Sensing of transition metals through fluorescence quenching or enhancement - A review

A series of fluorescent sensors for transition metal ions were synthesized by linking a light-emitting subunit, anthracene, to a polyaza chelating subunit, either a dioxotetraamine or a tetraamine. Sensing of the divalent cations Cu-II, Ni-II and Zn-II was investigated through spectrofluorimetric titrations in acetonitrile-N mater (4:1) solutions, The selective recognition of Cu-II and Ni-II among other transition and non-transition metal ions is signalled through full quenching of fluorescence; discrimination between the two ions can be achieved by performing titrations at controlled pH. The system containing the tetraamine fragment, whose interaction with Cu-II and Ni-II induces fluorescence quenching, is also sensitive to Zn-II, but in this case the recognition is signalled-through a fluorescence enhancement.