Ratiometric fluorescence detection of fluoride ion by indole-based receptor

An indolocarbazole-based colorimetric and ratiometric fluorescent receptor 1 was synthesized and exhibited high selectivity and sensitivity toward fluoride ion over other common anions. The recognition properties of receptor 1 were investigated by 1H NMR, UV-vis, and fluorescence titration experiments. In addition, the theoretical calculations were also carried out to reveal the role of intramolecular charge transfer in the recognition process.