Vibrational spectroscopy on pristine and doped pDTT3 ? a low band gap polymer based on polidithienothiophene.

Attenuated total reflection Fourier transform infrared studies of the electrochemical redox processes of poly-(dithieno[3,4-b:2¢,3¢-d]thiophene) (pDTT3), a low band gap conjugated polymer with a “polythiophene-like” backbone, where an aromatic moiety is fused to each thiophene ring, are reported. Vibrational spectroscopic studies are performed in situ during electrochemical oxidation (p-doping) and reduction (n-doping). Infrared active vibration bands due to charge carriers injected to the polymer chain are compared to photoinduced IR bands and to Raman spectra of the neutral polymer. The similar spectral features, observed during p- and n-doping processes, indicate a high charge carrier delocalization for both signs of carriers. Furthermore, the spectral evidence of the strong involvement of the fused aromatic rings to the ð-electronic structure of this low band gap polymer has been obtained.