A fluorescence on-off sensor for Cu2+ and its resultant complex as an off-on sensor for Cr3+ in aqueous media

A new coumarin-quinoline based sensor 1 has been synthesized. The paramagnetic Cu2+ ion turned off the fluorescence of sensor 1 with a 1 : 1 binding stoichiometry. The resultant 1-Cu2+ complex could act in situ as an efficient off-on fluorescence sensor for the paramagnetic Cr3+ ion triggered by the 1 : 1 replacement of Cu2+ with Cr3+. This selective fluorescence on-off-on sensor was used to identify Cu2+ and Cr3+ in living breast cancer MCF-7 cells using confocal fluorescence microscopy, indicating that sensor 1 has a potential application for the selective detection of Cu2+ and Cr3+ in living cells.