Synthesis And Photoresponsive Properties Of Cyanostilbene Derivatives

Smart responsive materials that exhibit mechanically dynamic properties upon external stimuli(e.g.,heat,pressure,light and solvent atmosphere)have been the focus of broad and intense research owing to their promising applications to actuators,molecular robotics,artificial muscles,and biomimetics.Various photomechanical materials,such as polymers,elastomers,liquid crystal materials and molecular crystals,have been widely reported.Photomechanical molecular crystals have a wide range of potential applications in intelligent switches,mechanical actuators,artificial muscle,optical sensors and light capture due to the advantages of fast response,short recovery time,high Young’s modulus and highly ordered structure.However,photomechanical response materials reported at present mainly focus on polymers and liquid crystals.The exploration of the photomechanical motion of molecular crystals is still very limited,this field is still in a state of discovery.Therefore,it is of great scientific significance and application value to design novel organic molecules with simple structure,high efficiency photoactivity and explore molecular crystals with excellent photomechanical properties.According to literature investigation,molecular crystals with excellent photomechanical properties should have the following characteristics: 1.Highly photoactive functional groups.2.Effective stacking and arrangement of molecules in crystals.In this thesis,a series of compounds with photomechanical response behaviors in crystal state were synthesized by functionalized modification of cyano-stilbene molecules.Based on theoretical simulation and performance characterization,the relationship between molecular structure,molecular aggregates and material properties was revealed,and the following innovative research results were obtained:1.Cyano-stilbene derivatives were designed and synthesized.Cyano-stilbene compounds with simple and novel structure were synthesized by linking cyano-stilbene with cyclohexane through ester group using cyano-stilbene as parent nucleus and C=C as the active group for photochemical reaction.The weak π-π stacking between molecules is used to achieve micro-regulation of molecular properties.However,weak van der Waals forces impair the ability of organic molecules to form a specific shape during crystallization.Controlling the same molecule to achieve both flexible and rigid motions(disintegration,cracking,twisting and bending)remains a challenge.In the process of experimental exploration,we are delighted to find that by controlling different growth conditions,CSHe microcrystals with different shapes can be obtained.Moreover,microcrystals with different shapes exhibit a variety of photomechanical motion behaviors under ultraviolet light irradiation.In conclusion,we explored the relationship between molecular structure and photomechanical effects based on the cyano-stilbene derivative(CSHe).The application range of cyano-stilbene molecules in the aggregate state has been expanded.This work developed diversified shape-dependent photomechanical motions based on a cyano-stilbene derivative shedding light on developing the innovative photomechanical materials.2.Cyano-stilbene derivatives were selected as parent nucleus because of their excellent aggregation induced emission(AIE)properties and potential [2+2] cycloaddition reactivity in solid state.By a simple and precise design strategy,one of the benzene ring was replaced by a thiophene in the cyano-stilbene molecule,and isopropyl was introduced at both ends of the esterification reaction to regulate the packing model of the molecule.Alkyl engineering affects the molecule packing model,resulting in different photophysical and photochemical properties of the molecules in the solid state.The dynamic photomechanical and static fluorescence properties of molecular crystals were studied by ingenious alkyl functionalization.The advantages of rapid light response behavior and the visualization of the obviously changed fluorescence endow the molecular crystal with great potential for the design of high-performance actuators and two-mode UV detection based on crystal engineering.