Concepts for metal complex chromophores absorbing in the near infrared

The near-infrared (750–2500 nm) region of the electromagnetic spectrum has received enhanced attention recently from the areas of atmospheric and analytical chemistry, from communications technology, and from the side of medical applications. Coordination compounds absorbing strongly in this region can do so because of extended ligand π systems, mixed valency, or the presence of radical ion ligands. The background of such low-energy absorptivity is provided, together with examples from the inorganic and organometallic coordination chemistry of Mo, Mn, Fe, Ru, Os, Rh, Ir, Pt and Cu.