Design,synthesis And Applications Of Photo/acid-responsive Dyes

Responsive materials are a new type of functional materials that can respond to external stimuli such as light,force,temperature,humidity and pH.It is widely used in chemical sensors,self-healing materials,data storage,biomedicine and other fields.Organic dye molecules commonly used to construct responsive materials include azobenzene and spiropyran,etc.However,the stimuli-responsive behaviors of these dye molecules are confined to the monomeric state in solution or polymer film,which cannot occur in the aggregation state,greatly limiting the application of responsive materials.Thus,it will be an innovative and challenging subject to realize the efficient stimuli-responsive ability in aggregation state or solid state,to expand their application scope.In this paper,spiropyran/azobenzene dye molecules were optimized to synthesize a series of compounds that responded to light/acid in the aggregation state.Together with theoretical simulation and properties characterization,the relationship between molecular structure,molecular aggregation and material properties was revealed.The research contents are as follows:1.In order to obtain a turnable morphology,spiropyran S1 modified by carboxyl group was designed and synthesized.Carboxyl group provided hydrogen bonding for driving force of self-assembly,and the hydrogen bonding could also be destroyed by acid.The acid-responsive properties of S1 were then studied.When acetic acid was added to S1 solution,S1 changed from ring-closed state to ring-open state,and the solution changed from colorless to red.Further invetagation on the morphology of S1 showed that spiropyran presented a spherelike structure in methanol.After the addition of acetic acid solution,the morphology of S1 turned into a rod-like structure.The hydrogen bonding in S1 plays an important role in the regulation of the assembly morphology.After the addition of acetic acid,the hydrogen bonding of S1 was destroyed and SP isomerized to MCH+,eventually resulting in a strong π-π stacking and rod-like morphology.In a word,pH-responsive S1 bearing carboxyl groups can undergo a large morphology variation from sphere to rod-like structure by acid-adjustment.,showing the application of spiropyran molecule in the preparation of smart nanomaterials.Furthermore,the morphology of the SP-TPE-SP solid surface can be regulated by ultraviolet light irradiation.The contact angles of the SP-TPE-SP solid surface can be decreased,changing from hydrophobic to hydrophilic.2.In order to achieve photochromism of spiropyran in solid state,SP-TPE-SP was obtained by covalent modification of tetraphenylethene(TPE-1)between two spiropyran molecules through esterification reaction.Efficient photoswitching of SP-TPE-SP is assisted by the large free volumes caused by the nonplanar molecular structures of the TPE moieties.SP-TPE-SP powder is in amorphous state,with loose molecular arrangements.Thus,the color of SP-TPE-SP can gradually change from light yellow to dark blue with UV light irradiation time.The control structures of SP1 and SP2 without the modification of TPE1 have a close molecular packing and lack enough free volumes to isomerize.SP2,as well as SP1 does not show photochromism in the solid state.The free volumes are large enough to allow for the transport of HCl and NH3 gas molecules for an acidochromic response.SP-TPE-SP affords an unusual example of combined photochromism,acidochromism,and photoresponsive wettability properties for a single compound in the solid state.Our study provides a new strategy for the development of advanced multifunctional materials in the solid state with simple structures.3.In order to achieve light-triggered phase transition,a series of azobenzene derivatives were obtained by gentle esterification.The appropriate length of alkyl chains combined with binaphthol moieties allow one to tune the melting point of PI to a range slightly above room temperature.The azobenzene moieties form aggregates in the solid sate,showing intense absorption bands in the visible region.Upon green light irradiation,the generated heat triggers the phase transitions.The liquid-state of P1 fast and spontaneously solidify again due to heat release in a purely physical fashion.The highly reversible and fast phase transition provides a platform for designing a photoswitchable and reversible adhesive.PI adhesives could not adhere to the glass plates after green light irradiation and show a strong adhesion strength after they solidify again.Furthermore,the introduced alkyl linkages can afford good solubility,so P1 exhibit excellent cleanability with common solvents such as DCM for practical and resource saving adhesive application.