Redox-Stability of Alkoxy-BDT Copolymers and their Use for Organic Bioelectronic Devices

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. We observed that alkoxy BDT copolymers can be extremely unstable when they are oxidised in aqueous solutions. The redox stability of these copolymers could be improved by molecular design of the copolymer where it was observed that the electron rich comonomer 3,3' dimethoxy-2,2'-bithiophene 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 stabilise positive charges, irreversible redox reactions were 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 was 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 was 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.