Starting with the initial reference spectrum obtained at the open-circuit voltage, the symmetric C=O stretching band at 1708 cm -1 can be used as an indicator for neutral repeat units as it has been shown to disappear as NDI-T2 becomes highly reduced. As the applied voltage reaches 0.4 V vs. RHE and the material is reduced to its singly-reduced, electron polaron state, two new bands at 1538 and 1370 cm -1 arise. These bands can be ascribed to a shift of the pristine bands at 1610 and 1572 cm -1 , associated with the C-C stretching in the NDI unit. The intensities of these vibrations increase with applied voltage and are assigned to electron polaron formation. Moreover, the intensity ratio of the triplet bands between 1496 and 1400 cm -1 undergoes a few changes, with a substantial drop of intensity of the bands at 1434 and 1406 cm -1 , assigned to collective vibrational displacements of the C-C stretching of the NDI and the T2 units. When the applied voltage reaches 0.2 V vs. RHE, the bands assigned to the electron polaron at 1583 cm -1 and 1370 cm -1 gain further intensity, while the triplet between 1496 and 1400 cm -1 broadens and loses intensity. Additionally, at this voltage, the band at 1708 cm -1 , which can be used to indicate the presence of neutral NDI-T2 repeat units, disappears. Once -0.1 V vs. RHE is applied, new vibrational features arise that have not previously been reported, namely the bands at 1344 and 1137 cm -1 , which, based on the associated electrochemical features, are likely associated with the formation of the electron bipolaron.