Water-Soluble Pd₈L₄ Barrel for Binding of Versatile Hydrophobic Dyes and Visible-Light Promoted Catalysis in Aqueous Medium.

Achieving efficient supramolecular recognition of hydrophobic dyes and their use as photosensitizers in water remain a major challenge because of their inherent insolubility and loss of activity in aqueous medium. We address this issue by designing a metal-organic barrel (M) that combines water solubility with a spacious hydrophobic cavity. This barrel functions as a versatile host capable of binding a broad range of polyaromatic guests, from small hydrocarbons to fullerenes. Interestingly, the barrel protects fragile fluorophores such as benzothiadiazole, benzoselenadiazole, quinoxaline, and BODIPY dyes from aggregation-caused quenching (ACQ), thereby preserving their excited-state integrity in water. Binding of the hydrophobic benzothiadiazole-dithiophene (BDT) photosensitizer within the barrel transforms it into an efficient photocatalyst in water, enabling C─H functionalization of indole derivatives with malonate. Overall, this work demonstrates a water-soluble barrel that serves as a powerful host capable of solubilizing hydrophobic dyes and enabling interesting catalytic reactivity directly in water.