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

Abstract

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.

Interrogating Cocrystallization and Microphase Segregation in Meticulously Engineered Rod–Rod Poly(thieno)thiophene-Based Block Copolymers for Organic Field-Effect Transistors

“…In the past decade, rod–rod block copolymers (BCPs) comprising different conjugated polymers have drawn significant attention because of the combined optoelectronic properties of their respective conjugated components and the intriguing microphase segregation characteristics of BCPs. − With the advancement of Kumada catalyst transfer polymerization (KCTP), , various conjugated BCPs have been synthesized, among which poly­(3-alkylthiophene) (P3AT)-based BCPs have been explored the most. − As conjugated polymers possess crystallization ability, all-conjugated BCPs provide a promising platform for investigating the competition and interplay between microphase segregation and crystallization in polymers. − Nonetheless, due to the semirigid chain characteristic of rod polymers, some additional structural parameters are involved compared to coil–coil BCPs, such as the Maier–Saupe interaction strength (μN) and the geometrical asymmetry parameter ( v ). , Thus, the phase behavior of conjugated rod–rod BCPs is intricate, and a thorough understanding of their microphase segregation and crystallization is still lacking theoretically and experimentally. Clearly, the ability to synthesize more conjugated rod–rod BCPs and investigate their phase behaviors is highly desirable.…”