Mono and Dumbbell Silsesquioxane Cages as Dual-Response Fluorescent Chemosensors for Fluoride and Polycyclic Aromatic Hydrocarbons

Pyrene-conjugated monomeric (2) and dimeric (5) shaped-silsesquioxane (SQ) cages, as chemical sensors for detecting fluoride and polycyclic aromatic hydrocarbons (PAHs), were prepared by Heck-coupling reactions between vinyl-functionalized SQ cages and bromo-substituted pyrenes. These sensors give a remarkable deep-blue fluorescence, which could be quenched in the presence of fluoride and electron-withdrawing PAHs. Interestingly, both sensors 2 and 5 show a rapid detection toward PAHs, while a high number of vinylic silicon atoms in a monomeric cage-based sensor 2 detected fluoride relatively faster than a bulky dumbbell sensor 5. In addition, these sensors also provide a naked-eye color of fluoride detection through an intramolecular charge-transfer presenting in yellow and pink (λmax ∼495 and 520 nm) for mono and dumbbell sensors, respectively. The limit of detection for fluoride and PAH (e.g., 1-pyrenecarboxaldehyde and 1-nitropyrene) detections is approximately 1-3 μM. The computational calculation for the further mechanistic study of PAHs detection revealed that an emission of SQ was absorbed by PAHs, thereby resulting in aggregation-caused quenching.