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

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.