Synthesis of Mixed Tail Triphenylene Discotic Liquid Crystals: Molecular Symmetry and Oxygen‐Atom Effect on the Stabilization of Columnar Mesophases

Abstract

Small change in chemical structure of discotic liquid crystals can cause big difference in their mesomorphism. Replacing of the alkoxy peripheral chains of triphenylene by oxygen-atom containing ester chains would result in novel mesomorphism. A series of mixed tail triphenylenes containing propoxyacetyloxy and alkoxy, abbreviated as C 18 H 6 (OC n H 2n＋1 ) 3 (OCOCH 2 OC 3 H 7 ) 3 , n＝4-8, and hexa(propyloxyacetyloxy)triphenylene, C 18 H 6 (OCOCH 2 -OC 3 H 7 ) 6 were synthesized. Thermal gravimetry analysis (TGA) of three discogens showed that they had good thermal stability till 350 ℃. The mesomorphism was investigated through differential scanning calorimetry (DSC) and polarized optical microscopy (POM). The preliminary X-ray diffraction (XRD) results of one compound showed that it exhibited ordered hexagonal columnar (Col ho ) mesophase. These mixed tail triphenylene derivatives possessed much stable Col ho mesophase and wider mesophase ranges than their hexaalkoxytriphenylene C 18 H 6 (OR) 6 and hexaalkanoyloxytriphenylene C 18 H 6 (OCOR') 6 analogues. The asymmetrical compounds 2,6,11-trialkoxy-3,7,10-tri(2-propyloxyacetyloxy)triphenylenes with n＝5-8 displayed higher clearing points and wider temperature ranges than their symmetrical isomers 2,6,10-trialkoxy-3,7,11-tri(2-propyloxyacetyloxy)-triphenylenes, while C 18 H 6 (OCOCH 2 OC 3 H 7 ) 6 had the highest clearing point due to the β-oxygen-atom effect.

Mesomorphic properties of linear and branched new triphenylene‐based poly(ester‐ether)s

“…The fact that mixed ether‐ester monomeric triphenylenes exhibit a wider LC thermal range has been pointed out previously and might be ascribed to the enhanced core–core interactions of the carboxylic groups, perpendicular to the T plane, can induce in the Col mesophase, thus increasing the clearing temperature. Although this perpendicular orientation could in principle destabilize the crystalline packing, thus lowering the melting point, the experimental trend found for mixed‐tail monomeric triphenylenes is opposite to this prediction, likely due to the fact that dipolar core–core interactions could also be intensified in the crystalline phase.…”

Synthesis and mesomorphism of mixed ether-ester tail triphenylene discotic liquid crystals with long alkyloxy peripheral chains

“…The asymmetrical isomers may have stronger intracolumnar intermolecular interaction, such as the dipole interaction, and therefore could cause their clearing points to be higher. The β-oxygen containing ester derivatives showing higher clearing points than that of the aliphatic ester derivatives can be explained by the same reason [13][14][15][16]. However, the oxygen atom in the other place of soft chain (not the beta position) would have opposite effect [34].…”

“…It is also explained by the betaoxygen substituted peripheral chains that the intermolecular interaction increased compared with the aliphatic acid derivatives [13][14][15][16]. 6 , with just the aromatic π-π interactions promoted the columnar molecular self assembly.…”

“…On one hand, the aromatic core can be modified by introducing hetero-atoms instead of carbon atoms, such as triphenylene and hexaazotriphenylene, and aromatic core size with different number of carbon atoms, for example, triphenylene and hexabenzocoronene. On the other hand, peripheral chains can be modified by variation of chain length, or introducing hydrophilic, hydrophobic, hydrogen bonding, perfluorinated chains, metal-containing chains, and polymerisable functional groups [13][14][15][16]. Mesomorphism and charged carrier mobility behaviors of discotic liquid crystals depend both on the aromatic cores and peripheral chains.…”

Synthesis of functionalized triphenylene discotic liquid crystals and the influence of unsaturated periphery on mesomorphism

“…The intermediates, 2-hydroxy-3,6,7,10,11-penta(pentoxy) triphenylene [27,37], 2,7-dihydroxy-3,6,10,11-tetra(pentoxy)triphenylene [38], 2,6,10-trihydroxy-3,7,11-tri(pentoxy) triphenylene [39][40][41], and 2,6,11-trihydroxy-3,7,10-tri(pentoxy) triphenylene [39][40][41] were synthesized according the reported methods.…”