Fluorescence Quenching of a Conjugated Polymer by Synergistic Amine-Carboxylic Acid and π-π Interactions for Selective Detection of Aromatic Amines in Aqueous Solution

Fluorescence sensing of amine in aqueous solution is challenging. The various basicity and chemical structures of amines may lead to poor selectivity in aqueous solution, and selective fluorescence detection of primary aromatic amine is rarely reported. This paper presents design and synthesis of a fluorescent conjugated polymer for rapid and selective sensing of aromatic amines in aqueous solution. The fluorescent conjugated polymer, poly[fluorenyl-alt-p-phenyleneethynylene] with pendant carboxylic acid groups and long alky chains, is synthesized via palladium-catalyzed Sonogashira coupling reaction. The fluorescence of the polymer is selectively quenched by the aromatic amines in aqueous solution, whereas the aliphatic amines enhance the fluorescence of the polymer. The high selectivity to the aromatic amines, particularly to the environmentally important p-phenylenediamine, likely originates from the amplified π-π fluorescence quenching synergized by amine and carboxylic acid interaction. Our results demonstrate an effective material design strategy that may be extended to fluorescence sensing of other aromatic compounds.