Research Of Red Thermally Activated Delayed Fluorescent Materials Based On Different N-heterocyclic Donor Units

In recent years,organic light-emitting devices(OLEDs)have been gradually commercial due to their advantages of self-luminescence,color saturation,and short response time.Thermally activated delayed fluorescence(TADF)materials have been known as the third-generation OLED light-emitting materials,which can realize the utilization of 100%excitons theoretically.In addition,TADF materials is easily available and cheap,which is a promising luminescent material.At present,TADF materials have achieved excellent results in blue and green emission.Research on red TADF materials still needs to achieve breakthroughs.The red TADF molecule is composed of a strong donor unit and a strong acceptor unit,forming a strong intramolecular charge transfer,which promotes the red shift of the emission wavelength.Due to the strong electron-withdrawing properties of cyano groups,cyano-based acceptor units often constitute red-light TADF molecules.Compared with acceptor units,there are many types of donor units.For example,red light TADF molecules with triphenylamine as the donor have achieved excellent results.Therefore,this paper mainly studies red TADF materials based on different N-heterocyclic donor units including their photophysical properties,thermal stability,electrochemical properties,and electroluminescence properties.1.The second chapter studies the design,synthesis and electroluminescence properties of red TADF materials based on N-heterocyclic spiro acridine donor units.Based on the 10H-spiro[acridine-9,9’-fluorene]donor unit,four red TADFs,BPCN-spAc,FBPCN-spAc,DBQ-spAc and DBPz-spAc,were designed and synthesized.All four TADFs achieved small ΔEST by designing and kRISC as high as 106 s-1.Most importantly,the fluorescence quantum yields(PLQYs)of the four emitters in solid-state thin films were all above 90.0%.The maximum external quantum efficiency(EQE)of the four devices were higher than 20%.Among them,the OLED device of BPCN-spAc emits at 592 nm,the external quantum efficiency was close to 30%,the maximum current efficiency and power efficiency were 70 cd/A and 82.68 lm/W,respectively,with CIE coordinates(0.55,0.45).2.The third chapter studies the design,synthesis and electroluminescence properties of red TADF materials based on N-heterocyclic carbazole donor units.Based on multiple carbazole units as donor and combined with strong electron acceptor units,three new red TADFs,4Cz-2CN,4Cz-2N and 2Cz2Ph-2CN,were synthesized and purified.The TADF molecules with multiple donors generally form chargeresonance-type hybrid triplet states,which is beneficial to the RISC process.The twisted structure also suppresses vibrational relaxation,reducing exciton quenching.Not surprisingly,all three TADFs have smaller ΔESTs.The luminescence performance of the 2Cz2Ph-2CN was the best,the external quantum efficiency of the device was 14.64%,and the CIE coordinates was(0.59,0.41).3.The fourth chapter studies the design,synthesis and electroluminescence properties of red TADF materials based on N-heterocyclic bridged triphenylamine donor units.The bridged triphenylamine(BOP)of donor unit was designed and synthesized by introducing two oxygen atoms into the triphenylamine structure.Three red TADFs based on donor-acceptor(D-A)type,APDC-BOP,AQDC-BOP and TFQ-BOP,were designed and synthesized by combining donor BOP with acceptor acenaphthene.The device with APDC-BOP as the luminescent guest showed a device efficiency of 6.95%at 653 nm and CIE of(0.64,0.35).