Synthesis And Property Of D-A Type Thermally Activated Delayed Fluorescence Materials With Large Twist Structure

With amount of OLED electronic product sold in market,people are paying more and more attention on organic electroluminescence filed.One of hot spot in this filed is developing high efficiency,stable and low-cost emitting materials.Thermally activated delayed fluorescence（TADF）materials were developed as new generation pure organic emitting materials,TADF materials can achieve as high as 100%theoretical internal quantum efficiency with pure-organic molecular structure.TADF materials demonstrate advantages compare with traditional fluorescent and phosphorescent materials including high efficiency,low cost,and environmental friendliness,etc,and thus,owing broad prospects.However,there were still few TADF materials could perform high efficiency and stable in OLED.The main focus of this thesis is to design,synthesis and study photoelectric properties of TADF materials with large twist structure,and give some design ideas for high efficiency and stable TADF materials.In Chapter 2,A series of novel TADF emitters which used 9,9-dimethylacridine as donors and with combination of diphenylmethanone and sulfur or sulfuryl unit in D-A-D or D-A type structure were synthesized.A thoroughly investigation about their thermal,photophysical and electroluminescent properties were done to clarify the structure-activity relationship about these emitters.The fully HOMO/LUMO separation arised from large twist structure of molecule and small singlet-triplet splitting energy(?E_st)can achive in these emitters.All the OLEDs based on these emitters performed reduced roll-off with high operating brightness.Both mACRSO and pACRSO which contain sulfuryl unit gave a maximum external quatum effieciency（EQE）exceeding 20%and can keep over 18%EQE value at 1000 cd m^-2.By changing the sulfur atom valence state to break the conjugation of emitters,mACRS and pACRS can achieve over 17%maximum EQE value in non-doping device.Especially for pACRS based non-doped devices,the performance at high brightness was outstanding with the EQE values could maintain 15.9%at 5000 cd m^-2 and 14.6%at 10000 cd m^-2.Futhermore,non-doped solution-process devices of pACRS and mACRS were also fabricated and got above 10%maximum EQE.The versatile of these series emitters in several types of OLEDs will make them having broader application in future work.In chapter 3,a new donor derived from the spiroacridine derivative by adding a carbonyl unit was designed and synthesized.With pare-or meta-connection to central benzene of triphenyl-triazine unit,two greenlish TADF materials named SpirocoTRZ and SpiromcoTRZ,respectively,were synthesized.Adding stable carbonyl unit into the donor unit can not only keep high PLQY and small?E_st,but also improve electron injecting and transporting ability of molecule.The maximum EQE of OLEDs based on these two emitters can reach to 28.0%and17.7%,respectively,and retain 22.1%and 13.5%at 1000 cd m^-2.Furthermore,two more PHOLEDs were fabricated based on phosphorescence emitter PO-01 and using SpirocoTRZ and SpiromcoTRZ as host because of their favorable T₁ and bipolar transport ability.The maximum EQE of phosphorescence OLEDs can reach to 25.5%and 25.2%,respectively,and maximum power efficiency can reach to 115.16 lm W^-1 and 102.63 lm W^-1.The turn-on voltage of the phosphorescence devices based on SpirocoTRZ is among one of lowest in single host OLED devices.Although SpirocoTRZ based device owed higher maximum efficiency andlower turn-on voltage,the SpiromcoTRZ based device demonstrated compresensive advantages including lower driving voltage and reduced roll-off with comparable efficiency.SpiromcoTRZ should be a better host for phosphorescence OLED devices.In chapter 4,based on the molecular structure of SpirocoTRZ in Chapter 3,the carbonyl unit was replaced by sulfur or sulfuryl unit to get two blue emission TADF materials which named SpirosTRZ and SpirosoTRZ,respectively.Moreover,we added one more bulky and rigid spirobiphenyl in donor,the TADF emitter with longer molecular structure named TripirosTRZ.The maximum EQE of vacuum deposition devices based on SpirosTRZ,SpirosoTRZ and TripirosTRZ can reach to 32.2%,32.0%and 29.7%,respectively.The CIE coordinate of three devices are（0.17,0.38）,（0.16,0.28）and（0.18,0.38）.Compared with the previous reported high effciency compound SpiroAC-TRZ,the devices based on emitters which introduced in this chapter could reach higher efficiency and hypsochromic shift emission.This work present valid molecule design strategy of high efficiency blue TADF emitters.