Next, a second proton is attached to the structure Proton-2 on donor unit D4. This process may occur with increasing probability in systems with elevated acid concentrations. For a more complete picture, two possible positions of the second proton are considered: once on the right side of the donor unit (green number 1 in Fig. ), designated Double-1, and once on the left side of the of the donor unit (green number 2 in Fig. ), designated Double-2. A clear broken-spin symmetry is formed for Double-1 in its optimized structure, as shown in Fig. . The α-SUMO and β -SUMO are very close to each other in energy and the orbital profiles show a close resemblance (not shown). Both are located near the right edge of the chain with an orbital nature similar to that of the LUMO in Proton-2 and do not represent polaron states. Instead, the proton-induced polaron state is found to be the α-SUMO+1 state, which is energetically very close to the α-SUMO (significantly overlapping in the DOS plot) but spatially well separated and of entirely different electronic nature. It is located on the left side of the conjugated chain as shown in Fig. and the polaronic nature is reflected in the bonding state appearance and delocalization. In addition, the polaronic α-SUMO+1 state is accompanied by a high total amount of positive charge of about 0.96e on the donor units D1 to D3 (Fig. , red bars) and leads to IVMs for frequencies below 1050 cm -1 , as shown in Fig. .