Energetic studies and developments are being made as to organic electroluminescent devices (organic EL devices), because highly luminescent emission is obtained from these devices with low-voltage driving. Generally, the organic EL devices are constituted of an organic layer including a light-emitting layer, and a pair of electrodes between which the organic layer is sandwiched, and, in such devices, electrons injected from the cathode are recombined, in the light-emitting layer, with holes injected from the anode, to produce excitons, whose energy is utilized to emit light.
Improvement in the efficiency of devices has been recently made by using a phosphorescence-emitting material. Iridium complexes, platinum complexes, and the like are such a phosphorescence-emitting material (see, for example, U.S. Pat. No. 6,303,238 and WO 00/57676). However, devices having both high efficiency and high durability have not been developed. There has been a need for development of phosphorescent materials capable of satisfying both.
Also, use of a platinum complex having a quadridentate ligand as a phosphorescent material is known (see U.S. Pat. No. 6,653,654). However, the ligand is limited to a ligand having a bipyridyl or phenanthroline skeleton, and also the wavelength of luminescent color is longer than that of yellow. Therefore, there is a strong need for development of a complex that emits light of a shorter wavelength (from green to blue).
USPTO Backgrounds
USPTO Backgrounds