Theoretical Studies On The Excited State And Spectral Properties Of Iridium/ruthenium Complexes

The greenish–yellow or yellow emission is one crucial chromaticity component to high-performance white OLEDs（WOLEDs）. Usually, the WOLEDs are made up of three primary colors（RGB）, so there is a great gap（up to 100 nm） in the white-light spectrum because the wavelengths of typical green and red emitters are 520 and 620 nm, respectively, leading to the uncontinuity of the spectrum of WOLEDs. To solve this problem, one way is to incorporate yellow emitter into RGBbased WOLEDs, and the other is to directly replace the green emitter or replace both green and red emitters by a greenish–yellow emitter with broad full width at half maximum（FWHM）. Considering that the performance of greenish–yellow or yellow emitters is significantly behind those emitting in the three primary colors, it is urgent to design and synthesize these phosphorescent emitters with high quantum efficiency and broad width at half maximum. Phenylquinoline（PQ） is a kind of excellent ring metal ligand, red luminescent materials based on the luminescent quantum efficiency is higher, and the luminescent material based on yellow green or yellow phenylquinoline very rare. From the view of molecular design, it can be controlled by the metal center or transform using a special functional group in the ligand on the phosphorescent light the physical properties of the complexes. Starting from the microscopic structure of molecule by quantum chemistry calculation method, in-depth analysis of the molecular ground state, excited state properties, optical properties and charge transfer properties, reveal the essential geometric structure and photoelectric properties, further prediction of luminescent properties of new materials. calculation of the absorption quantity of the electronic substituent using the theory of position, and different types of ring. The effect of metal ligand on the structure and the excited state properties of the iridium complexes based on the structure of the complexes of the benzene and its compounds, in order to guide the design of the yellow-green material in theory.Main research contents are as follows:1. Fluorine atom has a strong electron withdrawing effect, the CF3 group also has a strong electron withdrawing effect, introducing fluorine atoms in the ring metal ligand complexes can reduce the HOMO level and improve the electron transfer rate of the phosphorescent transition metal complexes. We designed the phenylquinoline iridium（III） complexes（Ir MePQ2）（acac）（the experiment in dichloromethane solution was orange light with the emission at 597 nm.）. In order to further blue shift of emission, we have designed a series different substituent number, location, and type of the fluorine of cyclometalated iridium complexes, through the research of the density functional theory, revealed the factors that affect the luminescence efficiency. It was found that the complexes with single fluorine, double fluorine, three fluorine or CF3, their emission basically shows a blue shift trend, blue shift the most is complexes 9 which was substituted by CF3, up to 37 nm. Fluorine substituted complexes 6,7 have more blue shift and up to 30 nm. Therefore the best way to control the blue shift is that the complexes substituted with three fluorine atoms, and the place is near the metal interproximal counterpoint.2. 4FPZ is a significant blue shift as everyone knows auxiliary ligand, mainly by decreasing the HOMO level of Ir complexes. We have designed a series of iridium complexes based on Mepq derivatives with 4FPZ as auxiliary ligands. The electronic structure, excited state properties and spectral properties are studied through theoretical calculation, and the properties of the complexes were compared with that of the last chapter. The study found that the electron donating ability of 4FPZ auxiliary ligand is weak, the energy level of HOMO is lower, the energy gap becomes larger and the emission spectrum is blue shifted. The fluorine substitution is one of the methods to control the luminescence blue shift of the complexes on the basis of 4FPZ assiatant ligands. It is more suitable as yellow or yellow-green light materials.3. Here, we use the density functional theory to study the response of Ru complexes to hydrogen ion, explained the reasons for the response from the theoretical calculation. The study found that adding HSO3- ions in solution of Ru-1, the HOMO of the complex Ru-1 from 2-phenyl pyridine of the ring metal ligands and the metal center transfer to the methylene of the benzo [e] indole ligand. LUMO is distributed over the whole ring metal ligand, LUMO+1 and LUMO+2 are mainly distributed in the two bpy ligand system onto π* bpy ligands. The significant decrease in the energy gap of HOMO-LUMO leads to a red shift of the absorption of the complex Ru-1 with the addition of HSO₃- ions.