Topology-Controlled Proton Transport in Thermotropic Liquid-Crystalline Acid–Base Complexes

Abstract The construction of efficient proton-transport channels is of great interest for applications in fuel cells and biological systems. In particular, three-dimensionally interconnected bicontinuous networks in liquid-crystalline (LC) assemblies provide an attractive platform for enabling efficient proton transport. However, the realization of anhydrous proton-conducting gyroid cubic LC assemblies remains a significant challenge. Here we report a strategy to control the dimensionality and connectivity of proton-transport pathways through Brønsted base-acid complexation. A series of wedge-shaped amphiphiles bearing a common imidazole/amide headgroup and varying alkyl-chain lengths (IM8, IM10, and IM12) were complexed with two Brønsted acids with distinct anion characteristics, benzenesulfonic acid (BS) and bis(trifluoromethanesulfonyl)imide (HTFSI). Systematic variation of acid fraction and temperature under nonhumidified conditions revealed that IM12 exhibits curvature-driven polymorphism, including a hexagonal columnar (Colh) phase at low acid fractions and a bicontinuous Ia3̅d gyroid (Gyr) phase at intermediate acid contents, whereas IM8 and IM10 form only smectic A (SmA) phases over broad compositions. 1H NMR titration indicates that imidazole protonation and ion-pair formation dominate the base–acid equilibrium, while weaker secondary interactions involve the amide group. Variable-temperature FT-IR measurements reveal progressive strengthening of the polar interaction network upon cooling. Proton-transport measurements show that the Gyr base–acid complexes exhibit the highest conductivity, the lowest apparent activation energy, and weaker viscosity–conductivity coupling in Walden-type analysis. Dielectric modulus and rheological measurements further support faster bulk relaxation and a more robust elastic framework in the gyroid phase. These findings establish design principles for proton-conducting LC materials based on curvature-controlled, three-dimensionally interconnected ionophilic nanochannels formed through base–acid complexation.