CHARGE DYNAMICS AND RECOMBINATION KINETICS IN COLUMNAR DISCOTIC LIQUID-CRYSTALS

The time-dependent quasi-one-dimensional transport of electrons or hol es along the molecular columns in columnar liquid crystals has been st udied. Recent mobility measurements on the tryphenylene-based HAT-n ma terials have revealed Gaussian transits in the liquid crystalline phas es but dispersion in the crystalline phases. In this work the factors governing the photoconductivity are rigorously analyzed using random-w alk methods. Strong evidence for one dimensionality is found in the ti me- and electric-field-dependent photocurrent decays. The field begins to affect the decay for values of field energy per hop which are well below kT and comparable with trap concentration as predicted by theor y. The trap concentration in the crystalline phase is governed by stru ctural disorder. The traps however appear ''shallow'' and the long tim e current disagrees with the deep trap theory. In the liquid crystalli ne phase, these traps are annealed out by thermal fluctuations and, as consequence, no direct kinetic proof of one-dimensional kinetics is o btainable. This observation of quasi-one-dimensional transport of char ge is in keeping with earlier findings for exciton motion in these mat erials.