Red‐to‐NIR Iridium(III) Emitters: Synthesis, Photophysical and Computational Study, the Effects of Cyclometallating and β‐Diketonate Ligands

Abstract

Abstract In this work nine novel heteroleptic Ir(III) complexes of general formulae [Ir( # ) 2 ( # )] 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 ( 1 ) and 2‐(benzo[b]thiophen‐2‐yl)pyridine ( 2 ) ligands give non‐emissive complexes, whereas those with methyl 2‐phenylquinoline‐4‐carboxylate ( 3 ) and 6‐(benzo[b]thiophen‐2‐yl)phenanthridine) ( 4 ) are luminescent, but display different character of electronic transitions responsible for absorption and emission. Complexes with the 3 ligand luminesce from 3 LC 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 4 cyclometalating ligand emit from the excited state with considerable contribution of 3 MLCT character and show systematic bathochromic shift of absorption and emission bands upon increase in electron donicity of # ligands. This conclusion was supported by DFT and TD‐DFT calculations and by the analysis of correlations between the 13 C chemical shift of the diketonate C(H) carbon and emission maxima of the compounds under study.