Color Tuning of Iridium Complexes through Heteroleptic Tris-cyclometallated Ligands

Abstract

White organic light-emitting devices (WOLEDs) consist of a fluorescent blue material doped in a region spatially separate from the phosphorescent dopant iridium complex. This study evaluated two potential new phosphorescent materials, the heteroleptic tris-cyclometallated iridium complexes Ir(tpy)2(btp) and Ir(btp)2(tpy), where tpy and btp are “2-(p-tolyl)pyridine” and “2-(2′-benzothienyl)pyridine”, respectively. The luminescence mechanism in heteroleptic iridium complexes is determined by the rates of decay from two different species of ligands. The quantum yields (lifetime) of fac-Ir(tpy)3 and fac-Ir(btp)3 were reported as 0.5 (2.0 μs) and 0.12 (4.0 μs), respectively. Thus, the radiative decay rate (k r ) of fac-Ir(tpy)3 and fac-Ir(btp)3 can be calculated as 2.5 × 105/s and 3.0 × 104/s, respectively. Heteroleptic tris-cyclometallated iridium complexes were able to tune the color for white phosphorescent materials, by controlling the radiative decay rate of ligands and number of ligands in complexes.