Inorganic anions have recently been gaining increasing attention due to their pivotal roles in biology, medicine and the environment. Chemosensors that selectively sense and respond to inorganic anions have consequently gained interest. In particular, the monitoring of fluoride ions is of interest due to their toxicity.

Chang-Hee Lee and co-workers, Kangwon National University, Korea, have developed a F^– sensor that displays a sensitive “Turn-On” fluorescence in the presence of fluoride anions. The sensor is based on calix[4]pyrrole and forms a complex with F^– that results in fluorescence. The fluoride ion can be displaced by Li⁺, resulting in quenching of the fluorescence and turning the indicator off. The “Off-On” switching was completely reversible and could be repeated many times.

This is the first sensor that turns on in the presence of F^– and could additionally present a model for a fluorescence-based logic system.

• Salt (LiF) Regulated Fluorescence Switching
  P. Sokkalingam, J. Yoo, H. Hwang, P. H. Lee, Y. M. Jung, C.-H. Lee,
  Eur. J. Org. Chem. 2011.
  DOI: 10.1002/ejoc.201100359