Quantum chemistry methods are applied to investigate the electronic structures, injection and transport properties, absorption and phosphorescence mechanism of a series of Iridium (III) complexes [Ir(C∧N)2(L)2]+ (L = 4-pyCO2Et; C∧N = 2-phenylpyridine, 1; 2-(4-tolyl)pyridine, 2; 2-(4,6-difluorophenyl)pyridimato, 3; benzoquinoline, 4), which may be used as emitters on organic light emitting diodes (OLEDs). Calculations of ionization potentials and electron affinities are used to evaluate the injection abilities of holes and electrons into these complexes. The reorganization energy (λ) calculations show that the four complexes are suitable as emitters in OLEDs. The absorptions and emissions can be tuned by adding substituent to the ppy ligand or extending the π-conjugation effect of the C∧N ligand, and quantum yields of 1–4 are investigated. In addition, no solvent effect is observed in the absorption and emission spectra. © 2012 Wiley Periodicals, Inc.