pubs.acs.org/cm Published on Web 06/08/2009 r 2009 American Chemical Society Chem. Mater. 2009, 21, 2565–2567 2565 DOI:10.1021/cm900387a Solution-Processable, High-Molecule-Based Trifluoromethyl-Iridium Complex for Extraordinarily High Efficiency Blue-Green Organic Light-Emitting Diode Jwo-Huei Jou,* ,† Mao-Feng Hsu, † Wei-Ben Wang, † Chih-Lung Chin, ‡ Yu-Chiao Chung, † Chin-Ti Chen, § Jing-Jong Shyue, ) Shih-Ming Shen, † Ming-Hsuan Wu, † Wen-Chuan Chang, † Chi-Ping Liu, † Sun-Zen Chen, ^ and Hung-Yang Chen § † Department of Materials Science and Engineering, National Tsing Hua University, Hsin-Chu, Taiwan 30013, Republic of China, ‡ Material and Chemical Research Laboratories, Industrial Technology Research Institute, Hsin-Chu, Taiwan 30013, Republic of China, § Institute of Chemistry, Academia Sinica, Taipei, Taiwan 11529, Republic of China, ) Research Center for Applied Sciences, Academia Sinica, Taipei, Taiwan 11529, Republic of China, and ^ Center for Nanotechology, Materials Science, and Microsystems, National Tsing Hua University, Hsin- Chu, Taiwan 30013, Republic of China Received March 4, 2009 Revised Manuscript Received May 4, 2009 Organic light-emitting diodes (OLEDs) possess high po- tential in flat panel displays and solid-state illumination applications. 1 To replace current display and illumination technologies, and to make the resultant products more energy saving and make them last longer, OLEDs with higher power efficiency are demanded. Recently, phosphorescent materials have drawn great attention because of their ability to harvest both singlet and triplet excitons, achieving nearly 100% internal quantum efficiency. 2 Among them, green light-emit- ting iridium complexes show relatively high efficiency. 3,4 For example, Chi’s group reported a green device with efficiency of 23.2 cd A -1 by using an pyrazolyl-containing iridium complex that exhibited a short excited-state lifetime. 5 Lin’s group achieved 61 cd A -1 with an iridium complex contain- ing 1,2-diphenyl-1H-benzoimidazole that exhibited high quantum yield. 6 Designing new phosphorescent materials, such as iridium-based complexes, that possess both short excited-state lifetime and high quantum yield may markedly enhance the efficiency. However, different functional groups may consequently be needed to introduce to the base mole- cules. This will inevitably result in an increase in molecular weight, which will in turn make the resultant molecules difficult, if not at all impossible, to vacuum-evaporate. This will hence make solution process a must choice, especially when the molecular weight of employed materials is further increased. In fact, the wet process is a requirement for large- area devices or roll-to-roll production. 7 In this study, we report a novel high-molecular- based iridium complex, bis[5-methyl-7-trifluoromethyl- 5H-benzo(c)(1,5)naphthyridin-6-one]iridium(picolinate) (CF 3 BNO), which exhibits both a short excited-state lifetime and a high quantum yield. Although CF 3 BNO has a comparatively high molecular weight (869 g mol -1 ), which is difficult to vacuum-evaporate, the resultant blue- green device via solution process shows a current efficiency of 89.1 cd A -1 at 100 cd m -2 , which is the highest among all the reported green devices via a solution process. Scheme 1 shows the synthesis of CF 3 BNO and bis[5- methyl-5H-benzo[c][1,5] naphthyridin-6-one]iridium(pico- linate) (BNO). Iridium trichloride hydrate was reacted with 5-methyl-7-trifluoromethyl-5H-benzo[c][1,5]naphthyridin- 6-one or 5-methyl-5H-benzo[c][1, 5]naphthyridin-6-one to give the corresponding cyclometalated Ir(III)-μ- chloro-bridged dimers. Further reaction of the dimers with picolinic acid and sodium carbonate formed the desired iridium complex, CF 3 BNO or BNO. Table 1 lists the physical characteristics of the novel blue-green guest, CF 3 BNO, and the other two com- pared counterparts, BNO and tris(2-phenylpyridine) iridium(III) (Ir(ppy) 3 ). The excited-state lifetimes were 0.30, 0.32, and 1.2 μs for CF 3 BNO, BNO, and Ir(ppy) 3 , respectively. Compared with that in Ir(ppy) 3 , the shorter excited-state lifetime exhibited in CF 3 BNO and BNO should presumably favor the fabrication of a high- efficiency device, as mentioned above. 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