Studies On Polymeric And NCs Self-assembly Via Inclusion Interaction

Studies on Polymeric and NCs Self-assembly via Inclusion InteractionMolecular self-assembly, the most important area in suprachemistry, means spontaneous building-up of complex structures via intermolecular interaction, from various building blocks including inorganic and organic molecules and macromolecules, etc. Among different kinds of driving forces leading to self-assembly, the host-guest inclusion plays an important role. Cyclodextrins (CD) seem to be the most extensively studied host compounds characteristic of a hydrophilic exterior surface and hydrophobic interior cavity, which can accommodate a wide range of molecules as guests. Among the varieties of such host-guest pairs,β-CD and adamtantly group (ADA) has been mostly investigated due to their high association constant (～10⁵).In recent years our group has developed 'block-copolymer-free strategies' to fabricate polymeric micelles using polymer pairs as building blocks. These novel approaches result in noncovalently connected micelles (NCCM), in which intermolecular specific interactions (hydrogen bonding and hydrophobic interaction etc.) rather than chemical bonding exist between the shell and core. Being a substantial progress in the studies on NCCMs, in this thesis we investigate a series of new self-assembly systems including polymeric micelles and hollow spheres and structured films of nanocrystals, by introducing the inclusion complexes ofβ-CD and adamantane into our work. The thesis is constituted of five parts:Firstly, a hydrophilic polymer PGMA-CD containingβ-CD and hydrophobic ADA-containing polymer PtBA-ADA were used as building blocks to construct micelles. Driven by the inclusion interaction betweenβ-CD and ADA, the micelles in aqueous media with PtBA-ADA as the core and PGMA-CD as the shell are formed. The resultant micelles stably dispersed in water possess unique characters: it contains both a hydrophobic PtBA-ADA core on a scale of hundreds of nanometers and hydrophobic cavities of CD in a size of 0.7 nm in the shell. Taking advantages of the cavities being able to accommodate different molecules, the micellar surface can be easily modified to either hydrophobic or charged ones. Besides, by subsequently crosslinking the shell and dissolving the core, the micelles can be converted toβ-CD-containing nanocages. The resultant hollow spheres contain multi-scale holes: the large central one andβ-CD interior cavities. These CD cavities provide a broad range of opportunities for further surface modifications of the micelles or hollow spheres by incorporating different kinds of functional molecules. Thus, a neutral surface is converted to an anionic or a cationic surface via the inclusion interaction between the CD cavities and adamantly groups.Secondly, the self-assembly of inorganic nanocrystals (NCs) into hierarchical structures is pivotal in preparation of nano-functional materials. The interfacial ordering effects in NCs arrangement can be utilized since good fluidity of NCs is kept on the immiscible liquid-liquid interface. Herein, interfacially self-assembly of NCs is demonstrated driven by the inclusion interaction betweenβ-CD and adamantyl groups. The hydrophobic NCs (CoPt₃, Fe₃O₄) with surface modified by adamantyl groups dispersed in organic solvent, i.e. toluene, was mixed withβ-CD water solution. A phase transition of NCs would occur from toluene to water/oil interface via the inclusion interaction from adamantyl groups on NCs surface andβ-CDs. Furthermore,β-CDs functionalized with one SH or NH₂ group were recruited as new ligands to direct consecutively metal NCs(Ag, Au) onto magnetic monolayers of CoPt₃ or Fe₃O₄ NCs between water/oil interface. Thus, these heterogeneous bi- or trilayers composed of different NCs may be generated, which possess novel optical and magnetic properties.Thirdly, we concentrate on self-assembly of rigid low-molecular-weight polyimide with two carboxyl ends (CPI) via microphase inversion by adding water with different pH into CPI/THF solutions. The aggregates with multiple morphologies including dimpled-beads, porous spheres and vesicles were obtained and investigated by TEM, SEM, DLS andζ-potential technologies. The rigid structure of CPI plays an important role in the formation of the multiple morphologies.In the fourth part, we present self-assembly of luminescent conjugated polymer via inclusion interaction betweenβ-CD and adamantane. Aggregates are fabricated by addingβ-CD water solution into low-molecular-weight polyfluorene (PF) with adamantyl-terminated group (PF-ADA) in THF. The luminescent polymer PF-ADA acts as fluorescent donor while fluorescent dye fluorescein as an acceptor. Therefore, CD-FITC, a CD derivative containing fluorescein group, is used to induce the self-assembly of polyfluorene. FRET (fluorescence resonance energy transfer) behavior of the assembly was investigated as FITC and polyfluorene are close to each other.Finally, great deals of CD cavities remain intact in both CD polymer (PGMA-CD) and the micelles with PGMA-CD as the shell. Two ADA modified fluorescent dyes, fluorescein and rhodamine, were synthesized and used to investigate the dye loading onto the CD polymer chain or micelle surface. The inclusion complexation of the modified dyes and CD causes fluorescent quenching. Afterwards dye release and fluorescence recovery could be realized by supramolecular replacement, i.e. the dye molecule is excluded from the CD cavities by adding excess ACA (1-adamantylcarboxylic acid). Our work provides wide potential for introducing the inclusion interaction into fluorophore-based biodetection field in future research.