Pyridinium and indole orientation determines the mitochondrial uncoupling and anti-cancer efficiency of F16

F16 is a mitochondria-targeted, broad-spectrum anticancer agent in the pre-clinic cancer therapy. Here we developed two fluorescent isomers of F16 (o-F16 and m-F16) with entirely different photophysical properties, uncoupling activity, and cytotoxicity by merely modifying the linking orientation of pyridinium and indole units. Individually, o-F16 acted as a strong uncoupler to reduce the mitochondrial respiration efficiency, while m-F16 could hardly uncouple the mitochondrial respiration due to its poor proton dissociation capability. Owing to their intrinsic fluorescence, o-F16 and m-F16 could specifically image mitochondria in the green and red channel, respectively. This work could provide useful information for the development of uncouplers and design of mitochondrial-targeted drugs.