Anion sensing using colorimetric amidourea based receptors incorporated into a 1,3-disubstituted calix[4]arene

The synthesis of amidourea-based colorimetric anion sensors 1 and 2 and the evaluation of these sensors using anions such as acetate (CH3CO2-), fluoride (F−), hydrogen phosphate (H2PO4-) and hydrogenpyrophosphate (pyr) in DMSO is described. While 1 has a single amidourea moiety, 2 has two such receptors incorporated into a lower-rim 1,3-disubstituted calix[4]arene scaffold. Whilst both sensors gave rise to red shifts in their absorption spectra upon anion recognition, the sensing of F− and pyr gave rise to large changes with concomitant colour changes from yellow to purple, which were visible to the naked eye.