Supramolecular Polymers Based On Crown Ethers And Cryptands

Self-assembly is ubiquitous in nature, and biological systems utilize noncovalent forces to control the self-assembly process precisely, resulting in the formation of complicated structures with multiple functions. For example, enormous amount of information are stored in DNA with double helix structure, which further lead to its replication and transcription. Inspired by the structure of biological macromolecules, chemists are engaged in developing highly-ordered artificial supramolecular assemblies such as supramolecular polymers, which exhibit great significance in the formation of various supramolecular architectures, and more importantly, the potential applications for dynamic supramolecular materials. In recent years more and more attentions have been paid to crown ethers, one of the most common hosts in the supramolecular chemistry, which serves as the building blocks to construct functional supramolecular assemblies due to its facilitated synthesis, convenient structure modification, and unique complexation properties with a variety of guest molecules. This dissertation, comprising four parts, focuses on the self-assembly of supramolecular polymers based on crown ethers and their derivative cryptands.In the first part, a novel bis(m-phenylene)-26-crown-8-based cryptand has been designed and synthesized. It has been used to prepare two 1:1 complexes with two paraquat derivatives with high association constants (6.5×105 and 4.0×105 M-1) in acetone, which are determined by probing the charge-transfer band of the complexes by UV-Vis spectroscopy and employing a titration method. In the solid state the cryptand forms a 2:1 threaded structure with methyl-substituted paraquat, which is not consistent with their 1:1 complexation stoichiometry in solution. On the other hand, dihydroxyethyl-substituted paraquat is threaded unsymmetrically into the cavity of bis(m-phenylene)-26-crown-8-based cryptand. Moreover, the neighboring [2]pseudorotaxanes are arranged linearly to form an interesting supramolecualr poly[2]pseudorotaxane threaded structure. It has been further used to prepare cryptand/paraquat derivative [2]rotaxanes efficiently using easily available 3,5-dimethylphenyl groups as the stoppers by the immediate solvent evaporation method (ISEM), which accelerates organic reactions significantly due to the remarkable enhancement of molecule-to-molecule contacts between reactants.In the second part, based on the bis(p-phenylene)-34-crown-10/paraquat derivative and dibenzo-24-crown-8/dibenzylammonium salt recognition motifs, self-sorting organization of two AB-type heteroditopic monomers leads to the formation of linear supramolecular alternating copolymers driven by host-guest noncovalent interactions, which are confirmed by 1H NMR, cyclic voltammetry, dynamic light scattering, viscosity measurements and scanning electron microscopy. In addition, the linkers between host and guest moieties on the two monomers play an important role in the formation of supramolecular polymers. The flexible alkyl chain, consisting of totally more than 20 atoms, is designed and served as the linker in anticipation for a relatively low critical polymerization concentration.In the third part, based on the above two self-sorting host-guest recognition motifs, polypseudorotaxanes can be fabricated with supramolecular polymers as the backbones. Both the feed ratio and monomer concentration have significant influence on the formation of polypseudorotaxanes. The polypseudorotaxanes exhibit unique rheological properties in solution due to the complexation between the axle molecules and the macrocyclic host units of the supramolecular polymer backbones. Moreover, the flower-shaped microspherical morphologies are observed for both the supramolecular polypseudorotaxanes and their supramolecular polymer backbones, which are believed to be the first examples of such kind of architectures resulted from the self-assembly of supramolecular polymers. The results demonstrated that, supramolecular polymer can be assembled to higher-order aggregates through the noncovalent recognition of organic molecules.In the last part, a heteroditopic AB monomer based on the bis(m-phenylene)-32-crown-10-based cryptand/paraquat recognition motif is designed and synthesized.1H NMR as well as viscosity investigations reveal that the supramolecular assemblies show characteristic polymer properties due to the high association constants between the host and the guest. Furthermore, addition of PdCl2(PhCN)2 into the heteroditopic monomer results in the formation of supramolecular crosslinking polymer. The remarkable plasticity of the system is proven by the ligand triggered reversible switch between the linear and crosslinking supramolecualr polymers. The project is proceeding smoothly.