Host-Guest Recognition Based On Pillar[6]arenes And Their Applications

Supramolecular chemistry,as a new discipline,has developed rapidly and obtained a rich connotation of the systematic results.It has attracted considerable attention from the scientific communityto design and prepare macrocyclic molecules because of they play important roles inthe development of supramolecular chemistry.The design and synthesis of new macrocyclic host molecules represent one of the challenging research areas.There has been four representative generations of macrocyclic molecules,which are crown ethers,cyclodextrins,calixarenes and cucurbiturils.In 2008,a new class of macrocyclic hosts was reported,which is known as "pillar[n]arene".pillararenes have played an important role in supramolecular chemistry due totheir special structure and excellent host-guest properties,Pillar[5]arenes and Pillar[6]arenes have been studied more extensive than other pillararenes because of their easier synthetic routes and higher yields.Moreover,most of the methods of functionalization of pillararenes can only be suited for pillar[5]arenes.Therefore,pillar[5]arenes are the most popular among the other pillararenes.However,the cavity size of pillar[6]arenes is larger than pillar[5]arenes,which leads to the different properties of pillar[6]arenes,such as host-guest chemistry.The study of pillar[6]arenes will enrich the field of pillararene chemistry.This dissertation is mainly about host-guest molecular recognition based on pillar[6]arenes and their related applications.In the first part,a photo-controllable threading-dethreading recognition motif in waterbased on a water-soluble pillar[6]arene host and an azobenzene-containing guest was constructed.Then photo-responsive self-assembly in water was achieved based on the photo-controllable threading-dethreading switch between the water-soluble pillar[6]arene and azobenzene-containing amphiphilic guest.The azobenzene group can undergo photoisomerization,causing the different binding modes with water-soluble pillar[6]arene and different self-assembly morphologies.The guest itself self-assembled into solid nanoparticles before complexation with the host.Upon addition of the host,vesicles were obtained.Reversible transitions between vesicles and solid nanoparticles were controlled by UV and visible light irradiations due to the photo-responsiveness of the guest.Thus the photo-responsive self-assembly system was realized.In the second part,a new dual-responsive host-guest recognition motif based on a naphthalene group-modified azobenzene-containing guest and a water-soluble pillar[6]arene was constructed in aqueous media.Importantly,we modified the azobenzene guest,causing that the host-guest complexation between the water-soluble pillar[6]arene and the azobenzene-containing guest could be destroyed by UV light,which is different from the work in the first part.It improved the sensitivity of the system to UV light stimuli which is of great importance to construct stimuli-responsive supramolecular systems.In addition,the host-guest system was also responsive to pH stimuli because of the sensitivity of the water-soluble pillar[6]arene to pH changes.Moreover,the dual-responsive host-guest system was used to construct a dual-responsive self-assembly systems.The guest itself self-assembled into nanosheets,while the bola-type supra-amphiphile based on the host and guest self-assembled into vesicles.Reversible transitions between vesicles and nanosheets were achieved due to the photo-responsiveness of the guest and pH-responsiveness of the host.Moreover,the dual-responsive self-assembly system was used for controlled release.This stimuli-responsive host-guest system can enrich the field of pillararene chemistry.In the third part,we fabricated a new host-guest recognition motif based on a mono(ethylene oxide)substituted pillar[6]arene and an azastilbene derivative guest,(E)-4,4'-dimethyl-4,4'-diazoniastilbene dihexafluorophosphate,which can undergo UV light-induced isomerization.When the guest was in its trans state,it can complex with the host to form a[2]pseudorotaxane,while its cis state cannot,indicating that UV light can completely destroy the host-guest interaction.It is different from the work in the second part that there is no tedious organic synthesis.More importantly,the cis state guest is much more stable than cis-azobenzene group,facilitating the characterization process.In the fourth part,a host-guest recognition motif based on a water-soluble pillar[6]arene and an azastilbene derivative,(E)-4,4'-dimethyl-4,4'-diazoniastilbene diiodide,was constructed in water.Then we used the water-soluble pillar[6]arene to successfully control the photohydration of the azastilbene derivative in water as a"protective agent".1H NMR,UV-vis absorption spectroscopy and transmission electron microscopy were carried out to investigate the process.In this work,pillararene was successfully used in controlling photochemistry,extending the application area of pillararene chemistry.