The Effect of Aryl Substitution on the Properties of a Series of Highly Absorptive Cationic Iridium(III) Complexes Bearing Ancillary Bis(arylimino)acenaphthene Ligands

A family of cationic heteroleptic iridium(III) complexes of the form [Ir(ppy)2(Ar-BIAN)]PF6 (ppyH = 2-phenylpyridine) in which Ar-BIAN [bis(arylimino)acenaphthene] acts as an ancillary ligand were synthesized and characterized. Their ground-state electronic structures were probed by UV/Vis spectroscopy and cyclic voltammetry. The X-ray structure of [Ir(ppy)2(4-MeO2CPh-BIAN)]PF6 was solved. The first and second reduction wave potentials are strongly influenced by the substituent on the Ar-BIAN ligand and follow a Hammett relationship. The absorption spectra for complexes incorporating an electron-donating Ar-BIAN ligand are noticeably redshifted, and absorption tails off past 800 nm. Notably, the absorption spectrum for [Ir(ppy)2(4-NMe2Ph-BIAN)]PF6 shows an intense band centered at 576 nm, and it was assigned computationally to a mixed metal-to-ligand charge-transfer/ligand-to-ligand charge-transfer state.