| Organic light-emitting diodes(OLEDs),as the most promising display technology at present,OLEDs are widely used,especially in mobile phones and other devices that need to use display panels.The development of new and high-performance OLED light-0emitting materials is not only the direction of researchers,but also the way to promote OLED technology.At present,the OLED panels on the market are mainly phosphorescence devices,because the luminescent materials based on platinum,iridium and other rare metal complexes have good performance and long lifetime.However,due to the high price,serious pollution and lack of blue emitters,rare metal phosphorescence materials need to be developed to meet the demand.At the same time,in order to reduce Triplet-Triplet Annihilation,OLED devices usually use host-guest doping structure as the emitting layer,but there are not enough host materials to choose.In this thesis,two high efficient OLED materials based on nitrogen heterocycles have been developed.The results are as follows:(1)Based on nitrogen heterocycle and phenanthroline imidazole,the compound Zn(TPPI)2 was synthesized.Its thermodynamic,electrochemical and photophysical properties were systematically characterized and analyzed,and the device with it as the emitter was fabricated.The decomposition temperature of Zn(TPPI)2 is 495oC,and it has suitable HOMO(-5.33 e V)and LUMO(-2.27 e V)energy level,high and balanced bipolar transporting ability,and small singlet-triplet energy level gap(0.32 e V).Yellow and red phosphorescent doped devices which utilize Zn(TPPI)2 as host display high efficiencies(yellow:58.35 cd/A,70.52 lm/W,20.82%)(red:15.89 cd/A,16.09 lm/W and 19.05%).Both device performances are comparable to the best results of previous publications.Meanwhile,the undoped device of Zn(TPPI)2 exhibits the highest efficiencies(3.79 cd/A,3.97 lm/W,2.47%)for zinc-complex blue emitters.These results demonstrate that Zn(TPPI)2 is a good blue emitter and host material.(2)Based on dimethylacridin and methoxyphenyl)nicotinonitrile,the nitrogen heterocyclic delayed fluorescence material 6-(4-(9,9-dimethylacridin-10(9H)-yl)-2-methoxyphenyl)nicotinonitrile(DMPN)was synthesized.The thermodynamic and photophysical properties of DMPN were investigated systematically,single carrier devices and doped/undoped devices with DMPN as emitter were fabricated to characterize the electroluminescent properties of DMPN.The solvation model of DMPN has typical delayed fluorescence characteristics,and the maximum external quantum efficiency of its undoped device is 7.5%,which exceeds the theoretical upper limit of fluorescent materials.The performance of the device(21.2 cd/A,20.8lm/W,7.5%)shows that DMPN is an excellent delayed fluorescent material.At the same time,the device doped with the host-guest structure of DMPN(23.8 cd/A,23.4lm/W,11.7%)are also fabricated,which has good electroluminescent color stability,indicating that DMPN is an excellent emitter.In summary,based on the nitrogen heterocyclic structure,a zinc complex material Zn(TPPI)2 and a blue light delayed fluorescent material DMPN were designed and synthesized.According to the material properties,high-performance monochromatic OLED devices are fabricated,which provides a reference for the design and research of nitrogen heterocyclic organic light-emitting materials. |
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