Switching and fluorescence signal amplification with metal ions in allosteric systems based on 1, 3-alternate thiacalix[4]crown

New thiacalix[4] crown derivatives 4 and 5 of 1,3-alternate conformation possessing anthracene and quinoline moieties respectively were synthesised and examined for their cation recognition abilities toward different cations by fluorescence spectroscopy. Selective optical recognition with fluorescence amplification was observed for Fe3+/K+ and Hg2+/K+ in chemosensors 4 and 5 respectively. Further it was observed that the formation of 4 center dot Fe3+ complex triggers the decomplexation of K+ ion. Similar allosteric behaviour between Hg2+ and K+ was observed in chemosensor 5.