Construction And Modulation Of Supramolecular Aggregates Based On Ferrocene Derivatives

The supramolecular ordered aggregates via noncovalent interactions have attracted much interest in the past century due to their promising applications in diverse fields such as catalysis, material preparation, smart devices, information science, and nanotechnology. This dissertation is focused on the design and assembly of stimuli-responsive supramolecular aggregates based on ionic self-assembly strategies, and the inclusion of cyclodextrins and redox were applied to tune the aggregates. There are three main experimental studies in this dissertation as following.1. The study of tuning supramolecular aggregates assembled by ferrocene derivatives. Based on the experimental results, two researches were attempted:redox tuning of vesicles prepared in an aqueous solution through self-assembly of ferrocene derivative molecules and sodium bis(2-ethyl-l-hexyl) sulfosuccinate (AOT); the study of tuning of supramolecular aggregates assembled by ferrocene quaternary ammonium salt and sodium deoxycholate (NaDC). Following results are obtained.(1) Vesicles prepared in an aqueous solution through self-assembly of the oxidized form of N,N-dimethylaminomethylferrocene (Fc+M) and a double-tailed anionic surfactant, aerosol AOT, can be reversibly transformed by redox reactions. Adding the hydroquinone as a reducing agent will cause the dissociation of vesicles and change the solution into emulsion. Subsequent oxidization by adding Ce(SO4)2 will regenerate vesicles. The vesicle structure and morphology are characterized by transmission electron microscopy (TEM) and dynamic light scattering (DLS), respectively and the mean particle size is about 200 nm. The mechanism of vesicle formation and disruption caused by redox reactions is discussed along with the data obtained from cyclic voltammetry (CV) and UV-vis spectroscopy measurements. The redox state changes of the ferrocenyl moiety may influence the noncovalent interactions between FcM and AOT. Meanwhile, theπ-πstacking and amphiphilic hydrophobic association are also included during such a redox modulated process. These results provide guidance for the design of surfactant and small molecular systems that permit active control of self-assembly.(2) We employ a facile ionic self-assembly (ISA) route, through the complexation between (ferrocenylmethyl)trimethylammonium iodide (FcMI) and NaDC, to fabricate the complexes, and their structure and morphology can be tuned by electrochemical redox and the inclusion of cyclodextrins. The amorphous network structure can be observed by TEM when FcMI and NaDC are mixed together, and the electr-oxidation of ferrocene will induced the formation of stable vesicles due to the increase of hydrophilicity of supramolecular complexes. The vesicle structure and morphology are characterized respectively by TEM, DLS and atomic force microscopy (AFM). Their shells can be clearly noted by TEM observation with the thickness at the range of several to several tens of nanometers and their outer diameters at the range of 50-200 nm. The formation of vesicular structures is also supported via AFM observation. The ratio of the diameter and height of the nanospheres is estimated to be ca.10, which should indicate the shell collapse. What' s more,β-CD can include Fc blocks to form stable supramolecular inclusion complexes, which look like the amphiphiles and can assemble to vesicles. With the increase of standing time, the vesicles will be transformed into nanotubes. This finding might be important for the preparation of stimuli-responsive supramolecular aggregates2. Wormlike nanowires have been successfully prepared via the ISA route from the cationic FcMI and the anionic AOT complexes. Their properties and structures are characterized respectively by 1H NMR, SEM, POM, SAXS, UV-visible spectroscopy and cyclic voltammetry. The stoichiometry between AOT and Fc in the complexes is determined as a 1:1 molar ratio. FcM-AOT complexes exhibit an ordered hexagonal columnar structure with the lattice spacing D of 2.49 nm, which is derived from the reverse hexagonal lattice of pure AOT with Fc blocks inside. More interestingly, the wormlike nanowires interweave themselves together to form a net-like structure, and some of them are large enough to exhibit a high-order crystal structure. The formed FcM-AOT complexes show good redox activity also due to the introduction of organic metal ferrocene. circle. Such easily fabricated nanowires with special properties (photo, electric and magnetic) may be used to tailor the parts of nanomachine. Considering the inclusion ofβ-CD with Fc, such an ISA organized aggregate can be changed into vesicles by including the Fc blocks intoβ-CD to form another supramolecular complex. The supramolecular structure and morphology of the vesicles were characterized by TEM and DLS, respectively. Using the uranyl acetate as a negative staining agent, we observe the closed spherical vesicles in the systems, with their outer diameters in the range of 30-300 nm. DLS measurements are also performed to measure the average diameters of vesicles. Results obtained are consistent with the ones observed with TEM, showing an average hydrodynamic diameter of about 108 nm. The mechanism of the complex formation and transition is discussed along with the data of induced cyclic voltammetry, UV-visible spectroscopy, and 1H NMR. And the transformation process are discussed and found to be controlled by the inclusion equilibrium and the cooperative binding of noncovalent interactions, including the electrostatic interactions,π-πstacking, and amphiphilic hydrophobic association. What' s more, controlling aggregates transformations of FcM-AOT complexes are achieved by electrochemical method due to the property change of ferrocene with different form. In response to redox stimuli, the self-assembly nanostructures of supramolecular amphiphile formed by ISA can change between nanowires and vesicles. The wormlike nanowires disappear when constant potential+0.7 V are applied, and TEM observation indicates the formation of vesicles with diameters at the range of 50-300 nm, which is consistent with the ones observed with DLS measurements (about 110 nm). The application of reduction potential-0.1 V to the mixed system will induce the reformation. Such a morphology transition exhibits a reversible modulation on aggregate structures by electrochemical method. The transformation of self-assembly aggregates induced by redox reactions were found to be brought out by drastic change in amphiphilicity of the supramolecular complexes due to the oxidation and reduction of a ferrocenyl moiety. Moreover, the construction-deconstruction process can be controlled reversibly for at least three times because of without the introducing of a third substance. Therefore, through simple ISA strategy, we could expediently acquire many unique soft materials with various structures and functions from aqueous environment, and the design and construction of stable ordered assemblies and the development of smart material will be expected as one remarkable study thought.3. Redox-active polyelectrolyte-surfactant complexes (PSC) are prepared via the ionic self-assembly of sodium polyacrylate (PAAS) and ferrocenyl surfactant, n-alkyl (ferrocenylmethyl)ammonium bromide (Fcn, n=8,12,16, where n is the carbon number of the alkyl chain), in solution. Their structures and properties are characterized respectively by XRD, TG, UV-visible spectroscopy and CV. The results show that PAAS-Fcn complex exhibited an ordered lamellar mesomorphous structure with the ferrocenyl moieties forming H-aggregation as known from the blue shift in the UV spectrum. With increasing the length of surfactant alkyl chain, the stacking order is improved. CV measurements indicate that the reversibility of the electrode process becomes worse for the PAAS-Fcl2 and PAAS-Fcl6 films than that for the PAAS-Fc8. The present results demonstrate that the electrochemical activity of the redox-active polyacrylate-ferrocenyl surfactant complex can be easily tuned by changing the surfactant tail length. Our work provides a simple and facile approach to the preparation of redox-active polymers with ordered mesomorphous structure by the ionic self-assembly.