Introduction of the Benzoquinoline Ancillary Ligand to the Iridium Complexes for Organic Light-Emitting Diodes

The new iridium complexes, Ir((CN)-N-boolean AND)(2)(bq), ((CN)-N-boolean AND = ppy, F-2-ppy, 2,3-dpqx-F-2 or 4-Me-2,3-dpq) were prepared and their luminescence properties were investigated, where ppy, F-2-ppy, 2,3-dpqx-F-2, 4-Me-2,3-dpq and bq represent 2-phenylpyridine, 2-(4',6'-difluorophenyl)-pyridine, 2,3-bis (4'-fluorophenyl)quinoxaline, 4-methyl-2,3-diphenylquinoline and 10-hydroxybenzoquinoline ligands, respectively. We expected that the relative energy levels of the main ligands (CAN) and ancillary ligand, bq, in the complexes could determine the possibility of interligand energy transfer (ILET) in the complexes and thereby luminescence properties. The main ligands, F-2-ppy and 2,3-dpqx-F-2, which have drastically different energy gaps between the HOMO and LUMO energy levels were chosen and their complexes were synthesized. The photoabsorption, photoluminescence and electroluminescence of the complexes were studied. Ir(ppy)(2)(bq), Ir(F-2-ppy)(2)(bq) Ir(2,3-dpqx-F-2)(2)(bq) and Ir(4-Me-2,3-dpq)(2)(bq) exhibited the luminescence maxima between 600 similar to 694 nm and their efficiencies were affected by the main ligands. While Ir(ppy)(2)(bq) and Ir(F-2-ppy)(2)(bq) showed relatively high luminous efficiencies (>10 cd/A), Ir(2,3-dpqx-F-2)(bq) had poor luminous efficiency (0.30 cd/A). The electrochemical properties were studied to support ILET in the ppy-based iridium complexes. Their luminescence performances were compared with those of the complexes containing acetylacetonate (acac) ancillary ligand which are not allowed to have ILET.