Synthesis, Characterization, and Photophysical Properties of Os(II) Diimine Complexes [Os(N∧N)(CO)₂l₂] (N∧N = Bipyridine, Phenanthroline, and Pyridyl Benzoxazole)

A new series of Os(II) diimine complexes with the general formula [Os(N∧N)(CO)₂I₂], N∧N = 2,2‘-bipyridine (bpy) (1), 4,4‘-di-tert-butyl-2,2‘-bipyridine (dbubpy) (2), 4,7-diphenyl-1,10-phenanthroline (dpphen) (3), 2-(2‘-pyridyl)benzoxazole (pboz) (4), and 5-tert-butyl-2-(2‘-pyridyl)benzoxazole (bupboz) (5), were synthesized and characterized by spectroscopic methods and by a single-crystal X-ray diffraction study on the dpphen complex 3. The corresponding photophysical properties were studied using UV−vis and emission spectrometry. The resulting phosphorescence features both in solution and as a solid film, in combination with the MO calculation, lead us to conclude that the emissions originate from mixed halide-to-ligand (XLCT ∼70%) and metal-to-ligand (MLCT ∼30%) transitions instead of the typical MLCT transition. Using complexes 4 and 5as the dopant emitters, we evaluated their potential to serve as a phosphor for organic light emitting diodes by examining their electroluminescent performances. Reddish orange electroluminescence centered around 600 nm was observed for organic light emitting diodes (OLEDs) fabricated using complex 5 as the emitter; the device efficiency was shown to be as high as 2.8% (and 5.0 cd/A or 2.7 lm/W), and the peak luminance was shown to be 5600 cd/m² at a driving voltage of ∼15 V.