Intense Red-Blue Luminescence Based on Superfine Control of Metal-Metal Interactions for Self-Assembled Platinum(II) Complexes.

A series of assembled PtII complexes comprising N-heterocyclic carbene and cyanide ligands was constructed using different substituent groups, [Pt(CN)2 (R-impy)] (R-impyH+ =1-alkyl-3-(2-pyridyl)-1H-imidazolium, R=Me (Pt-Me), Et (Pt-Et), i Pr (Pt-i Pr), and t Bu (Pt-t Bu)). All the complexes exhibited highly efficient photoluminescence with an emission quantum yield of 0.51-0.81 in the solid state at room temperature, originating from the triplet metal-metal-to-ligand charge transfer (3 MMLCT) state. Their emission colors cover the entire visible region from red for Pt-Me to blue for Pt-t Bu. Importantly, Pt-t Bu is the first example that exhibits blue 3 MMLCT emission. The 3 MMLCT emission was proved and characterized based on the temperature dependences of the crystal structures and emission properties. The wide-range color tuning of luminescence using the 3 MMLCT emission presents a new strategy of superfine control of the emission color.