On-Off Switchable Binuclear Chemosensor Based on Thiacalix[4]crown Armed with Pyrene Moieties

A new fluorescent on-off switchable chemosensor 2 based on a thiacalix[4] arene with a 1,3-alternate conformation and two different types of cation binding sites has been synthesized. Two pyrene moieties linked to a cation recognition unit composed of two imine groups form a strong excimer in solution. Of the metal ions tested, the fluorescence of 2 was strongly quenched by Hg2+, Pb2+ and Cu2+ ions. The fluorescence was revived by the addition of only K+ to the Cu2+ ligand complex. Thus, metal-ion exchange triggers an on-off switchable fluorescent chemosensor. ((C) Wfley-VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2009)