Design, Synthesis And Application Of Host And Emitting Materials For Organic White-Light-Emitting Devices

Organic light-emitting devices (OLEDs) have attracted intense attention high research enthusiasm in both scientific and industrial communities due to their many unique advantages, such as ease of fabrication, low-cost manufacturing using solution-processed technology, and tunable molecule structure and emission color, and its potential applications in next generation flat-panel displays and solid-state lighting sources. The performances of white organic light-emitting devices (WOLEDs) base on solution process are still much lower than vapor deposition technology at present, expecially in terms of efficiencies and stability. In most of the solution process WOLEDs, polymers and metal-containing phosphorescent were used as the host and dopant. Therefor, the high efficiency of WOLEDs depends on the development of the phosphorescent guest and the host materials. Herein, the mainly purpose of this study is to design and synthesis host and phosphor materials, optimizing device structure and realize efficient WOLEDs.1. Based on the concept of "D-A" polymers, two blue-emitting fluorescent polymers with small singlet-triplet splitting and intermolecular charge transfer (ICT) have been designed and synthesized as host materials. These polymers show high ET, high thermal stability, bipolar transporting properties and suitable energy levels. An appropriate overlap between the HOMO and LUMO in these compounds was realized and this endows the two blue-emitting polymers with higher fluorescence quantum yield and small singlet-triplet splitting (<0.5eV). By comparing the two polymers, the electrochemistry, thermal stability and bipolar transporting properties have been improved after the introduction of phosphine oxide. Single emission layer F-P hybrid WOLEDs using polymer as the blue fluorescent emitters and hosts for phosphors have been fabricated based on a simple configuration and all the organic layers were deposited by a solution process. There is no need to incorporate an interlayer between the fluorescent and the phosphorescent dopant layers to separate and utilizate of singlet and triplet excitons, which simplified the fabrication process. The device showed a high device performance with a maximum CE of10.5cd A-1and a maximum EQE of6.1%. The excellent electrochemistry, electroluminescent properties and bipolar properties show that The D-A design strategy provided a method for preparation F-P WOLEDs host.2. A series partially conjugated polymer host containing phenylcarbazole and heteroatom-containing groups as a building blocks have been designed and synthesized. The copolymers realized a twisted molecular configuration, high ET and thermal stability by comprising a rigid phenyl-substituted carbazole plane and bulky heteroatom-containing triangular pyramid or tetrahedron, and they can be used as the blue phosphor host. The quantum calculation also show the conjugation of the polymer mainchain can be partially interrupted by the incorporation of heteroatoms, and the triplet energy of the polymers can be maintain (>2.72eV). On the other hand, introduction of the phosphine oxide units and carbazole units into the polymers endow them excellent electron/hole injection/transporting capabilities and balancedcarriers transporting properties. In the absence of the electron transport layer, the blue device based the polymers as hosts were fabricated by solution method. The efficiency and luminances of these devices are higher than PVK based devices (2-9and2-3fold respectively). In this contribution, we present another way to construct stable, high ET and solution processable polymers.3. The relationship between the molecular frontier orbital and structure of complexs based on2-phenyl-benzothiazole ligand were studied in experiment and theory and the methods of tuning the band gap and bathochromic-shift emission wavelength were summed. We achieved different red shift emission phosphors by introduction electron donating/withdrawing groups into the2-phenyl-benzothiazole ligand. At the same time, the phosphorescence quantum yield was improved while the exciton lifetime reduced since the CF3group was introducted. The most interesting is the phosphors show almost the same PL and EL emission spectrum in solid state compared with that in solution. The method of tuning the emission color and intermolecular interaction of cyclometalated ligands provided a possibility to improve the device performance.4. Two long wavelength emission phosphors base on2-phenyl-benzothiazole ligand have been synthesized as acomplementary of sky-blue (FIrpic) emission. The solution processed single emission layer OLEDs with these phosphors as dopant shoe excellent performances. In the absence of electron transporting layer, highly efficient orange electroluminescence with a maximum efficiency of10.5cd A-1and two-element WOLEDs exhibited a high efficiency of28.3cd A-1were realized. The two-element and three-element WOLEDs based the red phosphors also exhibited excellent performances. The three-element WOLEDs with a maximum luminances20000cd m-2and the maxmium current efficiency14.6cd A-1was achieved.