Polymeric Chemosensors: A Conventional Platform with New Click Chemistry

Abstract

Abstract Polymers are a good platform for the production of various functional materials, since functional moieties can be introduced into both the main chain backbone and side chain pendants by elegant molecular design and utilizing efficient synthetic protocols. Highly colored and fluorescent π-systems have often been employed as ion sensing units especially when heteroaromatic rings are included. The heteroaromatic rings can form supramolecular complexes with metal ions or anions, resulting in the visual color changes of absorption and fluorescence. Conjugated polymers have been traditionally employed to this end, because they are highly emissive and very sensitive to various ions. However, most of such conjugated polymers are synthesized by costly cross-coupling polycondensations, which do not meet the green chemistry concepts of this century. Click chemistry is a new concept representing an efficient and atom-economic synthesis, and one of the most common reactions is the Cu(I)-catalyzed azide-alkyne cycloaddition (CuAAC) yielding 1,2,3-triazole rings. The 1,2,3-triazole derivatives are electronically almost inert, but they possess fluorescent chemosensor properties. Recent examples of polymeric chemosensors based on the 1,2,3-triazole derivatives are introduced. Furthermore, an emerging click chemistry reaction, i.e., the alkyne-acceptor click chemistry, is also introduced. This reaction produces highly colored donor-acceptor (D-A) chromophores on a polymer platform, enabling visual detection of the ion sensing behavior. The polymeric chemosensors with the D-A chromophores show a specific discrimination between hard and soft metal ions by different color changes. These polymers are also useful for anion sensing.