Research Of Thermally Activated Delayed Fluorescent Organic Electroluminescent Materials Based On Benzophenone

Organic light emitting diode?OLED?has been widely recognized as a new generation of display and lighting technology.Therefore,as a core part of the device,organic electroluminescent materials have been a research hotspot.Thermally activated delayed fluorescence?TADF?emitters overcome the shortcomings of the first two generations of luminescent materials,such as low efficiency and high cost,and are considered to be the most promising new generation of organic electroluminescent materials.Based on the TADF mechanism,a series of TADF emitters were designed based on the benzophenone group.The specific work results are as follows:?1?A novel yellow TADF emitter TBP-PXZ was designed and synthesized,in which benzophenone derivative was used as electron acceptor and phenoxazine was used as electron donor.Since there is a nearly vertical dihedral angle between D and A,the overlap between the highest occupied molecular orbital and the lowest unoccupied orbit of TBP-PXZ is very small,so its singlet-triplet energy gap(?E_ST)is only 0.02.eV.The maximum external quantum efficiencies?EQE?of the TBP-PXZ-based device is as high as 17.7%,What is more remarkable is that the device has very small efficiency roll-off.The EQEs remain at 16.0%and 12.7%at luminances of 1000 cd m^-2 and 10000 cd m^-2respectively.More particularly,at an extremely high luminance of 30000 cd m^-2,the EQE of the TBP-PXZ-based device is still as high as 10.5%.These results indicate that the star molecule TBP-PXZ is an ideal model for the development of new high efficiency,low efficiency roll-off TADF emitters.?2?Subsequently,we designed three novel green light TADF emitters TBP-Cz?TBP-DmCz and TBP-TmCz,the benzophenone derivative was used as electron acceptor,carbazole,1,8-dimethylcarbazole and 1,3,6,8-tetramethylcarbazole was used as electron donor,respectively.The maximum EQEs of OLED devices based on these three emitters is 11.1%,13.6%and 18.3%respectively,and the emission wavelengths are 484 nm,496nm,and 508 nm,corresponding to CIE coordinates of?0.20,0.33?,?0.20,0.41?,and?0.24,0.49?,belonging to the green area,which belong to the blue-green region.Compared with TBP-PXZ,the emission wavelengths of these three TADF emitters have a significant blue shift.The results of this research indicate that the emission spectra of the material can be adjusted by changing the electron-donating ability of the donor fragment,and then luminescence spectrum of OLED devices will also be changed.?3?In order to further blue shift the emission spectrum,we redesigned three butterfly-shaped materials DBP-Cz,DBP-DmCz and DBP-TmCz.Compared with the TBP group,the pull-electron ability of the DBP group is reduced,so the emission spectrum of the material can be blue-shifted.Among the three materials,DBP-Cz has a large?E_ST of 0.15 eV,so it has almost no TADF characteristics;while DBP-DmCz and DBP-TmCz both achieve efficient TADF characteristics with small?E_STs of 0.06 eV and0.04 eV.The emission peaks of OLEDs based on three emitters were 459 nm,476 nm,and 501 nm,respectively,and the maximum EQEs were 4.6%,11.6%,and 12.9%.