Synthesis and Reactivity of Subvalent Compounds, 8 Aromatic Phosphenium Cations

The fluorescent emission of the N,N-dimethylaniline fragment of the tetramine system 3 varies with pH, displaying a maximum of the fluorescent intensity, IF, at pH = 5. Binding of transition metals (CuII, NiII) induces fluorescence quenching and modifies the IF vs. pH profile, giving rise to an OFF-ON-OFF type of sensor. The [ZnII(3)]2+ complex recognises carboxylate anions, both aliphatic and aromatic. Recognition is signalled via fluorescence quenching only for aromatic carboxylates.