The Influence of Interlocking Effects in Conjugated Polymers Synthesized by Aldol Polycondensation on Field-Effect Transistor Properties and Morphology

The environmental and economic drawbacks of traditional palladium-catalyzed coupling reactions in the synthesis of conjugated polymers have prompted the exploration of green alternatives. This study presents the synthesis and characterization of a series of ladder-type conjugated polymers via aldol and Knoevenagel condensation reactions, which use simple acid or base catalysts and produce only water as a byproduct. We explore the interlocking effect of the backbone and study its role in enhancing the backbone planarity, charge transport, and morphology. Intramolecular hydrogen bonding in polymers P1 and P5 promotes strong interlocking interactions, resulting in high electron mobilities (2.09 × 10^–2 cm² V^–1 s^–1 and 8.26 × 10^–2 cm² V^–1 s^–1, respectively) and crystalline order. In contrast, their random copolymers (P2–P4) exhibited disrupted interlocking effects, leading to irregular backbone distortions and reduced charge transport. P6, designed with a rigid ladder-type backbone and bulky side chains, exhibits an exceptional hole mobility (3.27 × 10^–1 s cm² V^–1 s^–1) despite an amorphous morphology, which is attributed to efficient intrachain transport. These findings demonstrate the potential of the green condensation approach in developing conjugated polymers with high charge transport properties and different morphologies through intramolecular interlocking effects.