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

Abstract

Herein, we report a novel method for constructing polymeric conjugated radicals, introducing an open-shell benzobisthiadiazole (BBT) unit to a (3 E,7 E )-3,7-bis(2-oxo-1 H -pyrrolo[2,3- b ]pyridine-3(2 H )ylidene)benzo[1,2- b:4,5- b ′]difuran-2,6(3 H,7 H )-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 cm 2 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.