Novel Divalent Osmium Complexes: Synthesis, Characterization, Tuning of Emission, and use in Organic Light Emitting Diod
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Novel Divalent Osmium Complexes: Synthesis, Characterization, Tuning of Emission, and use in Organic Light Emitting Diodes Brenden Carlson1, 3, Gregory D. Phelan1, 4, Joo H. Kim2, Alex K.-Y. Jen2, Larry Dalton1 1 Chemistry Department, University of Washington BOX 351700, Seattle, WA 98195 2 Department of Materials Science and Engineering, University of Washington BOX, Seattle, WA, 98195 3 Applied Research Associates 215 Harrison Ave., Panama City Fl, 32401 4 Seattle Pacific University 3307 3rd Avenue West, Seattle. WA, 98107 ABSTRACT In this work we present the synthesis and characterization of several novel osmium complexes of the form [Os(N-N)2 L-L]2+ 2Ts- or [Os(L-L)2 N-N]2+ 2Ts- designed for organic light emitting device (OLED) applications. In the complex notation N-N represents a derivative of 2,2’-bipyridine or 1,10-phenanthroline and L-L represents a strong π-acid arsine or phosphine ligand. Several counterions have been used and include tosylate, hexafluorophosphate, triflate, heptafluorobutyrate, chloride, bromide, and iodide. The complexes feature 3MLCT emission that ranges from 611-650 nm, which makes them suitable as an emission source for red OLEDs. Phosphorescent quantum yields as high as 45% and emission lifetimes as short as 400 nanoseconds have been reached. The complexes were incorporated into OLED and give off red, orange, yellow, and green electrophosphorescence. Red devices have been created using polyvinylcarb/2-tert-butylphenyl-5-biphenyl-1,3,4-oxadiazole, polyvinylnapthalene/2tert-butylphenyl-5-biphenyl-1,3,4-oxadiazole, and polyfluorene host materials. OLEDs have been created which give brightness up to 3000 cd m-2 and efficiency up to 2.2% at 632 nm emission. INTRODUCTION Rapid growth in the use of OLED’s is expected in the coming years1 due to their potential application in large screen flat panel displays.2-4 If full-color displays are going to be developed and achieve commercial success, efficient, long-life OLEDs emitting three primary colors, i.e., blue, green and red, are required. Pure red color has been intrinsically difficult to obtain from conjugated polymers and small molecules. This is due to difficulty in tuning the HOMO-LUMO energy levels of small organics and polymers and the energy gap law, which decreases luminescence intensity with red shifting emission. There has been a great deal of interest in phosphorescent materials in OLEDs because the use of triplet emitters allows for the avoidance of spin statistics and brings the possibility of highly efficient OLEDs. Osmium complexes feature orange and red phosphorescence with high photoluminescence quantum yields up to 45%. Although Eu, Pt and Ir complexes have been studied to some extent, the application of Os complexes in OLED has barely been explored.5-9 In this paper we report the use of
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