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 diminished electron pairing. However, the structural heterogeneities that define these complicate bandgap control at low energies connections linking topology, exchange interactions, (opto)electronic functionality remain nascent. To address challenges, we demonstrate structurally rigid strongly ?-conjugated copolymers comprised a solubilizing thiadiazoloquinoxaline acceptor cyclopenta[2,1-b:3,4-b?]dithiophene or dithieno[3,2-b:2?,3?-d]thiophene donors. Atom-specific substitution modulates local aromatic within donor resulting in dramatic differences structural, physicochemical, electronic, magnetic polymers. These long-range ?-mediated interactions facilitate between low-spin high-spin quinoidal forms. This work provides strategy to understand evolution structure DA CPs, ground state spin multiplicity, tune spin-spin articulate emergence novel properties.