Mechanism of charge transport in discotic liquid crystals

A comparative study is reported of transient photoconductivity and ac conductivity in the liquid-crystalline columnar hexagonal (Dₕ) phase of pure and p-doped hexakis(n-hexyloxy)triphenylene. In both materials, charge-carrier transport is dispersive, and the measured carrier mobilities along the direction of the molecular columns are very similar, μ_∥{~}1×{}10^-4 cm² V^-1 s^-1. The dispersion arises from the intrinsic liquidlike disorder in the face-to-face packing of the triphenylene rings within the columns. Charge transport is found to be highly anisotropic (μ_∥/μ_⊥{~}10³). These results are discussed in terms of possible mechanisms for carrier transport in discotic liquid crystals.