HIGHLY PHOTOCONDUCTIVE DISCOTIC LIQUID-CRYSTALS - STRUCTURE-PROPERTY RELATIONS IN THE HOMOLOGOUS SERIES OF HEXA-ALKOXYTRIPHENYLENES

Four discotic liquid crystals (LCs) from the hexa-alkoxytriphenylene series (R=C(n)H2n+1, n=5, 7, 9, 11) classified as D(ho) phases were investigated with respect to their photoconducting properties. Under irradiation, all samples show photoconductivity within the mesophase, whereas in the isotropic phase the photocurrent drops to zero. All of the observed effects, the phase dependence of the photocurrent, the increasing values of the photocurrent with decreasing length of the side chains, and the higher photoconductivity during the cooling process, can be explained in terms of the transition temperatures, the intercolumnar distances and the orientation behaviour. Comparison of the photocurrents of the investigated homologues at a reduced temperature leads to an activation energy of 0.67 eV for the charge transport.