Interesting phase behaviors and ion-conducting properties of dicationic N-alkylimidazolium tetrafluoroborate salts

A series of dicationic imidazolium bis(tetrafluoroborate) salts were newly synthesized, and their phase transition behaviors were correlated with thermal, scattering, optical and conductivity results. The bis-imidazolium salts having side-chain lengths of C ₆ -C ₁₀ showed plastic crystal mesophases, while a liquid crystal mesophase was formed in the bis-imidazolium salts with long side-chains (C ₁₁ and C ₁₂ ). Soft plastic and liquid crystalline phases were also confirmed by wide-angle X-ray diffraction. For the bis-imidazolium salts exhibiting a plastic crystal mesophase, the ionic conductivity suddenly increased at the melting temperature. However, the bis-imidazolium salts with long side-chains showed a slope increase during the liquid crystal-liquid crystal transition.