Studies Of Rotaxanes And [c2]Daisy Chains Based On Benzo-21-Crown-7and Its Derivatives

During the past decades, supramolecular chemistry has developed rapidly with the purpose of mimicking nature and going beyond that to facilitate the construction of supramolecular structures with novel topologies and/or important functions. Host-guest recognition has played a significant role in the development of supramolecular chemistry. Based on macrocylic hosts and other moieties, different threaded structures, like (pesudo)rotaxanes, catenanes, daisy chains and supramolecular polymers, have been constructed.Rotaxanes, mechanically interlocked structures that contain macrocyclic molecules trapped by dumbbell shaped axles with bulky stoppers, have progressed from a kind of molecular architecture to a promising class of nanoscale devices. Benzo-21-crown-7(B21C7) has the smallest cavity threaded by secondary dialkylammonium salts. Derived from the small cavity of B21C7, it is easier to cap its pseudorotaxanes with phenyl rings to construct stable mechanically interlocked threaded structures. In order to find the smallest group to prevent the dethreading process, a series of ester units used as end groups of the axle component in B21C7-based threaded structures was introduced. They showed surprising gradual changes for the stability of these rotaxane-like entities. When the tail is an isopropyl group, a mechanically interlocked rotaxane can be constructed, which is stable even in extremely polar solvent at high temperature. The carbonyl group could slow down the dissociation process of the threaded structures and the alkyl tails endowed these structures further stability. As shown in the crystal structures of those B21C7-based threaded complexes, the small cavity of B21C7is almost filled by the alkyl axles, which means that even a slight size increase of the end groups may change the pseudorotaxanes into rotaxanes. Probably one of the smallest steric changes which can be made in a molecule is the replacement of hydrogen atoms by halogen atoms, which has been still rarely introduced into the structures of rotaxanes, either in the wheels or in the axles. It is well-known that fluorine is the most electronegative element and fluorine atoms are high in electron density. Besides, the van de Waals radius of chlorine is larger than that of fluorine. Herein, we choose two fluorocarbon groups and a chlorocarbon group to replace the alkyl groups on the ester units, and expect to find a new type of end groups for the construction of rotaxanes and enrich the variety of B21C7-based host-guest systems.A special case of mechanically interlocked macromolecules are daisy chains, coupling of a rotaxane thread to the encircling macrocycle. They have been often constructed from the dimerization of AB-type plerotopic monomers with two self-complementary units A (host) and B (guest). On the other side, nature efficiently and successfully generates intricate and highly complex functional architectures. In these biological systems, high-fidelity self-sorting is ubiquitous. The polymerization of heterodimer base pairs leads to the formation of the well-known and sophisticated superstructures of the DNA double helix, which can store information and allow the cell to replicate and transcribe them. The formation of specific heterodimers (AT and GC) relies heavily on self-sorting and requires the self-discrimination and the simultaneous recognition of the complementary. Four different but similar monomers were designed which are constructed from two different crown ethers, benzo-21-crown-7and dibenzo-24-crown-8, and two different secondary ammonium salts, BBA and DBA. Herein, we report heterodimer [c2]daisy chains that self-sort and investigate the intrinsic recognition and sorting processes of the formation of the daisy chains.Gels are everyday materials applied in a widerange of different technologies we are all familiar with their use in cosmetic products, lubricants and foodstuffs. Recently, much attention has begun to focus on small molecules, which can also form gel-phase materials. These molecules are called low molecular weight organic gelators (LMOGs) We designed a series of gelators based on crown ether derivatives. We want to find out the mechanism through which such molecular gels should be able to gelate large volumes of solvent and develop a fundamental understanding of the factors which affect the gelation processes.