Imidazolium–POSS–anthracene hybridfluorophores for sensitive and selective detection of nitroaromatic compounds (NACs) and polycyclic aromatic hydrocarbon (PAH) derivatives

Abstract

Driven by environmental concerns and associated health risks, the chemical sensing of nitroaromatic compounds (NACs) and polycyclic aromatic hydrocarbon derivatives (PAH derivatives) has gained critical importance for monitoring organic pollutants. In this study, we report the design and synthesis of dual-responsive fluorescent sensors based on an imidazolium-functionalized polyhedral oligomeric silsesquioxane (POSS) scaffold incorporating an anthracene fluorophore (POSS–Im–An·X, where X = Br, BF₄, PF₆). The cooperative functions between the inorganic POSS core and the imidazolium unit enhance both the binding affinity toward electron-deficient organic guests and the stability of the anthracene emission unit in aqueous media. Photophysical studies revealed strong fluorescence in mixed aqueous–organic media (up to 15% v/v water) and a preferential response toward picric acid (PA), 2,4-dinitrophenol (DNP), and electron-deficient PAH derivatives. ¹H NMR titration and density functional theory (DFT) calculations indicate that the binding mechanism is primarily governed by charge–dipole and π–π interactions, leading to fluorescence quenching upon guest binding through donor-photoinduced electron transfer (d-PET) processes. Furthermore, the counter anion significantly influences solid-state emission through ion-pairing and molecular packing effects. These findings position POSS–Im–An·X as a versatile and robust fluorescent sensor for the simultaneous detection of NACs and PAH derivatives, offering a promising platform for environmental monitoring and pollutant remediation.