Liquid-crystalline behavior and ferroelectric property of viologen-based ionic liquid crystals

Viologen-based ionic liquid crystals (VILCs) bearing viologen cations and various counter anions (Br − 1 , CsO − , PF 6 − 1 , CF 3 COO − , TsO − , and BF 4 − 1 ) were prepared using cholesterol, bromobutanoyl chloride, bipyridine and different anionic salts. The chemical structures and the SmC ⁎ phase were identified, and the effect of different anions on both liquid crystalline behavior and ferroelectric property was investigated. Melting temperatures of these VILCs with different anions were similar, but SmC*-isotropic phase transition temperatures were elevated in sequence of TsO − , CsO − , CF3COO − , PF6 − , Br − and BF4 − . They showed different polarization values changed from −9.1 to 9 nC/cm 2 as the electric field changed from −10 V to 10 V. The ferroelectric parameters ± E c , ± P r , and ± P s changed a little due to the different counter anions. The VILC with BF 4 − anion showed the optimal ferroelectric properties in these VILCs series. Unlike conventional ferroelectric liquid crystals, the VILCs displayed asymmetry in the hysteresis loops due to formation of double electrical layers in the ordered SmC ⁎ phase.