Fabrication Of Stimuli-responsive Supramolecular Gels And Nanostructure Materials Based On Cyanostilbene Derivatives

Aggregation-induced Emission?AIE?effect refers to the phenomenon that the luminogen emits very weakly in the dilute solution or monodisperse state but is highly emissive in the solid or aggregated state.Because AIE compounds overcome the disadvantages of aggregation-caused quenching effect existed in most traditional?-conjugated molecules in solids,thin films or other aggregated states,they have been extensively developed as solid materials,liquid crystals,nanostructure materials,gels etc.And the materials are further applied in organic light-emitting diodes,sensors,optical waveguides,bioimaging and diagnosis,smart responsive materials?such as force,heat or light response?and so on.As one representative kind of these molecules,compounds based on cyanostilbene derivatives have attracted increasing attention and discussion in recent years.Since molecular structures of cyanostilbene derivatives are easy to be synthesized and can be modified on the benzene ring or double bond,they can meet various structural design requirements.As a result,they have great potential in different application fields.Our works mainly aim to construct smart stimuli-responsive supramolecular gels and nanostructure materials by modifying the molecular structure of cyanostilbene derivatives.Smart responsive supramolecular gels based on cyanostilbene derivatives can show remarkable fluorescence modulation when exposed to outer stimimuli.Achievement of well-defined,controllable,and reversible macroscopic response represents one of the most fascinating and challenging goals of current research based on above gel materials.Herein,a series of V-shaped molecular structures are designed?VOR-4,VOR-8 and VOR-12?based on an isophthalamide core decorated with two cyanostilbene units via amidic bonds and with a hydrophobic alkyl tail of different lengthes.The AIE supramolecular gel fabricated by VOR-8 shows smart bi-responsive properties.First,it can respond to light.Exposure to 365 nm irradiation will cause a gel-breaking phenomenon.Second,fumigation with TFA and TEA vapors induced the switching between the gel and solution state,with consequent fluorescence quenching and restoration,a cycle that can be repeated several times.The response of VOR-8 gels to to acidic TFA was found selective,as the exposure of the gel sample to other acid vapors?such as HCl,HBr,formic acid and acetic acid?did not arise any significant effect.CO₂ sensors based on fluorescent techniques have been drawing more and more attention.However,the strategies to achieve the sensing process are still very limited.Herein,we introduce a novel strategy for CO₂ sensing based on molecular recognition principles.In this work,the length of the alkyl chain on V-shaped structure is increased and compound VOR-16 is synthesized.The fluorescent CO₂ gas sensors have been achieved made of gel aggregates or a xerogel film of VOR-16.CO₂ sensing is realized through hydrogen bonding driven recognition of the CIL anion to VOR-16,where CIL was in situ formed by the reaction of CO₂ with diethyl-aimne.The combination of CIL anion with VOR-16 influenced the aggregated state of VOR-16,thus induced emission modulation.The xerogel film reaches a very high sensitivity and a low detection limit,as low as 4.5 ppm.Meanwhile,it allows a dual mode detection for monitoring CO₂concentration,both by emission quenching and emission modulation.For a smart or more controllable assembly,a sophisticated molecular design on cyanostilbene amphiphilic compounds that leads to an AIE system with a well-organized thermodynamic structure is not enough;for the further advancement,methodologies that enable the system to modulate between different structures by means of external stimuli are of equal importance.Herein,an ethylene glycol-based block was modified in to the V-shaped structure instead of alkyl chains and amphphilic compound VOEG is synthesized.A smart responsive system is achieved that can realize different assembling structures through UV light stimuli.The hot solution of VOEG in THF/water can form sky blue emissive microbelts after aging in the dark at room temperature.When the hot solution is firstly irradiated for 30 minutes at room temperature,nanoshepres with holes are obtained after aging in the dark.Besides,the two assemblies exhibited different performances and characteristics.For the moment,the correlations between molecular structures and gelation properties still remains to be insufficiently understood.Minor variety of molecular structures may bring about obvious promotions on gel materials.Herein,by utilizing glyoxamide,the methyl-pyridines with different nitrogen atom positions are modified onto cyanostilbene.CO-o-Py,CO-m-Py and CO-p-Py are synthesized.With unchanged main molecular structures,the tiny position differences of the nitrogen atom tremendously influence their gelation ability.And the construction of organogels,hydrogel induced by HCl and metallogels coordinated with Cu²⁺is achieved on one gelator CO-o-Py.In comparison to CO-o-Py,CO-m-Py can only form HCl induced hydrogel and CO-p-Py can form a strong blue fluorescent metallogel with HgCl₂.The response of CO-o-Py and CO-m-Py to HCl is selective,while HBr,HNO₃,H₂SO₄,H₃PO₄,HCOOH or CH₃COOH can not bring about the formation of hydrogels.Besides,a gradual transition to the Cu²⁺coordinated metallogel can be induced by adding a few drops of concentrated CuCl₂ aqueous solution on top of the CO-o-Py-DMSO/water organogel.Totally,we have realized smart responsive supramolecular gels and nanostructure materials by utilizing VOR,CO-Py and VOEG compounds.We believe that these results will broaden the applications of aggregation-induced emissive materials and provide new molecular design strategies for the development of cyanostilbene based structures.