The Influence of Regiochemistry on the Performance of Organic Mixed Ionic and Electronic Conductors

Thiophenes functionalised in the 3-position are ubiquitous building blocks for the design and synthesis of organic semiconductors. Their non-centrosymmetric nature has long been used as a powerful synthetic design tool exemplified by the vastly different properties of regiorandom and regioregular poly(3-hexylthiophene) owing to the repulsive head-to-head interactions between neighbouring side chains in the regiorandom polymer. The renewed interest in highly electron-rich 3-alkoxythiophene based polymers for bioelectronic applications opens up new considerations around the regiochemistry of these systems as both the head-to-tail and head-to-head couplings adopt near-planar conformations due to attractive intramolecular S-O interactions. To understand how this increased flexibility in the molecular design can be used advantageously, we explore in detail the geometrical and electronic effects that influence the optical, electrochemical, structural, and electrical properties of a series of six polythiophene derivatives with varying regiochemistry and comonomer composition. We show how the interplay between conformational disorder, backbone coplanarity and polaron distribution affects the mixed ionic-electronic conduction. Ultimately, we use these findings to identify a new conformationally restricted polythiophene derivative for p-type accumulation-mode organic electrochemical transistor applications with performance on par with state-of-the-art mixed conductors evidenced by a mu C* product of 267 F V-1 cm(-1) s(-1).

Automated summary

Functionalized thiophenes in the 3-position are commonly used as building blocks for organic semiconductors. The non-centrosymmetric nature of these compounds has been utilized in synthetic design and has led to the development of polymers with different properties. The recent interest in 3-alkoxythiophene based polymers for bioelectronic applications brings attention to the regiochemistry of these systems and their attractive intramolecular interactions. By studying a series of six polythiophene derivatives with varying regiochemistry and comonomer composition, we investigate the geometrical and electronic effects on their properties.