DFT Study On Electronic Structures And Spectroscopic Properties Of A New Type Of Iridium (â…¢) Complexes

Recent years, transition metal complexes have attracted considerable attention due to their potential applications in organic light-emitting diodes (OLEDs).Up to now, high efficient Ir(Ⅲ) complexes have been extensively studied by optical spectroscopy and electrochemistry techniques, but the processes of luminescence and charge carrier transporting were still not understood distinctly. So the theory studies of the Ir(Ⅲ) metal complexes have attracted more and more attention. Now, the quantum chemistry calculation method, especially the density functional theory, was applied to solve the problems such as the design of molecular structure^ charge transition and the relationship of electronic structure and spectroscopy property. It can provide theory guides for efficient complexes as well as large support in experimental data. In this paper, the electronic structures and spectroscopy property was studied deeply for a new type of Iridium metal complexes by density functional theory, and the desired results were obtained.1,The experimental study revealed that (ppy)2Ir(R-BTZ) ((ppy=2-phen ypyriryl,2-(2'-hydroxyphenyl) benzothiazole (BTZ),2-(3-methyl-2'-hydroxy-phenyl) benzothiazole (3-MeBTZ),2-(4-methyl-2'-hydroxyphenyl) benzothiazole (4-MeBTZ),2-(4-trifluoromethyl-2'-hydroxyphenyl) benzothiazole(4-TfmBTZ)) is a new type of single component complexes with multicolor emitting at room temperature. In this paper, the luminescent mechanism was investigated by quantum chemical calculations based on density functional theory (DFT) and the calculation results are consistent with the experimental data. The-CH3 on 4-position of BTZ influences the electronic structure and the distribution of HOMOs and LUMOs more obvious so that makes the absorption and emission spectra red-shift more distinctively. It is found that the multi-emission bands under ultraviolet light excitation at room temperature were caused by the different energy transfers between different excited states. The blue emitting relates to the ligand center (π→π*) of R-BTZ and the green emission originates in MLCT (ppy→Ir) emission of Ir(ppy)2 fragment. The red emission corresponds to LLCT transition (R-BTZ→ppy) for complexes 1-3, but MLCT (4-TfmBTZ→Ir) transition of Ir(4-TfmBTZ)2 fragment for 4. It can reveal that it is possible to realize a single compound material with broad white emission.2,We all know that Ir(ppz)3 with the 1-phenylpyrazole (ppz) ligand is no-luminous at room temperature. A new type of Ir(Ⅲ) complexes (ppz)2Ir(R-BTZ) (R-BTZ=BTZ,3-MeBTZ,4-MeBTZ,4-TfmBTZ) which were luminous at room temperature were synthesized and the photoluminescence property was measured. In this paper, the relationship of electronic structure and spectroscopy property of these complexes were investigated by quantum chemical calculations based on DFT to provide theory guides for experimental data. It found that the low-lying emission relates to the MLCT (R-BTZ→Ir) of Ir(R-BTZ) fragment and the electronic transition of HOMOs to LUMOs. The red emission peak wavelengths can be fine-tuned from 653 to 689 nm by the electron withdrawing or donating substituent at 3- or 4-position of BTZ ligand. R-BTZ plays an important part in color tuning, and obtained the luminescence mechanism with new ancillary ligand 2-(2-hydroxyphenyl) benzothiazole.