The invention is reversibly reducible metal complexes and materials and an organic light emitting device, having an anode; a cathode; and at least one organic layer disposed between the anode and the cathode, made with the complexes of the invention. The reversibly reducible metal complexes are complexes a redox active metal center and at least one ligand; wherein; following a reduction of the complex, adding 1 extra electron to the complex, the extra electron is localized on the metal center. The complexes may function as an ETL or a host material.