Comparison of Emission Characteristics with 4-, 5-, 6-Membered Iridium Complexes for OLEDs

Abstract

To compare luminance efficiency, emission colors and stability of the iridium (III) complexes, we designed the four, five, six membered metallacycles of iridium with the various ancillary ligands. Picolinate as an ancillary ligand was known to form a stable five-membered metallacycle with the iridium center. In this study, 4-, 5-, and 6-membered metallacyclic iridium complexes chelated with acetanilide, (ace), picolinate (pic) and 8-quinolinecarboxylate (qc) were prepared, respectively, and their photophysical properties were investigated. As a main ligand, we introduced 2-phenylpyridine (ppy) and 2-(2,4-difluorophenyl)pyridine (F2-ppy). The resulting Ir(ppy)2(ace), Ir(ppy)2(pic), Ir(ppy)2(qc), Ir(F2-ppy)2(ace), Ir(F2-ppy)2(pic) and Ir(F2-ppy)2(qc) showed various emission maxima from 468 to 608 nm, depending upon the relative energy levels of their main and ancillary ligands. The emission preperties of the new iridium complexes revealed how the different ancillary ligands have influence on the luminous efficiency, emisson wavelength and stability of the iridium complexes, depending on the size of the metallacycle.