5-coordinated aluminum complexes having two 2,4-dimethyl-8-hydroxylquinoline ligands and a phenolic ligand as possible materials for white emission organic light-emitting devices

New 5-coordinated aluminum complexes bearing a phenolic ligand and two 2,4-dimethyl-8-hydroxyquinoline ligands were synthesized for application to organic light-emitting devices. The effects of the difference in the structure of the phenolic ligands on the photoluminescence (PL) and electroluminescence (EL) properties were studied. The PL properties were measured in solution, powder, and vacuum-sublimed film states, and the EL properties were measured for devices with an organic double-layer structure. In all cases, the emissions (PL and EL) from these complexes were attributed to the π-π* transitions in the 2,4-dimethyl-8-hydroxyquinoline ligand. The 5-coordinated Al complexes with a phenolic ligand show an emission band in a shorter wavelength region than that of the 6-coordinated complexes bearing three 8-hydroxyquinoline ligands. As a result of the blue-shift of the emission band, the 5-coordinated Al complexes show bluish emission, which is advantageous for fabrication of white color light-emitting devices. Although the effect of the structure of the phenolic ligands on the spectroscopic properties of the films was very small, it affected the characteristics of the light-emitting devices to some extent.