Ratiometric fluorescence detection of fluoride ion by indole-based receptor.

A novel artificial receptor 1 containing the indolocarbazole-NH moieties as the recognition sites exhibited high selectivity and sensitivity toward F(-) over other typical anionic species in DMSO solution. Upon addition of F(-) into the solution, receptor 1 showed a remarkable ratiometric shift of the fluorescence maximum from 535 to 590 nm, and also a prominent color change from light yellow to orange, which was observable by the naked eye. The recognition properties of receptor 1 were investigated by (1)H NMR, UV-vis, and fluorescence titration experiments, with the results suggesting a two-step strategy of binding with F(-). In addition, the theoretical calculations were carried out to reveal the role of intramolecular charge transfer in the ratiometric fluorescence recognition process.