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

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 ß-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)2 Ir(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-2 and 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 ß-diketone ligands.

Fluorocarbon and hydrocarbon N-heterocyclic (C5-C7) imidazole-based liquid crystals.

By using three synthetic protocols, a series of fluorocarbon and hydrocarbon N-heterocyclic imidazole-based liquid crystals (LCs) and related imidazolium-based ionic liquid crystals (ILCs) have been prepared. The ring size of the N-heterocycle and the length of the N-terminal chain (on the imidazolium unit in the ILCs) were modified, and the influence of these structural parameters on liquid-crystal phases was investigated by means of polarizing optical microscopy (POM), differential scanning calorimetry (DSC), and X-ray diffraction (XRD). These new ILCs exhibit a disordered smectic phase (SmA), good thermal stabilities, a broad smectic phase range, a high dipole moment, relatively low melting points, but high clearing points and strong emission fluorescence relative to imidazole-based LCs. These encouraging results have led us to believe these fluorocarbon and hydrocarbon N-heterocyclic imidazole-based LCs and related imidazolium-based ILCs could be used as new liquid-crystalline materials.