Impact of open‐shell loading on mass transport and doping in conjugated radical polymers

Abstract

Radical-containing polymers are an evolving class of redox-active macromolecules that have received great interest; however, most reports regarding radical polymers have focused on materials with nonconjugated backbones because their application drivers did not require this conjugation. Conversely, there has been a recent rise in the development of radical polymers for nextgeneration applications where imparting conjugation to the backbone of the radical polymer could be of significant benefit. To this end, we designed and synthesized a series of 3,4-propylenedioxythiophene (ProDOT)-based polymers bearing nitroxide radical pendent groups via direct arylation polymerization. Specifically, we present four radical polymers with open-shell loadings ranging from 24% to 82% of the total number of repeat units per polymer chain. The impact of openshell loading on the electrochemical behaviors of these polymers in different electrolytes was then established using cyclic voltammetry, spectroelectrochemical analyses, and electrochemical quartz-crystal microbalance with dissipation monitoring. We demonstrate that incorporating the open-shell moieties in the ProDOT-based polymers lowers the oxidation onset potential of the conjugated backbone and increases the solvent and ion uptake significantly. Thus, this effort provides a clear picture of the mass transfer and doping mechanism of the ProDOT-based radical polymers to aid in guiding their future design.

Electronic and Spintronic Open-Shell Macromolecules,Quo Vadis?

“…As the name implies, the primary difference from their non-conjugated radical polymer counterparts is the replacement of non-conjugated backbones with π-conjugated backbones (Figure a). − Moreover, the syntheses of CRPs are not amenable to frequently used polymerization strategies for non-conjugated polymers. Instead, techniques such as oxidative polymerization using a chemical agent or electrochemical polymerization have been commonly implemented for polythiophene-based CRPs; however, some oxidative impurities can be retained in the final products. , To circumvent this issue, direct arylation polymerization (DArP) has been used to synthesize a TEMPO-based CRP with little or no metallic residues . In a similar manner, Stille coupling and Grignard metathesis (GRIM) polymerization methods have been applied to offer copolymers of CRPs that contain little or no residual impurities …”

“…45,48 To circumvent this issue, direct arylation polymerization (DArP) has been used to synthesize a TEMPO-based CRP with little or no metallic residues. 51 In a similar manner, Stille coupling and Grignard metathesis (GRIM) polymerization methods have been applied to offer copolymers of CRPs that contain little or no residual impurities. 50 Beyond the above-mentioned, oft-used design paradigm to generate CRPs, low-bandgap, open-shell donor−acceptor conjugated polymers have recently arrived as a new representative, as demonstrated primarily by the Azoulay group (Figure 5b).…”