| Organic light-emitting diodes (OLEDs) hold potential for application in flat-panel displays owing to rapid progress in material design and device fabrication. Of the organic light-emitting materials, phosphorescent materials are particularly promising because they can harvest light from both singlet and triplet excitons, enabling the fabrication of devices with internal quantum efficiency close to100%.The purpose of this paper is to design and synthesize novel electrophosphorescent materials and to fabricate highly efficient OLEDs. As well known, the iridium complexes containing2-phenylbenzothiazole as cyclometalating ligands are a series of yellow-emitting phosphors that are widely used in monochromatic and white OLEDs. However, there have been scarce derivatives of the iridium complexes that containing benzothiazole moiety in ligands so far. Most of the thiazole-based ligands are based on2-aryl-benzothiazole ligand frameworks. Furthermore, the emitting color of the current derivatives are only limited in yellow range. On the other hand, linear-or cyclo-alkenyls have been used to construct cyclometalating ligands for iridium complexes. In this dissertation, for the first time we introduced the cycloalkenyls (from6-membered to8-membered ring) to design and synthesize2-cycloalkenyl-benzothiazole ligand frameworks and their iridium complexes with acetylacetone (acac) with ancillary ligand, M1-M6. The photophysical, electrochemical, and electroluminescent properties of these novel iridium complexes are investigated. The specific work is as follows:(1) Six novel benzothiazole-based cylcometalating ligands frameworks,2-cycloalkenyl-benzothiazoles, have been designed and synthesized. The heteroleptic iridium complexes using them as major ligands and acac as ancillary ligand, M1-M6, have been prepared and characterized. The photophysical study via electronic absorption and photoluminescent spectra reveals that these iridium complexes are phosphorescent in orange to red range with emission peaks at578-612nm. The roome-temperature phosphorescent quantum yields were determined as15-32%. The electrochemical study shows a reversible redox wave for each iridium complex. The HOMO and LUMO levels were calculated from electrochemical data together with absorption edge data.(2) These iridium complexes have been used as doped emitters to fabricate phosphorescent OLEDs and excellent performance data were obtained. As examples, the device structure for M1, M2and M3is ITO/PEDOT (40nm)/NPB(20nm)/TCTA(10nm) /M1(M2或M3)(5wt%):CBP(30nm)/TPBI (40nm)/LiF (1nm)/Al(100nm). M1-based OLED exhibited the best device performance with a maximum luminance of46260cd m-2. a peak current efficiency of49.1cd A-1and a power efficiency of22.0lm W-1. which are among the highest values for orange OLEDs reported so far.The results indicate that these novel iridium complexes containing2-cycloalkenyl-benzothiazole ligands are promising orange to red phosphors to fabricate highly efficient OLEDs for both reseach purpose and practical applications. |
