| Organic light emitting diode(OLED), which is widely used in lighting, full-color display, flat panel display for background source, has become a research focus with the advantages of low power consumption, short response time, wide viewing angle and self-luminous. Recently, researchers have developed a variety of organic electroluminescent materials. Metal complexes of quinoline system are widely applied to the OLED with good transmission performance, good vacuum evaporation film-forming properties, high quantum efficiency, good stability.The8-hydroxyquinoline aluminum,8-hydroxyquinoline gallium and8-hydroxyquinoline zinc are known as fluorescent materials. Iridium complexes of quinoline and its derivatives are also widely used in the phosphorescent materials. Compared with fluorescent materials, organic electroluminescent devices based on phosphorescent materials own more advantages. The introduction of metal atoms produces strong spin orbit coupling in the phosphorescent materials. Therefore, internal quantum efficiency can reach 100%theoretically. Iridium complexes have obvious phosphorescence at room temperature because of their strong spin orbit coupling phenomenon.At present, quinoline indium complexes are concentrated in the range of deep red and orange light. However, the yellow, green and blue spectral is less studied. Therefore, quinoline system iridium complexes show a narrow range of the emission spectra. We designed and synthesized six2-substituted quinoline ligands to achieve quinoline system iridium complex of yellow and green light emission by introducing a nitrogen-containing group in ring group with small electron cloud density.Ir(2-phq)3has been reported as red phosphorescent material, with the emission wavelength at600rm.4-Methyl-2-phenyl quinolinethe was used as auxiliary ligands. The introduction of1-phenylpyrazole (ppzH) as main ligands was to reduce the conjugated group. Such combination was to achieve orange light by blue shift. The synthesis of (ppz)2Ir(tbq) was a great encouragement with the emission peak of575nm. By adjusting the structure of the auxiliary ligand from benzene ring(tbqH) to thiophene(tpqH), pyridine(tdqH) and pyrimidine(tmqH), we obtained a series of phosphorescent materials with the emission peak from558-619nm. The compounds were characterized by1H NMR and single crystal analysis. UV-vis absorption and photoluminescence(PL) spectra were measured in CH2CI2. The emission peak of (ppz)2Ir(tpq) was located at590and619nm, and (ppz)2Ir(tmq) at558nm. The phosphorescent emissions of other materials were observed with peaks between558and594nm. In the iridium complexes containing different substituents:(ppz)2Ir(tpq),(ppz)2Ir(tbq),(ppz)2Ir(tdq),(ppz)2Ir(tmq), electron cloud density reduced in the order of the substituted:thiophene> benzene ring> pyridine> pyrimidine, which caused the blue shift of emission wavelength. The cyclic voltammograms of iridium complexes presented reversible redox peaks. The energy gap of (ppz)2Ir(tpq),(ppz)2Ir(tbq),(ppz)2Ir(tdq),(ppy)2Ir(tdq),(ppz)2Ir(tmq),(ppy)2Ir(tmq) were2.21,2.52,2.42,2.47,2.64and2.48eV, respectively. The device structure was ITO/NPB(40nm)/CBP:iridium complex8wt%(30nm)/Bphen(40nm)TPBi(40nm)/LiF(1nm)/Al(200nm) based on the system of iridium complexes doped into CBP. The electroluminescence (EL) spectrum of (ppz)2Ir(tdq) and (ppy)2Ir(tdq) gave emission peak at about510and540nm, which realised quinoline system iridium complex green light. The maximum luminance of (ppy)2Ir(tdq) achieve26650cd·m-2, and maximum current efficiency at16.76cd·A-1.The iridium complexes with monodentate ligand (ppz)2Ir(tdq),(ppy)2Ir(tdq),(ppz)2Ir(tmq) and (ppy)2Ir(tmq) had extremely high yield at mild reaction conditions (70℃). The PL spectra of complexes showed strong solvent effects, while the EL spectra owned high brightness and current efficiency. The mechanism of this phenomenon are under further discussion. |
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