Robust Triplatinum Redox-Chromophore for a Post-Synthetic Color-Tunable Electrochromic System.

An electrochromic system showing ease of color tunability has been constructed using a triple-decker PtII complex [Pt3 (µ3 -pydt)2 (bpy)3 ]2+ (H2 pydt=2,6-pyridinedithiol, bpy=2,2'-bipyridine). The divalent complex undergoes electrochemically quasi-reversible two-electron transfer coupled with the coordination/dissociation of axial ligands, forming higher valent Pt(+2.67) species [Pt3 X2 (µ3 -pydt)2 (bpy)3 ]2+ (X=Cl- , Br- , and SCN- ). These higher valent species exhibit characteristic colors ranging from red to cyan depending on the counter anion X- of the electrolyte. The triple-decker structure provides a novel multicolor electrochromic system with favorable stability and reversibility. Theoretical calculations indicate that the colors of the Pt(+2.67) species are tunable by the trans influence of the axial ligand X- . This novel strategy of post-synthetic color-tuning using triplatinum systems should enable the facile preparation of colorful electrochromic devices without any complicated procedures, which may find application in flexible displays, optical devices, and sensors.

A Redox-Active Dinuclear Platinum Complex Exhibiting Multicolored Electrochromism and Luminescence.

A redox series of cyclometalated platinum complexes based on a dinuclear motif linked by acetamidato (aam) bridging ligands, [Pt2 (µ-aam)2 (ppy)2 ] (ppy(-) =2-phenylpyridinate ion), has been synthesized. The complexes in this series are easily oxidized and reduced by both electrochemical and chemical methods, and this is accompanied by multistep changes in their optical properties, that is, multiple color changes and luminescence. Isolation of the complexes and the structural determination of three oxidation states, +2, +2.33, and +3, have been achieved. The mixed-valent complex, with an average oxidation state of +2.33, forms a trimer based on the dinuclear motif. The mixed-valent complex has a characteristic color owing to intervalence transitions in the platinum chain. In contrast, the divalent complex exhibits strong red phosphorescence originating from a triplet metal-metal-to-ligand charge transfer ((3) MMLCT) state. This study demonstrates the unique chromic behavior of a redox-active and luminescent platinum complex.