Optimized charge transport in N-substituted isatin-based acceptor–donor–acceptor small molecules by regulating the side chain length for solution-processable organic thin-film transistors

Side chains are necessary components of solution-processable semiconductors and exert a significant influence on charge transport. In this work, a series of acceptor-donor-acceptor (A-D-A) small molecules (C1-C10) based on indacenodithieno[3,2-b]thiophene (IDTT) as the donor and N-substituted isatin with different side-chains (from methyl to n-decyl) as acceptors were designed and synthesized for solution-processable organic thin-film transistors. The side chain length had an obvious influence on the field-effect mobility with a nearly odd-even effect. The small molecule with the methyl side chain did not exhibit any field-effect performance, while the other small molecules with longer alkyl chains showed excellent device performance with field-effect mobilities of over 1 cm(2) V-1 s(-1). In particular, the small molecules with ethyl and hexyl side-chains exhibited the highest mobilities of similar to 6 cm(2) V-1 s(-1). These results indicate that the minor structural modification of the side chain in A-D-A small molecules significantly affects the structural order and resulting device performance.