Alignment behavior for novel triphenylene compounds possessing fluoroalkylated side chains on modified substrates

The alignment behavior of the triphenylene compounds possessing fluoroalkylated side chains was investigated for the hexagonal columnar (Colh) mesophase on the polyimide-, cetyltrimethylammonium bromide (CTAB)-, and indium-SnO2 (ITO)-coated glass substrates by polarizing optical microscopy. It was found that 2,3,6,7,10,11-hexakis(1H,1H,2H,2H,3H,3H-perfluoroheptyloxy)- and 2,3,6,7,10,11-hexakis(1H,1H,2H,2H,3H,3H-perfluorononyloxy)-triphenylenes exhibit a spontaneous homeotropic alignment on these substrates, in contrast to the non-uniformity of alignment of Colh phase in the corresponding hydrocarbon mesogens. On the other hand, it was also found that 4,4,4-trifluorobutyloxy, 4,4,5,5,5-pentafluoropentyloxy and 4,4,5,5,6,6,6-heptafluorohexyloxy derivatives do not show such a spontaneous homeotropic alignment on these substrates. These results indicate that the spontaneous homeotropic alignment of the Colh phase could be easily attained by the introduction of an appropriate number and length of the fluoromethylene chains in the peripheral parts of discogens.