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 (D-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, mu(parallel to)similar to 1X10(-4) cm(2) 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 (mu(parallel to)/mu(perpendicular to)similar to 10(3)). These results are discussed in terms of possible mechanisms for carrier transport in discotic liquid crystals.