Self-assembled liquid-crystalline ion conductors: Odd-even effects of flexible spacers binding a carbonate moiety and an aliphatic rod-like core on phase transition properties and ion conductivities

Abstract

Liquid-crystalline compounds consisting of mesogenic cores linked to cyclic carbonates through flexible spacers have been developed. These liquid crystals form complexes with lithium salts and self-assemble into nanostructures with well-defined ion pathways. It is found that the type and length of the intra-molecular spacer affects the liquid crystallinity and ion conductivity of the materials. Mesogenic compounds based on alkylene-based spacers show odd-even effects on the liquid-crystalline properties of the compounds. The liquid crystals based on spacers with an even number of carbon atoms show liquid crystallinity in wider temperature ranges and higher ion conductivities as compared to the liquid crystals based on spacers with an odd number of carbon atoms. On the other hand, liquid crystals based on polar oligooxyethylene spacers are observed to show liquid-crystallinity in wider temperature ranges and higher ion conductivities as compared to the alkylene-based liquid crystals. The liquid crystals with more polar and more flexible spacers, that is, oligooxyethylene groups show higher ion conductivities than those of the liquid crystal with alkylene spacers. This enhanced behavior may be due to the increase in the fluidity of the ionic pathways. These findings may provide us with new designs of self-assembled ion conductors.