Study on host–guest complexation of anions based on a tripodal naphthylurea derivative

Abstract

In this paper, we report the synthesis of tripodal naphthylurea tri(2-aminoethyl)amine (1) designed for the recognition of anions (e.g., H₂PO₄^- and HSO₄^-) by complexation-enhanced changes of fluorescence in DMF solution. The effect of protonation and addition of anions upon the photophysical properties of 1 was investigated for comparison with those of analogous receptors, 1·HCl and the di(2-aminoethyl)amine (2) and n-amylamine (3) naphthylurea derivatives. The fluorescent chemosensor 1 shows obvious changes in its fluorescence spectrum upon addition of H₂PO₄^- and HSO₄^- anions. The association constants for the complexes of 1 with anions were measured by fluorometric titration and show a higher specific selectivity for the H₂PO₄^- anion with a 1:1 stoichiometry of the complex. These effects, which strongly depend on the interaction of hydrogen-containing oxoanions with the receptor, can be interpreted in terms of anion-induced reduction of the efficiency of photoinduced electron transfer (PET). The results were also confirmed by ¹H NMR spectra and a plausible structure for the complex of 1·H⁺ with HPO₄^2- is proposed.