Study on host–guest complexation of anions based on tri-podal naphthylthiourea derivatives

A new host tris[N′-naphthyl-N-(2-aminoethyl)thiourea]amine (3) and the reference compounds bis[N′-naphthyl-N-(2-aminoethyl)thiourea]amine (2) and N′-naphthyl-N-n-amylthiourea (1) were synthesized and used for the recognition of anionic species. Considerable changes in UV/Vis absorption of host 3 induced by complexation with H₂PO₄^– (or HSO₄^–) were observed. UV/Vis spectroscopy titration experiments and ¹H-NMR results both indicated the formation of 1∶1 stable complexes between 3 and H₂PO₄^– (or HSO₄^–). The stability constants of the complexes were determined in DMF. The results demonstrate that optically changeable receptors for anions may be constructed by appropriate design of host molecules.