Chalcogenopheno[3,2- b ]pyrrole-Containing Donor-Acceptor-Donor Organic Semiconducting Small Molecules for Organic Field-Effect Transistors.

A group of chalcogenopheno[3,2- b ]pyrroles, including thieno[3,2- b ]pyrrole (TP), furo[3,2- b ]pyrrole (FP), and selenopheno[3,2- b ]pyrrole (SeP), and thieno[3,2- b ]thiophene (TT) electron-donating units were coupled with a thiophene-flanked diketopyrrolo[3,4- c ]pyrrole (ThDPP) acceptor to generate four donor-acceptor-donor (D-A-D) semiconducting small molecules ( ThDPP-TT , ThDPP-FP , ThDPP-TP , and ThDPP-SeP ). This study systematically investigated the differences between chalcogenopheno[3,2- b ]pyrroles and TT. From the characterizations, chalcogenopheno[3,2- b ]pyrrole-containing molecules showed lower band gaps and binding-energy cold crystallization behavior. The enthalpies of cold crystallization were correlated with the weight of the chalcogen in ThDPP-FP , ThDPP-TP , and ThDPP-SeP , which were evaluated as intermolecular chalcogen-bond interactions between chalcogen and pyrrole nitrogen in chalcogenopheno[3,2- b ]pyrroles. A stronger chalcogen bond interaction resulted in stronger self-aggregation in thin films with thermal treatment, which resulted in a polycrystalline structure in chalcogenopheno[3,2- b ]pyrrole-containing molecules. For the application in an organic field-effect transistor, all four molecules showed good performance with the highest hole mobilities as 6.33 × 10 -3 cm 2 V -1 s -1 for ThDPP-TT , 2.08 × 10 -2 cm 2 V -1 s -1 for ThDPP-FP , 1.87 × 10 -2 cm 2 V -1 s -1 for ThDPP-TP , and 6.32 × 10 -3 cm 2 V -1 s -1 for ThDPP-SeP , and the change of mobility is well correlated to the root-mean-square roughness of the thin films. Overall, all the chalcogenopheno[3,2- b ]pyrrole-containing molecules showed lower band gaps, polymorphism, and better charge transport properties compared to TT-containing molecules, which motivates replacing TT with chalcogenopheno[3,2- b ]pyrroles in conjugated polymers, non-fullerene small molecular acceptors, and narrow-band-gap donors.