Recognition,Assembly,and Construction Of Dynamic Materials Based On Pillararenes

It is of great importance for the study of macrocycle-based recognition and assembly,and subsequent construction of supramolecular dynamic materials in supramolecular chemistry.In recent years,supramolecular chemists have paid more attention to the study of supramolecular dynamic materials since the overlap between supramolecular chemistry and other subjects such as life science and material science.Thanks to the reversibility and controllability of host-guest interactions,macrocycles begin to play a significant role in scientific frontiers including drug delivery,dynamic materials and bioprobe.Pillararenes are a new type of macrocycles with unique structures and excellent host-guest properties.Besides,pillararenes possess rigid skeletons,and are facile to be functionalized,including per-functionalization,mono-functionalization,and multi-functionalization.These characteristics of pillararenes enable them suitable as a platform for the fabrication of various functional systems and dynamic materials.Therefore,this dissertation focuses on the ion pair recognition and self-assembly of pillararenes,and subsequent construction of photo-responsive liquid crystal materials and hydrogels with controllable swelling behaviors based on pillararenes.Part 1.We designed to introduce a urea group to the pillar[5]arene skeleton and thus obtained a heteroditopic receptor.Thus the pillar[5]arene cavity could form host-guest complexes with alkylammoniums,and meanwhile the urea group could bind counterions(anions).This cooperative binding could effectively weaken the ion pairing between alkylammoniums and counterions,which therefore greatly improved the binding affinity between pillar[5]arene and alkylammoniums.We employed NMR and ESI-MS to identify the ion pair recognition phenomenon.By nonlinear fitting the association constants between the receptor and butylammonium with Cl-,Br-,and CF3COO-as the counterions could be obtained,respectively.It was found that the promotion of the binding affinity to butylammonium chloride was the strongest for the pillar[5]arene receptor after the introduction of urea group(71 fold).Therefore,the strong hydrogen bonding between urea and counterion was favorable to weaken the ion pairing,which was beneficial to the inclusion of the cationic guest into the pillar[5]arene cavity.Part 2,The unusual self-assembly phenomena of mono-urea-functionalized pillar[5]arenes were investigated.When the substituent of urea was an aromatic group,the self-assembly of the mono-urea-functionalized pillar[5]arene based on host-guest interactions could not be observed due to the steric effect.However,when the substituent of urea was alkyl chains,the self-assembly of the mono-urea-functionalized pillar[5]arenes could be formed by the threading of the alkyl chains into the pillar[5]arene cavity.The X-ray analysis revealed that the assembly in solid state was a cyclic dimer with abnormal urea behaviors.In the further study,we found that the mono-urea-functionalized pillar[5]arenes could form self-inclusion structures in solution(nonpolar solvents)by 1H NMR,DOSY,ESI-MS,IR,and theoretical calculations.Because of the reversibility of host-guest interactions,the formation and dissociation of the self-inclusion structures in solution could be tuned by changing the polarity of the solvent.Furthermore,the mono-urea-functionalized pillar[5]arenes showed very weak response to anions due to the formation of self-inclusion structures,which made the urea group partly included into the pillar[5]arene cavity.Part 3.We designed to introduce azobenzene groups to the pillar[5]arene skeleton to prepare photo-responsive liquid crystals.Two precursors,a pillar[5]arene with ten alkynyl groups and an alkyl azide with an azobenzene group were prepared and subsequently underwent the efficient click reaction with CuSO4·5H2O/sodium ascorbate as the catalyst(Yields:ca.30%).The structure and monodispersity of the target products were identified by 1H NMR,13C NMR,elemental analysis,IR,and HPLC.DSC and POM revealed the very wide temperature range lamellar liquid crystalline mesophases of the target products.The shorter flexible spacers between azobenzene groups and pillar[5]arene skeleton could make the molecule more rigid,and thus led to the wider temperature range liquid crystalline mesophases.In solid films the UV-vis absorption peak of the target product exhibited only a weak hypsochromic shift compared with its corresponding UV-vis absorption peak in solution.This spectroscopic phenomenon indicated that the rigid pillar[5]arene skeleton could afford effective free volume for the isomerization of azobenzene groups,and thus remarkably reduced the strong H-aggregation of azobenzene groups in solid films.Part 4.We fabricated a smart hydrogel with multi-stimuli responsive swelling behaviors based on the host-guest interaction between water-soluble pillar[6]arene(WP6)and ferrocene.Polymer networks with polyacrylamide/polyacrylate as the main chain and ferrocene groups on side chains were prepared,which showed low swelling degree in pure water due to the strong hydrophobicity of ferrocene groups.When the hydrogel was immersed in WP6 aqueous solution,it could be greatly swollen,which was an approximately 11-fold promotion in weight compared with that in pure water.It was because the inclusion complexes between WP6 and ferrocene groups in the hydrogel were formed,which transformed the hydrophobic ferrocene groups to hydrophilic moieties and meanwhile generated strong electrostatic repulsion between polymer chains due to the negatively charged carboxylates of WP6.In particular,the well-swollen hydrogel showed good responsiveness to multi-stimuli including temperature,pH,redox,and competitive guests by tuning the dissociation/formation of WP6-ferrocene inclusion complexes or the strength of charges on polymer networks.More importantly,potential application of such a smart hydrogel in controlled drug release was investigated as well.In summary,this dissertation has investigated the ion pair recognition and self-assembly phenomena of mono-urea-functionalized pillar[5]arenes,the construction of photo-responsive liquid crystalline materials based on pillar[5]arene skeleton,and the fabrication of a smart hydrogel with multi-stimuli responsive swelling behaviors based on the host-guest interaction between WP6 and ferrocene.These researches will pave a way for the further study of functional systems and dynamic materials based on pillararenes.