Diphenylphosphorylpyridine-functionalized iridium complexes for high-efficiency monochromic and white organic light-emitting diodes

Abstract

Four new cyclometalated iridium(III) complexes containing 2-aryl-5-diphenylphosphorylpyridine ligands, in which the aryl was difluorophenyl (Ir-1), phenyl (Ir-2), 4-(diphenylamino)phenyl (Ir-3) and 2-naphthyl (Ir-4), have been synthesized for application in organic light-emitting diodes (OLEDs). The incorporation of diphenylphosphoryl on the pyridine causes a decrease of the lowest unoccupied molecular orbital (LUMO) for the iridium complexes and the universal bathochromic shift by as much as 50 nm in their phosphorescence. In particular, the presence of the diphenylphosphoryl group on the 2-difluorophenylpyridine ligand of iridium(III)bis(4,6-(difluorophenyl)pyridinato-N,C²′)picolinate (FIrpic) redistributed the LUMO from the ancillary ligand entirely to the cyclometalating ligand. These complexes were used as doped emitters to fabricate OLEDs. The bluish-green device based on Ir-1 exhibited a maximum luminance efficiency of 43.6 cd A⁻¹ (22.8 lm W⁻¹, 9.5%). Highly efficient yellow devices were obtained with 51.6 cd A⁻¹ (27 lm W⁻¹, 14.5%) and 29.6 cd A⁻¹ (15.5 lm W⁻¹, 8.8%) for Ir-2 and Ir-3, respectively. The maximum luminance efficiency of 27.2 cd A⁻¹ (15.5 lm W⁻¹, 9.7%) was achieved for the orange-red device containing Ir-4. Furthermore, a two-emitting-component white OLED was fabricated with Ir-4 in combination with the traditional sky-blue FIrpic and a high efficiency of 23.9 cd A⁻¹ (13.9 lm W⁻¹, 5.4%) with CIE (0.29, 0.43) was realized.