A Water-Soluble Cycloparaphenylene: Synthesis and Application as a Supramolecular Receptor with Visible Fluorescence

We report the first synthesis of water-soluble [9]cycloparaphenylene derivative containing three hydrindacene (1,2,3,5,6,7-hexahydro-s-indacene) units with four carboxylates at the 2,6-positions via a macrocyclic gold complex. This crown-shaped macrocyclic compound exhibits remarkable water solubility, with a maximum solubility of 16 mmol L-1 (2.6 g/100 mL), as well as strong visible fluorescence in water (λem = 447 nm, φF = 0.64, brightness (ε×φF) = 5.1×104). This molecule effectively encapsulates cationic guest compounds, such as methyl viologen dichloride, as indicated by a change in visible fluorescence.