The absorption–emission processes that characterize the fluorescent phenomena are analyzed by assuming that the changes in the ground state electronic density, when the system is promoted to the first excited state, and that the changes in the first excited state electronic density, when the system decays to a ground state with a distorted geometry, can be interpreted as intramolecular charge transfer processes. Thus, it is shown that in this context the hardness is the property that describes the absorption and the emission energies. Additionally, it is indicated that the substituent effects on the oscillator strengths may be described through the frontier molecular orbital condensed Fukui functions for the charge donating process.