Electrical properties of discotic liquid crystal hexahexyloxytriphenylene

Carrier transport of 2,3;6:7,10,11-hexahexyloxytriphenylene (HHOTP) in the discotic phase and the effects of C-60 doping and shear stress have been studied by a time-of-flight method. The relatively high mobility of positive carriers insensitive to temperature and also C-60 doping are interpreted to be the hole mobility. The hole mobility decreases on applying shear stress which deforms the columnar structure in the discotic phase. Small and temperature-dependent mobility (with activation energy of 0.3eV) of negative carriers which are influenced by C-60 doping is interpreted to be that of ionic carriers. Electronic band schemes of HHOTP in various phases (solid, discotic and isotropic) have been evaluated by absorption and photoelectron emission spectra measurements.