Spectroscopic characterization and in silico modelling of polyvinylpyrrolidone as an anion-responsive fluorescent polymer in aqueous media

Aqueous anion recognition has been a long-standing challenge in molecular recognition. The use of synthetic polymers is an emerging area of interest due to their conformational flexibility, creating microdomains that favor the desolvation and binding of anions in water. Here, we report that the fluorescence of off-the-shelf polyvinylpyrrolidone (PVP) can be used to detect the presence of not only nitrate, as previously reported, but also nitrite, iodide, and thiocyanate in aqueous media. The extent of quenching and anion affinity is dependent on the solution pH and the molecular weight of PVP, while showing close correlation with the Hofmeister series. Moreover, molecular dynamics simulations support our experimental findings, suggesting that anions associating closest to the surface of PVP quench its fluorescence to the greatest extent. Combined with the versatility of PVP, this fundamental study provides a starting point to confer anion binding properties with a fluorescence output in new materials.