High stability light-emitting electrochemical cells from cationic iridium complexes with bulky 5,5′ substituents

We explore the photophysical, electrochemical, and electroluminescent properties of the ionic transition metal complex [(ppy)(2)Ir(bpy*)](PF6) where ppyH is 2-phenylpyridine and bpy* is 5,5'-diaryl-2,2'-bipyridine. Single layer devices of the structure ITO/[(ppy)(2)Ir(bpy*)](PF6)/Au exhibited high stability, with half-lives on the order of 100 h at a bias of -4 V. Long lifetimes are achieved through the bulky nature of the aryl substituents, which serves to limit chromophore-chromophore self-quenching, and 5,5' positioning of these bulky groups is clearly advantageous for device performance.