A DFT/TDDFT method was applied to explore the geometrical, electronic and photophysical properties of the recently reported oxazoline- and thiazoline-containing iridium(III) complexes [(ppy)₂Ir(oz)] (1) and [(ppy)₂Ir(thoz)] (2). The calculated absorption and emission wavelengths are in agreement with experimental data. Based on complexes 1 and 2, a series of Ir(III) complexes 3, 4, 5 and 6 with different N^O ligands have been designed. The calculated results reveal that the different ancillary ligands not only affect the absorption spectra properties but also tune the emission colour. Compared with 2, the higher quantum yield of the experimental observation for 1 was explained by its larger MLCT contribution and smaller singlet–triplet splitting energy (ΔE_S1–T1). From this point of view, the designed complexes 3, 5 and 6 are expected to be potential phosphorescence emitters in OLEDs with high quantum efficiency.