New family of fluorogenic azacrown probes with identical cavity size but different electronic environment outside the macrocycle: effects on sensitivity of Cu2+ detection

摘要

Benzimidazoles derived from lactic acid and mandelic acid were employed as photosignaling synthons to construct 15-C-5 azacrowns 3 & 4 with difference in electronic environments at the carbon attached to 2-position. These receptors were used as probes for cation sensing using UV-Vis and fluorescence titration techniques. Although both the receptors have identical macrocyclic backbone and are found selective for Cu2+, receptor 3 displayed stronger binding towards Cu2+ in comparison to 4. The addition of Cu2+ to the probes 3 & 4 in solution caused quenching of fluorescence. The results clearly indicate that the stability of Cu2+ complexes of 3 and 4 depends on different factors. The association constant, K-SV for 3 with Cu2+ was (1.53 x 10(5) M-1) an order higher than that exhibited by 4 for Cu2+ (9.27 x 10(4) M-1).