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

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