Charge carrier transport in liquid crystals

•Liquid crystals exhibit charge mobility ranging from 10–3 to 0.1 cm2/Vs.•Electronic (intrinsic) and ionic (extrinsic) conductions in liquid crystals•Unique charge carrier transport properties in liquid crystals•Effect of molecular alignment in mesophases on charge carrier transport•Conduction mechanism in smectic liquid crystals

The materials exhibiting charge carrier mobility ranging from 10− 3 to 0.1 cm2/Vs, i.e., between those of amorphous and crystalline materials, had been missing before the 1990s when the electronic conduction in liquid crystals was discovered. Since then, various liquid crystalline materials including discotic and calamitic liquid crystals have been studied in order to clarify their charge carrier transport properties in liquid crystalline mesophases. In this article, the historical background of the discovery of electronic conduction in liquid crystals, intrinsic and extrinsic conductions, unique properties of the charge carrier transport, the effect of molecular alignment on it, and the conduction mechanism in liquid crystalline mesophases are shortly described on the basis of the experimental and theoretical studies accumulated in these two decades, noting that the missing materials were liquid crystals.