Preparation Of Orange/Greenish Yellow Phosphorescent Iridium(?) Complexes For Highly Efficient Organic Light-emitting Diodes

Recently,owing to their excellent performance,such as super-thin thickness,flexibility,high color gamut,organic light-emitting diodes(OLEDs)have been attracting considerable attentions.OLEDs will play an important role in the flat panel displays and solid-state lightings in the future.Phosphorescent iridium(?)complexes are considered to be one of the most promising candidates because of their stable chemical structure,high quantum efficiency,relatively short excited lifetimes and tunable emission wavelengths in the range of visible light.However,the current Orange and greenish yellow phosphorescent emitters often suffered from the relatively low quantum efficiency and the aggregation caused phosphorescence quenching.In this thesis,we designed and synthesized a series of novel phosphorescent iridium(?)complexes featuring different emission wavelength by utilizing various cyclometalated ligands and their substituent engineering.The photophysical properties of the iridium(?)complexes designed were comprehensively investigated.The electroluminescence performance was evaluated by employing the iridium(?)complexes as the dopants.The detailed work is as follows:Firstly,by selecting two pyridylimidazole derivatives as the ancillary ligands,we rationally designed and synthesized two highly efficient Orange neutral iridium(?)complexes(Ir1 and Ir2).Their photoluminescence emissions exhibited the maximum peak at 595 nm with maximum solution quantum yields up to 0.57.Employing Ir1 and Ir2 as emitters,the fabricated Orange organic light-emitting diodes show excellent performance with the maximum external quantum efficiency(EQE),current efficiency(CE),and power efficiency(PE)of up to 22.15 %,36.89 cd/A,and 35.85 lm/W,respectively.Furthermore,using Ir2 as Orange emitter,a tri-chromatic hybrid white OLED was fabricated,showing good warm white emission with low correlated colour temperature(CCT)of < 2200 K under the voltage of 4-6 V.The white device also realizes excellent device efficiencies with the maximum EQE reaching 22.74%.To the best of our knowledge,the EQE value is the highest record so far for hybrid white OLEDs with low CCT below 2500 K.Secondly,we designed and synthesized a novel bis(trifluoromethyl)phenyl functionalized iridium(?)complex.The complex shows intensive greenish yellow phosphorescence with the maximum peak at 525 nm,high photoluminescence efficiency(0.90)and moderate full width at half maximum(72 nm).The bulky bis(trifluoromethyl)phenyl moiety introduced into the complex provides the excellent solubility for solution-processed organic light-emitting diodes.The maximum power efficiency and current efficiency of electroluminescence are 4.13 lm/W and 9.54 cd/A,respectively.Thirdly,a novel and highly efficient thiophenquinolone-based Orange iridium(?)complex bearing a bulky fluorophenyl moiety was designed and synthesized.Its photoluminescence emission showed the maximum peak at 596 nm,high photoluminescence efficiency(0.62)and broad full width at half maximum(81 nm).The bulky fluorophenyl moiety introduced into the complex could improve the efficiency of electroluminescence due to the effective steric hindrance in solid states.The maximum current efficiency,power efficiency and the external quantum efficiency of the fabricated orange OLEDs could be up to 29.0 cd/A,30.4 lm/W and 17.6%,respectively.