Generally speaking, radical species can undergo two possible electronic transitions from the ground state to the excited state, i.e., 1) from the b-HOMO to the b-SOMO and 2) from the a-SOMO to the a-LUMO (Figure ). Similarly, two types of electronic transitions from the excited state to the ground state are possible. In order to investigate which transition is more dominant in the DAAN derivatives, the electronic transitions for absorption and emission were evaluated based on the results of the TD-DFT calculations. The obtained results indicate that for almost all derivatives, except for NO2/OMe, the HOMO-SOMO electronic transition is dominant in both the ground-toexcited-state and the excited-to-ground-state transitions (Tables S2 and S3). They also confirm that this trend increases with the strength of the electron-donating properties of the substituents. This reflects the fact that the introduction of electron-withdrawing substituents decreases the LUMO energy, which decreases the SOMO-LUMO gap (Table , Figures ).