Nucleophile-induced fluorescence activation in Seleno-BODIPY: Mechanistic insights and OH− sensing at extreme alkalinity

In this work, a seleno-BODIPY derivative (BDP-Se) was synthesized, and its reactivity towards a set of representative nucleophiles (including RNH2, PhO-, OH-, PhS-, among others) was investigated. Spectroscopic and kinetic studies were conducted, enabling a comparative evaluation of the reactivity of BDP-Se with the selected analytes. The structures of the resulting products were confirmed through mass spectrometry. An unexpected substitution reaction of the “SePh” groups on the BODIPY core was accompanied by a turn-on fluorescence response, attributed to the inhibition of the Photoinduced Electron Transfer (PET) process. The reaction mechanism was investigated using a combination of spectroscopic experiments and computational analysis, supporting a Nucleophilic Aromatic Substitution mechanism in which the chalcogen substituents act as leaving groups. Remarkably, reaction with OH- (Φ = 72%) at pH ≥ 12 in aqueous solution (H2O/THF, 50:50 v/v) leads to intense fluorescence, enabling selective detection of OH- under extreme alkaline conditions.