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

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 H-1 NMR spectra and a plausible structure for the complex of 1 . H+ with HPO42- is proposed.