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 (Fig. S3) [43]. Furthermore, the positive-ion mass spectrum for the reaction of 1 with Al3þ confirmed the formation of the 1 þ Al3þ þ 2DMSO complex [m/z: 494.00; calcd, 494.10] (Fig. S4), indicating that the
binding of Al3þ to 1 induced deprotonation of the hydroxyl group of 1. From the fluorescence titration, the association constant was calculated to be 3.3 103 M-1 from a Benesi-Hildebrand plot (Fig. S5) [44]. This value was within the range 103w109 of those reported for Al3þ-binding sensors [45e50]. The detection limit of receptor 1 for Al3þ ions was found to be 1.0 105 M (Fig. S6) [51] and the fluorescence quantum yields of receptor 1 without and with Al3þ were 0.02 and 0.15, respectively
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 (Fig. S3) [43]. Furthermore, the positive-ion mass spectrum for the reaction of 1 with Al3þ confirmed the formation of the 1 þ Al3þ þ 2DMSO complex [m/z: 494.00; calcd, 494.10] (Fig. S4), indicating that thebinding of Al3þ to 1 induced deprotonation of the hydroxyl group of 1. From the fluorescence titration, the association constant was calculated to be 3.3 103 M-1 from a Benesi-Hildebrand plot (Fig. S5) [44]. This value was within the range 103w109 of those reported for Al3þ-binding sensors [45e50]. The detection limit of receptor 1 for Al3þ ions was found to be 1.0 105 M (Fig. S6) [51] and the fluorescence quantum yields of receptor 1 without and with Al3þ were 0.02 and 0.15, respectively
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