On/off fluorescence switch of a calix[4]arene by metal ion exchange

A new calix[4]arene-based fluorescence chemosensor displaying a strong excimer emission was prepared. When a Pb2+ ion is bound to the two amide oxygen atoms linked to the fluorophores, the ligand exhibits a marked quenched excimer emission due to its geometrical change during the complexation. By the addition of Ca2+ ion into the 1·Pb2+, the excimer emission band was revived, by which an interesting on/off switch process is proposed.