Unraveling Intrinsic Polymer Structure–Property Relationships to Advance Molecular Electronics

Conspectus Unraveling the intrinsic polymer structure–property relationship is essential not only for a clearer understanding of fundamental principles in materials science but also ultimately for achieving very large-scale integrated molecular electronics. However, this has been challenging for traditional research strategies due to increased entropy and unsatisfactory dynamics during polymer synthesis and processing. Variations in polymer molecular weights, orientation, aggregation, and electrical characteristics in solid-state devices caused by intermolecular crosstalk in charge transport prevent clear identification of intrinsic optoelectronic polymer properties. Our group has developed a surface-initiated, bottom-up, rapid, repairable, and precise monomer-by-monomer electrosynthesis method, termed solid-phase electrosynthesis, which simultaneously enables in situ parallel synthesis and unidirectional orientation of polymers on a macroscopic substrate. The redox-bifunctional monomers are added onto the monolayer by alternating positive and negative potentials, while the oxidation and reduction are performed in separate solutions to avoid the addition of dimer byproducts. The monomer vacancies and morphological defects can be efficiently repaired by repeating the identical reaction once or twice. Eventually, the precise electrosynthesis of polymer monolayers can be statistically demonstrated by near-ideal linear relationships of length-dependent UV–vis absorption and current densities as a function of molecular length. First, the resulting crystalline polymer monolayers have thicknesses that match the theoretical molecular lengths (up to 99%), while the height change of the monolayer is comparable to the length of a single monomer (1–2 nm). These monolayer features confirm that the polymer backbones are aligned both parallel and perpendicular to the electrode surface. This molecular nanoarchitecture, with reproducible polymer structure and aggregation, can restrict intermolecular electron-transfer crosstalk and stochastic conductive filaments, enabling the elucidation of how intrinsic structural complexity relates to the resistive-switching characteristics. Second, the electrosynthesis exhibits high-dimensional structural controllability, including polymer length, monomer/ion composition and sequence, hetero- and homocoupling reactions, and π-electron localization and delocalization along the polymer backbone, providing a rich library of polymer structures to unravel the intrinsic structure–property relationships. Third, advantages in tailoring the intrinsic physical functions and performance of polymers─including negative differential resistance, decay constant of electron transport, and electrocatalytic activity─are demonstrated. Although electrosynthesis is still in its early stages for practical application in molecular electronics, it offers advantages in tailoring and optimizing nonlinear resistive functions and performance compared to other synthetic methods or materials. Owing to their superior reproducibility, functionality, addressability, physical optimization, and yield of devices compared to general SAMs, the polymer monolayers will not only advance the fundamental understanding of molecular electronics but also provide a potential solution for achieving very large-scale integrated molecular electronics.