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%.