Electrochemical Synthesis of Phenothiazinone as Fluorophore and its Application in Bioimaging

Phenothiazinone is a promising yet underutilized fluorophore, possibly due to the lack of a general accessibility. Herein, we report a robust and scalable TEMPO‐mediated electrochemical method to access a variety of phenothiazinones from 2‐aminothiophenols and quinones. The electrosynthesis proceeds in a simple cell architecture under mild condition, and notably carbon–halogen bond in quinones remains compared to conventional methods, enabling orthogonal downstream functionalization. Mechanistic studies corroborate that TEMPO exert a protective effect in avoiding product decomposition at the cathode. In particular, benzophenothiazinones show intriguing luminescence in the states of both solid and solution, and thus their photophysical properties are scrutinized in detail. Further bio‐imaging of the lipid droplets in living cells highlights the considerable promise of benzophenothiazinones as fluorescent dye in the biomedical fields.