1‑D “Platinum Wire” Stacking Structure Built of Platinum(II) Diimine Bis(σ-acetylide) Units with Luminescence in the NIR Region

A square-planar platinum­(II) complex, Pt­(DiBrbpy)­(CCC₆H₄Et-4)₂ (1) (DiBrbpy = 4,4-dibromo-2,2′-bipyridine), and crystals of its three solvated forms, namely, 1·DMSO, 1·1/2­(CH₃CN), and 1·1/8­(CH₂Cl₂), were developed and characterized. 1·DMSO and 1·1/2­(CH₃CN) contain quasi-dimeric and dimeric structures with luminescence in the visible range, whereas 1·1/8­(CH₂Cl₂) exhibits NIR luminescence at 1022 nm due to its intrinsic 1-D “platinum wire” stacking structure with strong Pt–Pt interactions. 1·1/8­(CH₂Cl₂) represents the first compound based on platinum­(II) diimine bis­(σ-acetylide) molecular units with the NIR luminescence beyond 1000 nm. 1 selectively responds to DMSO and CH₃CN by changing its color and luminescence property and the three solvated forms can be reversibly converted to each other upon exposure to corresponding solvent vapors. Their desolvated forms, namely 1a, 1b, and 1c, obtained after heating 1·DMSO, 1·1/2­(CH₃CN), and 1·1/8­(CH₂Cl₂), respectively, can also be restored to the original solvated forms upon exposure to corresponding solvent vapors. 1a and 1b emit NIR luminescence peaked at 998 and 1018 nm respectively, suggesting indirect synthetic methods as powerful alternatives to achieve NIR luminescence with long wavelength. In contrast, 1c exhibits a red luminescence with a broad unstructured emission band centered at 667 nm. All the responses to organic solvent vapors and heating are due to the structural transformations which result in the conversion of the lowest energy excited states between ³MLCT/³LLCT and ³MMLCT in solid-state as supported by time-dependent density functional theory (TD-DFT) calculations.