How are the energies of Fermi level and the frontier orbitals determined?
The Fermi level is determined by the potential applied to the electrode; that is, varying the applied potential changes the oxidizing/reducing ability of the electrode. For example, more negative potentials increase the reducing ability of the electrode. In contrast, the energies of the molecular frontier orbitals are determined by the molecular structure and can be considered to be constant. Therefore, a common approach in voltammetry experiments is to vary the applied potential, and to record the potential at which a current response is detected; that is, the energy at which oxidation or reduction occurs. The redox potential is a measure of this energy. Do all molecules have a measurable redox potential? Although all molecules do have frontier orbitals, in practice these are not always accessible in a voltammetry experiment. Molecules for which a redox potential can be measured are referred to as electrochemically active. Examples of electrochemically active molecules include organic
