Synthesis And Properties Of Thermally Activated Delayed Fluorescent Materials Based On Anthraquinone

Due to the unique display superiority,organic light-emitting diodes(OLEDs)have been developing rapidly.As the core materials of the OLEDs,organic light-emitting materials are focused on by the researchers.As the most promising emitters for OLEDs,thermal activation delay fluorescent materials(TADF)without precious metals can harvest singlet excitons and triplet excitons to achieve theoretically 100%internal quantum efficiency,friendly to environment.So the TADF materials can gradually take the place of the previous materials of the OLEDs,and get rapid development.The ideal TADF materials have smaller energy level difference(?E_ST)between single excited state and triple excited state and higher photoluminescence quantum yields(PLQYs).However,the smaller?E_ST need the frontier molecular orbits(FMO_S)as separated as possible,which is not conducive to obtain higher PLQY.So it became the problem of designing TADF material and the research emphasis of the researchers.Now,many efficient TADF materials have been reported,but the performance of the materials and devices are far from reaching the commercial standards and still needs to be improved.So,to achieve novel effective TADF materials and improving device performance,we designed and synthesized nine kinds of pure organic small molecule TADF materials with anthraquinone as an acceptor.The structures of the TADF materials were characterized and analyzed by ¹H NMR,¹³C NMR and MS.And the electron cloud distribution,photoelectric performance,thermal properties and device performances of them are explored.The main results are summarized as follows:1.Four TADF materials with anthracene-9,10-dione as acceptor,C-O bond as?bond,Cz,TCz,DPA and DMAC as donor,were designed and synthesized(AQ-O-Cz,AQ-O-TCz,AQ-O-DPA and AQ-O-DMAC).The photoelectric performances,thermal stability properties of the TADF emitters were measured,and the results exhibit the TADF materials obtain smaller?E_ST(<0.1 e V)and better lifetime of the delayed fluorescent(?_Dare 1.31,0.63,0.09 and 0.45?s,respectively).Meanwhile,the process of radiation was enhanced by strengthening the rigid of the donor,which can achieve higher PLQYs(31.26%,27.71%,16.82%and 37.64%).The four TADF materials have intermolecular charge transfer effect(Inter-CT)and realize the orange red,red emission(neat film).The AQ-O-CZ,AQ-O-DPA and AQ-O-DMAC were chosen as Light-emitting layer of the device,and experimental results show that the turn on voltage of the devices are low(V_on:3.5,3.6 and 3.5 V).Compared with AQ-O-DMAC and AQ-O-DPA,the device based on AQ-O-CZ achieves highest maximum luminescence(8320 cd m^-2)and highest maximum external quantum efficiency(EQE_max of 6.07%).(The second chapter)2.In order to obtain D-?-A structure TADF materials with better luminescence performance and better device performances,sulfur atom with less electronegative was selected to replace oxygen atom to partially destroy the conjugated system of molecules on the basis of the second chapter.Four D-?-A type thermally activated delayed fluorescent materials(TADF),AQ-S-CZ,AQ-S-TCZ,AQ-S-DPA and AQ-S-DMAC,with AQ as acceptor,sulfide bond as?bond,Cz,TCz,DPA and DMAC as donors,were designed and synthesized.The photoelectric performances,thermal stability properties and device performances of the four emitters were measured,and the results demonstrate that all materials achieve smaller?E_ST(<0.2 e V)and better delayed fluorescence properties(?_D:0.32,0.41,0.15 and 0.28?s).Compared with TADF materials of the Chapter 2,the PLQYs of AQ-S-CZ AQ-S-TCZ AQ-S-DPA and AQ-S-DMAC are significantly increased(35.37%?32.71%?20.36%and 47.10%).Due to the introduction of sulfur atoms with the lower electronegativity,the four TADF materials exhibit not only inter-molecular charge transfer effect(inter-CT),but also obvious intra-molecular charge transfer effect(intra-CT).The luminescence of these four materials can be effectively regulated by intra-CT,especially inter-CT,to realize the orange red,red emission(neat film).The AQ-S-CZ,AQ-S-DPA and AQ-S-DMAC were chosen as light-emitting layer of the devices.Compared with that of other two materials,the device based on AQ-S-DMAC obtained highest EQE_max of 7.17%with turn-on voltage of 3.5 V.This work enriches the D-?-A type TADF materials and provides a perspective approach of developing long wavelength TADF emitters.3.Based on the research of the first two chapters,for further obtaining high efficiency red TADF material,the chapter synthesized asymmetric D-A-D'structure TADF material TPA-AQ-DCP,with AQ was as the accepter,triphenylamine and 9,9'-p-phenyldicarbazole(DCP)with host material properties was part of the donor.The experimental results manifest that the TPA-AQ-DCP obtained smaller?E_ST(0.09 e V)and higher PLQY(76.69%).Meanwhile,the transient PL spectrum of TPA-AQ DCP is double exponential decay,and the delayed fluorescence lifetime of TPA-AQ DCP is 9.21?s,which indicates that TPA-AQ DCP has obvious delayed fluorescence performance.The experimental results show that the luminescence performance of TADF material can be significantly improved by using DCP with host material properties as part of the donor.The device with 20 wt%TPA-AQ-DCP as dopant exhibits EL emission of 616 nm,EQE_max of 17.60%,which is the highest date in TPA-AQ-DCP devices.Compared with that based on TPA-AQ devices reported in literature,the EQE_max of the device based on TPA-AQ-DCP increased by 2.3 times.Using host materials as part of the donor to construct TADF materials is an effective way to design high efficiency red TADF materials and fabricate high performance OLED devices.