Four emission bands from a mixed-ligand iridium complex IrQ(ppy)₂ at room temperature

Four photoluminescence bands are observed from iridium complex in UV, violet, green, and red spectral regions at room temperature. Such a multiple emission is found from a mixed-ligand iridium(III) complex, (8-quinolinolato) bis(2-phenylpyridyl) iridium IrQ(ppy)₂, which consists of IrQ and Ir(ppy)₂ components (Q: 8-quinolinolato, ppy: phenylpyridyl). Of the four emission bands, the UV emission band with maximum at about 330 nm and the red emission band are attributed to the ligand-centered (¹LC) ¹nπ^∗ and metal-to-ligand charge transfer (³MLCT) ³(ππ^∗) states from IrQ, respectively, while the violet emission band with maximum at about 400 nm and the green emission band at about 513 nm are attributed to the ¹LC ¹(nπ^∗) and ³MLCT ³ππ^∗ states from Ir(ppy). It is suggested that (1) IrQ and Ir(ppy) generate their own emissions by the inefficient Förster energy transfer between IrQ and Ir(ppy) due to the orientation factor of nearly zero, and (2) each of IrQ and Ir(ppy) gives rise to two emissions from the singlet and triplet states by the inefficient intersystem crossing.