Room temperature discotic liquid crystalline thin films of hexa-peri-hexabenzocoronene: Synthesis and optoelectronic properties

The compound hexa-(3,7,11,15-tetramethylhexadecanyl)hexa-peri-hexabenzocoronene (HBC-C_4/16), soluble in most organic solvents such as chloroform and THF, was synthesized. This compound shows a stable discotic hexagonal columnar mesophase between -36 and 231 °C. Symmetrical sandwich cells of ITO/HBC-C_4/16/ITO (∼1μm thick) were prepared by capillary filling by the molten state for the studies of their optical and optoelectronic properties. Two distinct textures, one very bright and the other gray, were clearly seen in thin films of HBC-C_4/16 between two crossed polarizers in an optical microscope at room temperature. Short-circuit photocurrents (I_sc) were obtained with such cells, and the gray areas generated a much higher short circuit photocurrent compared to that of the bright spots. This photocurrent difference was attributed to different orientations of the HBC-C_4/16 molecular columns relative to the ITO electrode surface. The charge trapping and detrapping effects found earlier with other materials, such as zinc porphyrins (ZnODEP), and of potential use in optoelectronic data storage were also observed with these cells.