Controllable Assembly And Functionality Of Crown Ether Derivatives

The development of supramolecular chemistry expands the research objects of chemists from small molecules to molecular aggregates, which is consistent with the aim of the popular "bottom-up" approach. Host-guest systems play a significant role in the development of advanced supramolecular aggregates because their good selectivity, high efficiency and convenient responsiveness make them excellent building blocks for the construction of supramolecular materials. As the first-generation of hosts in host-guest chemistry, crown ethers have been widely used in various areas such as artificial molecular machines, drug delivery materials and supramolecular polymers. We have devoted more than ten years to the study of recognition of crown ethers by organic guests and developed cryptands as a new type of hosts, increasing the host-guest association constants greatly. Now, we are focus on the study of functional supramolecular aggregates acting as stimuli-responsive supramolecular polymers, elastomers and self-healing materials, leading the development of crown ether-based materials.It is a convenient and effective way to introduce extra functional groups into the hosts to get host-guest systems with high affinities. By the introduction of more binding sites (more substituent groups or more chains), we can not only increase the association constants between the hosts and guests but also change the geometries of the binding systems. If we want to get macrocycle hosts with higher binding affinities for guests, both enough binding sites and proper cavity size of the hosts are needed. Furthermore, stimuli-responsive host-guest systems could be got by the introduction of new binding sites, which will do good to the construction of molecular machines and stimuli-responsive supramolecular polymers.During the construction of functional supramolecular materials, we are focusing on the properties from the noncovalent interactions which are different from conventional materials, such as intermolecular mechanical motion of mechanically interlocked molecules, the stimuli-responsiveness and self-healing properties of supramolecular gels. We constructed a daisy chain using the "threading-followed-by-polymerization" approach based on the host-guest interactions of dibenzo-24-crown-8and1,2-bis(pyridinium)ethane. It has a molecular weight of Mn64kDa, indicating that45repeating units exist in a single polymer chain. It is another example to demonstrate that dynamic supramolecular monomers (monomers with different parts linked by non-covalent bonds) can be used to construct mechanically interlocked polymers conveniently. We prepared two supramolecular gels by cross-linking a PMMA polymer with pendent dibenzo-24-crown-8moieties using two bisammonium salts with different end-groups based on the host-guest interactions of dibenzo-24-crown-8units and secondary ammonium salt moieties. Due to the intrinsic pH-controllable properties of the host-guest recognition motif, the two gels can both act as degradable materials triggered by pH stimuli. Moreover, the gels exhibit excellent self-healing properties which not only can be seen from our naked eyes directly, but also were fully studied by rheological data for many times. The study of pH-responsiveness and self-healing of supramolecular gels will undoubtedly shed light on the exploration of the properties of supramolecular cross-linked polymer and polymer gel networks acting as adaptive and smart materials.