Ratiometric/‘On–Off’ sensing of Pb2+ ion using pyrene-appended calix[4]arenes

New fluorescent sensors 6, 7 and 9 based on calix[4]arenes have been synthesized and examined for their binding abilities towards different metal ions (Li+, Na+, K+, Pb2+, Zn2+, Hg2+ and Ag+) by UV and fluorescence spectroscopy. Two of these receptors (6 and 7) show ratiometric sensing while the third receptor (9) shows ‘On–Off’ signaling of Pb2+ ion among the various metal ions tested. The stoichiometry of the complexation was found to be 1:1 as established by Job's plot.