Electroluminescence from two new ruthenium(II) complexes as phosphorescent dopant: Positive effect of swallow-tail bipyridyl ligand

Two new orange-red emitting ruthenium complexes, [Ru(bpy)2(4,4'-bis(3-ethylheptyl)-2,2'-bipyridine)](PF6)(2) and [Ru(bpy)2(4-dihexylmethyl-4'-heptyl-2,2'-bipyridine)](PF6)(2) with branched alkyl side groups on the bipyridyl ligand have been synthesized and used as dopants in an organic light emitting device. The device that contains the complex containing the 4-dihexylmethyl-4'-heptyl-2,2'-bipyridine ligand 1.0 wt.% doped polymer blends of poly(vinylcarbazole) and 2-tert-butylphenyl-5-biphenyl-1,3,4-oxadiazol as the emitting layer reached to a luminous efficiency of 7 cd/A, and a maximum brightness of 3824 cd/m(2) with an electroluminescence spectral peak at 600 nm and Commission Internationale de L'Eclairage chromaticity coordinates of (0.57, 0.39). The swallow-tail alkyl substituent in this complex played a significant role in lowering the tendency to aggregate and presenting a better electroluminescence efficiency than that of the complex derived from the 4,4'-bis(3-ethylheptyl)-2,2'-bipyridine) ligand in a device. (C) 2012 Elsevier Ltd. All rights reserved.