A Bambusuril That Responds to Anion Binding in Its Absorption Spectrum

We report the design, synthesis, and characterization of BU1, the first bambusuril derivative bearing phenyl substituents directly attached to the glycoluril nitrogen atoms. The macrocycle BU1, decorated with p-nitrophenyl groups, exhibits distinct optical responses upon anion binding, enabling the evaluation of anion affinity by UV-Vis spectroscopy for the first time. Complementary ¹H NMR titrations confirmed a 1:1 host-guest stoichiometry and yielded association constants consistent with the UV-Vis data. Despite the presence of electron-withdrawing p-nitrophenyl groups, BU1 forms relatively weak complexes with halide and perchlorate anions. NMR experiments and molecular modeling suggest that direct N-aryl substitution induces cavity distortion and reduces flexibility, which likely accounts for the observed decrease in binding strength.