Preparation,Characterization And Properties Of Thermoactivated Delayed Fluorescence Materials Based On Phenoxazine And Carbazole As Donors

Organic light-emitting diodes(OLEDs)have always been the focus of research,and thermally activated delayed fluorescent materials have become popular in the field in recent years.Compared with the common organic fluorescent and phosphorescent materials,the organic TADF material has a theoretical internal quantum efficiency of 100%,and is green,economical,and high in luminous efficiency,so people call it the third generation OLED material.In addition,the aggregation-induced effect(AIE)is a diametrically opposite phenomenon to the aggregation-induced quenching(ACQ)of the more common fluorescent materials.In this paper,a series of D-A type aggregation-induced delayed fluorescence compounds with aggregation-inducing effect and delayed fluorescence properties were prepared through rational molecular design,and their photophysical properties and delayed fluorescence properties were studied.The main research contents are as follows:(1)Five D-A type fluorescent compounds were prepared by using phenoxazine as the electron donor and changing the chemical structure of the electron acceptor,the structures were characterized by Fourier transform infrared spectroscopy(FT-IR)and~1 H NMR.The UV-Vis spectrophotometer,fluorescence spectrometer,steady state and transient fluorescence spectrometer were used to study the photophysical properties,aggregation-induced luminescence and delayed fluorescence properties of the target compounds.The results showedt the molecular structure of this series of fluorescent molecules had ignificant effect on their aggregation-induced luminescence properties.With the enhancement of the electron-withdrawing ability of the receptor,the fluorescence intensity and AIE characteristics of the fluorescent molecules hadbeen significantly improved(POBN>POBA).In addition,the steric hindrance of the molecule will also affect its aggregation-induced luminescence performance.As the number of Fsubstituents increased,the AIE characteristic of the molecule gradually was decreased,and its solid-state fluorescence emissionwassignificantly reduced(POBA>FPOBA>DFPOBA and POBN>FPOBN).The target compounds(POBA、FPOBA、DFPOBA、POBN、FPOBN)all exhibited aggregation-induced delayed fluorescence performance,and the delayed fluorescence lifetimes were 0.382μs,1.24μs,0.42μs,1.78μs,and 1.68μs,respectively.By optimizing the chemical structure of the electron acceptor,a better delayed fluorescent material can be obtained;and the stronger the electron withdrawing ability of the electron acceptor,the better its delayed fluorescence performance.(2)Three D-A type fluorescent compounds were designed and synthesized,the number of electron acceptors and the conjugation length of the system had changed by using carbazole as the electron donor The structure of the D-Atype fluorescent compoundswas characterized by Fourier transform infrared spectroscopy(FT-IR)and~1 H NMR.The UV-Vis spectrophotometer,fluorescence spectrometer,steady-state and transient fluorescence spectrometerwas used to study the photophysical properties,aggregation-induced luminescence and delayed fluorescence properties of the target compounds.The results of the study indicate that three target compounds all exhibit the characteristics of twisted intramolecular charge transfer(TICT),that is,as the polarity of the solvent becomes larger,the fluorescence will be weakened and red-shifted;they also have AIE characteristics and aggregate under the same conditions The order of induced luminous intensity from strong to weak is DTF-BISCAZ>SCN-BISCAZ>DSCN-CAZ.In terms of delayed fluorescence performance,the lifetimes of the three target compounds DTF-BISCAZ,SCN-BISCAZ,and DSCN-CAZ are 98.85 ns,112 ns and 9.1 ns.