The synthesis and luminescent properties of trichromatic iridium complexes based on 2-(4-bromophenyl)-1-hydrogen-benzimidazole

- Three novel trichromatic iridium complexes based on 2-(4-bromophenyl)-1-hydrogen-benzimidazole are obtained and the phosphorescent quantum efficiencies for Ir(pbi)3, (pbi)2Ir(acac) and (pbi)2Ir(phen) in CH2Cl2 solution are found to be 9.35, 10.63 and 25.14 %.
- Excited-state lifetimes for these iridium complexes are in the microsecond regime (0.13 0.55 us), the faster decay times suggest that the emitting state has triplet character with strong spin-orbital coupling.
- The trichromatic iridium complexes not only can be directly used as luminescent materials, but also can be used as reactive monomers for the development of trichromatic polymer luminescent materials owing to the bromine atom in the structure by the Suzuki polycondensation.

The tris-cyclometalated iridium complex Ir(pbi)3 was synthesized regarding 2-(4-bromophenyl)-1-hydrogen-benzimidazole(pbi) as cyclometalated ligand and the heteroleptic iridium complexes (pbi)2Ir(acac) and (pbi)2Ir(phen) were prepared through the ancillary ligands acetylacetone(acac) and 1,10-phenanthroline(phen), respectively. Wherein the complex Ir(pbi)3 gives the maximum emission peak of 436 nm at 365 nm excitation and color coordinate of (0.173, 0.144) as a blue light-emitting. The complexes (pbi)2Ir(acac) and (pbi)2Ir(phen) present the maximum emission wavelength of 536 nm and 616 nm and color coordinates (0.301, 0.591) and (0.630, 0.345) respectively corresponding to the green and red emission. The phosphorescent quantum efficiencies for Ir(pbi)3, (pbi)2Ir(acac) and (pbi)2Ir(phen) in CH2Cl2 are found to be 9.35%, 10.63% and 25.14% respectively, and their quantum efficiencies in powder are found to be 3.27%, 2.74% and 12.21% respectively. Excited-state lifetimes for these iridium complexes are in the microsecond regime(0.13-0.55 us). Such long-lived excited states clearly suggest that the emitting state has triplet character. The cyclic voltammetry curves showed the HOMO energy levels of the trichromatic complexes and the LUMO energy levels were obtained combining the HOMO energy levels and optical band gaps. The optimal molecular structures and the HOMO and LUMO orbital energy levels of the complexes were figured up through DFT theory Gaussian simulation, indicating the basic numerical coincide of theory and experimental values.