Synergistic Improvement of the Charge Transport Property of Difluoroethylene-Bridged Bisazathienoisoindigo-Based Conjugated Polymers through Conformation Locking and Side-Chain Engineering

Herein, the design, synthesis, and characterization of two novel electron-deficient building blocks were reported, namely, difluoroethylene-bridged bisazathienoisoindigos (MFn, n = 1 and 2), and their polymer derivatives P1–P4. Crystal analysis and theoretical computations indicated that these building blocks have highly planar backbone conformation. Electrochemical testing revealed that they also have low-lying frontier orbital energetics, an indication of great potential as electron acceptors. We found that when the “conformation locking” strategy works alone, the resulting MF1-based conjugated polymers P1 and P2 afford just slightly improved charge transport properties compared with that of the unlocked control. On the contrary, when “conformation locking” and side-chain engineering work together, the corresponding MF2-based conjugated polymer P4 exhibits significantly increased charge transport property, with high hole/electron mobilities up to 3.06/0.64 cm2 V–1 s–1. Microstructural analyses indicated that the P4 thin films have highly ordered and dense molecular packing, with a small π–π stacking distance of 3.40 Å.