Pillararenes-basecd Self-assemblies And Their Applications

The emergence of any new macrocycles can promote the development of supramolecular chemistry.Pillar[n]arenes,recognized as the fifth generation of macrocyclic host molecules,have become star receptors in the supramolecular community since their first synthesis in 2008.Different from traditional macrocycles,such as crown ethers,cyclodextrins,calixarenes and cucurbiturils,pillar[n]arenes possess a perfectly symmetric structure,providing a promising platform for the construction of diverse supramolecular systems.Pillar[n]arenes-based host-guest complexes have been applied in various fields including supramolecular polymers,light-harvesting systems,biomedical materials,adsorptive separation and surface modification.This dissertation is mainly focused on the stimuli-responsive self-assemblies based on pillar[n]arenes and their related applications in sensors,molecular switches and biomaterials.In the first part,we firstly reported a dual-responsive supra-amphiphile based on a water-soluble pillar[7]arene(WP7)and a NDI-containing guest(G).Size-selective complexation was achieved between WP7 and G,because the size of NDI was suitable for the cavity of pillar[7]arenes rather than pillar[5]arenes and pillar[6]arenes.Moreover,the supra-amphiphile constructed by WP7(?)G exhibited dual-responsiveness.The morphologies of the self-assemblies formed from the supra-amphiphile could be regulated by changing the solution pH or adding a-CD.On one hand,the nanofibers formed by G and the solid nanospheres self-assembled from WP7(?)G could be reversibly adjusted by changing the solution pH due to the pH-controlled association and disassociation between WP7 and G,which resulted from the deprotonation and protonation of WP7.Furthermore,the nanospheres transformed into nanoparticles upon addition of a-CD due to the hydrophobic interactions between a-CD and the alkyl chain,resulting in the formation of a water-soluble hetero[3]pseudorotaxane.This dual-responsive supra-amphiphile can be used to fabricate nanostructures which have potential applications in biological/pharmaceutical fields,such as drug delivery and controlled release.In the second part,we synthesized a TPE-containing conjugated polymer with pendent pillar[5]arene units(P5-TPE)and a symmetric BB type crosslinker(G)to construct a supramolecular polymer network through pillar[5]arene-based host-guest interactions.The prepared supramolecular polymer network not only retained inherent fluorescence emission of the TPE-containing conjugated polymer but also activated its aggregation induced enhanced emission(AIEE)feature,leading to a brighter fluorescence emission.The crosslinking and decrosslinking processes of the supramolecular polymer network could be controlled by external stimuli including temperature and addition of competitive guests,consequently leading to changes of fluorescence intensity.Moreover,the fluorescent supramolecular polymer network could be further used for detection of nitro-compound explosives,exhibiting its practical application in our daily life.This work is the combination of supramolecular chemistry and conjugated polymer science and the co-built supramolecular network system may pave a new way to develop novel multi-functional fluorescent materials in the future.In the third part,we first developed a novel ion-pair recognition motif based on a perbromoethylated pillar[5]arene(BrP5)host and a 1,4-dimethylpyridinium iodide(1I)guest.Experimental results demonstrated that the host-guest complex had a[2]pseudorotaxane structure with high binding affinity in solution,which was attributed to dual recognition effects.On one hand,strong charge-transfer interactions existed between the electron-rich cavity of BrP5 and the cationic pyridinium ring.On the other hand,hydrogen bonds between iodide anion and hydrogen atoms on the bromoethyl chains of BrP5 also contributed.Furthermore,a novel[3]pseudorotaxane BrP52(?)2I was constructed by introducing a bispyridinium salt 21 with two cationic pyridinium binding sites in solution and in the solid state.These interesting pseudorotaxanes may be further used as intermediates to fabricate sensors,supramolecular polymers and molecular switches.In the fourth part,we designed and synthesized a supramolecular photosensitizer containing a water-soluble pillar[5]arene(WP5)and an AIEgen photosensitizer(G).G is an efficient photosensitizer with a higher ROS productivity than commercial dye,chlorin e6.Expectedly,G can complex with WP5 to form a pseudorotaxane structure.By the formation of host-guest complex,the photosensitizing effect of the supramolecular photosensitizer WP5(?)G was shut down,greatly reducing the dark and light toxicity.Interestingly,benefitting from the pH-responsiveness of WP5,the binding site between G and WP5 was changed in acidic environment through a shuttle movement.The fluorescence and ROS generation of this pseudorotaxane can be switched on at pH 5.0.In vitro experiments demonstrated that the fluorescence can be selectively turned on in lysosome,indicating the PDT efficacy can be preserved in cancer cells.Therefore,this supramolecular photosensitizer offers a new paradigm for the construction of ROS switch by using supramolecular method,which provides novel opportunities for clinical PDT treatment.