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

Abstract

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 ( E g el ) 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.