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

Four discotic liquid crystals (LCs) from the hexa-alkoxytriphenylene s eries (R=C(n)H2n+1, n=5, 7, 9, 11) classified as D(ho) phases were inv estigated with respect to their photoconducting properties. Under irra diation, all samples show photoconductivity within the mesophase, wher eas in the isotropic phase the photocurrent drops to zero. All of the observed effects, the phase dependence of the photocurrent, the increa sing values of the photocurrent with decreasing length of the side cha ins, and the higher photoconductivity during the cooling process, can be explained in terms of the transition temperatures, the intercolumna r distances and the orientation behaviour. Comparison of the photocurr ents of the investigated homologues at a reduced temperature leads to an activation energy of 0.67 eV for the charge transport.