‘Naked-eye’ detection of F− ions by two novel colorimetric receptors

Two novel colorimetric receptors, S1 and S2, linked to one or two nitrophenylurea groups were synthesized in good yields, characterized and their chromogenic properties investigated towards various anions (F−, Cl−, Br−, I−, NO3−, AcO−, ClO4−, HSO4−, and H2PO4−) by UV–vis and 1H NMR techniques. The receptors, effectively and selectively, recognized and distinguished the biologically important F− from other anions such as Cl−, Br−, I− etc. in CH3CN. This selectivity could be easily observed by the naked eye, indicating that receptors S1 and S2 are potential colorimetric sensors for fluoride ion.