Supramolecular Self-Assembly of Ionic Discotic Liquid Crystalline Dimer with DNA at Interfaces

Core charge of imidazolium annulated triphenylene derivatives induces discotic columnar mesomorphism

Thermotropic ionic liquid crystals have remained a relatively little studied group of materials despite their many potential applications as anisotropic ionic liquids and charge (ion and electron/hole) transporting materials. Particularly rare are core charged discotic liquid crystals because their synthesis is usually more involved, and their molecular design is less established. Presented here is a straightforward and versatile synthetic approach to imidazolium annulated triphenylene derivatives. Their neutral imidazole precursors are not liquid crystalline while the imidazolium salts display hexagonal discotic columnar mesophases over a wide range of temperatures and as low as 47 °C. Computational studies at the DFT and PM6 levels of theory confirmed much higher stacking energies for the imidazolium salts compared to the neutral imidazole precursors. They also predicted the anions of columnar stacks of imidazolium salts to be positioned in the bay-positions next to the imidazolium unit and in-plane with the polyaromatic system. The anions were stabilized in the bay position by multiple interactions with partially positively charged H atoms and do not interfere with π-π stacking.

Phase Behavior and DFT Calculations of Laterally Methyl Supramolecular Hydrogen-Bonding Complexes

Four new series of laterally methyl-substituted hydrogen-bonded supramolecular complexes were prepared. The prepared complexes were thermally investigated by differential scanning calorimetry (DSC) and phases identified by polarized light microscopy (PLM). Supramolecular hydrogen-bonded complexes formed from a 1:1 mixture of any two derivatives, bearing different alkoxy chains, of 4-alkoxyphenylazobenzoic acid and 4-(2-(pyridin-4-yl)diazenyl-(2-(or 3-)methylphenyl) 4-alkoxybenzoate. The investigated 1:1 mixture made by introducing a lateral methyl group by different spatial orientation angles into pyridine-based components. All new complexes were confirmed by Fourier-transform infrared spectroscopy (FTIR) and computational calculations used to study their stabilities. It is found that the prepared complexes are dimorphic, exhibiting smectic C and enhanced nematic phases. A comparison was made between the new series and previously investigated simpler complexes, revealed that the incorporation of the phenylazo group elongate the mesogenic part and hence broad nematic phases were obtained with high stability.