A dipyrenyl calixazacrown chemosensor for Mg2+

A new fluorogenic calix[4]tetraaza-crown-6 (4) bearing two pyrene amide groups has been prepared. It was shown to be selective for Mg2+. When Mg2+ is bound to 4, the pyrene monomer emission increased while the excimer emission declined in a ratiometric manner. It is shown by 1H NMR that this ratiometric change is due to the conformational changes of the pyrenes during the chelation of Mg2+ by the amide functions to form a 1:1 complex.