Pillararene-Based Molecular Recognition And Applications

The development of supramolecular chemistry accompanys the study of macrocyclic hosts. Therefore, the discovery of novel macrocyclic hosts with fascinating structures and properties has greatly promoted the development of supramolecular chemistry. It is clear that the arrival of crown ethers in 1960s triggered an intense period of research and development in the field of supramolecular chemistry. Four generations of macrocyclic molecules, which are crown ethers, cyclodextrins, calixarenes and cucurbiturils, have been investigated by now. They have been applied in a variety of areas, including molecular recognition, nanotechnology, fluorescent chemosensors, drug delivery systems and supramolecular polymers.In 2008, a new class of pillar-shaped macrocyclic hosts was reported, which is known as "pillar[n]arene". Till now, pillar[n]arenes have played an important role in supramolecular chemistry because of their special structure and excellent host-guest properties. This dissertation is mainly about the host-guest properties between pillar[5]arenes and probes, self-assembly systems and molecular recognition.In the first part, we prepare a host-guest complex between a water-soluble pillar[6]arene and a tetraphenylethene derivative. The intramolecular rotation of the phenyl rings of tetraphenylethene derivative is hindered upon the addition of water-soluble pillar[6]arene, so the complex emits strong fluorescence in dilute solution. This host-guest complex can be used as a novel detecting material to probe paraquat because of the competitive host-guest complexation. In addition, the complex between water-soluble pillar[6]arene and tetraphenylethene derivative self-assembles into interesting wheel-like structures in water, which are different from the small spherical micelles formed by self-assembly of the amphiphilic molecule tetraphenylethene derivative alone. We expect that this design strategy of host-guest complexation induced emission will provide a sophisticated pathway for guiding the future design of supramolecular functional materials,In the second part, we successfully construct a novel recogition motif of water-soluble pillar[5]arene to cysteine probe in water. The host-guest complex of water-soluble pillar[5]arene and cysteine probe exhibites no responsiveness to cysteine under neutral condition. The reason is that the formation of the stable inclusion complex inhibits the interaction between probe cysteine probe and cysteine. The encapsulated cysteine probe can be released from the cavity of water-soluble pillar[5]arene upon the addition of acid into water, recovering the formation of cysteine probe-cysteine adduct. This acidic microenvironment triggered release behavior has potential applications in the quantitative detection of thiols in tumor cells, and the novel supramolecular inclusion complex of water-soluble pillar[5]arene(?) cysteine probe will provide an important pathway for guiding the design of functional supramolecular biomaterials.In the third part, we synthesize a novel heteroditopic A-B monomer which can self-organize into linear supramolecular polymers at high concentration utilizing pillar[5]arene-based host-guest interactions. Due to the presence of mesogenic bidentate Schiff base group in the middle of the monomer, the supramolecular polymer chains can be crosslinked through metal-ligand interactions upon the addition of Cu2+ ions, resulting in the formation of a supramolecular polymer gel. Interestingly, since this Schiff base group has special recognition to Cu2+ ion, this self-organized supramolecular polymer can be ultized as a novel fluorescent sensor for detecting Cu2+ ions. This new type of pillar[5]arene- and copper-based supramolecular polymer gel is of great importance for developing novel functional fluorescent materials and molecular devices in the future.In the fourth part, a new multi-functional fluorescent chemosensor based on the host-guest complexation between water-soluble pillar[5]arene and 10-methylacridinium iodide in water is constructed. This non-fluorescent complex can serve as a fluorescence "turn-on" probe to detect paraquat because of the much higher binding constant of water-soluble pillar[5]arene(?)paraquat than that of water-soluble pillar[5]arene(?)10-methylacridinium iodide. This molecular recognition not only has different binding strengths for paraquat and water-soluble pillar[5]arene but also is pH-responsive. The assembly and disassembly processes are reversibly controlled by changing pH of the solution. Meanwhile, a ratiometric fluorescent probe is developed based on the addition of nucleophilic cyanide to the 9-position of water-soluble pillar[5]arene for the determination of cyanide in water. We expect that this design strategy of multi-functional fluorescent chemosensors based on host-guest interactions can be used for other sensing systems and practical applications.