The evaluation of new and isotopically labeled isoindoline nitroxides and an azaphenalene nitroxide for EPR oximetry

► Isoindoline nitroxides are promising in vivo and in vitro EPR oximetry probes. ► Isoindoline nitroxides exhibit high oxygen sensitivity without isotopic labeling. ► Active ester isoindoline nitroxide is non-toxic and partially localises in cells. ► Rigid structure of azaphenalene nitroxide results in highly-resolved EPR spectra.