Synthesis Of Delayed Fluorescence Materials With Diphenylsulfone As Acceptor And Their Applications In Non-doped Light Emitting Devices

Organic light-emitting diodes（OLEDs）are considered to be the most potential for new generation display technology,due to their advantages such as wide viewing angles,self-luminescence,low power consumption,flexibility and so on.By reverse intersystem crossing,TADF materials can achieve 100%internal quantum efficiency,which has aroused extensive attention in the display field.After a few years of development,the maximum external quantum efficiency(EQE_max)of TADF materials have exceeded 36%,but the serious efficiency roll-off under high brightness needs to be resolved.Although most TADF materials use host-guest doping mechanism to slow down the device’s efficiency roll-off,the problem is still very serious.Unfortunately,compared with non-doped devices,the host-guest doped devices have more complicated manufacturing process,and the doping concentration is difficult to control accurately,resulting in device instability.Therefore,it is necessary to develop high efficiency and low roll-off non-doped OLEDs.In this paper,the diphenylsulfone is used as acceptor group to design TADF materials for undoped devices.As follow aspects:1.We change the type of electron-donating group to study the effect of donors on the luminescence properties of aggregation-induced luminescence-thermally delayed fluorescence（AIE-TADF）materials;2.In order to explore the effect of different connection positions on the luminescence properties of AIE-TADF material,we change the substitution position of the donor9-phenylcarbazole;3.Combined AIE-TADF with host-substituents to form self-host TADF molecules,which can reduce efficiency roll-off due to the host-substituents can disperse exictons.The details are as follow:（1）Based on the D-A-D’structure,using diphenylsulfone as the acceptor,9-phenylcarbazole and phenothiazine,phenoxazine,and 9,9-dimethylacridine as the donor,three AIE-TADF materials were designed and synthesized（3CP-DPS-PXZ,3CP-DPS-PTZ and 3CP-DPS-DMAC）,to study the effect of different donors on the luminescence properties of AIE-TADF materials.All three materials have AIE properties,high thermal stability,and high photoluminescence quantum yield（PLQY）in the neat film,so they are suitable as luminescent materials to make undoped devices.The EQE_max of devices based on three materials in the non-doped devices are 17.9%,13.1%,and 9.1%,respectively.（2）Two green light AIE-TADF materials,2CP-DPS-PXZ and 4CP-DPS-PXZ,were designed and synthesized by changing the connection position of the donor9-phenylcarbazole,based on 3CP-DPS-PXZ.The effects of different bonding methods on the performance of AIE-TADF were studied.Both materials have AIE properties,higher thermal stability,and higher PLQY in the pure film.Compared with the previous chapter3CP-DPS-PXZ,2CP-DPS-PXZ device performance is further improved.The maximum power efficiency and maximum current efficiency of undoped devices based on2CP-DPS-PXZ are 64.6 lm/W and 50.7 cd/A,respectively,which are higher than those based on 3CP-DPS-PXZ undoped devices（50.4 lm/W and 48.1 cd/A）.The EQE_maxof the non-doped device based on 2CP-DPS-PXZ,3CP-DPS-PXZ and 4CP-DPS-PXZ are16.3%,16.6%,and 15.2%,respectively,and the efficiency roll-off at 1000 cd/m² is 11.4%,10.8%,and 10.8%.（3）Two self-host green AIE-TADF emitters,by introducing host-substituents p PDCz and m PDCz,was designed and synthesized,namely:p PDCz DPSPXZ and m PDCz DPSPXZ,which based on DPS-PXZ.We discussed the effect of host-substituents on AIE-TADF properties.These two materials are prepared into non-doped devices.The EQE_max of p PDCz DPSPXZ and m PDCz DPSPXZ are 17.1%and 18.1%,respectively.In particular,the EQE are still 15.4%and 16.7%at 1000 cd/m²,and the efficiency roll-off is only 9.9%and 7.7%.