Synthesis And Electroluminescence Of Red Organic Fluorescent And Phosphorescent Materials

Organic light-emitting diodes (OLEDs) have been one of the research focuses in science and industry due to their great application prospects in flat-panel displays and white-light lighting. As one of the primary colors (red, green and blue), the red emitters are required for full-color applications and white-light lighting. However, they are scarce with low efficiency among emitting materials. It is essential to develop new red emitters and improve the luminance and efficiency. In this dissertation, a series of red fluorescent and phosphorescent materials were designed and synthesized. The electroluminescent properties of these materials were studied.First, an effective way to solve the fluorescent quenching effect and reduce the cost of device production is to design and synthesize red host emttiers that are capable of being made non-doped OLEDs by solution-processing methods. Dendrimers with well-defind three dimensional dendritic structures are perfectly able to be served for this demand. Therefore, a series of red light-emitting dendrimers up to second generation based on a perylenediimide (PBI) core and polyphenylene dendron with pentafluorophenyl, cyano, carbazole and N-phenyl-1-naphthalenamine surface groups, were prepared via Diels-Alder cycloaddition. The second generation dendrimers were obtained by the traditional divergent way. The maximum molecular weight of these dendrimers approached ten thousands. And they show good solubility in common organic solvents so that it is possible to fabricate devices by solution methods such as spin-coating. The hypsochromic effect was observed for these dendrimers in both absorption and fluorescence spectra of the solid film compared with their solution. This implies the excellent site-isolation effect of the bulky dendrons and surface groups on the PBI emissive core. These dendrimers show strong red fluorescence in solution and the highest quantum yield is95%. The cyclic voltammty measurements were performed to investigate the redox properties of these compounds. Two reversible reduction waves were observed for all of them, indicating that they possessed good electron transport properties. And the dendrimers with carbazole surface groups show an additional oxidation peak, demonstrating the hole transport nature of them. All the dendrimers start to decompose at a high temperature up to400℃, indicating the excellent thermal stability. They were used as non-doped emitting layer to fabricate OLEDs by spin-coating method. The EL spectra are located at orange-red region. The OLED based on Gl-Cz has the highest luminance and current efficiency as220.7cd m-2and0.22cd A-1, respectively. This is the better data among the devices based on PBIs materials.Second, in order to increase the emission efficiency, novel phosphorescent iridium complexes were developed for use in red OLEDs, since electrophosphorescent materials are advantageous over fluorescent materials in much higher device efficiency. The Ir(Ⅲ) complexes containing2-phenylbenzothiazole and its derivatives as major cyclometalating ligands are typical yellow/orange phosphorescent materials, which are widely used in both single color and white OLEDs. These iridium complexes have merits such as high phosphorescent quantum yields and easy synthesis in comparison with other analogues. However, the few derivatives are only those with simple substituents on the2-phenylbenzothiazole ligands, the emitting color of whom are also limited in yellow or orange range. In order to develop novel phosphorescent materials with excellent performance and various emitting colors, four2-arylbenzothiazole ligands frameworks were designed and synthesized by introducing dibenzofuran, dibenzothiophene, dibenzothiophene-5,5-dioxide, or dipenylphosphine oxide into the2-position of benzothiazole moiety. Their biscyclometalated iridium (Ⅲ) complexes with acetylacetone (acac) as ancillary ligand were then prepared. These complexes emit orange-red phosphorescence at room temperatures in solid films with emission peaks at590nm to610nm. And the phosphorescence shows red-shift trend with increasing electron-withdrawing ability of the aryl part. The high performance phosphorescent OLEDs were fabricated using these complexes as doped emitters. One of these OLEDs exhibited a maximum luminance of55530cd m-2and the highest efficiency of54cd A-1, which are among the best results reported for orange OLEDs so far. All the data indicate that these Ir(Ⅲ) complexes are promising yellow to orange-red organic phosphorescent materials.