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

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 cm² V^-1 s^-1 and an on/off ratio near 6 × 10⁶. 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.