A coumarin-derived fluorescence chemosensors selective for copper(II)

Two different coumarin derivatives have been connected via animine linkage to obtain a new fluorescence signaling system. The coumarin derivative (L) containing a C=N group was designed as an example for illustration. The free ligand L is almost nonfluorescent due to the isomerization of C=N double bond in the excited state. However, in the presence of a Cu(II) ion, this isomerization is stopped because of bonding to the metal ion, resulting in a high-intensity (400-fold) emission. In this way, we designed a new compound for copper-selective and ratiometric chemosensors.