Self-assembly And Application Of A Novel Monofunctional Modified Pillar[5] Arene

Supramolecular chemistry is a new science born in the 20th century.Compared with traditional chemistry based on covalent bonds,the main research objects of supramolecular chemistry is the non-covalent bond such as metal-coordination bonds,hydrogen bonds,electrostatic,hydrophilic and hydrophobic.With the in-depth study of supramolecular chemistry,supramolecular assembly with non-covalent bond interactions between molecules as the core has become the main research direction in the field of supramolecules.Supramolecular assembly is a process in which two or more molecules form ordered aggregates under the interaction of non-covalent bonds.Affected by the non-covalent bond interaction mode and the environment,molecular aggregates can exhibit rich assembly morphologies such as spherical,sheet,fibrous,or three-dimensional network.At the same time,based on the strength of non-covalent interactions that are susceptible to different environmental factors,supramolecular assembly can produce dynamic changes in different states.Inspired by these phenomena,supramolecular assembly has been continuously developed in the fields of liquid crystal display,gas adsorption,drug delivery,and cell imaging,and has become an important branch of supramolecular chemistry.According to the basic characteristics of the building blocks of supramolecular self-assembly system,supramolecular self-assembly can be divided into host-guest self-assembly and small molecule ordered self-assembly.Compared with the ordered self-assembly of small molecules,the host-guest self-assembly is mainly based on the process of forming a series of ordered aggregates based on the cation···?,hydrophilic,hydrophobic,and electrostatic interactions between the host like cyclic molecule and the small molecule guest.The introduction of host like cyclic molecules not only increases the mode of interaction between molecules,but also enriches the research content of the ordered assembly system of small molecules.At the same time,the special cavity structure of the host and the specificity of the host-guest interaction promote the assembly structure.It has played an important role in biology and materials,and promoted the continuous development of host-guest chemistry.As an important part of the host-guest self-assembly,the development of supramolecular macrocyclic compounds such as cyclodextrin,calixarene,columnarene,etc.has greatly promoted the research boom in the host-guest field.Among them,the supramolecular ring represented by pillararenes Since it was first reported by Japanese scientist Tomoki Ogoshi in 2008,due to its simple preparation method,easy functional modification,and electrically-rich cavity structure with adjustable size,it has been used in molecular machines,supramolecular polymers and supramolecular condensation.Glue has been extensively studied.Based on the above background research,this paper mainly describes the design of a new type of monofunctional modified pillar[5]arenes,and studies the dynamic characteristics of its environmental response.1)Through a series of systematic synthesis,monofunctional modified pillar[5]arene was prepared.Based on the host-guest interaction between pillar[5]arene and pyridine salt,we further combined it with triphenylamine derivatives with pyridine units to obtain a solvent-responsive dendritic rotaxane molecule H4.Through ¹H NMR,²D ¹H-¹H NOSEY,2D ¹H-¹H COSY and 2D¹H-¹³C HSQC,a series of NMR spectrums show that the dendrimer molecule H4exhibits the properties of a reversible molecular switch under solvent stimulation.In chloroform,the dendrimer molecule H4 exists as a self-inclusion assembly structure;in DMSO-d₆,due to the destruction of the host-guest interaction by the strong polarity of the solvent,the rotaxane H4 exists in the form of fully extended molecules.This solvent-responsive rotaxane structure provides ideas for the design of other new functional self-assembled supramolecular systems.2)Based on previous work,we successfully constructed a dendrimer T5 with an amide group by connecting an amino-modified monofunctional pillar[5]arene withacarboxyl-modifiedtriphenylaminederivative.Using2,4-dihydroxybenzaldehyde,7-bromoheptonitrile and hydrazine hydrate as raw materials,a fluorescent guest molecule D2 of salicylaldehyde azide was designed and synthesized.In chloroform,through host-guest and intermolecular hydrogen bonding,dendrimer T5 and AIE guest molecule D2 can be assembled into an ordered fluorescent hyperbranched polymer.In addition,at high concentrations,the polymer can form the supramolecular gel.Because the hyperbranched polymer is endowed with AIE characteristics by the salicylaldehyde azide group,as the concentration of the host T5 and the guest D2 in chloroform increases,the salicylaldehyde azide group aggregates under the action of the host and guest of the aromatic hydrocarbon in the pillar[5]arene,The fluorescence emission is enhanced,when Cu²⁺is added,the fluorescence is quenched.This self-assembled supramolecular polymer can be used not only as a new type of fluorescence sensor for detecting Cu²⁺,but also as an ideal candidate for other advanced materials such as metal gels,sensors and adaptive coatings.