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

In this work nine novel heteroleptic Ir(III) complexes of general formulae [Ir(N perpendicular to C #)(2)(O perpendicular to O #)] containing four different cyclometallating and four beta-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 (N perpendicular to C 1) and 2-(benzo[b]thiophen-2-yl)pyridine (N perpendicular to C 2) ligands give non-emissive complexes, whereas those with methyl 2-phenylquinoline-4-carboxylate (N perpendicular to C 3) and 6-(benzo[b]thiophen-2-yl)phenanthridine) (N perpendicular to C 4) are luminescent, but display different character of electronic transitions responsible for absorption and emission. Complexes with the N perpendicular to C 3 ligand luminesce from (LC)-L-3 excited state and do not change their emission characteristics upon variations in the nature of beta-diketonates. On the contrary, the compounds based on the N perpendicular to C 4 cyclometalating ligand emit from the excited state with considerable contribution of (MLCT)-M-3 character and show systematic bathochromic shift of absorption and emission bands upon increase in electron donicity of O perpendicular to O # ligands. This conclusion was supported by DFT and TD-DFT calculations and by the analysis of correlations between the C-13 chemical shift of the diketonate C(H) carbon and emission maxima of the compounds under study.

Automated summary

Nine novel heteroleptic Ir(III) complexes were synthesized, with six of them displaying phosphorescence in the deep red and NIR regions. The variation in orthometalating ligands resulted in dramatic changes in photophysical behavior, affecting the emission characteristics of the compounds.