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

Abstract

AbstractIn 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 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 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 # 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.