Electroluminescence (referred to as EL, hereinafter) devices using organic substances are expected to be used for inexpensive full color display devices of the solid light emission type which can display a large area and development thereof has been actively conducted. In general, an EL device is constituted with a light emitting layer and a pair of electrodes faced to each other at both sides of the light emitting layer. When a voltage is applied between the electrodes, electrons are injected at the side of the cathode and holes are injected at the side of the anode. The electrons are combined with the holes in the light emitting layer and an excited state is formed. When the excited state returns to the ground state, the energy is emitted as light.
Organic EL devices used heretofore have higher driving voltages, lower luminances of emitted light and lower efficiencies of light emission than inorganic light emitting diodes and, moreover, the properties of organic EL devices deteriorate rather rapidly. Therefore, organic EL devices have not been used for practical applications. Although the properties of recent organic EL devices have been improved remarkably, the efficiency of light emission, the heat resistance and the life are not sufficient for practical applications.
For example, an organic EL device using a dimer or a trimer of phenylanthracene is disclosed in Japanese Patent Application Laid-Open No. Heisei 8(1996)-12600. However, since the above compound used in the device contains two or three anthracene structures bonded through a conjugated group, the organic EL device has a small energy gap and exhibits poor purity of color in emission of blue light. Moreover, since this compound is easily oxidized, impurities tend to be contained and a problem arises with respect to purification. To overcome the above problems, preparation of organic EL devices using a compound in which the 1-position and the 9-position of anthracene are substituted with naphthalene or a compound in which m-position of phenyl group in diphenylanthracene is substituted with an aryl group have been examined. However, the prepared organic EL devices exhibit low efficiencies of light emission and cannot be used for practical applications.
An organic EL device using a monoanthracene derivative substituted with naphthalene is disclosed in Japanese Patent Application Laid-Open No. Heisei 11(1999)-3782. However, this device exhibits an efficiency of light emission as low as 1 cd/a and cannot be used for practical applications. An organic EL device using a compound having a phenylanthracene structure is disclosed in U.S. Pat. No. 5,972,247. However, this device exhibits an efficiency of light emission as low as 2 cd/A and cannot be used for practical applications although the device exhibits excellent heat resistance due to the substitution with an aryl group at the m-position.