Supramolecular Polymers Constructed From Pillararene-based Schiff-base Derivatives And Their Applications

Supramolecular chemistry is a new interdisciplinary subject that studies the complex and ordered molecular aggregates with specific functions formed by non-covalent bond interactions between molecules.Supramolecular chemistry originated from host-guest chemistry,and its development also largely depends on host-guest chemistry.As an important part of host-guest chemistry,macrocyclic molecules have gradually shown their infinite charm in the construction of organic functional materials.Among the numerous supramolecular macrocyclic compounds,pillararenes,as a new type of easy-to-functionalized macrocyclic host molecules,have received extensive attention due to their unique molecular structure and excellent host-guest chemical properties.It provides more possibilities for the preparation of organic functional materials and the development of supramolecular chemistry.Schiff-base are a kind of organic ligands containing C?N.The nitrogen atoms on the hybrid orbitals of the imine groups have lone pairs of electrons,which give them important chemical and biological significance.The introduction of Schiff-base into the pillararene system can obtain a series of pillararene derivatives with good coordination ability to metal ions,which is of great significance for expanding the application scope of pillararene derivatives.Therefore,the importance of Schiff base ligands in ion detection and supramolecular chemistry is important.The main research contents of this paper are as follows:In the first part of our work,we successfully designed and synthesized a salicylaldehyde azine-containing pillar[5]arene dimer(P5D)through the simple and efficient synthesis method of generating salicylaldehyde Schiff base.And through the host-guest recognition mechanism between it and the neutral guest(G)containing two cyano groups at both ends,a linear supramolecular polymer was further constructed.Due to the presence of the AIE group salicylaldehyde azine,the linear supramolecular polymer possesses strong fluorescence emission at high concentrations.Subsequently,Cu²⁺is further added.Since the salicylaldehyde Schiff base can coordinate with Cu²⁺,the linear supramolecular polymer is cross-linked to form a supramolecular polymer network.At the same time,due to the light-induced electron transfer mechanism triggered by copper ions,the fluorescence of the supramolecular polymer network is quenched.In addition,because cyanide is known to react with Cu²⁺to form very stable Cu(CN)₂species,the linear supramolecular polymer recovered after the addition of tetrabutylammonium cyanide(TBACN).Based on this,we successfully achieved the reversible crosslinking of supramolecular polymers and the reversible conversion of fluorescence properties through Cu²⁺and cyanide.This work reported for the first time a reversibly cross-linked AIE supramolecular polymer prepared from a Salicylaldehyde Azine-Containing Pillararene dimer,which enriched pillararene chemistry and successfully applied the system to ion detection.In the second part of our work,we introduced the cholesterol group into the pillararene chemistry by generating Schiff bases,and successfully designed and synthesized a new type of rigid Schiff base-bridged pillar[5]arene cholesterol derivative(P5A-Chol).And through the host-guest recognition mechanism between it and the neutral guest(K)containing two cyano groups at both ends,[3]pseudorotaxane was further constructed.Due to the existence of the Schiff base group,the[3]pseudorotaxane can be further cross-linked to obtain a three-dimensional supramolecular polymer network.More importantly,due to the introduction of cholesterol groups in pillararene chemistry,the supramolecular polymer network is endowed with unique liquid crystal properties.We firmly believe that this work opens up new prospects for the design of supramolecular liquid crystal materials while enriching pillararene chemistry.