An integrated system of pyrene and rhodamine-6G for selective colorimetric and fluorometric sensing of mercury(II)

A pyrene and rhodamine-6G functionalized simple chemosensor L is studied toward sensing of metal ions in solution extensively. L shows selective color change from colorless to pink in the presence of Hg<SUP>2+</SUP> in acetonitrile and the UV–Vis study shows peak at 525 nm with a ε value of 5.2 × 10<SUP>4</SUP> M<SUP>−1</SUP> cm<SUP>−1</SUP> due to selective ring opening of rhodamine spirolactam moiety. The selective sensing of Hg<SUP>2+</SUP> by L in the presence of other metal ions and reversible nature of “OFF–ON–OFF” functionality of L by Hg<SUP>2+</SUP> and EDTA, respectively, are also established. The fluorescence study of L in the presence of Hg<SUP>2+</SUP> shows emission at 550 nm when excited at 525 nm (ring opened rhodamine wavelength) or 340 nm (pyrene wavelength) in dry CH<SUB>3</SUB>CN. Thus L acts as a selective colorimetric and fluorometric probe (dual probe) for the Hg<SUP>2+</SUP> in solution. Metal ion sensing ability of L is also carried out in water as well as in aqueous Hepes buffer. These studies suggest that the fluorescence output of L in presence of Hg<SUP>2+</SUP> in aqueous environment is apparently due to the generation of acid upon addition of Hg<SUP>2+</SUP> salt in water