Predicting Molecular Charge Transport in Radical Polymers

Nonconjugated macromolecules bearing stable radical pendent groups (i.e., radical polymers) exhibit unique redox and optoelectronic attributes compared with conventional doped conjugated polymers. However, critical questions remain on ultimate limits of charge transport in these materials and whether some of the deficiencies exhibited by contemporary materials are due to the choice of radical chemistry. To address these questions, density functional theory was used to evaluate the charge transfer characteristics of a broad range of pairwise open-shell chemistries relevant to radical conductors, including p-type (i.e., hole-transporting), n-type (i.e., electron-transporting), and ambipolar species based on Marcus theory. We have observed an apparent mismatch between the configurations that are energetically favorable and those that maximize charge transfer, and the configurational averaging for these quantities could vary by several orders of magnitude. These results highlight the significance of modular design approaches for fine-tuning the radical orientation to promote charge transport in radical polymers.