Synthesis And Electroluminescence Properties Of Phosphorescent Iridium Complex Based On Phenylpyrimidine And Phenylpyridazine Ligands

Organic light-emitting diodes?OLEDs?have been widely used in the field of display and lighting due to their advantages such as low cost,autonomous light emission,high efficiency,and short response time.Compared with traditional fluorescent materials,phosphorescent materials can make full use of their singlet and triplet excitons due to the spin-orbit coupling of heavy metals,which can achieve 100%theoretical internal quantum efficiency,and it has been a research hotspot in the field of OLED.Cyclometallated iridium complexes are currently the most widely studied and applied electrophosphorescent materials,which have high luminous efficiency and stable chemical properties.By changing the structure of the ligands to adjust the light-emitting properties of the materials,full-color display of the devices can be achieved.In recent years,iridium complexes using 2-arylpyrimidine as cyclometalating ligands have attracted widespread attention from researchers due to their high phosphorescent quantum efficiency,excellent chemical and optical stability.However,the phosphorescent emission of most pyrimidine-based phosphors reported in the literatures is green or blue-green.In order to obtain bluer emission,four kinds of 2-phenylpyrimidine main ligands were synthesized by introducing fluorine atoms and trifluoromethyl into the 2-phenylpyrimidine system,and combined different ancillary ligands picolinic acid?pic?,2-?3-?trifluoromethyl?-1H-pyrazol-5-yl?pyridine?fppz? and 2-?5-?4-?trifluoromethyl?phenyl?-2H-1,2,4-triazol-3-yl?pyridine?Htaz?to construct four sky blue iridium complexes?Ir1-Ir4?,and the photoluminescent and electroluminescent properties of these iridium complexes were studied systematically.At the same time,considering the advantages of the heterocyclic pyridazine-based iridium complexes,such as high synthesis yield and high luminescent efficiency,we replaced the pyrimidine part of the cyclometalating ligands with pyridazine.A series of new pyridazine-based phosphorescent iridium complexes?Ir5-Ir8?were obtained by introducing different substitution groups such as dimethylamine,tert-butyldiphenylamine and tert-butyl into the cyclometalating ligand and using picolinic acid?pic?as an ancillary ligand.The photoluminescent and electroluminescent properties of these iridium complexes were also studied systematically.All compounds were confirmed by mass spectrometry and nuclear magnetic resonance spectroscopy.Furthermore,the HOMO and LUMO distributions of the compounds were calculated by DFT method.Their photophysical and electrochemical properties were studied by UV-visible absorption spectrum,emission spectrum,low-temperature phosphorescence spectrum and cyclic voltammetry.Photophysical tests show that the emission wavelength is in the range of 555-577 nm for Ir5-Ir8 and 457-466 nm for Ir1-Ir4.Owing to the introduction of strong-field CF₃-containing ancillary ligand and incorporation of electron-withdrawing F or CF₃ groups on the HOMO-lying C-related aromatic rings of the C^N cyclometalating ligands,Ir1-Ir4 exhibited narrowed and blue shifted phosphorescence spectra relative to FIrpic and other pyrimidine-based phosphors reported in the literatures.Furthermore,Ir1-Ir4 have a short phosphorescence lifetime?0.53-1.64ms?and high phosphorescence quantum yield,which indicating high-performance PhOLEDs can be obtained when utilize these compounds as the triplet emitter.In order to explore the influence of different host materials on the device performance,Ir2 was doped as a light-emitting material at a concentration of 7%into the host materials mCP and PPF,respectively.The results show that the device B2 based on the host material PPF has better performance.Based on the above experimental results,the corresponding electroluminescent devices B1,B3,B4 and B5 were constructed by doping Ir1,Ir3,Ir4 and commercial phosphorescent material FIrpic in the PPF with 7%doping concentration,respectively.The results show that these devices all obtained outstanding performance.Among them,the maximum external quantum efficiency of device B4 reached 21.23%,which is far higher than that of device B5?16.63%?,and the color coordinate of B4?0.15,0.26?is much closer to the pure blue in comparison with device B5?0.15,0.36?.