The effect of chain microstructure on electrochemical and spectroelectrochemical properties of fluorenone-dialkyl bithiophene alternate copolymers

Voltammetric and spectroelectrochemical behavior of two newly synthesized conjugated polymers, which show the same chemical constitution but different type of regioregularity, is compared. These are poly(fluorenone-alt-dioctyl bithiophene)s in which the alkylthiophene rings are either head to head (HH) or tail to tail (TT) coupled, termed PFDOBT-HH and PFDOBT-TT, respectively. Both polymers can be electrochemically p- and n-doped and show the electrochemical energy gap (Egel) of the order of 2 eV. In the oxidation side of the voltammogram PFDOBT-HH gives a relatively narrow anodic peak with a maximum at E = 0.78 V versus Fc/Fc+. The corresponding peak of PFDOBT-TT is much broader with the maximum shifted to slightly lower potentials (E = 0.74 V versus Fc/Fc+). UV-vis-NIR and Raman spectroelectrochemical studies confirm that the oxidative doping of PFDOBT-TT starts at lower potentials and indicate significant differences in the anodic oxidation in both cases. In PFDOBT-HH the doping is sequential, which means that it starts by the oxidation of the bithiophene sub-units and is completed by the oxidation of the fluorenone ones. In the case of PFDOBT-TT both sub-units are doped simultaneously.