Fast photoconduction in the highly ordered columnar phase of a discotic liquid crystal

THE search for organic materials suitable for electronic applica-tions dates back to the early 1950s. But the only organic systems known so far to show electronic charge-carrier mobilities comparable to the amorphous inorganic semiconductors that are the main-stay of the microelectronics industry are zone-refined organic single crystals1–4. Single crystals are difficult and costly to process, however, and are not suitable for device applications. Here we show that a highly ordered columnar (stacked) phase of disk-like organic molecules can exhibit high mobilities for photoinduced charge carriers, of the order of 0.1 cm2 V-1 s-1—higher than for any organic material other than single-crystal phases. Specifically, we study the helical columnar phase of 2,3,6,7,10,11-hexahexylthiotriphenylene, which can be prepared simply by cooling the isotropic liquid melt via the discotic liquid-crystal phase, in which the molecules are already stacked with a high degree of order.