Direction-dependent ion transport in an anisotropic conductor probed by tensor-resolved NMR

Controlling the dimensionality of ion transport is a powerful strategy for designing high-performance electrolytes, yet direct experimental access to anisotropic ion dynamics at the molecular level remains limited. Here, we apply an orientation-selective NMR methodology to determine temperature-dependent diffusion and electrophoretic mobility tensors of the ionic liquid crystal C₁₂mimBF₄ across its isotropic and smectic phases. The results reveal a pronounced reorganization of transport at the isotropic-smectic transition: isotropic, spatially homogeneous motion transforms into anisotropic transport with enhanced in-layer mobility and suppressed cross-layer migration. Despite this redistribution, orientationally averaged transport coefficients remain continuous across the transition, indicating that structural ordering redirects rather than amplifies ion motion. Electrophoretic mobilities show near-quantitative agreement with macroscopic conductivity, while only minor deviations from the Einstein-Smoluchowski relation are observed for the anions, consistent with weak ion-ion correlations. Our findings identify anions as the dominant charge carriers within polar channels and demonstrate how self-assembled structure enforces quasi-two-dimensional ion conduction. The approach provides a general framework for resolving anisotropic transport in soft matter electrolytes.