Confined Water Wires as Anisotropic Proton Highways in a Neutral Polymer Single Crystal

Abstract Directional proton transport is central to bioenergetics and emerging electrochemical technologies, yet achieving high and anisotropic proton conductivity in fully covalent, charge-neutral crystalline materials remains a challenge. Here, we report anisotropic proton conduction in a one-dimensional covalent polymer single crystal mediated by confined water wires. A phenylalanine-tyrosine-based monomer bearing azide and alkyne termini undergoes topochemical click reaction via large-amplitude molecular rotations, yielding a 1,4-triazole-linked one-dimensional polymer through a single-crystal-to-single-crystal transformation. The polymerization concomitantly generates hydrophobic nanochannels that reversibly capture atmospheric water, within which water molecules self-assemble into extended hydrogen-bonded chains. Proton conductivity measured on individual crystals is significantly higher along the channels than perpendicular to them, revealing an intrinsic anisotropic transport. Notably, this fully organic polymer crystal, capable of harvesting atmospheric water, represents the highest-performing proton-conducting organic crystalline material without external charged species or proton carriers, establishing a blueprint for designing bioinspired peptide-based neutral systems with directional proton transport.