Alignment behaviour of symmetrical and asymmetrical triphenylenes possessing fluoroalkylated side chains on modified substrates

Abstract

The alignment behaviour of triphenylene‐based compounds possessing fluoroalkylated and alkyl side chains was investigated for the hexagonal columnar (Col_h) mesophase on polyimide‐, cetyltrimethylammonium bromide (CTAB)‐, and indium tin oxide‐coated glass substrates by polarizing optical microscopy. It was found that 2,6,10‐trinonyloxy‐3,7,11‐tris(1H,1H,2H,2H,3H,3H‐perfluorononyloxy)triphenylene and 2,6,11‐trinonyloxy‐3,7,10‐tris(1H,1H,2H,2H,3H,3H‐perfluorononyloxy)triphenylene exhibit spontaneous homeotropic alignment on these substrates. On the other hand, it was found that 2,6,10‐triheptyloxy‐3,7,11‐tris(1H,1H,2H,2H,3H,3H‐perfluoroheptyloxy)triphenylene, 2,6,11‐triheptyloxy‐3,7,10‐tris(1H,1H,2H,2H,3H,3H‐perfluoroheptyloxy)triphenylene, 2,6,10‐trihexyloxy‐3,7,11‐tris(1H,1H,2H,2H,3H,3H‐perfluorohexyloxy)triphenylene, 2,6,11‐trihexyloxy‐3,7,10‐tris(1H,1H,2H,2H,3H,3H‐perfluorohexyloxy)triphenylene, 2,6,10‐tributyloxy‐3,7,11‐tris(1H,1H,2H,2H,3H,3H‐perfluorobutyloxy)triphenylene and 2,6,11‐tributyloxy‐3,7,10‐tris(1H,1H,2H,2H,3H,3H‐perfluorobutyloxy)triphenylene do not show such spontaneous homeotropic alignment on these substrates. These results indicate that the spontaneous homeotropic alignment of the Col_h phase could be easily attained by the introduction of an appropriate length of the fluoromethylene chains in the peripheral parts of discogens. Therefore, it is suggested that the balance between the hydrocarbon part including the triphenylene core and the fluoroalkyl part determines the alignment control behaviour. Furthermore, it was found that alignment behaviour is independent of the rotation symmetry of the chemical structure but is dependent on the number of fluoromethylene chains in the chemical structure.