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 (${\mathit{D}}_{\mathit{h}}$) 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, ${\mathrm{\mu }}_{\mathrm{\parallel }}$∼1×${10}^{\mathrm{-}4}$ ${\mathrm{cm}}^2$ ${\mathrm{V}}^{\mathrm{-}1}$ ${\mathrm{s}}^{\mathrm{-}1}$. 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 (${\mathrm{\mu }}_{\mathrm{\parallel }}$/${\mathrm{\mu }}_{\mathrm{\perp }}$∼${10}^3$). These results are discussed in terms of possible mechanisms for carrier transport in discotic liquid crystals.