Hopping conduction in the columnar liquid crystal phase of a dipolar discogen

Hole transport has been investigated by the time-of-flight method for the hexagonal columnar phase of a discogen containing a strongly dipolar nitro substituent; 1-nitro-2,3,6,7,10,11-hexakis(hexyloxy)triphenylene (HAT6-NO2). Unlike the corresponding unsubstituted system, 2,3,6,7,10,11-hexakis(hexyloxy)triphenylene (HAT6), and unlike most other liquid crystals, the mobility in HAT-NO2 depends strongly on both electric field and temperature. As in amorphous solids there is disorder dominated hopping and the mobility can be modeled using an energy disorder parameter, σ of just over 100meV. Compared to HAT6, the disorder in HAT6-NO2 is enhanced because of the strong dipole of the nitro group.