Ratiometric/'turn-on' fluorescent chemosensor for CN-: mimicking XNOR logic function with Fe3+ ions

The naphthyl-appended chemosensors 5-7 based on thiacalix[4]arene of cone and 1,3-alternate conformations have been synthesized which show high selectivity toward CN(-) ions by using hydrogen bonding and displacement approach. The presence of CN(-) induces quenching of fluorescence emission of compound 5 and ratiometric fluorescence behaviour of compounds 6 and 7 through hydrogen bonding interactions. Further, chemosensors 5-7 show high affinity for Fe(3+) ions with quenching of fluorescence emission, among all the metal ions tested. The 'in situ' prepared iron complexes of compounds 5-7 shows high "turn-on" selectivity toward CN(-) ions over the other anions. The molecular switching has been observed between chemical inputs of Fe(3+) and CN(-) ions which mimics the operation of an exclusive-NOR (XNOR) logic gate.