To further study the fluorescence-sensing behavior of 1, a quantitative investigation of the binding affinity of 1 with Al3þ was
studied by fluorescence titration (Fig. 4). When the receptor 1 was titrated with Al3þ, the fluorescence intensity increased up to 7 equiv and then no change was observed. The Job plot for the binding between 1 and Al3þ exhibited a 1:1 stoichiometry