Bright and stable light-emitting electrochemical cells based on an intramolecularly π-stacked, 2-naphthyl-substituted iridium complex

Abstract

The synthesis and characterization of a new cationic bis-cyclometallated iridium(III) complex and its use in solid-state light-emitting electrochemical cells (LECs) are described. The complex [Ir(ppy)₂(Naphbpy)][PF₆], where Hppy = 2-phenylpyridine and Naphbpy = 6-(2-naphthyl)-2,2′-bipyridine, incorporates a pendant 2-naphthyl unit that π-stacks face-to-face with the adjacent ppy⁻ ligand and acts as a peripheral bulky group. The complex presents a structureless emission centred around 595–600 nm both in solution and in thin film with relatively low photoluminescence quantum yields compared with analogous systems. Density functional theory calculations support the charge transfer character of the emitting triplet state and rationalize the low quantum yields in terms of a ligand-centred triplet localized on the 2-naphthyl unit that lies close in energy to the emitting state. LECs incorporating the [Ir(ppy)₂(Naphbpy)][PF₆] complex as the electroluminescent material are driven using a pulsed current operation mode and show high luminance, exceeding 300 cd m⁻², and exceptional stabilities.