Controllable Preparation And Property Studies Of Nanostructures From Self-assembled Small Organic Molecules

In this thesis, we devote to study the design and synthesis of small organic building blocks, mainly focusing on the novel building block topology, hierarchical self-assembly levels, multiple stimuli-responsiveness and morphological transformation. In addition, we also investigated the design and synthesis of luminous building block and the photochemical/physical behaviors during self-aggregation. This thesis shall contain the following four parts:1. Preparation and characterization of β-cyclodextrin gels.Via solvent strategy, we prepared β-cyclodextrin gels where β-cyclodextrin behaves as a dominated gelator. Electron microscopy and polarized microscopy were employed to investigate the morphologies of the gels.1) Induced by organic molecules, the gelation time, nanomorphology of gels from DMF/LiCl/β-Cyclodextrin system could be tuned flexibly. We studied the influence of functional groups of small organic additives on gelation time, and found that the capability of forming H-bonds plays an important role in gelation process. Interestingly, the small organic molecule-induced organogel could be formed at a high temperature, providing potential materials for some special production in industry.2) We found that, ethylene diamine was capable of inducing the gelation of DMF/LiCl/β-Cyclodextrin system selectively. Meanwhile, the gel was constituted by cystalline particles at microscale. Due to the existance of ethylene diamine, the multi-component system was endowed with multiple responsiveness to some stimuli like Cu(II) and pH.3) Relying on solvent strategy, in DMF/water solvent environment, β-Cyclodextrin can behave as gelator, giving salt-free gel. The rheological behaviors were investigated systematically. Also, for the first time, we utilized small angle X-ray scattering technique to reveal the tubular stacking and tetragonal packing of β-Cyclodextrin. This system was then subjected to prepare switchable multiple-component gelation system. We introduced a surfactant sodium laurate of which aggregation and complexation states could be shifted by external additives.2. Folic acid-based self-assembled nanoarchitectures.Though folic acid and its derivatives have proven to be effective building blocks in the formation of liquid crystal motifs, it remains challenges in the preparation of well-defined nanostructures. We used H-bonding and coordination interaction to trigger the self-assembly (gelation) of folic acid, and investigated the hierarchical self-assembly levels.1) Folic acid sodium salts, induced by transition metal ions, were capable of self-growing into hydrogel. Incomplete metal-ligand coordination, H-bonding and π-π-stacking are responsible for the gel formation. Meanwhile, due to the self-growth feature, we could fabricate multiple membranous hydrogel via spontaneous and artificial manners.2) Utilizing good/poor solvent strategy, we built supramolecular polymeric gel in DMSO/water mixture. We systematically studied the forming mechanism, morphology and mechanical property and revealed the hierarchial self-assembly levels of folic acid in good/poor solvent environments, e.g., from vesicles, fibers to nanospheres.3) The complexes from the hybridization of melamine and folic acid afforded multiple assemblies in water. At low concentration, the complex formed thin membranes, which transformed into spherulites and networks at high concentration ranges. This concentration-dependent hierarchical self-assembly provided new strategy for preparing folic acid-based materials.3. Self-assembly, chiral amplification and formation of graphene hybrids from aromatic amino acids.Aromatic peptides are capable of forming hydrogels due to the presence of adequate H-bonding interaction. But to aromatic amino acids, the gelation is quite difficult because the lack of enough H-bonding sites.1) We chose aromatic glutamic acid as a building block, and utilized good/poor solvent strategy to prepare supramolecular gel materials. We found that, in mixed solvents, fluorenyl-glutamic acid could form viscoelastic hydrogel from emulsion-like mixture. Using real time rheological technique, we studied the dynamic process.2) To stabilize and tune the property of aromatic amino acid gel, we introduced melamine as a modifier. Melamine could interact with the carboxylic acid moieties of glutamic acids. Without changing the basic aggregation mode, melamine could disperse and stabilize the gel fibers in aqueous media. For the first time, we revealed that, melamine without any chiral centers could reverse the supramolecular chirality of fluorenyl-glutamic acid.3) Novel aromatic amino acid conjugates could behave as liquid phase exfoliation agents for graphene production. We synthesized two glutamic acid appended with different luminophores. They could self-assemble into various nanostructures and could exfoliate graphite into few-layered graphene. After triggering the self-assembly of building blocks from the surface of exfolicated graphene sheets, we successfully fabricated graphene-fiber hybrids.4. Photophysical behaviors of luminous building blocks during self-organization.In this section, we attached luminophores onto building blocks, showing highly emissive properties in nanoaggregates. We studied luminescent properties during self-organization, including aggregation-induced-emission, aggregation-induced luminescent color conversion, energy transfer as well as preparation of white-light-emitting materials.1) Cholestrol-cyanostilbene conjugate could self-assemble into single-walled vesicle, of which size was tuned by controlling water fraction. During the vesicle forming process, the fluorescence of systems exhibit "turn on" behavior, can be seemed as a classical aggregation-induced-emission phenomenon. Photo-isomerization triggered the vesicle fusion into nanotubes, whereby system emission was quenched subsequently. Finally we utilized this system to detect the presence of hydrogen peroxide.2) We further synthesized cyanostilbene-pyridine salt amphiphile, which underwent self-assembly process into nanovesicles and nanobelts. After adding cucurbituril 7, nanoaggregates disappeared to produce inclusion complexes. At the same time, the system emission intensity was enhanced by a factor of 30, which was attributed by the free rotation restriction caused by the inclusion.3) We studied the luminescent color conversion phenomenon and affmitive co-assembly of pyrene-glutamic acid salt and naphthalic anhydride-glutamic acid salt. Both of the two building blocks gave nanovesicles separately in water. While mixing, they formed affinitive stacking and the complexes exhibit vesicle assembly as well. After being exciated, energy transferred from pyrene-glutamic acid to naphthalic anhydride-glutamic acid to achieve multiple luminescent color conversion.4) We also synthezied cholestrol-amide-naphthalic anhydride conjugate which composes of a flexible nonpolar tail and a rigid polar head. The conjugate afforded well-defined nanoassemblies in a wide range of solvents. For instance, in nonpolar solvent, it afforded super-gelation with high solvent content. In polar solvents, it formed nanosized toroids, helix, toroid-helix heterojunctions as well as vesicles. Finally, we elucidated the vesicle aggregation/fusion process of vesicles into nanotubes controlled by concentration.