It is apparent that the photoisomerization of the radical anion (1c .-) to 1o generates the EPR silent species. The mechanism of the conversion of 1c .-to 1o must involve an oxidation of 1c .-and a photoisomerization. Thus, chemical oxidation of 1c .-was carried out with an external oxidant, DDQ. The oxidized species was found to be spectroscopically identical with 1c. Upon chemical oxidation, the emission intensity of 1c .-gradually decreased upon the addition of DDQ (Figure ). This unequivocally demonstrates the correlation between the photogenerated radical species and those obtained through chemical reduction of 1c. These findings enhance our understanding of the reversible behavior of NDI-based radical systems.