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DFT/TDDFT investigation was performed on the electronic structures,basic photophysical properties and phosphorescence efficiency of a series of blue-emitting Ir(Ⅲ)complexes bearing two conjugated and nonconjugated carbene ligands respectively as cyclometalated ligands.It's found that the insertion of a saturated σ-bond methylene spacer into carbene ligand effectively breaks the π conjugation of cyclometalated carbene ligands,leading to an increase of the HOMO-LUMO energy gap.The absorption spectra are relatively red shifted with the inserted methylene spacer,but the absorption intensities are significantly weakened for these complexes.The emission spectra are slightly influenced by the switch between conjugated and nonconjugated ligands.The use of nonconjugated carbene ligands can greatly enhance the charge transfer balance performance.Furthermore,on the basis of our calculations,the different quantum yields of experimental complexes are also explained with the assistance of the metal contribution to the lowest excited states(MLCT%)and the S1-T2 splitting energies(ΔES1-T2).It's believed that the nonconjugated carbene ligand has a positive influence on enhancing the MLCT contribution and ISC rate,then increasing the quantum yield.At last,we carried out a prediction of the quantum yield for the designed complexes.