Cross-Linking Silsesquioxane Cages with Polyaromatics as Fluorescent Porous Polymers for Fluoride Sensing and Removal

Fluorescent polymer nanocomposites of silsesquioxane cage-based anthracene (An-PSQ) and pyrene (Py-PSQ) were obtained by cross-linked polymerization of octavinylsilsesquioxane (OVS) with 9,10-dibromoanthracene or 1,6-dibromopyrene, respectively. The fluorescent polymers are insoluble and were structurally characterized by FT-IR and NMR. Polyaromatic spacer groups incorporated into materials could tune and rigidify in both micro- and mesoporous structures with high surface area in comparison to silica-based materials in the range of 246–342 m2/g, and their XRD analyses also show the amorphous nature. Both An-PSQ and Py-PSQ exhibit solvent-polarity-dependent photophysical properties in both light absorption and emission, which were employed in the anion sensing (i.e., F–, CN–) in high polarity organic media. Importantly, excimer natures of polyaromatic spacer groups among silsesquioxane cages play an important role in the selectivity of anions in recognition. An-PSQ gives spectral changes in the presence of both F– and CN–, whereas replacing anthracenyl to pyrenyl group in Py-PSQ could selectively detect only F– because of a stronger excimer feature. Moreover, strong fluoride–silsesquioxane interaction has provided another function to these materials as adsorbent for highly hydrophilic F– anion from organic media containing water up to 77%.