ELECTRONIC-PROPERTIES OF DISCOTIC LC-MATERIALS

We have made extensive studies of the charge-carrier mobilities in the discotic hexagonal mesophases of triphenylene-based discotic liquid c rystals. Using the time-of-flight technique, transient photocurrents w ere measured yielding charge-carrier mobilities for various electric f ields and temperatures. Starting from promising results obtained with the monomeric discotic liquid crystalline model compound hexapentyloxy triphenylene (H5T), we synthesized a ''discotic twin'' with two triphe nylene units linked together by a suitable spacer. Additionally, we sy nthesized a discotic liquid crystalline oligomer consisting of four tr iphenylene units which are bound to a flexible cyclosiloxane ring. In the dimer and in the oligomer the discotic mesophase can be maintained in a discotic glass. Our data show that in both H5T as well as in the dimer and in the oligomer hole mobilities on the order of magnitude o f 10(-3)cm(2)/Vs can be reached. Since the mobilities obtained in the oligomeric compounds are comparable to those found in the monomeric mo del compound, it becomes clear that the excellent charge-carrier trans port properties in the discotic hexagonal mesophase can be preserved i n easily processible and anisotropic organic thin films. Therefore, ou r results are an important step towards the applicability of highly or dered discotic liquid crystalline materials in the field of electronic applications.