Temporal And Spatial Control Over Responsive Behavior Of Fluorescent Hydrogel And Its Application In Information Encryption

Anti-counterfeiting packaging technology is an important means for the country to curb counterfeit and inferior products from the source.Fluorescent information encryption is currently one of the most widely used anti-counterfeiting technologies due to its advantages of simple operation,time-saving and strong anti-counterfeiting performance.Fluorescent hydrogels,as a kind of intelligent materials that can respond to external stimuli and produce fluorescent color or shape changes,have broad application prospects in the field of encryption and anti-counterfeiting.However,traditional fluorescent hydrogels are applied to information encryption mainly based on the characteristics of single deformation or discoloration,which can only store single information,small information storage and low security performance,especially the risk of secondary leakage of decrypted information without proper processing,which limits their further application.Therefore,based on the synergistic deformation and fluorescence color change of fluorescent hydrogel,the fluorescence changes in this thesis would be regulated by the use of electrostatic interaction and dynamic covalent bond,and a multi-mode anti-counterfeiting system with multi-information encryption function were fabricated to realize multi-stage and multi-dimensional（spatial and temporal）optical information storage and information decryption and self-erasure.The security performance is greatly improved in the information transmission path.The main contents of this thesis are as follows:（1）Tetrakis（4-aminophenyl）ethylene（TPE4N）with AIE effect was synthesized from tetraphenylethene（TPE）by nitrification and reduction,and its structure was characterized by FTIR and NMR.The p H-responsive fluorescence changes of TPE4N solution and mechanism of fluorescence changes were studied.The results indicated that TPE4N showed good p H-responsive aggregation-induced emission（AIE）,accompanied by green fluorescence on/off change.This result lays a foundation for the development of information storage materials.（2）A water-soluble photoacid derivative zwitterionic protonated sulfonatomerocyanine（SMEH）was designed and synthesized.The photo-responsive properties of SMEH were studied in detail.The results indicated that the spiropyrane（ASP）in the form of anionic ions were formed by the ring closure when SMEH was exposed to 420 nm light.On this basis,the reversibility and stability of light-driven assembly and disassembly between SMEH and TPE4N⁴⁺can be investigated to realize the photo-responsive fluorescence on/off behavior.It was proved by ¹H NMR and theoretical calculation that the fluorescence enhancement was due to the electrostatic interaction between the benzene rings which limited the rotation of them.Further study suggests that the rate of fluorescence enhancement could be regulated by changing the SMEH concentration.Information storage and encryption based on fluorescence change in solution were realized by means of photomask or binary strategy.The effective control of AIE behavior by electrostatic action provides a new idea for more advanced information encryption.（3）Based on the above research,in order to introduce p H-responsive TPE4N molecules into the hydrogel network,a new AIE monomer TPE3N was synthesized by introducing a double bond into TPE4N.N,N-Dimethylacrylamide（DMA）was copolymerized with protonated TPE3N(TPE3N³⁺),and silica nanoparticles were introduced at the same time.TPE3N³⁺hydrogels with p H-responsive AIE fluorescence were obtained.Poly（sodium p-styrenesulfonate）（PSS）and formaldehyde（HCHO）solution were introduced into the fluorescent hydrogel system by iono-printing method.¹H NMR showed that electrostatic interaction and dynamic covalent bond（imine bond）were formed,respectively,which effectively limited the rotation of TPE3N benzene ring in the hydrogel.Electrostatic interaction and imine bond are p H responsive,and the fluorescence fading rate of imine bond is slower at low p H.Therefore,the application of electrostatic and dynamic covalent bonding to regulate the AIE behavior of hydrogels in 2D information encryption was explored.（4）By using polyacrylic acid（PAA）hydrogel as the active layer and TPE3N³⁺hydrogel as the passive layer,a novel double-layer hydrogel driver with complex synergistic deformation and fluorescence color change was constructed based on the force of poly N,N-dimethylacrylamide（PDMA）and silica nanoparticles.Due to the p H response of the double layer hydrogel,the synergistic deformation and fluorescence color change of hydrogel actuator was achieved under different p H.In addition,through the design of the initial shape,the 3D complex actuator was realized under the stimulation of p H.The application of double layer hydrogel in multi-dimensional information encryption was further explored.