“…In order to analyze the absorption and emission steps in fluorescence as intramolecular charge transfer processes, it is important to consider several aspects of the Fukui function, Equation (). One of them comes from the fact that since the electronic density as a function of , at zero temperature [65–68] and up to temperatures of chemical interest [69], is given by a series of straight lines connecting the integer values of , then the left and right derivatives are given by the expressions [53, 54] where , and are the electron densities, and the three densities are determined at the ground state geometry of the electron system. Also, it has been shown that the Fukui function is the one that minimizes the energy change associated with the removal or addition of charge [70], which implies that and correspond to the places where the charge is removed or added, respectively.…”