Selective fluorescent sensing of chloride

The urea functionalised phenanthroline sensor 1, which was characterised by several methods, including X-ray crystallography, gives rise to large changes in the fluorescence emission spectra upon interaction with several anions such as acetate, phosphate, fluoride and chloride in CH₃CN. However, only in the presence of Cl⁻ was the emission enhanced, as for the other ions photoinduced electron transfer (PET) quenching was observed. Fitting these fluorescence changes, using non-linear regression analysis, showed that these anions bind to 1 in 1:1 (anion:sensor) stoichiometry, with the exception of Cl⁻, which was shown to give rise to 1:1 as well as 1:2 binding, as a result of coordination of the chloride to two equivalents of 1.