Novel Redox Probes Based on Iridium Complexes for Electrogenerated Chemiluminescence

In this thesis we investigate the electrochemical and electrochemiluminescence (ECL) behavior of five cyclometalated Ir(III) complexes, namely MF115, MF118, MF122, MF135 and MF102, which share the same pyrazolyl-acetate ancillary ligand but differ in their cyclometalating ligands, giving rise to emission colors ranging from blue to deep red. The complexes were provided by Prof. Matteo Mauro (University of Padua and Institut de Physique et de Chinie des Materiaux de Strasbourg, IPCMS) and were characterized electrochemically by cyclic voltammetry in dichloromethane (DCM) and acetonitrile (ACN). The ECL was triggered by employing tri-n-propylamine (TPA) or benzoyl peroxide (BPO) as the sacrificial coreactants, while its response was investigated in detail. Cyclic voltammetry showed that in the positive-going scan most of the complexes are reversibly oxidized, while in the negative-going scan their reduction processes are irreversible in every case. How easily a complex is oxidized, and how reversible that oxidation is, depends on the electronic character of its cyclometalating ligand. The electron-donating substituent in MF122 decrease the oxidation potential, while the electron-withdrawing fluorine substituents in MF115 and MF102 increase it. All five complexes provide an ECL response with both TPA and BPO, confirming that the energy available from both coreactant pathways was thermodynamically sufficient to populate the emitting excited state. MF122 showed the highest relative ECL efficiency with both coreactant, although BPO generally produced stronger responses than TPA across the series. A comparison between the ECL and photoluminescence spectra showed a good agreement for most complexes, indicating that the same excited state is populated by both processes, with some differences noted for MF122 and MF102 that could not be fully explained with the present data. Overall, this work shows how small changes in the cyclometalating ligand of Ir(III) complexes can tune their redox behavior and ECL efficiency, providing structure–property information relevant to the design of future ECL luminophores.