Conjugated, redox-active polymers are unique materials, in that they can effectively transport both electronic and ionic charge. Because of this mixed conduction ability, they are being evaluated as active materials in various electrochemical applications ranging from charge storage, to electrochromism, to sensors and bioelectronics. Our group has developed a family of soluble, and therefore printable, dioxythiophene-based polymers to suit these applications. To induce solubility, the polymers are functionalized with long hydrocarbon chains. Previously, it was thought that these side chains had little impact on the redox properties of the polymer; however recently, there has been more effort put towards understanding how these side chains can affect the material properties of the conjugated systems. While these side chains do not induce any redox functionality, they do influence polymer morphology and intermolecular interactions that can affect the polymer’s redox properties.<br/>Here, we evaluate how choice of dioxythiophene repeat unit and the side chain substitution pattern affect the material properties such as solid-state conductivity, electrochemical conductance, charge mobility, charge capacity, ion diffusion, and morphology, and how these properties can influence the performance of electrochemical devices. In addition to these properties, we will discuss how the nature of side chain and repeat unit govern the frontier molecular orbitals the polymer, which can be modeled by DFT calculations, and how this relates to the degree of twisting of the conjugated backbone and ultimately the redox properties of the material. The film morphology and molecular ordering is analyzed by both Atomic Force Microscopy on microscale and by Grazing-Incidence Wide-Angle X-Ray Scattering, which is a technique that provides information about intermolecular interactions in the film. Finally, proof-of-principle electrochemical devices are assembled to demonstrate how these charge transport properties affect device performance.

Structural tuning of charge transport properties in dioxythiophene polymers for electrochemical device applications

256th National Meeting (2018)

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