Syntheses, characterizations and electrochemical properties of mesomorphic 4-(4′-alkoxy-(1,1′-biphenyl)-4-oxy)butane-1-sulfonic acids

• Smectic sulfonic derivatives were synthesized and characterized.
• Sulfonic acid moieties formed a head-to-head configuration in the smectic phase.
• Lamellar sulfonic acid pathways contributed greatly to the anhydrous proton conduction.
• Anhydrous proton conductivities in the smectic sulfonic derivatives followed the Arrhenius law.

Biphenyl based sulfonic acid derivatives have been synthesized for anhydrous proton conduction. The terminal sulfonic acid moiety was attached to a biphenyl core by ring-opening reaction of 1,4-butane sultone. The target compounds exhibited smectic phases in a temperature range of 180–220 °C. Polarizing optical microscopic observation and temperature dependent X-ray diffraction measurements suggested that sulfonic acid moieties formed a head-to-head configuration in the smectic assemblies. The mesomorphic sulfonic acid derivatives formed lamellar proton conducting pathways and the anhydrous proton conductivities determined by electrochemical impedance spectroscopy showed Arrhenius temperature dependence in the smectic phase.