Non‐Monotonic Sequence Control Maximizes Spin Transport in Conjugated Polymers at Room‐Temperature

Abstract Organic semiconductors have long spin lifetimes supporting non‐tunneling spin transport at room temperature, providing a window to control spin transport and enable charge‐spin co‐processing. Programmable diversity in backbones and side chains expands the design space for tuning structure‐transport relationships, yet links between structure and spin transport remain less explored than for charge transport. Focusing on repeat‐unit sequence effects on spin transport, a nonmonotonic dependence where intermediate sequence order optimizes π–π packing by balancing long‐range coherence and chain flexibility, maximizing spin‐transport efficiency is revealed. The three‐component regioregular copolymer tightens π–π spacing to 3.48 Å and extends coherence, yielding mobility 0.43 cm 2 V −1 s −1 and an on/off ratio near 6 × 10 6 . Stronger cohesion in a bicomponent alternating species flattens the backbone yet widens d π and shortens coherence; frontier levels and dihedral angles support this microstructural origin of lower mobility. Electron paramagnetic resonance gives a T1 of 101 ns for the alternating copolymer; spin valves show >8% room‐temperature non‐tunneling magnetoresistance ratio, ≈200% above bicomponent alternating species. This non‐monotonic design rule provides a synthesis strategy to extend spin lifetimes and spin diffusion length, thereby advancing conjugated polymers for applications in logic, memory, sensing, and wearable systems.