Fused Heptacyclic-Based Acceptor–Donor–Acceptor Small Molecules: N-Substitution toward High-Performance Solution-Processable Field-Effect Transistors

Although various donor–acceptor (D–A) small molecules with high power conversion efficiency have been reported, D–A small molecules with high field-effect mobility are still rare. In this work, two new A–D–A small molecules with a rigid indacenodithieno[3,2-b]thiophene (IDTT) moiety as the central core and both ends capped with strong electron-withdrawing indole-2,3-dione (IDD) and N-substituted pyrrolo[2,3-b]pyridine-2,3-dione (IDD-N) were synthesized and characterized for applications in solution-processable organic field-effect transistors (OFETs). A N atom was introduced to the IDD units to enhance the planarity and structural ordering by noncovalent interactions, leading to a dramatic effect on the small molecule. The unsubstituted small molecule (IDTT–IDD) did not show any field-effect performance, whereas an encouraging hole mobility of 7.7 cm2 V–1 s–1 with an average mobility of 6.1 cm2 V–1 s–1 was obtained for solution-processable OFETs based on the N-substituted one (IDTT–IDD-N). This work provided a simple and effective molecular strategy for the design of D–A small molecules for high-performance solution-processable OFETs.