Anion Binding Studies of Urea and Thiourea Functionalized Molecular Clefts

Two rationally designed 4-nitrophenyl-based molecular clefts functionalized with thiourea (L (1)) and urea (L (2)) have been synthesized and studied for a variety of anions by UV-Vis and colorimetric techniques in DMSO. Results from the binding studies suggest that both L (1) and L (2) bind halides showing the order: fluoride > chloride > bromide > iodide; and oxoanions showing the order: dihydrogen phosphate > hydrogen sulfate > nitrate > perchlorate. Each receptor has been shown to form a 1:1 complex with an anion via hydrogen bonding interactions, displaying distinct color change for fluoride and dihydrogen phosphate in solution. As compared to the urea-based receptor L (2), the thiourea-based receptor L (1) exhibits stronger affinity for anions due the presence of more acidic thiourea functional groups.