Efficient Light-Emitting Electrochemical Cells (LECs) Based on Ionic Iridium(III) Complexes with 1,3,4-Oxadiazole Ligands

Eight new iridium(III) complexes 1-8, with 1,3,4-oxadiazole (OXD) derivatives as the cyclometalated C<^>N ligand and/or the ancillary N<^>N ligands are synthesized and their electrochemical, photophysical, and solid-state light-emitting electrochemical cell (LEC) properties are investigated. Complexes 1, 2, 7 and 8 are additionally characterized by single crystal X-ray diffraction. LECs based on complexes 1-8 are fabricated with a structure indium tin oxide (ITO)/poly(3,4-ethylenedioxythiophene):poly(styrenesulfonate) (PEDOT:PSS)/cationic iridium complex:ionic liquid/Al. LECs of complexes 1-6 with OXD derivatives as the cyclometalated ligands and as the ancillary ligand show yellow luminescence (lambda(max) = 552-564 nm). LECs of complexes 7 and 8 with cyclometalated C<^>N phenylpyridine ligands and an ancillary N<^>N OXD ligand show red emission (lambda(max) 616-624 nm). Using complex 7 external quantum efficiency (EQE) values of >10% are obtained for devices (210 nm emission layer) at 3.5 V. For thinner devices (70 nm) high brightness is achieved: red emission for 7 (8528 cd m(-2) at 10 V) and yellow emission for 1 (3125 cd m(-2) at 14 V).