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

Reductive cleavage of alkenes is rarely reported in synthetic chemistry. Here we report a unique H2S-mediated reductive cleavage of C?C 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 C?C 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 C?C bonds is expected to be valuable for chemical synthesis, theoretical studies, and the design of new fluorescent H2S probes.