Redox‐Stability of Alkoxy‐BDT Copolymers and their Use for Organic Bioelectronic Devices. (21st February 2018) - Giovannitti, Alexander
Abstract: Organic semiconductors can be employed as the active layer in accumulation mode organic electrochemical transistors (OECTs), where redox stability in aqueous electrolytes is important for long‐term recordings of biological events. It is observed that alkoxy‐benzo[1, 2‐ b :4, 5‐ b ′]dithiophene (BDT) copolymers can be extremely unstable when they are oxidized in aqueous solutions. The redox stability of these copolymers can be improved by molecular design of the copolymer where it is observed that the electron rich comonomer 3, 3′‐dimethoxy‐2, 2′‐bithiophene (MeOT2) lowers the oxidation potential and also stabilizes positive charges through delocalization and resonance effects. For copolymers where the comonomers do not have the same ability to stabilize positive charges, irreversible redox reactions are observed with the formation of quinone structures, being detrimental to performance of the materials in OECTs. Charge distribution along the copolymer from density functional theory calculations is seen to be an important factor in the stability of the charged copolymer. As a result of the stabilizing effect of the comonomer, a highly stable OECT performance is observed with transconductances in the mS range. The analysis of the decomposition pathway also raises questions about the general stability of the alkoxy‐BDT unit, which is heavily used in donor–acceptor copolymers in the field of photovoltaics. Abstract : The redox‐stability of benzodithiophene copolymers is analyzed where it is found that copolymers with large ionization potentials (IPs) degrade during electrochemical oxidation in aqueous electrolytes while copolymers with a small IP can be charged reversibly. The degradation product is identified to be a quinone structure which has a significant impact on the performance of the copolymers in electronic devices.