On the basis of density functional theory (DFT) calculations, a new series of bipolar host molecules for efficient blue electrophosphorescence devices are designed by linkage of hole-transporting moiety carbazole (CZ) and electron-transporting unit diphenylphosphoryl (ph(2)P=O) to the core molecules with high triplet energies. The electronic structures in the ground states, cationic and anionic states, and lowest triplet states of the designed molecules have been Studied with emphasis on triplet energies, spin density distributions, ionization potentials, electron affinities, and the influence of molecular topology. Designed bipolar host molecules possess the following features: (I) relatively higher highest occupied molecular orbital (HOMO) for hole injection and, relatively lower lowest unoccupied molecular orbital (LUMO) for electron injection; (2) HOMO and LUMO separation and localization in the respective hole- and electron-transporting moieties; (3) dramatic bond length changes in ionic states occurring at different parts of the bipolar molecules with respect to their neutral states; (4) keeping higher triplet energy. The DFT results provide deep insight into the nature of bipolar molecules and Show that the designed molecules are feasible to meet the requirements of the host materials for blue triplet emissions.