Synthesis And Properties Of Iridium Phosphorescent Complexes Using Phenylpyridine Derivatives As Cyclometalated Ligands

Organic electroluminescence technology is a new generation of display technology.It has attracted people’s attention for its active light,low-voltage drive,ultra-thin,rich color,and full-color soft-screen display technology features.It is also known as a next-generation display technology which will replace the liquid crystal display.At present,organic electroluminescence technology has been widely used in the fields of display,lighting,wearable and other fields.One of the cores of organic electroluminescence technology is luminescent materials,and the development of high-performance,long-life luminescent materials is the key to this technology.Phosphorescent complex materials can fully realize the electroluminescence by using triplet excitons,and theoretically achieve 100% internal quantum efficiency(IQE),which is one of the research hotspots in this field,and further enhance its luminescence,efficiency and long lifetime have always been important aspects of the development of phosphorescent materials systems.The research focus of this thesis is on the design,synthesis and photoelectric properties of phosphorescent iridium complex materials based on phenylpyridine chelate ligands.We designed and synthesized seven homogeneous/mixed iridium complexes,and systematically studied their thermal stability,photophysical properties,electrochemical properties,crystal analysis,theoretical calculations and electroluminescence properties.And we discussed the relationship between the different structures and properties of molecules,further clarifying the relationship between the structures and properties of such materials.1.In the second chapter,we have detailed description and discussion on the synthesis of this series of iridium complexes,and detailed characterization of the structure and purity of the complexes by means of nuclear magnetic resonance,mass spectrometry,elemental analysis,liquid chromatography and other analytical instruments.The results show that the above complexes can be obtained in accordance with the purity which can be used in the electroluminescent device under a simple separation and purification process,which is beneficial to the later mass production and industrial application.Among them,the complex molecules of the mixed structure using two different chelating ligands,namely(C^N)x Ir(C^N)3-x,have the stability of the homologous compound molecules,and at the same time,they exert dual ligands.Luminous properties are conducive to enriching material design and improving the photoelectric properties of materials.2.In the third chapter,we obtained the crystal structures of five kinds of complexes by solvent diffusion method,and analyzed their molecular structure and stacked structure by single crystal diffractometer.The results show that the molecules in the crystal are combined by weak interaction force,and there are weak interactions between π…π between M3 molecules,and only C-H…π weak mutual interaction between other complex molecules.This relatively weak intermolecular interaction facilitates the phosphorescence self-quenching of the material molecules in a solid state(powder or film).In addition,the difference in ligand structure brings different stacking distances and tightness,indicating that we can change the material stacking structure by adjusting the ligand structure,thereby changing its photoelectric properties.3.In the fourth chapter,we characterized and analyzed the properties of thermal stability,photophysics and electrochemistry,the relationship between different molecular structures and properties of the complexes was systematically discussed.The results show that the series of complexes have good thermal stability and have a short photoluminescence lifetime.We also studied the frontier orbital distribution,orbital energy levels,and corresponding absorption and emission of different complexes between different complexes due to the different ligands used and the different ratios of the same ligands.Moreover,by comparison,it can be seen that the designed compound has more excellent performance,and the properties of the material can be adjusted through ligand adjustment.4.In the fifth chapter,we used six kinds of complexes as the luminescent objects,and were doped into the classical host material CBP.The electrophosphorescent device with simple structure was prepared and its electroluminescence properties were tested and characterized in detail.The results show that the fabricated devices have a low turn-on voltage,high brightness and high luminous efficiency,and the device has a small roll-off efficiency as the voltage increases.In contrast,the complexes with mixed chelating ligands not only achieve a fine regulation of the luminescent color to a certain extent,but also improve the electroluminescence efficiency,and avoid the process of complex structural modification of the ligand.It is a simpler and more efficient way to design and improve the molecular structure of complexes.