Synthesis of 1-Formyl-3-bromo-thieno[3,4-c]pyrrole-4,6-dione and the Application in A2-A1-D-A1-A2 Type Non-Fullerene Acceptor

Nonfullerene acceptors (NFAs) with an A(2)-A(1)-D-A(1)-A(2) skeleton have attracted more and more attention because they can realize high open-circuit voltage (V-OC) and also pair well with the classical p-type polymer of poly(3-hexylthiophene). As a versatile and useful building block, thieno[3,4-c]pyrrole-4,6-dione (TPD) has been widely utilized to construct high-performance p-type photovoltaic polymers but never been used in A(2)-A(1)-D-A(1)-A(2) type NFAs. The main reason is that the critical intermediate of 1-formyl-3-bromo-thieno[3,4-c]pyrrole-4,6-dione (Br-TPD-CHO) cannot be synthesized via traditional methods like Vilsmeier-Haack reaction or bromine-lithium exchange reaction. To solve this problem, here we use Gewald reactions to synthesize the methyl-substituted TPD and then successfully get the intermediate of Br-TPD-CHO by bromination and hydrolysis. Subsequently, a new A(2)-A(1)-D-A(1)-A(2) type NFA was synthesized and named as TPD3, where 2-(1,1-dicyanomethylene)rhodanine (RCN), TPD, and indacenodithiophene (IDT) were used as A(2), A(1), and D units, respectively. TPD3 exhibits a highly planar conjugated framework and broad absorption spectrum at 300-720 nm. Preliminary photovoltaic results reveal that TPD3 can realize a high open-circuit voltage (V-OC) of 0.97 V and a moderate power conversion efficiency (PCE) of 7.58% when paired with a benzotriazole-based p-type polymer of J52-CI. Our results open a unique way to utilize TPD unit for high-performance NFAs.