| Supramolecular polymers based on intermolecular interactions show potential applications in functional polymer materials,especially in sensing and intelligent response materials,because of their reversible bonding modes and diversified monomers.Using inorganic metal ions,metal cluster components and different kinds of inorganic nanoparticles as repeat units to form organic-inorganic hybrid supramolecular polymers,can expand assembly structure type and can take advantage of the additional properties of inorganic components.The organic-inorganic hybrid supramolecular polymers are expected to become a kind of supramolecular polymer that combines the flexibility of organic polymer and structural rigidity of inorganic components.At the same time,introducing inorganic components into supramolecular polymers can greatly improve the presence and processability of inorganic materials,and obtain enhanced functional properties that inorganic solid materials usually do not have.The hybrid supramolecular polymers can be classified into zero-dimensional oligomer,one-dimensional linear and branched structure and two/three-dimensional crosslinked network structure according to the classification of connection mode.Different structures have their advantages,among which zero-and one-dimensional structures,as low dimensional structures,have the characteristics of clear structure,and can also provide the understanding basis of synthesis method and formation mechanism for the construction of multidimensional structures,becoming an important breakthrough point for the development of new supramolecular polymer types.However,compared with supramolecular polymerization of pure organic components,supramolecular polymers of organic and inorganic hybrids are still in the initial stage,especially for the structural control of polymerization and structural transformation caused by stimulus-response has not been thoroughly studied.Polyoxometalates are typical large anion clusters at the nanometer scale,which have uniform distribution,definite chemical composition,consistent structure and morphology,rich surface charge,organic modification ability and various functions.However,as inorganic solid materials,polyoxometalates are difficult to recover in the water system,easy to agglomerate in the organic phase,and difficult to process,which greatly limits their applications.Therefore,how to change the existing state of polyoxometalates to meet the required performance has become one of the challenging scientific problems in polyoxometalate chemistry.If polyoxometalate can be used as the construction unit to construct hybrid supramolecular polymers,a class of different supramolecular polymer systems can be established,and polyoxometalate hybrid soft materials can be obtained,which is expected to bring new opportunities to solve the core problems in different fields.Based on this idea,in this thesis,a series of low-dimensional hybrid supramolecular polymers were prepared using the organic covalently modified Anderson-type polyoxometalate as the building blocks.Considering the importance of chiral properties in the functionalization of polyoxometalate and its optical responsiveness in the change of the assembly structure,the influence of the introduction of chiral factors in the hybrid supramolecular polymer on the assembled structure and the structure-directed chirality amplification effect was also studied.Therefore,this paper has carried out the following research work.(I)One-dimensional hybrid supramolecular polymers were developed with electrostatic interaction as the driving force,and the structural effects of chiral introduction were investigated.When anthracenes are used as modification groups and achiral amino acids are used as linking groups,the bilaterally modified Anderson-type polyoxometalates are used as repeating units,and one-dimensional hybrid supramolecular polymers are formed spontaneously.The main driving force comes from the ionic interaction of the sodium ion as a salt bridge with the terminal oxygen of the polyoxometalate and the ionic dipole interaction with the carbonyl group on the modified chain.The rigidity of the connection of polyoxometalates and modifying groups and the incomplete orientation of multiple intermolecular forces facilitate the formation of onedimensional chain structures.When the bridging group is a chiral amino acid,the torsional rigidity caused by the asymmetry of the building block is difficult to overcome,and the increase of the interaction site with the sodium ion intensifies the interaction between the adjacent cluster environments,which cannot form a common helical structure assembly,which can only form rare chiral hexamer structures.These results demonstrate that the non-directionality of ionic interactions and the reduced structural flexibility of the chiral units together contribute to lower chiral polyoxometalate clusters in ionic-driven hybrid supramolecular polymers.Compared with the usual route of singlemolecule chirality induction and asymmetric synthesis of chiral polyoxometalates,here we provide a strategy to construct chiral oligomers to realize zero-dimensional clusterbased hybrid chiral supramolecular polymer.Such chiral oligomers possess circularly polarized absorption properties and can exist in a monodisperse form in suitable solvents for further chiral assembly and asymmetric catalytic functionalization.