This project targets the synthesis of lanthanide(III) complexes with redox-sensitive ligands for monitoring of the redox status. A major downstream application is the non-invasive preclinical and biomedical imaging. We hypothesize that a change in the redox state of the ligand will influence both the lanthanide-based luminescence and the relaxation times (coordinated water molecules) for magnetic resonance imaging (MRI). Thus, the ligand will be the probe of the redox-status and the lanthanide will be the reporter. Polydentate ligands appended by pro-phenoxyl, pro-iminosemiquinonate and nitronyl nitroxide units will be prepared and chelated to a series of lanthanide ions: TbIII, EuIII for luminescence detection in the visible region, NdIII and YbIII for a luminescence in the NIR region and GdIII for application as contrast agents. The stability constants of the complexes will be determined and structural characterizations will be conducted. With the aim of improving the solubility and targeting the ligands will be appended by cell penetrating peptides or integrin recognition peptides. The operating potentials of the probes will be next investigated by electrochemical techniques (cyclic voltammetry, electrolysis). The complexes under their different redox states (radical or not) will be prepared both electrochemically and in vitro with biologically relevant reactants, and characterized by luminescence and relaxometric techniques. Having established that the oxidation state of the complexes could be monitored by luminescence and relaxivity, biological studies will be undertaken. They include MTT assays in order to ensure that the probes are non-toxic. Further in cellulo luminescence measurements (2D/3Dfluorescence microscopy) and relaxivity studies will be conducted on cells under various redox status (oxidative stress or hypoxia) for assessing the sensitivity of the probes. Finally, a thorough investigation of the magnetic coupling between the ligand radical and the lanthanide ions will give us major insight onto the operating mode of the complexes.