Application of Heterocyclic Polymers in the Ratiometric Spectrophotometric Determination of Fluoride

Herein we report the use of heterocyclic functional polymers in the ratiometric spectrophotometric determination of fluoride (F^-). Polymers incorporating benzo[d][1,2,3]triazole moieties linked to the polymer backbone via urea links are demonstrated to have utility for the ratiometric detection of the F^- ion, with a detection limit in the order of ∼2 μM. The hydrogen-bonding recognition between the benzo[d][1,2,3]triazole moiety and F^- ion was investigated using UV-vis spectrophotometry and NMR analysis. The importance of the urea linkage was elucidated by investigating a second benzo[d][1,2,3]triazole functional monomer wherein the heterocyclic group is attached to the polymerizable group via a carbamate linkage. The replacement of the urea link with a carbamate group led to significantly reduced F^- sensitivity. Moreover, by examining an analogous benzo[d]imidazole monomer it was demonstrated that having a nitrogen atom in the 2-position of the heterocycle was important for maximizing the sensitivity of the assay. Taken together, these results demonstrated that the urea-substituted benzo[d][1,2,3]triazole motif greatly enhances F^- ion detection. Importantly, the F^- ion sensing capability of the monomer is retained after incorporating into a diblock copolymer using reversible addition-fragmentation chain transfer (RAFT) polymerization.