| Host-guest chemistry has undoubtedly played an important role in the development of various functional supramolecular materials on account of its good selectivity, high efficiency, and stimuli-responsiveness. However, the currently available hosts which show good host-guest properties are still limited. Therefore, developing new kinds of powerful hosts has attracted increasing attention. In general, the high binding strength between the components is crucial for the efficient preparation of host-guest complexes. In order to increase the association constants, crown ether-based cryptands were introduced as a new type of hosts. Crown ether-based cryptands have attracted much attention not only because of their 3D spatial architectures but also due to their good application prospects. A series of novel crown-ether-based cryptands were elegantly designed and prepared during the past decades, which complex with guest molecules much more strongly than those of their corresponding simple crown ethers because of the introduction of additional binding sites and the preorganization of the host structures during the association process.Along this line of consideration, the research content of this dissertation mainly includes the following aspects:In the first part, by attaching a bisthiotetrathiafulvalene (STTFS) unit to the third arm of the cryptand, a redox-switchable bis(m-phenylene)-32-crown-10(BMP32C10) -based cryptand was synthesized successfully. It was found that this cryptand host exhibited ON-OFF binding abilities with paraquat/vinylogous viologen owing to the specific redox-active property of the STTFS unit, and as a result the dethreading-rethreading processes between this cryptand host and two guests could be well-controlled in different chemical redox states. This new efficient reversible process provides a convenient ON-OFF switch by simple chemical redox methods, which could be used in the fabrication of smart molecular shuttles and machines.In the second part, two novel BMP32C10-based cryptands that are bridged by P=O functional groups were synthesized, in which P=O functional groups are located at different positions on the third arms of the cryptands. These new cryptands were capable of forming [2]pseudorotaxanes with the paraquat guest both in solution and in the solid state. Moreover, the generated [2]pseudorotaxanes could further self-assemble into supramolecular poly[2]pseudorotaxanes in the solid state driven by phosphine oxide-based hydrogen bonding interactions and C-H-…π interactions. Interestingly, it was found that two different types of supramolecular poly[2]pseudorotaxanes were formed in almost linear and zigzag shapes in the solid state because of the slight difference between the two cryptands.In the third part, a novel pillar[5]arene-fused cryptand was synthesized by the integration of a BMP32C10 subunit and a pillar[5] arene subunit into a single molecule, and it is also the first example of pillar[n]arene-fused cryptand. The cavity of BMP32C10-based cryptand in this tricyclic host molecule could selectively interact with the paraquat guest, while the cavity of the pillar[5] arene unit of this tricyclic host molecule was found to exclusively form a host-guest complex with the triazole guest. The complexation behaviours between host and two different guest species were selectively, and more importantly, in an orthogonal fashion. Then, by unifying the themes of two independent host-guest interactions, including cryptand-based host-guest recognition and pillar[5]arene-based host-guest interaction, the novel supramolecular polymer could be easily and efficiently constructed in an orthogonal way.In summary, a series of self-assembled structures including pseudorotaxanes, molecular switches, supramolecular poly[2]pseudorotaxanes and supramolecular polymer by orthogonal self-assembly have been constructed using the cryptand-based recognition motifs. The results we obtained can provide further insights into molecular devices and molecular machines in future. |
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