Synthesis And Self-assembly Properties Of Rigid-Flexible Block Oligomers With Different Shapes

It’s the focus of current nanomaterials research that effectively morphological control of self-assembled nanostructures to achieve some different properties.Supramolecular assemblies provide a powerful method to obtain functional organic nanomaterials with well-defined structures induced by external stimulus.Amphiphilic rigid-flex block oligomers can be assembled into various aggregates in bulk and solution due to the microphase separation between the rod and the coil and the anisotropic interaction between the rigid blocks.We designed and synthesized a series of V-type,X-type,and n-type rigid-flexible block oligomers in this thesis.From experimental and theoretical perspectives,we controlled self-assembled nanostructures through external stimulus changes(solvent,temperature,light,donor-acceptor interactions,and self-regulation(changing the type of flexible chain,the shape of the rigid rod,etc.).1.The n-type rigid-flexible block oligomers with an anthracene building block in the rigid center have been investigated through introducing lateral alkyl groups and thermal stimulation of the system in the bulk and in aqueous solution.The following conclusions are listed:(1)The introduction of side groups weakens the interaction between molecules,and the morphology of molecular assembly changes from fiber to helical fiber aggregates;(2)In the aqueous solution of molecule 3,when the temperature of the system is heated to 50℃,the supramolecular chiral signal induced by chiral groups is observed to be inverted by CD spectroscopy,while the molecule 2 with no butyl group at the rigid center is not found;(3)Increasing the length of the PEO segment and adding the TCNQ guest molecule to the system can fix the molecular chirality but cause the change of the morphology.2.New n-type molecules containing a light-responsive azobenzene group were studied by introducing the side group between the rigid-flexible interface,changing the polarity of the solvent and lighting stimulation.The results of the assembly show that:(1)n-type molecules with large regional plane self-assembled into a lamellar phase in bulk states;(2)In solution system,the new n-type amphiphilic rigid-block molecules 6a and 6b containing azo groups self-assembled into nano sheets and vesicle aggregates in aqueous solution,respectively.And by controlling the polarity of the solution,it was found that 6a and 6b self-assembled to form nanofibers and platelet-like supramolecular aggregates,respectively;(3)By adding TCNQ guest to the aqueous solution,compounds of 6a and 6b with TCNQ are obtained by charge transfer interaction,and assembled into disk-like aggregates in aqueous solution;(4)UV 365 nm light irradiation initiates photoisomerization of the molecule,which induces a cis conformation that is not conducive to assembly,resulting in the aggregation of a short fiber structure.3.V-type rigid-flexible block copolymer containing m-terphenyl at the rigid center was studied in detail by changing the rigid sequence and introducing side groups to the molecules in the bulk and solution.The following conclusions were listed from the theoretical basis and experimental results:(1)The introduced side groups weaken the interaction between molecules and make the molecules loosely arrange;(2)The difference in the position of the acetylene bond to the m-terphenyl changes the molecular rigidity sequence,resulting in different molecular shapes.When the other conditions are the same,the intermolecular forces of isomers are also weakened;(3)The nanostructures change from a lamellar phase to a columnar phase in a liquid crystal state or a crystalline state.In solution,sheet-like(ribbon)aggregates transform to spiral fibers or helical nanoring aggregates.4.X-type rigid-flexible block copolymer incorporating a pyrene unit in the rigid center were studied in detail by changing the length or cross-sectional area of the coil segment(the same volume fraction),introducing a chiral group between rigid-flexible interface,and by adding the guest molecule 2,4,5,7-trinitrofluorenone(through the interaction of host and guest),etc.The following conclusions were listed:(1)The introduction of chiral groups and increased the area of the cross-section will both reduce the forces required for the arrangement of molecules;(2)The chiral groups induce molecules to produce supramolecular chirality in aqueous solution and assemble into novel helical structures;(3)By adding the guest molecule TNF,the compounds assembled more closely and exhibited sheet-like structures accompanying the fluorescence changes obviously.