Thiourea- and Amino-Substituted Benzoxadiazole Dyes with Large Stokes Shifts as Red-Emitting Probe Monomers for Imprinted Polymer Layers Targeting Carboxylate-Containing Antibiotics.

Abstract

Bifunctional fluorescent molecular oxoanion probes based on the benzoxadiazole (BD) chromophore are described which integrate a thiourea binding motif and a polymerizable 2‐aminoethyl methacrylate unit in the 4,7‐positions of the BD core. Concerted charge transfer in this electron donor‐acceptor‐donor architecture endows the dyes with strongly Stokes shifted (up to >250 nm) absorption and fluorescence. Binding of electron‐rich carboxylate guests at the thiourea receptor leads to further analyte‐induced red‐shifts of the emission, shifting the fluorescence maximum of the complexes to ≥700 nm. Association constants for acetate are ranging from 1–5×105 M−1 in acetonitrile. Integration of one of the fluorescent probes through its polymerizable moiety into molecularly imprinted polymers (MIPs) grafted from the surface of submicron silica cores yielded fluorescent MIP‐coated particle probes for the selective detection of antibiotics containing aliphatic carboxylate groups such as enoxacin (ENOX) at micromolar concentrations in highly polar solvents like acetonitrile.