Preparation And Properties Of Cyanostilbene Photoresponsive Supramolecular Self-assembly System

In recent years,photoresponsive supramolecular self-assembly materials have attracted extensive attention from scientists due to their remarkable application prospects in the fields of photo-operated mechanical motion machines,logic gates,information recording and storage,multi-photon devices,and photo switches.However,the response behavior to light in most supramolecular self-assemblies is too simple.As multiple functional materials have become more and more important nowadays,it is obvious that a single structure or property change cannot meet the demand of diversified performance regulation.Cyanostilbene,as a typical photoresponsive group,can satisfy the above requirements well.The aggregation structure of cyanostilbene is sensitive to the external environment and possesses aggregation induced emission enhancement(AIEE)properties,which endows supramolecular self-assemblies based on cyanostilbene backbones with special stacking morphologies and fluorescent properties.Therefore,during the photoisomerization of cyanostilbene,the newly generated products have different structures,and the packing modes of the self-assemblies make a difference with it.Correspondingly,the fluorescent properties of the self-assemblies are affected by a variety of factors,such as the degree of photoisomerization and the self-assembly behaviors,so as to produce diversified changes.To sum up,constructing supramolecular self-assembly system with cyanostilbene as the core and exploring the influence of its light response behavior on the self-assembly structure,fluorescence and other properties are not only of academic interest but also of practical application prospects.Firstly,we introduce amide bond to cyanostilbene backbone,changing the position of the cyano group,and design and synthesize four compounds,which named?-PBA,?-PBA,?-BTTPA and ?-BTTPA.By the virtue of the strong hydrogen bonding driving force provided by multiple amide bonds,the effects of molecularstructure and photoinduced trans-cis isomerization on self-assembly morphologies and fluorescence properties are investigated.Studies have shown that different cyano positions influence the fluorescent properties of cis-isomers in the monomer state.In solution state,the fluorescence of ?-PBA and ?-BTTPA decreases,while that of?-PBA and ?-BTTPA increases upon UV light irradiation.At the same time,the different positions of cyano groups also affect the self-assembly properties of?-BTTPA and ?-BTTPA,with the former forming micron-level ribbons like structures emitting pure blue emission,while the latter forming nano-level fibrous structures emitting blue-green emission.Driven by trans-cis isomerization,both of them form similar size-like spherical assemblies accompanied with fluorescence quenching.Moreover,the spheres like self-assemblies after illumination have stronger hydrophobic properties.This work provides the foundation for the development of multiple functional materials.Secondly,we probe the gelation ability,fluorescent properties and light response behaviors of ?-BTTPA in gel state.It is found that ?-BTTPA can form two kinds of gels with different stacking manners in the mixed solvents of dimethyl sulfoxide and water.Depending on the water content,one kind of gel emits green fluorescence(G-gel),while the other one emits blue fluorescence(B-gel).In addition,upon UV light irradiation,sensitive gel-to-sol transition accompanied by fluorescence quenching is observed in G-gel due to the trans-cis isomerization reaction of cyanostilbene.But B-gel exhibits excellent photostability on account of its compact packing structures.These properties have been further applied to the graphic photoinduced confidentiality pattern.This work not only fully explains the relationship between molecular arrangement and material properties but also sets the tone for the development of smart responsive supramolecular materials.