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 RNH 2 , 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 (H 2 O/THF, 50:50 v /v) leads to intense fluorescence, enabling selective detection of OH − under extreme alkaline conditions. • The reactivity of seleno-BODIPY ( BDP-Se ) towards representative nucleophiles was investigated. • An unexpected substitution reaction mechanism was identified in which the “SePh” group functions as the leaving group, as supported by DFT calculations. • BDP-Se exhibits an expressive response for hydroxide ions (OH − ), yielding a highly fluorescent product (Φ = 72%) in aqueous media (H 2 O/THF, 50:50 v /v) in a turn-on fluorescent process. • BDP-Se can be applied as a fluorescent sensor for extremely alkaline media (pH ≥ 12).