A rhodamine-based off-on fluorescent chemosensor for selectively sensing Cu(II) in aqueous solution.

A novel chromogenic and fluorogenic chemosensor RhB-pMOSal comprising a rhodamine fluorophore and a salicylaldehyde receptor being connected by an iminohydrazine link was synthesized and fully characterized. Its sensing behavior toward various metal ions in neutral aqueous solution was investigated by absorption and fluorescence spectroscopy. RhB-pMOSal exhibited a reversible and sensitive "turn-on" response of absorption and fluorescence toward Cu(2+) in aqueous acetonitrile solution. Approximate 65 and 6-fold enhancement in the absorbance at 556 nm and fluorescence intensity at 573 nm were estimated when equivalent Cu(2+) was added to the RhB-pMOSal solution. Under the same conditions, RhB-pMOSal displayed more sensitive than a reported analogue RhB-Sal to Cu(2+) ion. The competition experiments for Cu(2+) mixed with common metal ions exhibited no obvious change in absorption and emission except Cr(3+) ion that can induce the fluorescence quenching of RhB-pMOSal to some extent.