Synthesis, characterization, and photoelectric properties of iridium(iii) complexes containing an N hetero-dibenzofuran C^N ligand

In this study, three high-efficient green light iridium(iii) complexes were designed and synthesized, wherein 2-methyl-8-(2-pyridine) benzofuran [2,3-B] pyridine (MPBFP) is the main ligand and three β-diketone derivatives, namely 3,7-diethyl-4,6-nondiazone (detd), 2,2,6,6-tetramethyl-3,5-heptyldione (tmd) and acetylacetone (acac), are ancillary ligands. The thermal stabilities, electrochemical properties, and electroluminescence (EL) performance of these three complexes, namely (MPBFP)₂Ir(detd), (MPBFP)₂Ir(tmd) and (MPBFP)₂Ir(acac), were investigated. The results show that the absorption peaks of the three complexes range from 260 to 340 nm, and the maximum emission wavelengths are 537 nm, 544 nm and 540 nm, respectively. The LUMO level is −2.18 eV, −2.20 eV, −2.21 eV, and the HOMO level is −5.30 eV, −5.25 eV, and −5.25 eV, respectively. The thermal decomposition temperatures of each of the three compounds are 359 °C, 389 °C and 410 °C respectively, with a weight loss of 5%. Green phosphorescent electroluminescent devices were prepared with the structure of ITO/HAT-CN/TAPC/TCTA/TCTA:X/Bepp2/LiF/Al, and the three complexes were dispersed in the organic light-emitting layer as the guest material X. The maximum external quantum efficiency of the devices is 17.2%, 16.7%, and 16.5%, respectively. The maximum brightness is 57 328 cd m⁻², 69 267 cd m⁻²and 69 267 cd m⁻², respectively. With respect to the EL properties, (MPBFP)₂Ir(detd) is the best performer among the three complexes. The different performances exhibited by these complexes were discussed from the view point of substituent effect on the β-diketone ligands.