RESUMEN
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.
RESUMEN
A series of new tetrakis(dialkoxyphenyl) dicyanotetraoxapentacene derivatives (1 a-c) were prepared by reaction of the appropriate terphenyl diols with tetrafluoroterephthalonitrile in good yields. Compounds 1 b and 1 c, which bear hexyloxy and decyloxy side chains, exhibited columnar hexagonal mesophases, as shown by polarized optical microscopy, variable-temperature powder X-ray diffraction, and differential scanning calorimetry. Single-crystal X-ray diffraction of methoxy-substituted 1 a revealed that the dicyanotetraoxapentacene core is highly planar, consistent with the notion that these molecules are able to stack in columnar mesophases. A detailed photophysical characterization showed that these compounds exhibit aggregation-induced emission in solution, emission in nonpolar solvents, weak emission in polar solvents, and strong emission in the solid state both as powder and in thin films. These observations are consistent with a weakly emissive charge-transfer state in polar solvents and a more highly emissive locally excited state in nonpolar solvents.
RESUMEN
We report the synthesis and properties of a series of novel triphenylenedicarboxyimides and thioimides (4-6) to probe the effect of thionation on the formation of columnar mesophases. These materials display broad columnar mesophases and high clearing points and self-associate in solution to form dimers. Overall, thionation improved the self-assembly in solution and led to a stabilization of the columnar mesophase. Furthermore, increasing the thionation of these materials led to a lowering of the lowest unoccupied molecular orbital (LUMO) energy level and a narrowing of the highest occupied molecular orbital-LUMO gap.
RESUMEN
We report the synthesis of novel polycatenar dibenzopentacenequinones 1 and 2 that are designed to form columnar liquid crystalline phases. The mesomorphic properties of these compounds were investigated by polarized optical microscopy, differential scanning calorimetry, and powder X-ray diffraction. While compound 1 exhibits two distinct columnar mesophases between 148 and 177 °C, fluorinated 2 exhibits a columnar mesophase from 121 to 336 °C. This dramatic stabilization of the columnar mesophase of 2 can be attributed to improved π-stacking as a result of arene-perfluoroarene interactions.
RESUMEN
Diketopyrrolopyrrole and isoindigo are commercially important dyes that have recently found broad application as electron acceptor and light-absorbing groups in organic semiconductors. Their self-assembly into specific supramolecular structures to control optoelectronic properties has been hampered by limited options for substitution and their high propensity for crystallization. Reported here is a molecular design that directs self-assembly into previously elusive columnar mesophases of π-π stacking cores. Although attachment of bis(trisoctyloxyphenyl)-1,3,5-triazine groups to both ends of diketopyrrolopyrrole-thiophene and isoindigo cores generated mesomorphic dyes of similar overall shapes and dimensions, distinct differences in their mesomorphism and optoelectronic properties were observed.