A novel chemosensor based on rhodamine derivative for colorimetric and fluorometric detection of Cu2+ in aqueous solution

A new rhodamine-based reversible chemosensor (2) was synthesized, which exhibits high sensitivity and selectivity for Cu(2+) but no significant response toward other competitive metal ions in aqueous solution. Upon the addition of Cu(2+), the spirolactam ring of 2 was opened and the solution color changed from colorless to red. Strangely, an unexpected fluorescence quenching was observed, which is contrary to the fluorescence turn-on of the most rhodamine-based chemosensors. The likely novel sensing mechanism has been proposed.