Structure-Property Relationship of Red- and Green-Emitting Iridium(III) Complexes with Respect to Their Temperature and Oxygen Sensitivity

We report on the structural design and characterization of a series of neutral heteroleptic iridium(III) complexes equipped with 2-phenylpyridine, 2-(naphthalen-1-yl)pyridine, and 1-phenylisoquinoline as cyclometalating ligands. To gradually increase the unsymmetrical architecture of the heteroleptic iridium(III) complexes, they have been furnished with 2,2,6,6-tetramethylheptane-3,5-dione, 1-(9H-carbazol-9-yl)-5,5-dimethylhexane-2,4-dione, and 1-[3,6-bis(4-hexylphenyl)-9H-carbazol-9-yl]-5,5-dimethylhexane-2,4-dione as ancillary ligands. The photophysical and electrochemical properties of these asymmetric Ir-III complexes have been investigated experimentally as well as theoretically by using density functional theory (DFT) calculations. The properties of these new neutral heteroleptic iridium(III) complexes have been experimentally compared to homoleptic Ir-III complex structures that reveal symmetrical architectures due to three similar cyclometalating ligands. The emission intensity of the herein described two classes of Ir-III complexes is clearly influenced by applying changes to temperature and air pressure. The emphasis is on general design rules for oxygen-sensitive Ir-III emitters due to the correlation of the structure-dependent oxygen sensitivity to their phosphorescence lifetimes.