The Construction Of Thermally Activated Delayed Fluorescence Material Systems Based On Triazine Acceptor

Organic light-emitting diodes（OLEDs）are considered as the new generation of displays and lighting to take advantage of their high efficiency,self-luminescence,lightweight,thin thickness and mechanical flexibility.By harvesting all the electrically generated singlet and triplet excitons for 100%theoretical internal quantum efficiency（IQE）,phosphorescent organic light-emitting diodes（Ph OLEDs）have been intensively investigated.However,the expensive cost of phosphorescent materials containing precious metals greatly limits their large-scale application in industry.Recently,thermally activated delayed fluorescence（TADF）molecules have been considered as one of the most promising emitting materials for organic light-emitting diodes（OLEDs）because they can harvest electro-generated triplet excitons for light emission and achieve theoretical 100%internal quantum efficiency（IQE）via efficient reverse intersystem crossing（RISC）process from the lowest triplet state（T₁）to the lowest singlet state（S₁）.After years of development,the device performances of TADF based OLEDs with respect to luminance and efficiency are now in close proximity to those of Ph OLEDs.However,resulting from the long exciton lifetime,TADF emitters suffer from serious efficiency roll-off at high exciton densities.Therefore,the development of TADF emitters with high efficiency and low roll-off is a great challenge.In this thesis,we designed and synthesized a series of green photothermal activated delayed fluorescence（TADF）materials by incorporation of triazine acceptor and diaromatic amine donor derivatives,mainly including the following aspects:1、In chapter Ⅱ,we developed five TADF materials DDPA-TRZ、DISB-TRZ、DDMAc-TRZ、DPTZ-TRZ和DPXZ-TRZ based on triazine acceptor and diaromatic amine donors by simple reaction steps,and their molecular structures identified by ¹H nuclear magnetic resonance（NMR）spectroscopy,mass spectrometry and elemental analysis.In addition,we also obtained the single crystal structure of DDMAc-TRZ、DISB-TRZ and DPXZ-TRZ via vacuum vapor deposition method.Through the systematic study on the crystal structures,intramolecular/intermolecular interactions and molecular stacking structures of these materials in the solid state,the relationship between the material structure and luminescence performance was deeply explored.2、In chapter Ⅲ,we investigated the thermal,electrochemical,theoretical calculation and photophysical properties of these TADF materials.Thermal and electrochemical measurements show that these compounds have good thermal and electrochemical stabilities.The theoretical calculation results indicate that these emitters exhibit highly twisted geometric configurations.Their HOMO and LUMO distributions are localized on donors and receptors,respectively,with a small overlap on the phenyl linker unit,which is advantageous to achieve smallΔE_STand high photoluminescence efficiency at the same time.The photophysical results reveal that these donor-acceptor compounds show green light emission,strong intramolecular charge-transfer characteristics,and smallΔE_ST,indicating their typical TADF characters.Based on the above results,compound DDMAc-TRZ possess the highest photoluminescence efficiency and a smallΔE_ST,and it is expected to achieve high-efficiency electroluminescence performance as a dopant.Therefore,we doped DDMAc-TRZ into m CBP matrix as the emitting layer to fabricate a doped OLED.The optimized device exhibits the best device performance(L_max=11680 cd/m²、CE_max=48.8 cd/A、PE_max=46.4 lm/W、EQE_max=17.7%).In addition,the device also achieved extremely low efficiency roll-off with EQE of 14.2 and 9.9%at the brightness of 100 and 1000 cd/m².These performance parameters are comparable to those of Ph OLEDs with similar spectra.