Redox potential in solution (homogeneous) phase The redox properties of the considered molecules can be described as a proton coupled electron transfer (PCET) where the electron and proton transfer simultaneously or by a decoupled sequence of an electron transfer (ET; blue arrows in Figure ) and a proton transfer (PT; green arrows in Figure ) step. Readers interested in this topic are referred to the literature. Combining these possible reaction paths results in "scheme of squares" which is commonly used to evaluate and represent their redox properties (Figure ).