Investigation of Charge Transport in Low-Dimensional Conjugated Oligomers and Polymers

In low-dimensional conjugated systems, the charge transport mechanisms and behaviors exhibit a certain degree of complexity and evolutionary patterns, strongly dependent on the chain length along the conjugated backbone and the spatial dimensionality of the materials. This review systematically elaborates on the evolution of directional charge transport and characterization techniques using the length along the conjugated backbone as the fundamental framework, ranging from oligomeric small molecules and one-dimensional molecular wires to two-dimensional polymer crystals. When the molecular scale is less than approximately 5 nm, quantum coherent tunneling dominates the transport, exhibiting an exponentially decaying conductance sensitive to the molecular conformation. When the oligomer length exceeds 5 nm, the transport transitions to a thermally activated hopping mechanism, with its efficiency influenced by intrachain order and interchain packing. When the length of a single polymer chain reaches the hundred nanometer scale, and the molecular wire is fully isolated with optimal interfacial contacts, it exhibits intrinsic intrachain transport behavior. When polymer chains are confined within nanochannels of a certain diameter, intrachain-dominated transport with reduced grain boundary scattering can be achieved. Furthermore, when one-dimensional chains are extended to two-dimensional covalent crystals, anisotropic metal-like conductive behavior emerges. This review systematically outlines the key characterization techniques corresponding to each scale and emphasizes the fundamental guiding significance of understanding "length critical points" and "dimensional transitions" for designing next-generation, high-performance, high-reliability organic electronic devices.