Synthesis and mesomorphism of triphenylene-based dimers with a highly ordered columnar plastic phase

Abstract

A series of triphenylene-based discotic dimers have been synthesized, each of the triphenylene nuclei bears five β-OC₄H₉ substituents, which are linked through the remaining β-positions by a flexible O(CH₂)_nO polymethylene chain (n = 2–12). Their chemical structures were confirmed by proton nuclear magnetic resonance spectroscopy, Fourier transform infrared spectroscopy, high-resolution mass spectrometry and elemental analysis. The mesomorphic properties of these compounds were investigated by differential scanning calorimetry, polarizing optical microscopy and X-ray diffraction. It was found that these dimers for which n > 4 formed a highly ordered columnar plastic phase and some of them (n = 6, 7, 10, 11, and 12) exhibited multiple mesophases. This is the first time that the rectangular columnar plastic phase was defined by us as a novel liquid crystal phase of compound 4d (n = 5). The introduction of a single interconnecting chain between adjacent molecules does not significantly perturb the formation of a columnar plastic phase but enriches the mesophases of discotic molecules and hinders the crystallization; the mesophases of 4e–k (n = 6–12) can be supercooled into a glass state in which the self-assembly columnar structures are retained.