Design of C^NN type iridium(iii) complexes towards short-wavelength emission for high efficiency organic light-emitting diodes

Abstract

In this paper, by introducing the strong electron-withdrawing moiety of difluoropyridinyl to the C^NN type main-ligand, and combining a trifluoromethylated-triazole (fptz) or a picolinate (pic) as the ancillary ligand, we have synthesized two new iridium(III) complexes with blue emission, i.e., iridium(III) bis[3-methyl-6-(2′,4′-difluoro-pyridinato)pyridazine] trifluoromethylated-triazole (1) and iridium(III) bis[3-methyl-6-(2′,4′-difluoro-pyridinato)pyridazine] picolinate (2). These are the first C^NN type iridium(III) complexes with an emission wavelength shorter than 500 nm. In particular, with the increased electron withdrawing property from the ancillary ligand of fptz, the emission from 1 is more blue. Additionally, based on quantum chemistry calculations, it was found that, different from the general case of the main-ligand and Ir-atom distribution, the electrons of the highest occupied molecular orbital (HOMO) also partially locate at the ancillary ligand with very strong electron withdrawing properties. This phenomena is seldom reported in the literature. Organic light-emitting diodes with 1 or 2 as a dopant have been fabricated. High efficiencies of 41.6 cd A⁻¹ (20.1%) with sky-blue emission and 62.8 cd A⁻¹ (26.5%) with blue-green emission were obtained. These are the first blue electroluminescent materials based on iridium complexes with a C^NN type ligand so far.