Synthesis And Properties Of Fluorescent Dye Molecules Based On AIEE And ESIPT

Aggregation Induced Emission?AIE?had become a hot topic in China and abroad.Such molecules had special optical properties and broad development prospects,so could be applied to fluorescent sensors,photodynamic therapy,biological imaging and anti-counterfeiting materials,etc.,but AIE system also had many shortcomings.In this paper,we tried to overcome the disadvantages of AIE by using special structure.We tried to combine AIE and intramolecular proton transfer?ESIPT?,which could overcome the disadvantages of AIE molecules and generate a large Stokes shift.In addition,the characteristics of AIE molecules also overcome the ACQ phenomenon that existing in traditional ESIPT molecules.In this paper,we first synthesized the functional target products of Hydroxyphenyl benzimidazole?HBI?containing the structure of tetraphenyl ethylene?TPE?,and characterized the structure of the three compounds by means of ¹HNMR,¹³CNMR and EI-MS,so as to determine the structure of the synthesized intermediates and final products.Secondly,we studied the light physical properties of the three tetraphenyl ethylene derivatives that with different substituents,we found that in the mixed solvents of THF/H₂O system,the fluorescence intensity of three compounds had different changment,one of the TPE derivative's fluorescence intensity gradually increased with the increase of water content,when the water content reached 85%,the fluorescence intensity reached maximum.Subsequently,as the water content continued to increase,the fluorescence intensity decreased.This phenomenon indicated that the compound had typical properties of AIEE.However,the introduction of different substituents will restrict AIEE phenomenon to a certain extent.We had studied the photophysical properties of one TPE derivative crystal and found that it had the properties of crystallization induced luminescence enhancement?CIEE?,which is due to the formation of intramolecular hydrogen bond between THF and imidazole imide and the enhanced the intramolecular ESIPT process.Then,we studied the chromogenic properties with the external stimulus response of these molecules.The phenolic hydroxyl group and imidazole in HBI structure molecules form the intramolecular hydrogen bond.Meanwhile,phenolic hydroxyl groups acted as proton donors in ESIPT process,and imidazole as proton receptors.In the state of solid,ESIPT process occured in the three TPE derivatives,which emited fluorescence at a certain intensity.However,after the treatment of HCl fumigation,the tertiary amine group and the phenolic hydroxyl group of part of HBI are protonated by chloride ions,and the function of O-H···Cl^-and N-H···Cl destroyed the original molecular hydrogen bond and blocked the ESIPT process,thus leading to a significant blue shift in the emission wavelength of solid fluorescence.After fumigation with concentrated ammonia water or heating,the fluorescence emission wavelength would return to the initial state.These phenomena indicated that the discoloration of the external stimulus response of three HBI functionalized TPE derivatives in solid state was reversible.Finally,we studied the selective recognition of three compounds on metal ions in solution.We selected more than a dozen common metal ions for testing,and found that these three compounds can selectively recognize Cu²⁺.The Job's Plot curve was used to calculate the combination ratio of these three compounds with Cu²⁺.The results showed that these compounds had a high selectivity for Cu²⁺detection.The results of this study could be used in the detection of Cu²⁺concentration in factory wastewater or other pollutants in the future.