Synergistic Manipulation of Phase Transition between Cocrystallization and Microphase Segregation in Conjugated Triblock Copolymers for Organic Field-Effect Transistors

Compared to the impressive advances achieved in coil–coil block copolymers (BCPs) capable of crystallization, advances in conjugated rod–rod BCPs are somewhat limited owing to their semirigid characteristics. The ability to tune crystallization and microphase segregation in this class of BCPs enables efficient control of the microstructures and the physical and optoelectronic properties. Herein, we report the effective manipulation of the cocrystallization and microphase segregation in a series of conjugated triblock copolymers through meticulous control of the length of the middle amorphous block at the molecular level and scrutinize the close correlation between their crystalline structures and charge transport properties. Specifically, a family of poly(3-hexylthiophene)-block-poly[3-(6-bromohexyl)-thiophene]-block-poly(3-decylthiophene) (P3HT-b-P3BrHT-b-P3DT) BCPs was designed and synthesized, in which the central P3BrHT had a low rigidity and negligible crystalline property compared with the two outer P3HT and P3DT blocks. The shorter P3BrHT was favorable to the cocrystallization of the two outer P3HT and P3DT. Moreover, the phase transition from the cocrystallization of P3HT and P3DT to their microphase segregation was facilitated by increasing the length of the central P3BrHT (intrinsic factor) in conjunction with slow solvent evaporation and thermal treatment (extrinsic factors). Finally, the different crystalline structures of P3HT-b-P3BrHT-b-P3DT are strongly correlated with their optical and charge transport properties. This study provides insights into cocrystallization and microphase segregation in conjugated BCPs via meticulous molecular design at the molecular level and external processing strategies.