Optical absorption measurements are widely used to identify the doping nature of OSC materials, with typical polaronic absorption features observed in the near infrared spectral range. Yurash et al. reported an increase of broad polaronic absorption features in the range of 1100 nm to 3000 nm in thin films of PCPDT-BT doped with increasing amounts of the Lewis acid BCF. Furthermore, measurements in solution (dry chlorobenzene) gave a more detailed insight into the absorption features below 1600 nm, revealing a doping induced absorption feature at about 800 nm (read value) quite close to the main absorption feature of pristine PCPDT-BT at 720 nm. The main absorption peak of pristine PCPDT-BT gets reduced accordingly in its amplitude as a result of the doping by BCF. In Fig. and we show the vertical absorption spectra calculated in gas-phase for each single and double protonated chain discussed in the present work. We also compare with the absorption spectra for pristine (neutral) PCPDT-BT and a singly positively charged (polaron) PCPDT-BT chain. Distinct differences are found for the singly protonated systems with (Proton-1) and without (Proton-2) polaron formation. As can be seen in Fig. (blue), the single proton position that does not lead to the formation of a polaron (Proton-2) still leads to a main peak reduced in intensity at 617 nm and an additional absorption feature at 795 nm. Both features together appear as a broadening of the main absorption peak compared to the pristine PCPDT-BT (neutral). In contrast, the polaron induced for the other proton position in Proton-1 does lead to completely dif- ferent absorption features (Fig. , green). Comparing with the spectrum for the singly positively charged PCPDT-BT in Fig. (polaron), in Proton-1 we observe typical polaronic absorption features at 1114 nm and 1981 nm. The positions of the polaronic absorption peaks are slightly shifted compared to the polaron of PCPDT-BT (Fig. , red) which is a result of the slightly reduced spatial extend of the polaron induced by the protonation. The double protonated structures appear to show the general features of both singly protonated structures as shown in Fig. (orange and purple). We note that the spectral positions of absorption bands in the simulated spectra typically do not match the experimental values and depend on the method used. However, the appearance of doping induced features and relative trends and changes closely resemble the experimental observations as discussed further in the following. We also note that due to the increased computational cost, we do not explicitly study the vertical excitation of complexes with interchain electron transfer as shown in Fig. here.