Carrier transport and viscosity of discotic liquid-crystalline photoconductor hexaoctylthio-triphenylene

In this study, the electronic and ionic carrier transports and viscosity of 2,3,6,7,10,11-hexaoctylthio-triphenylene (C8STP) were studied by a time-of-flight method and using a rotational viscometer. Ambipolar charge carrier transport was investigated in the isotropic liquid (Iso) phase of C8STP, similarly to the columnar hexagonal mesophase, and the activation energies were estimated to be 0.1 eV for one positive and one negative, and 0.4 eV for the other negative charge carrier mobility in Iso. The viscosity of C8STP was investigated using a rotation viscometer, and relative viscosity was measured by a capillary method in the isotropic phase, and the activation energy of viscosity was 0.4 eV. The Stokes radii of ionic carriers were experimentally estimated using Walden's rule. The existence of ionic and electronic (hopping) carrier transports in Iso was implied for the discotic liquid crystalline photoconductor. (C) 2014 The Japan Society of Applied Physics