Self-assembly, Fluorescence Sensing And Mechanochromism Properties Of Cyanostyrene Derivatives

Recently,functional external responsive materials have received widespread attention from the scientific community.Supramolecular gels,an important branch of supramolecular chemistry,have attracted natural attention due to their natural thermal stimulus response.These gelators usually self-assembled into nano-aggregates with different morphologies by weak intermolecular interactions.These weak interactions can easily change and give the supramolecular gels the ability to respond to external stimuli,especially the fluorescenceπ-gels.Moreover,up to now force-induced fluorochrome organic materials that change fluorescence intensity and color by mechanical stimulation have been widely studied due to their potential application prospects.However,organic materials with simultaneous gelling ability,gas fluorescence sensing,and mechanochromism（MFC）have rarely been reported.This paper is based on the design and synthesis of organic low molecule gels which contains cyanostyrene groups.The introduction of functionalized groups such as anthracen,acridine and benzoxazole into the molecular structure to achieve not only the ability of the molecule to gel,but also have an intelligent response to acids and organic amines,as well as mechanical forces.Some results have been obtained,and outlined below:（1）We designed and synthesized PC2AN and PC3AN,which are derivatives of N-dodecyl-L-phenylalanine amide and cyanostyrylhydrazine,respectively,bridged by succinyl and glutaryl groups.The effects of bridging groups on their self-assembly and mechanochromism were investigated.Fortunately,the two compounds formed gels in certain solvents and also exhibited gelation-induced emission enhancement.Moreover,PC3AN possessed better gel abilities than PC2AN.Spectrum showed that the hydrogen bonding between aromatic amide groups and theπ-πinteraction in the PC3AN gel are stronger than those in the PC2AN gel.Moreover,solid PC3AN did not change its emission color after applying mechanical force.Interestingly,PC2AN exhibited significant MFC.Thus,only one methylene group has significant effects on gelation ability and MFC.（2）We designed and synthesized succinyl and glutaryl groups as bridging bonds to link N-dodecyl-L-phenylalaninamide and cyanostyryl of acridine derivatives PC2VA and PC3VA.Among them,the introduction of an acridine unit not only provides a binding site that responds to the volatile acid vapor,but also reduces the HOMO energy level of the molecule,making the molecule potentially responsive to organic amine vapor.Research showed,the presence of the cyano group caused PC2VA and PC3VA showed great the AIE and MFC active.In addition,although the two compounds can form organogel,only the gel of PC2VA can form a uniform xerogel film that can be quenched by volatile acid and aromatic amine gases.The detection limit（DL）of aniline reaches 1.3mg/m³.Moreover,the DL for trifluoroacetic acid（TFA）is low and determined to be 2.3mg/m³.（3）Then,A cyanostyrene derivative 3C16PBCP consists of a fluorophore with benzoxazole and galunamide unit was designed and synthesized to realize dual response to acid vapor and mechanical force.3C16PBCP can form gels in many solvents,especially the minimum gelation concentration in DMSO is as low as 2.1×10^-4 mol/L.Photophysical studies have shown that the driving forces for gel formation are hydrogen bonding interactions between amide groups,π-πinteractions between aromatic moieties,and van der Waals forces of aliphatic alkyl chains.The fluorescence of xerogel film is sensitive to TFA vapor.The DL is as low as 70 ppb for TFA.The intermolecular hydrogen bonds and pristineπ–πinteraction of 3C16PBCP solid were destroyed by mechanical force.Leading to the fluorescent color change from green to orange.The results showed that the molecules had a double response to acid vapor and mechanical forces.