Sensory luminescent iridium(III) and platinum(II) complexes for cation recognition

This article presents the design and photophysical properties of platinum and iridium complexes incorporating a host receptor for metal cations, with particular attention to the changes in their luminescence properties upon addition of these ions in solution. Selected examples on cationic and neutral complexes within the families of Pt and Ir complexes will be presented. A series of platinum acetylide complexes incorporating a crown ether unit have been designed and prepared for the detection of alkali and alkaline-earth cations. Similarly, Ir complexes, cationic and neutral species, have been used as luminophores using the same receptor units. Metal-based chemosensors for transition-and heavy-metal ions have been also developed. The detection of divalent metal cations such as Zn2+, Cd2+ and Cu2+, has been achieved thanks to the interesting chelating properties of di(2-picolyl)amine (2,2'-DPA) ionophore. Introducing appropriate substituents (flavone, macrocyclic pyridine) on the ancillary acetylide ligand of cyclometalated platinum(II) allows the recognition of Pb2+ ions. Mercury(II), a thiophilic metal ion, interacts with the sulfur atom of cyclometalated ligands of iridium complexes inducing remarkable emission spectral changes. These luminescent metal-based sensors give rise to phosphorescence turn-on or turn-off effects as well as changes in the emission wavelength and/or emission lifetime. (C) 2011 Elsevier B.V. All rights reserved.