Development of cyclometallated iridium(III) complexes for light-emitting electrochemical cells

This chapter gives an overview of the development of cyclometallated iridium(III) complexes for application in light-emitting electrochemical cells (LECs) and highlights the ligand-design strategies employed to enhance device stability, operating efficiency and (critically for LECs in which the ion mobilities are typically low) turn-on times. Typical iridium-containing ionic transtion metal complexes (Ir-iTMCs) belong to the family of [Ir(C^N) 2 (N^N)] + complexes in which H(C^N) is a cyclometallating ligand and N^N is a diimine or related chelating ligand. The partitioning of Ir/C^N vs N^N character in the HOMO and LUMO of a [Ir(C^N) 2 (N^N)] + complex, respectively, lends itself to a ligand-functionalization driven method of varying the band-gap allowing emission-colour tuning. An important development in addressing device stability has been the design of ligands that can protect the iridium(III) centre through intra-cation π-stacking interactions, and progress in this area is discussed in detail. The need for deep-blue emitters has been addressed by introducing fluoro-substituents into the cyclometallating domain; however this can lead to lower stability of the LECs and alternative means of shifting the emission into the blue are discussed. Finally, we discuss how a move away from singly-charged, cationic Ir-iTMCs can be used to shorten the turn-on times of LECs