Concurrent Enhancements of the Conductivity and Spin Density via Cation–π Interactions in an n‐Type Conducting Polymer

Intrinsically conducting polymers have been attracting great attention because of their interesting electronic structures and properties, as well as their important applications in many areas. In conventional highly conductive polymers, enhancement in conductivity is typically accompanied by a decrease in spin density due to the formation of spinless bipolarons. Here, we demonstrate that both the conductivity and spin density of n‐type poly(benzodifurandione) (PBFDO) can be significantly enhanced simultaneously through a treatment with metal cations for the first time, representing an unusual deviation from the conventional doping behavior. Treatment of PBFDO films with a dimethyl sulfoxide (DMSO) solution of LiCl can enhance the conductivity from 1900 S cm − 1 to over 3100 S cm − 1 at room temperature, while the spin density is more than doubled. The conductivity enhancement is attributed to cation‐induced planarization of the PBFDO chains, which promotes the crystallinity and carrier mobility. Meanwhile, the concurrent increase in the spin density suggests the conversion of bipolarons to polarons, and it is attributed to the cation‐π coupling between the Li + cations and the π‐conjugated backbone of PBFDO. These results highlight the critical role of the cation–π coupling in modulating the electronic structure and charge transport in n‐type conducting polymers.