The presence of F
or CN substituents at boron in BODIPYs
causes
a dramatic effect on their reactivity, which allows their chemoselective
postfunctionalization. Thus, whereas 1,3,5,7-tetramethyl B(CN)2-BODIPYs displayed enhanced reactivity in Knoevenagel condensations
with aldehydes, the corresponding BF2-BODIPYs can experience
selective aromatic electrophilic substitution (SEAr) reactions
in the presence of the former. These (selective) reactions have been
employed in the preparation of BODIPY dimers and tetramers, with balanced
fluorescence and singlet oxygen formation, and all-BODIPY trimers
and heptamers, with potential application as light-harvesting systems.