Synthesis And Properties Of Tetraphenylethylene Fluorescent Molecules

With the progress of the society,people have an increasing demand for fluorescent materials in modern life.Fluorescent materials have been widely used in photochemical sensors,DNA diagnosis,photochemical sensors,dyes,fluorescent brighteners and Organic light-emitting device?OLED?,etc,which have been closely related to people's life.However,traditional fluorescent materials are subject to a problem of concentration quenching?ACQ?,which is greatly reduced when used as a film or solid.The appearance of aggregation-induced emission?AIE?materials perfectly solves this problem.Tetraphenylethylene?TPE?,as a"star molecule"in AIE materials,is simple to synthesize and easy to be functionalized,which can be easily combined with other fluorophore to obtain fluorescence molecules with excellent performance.Therefore,it has attracted extensive attention from researchers.In this paper,a series of AIE molecules were synthesized based on TPE groups,and their molecular structures were determined by nuclear magnetic resonance,mass spectrometry and other characterization methods.Then,their photophysical properties and applications in chemical sensing and OLED were studied.The main work includes the following aspects:First,two Schiff base probes,TPECN and TPEOCN were synthesized by introducing diaminomaleonitrile on TPE.Their fluorescence spectra showed that they could specifically identify Hg²⁺from 18 metal ions in aqueous solution,among which the minimum detection limit of Hg²⁺of TPEOCN reached 9.84 nM,and TPEOCN had naked eye recognition effect on Hg²⁺.It was found from the metal ion and anion interference experiment that the two probe molecules were hardly interfered by other ions in the detection of Hg²⁺,and they could work stably in a large pH range?5.5-12?.By means of fluorescence spectrometry titration and Job's Plot method,we determined that the coordination ratio between probe molecules and Hg²⁺was 2:1.Using gaussian calculation,we analyzed and discussed the mechanism of the probe.We tested and found that both of these molecules were less cytotoxic,and successfully applied them to cell imaging,and found that TPECN had a significant quenching response to Hg²⁺in cells.Next,we designed and synthesized three TPE-based monophenanthroimidazole molecules TPEO1-PI,TPEO4-PI,TPEO6-PI,and successfully obtained the single crystal structure of TPEO1-PI and TPEO6-PI,studied the crystal arrangement and intermolecular interaction.The fluorescence spectra showed that all the three molecules had obvious AIE characteristics,and the AIE of TPEO6-PI was the most obvious.Through thermal analysis,it was found that these three molecules have higher glass transition temperature and thermal decomposition temperature.Later,the three molecules are used as the luminescent layer to prepare non-doped OLED devices.Among them,TPEO4-PI has the best comprehensive performance,the maximum external quantum efficiency is 4.07%,the starting voltage is 2.7v,and the maximum brightness reaches 15995 cd m^-2.Finally,we synthesized two TPE-based bisphenanthroimidazole molecules TPE-BPI,TPE-tBu-BPI and two TriPE-based bisphenanthroimidazole molecules TriPE-BPI,TriPE-tBu-BPI on the basis of the previous ones,which have better photophysical properties and thermostability than the monophenanthroimidazole molecules.In addition,the introduction of tert-butyl group increased the fluorescence quantum yield and thermal decomposition temperature.The fluorescence quantum yield of the TPE-tBu-BPI film was 0.78,and the thermal decomposition temperature reached 513°C.Through solvation experiments,it was found that the excited state of TPE-based molecules is dominated by charge transfer state;while TriPE-based molecules exhibit a localized excited state relative,which can effectively reduce the red shift of molecules in the aggregate state.