Synthesis and Properties of Hydrazine‐Embedded Biphenothiazines and Application of Hydrazine‐Embedded Heterocyclic Compounds to Fluorescence Cell Imaging

Hydrazine‐embedded unsubstituted butterfly‐shaped biphenothiazine and its sulfoxides were synthesized by dimerization of 1,9‐dibromophenothiazine, which was prepared by realizing selective debromination at the 3,7‐positions of 1,3,7,9‐tetrabromophenothiazine. cis/trans ‐Biphenothiazine sulfoxide was selectively prepared by changing the oxidation temperature to control the inversion rate of the butterfly shape of the intermediate. Their butterfly‐shapes, conformations, photophysical properties (UV‐vis absorption, fluorescence), and redox properties were elucidated by X‐ray analysis, DFT calculations, spectral and electrochemical measurements. Fluorescent hydrazine‐embedded biphenothiazine sulfoxides and bicarbazoles were applied to cell imaging of HeLa cells. The bicarbazoles exhibited high fluorescence signals in the cells with low toxicity.