Accumulative Charging of Redox-Active Side-Chain-Modified Polymers: Experimental and Computational Insights from Oligo- to Polymeric Triarylamines

Abstract

The anionic polymerization of three functionalized styrenic triarylamines is presented, including a series of oligomers to analyze the configurational and conformational details. Advanced NMR techniques were utilized for end group analysis to enable definite peak assignments. An inferior preference for stereoregularity was found, i.e., the formation of diastereomers for each new chiral center (ca. 60/40 ratio). Chemical shift analysis revealed the degree of conformational flexibility, which is governed by the three nearest repeating units. The electrochemical properties were detailed by semidifferential analysis of conventional cyclovoltammetric data, showing fully reversible oxidation in all cases. The data deconvolution resolved the individual formal oxidation steps, which revealed the expected entropic peak broadening and additional contributions in a consistent manner. The effect was particularly pronounced for the densely decorated polymer, which displayed an anodic shift (+0.1) V for ca. 30% of all redox-active units. The origin was assigned to an electrostatic penalty due to the diminished charge compensation by the electrolyte-excluded volume. For example, microelectrode measurements of the trimer also revealed a slower transfer rate of the third oxidation step. A series of density functional theory calculations corroborated the assignments of accumulative charging, i.e., reproduced the steric and electrochemical features in good agreement. Spectroelectrochemical measurements revealed the occurrence of side reactions at higher applied potentials for the polymers, but not in the case of the oligomers. The presented analysis is expected to complement the general electrochemical characterization of redox-active polymers, e.g., to elucidate the precise role of solubilizing substituents or the architecture dictated by spacing units or upon copolymerization with various monomers.