The cocrystallization method that combines various constituents into cocrystals yields the newly formed materials with significantly enhanced charge transport properties. However, this strategy has not been greatly utilized in all-conjugated block copolymers (BCPs). Herein, we scrutinize the relationship between cocrystals and charge mobilities in all-conjugated BCPs (i.e., poly(3butylthiophene)-block-poly(3-hexylthiophene); denoted P3BT-b-P3HT) by tuning their molecular weights and thermal annealing process. All the rod−rod BCPs form cocrystals with high charge mobilities than P3BT and P3HT homopolymers and P3BT/P3HT blend, imparting the cocrystal-facilitated charge transport because of the synergy of two conjugated components. Upon 150 °C treatment, their crystallinities increase and their charge mobilities at 15k, 18k, and 28k increase slightly. In contrast, P3BT-b-P3HT-12k shows decreased charge mobilities. It is due to the preferential increase of crystal size and order through the π−π stacking direction in the former while through the alkyl stacking direction in the latter. Intriguingly, when these P3BT-b-P3HT cocrystals experience two-step thermal treatment, P3BT-b-P3HT-12k retains its cocrystalline structure, while microphase separation of P3BT and P3HT occurs in P3BT-b-P3HT-15k, 18k, and 28k with different degrees. All P3BT-b-P3HT BCPs exhibit decreased charge mobilities. This study demonstrates the cocrystallization-promoted charge mobility in all-conjugated BCPs, which may facilitate their application in a wide range of optoelectronic devices.

Despite recent impressive advances in synthesis of all-conjugated diblock copolymers via facile quasi-living Grignard metathesis (GRIM) polymerization, it remains challenging to achieve well-defined all-conjugated triblock copolymers of interest. Herein, we report the judicious design and synthesis of a series of all-conjugated triblock copoly­(3-alkylthiophene)­s consisting of poly­(3-butylthiophene) (P3BT), poly­(3-hexylthiophene) (P3HT), poly­(3-octylthiophene) (P3OT), or poly­(3-dodecylthiophene) (P3DDT) in all 12 possible combinations. The effects of block sequences and the length of alkyl side chains on their cocrystallization and microphase-separated structures are investigated. Moreover, the correlation between different crystalline structures and charge mobilities in organic field-effect transistors (OFETs) is scrutinized. These rationally synthesized triblock copoly­(3-alkylthiophene)­s self-assemble into cocrystals with an edge-on orientation in as-cast and 150 °C-annealed samples. Remarkably, the combinations with the shortest alkyl side chains placed as the central block (i.e., P3HT-b-P3BT-b-P3OT, P3HT-b-P3BT-b-P3DDT, P3OT-b-P3BT-b-P3DDT, and P3OT-b-P3HT-b-P3DDT) exhibit higher film crystallinity and charge mobilities than the other two combinations where the blocks with shortest alkyl side chains are located at two terminals. Intriguingly, upon thermal annealing near the melting temperature of these combinations, P3BT-b-P3OT-b-P3HT, P3BT-b-P3DDT-b-P3OT, and P3HT-b-P3DDT-b-P3OT can retain their cocrystalline structure while the other combinations are found to microphase separate. Finally, the all-conjugated triblock copoly­(3-alkylthiophene)­s with proper block sequence demonstrate stable charge mobilities at high temperatures and good flexibility in OFET devices. Taken together, this study elucidates that the block sequence is of key importance on control of the crystallization and charge transport behavior of poly­(3-alkylthiophene)-based triblock copolymers.

Conjugated rod−rod block copolymers (BCPs) are important semiconducting materials because they combine the unique microphase-separation characteristics of BCPs with the remarkable optoelectronic properties of conjugated polymers. The ability to tailor the two fundamental phase transitions (microphase separation and crystallization) in BCPs could enable efficient control over their physical and optoelectronic properties. Herein, a set of poly(3-butylthiophene)-block-poly(3-dodecylthiophene) (P3BT-b-P3DDT) BCPs with controlled block ratios are synthesized and the interplay between their microphase separation and cocrystallization is explored by tuning both the intrinsic (i.e., block ratios) and extrinsic factors (i.e., solvent and thermal annealing temperatures). An increased P3BT content, slower solvent evaporation, and higher thermal annealing temperatures favor microphase separation in P3BT-b-P3DDT. Furthermore, the relationship between various P3BT-b-P3DDT crystalline structures and their charge-transport properties is scrutinized. This work elucidates how P3BT-b-P3DDT BCPs undergo microphase separation and crystallization and how these processes can be tailored, strengthening our fundamental understanding of conjugated rod−rod BCP systems.

Despite significant advances in double-crystalline coil–coil block copolymers (BCPs), investigations into double-crystalline all-conjugated rod–rod BCPs have been comparatively fewer and are limited in scope. Moreover, the ability to control the crystalline structures of all-conjugated BCPs may endow the materials and devices with enhanced optoelectronic properties over the two respective constituents. Herein, we report the synthesis of a series of poly­(3-hexylthiophene)-block-poly­(3-butylselenophene) (P3HT-b-P3BS) BCPs with tunable block ratios and investigate the effects of block ratio and thermal annealing process on their crystallization and microphase-separated structures. These rod–rod BCPs exhibit a sole P3HT crystallization (P3HT/P3BS = 63:37) or individual P3HT and P3BS crystallization (P3HT/P3BS = 55:45 and 42:58) in as-cast thin films, influenced by the block ratio of P3HT/P3BS. Interestingly, upon 200 °C-annealing (i.e., annealed at the temperature below the melting points of P3HT and P3BS form I blocks), P3HT-b-P3BS (P3HT/P3BS = 63:37) remains the sole P3HT crystallization, while P3HT-b-P3BS (P3HT/P3BS = 55:45 and 42:58) transforms from two individual P3HT and P3BS crystal domains into cocrystals, accompanied by the phase transition of P3BS block from form II to I. Remarkably, after a higher thermal annealing at 230 °C (i.e., close to the melting point of P3HT block yet below the melting point of P3BS form I block), the cocrystalline structures originally existing in P3HT-b-P3BS (P3HT/P3BS = 55:45 and 42:58) at the 200 °C-annealing process do not form, and they reverse back to individual P3HT and P3BS form I crystals. Finally, the relationship between various structures of P3HT-b-P3BS and the resulting charge mobilities is clarified. This study provides an insight into the interplay between microphase separation of P3HT-b-P3BS and crystallization of both P3HT and P3BS blocks tailored by the block ratio and thermal annealing temperature and correlates their different structures with the charge transport properties.

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