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The hole transport properties of ester substituted hexaalkyloxytriphenylenes are investigated and compared with the materials without ester substituents. The high hole mobilities of the recently investigated discotic liquid crystals of the hexaalkyloxytriphenylene-type are restricted to the very small temperature range of their mesophase. It is extended substantially by substitution of one ester group, as this hinders crystallization and results in glass formation. It is found that the substitution of an ester group alters the temperature and Ðeld dependence of the mobility completely. In the ester substituted compounds the mobility k is not independent of temperature but follows a ln k P 1/T 2 law. We attribute this to the dipole moment of the ester group which causes random Ñuctuations in the local electric Ðeld and leads to disorder dominated charge carrier hopping as the prevailing transport mechanism.

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Discotic liquid crystalline materials characterized by the spontaneous formation of columns within the fluid phase display a set of interesting optoelectronic properties directly related to the state of order. The dispersion of such columnar discotics in solid polymer matrices results in geometric confinement effects controlling both the structure of the mesophase and dynamical properties related to transport properties. The confinement causes a reduction of the longitudinal and the transverse spatial correlation lengths which, in turn, gives rise to strong modifications of the absorption and emission properties as well as electronic transport processes.