An organic light emitting diode (OLED) architecture in which efficient operation is achieved without requiring a blocking layer by locating the recombination zone close to the hole transport side of the emissive layer. Aryl-based hosts and Ir-based dopants with suitable concentrations result in an efficient phosphorescent OLED structure. Previously, blocking layer utilization in phosphorescent OLED architectures was considered essential to avoid exciton and hole leakage from the emissive layer, and thus keep the recombination zone inside the emissive layer to provide high device efficiency and a pure emission spectrum.

Organometallic compounds comprising an imidazole carbene ligand having a N-containing ring fused to the imidazole ring are provided. In particular, the N-containing ring fused to the imidazole ring may contain one nitrogen atom or more than one nitrogen atom. These compounds may demonstrate high photoluminescent (PL) efficiency, Gaussian emission spectra, and/or short excited state lifetimes. These materials may be especially useful as blue phosphorescent emitters.

A triarylamine derivative represented by a general formula (G1) given below is provided. Note that in the formula, Ar represents either a substituted or unsubstituted phenyl group or a substituted or unsubstituted biphenyl group; represents a substituted or unsubstituted naphthyl group; represents either hydrogen or a substituted or unsubstituted naphthyl group; n and m each independently represent 1 or 2; and R.sup.1 to R.sup.8 each independently represent any of hydrogen, an alkyl group having 1 to 6 carbon atoms, or a phenyl group.

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There is provided a light emitting device which enables a color display with good color balance. A triplet compound is used for a light emitting layer of an EL element that emits red color, and a singlet compound is used for a light emitting layer of an EL element that emits green color and a light emitting layer of an EL element that emits blue color. Thus, an operation voltage of the EL element emitting red color may be made the same as the EL element emitting green color and the EL element emitting blue color. Accordingly, the color display with good color balance can be realized.

Organometallic compounds comprising an imidazole carbene ligand having a N-containing ring fused to the imidazole ring are provided. In particular, the N-containing ring fused to the imidazole ring may contain one nitrogen atom or more than one nitrogen atom. These compounds may demonstrate high photoluminescent (PL) efficiency, Gaussian emission spectra, and/or short excited state lifetimes. These materials may be especially useful as blue phosphorescent emitters.

The invention provides emissive materials and organic light emitting devices using the emissive materials in an emissive layer disposed between and electrically connected to an anode and a cathode. The emissive materials include compounds with the following structure:

##STR00001##

wherein at least one of R.sub.8 to R.sub.14 is phenyl or substituted phenyl, and/or at least two of R.sub.8 to R.sub.14 that are adjacent are part of a fluorenyl group. The emissive materials have enhanced electroluminescent efficiency and improved lifetime when incorporated into light emitting devices.

An anthracene derivative represented by a general formula (1) and an organic compound represented by a general formula (8) are provided. Further, by use of the anthracene derivative represented by the general formula (1), a light-emitting element with high emission efficiency can be obtained. Furthermore, by use of the anthracene derivative represented by the general formula (1), a light-emitting element that emits blue light with high color purity can be obtained.

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A triarylamine derivative represented by a general formula (G1) given below is provided. Note that in the formula, Ar represents either a substituted or unsubstituted phenyl group or a substituted or unsubstituted biphenyl group; represents a substituted or unsubstituted naphthyl group; represents either hydrogen or a substituted or unsubstituted naphthyl group; n and m each independently represent 1 or 2; and R.sup.1 to R.sup.8 each independently represent any of hydrogen, an alkyl group having 1 to 6 carbon atoms, or a phenyl group. ##STR00001##

It is an object of the present invention to provide a novel triazole derivative. Further, it is another object of the present invention to provide a light-emitting element having high luminous efficiency with the use of the novel triazole derivative. Moreover, it is still another object of the present invention to provide a light-emitting device and electronic devices which have low power consumption. A light-emitting element having high luminous efficiency can be manufactured with the use of a triazole derivative which is a 1,2,4-triazole derivative, in which an aryl group or a heteroaryl group is bonded to each of 3-position, 4-position, and 5-position, and in which any one of the aryl group or heteroaryl group has a 9H-carbazol-9-yl group.

There is provided a light emitting device which enables a color display with good color balance. A triplet compound is used for a light emitting layer of an EL element that emits red color, and a singlet compound is used for a light emitting layer of an EL element that emits green color and a light emitting layer of an EL element that emits blue color. Thus, an operation voltage of the EL element emitting red color may be made the same as the EL element emitting green color and the EL element emitting blue color. Accordingly, the color display with good color balance can be realized.