Synthesis And Characterization Of Phosphorescent Polymer Host Materials

Organic electroluminescent materials have dominant position of using the singletexcitons and triplet excitons in the meanwhile, and can make the theoretical internalquantum efficiency of the devices approach to100, so they have a great applicationprospect in OLEDs. However, when the phosphorescent materials are used aloneunder high concentration, there can be happening triplet-triplet annihilation, resultingin the devices efficiency reduced. To solve the problem, the Host-Geust doped systemwas created, namely a kind of phosphorescent guest material is evenly dispersed intoa host material, in order to reduce the interaction between luminescence centers, toavoid the occurrence of triplet excitons quenching, and in the the Host-Geust dopedsystem, the host materials usually accounte for more than90%. At present, the smallmolecular host materials have been studied by many scholars, and the RGBphosphorescent devices using small molecular as host material have been developed aexcellent level. But the small molecular host materials have stringent requirements formelting point and thermal stability of the phosphorescent materials, and thefabrication cost of devices is not low, and phase separation maybe occur. In contrast,the polymer host materials can be easily processed at room temperature by solutionmethods, such as spin coating, ink jet printing etc., and are very significant forachieving the outstanding performance of blue and white spin-coating devices, whichhas a very good prospects for development. But the conjugated polymers usually lowtriplet energy level and energy band, when doped with phosphorescent dye, which hasa high triplet energy level, the energy can be reversed transfer from host to geust,leading to the reduct of device efficiency. Therefore, it is very significant to developthe polymer host materials with high triplet energy level and energy band.The research work of this thesis is based on the development of excellentperformance polymer host materials, and their thermal stability and optical propertieswere studied. The main contents include two parts: Part One: the main work of this part is the synthesis of monomers.1,4-bromobenzene,1,3-bromobenzene,9,9-2,7-bromide-dioctylfluorene and n-butyllithium as the main raw materials, through alternating copolymerization, themonomers bis(4-bromobenzene)diphenylsilane, bis(3-bromobenzene)diphenylsilaneand9,9-dioctylfluorene-2,7-diboronicacid were synthesised. And their structures werecharacterized with1HNMR. Through comparing thermal stability and photophysicalproperty of the obtained polymers, we estimated the phosphorescent devicesperformance, the obtained polymers as host materials. The research results indicatedthat introducing Si atom into the copolymer backbone can enhance the distortion ofnon-coplanar effect, and broaden the energy band of polyfluorene derivatives hostmaterials, making them to be used widely in the phosphorescent devices.Part Two: Synthesis and properties of polycarbazole derivatives. Through theYamamoto reaction,3,6-dibromo-N-pyrancarbazole as main monomer and bis(3-bromobenzene)diphenylsilane as minor monomer with different proportion（5%,12.5%,50%）were copolymerized Through comparing thermal stability andphotophysical property of the obtained polymers, we make a further study on deviceperformance using the obtained polymers as host materials. The research resultsindicated that introducing bis(meta-diphenylsilane) into the copolymer backbone caneffectively improve the energy band of polycarbazole derivatives host materials. Inaddition, the carbazole groups can increase the hole performance of the obtainedpolymers, and alkyl oxygen groups and aromatic silicon segment can also enhancethe electron injection and transmission performance. The charge balance of injectionand transmission is the key factor to improve the efficiency of phosphorescentdevices.