Cyclometalated Iridium(III) Complexes of Azadipyrromethene Chromophores

Abstract

Azadipyrromethenes are bidentate ligands that absorb in the red-orange region of the spectrum, with applications as tags, light harvesters, and sensitizers. Reported here are boron-transmetalation reactions that bind azadipyrromethenes to cyclometalated iridium(III). The new species absorb both near 590 nm and into the near-ultraviolet. Two examples have been crystallographically characterized. Both intra- and intermolecular aromatic stacking interactions are found. Cyclic voltammetry experiments show that azadipyrromethene complexes of iridium(III) undergo reduction and oxidation at potentials that depend little on the cyclometalating ligands on iridium. Density functional theory calculations indicate a LUMO that is azadipyrromethene-centered, whereas the HOMO may localize on either the Ir(C∧N)2+ fragment or the azadipyrromethene.