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.