Luminescent materials have a wide range of applications as signaling devices, sensors, and bioimaging probes. Complexes of iridium, platinum, and rhenium are very suitable for these purposes, because they are chemically stable and can emit several colors of light even at room temperature. Cyclometalated iridium complexes with conjugated chelate ligands are especially promising in this regard. Complexes bearing tridentate cyclometalated ligands form more rigid and longer conjugated systems relative to those with bidentate ligands.

Yuji Koga, Kouki Matsubara and co-workers, Fukuoka University, Japan, have prepared a series of C^C^N cyclometallated iridium complexes for the first time. These complexes are luminescent in the deep red and near-infrared ranges at room temperature with luminescence at longer wavelengths than those of previously synthesized C^N^C cyclometallated iridium complexes.

• Synthesis, Structures, and Unique Luminescent Properties of Tridentate C∧C∧N Cyclometalated Complexes of Iridium
  Y. Koga, M. Kamo, Y. Yamada, T. Matsumoto, K. Matsubara,
  Eur. J. Inorg. Chem. 2011.
  DOI: 10.1002/ejic.201100055