Disabling photoinduced electron transfer in 4,4-difluoro-8(-4'-hydroxyphenyl)-1,3,5,7-tetramethyl-4-bora-3a,4a-diaza-s-indacene by phosphorylation.

The synthesis and photophysical characterization of the phosphorylated Bodipy dye 5 are reported and compared to those of its hydroxyphenyl counterpart 1. Conversion of the latter by three methods of phosphorylation yields the strongly fluorescent dye 5 which exhibits similar steady-state spectra like 1 but an approximately five times prolonged fluorescence lifetime tau(Fl). We attribute this distinct change from tau(Fl) = 0.7 ns for 1 to tau(Fl) = 3.7 ns for 5 to the suppression of photoinduced electron transfer in 5. This photochemical reaction was previously held responsible for fluorescence quenching in 1. Fluorescence correlation spectroscopy reveals that 5 can be detected by single-molecule methods and that uncaging of phosphate in 5 is a minor problem.