Supramolecular Architectures, Photophysics, and Electroluminescence of 1,3,4-Oxadiazole-Based Iridium(III) Complexes: From μ-Dichloro Bridged Dimer to Mononuclear Complexes

One μ-dichloro bridged diiridium complex and three mononuclear iridium(III) complexes based on the 1,3,4-oxadiazole derivatives as cyclometalated ligands and acetylacetonate (acac) or dithiolates O, O ‘-diethyldithiophosphate (Et 2 dtp) or N, N ‘-diethyldithiocarbamate (Et 2 dtc) as ancillary ligands have been synthesized and systematically studied by X-ray diffraction analysis. The results reveal that three mononuclear complexes all adopt distorted octahedral coordination geometry around the iridium center by two chelating ligands with cis -C−C and trans -N−N dispositions, which have the same coordination mode as the diiridium dimer. The dinuclear complex crystallizes in the monoclinic system and space group C 2/ c, whereas three mononuclear iridium complexes are all triclinic system and space group P 1̄. In the stacking structure of the dimer, one-dimensional tape-like chains along the b -axis are formed by hydrogen bondings, which are strengthened by π stacking interactions between phenyl rings of 1,3,4-oxadiazole ligands. Then these chains assemble a three-dimensional alternating peak and valley fused wave-shape structure. In each stacking structure of three mononuclear complexes, two molecules form a dimer by the C−H···O hydrogen bondings, and these dimers are connected by π stacking interactions along the b -axis, constructing a zigzag chain. Then these zigzag chains are interacted by π stacking along the a -axis, building up a two-dimensional structure. All complexes emit green with emission wavelengths in the range of 501−535 nm, depending on the structures of cyclometalated ligands and ancillary ligands. Electroluminescent devices using complexes 2 − 4 as phosphorescent dopants have been fabricated. A high-efficiency green emission device with a maximum luminous efficiency of 5.26 cd/A at a current density of 1.38 mA/cm 2 and a maximum brightness of 2594 cd/m 2 at 15.5 V has been achieved using 2 as the emitter.