Spectroelectrochemical behaviour of poly(2,5-dithienylene-isothianaphthene) and its analogue deuterated on the benzene ring

Poly(2,5-dithienylene-isothianaphthene) and its analogue, deutered on the benzene ring, have been prepared by voltammetric polymerization of the corresponding monomers in Bu₄NBF₄/acetonitrile solutions. The polymers obtained are electroactive, showing in cyclic voltammograms two oxidation peaks associated with p-type doping and two reduction peaks, originating from the de-doping process. The use of the polymer deuterated selectively on the benzene ring significantly facilitated the interpretation of Raman spectroelectrochemical data, since it allowed for a differentiation between the bands, originating from the benzene ring and those characteristic of the thiophene backbone. Similarly as cyclic voltammetry, Raman spectroelectrochemistry shows that the oxidative doping of the polymer is a two-step process. The spectral changes observed for the first step of the oxidation are consistent with the formation of the quinonoid sequence of bonds upon doping.