Supramolecular chirality largely modulates chemical doping of conjugated polymers

Chemical doping has unlocked the touted potential of conjugated polymers by significantly boosting their conductivity and device performance. Yet, the relationship between doping and the polymers’ complex, multiscale morphology remains elusive. Herein, we report a surprising find that supramolecular chirality, which up to now had not been considered a parameter relevant to doping, significantly boosts the underpinning redox reaction in conjugated polymer thin films. The chiral helical structures arise during an evaporative assembly process upon meniscus-guided coating, when the originally racemic conjugated polymer chains aggregate first and assemble into chiral twist-bent nematic mesophases which “imprint” their solution-state structure into solid thin films. By manipulating the solution aggregate structures through only subtle variations in the solvent nature, we modulate the structures of the liquid crystal phases to access a broad spectrum of supramolecular chirality, from achiral, to weakly chiral, and to strongly chiral. The differential solubilities of the side-chains and backbones in various solvent environments—elucidated by molecular dynamics simulations—underpin transitions in solution assembly behaviors. Upon sequential doping, the strongly chiral film exhibits a markedly higher charge carrier concentration leading to the highest doping efficiency and electrical conductivity, followed by the weakly chiral and the achiral films. Such increased conductivity in chiral structures is observed across three sets of polymer systems. We further suggest that enhanced crystallinity from chiral assembly facilitates the doping process, while chirality-induced spin selectivity may accelerate oxidation over reduction, together resulting in increased doping efficiency in chiral structures.