Structure and ionic conductivity of liquid crystals having propylene carbonate units

Liquid-crystalline compounds with a perfluorinated aromatic ring as the mesogenic core and a propylene carbonate unit were prepared and mixed with lithium bis(trifluoro-methanesulfonyl)-imide (LiTFSI). The self-assembly was driven by the interaction of the polar propylene carbonate unit. Thus it is one of the few examples of liquid crystals with only one phenyl group that is able to self-assemble. Small- and Wide angle X-ray scattering (SAXS/WAXS) measurements indicate that the molecules spontaneously formed a smectic phase. Calculation of the Li-salt dissociation from the data obtained by a combination of impedance spectroscopy measurements and diffusion experiments by ⁷Li and ¹⁹F pulsed field gradient (PFG) NMR revealed good dissociation properties of the compounds. The complex of (2-Oxo-1,3-dioxolan-4-yl)methyl 4-(decyloxy)-2,3,5,6-tetrafluorobenzoate (4b) with LiTFSI exhibited anisotropic conductivity. The conductivity parallel to the smectic orientation was 125 times higher than perpendicular and is one of the best reported for liquid crystals with propylene carbonate fragments.