Design, Synthesis And Characterization Of Organic Electrophosphorescent Host Materials Based On Triphenylamine

Based on advantages and applications in display panels and lighting appliances, organic light-emitting diodes (OLEDs) gradually take the dominant position in the field of optoelectronics. Because of holding all the energy of formed exciton after capturing electrons and holes, the organic electrophosphorescent emitters can reach 100% of the theoretical electroluminescent light emission efficiency. The achievement of highly efficient electrophosphorescence depends on host-guest system light-emitting layer. The host materials of host-guest system where the excitons formed need to meet certain requirements, as the entire energy of the host molecules should be delivered to the dopant phosphorescent emitters. Since the several factors restrict each other, the host molecular design needs to achieve a balance between the constraints and the design and synthsis is crucial to the system.In this thesis, we choose triphenylamine unit to construct bipolar host materials, compose the host-guest system and improve efficiency to stabilize device performance. The paper mainly refers to the design, synthesis and characterization of triphenylamine/benzimidazole phosphorescent host materials and oxadiazole, triazole/triphenylamine phosphorescent host materials. According to the characterization results, the problems are deeply analysed to design more suitable molecules and provide a richer selection for industrial applications.The main contents are introduced as follows:(1) Beginning from the market and the concept oforganic electroluminescence, we discuss its development and stage, the advantages in the field of optoelectronics, industrialization, and the light-emitting mechanism, device structure and evaluation parameters. We introduce the advantages of organic electrophosphorescence, mechanism, the electrode materials, transport materials, guest materials and host materials. We review the requirements and design of the host materials and propose the key ideas, the main contents, and the problems to be solved in this paper.(2) A series of triphenylamine/benzimidazole bipolar phosphorescent host materials is synthesized according to the synthetic route. After confirmation of the molecular structure by conventional characterization methods (NMR, mass spectrometry, elemental analysis), we test and analyse the properties in optical, thermal and electrical aspects. The host materials conjugation is well regulated by o-, m-, and p-connected configurations of benzene in order to adjust the intramolecular charge transfer, and the triplet energy levels. TPA-o-BZ and TPA-p-BZ have the higher Tg, which can form a smooth and uniform film and exhibit high morphological stability. Blue phosphorescent OLEDs hosted by TPA-o-BZ show a maximum external quantum efficiency of 10% and a maximum current efficiency of 19.1 cd/A.(3) A series of oxadiazole, triazole/triphenylamine phosphorescent host materials is designed and synthesized by Stille reaction and Suzuki coupling based on organoboron compounds. We analyse the relevant properties of the materials according to the results of characterizatin. Oxadiazole units and triazole unit have similar influence on thermal stability and HOMO/LUMO energy level. The introduction of the flexible a-bond can greatly suppress conjugation and ?-?* transition, which indicates the benefit of flexible a-bond linkages (-CH2-CH2-CH2-) in terms of riching molecular conformations. Blue phosphorescent OLEDs hosted by TPA-S-p-TAZ show a maximum external quantum efficiency of 11.8% and a maximum current efficiency of 22.8 cd/A.(4) A conclusion showing important results for this paper is drawn. An outlook of this field for the ind ustry and research is made.