The preparation of (8-hydroxyquinolinato)bis(2-phenylpyridyl)iridium complexes and their photophysical properties

Four derivatives of the titled compounds, (8-hydroxyquinoline)bis(2-phenylpyridyl)iridium (IrQ(ppy)(2)), were prepared. Two of them were confirmed by single crystal X-ray diffraction analyses, in which solvent molecules were found to be incorporated in the crystal lattices. Their emission spectra display separated dual bands in de-aerated solutions at about 515 and 645 nm upon excitation. These green and red emissions are attributed to the triplet metal-to-ligand charge transfer ((MLCT)-M-3) and triplet ligand centered ((LC)-L-3) transitions in Ir(PPY)(2) and IrQ, respectively. It is suggested that such a multiple emission is feasible by nearly orthogonal orientation between the ppy and quinoline ligands in the mixed-ligand Ir-compounds which prohibits energy transfer between the two different ligands. The electroluminescence (EL) of these compounds was examined by the fabrication of light-emitting diodes (LEDs). Unlike the spectra in solutions, their EL spectra displayed only the red emission band. Devices displaying white light can be obtained by mixing the red emission of IrQ(ppy)(2) With a compatible blue emitter (NPB) in separated layers.