8-Functionalization of alkyl-substituted-3,8-dimethyl BODIPYs by Knoevenagel condensation.

New 8-alkenylBODIPYs have been synthesized by Knoevenagel condensation between a series of alkyl-substituted-3,8-dimethylBODIPYs and aromatic or aliphatic aldehydes. This is in clear contrast with literature precedents, which indicate that this reaction occurs exclusively on the methyl group at C-3. The change in hybridization of the carbon at the 8-position (from sp(3) to sp(2)) determines the fluorescence emission of the BODIPY, while the presence of electron-donating or -withdrawing groups leads to intramolecular charge transfer processes.