Solvent‐Dependent Site‐Switching Nucleophilic Additions of BODIPY‐Malonitrile Conjugates

BODIPY-malonitrile conjugates showed intriguingly solvent-dependent site-switching nucleophilic additions by cyanide, acting as two-channel fluorescent receptors for rapid, selective, and sensitive detection of cyanide anion as low as 0.28 µM. In aqueous solution, the probes were found to rapidly react with cyanide anion via a typical Michael addition to the malonitrile group at vinyl β-carbon, giving a rapid, selective, and sensitive "turn-on" detection of the cyanide anion. Unprecedentedly, in THF solution, the cyanide anion showed an unprecedented conjugated addition to the azafulvene ring of the BODIPY unit at vinyl α-carbon, followed by a tautomerization reaction, exhibiting significant (up to ∼116 nm) blue shifts in the absorption maxima.