New nanostructured, ion-conductive, bent-core liquid crystals containing lithium and sodium salts as soft electrolyte candidates

Abstract

Two new tetraethylene glycol (TEG)-containing bent-core molecules are revealed as suitable, versatile supramolecular building blocks to form liquid crystalline phases and organogels in novel structured soft electrolytes. New amphiphilic bent-core molecules [TEG-Bx-10-14], composed of a short polar TEG-segment capping and well-defined bent-core, mesogenic-like structures, and a set of their [1/1] complexes with TfO⁻ and Tf₂N⁻/lithium and sodium salts [MA-TEG-Bx-10-14], are investigated for the first time. FT-IR, ¹³C CP-MAS-NMR and ¹H MAS-NMR studies at variable temperatures indicate the selective complexation of cations in the TEG regions. Although new bent-core molecular designs [TEG-10-Bx-14] do not exhibit liquid crystal order, most of their complexes [MA-TEG-10-Bx-14] stabilize an attractive number of bent-core lamellar mesophases (SmCP, HNF-like, USmCP and Col_ob). Diffusion coefficients (D) of lithium, favoured by the liquid crystal phase transition, are estimated by solid state NMR spectroscopy. The direct current values of σ_dc ∼ 10⁻⁴ S cm⁻¹ in the mid-high frequency range were found using dielectric spectroscopy, highlighting the potential of bent-core building blocks as organic and nanostructured soft electrolytes containing both lithium and sodium cations, whose ionic conductivities can be optimised through composition tuning and annealing.