Photochemistry and photophysics of coordination compounds: Platinum

This chapter provides an overview of the luminescence properties of platinum(II) complexes, exploring how the excited states involved in emission are influenced by the ligands around the metal ion. The square planar nature of d(8) Pt(II) complexes has many implications, leading to properties and applications that are not open to d(6) complexes. For example, axial intermolecular interactions can lead to new excited states not present in the isolated molecules. This review focuses on complexes containing one or more chelating ligands, of which at least one contains a heterocyclic ring such as pyridine. Thus, we explore the properties of a range of bipyridyl (bpy) and terpyridyl (tpy) complexes, and how they are influenced by the identity of the other ligands that complete the coordination sphere of the Pt(II) ion, such as halide, cyanide, thiolates and acetylides. We consider the sometimes dramatic influence of substituents in the bpy/tpy ligands in producing other excited states that may be much more intensely emissive than those of the parent complexes. The influence of cyclometallation on excited states is discussed, and how it can lead to highly emissive complexes: a range of cyclometallated systems are reviewed, with bidentate and terdentate ligands incorporating one or more metal-carbon bonds. Contemporary applications in areas such as sensors, photoinduced electron transfer, and organic light-emitting devices are highlighted.