The protonation is realized by explicit addition of hydrogen atoms bonded to the carbon-backbone of the PCPDT-BT conjugated oligomer as illustrated in Fig. with a +1e net positive charge per additional hydrogen atom. The resulting bonds are initiated with a typical carbon-hydrogen bond length of about 1.09 Å. All atoms including the additional hydrogen atoms are then freely relaxed in a geometry optimization procedure. As in our previous work on PCPDT-BT, alkyl side chains are assumed to be of little influence to the frontier orbitals of the backbone and are replaced by methyl groups to reduce computational cost. The PCPDT-BT polymer is modelled by a rather long hexamer as depicted in Fig. . All structures are optimized in their singlet state allowing broken spin symmetry, and in the triplet ground state, respectively, revealing the singlet ground state always to be energetically favorable. Thus, the results presented below address the spin-symmetry-broken singlet ground state.