Cation-controlled luminescence behavior of anionic cyclometalated platinum(II) complexes.

• The luminescence properties of anionic cyclometalated Pt(II) complexes are controlled by the cations. • The systems surrounded by bulky organic cations realize intense molecular-based luminescence. • Non-innocent cations enhance emission intensity and control of energy through dative bonds or charge transfer. • The systems with adaptable cations exhibit characteristic luminescence and stimulus-response based on the Pt⋯Pt interactions. The characteristic luminescence properties of anionic cyclometalated Pt(II) complexes are discussed from the viewpoint of the counter cations. To date, various cyclometalated Pt(II) complexes have been developed as promising luminescent materials because cyclometalating ligands provide stable and strong ligand fields. In addition to the molecular design of cyclometalated Pt(II) complexes, control of the intermolecular interactions is particularly important for Pt(II) complexes with square-planar geometry. In this context, we focus on the effects of counter cations on anionic cyclometalated Pt(II) complexes by classifying such complexes into three categories, i.e., (i) systems with bulky organic cations, which enable the formation of isolated Pt(II) complexes, (ii) systems with non-innocent cations, which interact with anionic Pt(II) complexes through dative bonds or charge transfer, and (iii) systems including adaptable cations, which support the assembly of the Pt(II) complexes by cancelling out the electrostatic repulsion between Pt(II) complex anions that form stacking structures with Pt⋯Pt interactions. For this category, the formation and properties of ionic liquids using asymmetric cations is discussed. [ABSTRACT FROM AUTHOR]