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.