Switching of ionic conductivities in columnar liquid-crystalline anilinium salts: effects of alkyl chains, ammonium cations and counter anions on thermal properties and switching temperatures

Abstract

Switching one-dimensional ion conductivities in organic materials is a challenging task. Recently we found that a liquid-crystalline (LC) N,N,N-trimethyl-3,4,5-tridodecyloxy-anilinium salt showed a remarkable change in the conductivities of about four orders of magnitude, which was triggered by a thermotropic LC phase transition between rectangular (Col_r) and hexagonal (Col_h) columnar phases. In the present study, we have succeeded in tuning the switching temperature by changing the length of the alkyl chains attached to the anilinium ring of LC materials. The size of the N,N,N-trialkylanilinium cations, that is, trimethyl, dimethylethyl and diethylmethyl, and the counterion (BF₄, PF₆ or CF₃SO₃) play a crucial role in the formation of successive Col_r and Col_h LC phases, which affect the switching behaviour. We have found that the temperature of the Col_r–Col_h phase transition and the switching of ion conductivity are tuned in N,N,N-trimethylanilinium tetrafluoroborates by changing the length of the alkyl chains. These results give new insights into the design of ion-conductive self-assembled molecular materials.