Intrinsic conducting polymers are promising candidates for bioelectronic devices due to their structural kinship to biological matter combined with electronic functionality. For sophisticated nano-scaled bioelectronic devices, P3RT-type polythiophene derivatives bearing water-soluble, biocompatible sidechains are particularly appealing due to their well-defined molecular structure and controllable end-group composition. However, their employment in bioelectronic devices is not as straightforward as expected. Challenging is their poor performance due to, e.g., the low charge carrier concentration in the native state. Partial oxidation of these polymers by strong electron acceptors, so-called p-type doping, can increase the charge carrier concentration, and thus, the conductivity. The solution-based molecular p-type doping of such a water-soluble polythiophene derivative by the dopant tetrafluoro-tetracyano-quinodimethane is reported. The mechanism of the doping process is thoroughly investigated by a combination of spectroscopic techniques covering the UV-VIS and IR regions. Furthermore, the morphological and electronic properties of polymer thin films are examined as a dependence on the dopant concentration.