Tuning Edge-On/Face-On Crystal Orientation in Conjugated Donor–Acceptor Block Copolymers via Molecular Engineering

The ability to exquisitely tailor the crystal orientation in conjugated polymers is highly desirable for improving device performance and establishing structure–property relationships. However, investigations into modulating crystal orientation in conjugated donor–acceptor (D–A) block copolymers (BCPs) remain limited. Herein, we report the tailoring of the orientation modes (i.e., edge-on and face-on) in a family of P3AT-b-PDPP and P3BT-b-P3BrHT-b-PDPP BCPs via molecular engineering. Specifically, the crystal orientation induction between the P3AT block (i.e., which intrinsically exhibits an edge-on orientation) and the PDPP block (i.e., which intrinsically forms a face-on orientation) was effectively controlled by systematically adjusting the molecular weight (MW) and alkyl side chain of the P3AT block and the MW of the middle P3BrHT block. An increased MW and a shorter alkyl side chain of the P3AT block were found to induce a transition of the PDPP block from an initial face-on to an edge-on orientation in P3AT-b-PDPP BCPs. This induction effect of the P3AT block on the PDPP block was progressively weakened by separating the two blocks with a P3BrHT block of increasing MW in P3BT-b-P3BrHT-b-PDPP BCPs. This study demonstrates that crystal orientations in conjugated D–A BCPs can be tailored through robust molecular engineering, thereby strengthening the fundamental understanding of the interplay among the different components in conjugated BCPs.