Electrochemiluminescence Studies of Phosphorescent Dopant and Host Molecules of Polymer Light-emitting Diodes

Electrochemiluminescence (ECL) from tris(2‐phenylpyridine)irdium [Ir(ppy)3] was investigated following cross reaction of its anion with oxidized poly(N‐vinyl‐carbazole) (PVK) and its cation with reduced 2‐(4‐biphenylyl)‐5‐(4‐tert‐butyl‐phenyl)‐1,3,4‐oxadiazole (PBD). Both cross reactions show Ir(ppy)3 emission and the cross reaction of PVK+·/Ir(ppy)−3 showed the highest ECL intensity. The comparisons of the reaction enthalpy and the energy of Ir(ppy)3 light emitting shows that reaction between PVK+· and Ir(ppy)−3 is energy sufficient to populate metal‐to‐ligand charge transfer (MLCT) excited singlet (3.04 eV) of Ir(ppy)3, while the reaction between Ir(ppy)+3 and PBD− · is energy efficient to populate MLCT excited triplet (2.4 eV). The ECL result in solution reveals that the energy released from charge transfer between the Ir(ppy)3 and PVK or PBD is sufficient to produce the excited state of Ir(ppy)3 in solid polymer light‐emitting diodes (PLEDs) based on PVK:PBD hosts doped by Ir(ppy)3. These results obtained will provide further insight into charge‐transfer excitation in PLEDs. In the paper, electrochemiluminescence behaviors from Ir(ppy)3 was investigated following cross reaction of its ions with PVK or PBD. We expect the results obtained will provide further insight into charge‐transfer excitation in polymer light‐emitting diodes based on phosphorescent Ir(ppy)3 doped blending host of PVK:PBD, and give some direction for future device design.