.Supramolecular metallogel constructed with cyclohexathiophene:preparation and characterizationBased on cyclooctathiophene as building block,ligands L3 and L4 were designed and synthesized via the attaching of 3-substituted and 4-substituted pyridyl groups as coordination groups.X-ray structures of L3 and L4 show a pair of racemate respectively,and the sulfur atom from the thiophene and the nitrogen atom from the pyridine of ligand L3 are in the cis or trans conformation due to the free rotation between the thiophene and the pyridine.In the presence of Ag⁺,Ligands L3 and L4 is formed supramolecular metallogel by coordination-driven self-assembly.The significant differences in mesoscopic morphology for two metallogels are originated from the positional isomerism of nitrogen atoms for L3 and L4,which cause the different assembly modes.In addition,nanofibers could be detected for L3-Ag from the scanning electron microscopy study,but only irregular flates could be found in the gel of L4-Ag.IR spectrum and XPS confirmed the produce for N-Ag bond in the two metallogels.Both gels have stimuli-responsive properties to halogen ions i.e.phase transitions,because of halogen ions can cause silver ions to precipitate.Acetonitrile or dimethyl sulfoxide can destroy the N-Ag bond,which could change the supramolecular system from gel type to solution state.More specifically,the L3-Ag gel emits orange light while the L4-Ag gel displays bright yellow light when excited with light??=365 nm?.The coagulation has significant fluorescence characteristics and forms 3D fibers structures or layered structure between molecules,which has potential application in fluorescence sensing,ion exchange and adsorption.