Synthesis, characterization and electrophosphorescent properties of mononuclear platinum(II) complexes based on 2-phenylbenzoimidazole derivatives

Abstract: The rational design, synthesis and characterization of five phosphorescent platinum complexes [(C^N)Pt(acac)] [Hacac=acetylacetone, HC^N=1-methyl-2-(4-fluorophenyl)benzoimidazole (H-FMBI), 1-methyl-2-phenylbenzoimidazole (H-MBI), 1,2-diphenyl-benzoimidazole (H-PBI), 1-(4-(3,6-di-t-butylcarbazol-9-yl))phenyl-2-phenylbenzoimidazole (t-BuCz-H-PBI), and 1-(4-(3,6-di-(3,6-di-t-butyl-carbazol-9-yl))carbazol-9-yl)phenyl-2-phenylbenzoimidazole (t-BuCzCz-H-PBI)] have been discussed. The crystal structure of (MBI)Pt(acac) shows a nearly ideal square planar geometry around Pt atom and the weak intermolecular interactions with π–π spacing of 3.55Å. All of the complexes emit green phosphorescence from the metal-to-ligand charge-transfer (MLCT) excited state with high quantum efficiency (0.08–0.17) at room temperature. A multilayer organic light-emitting diode (OLED) with (MBI)Pt(acac) as phosphorescent dopant was fabricated using the method of high-vacuum thermal evaporation, which gives a maximum brightness, luminous and power efficiency of 13605cd/m2, 15.1cd/A and 4.3lm/W, respectively. In contrast, the comparable performance can be achieved in the solution-processed OLED based on (t-BuCzPBI)Pt(acac) with a peak brightness, luminous and power efficiency of 13606cd/m2, 17.5cd/A and 8.4lm/W, respectively. The better device efficiency results from the good square plane of central Pt coordination unit and the inhibition of the aggregates due to bulky and rigid t-butylcarbazole dendrons. [Copyright &y& Elsevier]