We report a quantum chemical study of the electronic structures and spectral properties of three iridium(III) biscarbene complexes with different heteroleptic N boolean AND N ligands. The theoretical calculation reveals that the lowest-lying singlet absorptions at 434nm for 1 and 487nm for 3 are attributed to the mixed transition characters of metal-to-ligand charge transfer (MLCT) and ligand-to-ligand charge transfer (LLCT). However, for 2, the lowest-lying singlet absorption at 509nm is attributed to the MLCT. For 13, the phosphorescence at 739, 913, and 737nm are mainly attributed to (MLCT)-M-3 and (LLCT)-L-3 characters. For 1 and 3, the emission energies are nearly the same, which is larger than that of 2. Ionization potentials (IP) and electron affinities (EA) calculations show that the assumed complex 3 has large EA value and enhanced electron injection ability as compared to complexes 1 and 2. Moreover, the reasons for different transition characters and phosphorescence quantum yield for the three complexes have been discussed in this paper. This theoretical contribution allows the factors determining the efficiency of radiative and nonradiative decay pathways in the three complexes.