Synthesis And Characterization Of Wide Band-gap Organic Electro-optical Materials Based On Triphenyl Phosphine Oxide Derivatives

In recent thirty years, the academics have devoted a lot of time to study OLEDs(Organic Light-Emitting Diodes, OLEDs) for their wide applications in the next generation full color flat panel displays and low-cost solid-state lighting. However, the research progress of OLEDs has come up with the bottleneck. Although the theoretically internal quantum efficiency of the phosphorescence organic light-emitting diodes(Ph OLEDs) can reach up to 100%, the problem of looking for ideal host materials with excellent electrochemical properties and device performance still exsits. The introduction of the triphenylphosphine oxide as bridging groups to get bipolar host materials is a novel design idea. By using the electron-transporting characteristic of triphenylphosphine oxide, we can introduce different proportion of the electron-rich groups to the backbone. Carbazole and spiro[fluorene-9,9’-xanthene]-based moieties have been introduced to the triphenylphosphine oxide to prepare a series of small molecules and polymers in this work. The nuclear magnetic resonance(NMR), mass spectrometry(GC-MS) and elemental analysis is used to characterize the molecular composition and chemical structure of the material; The characterization of differential scanning calorimetry(DSC) and thermal gravimetric analyzer(TGA) is also conducted to investigate the thermal stability of the polymer; The measurement of cyclic voltammetry(CV), ultraviolet-photoluminescent spectra and device applications is also illustrated to study the energy band levels and luminescence properties of the material.Two novel wide band gap compounds 2SFOPO and SFOPO-CZ with the core of triphenyl phosphine oxide were synthesized and characterized as host materials for Ph OLEDs. Both of them show high thermal stability with glass transition temperatures in a range of 105-122 °C and thermal decomposition temperature at 5% weight loss in a range of 406-494 °C. The photoluminescence quantum efficiency up to 78 % in thin solid film is obtained. The optical band gaps of compounds 2SFOPO and SFOPO-CZ in CH2Cl2 solution are 3.46 and 3.35 e V, and their triplet energy levels are 2.51 e V and 2.52 e V, respectively. As a result, the green phosphorescent organic light-emitting diode of compound SFOPO-CZ doped with tris(2-phenylpyridine) iridium fabricated by vacuum evaporation method shows electroluminescent performance with a maximum current efficiency(CEmax) of 52.83 cd·A-1, maximum luminance of 34604 cd/m2, maximum power efficiency(PEmax) of 39.50 lm·W-1 and maximum external quantum efficiency(EQEmax) of 14.1%. However, the red phosphorescent organic light-emitting diode hosted by compound 2SFOPO with bis(2-phenylpyridine)(acetylacetonato) iridium(III) as the guest exhibits a CEmax of 20.99 cd·A-1, maximum luminance of 33032 cd/m2, PEmax of 20.72 lm·W-1 and EQEmax of 14.0%. Compound SFOPO-CZ exhibits better green device performance, while compound 2SFOPO shows better red device performance in phosphorescent organic light-emitting diodes.Then, we introduced carbazole to the different positions of benzene of triphenylphosphine oxide, which produced four polymers of PB13 CZ, PTPPO38 CZ, PTPPO13 CZ and PTTPO27 CZ. All the polymers exhibit good thermal stability with thermal decomposition temperature at 5% weight loss in a range of 411-428 °C. The energy band gaps of four polymers were calculated from ultraviolet absorption spectrum. The triplet energy level of four polymers can also be calculated by the characterization of low temperature phosphorescence spectrum, and the highest triplet energy level of polymer is 2.70 e V. The spin coating method was used to prepare the green Ph OLEDs with polymer PTPPO13 CZ and PTTPO27 CZ as the host materials. The green device of polymer PTTPO27 CZ as host shows the better electroluminescent performance with CEmax of 1.96 cd·A-1 and EQEmax of 0.55%. The green device of polymer PTPPO13 CZ as host shows electroluminescent performance with CEmax of 0.44cd·A-1 and EQEmax of 0.14%As illustrated in this thesis, the triphenylphosphine oxide has played an important role to improve the thermal stablity, photoelectric properties and device performance of host materials. We believe that it will show great significance to develop the new materials of organic electrophosphorescent devices based on triphenylphosphine oxide derivatives in the future.