High-efficiency Phosphorescence Iridium Complexes: Synthesis, Photophysical Characterization, And Use In Organic Light Emitting Diodes

In order to increase the performances of phosphorescent OLEDs, in this thesis, a series of phosphorescent iridium complexes were designed and twelve ligands (including nine of new ligands) and sixteen of cyclometalated iridium complexes (including fourteen of new complexes) with 2,5-diphenylpyridine, 2-phenylthiazole, arylquinoline (isoquinoline), and 2-benzo[b]-thiophen-2-yl-pyridine based ligands have been synthesized and characterized to investigate the effect of the simple ligand modification on photophysics, thermostability and electrochemistry. The majority of the complexes have the general structure (C^N)2Ir(acac), where acac is acetylacetone, (C^N)2 is a monoanionic cyclometalating ligand (e.g., 2,5-diphenylpyridyl (dppy), 2,5-di(4-methoxyphenyl)-pyridyl (dmoppy), 2,5-di(4-ethoxyphenyl)pyridyl (deoppy), 2,5-di(4-ethylphenyl)-pyridyl (deppy), 2-phenylthiazole (ptz), 2-(4-ethylphenyl)- thiazole (eptz), 2-(4-methoxyphenyl)quinoline (mopq), 2-(4-biphenyl)quinoline (bpq), 1-(4-biphenyl)isoquinoline (bpiq), 2-benzo[b]thio-phenyl-4-methylpyridine (btmp), and 2-benzo[b]thiophenyl-5-trifluoromethyl- pyridine (btfmp) ). The (dppy)2Ir(acac), (bpq)2Ir(acac), and (btmp)2Ir(acac) have been characterized using X-ray crystallography. Calculation on the electronic ground state of (dppy)2Ir(acac) and (btmp)2Ir(acac) were carried out using B3LYP density functional theory. HOMO levels are a mixture of Ir and ligand orbitals, while the LUMO is predominantly monoanionic cyclometalating ligand based. The absorption, emission, cyclic voltammetry and thermostability of the complexes were systematically investigated. The complexes emit green to red phosphorescence with wavelengths ranging from 531 to 648nm. The iridium complexes exhibit an reversible oxidation wave due to Ir(Ⅲ)→Ir(Ⅳ). The HOMO and LUMO energy levels for each complexes are located from the cyclic voltammogram and the absorption edge. The 10% weight reduction temperatures of the major complexes are in the range from 300 to 400oC, and suitable...