| Abstract
| - The synthesis and the spectroscopic studies of the amidourea based calix[4]arene sensors 1 and 2 aredescribed. The 4-nitrophenyl based sensor 1 was synthesized in two steps from the corresponding calix[4]arene tetraethyl ester and shown to give rise to color changes in the UV−vis spectra in DMSO uponrecognition of pyrophosphate and fluoride. Fitting the changes in the absorption spectra using nonlinearregression analysis indicated strong binding of several anions by 1 such as acetate and hydrogen phosphatein 1:1 (Host:Guest) stoichiometry, and at higher concentration in 1:2 stoichiometry. The preorganizedcalix-cavity was, however, not found to host chlorine while binding of bromide was determined. At highconcentrations of these anions, significant colorimetric changes were also observed that were clearlyvisible to the naked eye for both pyrophosphate and fluoride. The phenyl analogue 2 was made to enableanalysis of the anion recognition using 1H NMR titrations and showed that ions such as phosphate werebound in 1:1 stoichiometry, whereas the “urea” protons were shown to be significantly affected uponcoordination to the anion.
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