Red-emitting boron difluoride complexes with a mega-large Stokes shift and unexpectedly high fluorescence quantum yield.

Introduction of a tetrahydroquinoxaline donor into boron difluoride complexes largely extended their emissions (617-684 nm), highly improved their fluorescence quantum yields (up to 0.68) and greatly increased their Stokes shifts (up to 209 nm). These new fluorescent dyes showed reversible ratiometric solid-state fluorescence changes upon switched acid/base fumings. Significantly, these boron difluoride complexes were successfully utilized as imaging agents in living cells and zebrafish.