Color tuning from red to green of bis-cyclometalated iridium(III) emitters based on benzoimidazole ligands in OLEDs: A DFT and TD-DFT investigation

• The spectral nature is correlated with structural variation.
• Conjugation length of ligands affects the color tuning and quantum yield.
• Luminescent performance is evaluated by combining quantum yield and EL efficiency.
• The potential of Ir(III) complexes to be promising OLED materials are explored.

A DFT/TD-DFT theoretical study has been performed to elucidate the properties of a series of Ir(III) complexes {(xbi)2Ir(acac)}, where bi = cyclometalated benzoimidazole; acac = acetylacetonate; x = phenyl (pbi) (1); naphthalene (nbi) (2); phenanthrene (pnbi) (3); ph-cyclopentadiene-ph (fbi) (4); ph-pyrrol-ph (cbi) (5); ph-pyridine-ph (pybi) (6); ph-thiophene-ph (tabi) (7); thiophene (tbi) (8). By changing the conjugation length of benzoimidazole ligand and substitution on the benzoimidazole, the emitting color can be switched from red to green. The theoretical investigations shed some light on the reasons that phosphorescence performance of 1, 4, and 5 is better than others. These new structure–property relationships can guide an improved design and optimization of Ir-based emitting complexes.

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