Synthesis And Electroluminescence Properties Of Novel Red Iridium Complexes

Organic luminescent materials play a more and more important role in the fields of display,lighting and information security in recent years.Phosphorescent organic materials based on transition metal complexes as luminescent materials have drawn great interest since the strong spin-orbit coupling?SOC?and fast intersystem crossing could lead to a harvest of both singlet and triplet excitons in the emitting layer and achieve internal quantum efficiency as high as 100%theoretically.Among the reported heavy-metal complexes,Ir?III?complexes are considered as the most promising emitters in OLEDs based on their relatively high phosphorescence quantum yields,short triplet excited-state lifetimes,excellent color tunability from blue to deep-red and splendid thermal and electrochemical stability.Currently,great success has been acquired in green,yellow,and orange emitting complexes.Nevertheless,the highly efficient and stable saturated red to deep-red phosphorescent emitters remains an unresolved issue.According to the energy gap law,the nonradiative rates(k_nr)would increase,while the radiative rates?k_r?tend to decrease in the lower-energy regions of the visible spectrum?orange to red?.Meanwhile,the extension of the conjugated system would cause adjacent molecular packing,which lead to severe triplet-triplet annihilation?TTA?.In view of this,a series of novel orange-red to deep-red phosphorescent iridium complexes with 2-phenylquinoline derivatives or 2-aryl-6-trifluoromethylbenzothiazole as main ligands were designed and synthesized in this thesis.The photophysical properties,electrochemical properties,theoretical calculations and device performance were also studied.The specific research contents are as follows:1:Most of the reported iridium complexes with 2-arylquinoline or its derivatives as cyclometalating ligands are orange-red phosphorescent with peak wavelength below 600 nm.Herein,trifluoromethyl?CF₃?or Fluorine?F?is introduced into the 6-site of quinoline ring to design and synthesize the cyclometalated ligands 2-phenyl-6-CF₃/F-quinoline?CF₃-phq or F-phq?and heteroleptic iridium complexes Ir?CF₃-phq?₂?acac?,Ir?CF₃-phq?₂?tmd?,Ir?F-phq?₂?acac?and Ir?F-phq?₂?tmd?.Among them,the phosphorescence of CF₃–containing iridium complexes are saturated red with peaks at 627-630 nm.Especially the Ir?CF₃-phq?₂?tmd?based red OLED realized pure red electroluminescence with Commision Internationale de L'Eclairage?CIE?coordinates of?0.67,0.33?with a high brightness of 12695 cd m^-2 and a maximum external quantum efficiency of 14.96%,respectively.2:Because of the simple structure,easy modification,strong coordination ability,and high luminous efficiency and stability during device preparation,2-phenylbenzothiazole has been widely concerned as the ligand framework of iridium complexes.However,the luminescence wavelength of the complex Ir?bt?₂?acac?with 2-phenylbenzothiazole derivatives as the main ligand is in the range of orange to orange red,which is still a certain distance away from the wavelength of standard red light or even deep red light.Based on the above,we introduced substituents with different donor capabilities and different degrees of conjugation at the 2-or 6-position of the benzothiazole ring to synthesize four first ligands,and seven novel Iridium complexes were obtained using acac and tmd as auxiliary ligands.The emission wavelengths of these new complexes all show a red shift of 30-100 nm.In addition to the red-shift of the emission spectrum by the modified group,the steric effect of the group can also improve the luminous efficiency of the material and the stability of the device.The device D6 based on M6 showed a maximum emission of 584 nm?the parent is556 nm?,the maximum brightness(L_max)reached 40252 cd m^-2,the maximum power efficiency??_P?was 26.45 lm W^-1 and the maximum external quantum efficiency(?_ext)was 15.97%with the CIE coordinate of?0.56,0.43?.It is worth noting that at a high brightness of 10000 cd m^-2,the external quantum efficiency(?_ext)is still as high as 12.50%,which is only a decrease of21.7%.This indicates that the efficiency of the device is stable and the roll-off is small.