Colorimetric turn-on sensing of fluoride ions in H 2 O/ CHCl3 mixtures by pyridinium boranes
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As part of our interest in chemistry of cationic boron compounds as anion receptors, we have synthesized 2-(4'-dimestylborylphenyl)-N-methyl-pyridinium triflate (OTf) and 2-(5'-dimesitylborylthiophen-2-yl)-N-methyl-pyridinium triflate (OTf) by reaction of the corresponding pyridyl derivatives with MeOTf. Both OTf and OTf extract fluoride ions biphasically (H2O/CHCl3) to form the zwitterionic fluoroborates 3-F and 4-F, which have been structurally characterized. Remarkably, fluoride binding induces a red-shift of the low energy absorption band of these boranes (from 319 nm to 368 nm for 3/3-F and from 355 nm to 430 nm for 4/4-F) leading to the appearance of a yellow color. The origin of this turn-on colorimetric response is attributed to an intramolecular charge transfer process involving the triorganofluoroborate moiety as the donor and the pyridinium moiety as the acceptor.
author list (cited authors)
Wade, C. R., & Gabbaï, F. P.