In this work nine novel heteroleptic Ir(III) complexes of general formulae [Ir((Formula presented.) #)₂((Formula presented.) #)] containing four different cyclometallating and four β-diketonate ligands were synthesized and fully characterized. Six of them display phosphorescence in the deep red and NIR regions with quantum yields reaching 24.6 % in degassed solution for one of the NIR emitters. Variation in the nature of orthometalating ligands results in dramatic changes in photophysical behavior: the compounds containing 2-phenylpyridine ((Formula presented.) 1) and 2-(benzo[b]thiophen-2-yl)pyridine ((Formula presented.) 2) ligands give non-emissive complexes, whereas those with methyl 2-phenylquinoline-4-carboxylate ((Formula presented.) 3) and 6-(benzo[b]thiophen-2-yl)phenanthridine) ((Formula presented.) 4) are luminescent, but display different character of electronic transitions responsible for absorption and emission. Complexes with the (Formula presented.) 3 ligand luminesce from ³LC excited state and do not change their emission characteristics upon variations in the nature of β-diketonates. On the contrary, the compounds based on the (Formula presented.) 4 cyclometalating ligand emit from the excited state with considerable contribution of ³MLCT character and show systematic bathochromic shift of absorption and emission bands upon increase in electron donicity of (Formula presented.) # ligands. This conclusion was supported by DFT and TD-DFT calculations and by the analysis of correlations between the ¹³C chemical shift of the diketonate C(H) carbon and emission maxima of the compounds under study.