Topology and ground state control in open-shell donor-acceptor conjugated polymers

Donor-acceptor (DA) conjugated polymers (CPs) with narrow bandgaps and open-shell (diradical) character represent an emerging class of materials whose rich behavior emanates from their collective electronic properties and diminished electron pairing. However, the structural and electronic heterogeneities that define these materials complicate bandgap control at low energies and connections linking topology, exchange interactions, and (opto)electronic functionality remain nascent. To address these challenges, we demonstrate structurally rigid and strongly π-conjugated copolymers comprised of a solubilizing thiadiazoloquinoxaline acceptor and cyclopenta[2,1-b:3,4-b′]dithiophene or dithieno[3,2-b:2′,3′-d]thiophene donors. Atom-specific substitution modulates local aromatic character within the donor resulting in dramatic differences in structural, physicochemical, electronic, and magnetic properties of the polymers. These long-range π-mediated interactions facilitate control between low-spin aromatic and high-spin quinoidal forms. This work provides a strategy to understand the evolution of the electronic structure within DA CPs, control the ground state spin multiplicity, tune spin-spin interactions, and articulate the emergence of their novel properties. [Display omitted] Synthesis of low-spin and high-spin donor-acceptor conjugated polymersConnections linking structural, physicochemical, electronic, and magnetic propertiesOpen-shell donor-acceptor conjugated polymers with novel properties Donor-acceptor (DA) conjugated polymers (CPs) with narrow bandgaps and open-shell (diradical) character demonstrate emergent phenomena that emanate from their collective electronic properties and diminished electron pairing. Mayer et al. report DA CPs that enable a strategy to control the ground state spin multiplicity and connect structural, physicochemical, electronic, spin, and magnetic properties.