Double-Decker Platinum Complexes: From Visible to NIR-II Luminescence.

The Pt(II) dinuclear compounds [{Pt(C^N)(μ-S^N)}] [S^NH: 2-mercapto-1-methylimidazol; HC^N= 1-naphthalen-2-yl-1-pyrazole (naph-pz, ); benzo[]quinoline (bzq, )] were obtained by reaction of the corresponding mononuclear precursor [Pt(C^N)Cl(S^NH)] (C^N: naph-pz , bzq ) with NEt. Then, and were reacted with aqueous HX (X: Cl, Br, I) in molar ratio 1:2 to give the corresponding oxidized derivatives [{Pt(C^N)(μ-S^N)X}] (X = Cl , Br , I ). Their X-ray structures showed shorter Pt-Pt distances in the Pt(III) complexes (. 2.7 Å) than in the Pt(II) ones (. 3.0 Å) in agreement with the existence of a Pt-Pt bond. The photophysical properties were studied experimentally and theoretically by DFT and TD-DFT. The Pt(II) complexes exhibit an emission in the visible region (640 nm , 685 nm ) of mostly excimeric ππ* and MMLCT [dσ*(Pt) → π* (C^N)] character respectively, while the Pt(III) complexes emit in the NIR-II region with maxima reaching up to 1215 nm. The XMMCT nature of these emissions justify the influence of both the axial ligand (X) and the overlap of the dz orbitals on their energies; the latter being affected by the nature of the C^N and the bridging ligand.