**4. Conclusions**

At the moment, the *p*-nitrostilbene-*tert*-butyl-nitrone (**1**) seems to be best suited for investigations of ROS formation in mitochondria. Unfortunately, the cytotoxicity of the coumaryl derivative (**2**) limits it application potential. The third molecule, 4-pyrrolidine-1,8 naphthylimido-methylphenyl-*tert*-butyl-nitrone (**3**) still requires further detailed evaluation. If confirmed that it distributes fairly evenly throughout the cell it would nicely complement data from **1**. With respect to the bioreduction leading to fluorescence recovery and timedependent changes in fluorescence, although reproducible, we still have to make sure that this was not due to an experimental artifact employing different instrumentation.
