Colorimetric and turn-on fluorescent determination of Hg2+ ions based on a rhodamine-pyridine derivative

We report the design and synthesis of a novel rhodamine-pyridine derivative-based indicator for Hg2+ ion determination. The indicator exhibited highly selective and sensitive colorimetric and turn-on fluorescent responses toward Hg2+ ions based on the ring-opening mechanism of the rhodamine spirolactam in an acetonitrile: water (CH3CN:H2O) solution. The obvious change from colorless to pink upon the addition of Hg2+ could make it a suitable naked eye indicator for Hg2+. Finally, we proposed a reversible ring-opening mechanism (OFF-ON) of the rhodamine spirolactam induced by Hg2+ binding and a 1:1 stoichiometric structure between rhodamine-pyridine (RP) and Hg2+. More significantly, the RP-Hg2+ complex exhibited a dual-channel chromo fluorogenic response to biologically important cysteine with high sensitivity and selectivity over other natural amino acids. The sensors display a remarkably Hg2+-selective colorless fluorescence with a yellowish-green color switch over a wide range of tested metal ions. (C) 2014 Elsevier B.V. All rights reserved.