Cyclodextrin-and Its Derivative-based Multi-mode Molecular Machines

Since Richard Feynman's famous 1959 address entitled "There's Plenty of Room at the Bottom," scientists have contemplated the possibilities of constructing small but functional machines. Chemists have been pursuing machinery systems at molecular level for almost two decades, since these architectures are showing an increasing potential for materials and biological applications. Now we still meet challenges to develop multi-mode functional molecules in applications for sensors, digital information proceedings, supramolecule-to-supramolecule transformations, morphologies or phases changes, controlled release and drug delivery, or even useful work output.In this thesis, several cyclodextrin-based supramolecular rotaxanes or pseudorotaxanes systems that respond to multi-stimuli, such as light, redox, pH or even additional substances, were designed and developed. Besides the fundamental characterizations of these systems via MS, UV, NMR etc., we also develop their output signals in fluorescences, Fluorescence life-time, induced circular dichroism and cyclic voltammograms, allowing them to be used in more diverse applications and environments.The main contents and results are generalized as follows:In Chapter 1, an overview of the research background of molecular machinery systems, and the features and application of multi-mode molecular machines are introduced.In Chapter 2, an axle-like compound comprising azobenzene and alkoxy isophthalate moieties was synthesized first. It would form a switchable hemi-rotaxane structure with a-cyclodextrin ring encapsulated in aqueous solution. Next, The hemi-rotaxane was reacted with ethylene diamine palladium nitrate and ethylene diamine platinum nitrate, respectively, to quantitatively form two bis-branched molecular shuttles in situ. Transformation of ring shuttling direction could take place in the stable bis-branched Pt(II) complex. The steric effect of the co-stopper, namely the Pt(II) metal center, made the macroring dynamically shuttle inwards to the alkoxy isophthalate station with the azobenzene's photoisomerization, rather than shuttling outward from the axle.In Chapter 3, novel supramolecular periodic terpolymers from three LMWMs were prepared by dual-channel strategies, with stepwise introduction of two non-covalent interactions. Reversible polymer/oligomer transformation process could be realized in the terpolymers system, based on the assembly/disassembly of theβ-cyclodextrin ring with the azobenzenyl moieties'photoisomerization. In Chapter 4, an asymmetric guest compound comprising ferrocene and azobenzene moieties was synthesized. It can form multi-steady states of host-guest ensembles withβ-cyclodextrin complexed in aqueous solution. The complexation stoichiometries and sites can be selectively controlled by reversible redox and photoirradiation, resulting in the process of the interconversion for steady states of one 2:1 complex, two 1:1 complex and one guest compound.In Chapter 5, a novel pH-responsive and photoisomerizingβ-cyclodextrin derivative was synthesized and fully characterized in this work. At room temperature, this compound would self-assemble to layer aggregations in aqueous environment. The aggregated state can reversibly switch to monomeric solution state attribute to the hydrophobic competition of an additional substance toβ-CD cavity. By switch between the aggregated and monomeric state of this self-aggregatable cyclodextrin derivative based nanosystem, an effective address-crossing digital information system, in response to pH and UV stimuli, has been demonstrated.In Chapter 6, a prototype, based on light-active fluorescent rotor grafted toβ-cyclodextrin, shows a good solvent viscosity-sensitive behavior due to the environment-dependent non-radiative decay. With the reversible photoisomerization of the cyanostilbene unit, the viscosity sensitivity of the molecular rotor could be locked and activated, and the two switchable states can be distinguished by fluorescent signals. This cyclodextrin derivative was threaded to form a novel polypseudorotaxane and such supramolecular assembly displays a lockable ratiometric fluorescent viscosity sensitivity.In Chapter 7, a rotor-containing fluorescent dye was prepared, which can reveal a typical viscosity-sensitive behavior due to the environment-induced non-radiative decay. The viscosity-sensitive behavior of this dye could be tunable (locked and activated) in aqueous environment, either with the reversible light-driven trans/cis-photoisomerization of the cyanostilbene moiety, or with the reversible assembly/disassembly process ofβ-cyclodextrin to the rotor part. Such dual-mode tunable viscosity sensitivity can be well distinguished by fluorescent spectra.In Chapter 8, light-driven rotaxanes with fluorescent chromophores based on a-cyclodextrin have been doped into amphoteric thermo-reversible hydrosol-gels to form a new kind of disperse systems with reversible optical signals. The photoisomeriza-tions with a-CD shuttling have been studied by induced circular dichroism. Compared with their corresponding solutions, the rotaxane-doped hydrosol-gel systems produce much more obvious fluorescent binary signals.In Chapter 9, an amphophilic guest compound was designed and synthesized. It could be encapsulated by a-cyclodextrin to form a hemi-rotaxane structure. The a-CD encapsulation would destroy the self-aggregation of the amphophilic compound in water, further resulting in the formation of a more ordered and structured self-assembled monolayers on gold electrode. The shuttling of a-CD in the SAMs could be reflected by the CV signals change of the viologen group.Chapter 10 is the conclusion.