Synthesis And Properties Of A Novel Tetraphenylethene-based Schiff Base

The emission wavelength and intensity of aggregation-induced emission(AIE)-active compounds in the solid or aggregation state can be modulated by changing the composition of molecules,twist conformation and accumulation patterns,which endows these materials with promising application in organic light emitting diode(OLED),fluorescent probes,etc.Tetrastyrene(TPE),as a typical aggregation-induced luminescent material,has aroused widespread concern in recent years.In this paper,eight Schiff base compounds were synthesized by using tetramethylene and a series of salicylaldehyde derivatives.The photochemical properties of photochemical properties were studied systematically.The mechanism and application of crystallization-induced emission enhancement(CEE),intramolecular twisted charge transfer(TICT),piezallochromy,and intracellular proton transfer(ESIPT)were explored.The specific research contents are as follows:1.TPE-NH2 was synthesized from tetrastyrene,and a series of salicylaldehyde derivatives were also synthesized.Four Schiff base molecules were synthesized using TPE-NH2 and salicylaldehyde,5-bromosalicylaldehyde,5-chlorosalicylaldehyde 5-cyanoalicylaldehyde by aldol condensation,corresponding to Compound 1,Compound 2,Compound 3,Compound 4,respectively.By studying the optical properties of the target product,it was found that the fluorescence of the mixed solution gradually increased with the addition of the poor solvent water in tetrahydrofuran(THF),so the four kinds of Schiff base compounds had aggregation-induced luminescence nature.When the mixed solution of water was allowed to stand for a period of time,we found that the fluorescence intensity of the mixed solution of compound 2,compound 3 and compound 4 was significantly enhanced compared with that before standing,and the emission color shifted blue.The aggregated luminescence phenomenon of this series of compounds can be attributed to the crystallization of the aggregates.The time dependence of this change is related to the speed of crystallization and the degree of crystallization,that is,these materials not only have the AIE effect but also have the crystal luminescence enhancement(CEE)characteristics.2.Synthesis of Schiff Base NSTPE by the Reaction of TPE-NH2 with 5-Nitrosalicylaldehyde.Due to the strong electron-withdrawing properties of nitro groups,the compound NSTPE has a significant solvent effect.From the density functional theory of NSTPE,it can also be found that it has obvious tendency of intramolecular charge transfer.In the process of aggregation induction,the "open-off-open" nature of the fluorescence changes showed U-shape,showing AIE and intramolecular twisted charge transfer properties(TICT)of NSTPE.In addition,when recrystallized with different solvents,NSTPE with different solid colors and different fluorescence emission wavelengths is obtained.By grinding the solids recrystallized from different solvents,they will become another color at the same time.After fumigation with methylene chloride,the color of the solid powder after grinding is restored to its original color,i.e.,NSTPE has a discolored color.The results of the discoloration properties were further confirmed by testing the fluorescence emission spectra and XRD spectra of solid powders under three colors.3.Three kinds of Schiff base compounds were synthesized by the reaction of TPE-NH2 with 5-methoxysalicylaldehyde,vanillin and 3-ethoxy-o-hydroxybenzaldehyde.We found that the three compounds had ESIPT properties.When using UV light to stimulate their solid powder,the three compounds are immediately from the original yellow into red,at room temperature after 20min-2h different times from red to the original color.All three Schiff base molecules have hydroxyl hydrogen,so the proton transfer is likely to occur in the excited state.We tested the diffuse reflectance spectra of the three compounds at different colors to verify that the compounds changed from alcohol to ketone.