Fast Electron Transport in Discotic Columnar Phases of Triphenylene Derivatives

We investigated the negative carrier transport in discotic columnar phases of three triphenylene derivatives by time-of-flight experiments. We found that transient photocurrents had two transits of negative carriers, which appeared in different time ranges. The mobilities obtained from the fast transit were 2 × 10 -2 , 2 × 10 -3 , and 4 × 10 -4 cm 2 /(V·s) for 2,3,6,7,10,11-hexabutyloxytriphenylene (H4T), 2,3,6,7,10,11-hexapentyloxytriphenylene (H5T) and, 2,3,6,7,10,11-hexahexyloxytriphenylene (H6T), respectively. These mobilities are almost the same as hole mobilities for each triphenylene derivative, indicating electron transport. On the other hand, the mobilities from the slow transit were about 10 -5 cm 2 /(V·s), and exhibited the Arrhenius type of temperature dependence irrespective of the three triphenylene derivatives, indicating ionic transport. We discuss the nature of the negative carrier transport in triphenylene derivatives including the electronic and ionic transports.