where H 0 IJ is the diabatic electronic coupling at the closest donor-acceptor separation distance r = r 0 and β is the tunneling decay coefficient. The required energy to change the equilibrium configuration of initial state (I) into the equilibrium configuration of final state (J) while remaining on the same charge state as the initial one is called reorganization free energy, denoted by λ. Both reduction and oxidation processes are assumed to have the same λ value. In addition, h, k, and ⟨• • • ⟩ T are the reduced Planck constant, Boltzmann constant, and thermal averaging over nuclear configurations at temperature T , respectively. The activation barrier free energy ∆A ‡ IJ at constant volume and temperature can be estimated as