Synthesis of novel squaraine-bis(rhodamine-6G): A fluorescent chemosensor for the selective detection of Hg2+

We report the design and synthesis of a novel squaraine-bis(rhodamine-6G) (SR)-based indicator for selective detection of Hg2+ ion. Sensing behavior toward various metal ions (M = Li+, Na+, Mg2+, K+, Fe3+, Co2+, Ni2+, Cu2+, Zn2+, Ag+, Cs+, Hg2+, and Pb2+) was investigated by UV-vis and fluorescence spectroscopy in acetonitrile solution. The indicator exhibited highly selective and sensitive colorimetric and turn-on fluorescent responses compared with the other investigated metal ions because of the soft-acid nature and large size of mercuric ion. 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 forming a 1:1 stoichiometric complex of SR-Hg2+ which is supported by the density functional theory calculations. More significantly, the sensor displayed a remarkable blue-to-green fluorescence switch in the presence of Hg2+ ions. (C) 2014 Elsevier B.V. All rights reserved.