Reduction and oxidation doping kinetics of an electropolymerized donor-acceptor low-bandgap conjugated copolymer

The electrochemical synthesis of a new dithienylcyclopentadienone-derivative/3-methylthiopene copolymer was performed by cyclic voltammetry. The obtained material shows redox processes very close to those from the pristine DTCPD. A new redox process at -1.24 V, with a large anodic shift (0.51 V) related to the poly(3-methylthiophene) reduction, indicates the existence of a copolymer with a strong influence of the neighboring (n-doped) DTCPD comonomer. The new copolymer is electrochemically n-doped at more cathodic potentials than -750 mV and p-doped at more anodic potentials than 250 mV, with a bandgap of 1.0 eV. The cation's entrance in the film from the solution during n-doping and anion's entrance during p-doping for charge balance was checked by QCM. The reduction of the DTCPD part suffers a partial trapping of the negative charges that can be reoxidized only at high overpotentials (>1 V related to the reduction potentials). After polarization of the material at any potential inside the band gap, subsequent p- or n-doping reactions performed by potential steps start by nucleation-relaxation kinetic control, followed by anodic or cathodic, respectively, chronoamperometric maxima. At the maxima, both reactions were checked to occur under chemical kinetic control, allowing the determination of the reaction orders for p- and n-doping processes.