Turning On MLCT Phosphorescence of Iridium(III)–Borane Conjugates upon Fluoride Binding

The heteroleptic complexes (<i>C</i>^∧<i>N</i>)₂Ir^III (<i>C</i>^∧<i>N</i>: ppy, <b>2</b>; btp, <b>3</b>), bearing a 4-(dimesitylboryl)­benzoate (Bbz) auxiliary ligand, and their fluoride adducts were prepared and characterized. While the PL spectra of <b>2</b> and <b>3</b> exhibit very weak emission in solution, the addition of fluoride turned on (<i>C</i>^∧<i>N</i>)₂Ir-centered phosphorescence (λ_em 527 nm for <b>2</b> and 617 nm for <b>3</b>). Experimental and DFT calculations suggest that the weak emission is ascribable to a photoinduced electron transfer from the MLCT state of the (<i>C</i>^∧<i>N</i>)₂Ir moiety to the Bbz ligand and is switched on by fluoride binding to the boron center of the Bbz ligand