A careful analysis of electronic orbitals reveals that a pronounced intrachain electron transfer occurs in Double-1. The polaron turns out to be located on the left side of the chain as shown in Fig. which indicates a substantial reorganization of electronic states within the double-protonated polymer. As the result, an originally unoccupied orbital with an antibonding appearance similar to the LUMO of Proton-2, becomes the occupied α-SOMO as is shown in Fig. . The electron transferred and polaron formed correspondingly roughly carry a charge of 1e, such that we term the electron reorganization an intrachain electron transfer process, resulting in the polaronic α-SUMO+1 and occupied α-SOMO, accompanied by the formation of non-polaronic α-and β -SUMO. This picture appears to be in agreement with the mechanism proposed by Yurash et al. This interpretation is further supported by the calculated total change in electron density induced by the addition of the second proton. In the calculation, the second proton (green number 1 in Fig. and arrow in Fig. ) is removed from the optimized Double-1 structure and a single-point calculation is performed, including the first proton as indicated by the green arrow in Fig. . Then, the total electron density of the optimized Double-1 structure is subtracted from the total electron density resulting from this single-point calculation. The resulting change in electronic density is shown in Fig. which illustrates directly how the total electron density changes upon addition of the second proton. A reduction of the total electron density in the double bonds where the polaron is located is observed, which is the typical consequence of polaron formation in conjugated systems. This is accompanied by a localized, strong increase in the total electron density at the proton position indicated by the red arrow in Fig. . Note that the electron density reduction and increase spatially coincide with the α-SUMO+1 (Fig. ) and α-SOMO (Fig. ), respectively. A calculation for an extended Double-1 structure with two additional polymer repeat units added on the left edge shows that the polaron induced by the intrachain electron transfer has the same spatial distribution as for Double-1, but is shifted even further away from the proton positions to the left side of the elongated chain. This indicates that the polaron delocalization is finite but the polaron itself is rather decoupled from the proton positions and thus might act as a free positive charge.