meso-Substituted Bisanthenes as Soluble and Stable Near-infrared Dyes

Three meso-substituted bisanthenes, 4-6, were prepared in a short synthetic route from the bisanthenequinone. They exhibit largely improved stability and solubility in comparison to the parent bisanthene. All of these compounds also show near-infrared (NIR) absorption and emission with high to moderate fluorescence quantum yields. Amphoteric redox behavior was observed for 4-6 by cyclic voltammetry, and these compounds can be reversibly oxidized and reduced into respective cationic and anionic species by both electrochemical and chemical processes. In addition, compound 5 adopts a herringbone pi-stacking motif in the single crystal.