Intramolecular Pi-stacking in a Phenylpyrazole-based Iridium Complex and Its Use in Light-emitting Electrochemical Cells

A novel iridium(III) complex, [Ir(dmppz)(2)pbpy][PF(6)] (Hdmppz = 3,5-dimethyl-1-phenylpyrazole and pbpy = 6-phenyl-(2,2'-bipyridine)), is reported. The complex shows an intramolecular face-to-face pi-stacking between the phenyl ring of the dmppz ligand and the pendant phenyl of the pbpy ligand. This interaction provides a supramolecular cage formation that holds also in the excited states. Light-emitting electrochemical cells (LECs) using the novel complex show extraordinary lifetimes of approximately 2000 h. The high stability is favored by the presence of pendant methyl groups on the dmppz ligands that hinder the entrance of water molecules rendering the degradation of the complex more difficult.