Macrocyclic Steric Confinement at Heavy-Atom Sites to Suppress Spin-Orbit Coupling for Room-Temperature Spin Transport in Organic Semiconductors.

Electron spin transport in organic semiconductors (OSCs) at room temperature is fundamentally limited by an intrinsic trade-off between spin diffusion and spin relaxation, arising from spin-orbit coupling associated with heavy atoms in conjugated backbones. Here, we demonstrate that macrocyclic steric confinement at heavy-atom sites unlocks a previously inaccessible spin-transport regime in OSCs, in which efficient spin diffusion and long-lived spin coherence intrinsically coexist. Employing a previously reported macrocyclic-confined thiophene-based OSC as a model system, we show that a covalently linked macrocycle enforces a highly linear conjugated backbone while dispersing spin density away from heavy atoms. This unique combination suppresses spin-orbit coupling while preserving strong charge delocalization. Thus, the macrocyclic-confined molecule exhibits a concurrent and marked enhancement in both intrinsic spin diffusion coefficient and spin lifetime in pristine thin films. When implemented in organic spin valves, this molecule delivers a room-temperature spin diffusion length of 322 nm together with a spin lifetime of 253 µs, setting new benchmarks of both metrics for organic spintronic materials. These findings reveal how macrocyclic steric confinement fundamentally reshapes spin-orbit coupling in conjugated systems and establish a general chemical principle for reconciling structural order with long-lived spin coherence in OSCs.