Controlling the Columnar Order in a Discotic Liquid Crystal by Kinetic Arrest of Disc Tumbling

By cooling at different rates, the discotic liquid crystal (LC) phenanthro[1,2,3,4-ghi]perylene-1,6,7,12,13,16-hexacarboxylic 6,7,12,13-tetraethyl, 1,16-dimethyl ester (PNP) can form glasses of widely different columnar orders, including zero order. The temperature at which the columnar order is frozen at a given cooling rate corresponds to a slow relaxation mode revealed by dielectric spectroscopy and attributed to disc tumbling within the column. The control of the columnar order in this discotic LC is analogous to the control of the smectic order in calamitic LCs reported earlier. In both cases, kinetic arrest of a slow molecular rotation above the calorimetric Tg freezes the LC order. This principle can be applied to predict and control molecular packing in the fabrication of organic electronics.