Design,Synthesis And Properties Of Diphenylsulfone-Acridine Skeleton Based High Efficiency Solution-Processed Thermally Activated Delayed Fluorescence Material

Since Adachi’s group in 2009 reported the application of thermally active delayed fluorescence(TADF)materials in organic light-emitting diodes(OLEDs),TADF materials have been recognized for their 100%internal quantum efficiency,no heavy metal atoms and other advantages,which has won extensive attention of scientific researchers and become a research upsurge of organic electroluminescent materials.With the continuous development of TADF materials by many scholars,devices based on TADF materials have been continuously optimized,and their device efficiencies have begun to surpass those of traditional phosphorescent materials.Although TADF materials have made breakthroughs in the red,green,blue and near-infrared emission regions,they still face scientific problems such as few solution-processable materials and low device efficiency.In this thesis,a series of D-A TADF materials were constructed with 9,9dimethylacridine(Ac)as the donor unit and diphenylsulfone(DPS)as the acceptor unit,and the structure-property relationship of the materials was discussed in detail.The compounds’ structure was determined by hydrogen and carbon spectroscopy,time-of-flight mass spectrometry,high performance liquid chromatography and X-ray single crystal diffraction;the molecular configuration was optimized by density functional(DFT)theory calculation,hence we studied the electron cloud distribution and energy level of the material.And the thermodynamic,photophysical and chemical properties of the compounds were studied in detail by weight loss analysis,steady-state/transient fluorescence spectroscopy,differential scanning calorimetry(DSC),polarized optical microscopy(POM),small angle X-ray scattering(SAXS)and cyclic voltammetry.Using these TADF molecules doped host material as the lightemitting layer dopant was prepared by solution processing method to further explore the electroluminescence properties.Here are research results of the paper following:(1)In this thesis,the compounds m-DPSAc and p-DPSAc are used as luminescent cores,and mesogens are introduced into the 2 and 7 positions of the Ac donor unit to construct liquid crystal luminescent materials m-DPSAcLC and p-DPSAc-LC.The effect of material liquid crystal properties on its luminescent properties was investigated.The thermal decomposition temperature of both compounds exceeds 420℃,and both have smectic liquid crystals.Due to the difference in the attachment sites of the donor and acceptor,the compounds m-DPSAc-LC and p-DPSAc-LC in toluene solution and doped films exhibited blue and green emission,respectively,and p-DPSAc-LC possessed TADF properties.The corresponding solution-processed devices were prepared by doping the two materials in the mCP host,and the device based on compound p-DPSAc-LC obtained 14.9%of EQEmax.(2)A series of D-π-A compounds m-PyDPSAc,p-PyDPSAc and omPyDPSAc were constructed by using Ac as the donor,DPS as the acceptor,and the pyridine ring as the π bridge.By changing the connection position of Ac unit to the π bridge,regulating intramolecular ICT effects,and discussing the effect of positional isomerism on compound properties in detail.These compounds have good thermal stability,and their decomposition temperature is greater than 340℃ at 5%thermal weight loss.All compounds show blue emission and TADF properties in doped films.With mCP as the host material,these compounds D-π-A type compound is used as dopant material to prepare solution-processed blue device,in which the device based on p-PyDPSAc obtained an EQEmax of 6.68%.(3)In order to further improve the luminous efficiency and color purity of TADF materials,the thesis constructed a class of conjugated rigid π bridgedibenzofuran through intramolecular ring closure,and designed and synthesized the molecule DPS-BF-Ac.Compounds DPS-Ph-Ac,DPS-OMe-Ac and DPS-OH-Ac were prepared by changing the π bridge structure,and the effect of the π bridge structure on the photophysical properties of the materials was mainly discussed.These compounds all have good thermal stability(>380℃);both show blue emission(440-480 nm)in toluene and doped films,and all have obvious TADF properties.These compounds are doped with in mCP,solution-processed blue devices were prepared,in which the blue device based on the compound DPS-BF-Ac obtained an EQEmax of 24.69%.The blue material DPS-BF-Ac and the orange-red light material PO-01 were doped in mCP,a solution-processed hybrid white device was prepared,and its EQEmax was as high as 28.94%.The research results show that increasing the rigid structure of the molecule can effectively suppress the deformation of the excited state of the molecule,reduce the non-radiative transition of the molecule,and obtain a high-efficiency luminescent TADF material.