Dicyanovinyl-based fluorescent sensors for dual mechanism amine sensing

Food wastage due to spoiling is a global economic issue and contributes to over-farming and overfishing with real environmental consequences. Smart food packaging is a promising solution to this problem, the concept of which is to incorporate responsive sensors that allow direct monitoring of the gasses released from the decay of food into a label that provides a visual indicator to the consumer as to whether the food is fresh or has spoiled. Here we report two dicyanovinyl-fluorene-benzothiadiazole-based fluorescent compounds,K12andK12b, both of which showed rapid response to biogenic aminesviatwo independent mechanisms. When primary alkyl amines were present in solution, they underwent an aza-Michael addition with the dicyanovinyl group of the sensing material, resulting in a rapid colour change. The reaction products ofK12andK12bwith primary amines showed a decrease and increase in the fluorescence quantum yield, respectively, enabling a unique dual-sensor array with turn-off/turn-on response. In addition, fluorescence quenchingviaphotoinduced hole transfer was observed in the solid-state sensor films with a wide range of primary, secondary and tertiary amines, enabling rapid and sensitive detection of amine vapours. Finally, we show as proof-of-concept that the fluorescence quenching response of sensing films was observable at cadaverine concentrations relevant to the food industry.