Aarhus green: a tetrafluoro-substituted derivative of fluorescein

The synthesis and characterization of a 2',4',5',7' -tetrafluorinated derivative of fluorescein, called Aarhus Green, is reported. As with related 2 ',7'-difluorinated compounds, tetrafluorination of the xanthene-derived moiety ma kes the more fluorescent anion accessible over a larger pH range. However, in contrast to a p ublished report, we find that fluorination in the 4' and 5' positions does not appreciably decrea se the fluorescence quantum yield, φf. Rather, Aarhus Green has a reasonably large φf (0.79 ± 0.04). Moreover, Aarhus Green does not efficiently sensitize the production of singlet oxy gen and it is photostable. Thus, tetrafluorination of the xanthene moiety in fluorescein derivatives c an be a useful tool in the development of fluorescent probes.