Synthesis And Photoelctronic Properties Of Organic Compounds With Multiple Luminescence Properties

The emitting layer(EML)is of crucial role for organic light emitting diodes(OLEDs).In this dissertation,a series of organic materials with versatile luminescence properties were designed and synthesized.The electroluminescent devices based on these materials as emitters and hosts,respectively,were fabricated,and their properties were characterized and discussed.In chapter 1,a brief introduction of OLEDs,covering organic materials featuring thermally activated delayed fluorescence(TADF)/hybrid local and charge transfer state(HLCT),and host materials were generally addressed.The outline of this dissertation and the strategy to improve the performances of OLEDs were proposed.In chapter 2,two donor-acceptor type materials QLPXZ and QLmDPA,with diphenyl quinoline as acceptor and phenoxazine/dimethyldiphenylamine as donors,respectively,were designed and synthesized.The dihedral angle between the donor and the acceptor of QLPXZ was larger than that of QLmDPA,which induced a smaller singlet-triplet energy gap(△EST)0.09 eV compared with 0.30 eV of QLmDPA.Therefore,the former exhibited unique TADF property.The devices based on QLPXZ as the emitter were fabricated,which revealed an emission peak at 523 nm and a maximum external quantum efficiency(EQE)of 15.7%.In chapter 3,three fluorescent materials:DQLtBCz,DQLAC and DQLPZX with the dimer of diphenyl quinoline as acceptor and t-BuCz/DMAC/PXZ as donor,respectively,were designed and synthesized.The compounds exhibited high rigidity and thermostability.The solution-processed devices based on the compounds as the emitters exhibited emission peaks at 453,490 and 542 nm,and the maixmum EQEs of 0.36%,0.26%and 0.18,respectively.All of the three devices realized low efficinecy roll-offs at high current density.In chapter 4,a red fluorescent emitter NZ2AC by incorporating an naphthothiadiazole(NZ)unit as acceptor and a 9,9-dimethyl-9,10-dihydroacridine(DMAC)unit as donor was developed.The new fluorescent emitter simultaneously showed unique features of hybrid local and charge transfer excited state(HLCT)and aggregation-induced emission(AIE).As a result,the doped OLED based on NZ2AC as an emitter achieved a maximum EQE of 6.2%with a red emission peak at 612 nm.Attributed to the AIE feature of NZ2AC,the non-doped device also achieved a maximum EQE of 2.8%with a deep-red emission peak at 663 nm,accompanied by a very low efficiency roll-off value of ca.18%at the high luminance of 5000 cd m-2.In chapter 5,a new D-π-A-π-D type compound of NZ2TPA with NZ unit as acceptor,and diphenylamine(DPA)as donor,was densigned and synthesized,which exhibited both HLCT and AIE properties.The new emitter showed a emission peak at 683 nm,and a very high PLQY of 60%in the neat film,which was the highest among the reported small-molecule NIR organic emitters.The maximum EQE reached up to 3.9%in the non-doped OLED with the emission peak at 696 nm,which was among the highest in the reported non-doped fluorescent NIR OLEDs.Moreover,the device remained a high EQE of 2.8%at high brightness of 1000 cd m-2,with very low efficiency roll-off.In chapter 6,a novel and simple fluorophore of NZ2mDPA with intensive NIR emission peaking at 780 nm in solid state and the AIE property,was designed and synthesized.The solution-processed NIR OLEDs based on NZ2mDPA was optimized with an additional iridium complex as the sensitizer which further improved the electroluminescent performances.The optimized device exhibited an emission peak at 781 nm and a maximum EQE of 0.8%.For the first time,the NIR OLEDs based on a small molecular AIE lumogen were sensitized by the phosphorescent complex with a factor of 2.7 improvement in the external quantum efficiency(from 0.3%to 0.8%).In chapter 7,two novel spiro-annulated host materials NSF-SF and NSF-NSF by combining the characteristics of ortho-linked spirofluorene and triphenylamine were developed.The design endowed the two compounds with high triplet energy of 2.83 eV,high HOMO levels of ca.-5.31 eV and high Tg of ca.189 ℃,simultaneously.The blue phosphorescent OLEDs based on the NSF-NSF as the host material and FIrpic as the emitter,revealed a emission peak at 470 nm,and a maximum EQE of 19.1%.The device remained high EQE of 16.2%at a high brightness of 1000 cd m-2,and the efficiency roll-off was only 15%.In chapter 8,two bipolar host materials SOBPDPA and SOmBPDPA by linking an phenylsulfoneas acceptor and diphenylamine/4,4-dimethyldiphenylamine as donors,respectively,in the 2,2-position of the biphenyl skeleton,were synthesized and characterized.The two materials showed high triplet energy due to the twisty molecular structure.The device based on SOmBPDPA as the host exhibited a better performance than SOBPDPA,which can be assigned to the larger intermolecular distance induced by the methyl moiety.