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), iPr (Pt‐iPr), and tBu (Pt‐tBu)). 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 (3MMLCT) state. Their emission colors cover the entire visible region from red for Pt‐Me to blue for Pt‐tBu. Importantly, Pt‐tBu is the first example that exhibits blue 3MMLCT emission. The 3MMLCT 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 3MMLCT emission presents a new strategy of superfine control of the emission color. Intense blue emission originating from the triplet metal–metal‐to‐ligand charge transfer (3MMLCT) state has been achieved by the fine control of the stacking structure of PtII complexes bearing an N‐heterocyclic carbene (NHC). By the slight change of the stacking structures based on the steric effect of a substituent on the NHC ligand, the luminescence color is freely tuned from red to blue without changing the emission origin (i.e., 3MMLCT).