Synthesis and electroluminescence properties of fac-tris(2-phenylpyridine)- iridium derivatives containing hole-trapping moieties

In order to investigate an effective method for carrier injection into the phosphor of organic electroluminescent (EL) devices, we synthesized fac-tris(2-phenylpyridine)iridium [Ir(ppy)₃] derivatives containing hole-trapping moieties, such as diphenylamine, carbazole, and phenoxazine. Their photoluminescent maxima were observed around the maximum of Ir(ppy) ₃. These values were slightly shifted depending on the hole-trapping moieties: redshifted due to diphenylamine and blueshifted due to carbazole and phenoxazine. Further, these moieties affected the oxidation potentials of Ir complexes in cyclic voltammetry. EL devices using an Ir complex with diphenylamine exhibited high EL performance because 1,1-bis[4-(di-p-tolylamino) phenyl]cyclohexane (TAPC) was employed as a hole-transporting layer. The maximum external quantum efficiency (η_ext) was recorded as 12.2%. This value is comparable to that observed in a device using Ir(ppy)₃. These results indicate that the diphenylamino substituent is favorable to serve as a hole-trapping moiety of Ir(ppy)₃.