Preparation And Properties Of Supramolecular Gel Based On Pillar[n]arenes

Supramolecular chemistry is an emerging science formed by the intersection of chemistry and multiple disciplines.It is defined as“beyond the chemistry of molecules”,which is designed to construct a complex with ordered and uniquely functional chemical assembly system formed by molecules and molecules or molecules and ions via non-covalent interaction.Due to its unique structural properties,macrocyclic compounds have attracted much attention in the field of research and development of supramolecular assembly as well as polymer materials,the discovery of each macrocyclic compound has greatly promoted the development of supramolecular chemistry,and a series of related literatures have been reported.The fifth-generation of macrocyclic host compound named pillar[n]arenes,which was reported by Japanese scientist T.Ogoshi for the first time in 2008.Since then,the research on pillararenes-based supramolecular chemistry has attracted increasing scientists’attention and have been widely studied.Pillar[n]arenes possesses a rigid pillar structure which hydroquinone as the repeating units connected to each other by methylene bridges at para-positions.Due to its special symmetrical pillar architecture,electron-rich cavity,mild synthetic conditions,desirable modification and versatile host and guest performance.At the same time,pillar[n]arenes have also been given various self-assembly driving forces,such as hydrogen bonding,cation???π,π???π,metal-ligand coordination,van der Waals forces,and hydrophilic and hydrophobic effects.These wonderful characteristics giving pillar[n]arenes outstanding abilities to selectively bind different kinds of guests and providing a new platform for the construction of various supramolecular systems including chemical sensors,supramolecular polymers,artificial transmembrane channels,and molecular machines.This thesis focuses on the research of ion/molecular recognition,adsorption and separation as well as stimuli responsiveness of pillar[n]arene-based supramolecular polymer materials.This paper is divided into four parts:In the first part,we summarized recent studies of pillar[n]arene-based supramolecular polymer gels.In this section,we divided the gel into two categories,namely hydrogel and organogel from the perspective of what kind of liquid in the gel contains.The former is further classified into a one-component organogel,a two-component organogel,and a multi-component organogel according to the number of gel-forming components.The latter fabricated with pillar[n]arenes was further divided into supramolecular hydrogels based on low molecular weight compounds and hydrogels constructed with polymeric networks.Meanwhile,we also briefly introduced the applications of supramolecular gels based on pillar[n]arenes in ion/molecular recognition and detection,adsorption and separation,drug release,self-healing,electrical conductivity and so on.In the second part,we have designed and fabricated a novel supramolecular organic framework（SOF-AMP）with bis-naphthalimide modified pillar[5]arene and quaternary ammonium functionalized pillar[5]arene,which could further form a pleasant supramolecular organic framework gel（SOF-AMP-G）in cyclohexanol via multi-self-assembly driving forces.The SOF-AMP-G not only exhibited good thermal-responsiveness,but also could successively ultrasensitive fluorescence response Fe³⁺and H₂PO₄^-by the competition of cation???πandπ???πinteractions in gel states.Furthermore,prepared xerogel can also efficiently remove iron ions,and the adsorption rate to Fe³⁺is 99.85%.It is worth noting that this supramolecular organogel can also be used to construct logic gates for ultrasensitive response to Fe³⁺and H₂PO₄^-,which greatly expands the application range of supramolecular polymer materials based on pillar[n]arenes.In the third part,we reported a novel pseudorotaxane（WP5-PN）which was constructed from a water-soluble pillar[5]arene（WP5）and naphthalimide derivative（PN）via multiple non-covalent interactions.The obtained supramolecular assemblies were able to change into a supramolecular polymer gel（WP5-PN-G）and show AIE properties in DMSO–H₂O binary mixture solution.Interestingly,the resultant supramolecular polymer gels exhibited external stimuli-responsiveness to different parameters,such as temperature,acid/base,competitive guest molecule and mechanical stress.In addition,the WP5-PN-G not only shows ultrasensitive response for Fe³⁺and F^-as well as Cu²⁺and CN^-through the competition of cation???πand exo-wallπ???πinteractions,but also can effectively remove Fe³⁺and Cu²⁺from an aqueous solution.Simultaneously,thin films based on the supramolecular polymer gel and metallogels were prepared,which were confirmed to be a handy test tools for detecting Fe³⁺and Cu²⁺as well as F^-and CN^-,respectively.It suggested that the WP5-PN-G has potential applications in multi-analytes detection and separation as well as fluorescent display materials.In the fourth part,we designed and synthesized a novel functionalized pillar[5]arene-based gelator（MP5）,which could further self-assemble into a supramolecularπgel（MP5-G）byπ???πstacking interactions among the naphthalene rings and the pillar[5]arene groups.The naphthalimide moiety in MP5 not only be used as theπ???πinteraction site but also as a fluorophore,the MP5-G formed at high concentration has strong yellow fluorescence.This supramolecularπgel also exhibited favorable thermal-responsiveness,acid and base-responsiveness,cation and amino acid-responsiveness.An alternating fluorescent"off-on-off"phenomenon was accomplished by reversibly heating and cooling the solution of MP5-G.Interestingly,MP5-G could successively ultrasensitive detection to Fe³⁺and L-Cys by the competition ofπ???πstacking and cation???πinteractions in the gel state.Moreover,MP5-G shows excellent recyclable separation properties for Fe³⁺.More importantly,the‘‘competition ofπ???πstacking and cation???πinteractions’’strategy in supramolecularπ-gels provides a novel and facile methodology to construct smart stimuli-responsive supramolecular materials.