Incorporation of the Benzobisthiadiazole Unit Leads to Open-Shell Conjugated Polymers with n‑Type Charge Transport Properties

Herein, we report a novel method for constructing polymeric conjugated radicals, introducing an open-shell benzobisthiadiazole (BBT) unit to a (3E,7E)-3,7-bis(2-oxo-1H-pyrrolo[2,3-b]pyridine-3(2H)ylidene)benzo[1,2-b:4,5-b′]difuran-2,6(3H,7H)-dione-alt-(E)-1,2-di(thiophen-2-yl)ethene polymeric conjugated backbone (P1 with closed-shell structure) affording conjugated polymers P2–P4 with open-shell characteristics. Through this method, the spin characteristic of the polymer conjugated radicals can also be easily tuned, in which the spin concentration of P2–P4 increases with the increase of the BBT ratio. Moreover, P2–P4 have narrowed energy gaps and n-type charge transport properties with electron mobilities of 0.12–0.35 cm² V^–1 s^–1, comparable to or higher than those of BBT-containing conjugated polymers reported so far. Microstructural investigations indicated that the gradual decrease of μ_e from P1 to P4 originates from their BBT-caused deteriorating molecular aggregations in solid thin films. Our results show that incorporating an open-shell moiety into a high-performance conjugated backbone is a promising method for developing polymeric conjugated radicals with high mobility and tunable open-shell character.