Sterically crowded triarylphosphines and tetraaryldiphosphane bearing phenothiazinyl groups as redox sites were synthesized by using 2-bromo-1,3-dialkyl-5-phenothiazinylbenzenes as key synthetic intermediates. Cyclic voltammograms of these compounds show the first redox wave corresponding to the oxidation of the phosphorus redox center and the following waves corresponding to the oxidation of the phenothiazinyl groups. Introduction of more sterically crowded triarylphosphine moiety leads to more reversible oxidation of the phosphine as well as the phenothiazine moieties. A crowded tetraaryldiphosphane bearing four phenothiazinyl groups are oxidized in two steps. Four phenothiazine moieties are oxidized nearly at once after oxidation of the diphosphane moiety.