UV-VIS-NIR and Raman spectroelectrochemistry of regioregular poly(3-octylthiophene): Comparison with its non-regioregular analogue

Spectroelectrochemical behaviour of regioregular poly(3-octylthiophene) has been investigated using UV-VIS-NIR and Raman spectroscopies. Static and dynamic UV-VIS-NIR spectroelectrochemical experiments combined with cyclic voltammetry show that oxidative doping of the regioregular polymer is a two-step process in which polarons (radical cations) are first created which then recombine to bipolarons (dications). This two-step oxidative doping mechanism is corroborated by FT Raman spectroelectrochemical studies which show significant changes in the positions and intensities of the Raman bands coinciding with the first and second oxidation peaks in cyclic voltammetry. These changes can be interpreted in terms of the doping induced formation of quinoid sequence of bands in the oxidized polymer. Vibrational calculations carried out for undoped and doped poly(3-octylthiophene) gave a very good agreement between the calculated Raman band frequencies and those recorded experimentally for the regioregular polymer.