Diiridium(III) Complexes with Fluorenylpyridyl Cyclometalating and μ2-Oxamidato Bridging Ligands and their High Efficiency Phosphorescent Solution-Processed OLEDs

Three neutral diiridium(III) complexes with 2-fluorenylpyridyl (flpy) or 5-fluoro-2-fluorenylpyridyl (flpyF) as C<^>N cyclometalating ligands and a mu 2-oxamidato bridge have been synthesized. NMR spectroscopy shows that the complexes are inseparable mixtures of diastereomers (rac, Delta Delta/Lambda Lambda and meso, Delta Lambda) with bridges in anti and syn configurations. Each isomer was determined using 19F NMR data on the flpyF complex. Single crystal diffraction studies of two complexes revealed meso diastereomers with anti configuration of the bis-(t-butylphenyl)oxamidato bridge but an uncertain configuration of the unsubstituted mu 2-oxamidato bridge. The complexes are highly emissive (Phi PL 57-82 % in solution) with excited state lifetimes of tau p ca. 40 mu s. The vibronic emissions with maxima at 553-561 nm and at 587-595 nm in solution are attributed to mixed metal-ligand to ligand charge transfer (3MLLCT). Density functional theory (DFT) and time dependent-DFT (TD-DFT) calculations establish the involvement of the fluorenyl groups and the vibronic structures in the emissions. The bridge mediates intramolecular interactions between iridium centers based on electrochemical measurements Phosphorescent organic light-emitting diodes (PhOLEDs) using these complexes as the emissive dopants with a solution-processed active layer have bright greenish-yellow emission with lambda maxEL ca. 560 nm, luminous efficiency up to 26 cd/A and high external quantum efficiency (maximum eta ext ca. 20 %).