Synthesis of Double-Decker Cages by B(C(6)F(5))(3)-Catalyzed Silylation of BINOL with Silsesquioxanes: Structural Analysis for Selective Organic-Aqueous Fluoride Sensing.

The detection of fluoride ions (F) is critical for both environmental monitoring and human health. In this study, we report the design and synthesis of novel cage-like molecules (-) derived from double-decker silsesquioxane (DDSQ) hybridized with mono- or --BINOL fluorophores. These compounds were successfully synthesized through inter/intramolecular Piers-Rubinsztajn reactions, and their well-defined cage structures were confirmed by single-crystal X-ray diffraction. Photophysical investigation demonstrates that the hybrid molecules exhibit substantially enhanced fluorescence quantum yields in tetrahydrofuran (THF), showing up to an 8-fold improvement over the parent BINOL moiety. All three molecules display a highly selective fluorescence quenching response to fluoride ions, particularly in organic-aqueous systems, achieving detection limits of 2.87 μM, 2.86 μM, and 1.55 μM for , , and , respectively. A comprehensive structure-property analysis reveals that the enhanced sensitivity of molecule is attributed to its larger internal cavity, which enables pre-enrichment with fluoride ions. This structural feature facilitates the disassembly of the hybrid cage on interaction with F, leading to significant fluorescence quenching. This work provides an effective strategy for developing high-performance chemosensors for fluoride recognition through the strategic modification of the cavity environment within hybrid cage molecules.