The doping of organic semiconducting polymers was examined by studyingthe molecular vibrations through a combination of experimental spectroscopytechniques and the application of density functional theory (DFT) theoretical tools and the amplitude mode (AM) model. The IR spectra of the conjugated polymers P3HT, PFO and PCPDTBT were experimentally investigated. Particular focus was applied to PCPDTBT, where the effects of dopant electronegativity, dopant solvent choice and doping method were pursued. Doping induced vibrational modes in PCPDTBT were observed to have similar intensities to polaron absorption bands in the system. Comparisons to DFT calculations showed that these unusual intensity trends are the result of the molecular vibrations corresponding to the intense modes causing polaron displacement along the polymer backbone. Finally, a novel solution of the AM model was applied to the experimentally studied systems. The results of this suggest that PCPDTBT has the potential for higher carrier mobilities then P3HT.