Dual Bodipy fluorophores linked by polyethyleneglycol spacers

Several Bodipy dyes were synthesized with various substituents designed to potentially interact with adventurous cations including protons. Among the different synthetic strategies, protection of the amino group by a BOC appears efficient for the substitution of the fluoro groups on the boron by Grignard reagents. Single alkylation on the amino-Bodipy compounds by a polyethyleneglycol chain bearing an alkyne end group is feasible using a biphasic strategy. Linkage of a blue dye on the alkyne fragment is promoted by palladium(0) and it provides novel dual donor–acceptor dyes. Fluorescence of the monoalkylated amino dyes is heavily quenched but restored by protonation or interaction with Fe(II) salts. Very efficient energy transfer from the donor (energy input at 20,000 cm−1) to the acceptor (energy output at 15,100 cm−1) is quantitative and not distance dependent.