(II)To expand the connection mode of polyoxometalate hybrid supramolecular polymers and realize chiral-induced structural transformation and chiral amplification,the charge transfer interaction was introduced into the hybrid supramolecular polymer system.One-dimensional polyoxometalate hybrid supramolecular polymer was successfully induced by the formation of donor-acceptor overlapping stacks between Anderson-type polyoxometalates with pyrene groups modified on one side and 1,2,4,5-tetracyanobenzene(TCNB).According to various characterization methods such as the light-dark phase structure given by high-resolution transmission electron microscopy,it is proved that the one-dimensional chain single fiber of the hybrid supramolecular polymer with the organic donor-acceptor alternately stacked in the center and the polyoxometalates surrounded by the outer surface.Dispersed single polymer chains can be obtained by decreasing the concentration,enabling direct observation of donoracceptor hybrid supramolecular polymers.Based on the above results,the basic amino acid L-/D-arginine was introduced into the assembly system as a chiral functional component through ionic interaction by utilizing the anionic properties of the components exposed to the peripheral polyoxometalates,and the chirality was successfully incorporated.Introduced into supramolecular polymers,the transformation from onedimensional chain structures to two-dimensional planar intermediate structures was achieved.Using the method of increasing the system temperature to promote the assembly to reach equilibrium,it was found that the chirality-induced effect was significantly enhanced,and the tubular assembly and the enlarged chiral circular dichroism produced by the curling of the layer structure were obtained.In contrast,nonbasic amino acids are difficult to form positive charges,and thus cannot utilize additional electrostatic interactions to induce the one-dimensional chain structure transition of charge-transfer supramolecular polymers.This work also provides detection methods for judging whether the amino acids are basic amino acids or in the protonated state.(III)To introduce more forces to construct a hybrid supramolecular polymer with polyelectrolyte structural characteristics,and realize the transformation from intermolecular bond connection to covalent bond polymerization,the double-sided anthracene modified Anderson-type polyoxometalate is designed and used as the building block.Using the 2:1 host-guest inclusion interaction between anthracene and γ-cyclodextrin,the one-dimensional polyoxometalates hybrid supramolecular polymer with cyclodextrins on both sides were constructed.Using cyclodextrin as a linking group not only provided the driving force for polymerization but also provided induced chirality through the chiral microenvironment.Further,by utilizing the photodimerization properties of anthracenes,the in-situ coupling reaction was carried out in the cavity under ultraviolet light,and the supramolecular polymer was successfully converted into a onedimensional covalent hybrid polymer with polyoxometalates as the main chain.The resulting one-dimensional polymer has a more stable chain structure and can be diluted to obtain isolated single polymer fibers.Through high-resolution transmission electron microscopy characterization,a pearl necklace-type single-chain structure with alternating organic and inorganic components was visualized.Importantly,such supramolecular polymers containing polyoxometalates have more rigid structures,which still maintain a linear structure in the single-chain state.This linear one-dimensional structure not only realizes the directional assembly of polyoxometalates,but also provides a method to construct single-chain rigid supramolecular polymer fibers,and the fiber length can be used to accurately estimate the degree of polymerization.The results of this thesis show that the polyoxometalate hybrid supramolecular polymer can be constructed by using organically modified polyoxometalates and the introduction of different intermolecular forces into the building blocks with a variety of different driving forces(electrostatic,charge transfer,host-guest).The obtained supramolecular polymers have chirality-amplified asymmetric optical properties by changing the rigidity of polyoxometalates,the binding mode,and the introduction of chiral sites or components.Changes in polarity and temperature conditions or the application of external light will promote the transformation and property changes of the supramolecular polymer structure.The structural study results provide a new example for the expansion of supramolecular polymers and also provide a development idea different from that reported in the literature for the development of polyoxometalate polymerization methods.It is believed that based on the understanding of building element design,force optimization and assembly structure,the results obtained above will lay a methodological and material basis for future applications in template-induced fiber and nanotube synthesis,asymmetric catalysis,smart responsive materials and biomedical materials. |
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