One-Step, Four-Fold Schiff Base Reaction Constructing a Highly Fused π-Extended Lactam Acceptor toward n-Type Polymer

Fused lactam electron-deficient building blocks are significant for the advancement of n-type donor–acceptor (D–A) polymeric semiconductors; however, they are rarely reported due to the challenges associated with tedious synthetic routes, strict experimental operations, multiple purifications, and unstable intermediates. Herein, a highly fused electron-deficient lactam building block, as a novel acceptor unit, 6,15-bis(4-octadecyldocosyl)-6,15-dihydroisoquinolino[3,4-b]isoquinoline[4’,3′:5,6]pyrazino[2,3-g]quinoxaline-5,14-dione (IIPQD), was easily synthesized via a one-step 4-fold Schiff base reaction. This IIPQD unit features a rigid π-extended conjugation skeleton, which facilitates the construction of planar polymer backbones and dense, ordered packing motifs for charge transport, as well as a strong electron-withdrawing capacity for electron injection, stemming from the synergistic electron-withdrawing effects of its lactam structures and 1,4-pyrazine moieties. Consequently, the IIPQD-based D–A copolymer PIIPQD-BTF showed typical n-type charge transport characteristics. These results highlight that Schiff base synthesis of fused π-extended electron-deficient lactam building blocks has great potential in developing electron-deficient building blocks and n-type polymer semiconductors.