Two new calix[4]arene-based sensors containing fluorenone moieties 4 and 5 were synthesized and their structure were characterized by NMR and HRMS. Compound 4 shows a remarkable color change from yellow to orange-red in the presence of fluoride anion because of hydrogen bonding interaction of amidogroup with F−. Furthermore, this compound showed a UV–vis red shift and fluorescence quenching only in the presence of F−. 1H NMR titration of 4 with F−confirms strong hydrogen bonding formation of this anion with amido hydrogen and phenolic hydroxyl functional groups. Compound 5 did not show asignificant color change upon the addition of various anions, however, a fluorescence blue shift which can trace back to the interaction of F−, AcO−, NO3−and H2PO4−with phenolic and amido groups, was observed. The results showed that the receptor 4 is an ideal sensor for fluoride ion with high sensitivity and specificity.
