Synthesis And Properties Of Small-Molecular Organic Electroluminescent Materials Based On Polycyclic Aromatic Hydrocarbons

Organic light emitting diode (OLED) is considered as the most promising "dreaming" display technology in the 21st century because of its unique advantages such as self luminescent display, wide visual angle, fast response time and simple fabrication process. The OLED devices work on the principle of electroluminescence, which means holes and electrons are generated from each of the electrodes and recombined in the organic emissive layer to form excitons, then light is emitted with the process of excitonic radiative decay. However, the hole and electron mobility of organic materials are usually unmatched, which will leads to considerable carrier-imbalance in the emitting layer and ultimately impacts on the device efficiency and stability. Therefore, it is of most importance to design and synthesis new materials with desirable carrier transporting abilities and excellent thermal stability as well as the optimization of various functional layers of device structure in order to realize commercial OLED device requirements with high efficiency and long lifetime.The main contents and results are generalized as follows:In Chapter 1, recent progress of small-molecular organic light-emitting materials and devices, especially the application of polycyclic aromatic hydrocarbons (PAH) in OLED, is reviewed.In chapter 2, we synthesized two new unsymmetrically indene-substituted 10-naphthyl-anthracene derivatives, DMIP-1NA and DMIP-2-NA, investigated their photophysical and electrochemical properties, and fabricated their relative blue doped OLED devices as well. The two robust blue host materials process good thermal stabiliy and high HOMO/LUMO engery gap (Egap> 3.0 eV). The efficient doping concentraion of BD-1 blue dopant in these three-layer devices was under a wide range of 3%-7%. The operational lifetime of their relative 7%doped devices at an initial luminance value of 100 cd/m2 were 12500 h and 8600 h, respectively. Further optimized device structure based on DMIP-2-NA exhibited a maximum power efficiency of 8.39 lm/W (7.6 cd/A at 2.90 V).In chapter 3, we synthesized a series of 2,3;6,7-tetra(methoxyl)-9,10-diarylanthracene derivatives and investigated their photophysical and electrochemical properties. All of these compounds own low oxidation potentials, and their HOMO energy levels are in the range of-5.2 eV～5.3 eV, which is energetically favorable for hole injection. Device performance of these non-amine based hole transporting materials was much better compared with NPB-based control devices. Further optimized green doped device structure based on one of the compounds TMOADN exhibited a current efficiency of 25.6 cd/A (13.4 lm/W) at 20 mA/cm2 with external quantum efficiency of 7.05%.In chapter 4, we synthesized a series of diarylbenzo[k]fluoranthene PAH derivatives and investigated their photophysical and electrochemical properties. The aryl subsituents in C-3 position of diarylbenzo[k]fluoranthene can efficiently enhance the thermal stability (Tg: 174～219℃) and electrochemical stability of target compounds. OLED devices based on one of the C-3 substituted compounds, PDNBkF, exhibited deep blue emission with CIEx,y (0.15,0.14). The coupled dimer of diarylbenzo[k]fluoranthene (DNTPPF) is also a potential material for red fluorescent dopant in OLED. Device based on DNTPPF achieved good color purity and current efficiency under a wide range of doping concentration (3-5%), which is almost 10 times higher than the control device based on a commercial red dopant DBP.In chaper 5, a novel series of benzo[k]fluoranthene derivatives by incorporating diarylamine group have been synthesized and characterized. All the benzo[k]fluoranthenes process high thermal stability with glass transition temperature (Tg) of 162～205℃The employment of electron-donor diarylamine group efficiently elevated the HOMO energy level of these fluoranthene derivatives to about-5.3 eV, and enhanced the hole transporting ability as well. Two-layer electroluminescent devices employing them as the hole-transporting layer and light-emitting layer achieved efficient green emission under low driving voltage. A further optimized three-layer device based on one of these compounds, PNDPBF, exhibited a maximum current efficiency of 10.2 cd/A (6.7 lm/W). In addition, the unsymmetrical D-π-D molecular structure is favorable for two-photon fluorescence response. In chaper 6, we synthesized a series of C-2 substituted 2-methyl-di(2-napnthyl)anthracene (MADN) derivatives, and investigated their photophysical and electrochemical properties. These materials own high quantum efficiency, good thermal stability or high carrier mobility. Some of the materials, dimer of MADN and C-2 cyano-substituted CNADN, were successfully applied in OLED devices as blue host materials or electron transporting materials with superior performance compared with MADN-based devices, respectively. In Chapter 8 is conclusion.