Syntheses And Applications Of Copillararenes

The study of chemistry based on macrocyclic host is always an important aspect in supramolecular chemistry. We can say that the discovery of novel macrocyclic hosts with fascinating structures and properties has greatly promoted the development of supramolecular chemistry. The macrocycles that were discovered in the early years, such as crown ethers, cyclodextrins, calixarenes and cucurbiturils, have been investigated in a variety of areas, including molecular recognition, nanotechnology, fluorescent chemosensors, drug delivery systems and supramolecular polymers. In2008, a novel macrocycle, named as pillararene, was synthesized and reported. They have received a great attention from then on. In recent years, pillararenes have become a hot topic in supramolecular chemistry. In this dissertation, we mainly focus on the preparation of copillararenes, their host-guest properties and applications.In the first part, we successfully synthesized a pillar[5]arene dimer. Different from pillararene monomers, each pillararene dimer possesses two binding sites so that they have great potential applications in the construction of more sophisticated supramolecular structures, such as [n]rotaxanes and pillararene dimer based supramolecular polymers. We explored its host-guest binding ability with n-octyltrimethyl ammonium hexafluorophosphate. We found that they formed1:2complexes both in chloroform and in the gaseous state. We also found that the complexation between them is statistical with an average association constant of (6.0±0.4)×102M in chloroform.The second part is about a novel pH-responsive supramolecular polymer constructed by pillar[5]arene-based host-guest interactions. We successfully prerared a monomer based on the pillar[5]arene/imidazolium cation recognition motif. It was demonstrated that the binding strength between the monomer molecules in solution could be reduced by adding base, thereby leading to a decrease in the polymerization degree, while a reverse switch could be achieved by the addition of acid to change the monomer back to the cationic state. So, a reversible transition between the high-molecular-weight supramolecular polymer and the relatively low-molecular-weight one, that is, a control of the polymerization degree, was realized by simply altering the solution pH. These results are helpful for the future fabrication of adaptive and smart supramolecular materials with stimuli-responsiveness and special functions.In the third part, we designed and efficiently synthesized a pillar[5]arene-based [1]rotaxane. First, we prepared a monocarboxylic acid-functionalised pillar[5]arene and an alkyl chain guest with a stopper on one side and a primary amine group on the other side. Then, they were mixed in chloroform. C-H···π interactions made it possible for the alkyl chain part to thread through the cavity of the pillar[5]arene. Meanwhile, the primary amine group and the carboxylic acid group are expected to form an ion pair complex and self-assemble in solution. In this way, not only was the perfect pre-organization of pseudorotaxane achieved, but also much higher host-guest association strength was realized. Because of the ion pair interaction, the primary amine group and the carboxylic acid group have a good opportunity to combine via a covalent bond and form an amide-linked pillar[5]arene-based [1]rotaxane in a high yield of73%.