Products Cited in Publications Worldwide Shining Light on Electropolymerization: Spectroelectrochemistry Reveals Electrochemical-Chemical Dynamics in the Diffusion Layer and Their Impact on Polymer Film Quality

Shining Light on Electropolymerization: Spectroelectrochemistry Reveals Electrochemical-Chemical Dynamics in the Diffusion Layer and Their Impact on Polymer Film Quality

Conner, Nathan R; Holubowitch, Nicolas E

DOI:

Abstract

Conjugated polymers are easily synthesized by electrochemical oxidation; however, the process is often seen as a “black box”, with advances made through exhaustive trial-and-error approaches. Polythiophenes (PTh) are among the most well-studied conjugated (conductive) polymers, but their growth mechanism remains poorly understood, and their integration with practical devices is yet to be widely demonstrated. PThs prepared via electropolymerization from the Lewis acidic solvent system boron trifluoride-diethyl etherate (BFEE) reportedly afford thin films with properties superior to those prepared from alternative media. Nevertheless, the dynamic growth process of monomer oxidation, oligomerization, and polymer precipitation is challenging to interrogate. Thus, establishment of a structure-property type link between conductive polymer growth mechanisms in various media and ultimate film quality has proven elusive. Here, we employ in situ UV-visible-near infrared electronic spectroscopy to study the electropolymerization of various thiophenes from BFEE solutions for the first time. For P3HT, we correlate solution-phase dynamics during growth to ultimate critical polymer properties of conductivity, morphology, polydispersity index, and regioregularity. We find that BFEE-based PTh film quality is highly dependent on monomer concentration and identity, and a mechanism of oligomerization in the near-electrode region is developed. The presence of high concentrations of dicationic species in solution during growth appears to correlate with poorer film quality. The new findings linking solution-phase speciation during the growth phase to film properties have important implications that are broadly applicable to conductive polymers prepared by oxidative polymerization.

Keywords

Conjugated polymers ; electropolymerization ; P3HT ; polythiophene ; spectroelectrochemistry ; boron trifluoride diethyl etherate

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