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.

Keywords:

• cyclometallated iridium (III) complex
• organic light-emitting devices (OLEDs)

Acknowledgments

This work was supported by the Korea Research Foundation Grant Funded by the Korean Government (MOEHRD) (KRF-2007-313-D00290).