Alkyl acid hydrazide-containing liquid crystalline triphenylenedicarboxyimides

Seven hydrazide-containing triphenylenedicarboxyimides (TDIs) bearing four beta-octyloxy side chains and one alkyl acid amide group at the imide nitrogen have been synthesised. These TDIs exhibit enantiotropic mesophases with broad mesomorphic temperature ranges and high clearing temperatures between 258(degrees)C and 318(degrees)C. Notably, TDI-NHCO-C4H9 with a n-butyl side chain exhibits a wide mesomorphic temperature range of over 300(degrees)C extending from below room temperature to 303(degrees)C. In contrast, its branched isomer TDI-NHCO-C(CH3)(3 )carrying a bulky tert-butyl chain displays a hexagonal columnar mesophase between 105(degrees)C and 318(degrees)C with the highest clearing temperature within the series, indicating that branching leads to a stabilisation of the mesophase. On the other hand, the approximately 83(degrees)C increase in the clearing temperature of hydrazide TDI-NHCO-C4H9 relative to imide TDI-C4H9 lacking the hydrazide function indicates a significant enhancement of mesophase stability upon introducing the hydrazide functional group. However, variable-temperature infrared studies revealed the presence of weaker hydrogen bonds below the clearing temperature, which do not significantly contribute to the stabilisation of the columnar mesophase. Instead, the primary stabilisation mechanism is attributed to the synergistic effect of pi-pi interactions and dipole-dipole interactions. [GRAPHICS]