There is already known an organic electroluminescent device having a multilayer laminated structure and employing phosphorescence (an organic electroluminescent device employing phosphorescence being hereinafter referred to also as a phosphorescent device) (see U.S. Pat. No. 6,097,147). A device relying solely on fluorescence for emission of light has a theoretical limit of 25% as its internal quantum efficiency, since it employs an excited singlet state, but a phosphorescent device is considered to have a theoretical limit of 100% as its internal quantum efficiency, since excited energy of the triplet state contributes to emission of light. Accordingly, a phosphorescent device is superior to a fluorescent device, as it permits an improvement in luminous efficiency, or the ratio of luminous brightness to driving current density.
A phosphorescent device can be obtained by doping small amount of a phosphorescent dopant in a luminous layer of the host compound of the host compound. The host compound is required to have a higher level of excited triplet state energy than that of the phosphorescent dopant, and the compounds which can be employed are, therefore, limited. For example, the carbazole derivatives as disclosed in Appl. Phys. Lett., 75, 4 (1999), and the compounds as disclosed in JP-A-2004-103463 and Appl. Phys. Lett., 83, 3818 (2003) are used as the phosphorescent host compounds. However, it is considered necessary to develop a novel host compound, since the phosphorescent devices employing the existing phosphorescent host compounds have drawbacks including the necessity for a high driving voltage.
There are known several compounds as triphenylene compounds having substituents containing silicon (see JP-A-2003-252818, JP-A-11-255781 and JP-A-2003-252880). JP-A-2003-252818 and JP-A-255781 disclose compounds having a side chain containing silicon and bonded to a triphenylene backbone by an oxygen atom. JP-A-2003-252880 discloses a compound having a side chain containing silicon and bonded to a triphenylene backbone directly by silicon. However, there has not been known any triphenylene compound having a silylethynyl group. Attempts have been made to isolate a triphenylene compound (terminating at H) having a silylethynyl group by the desilylation reaction of 2,3,6,7,10,11-hexakis(trimethylsilylethynyl)triphenylene, but its isolation has been difficult, as it is unstable in the air and immediately undergoes a polymerization reaction to form a polymeric product.