Cyclometalated Iridium(III) Complexes of Azadipyrromethene Chromophores

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.