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 H-1-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.