Interrogating the Effect of Block Sequence on Cocrystallization, Microphase Separation, and Charge Transport in All-Conjugated Triblock Copolymers
Lixin Li, Hao Zhan, Shuwen Chen, Qingqing Zhao, Juan Peng
Abstract
Despite impressive progress in the research of all-conjugated diblock copolymers, there is a quite limited investigation into triblock counterparts. Moreover, regarding the block sequence, which is peculiar to triblock copolymers, its effect on their crystallization and microphase separation is still poorly understood. Herein, we design and synthesize a family of all-conjugated triblock copolymers comprising poly(3-butylthiophene) (P3BT), poly(3-hexylselenophene) (P3HS), and poly(3-dodecylthiophene) (P3DDT) of various block sequences, i.e., P3BT-b-P3DDT-b-P3HS, P3BT-b-P3HS-b-P3DDT, and P3HS-b-P3BT-b-P3DDT, elucidate the impact of the block sequence on their crystalline structures in conjunction by utilizing various solvents and thermal annealing, and investigate the charge transport properties of these different crystalline structures. Remarkably, the block sequence with the P3DDT block located in the central position (P3BT-b-P3DDT-b-P3HS) and faster solvent evaporation favor the cocrystals, while the P3DDT block situated at terminals (P3BT-b-P3HS-b-P3DDT and P3HS-b-P3BT-b-P3DDT), slower evaporation of the solvent, and heating lead to microphase separation over cocrystallization. Intriguingly, three different microphase-separated structures, which are correlated to the block sequence, are observed after high-temperature annealing (240 °C). Moreover, these various crystalline structures of triblock copolymers influence their charge mobilities in organic field-effect transistors (OFETs) closely. Thus, this work comprehensively elucidates the effect of the block sequence (intrinsic factor), solvent, and heating temperature (extrinsic factors) on the crystalline structure and electrical properties of conjugated triblock copolymers.