Switchable three-state fluorescence of a nonconjugated donor-acceptor triarylborane.

A nonconjugated fluorescent molecule with a triarylboron acceptor and an alkylamine donor has been found to display bright green fluorescence due to charge transfer through space, which can be reversibly deactivated by blocking either the donor or acceptor site. Binding of the fluoride ion to boron switches the fluorescence color to sky blue, while protonation of the amine with acid switches the emission color to the purple fluorescence of the acceptor chromophore.