Aarhus green: A tetrafluoro-substituted derivative of fluorescein

Abstract

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 makes the more fluorescent anion accessible over a larger pH range. However, in contrast to a published report, we find that fluorination in the 4′ and 5′ positions does not appreciably decrease 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 oxygen and it is photostable. Thus, tetrafluorination of the xanthene moiety in fluorescein derivatives can be a useful tool in the development of fluorescent probes.