Here is the transfer integral between the initial and final states, l is the reorganization energy which is defined as the energy change associated with the geometry relaxation during the charge transfer, and 𝜟𝑮 𝟎 is the relevant change of total Gibbs free energy it also relates smaller the homo lumo gap in the molecule smaller the 𝜟𝑮 𝟎 value hence high is the charge distribution increase the energy density.