Sensitive 1,1-dicyanovinyl push-pull dye for primary amine sensing in solution by fluorescence

1,1-dicyanovinyl push-pull dye PTTCN undergoes rapid and reversible aza-Michael addition with volatile primary aliphatic amines in solution in DMSO, yielding highly fluorescent imine derivatives. This reaction is accompanied by a dramatic colour change as well as a strong increase in fluorescence (1200-fold increase) allowing sensitive turn-on detection of primary amine in solution. In the solid state, PTTCN is emissive and reaction with primary amine vapours results in a shift in fluorescence and a possible ratiometric detection of primary amines. The selectivity is excellent for primary amines over secondary, tertiary and aromatic amines as well as over thiols and fluorescence spectroscopy allows to discriminate between primary amines and other nitrogen nucleophiles such as hydrazine and ammonia. Finally, we show as proof-of-concept that the fluorescence turn-on reaction can be used in response to the vapours of volatile amines released during food spoilage.