Reductive cleavage of CC bonds as a new strategy for turn-on dual fluorescence in effective sensing of H2S

Abstract

Reductive cleavage of alkenes is rarely reported in synthetic chemistry. Here we report a unique H₂S-mediated reductive cleavage of CC bonds under mild conditions, which is a successful new strategy for the design of probes for effective sensing of H₂S with turn-on dual-color fluorescence. A short series of phenothiazine ethylidene malononitrile derivatives were shown to react with H₂S, via reductive cleavage of CC bonds with intramolecular cyclization reactions to form thiophene rings. Enlightened by this new reaction mechanism, four effective probes with turn-off to turn-on fluorescence switches were successfully applied for sensing H₂S, an important gaseous signalling molecule in living systems, among which PTZ-P4 exhibited two fluorescent colors after reductive cleavage. The dual-color probe was applied for imaging endogenous H₂S and showed distinct differences in brightness in living C. elegans for wild type N2, glp-1 (e2144) mutants (higher levels of endogenous H₂S), and cth-1 (ok3319) mutants (lower levels of endogenous H₂S). The discovery of H₂S-mediated reductive cleavage of CC bonds is expected to be valuable for chemical synthesis, theoretical studies, and the design of new fluorescent H₂S probes.