Strong Acceptor Annulation Enables Control of Electronic Structure and Spin Configuration in Donor–Acceptor Conjugated Polymers

Open-shell conjugated polymers (CPs) offer new opportunities to integrate the spin degree of freedom within emerging technologies. Central to their realization are strong acceptors that stabilize unpaired spins within the π-conjugated backbones. Here, we demonstrate a high-spin CP composed of alternating benzo[1,2- b:4,5- b ′]dithiophene donors and a new, strongly electron-withdrawing 6,7,8,9-tetrachloro-[1,2,5]thiadiazolo[3,4- b ]phenazine acceptor. A comparative study with a 6,7-dimethyl-[1,2,5]thiadiazolo[3,4- g ]quinoxaline (TQ) acceptor demonstrates that annulation and chlorination of the TQ framework facilitates a transition between closed-shell aromatic and high-spin quinoidal forms. This is accompanied by a concomitant reduction of the bandgap, high electron affinity, delocalization of spin density, and n-type conduction. These insights enable access to a broader range of open-shell CPs and the manipulation of important properties such as topology, exchange interactions, and carrier polarity.