A columnar molecular glass at high temperature

Abstract

We prepared two triphenyltriazines decorated with three phenyltriazole and three tolanyl systems. To ensure mesophase formation, we introduced nine flexible dodecyloxy groups into the terminal phenyl rings. The tolanyl derivative did not present a mesophase. In contrast, the phenyltriazolyl derivative formed a columnar hexagonal mesophase, which conveniently rigidified to a columnar glass below 120 °C on cooling from the isotropic liquid. The extensive alkyl periphery induces a moderate clearing temperature below 200 °C, which is beneficial for forming uniform alignment on substrate surfaces at the isotropic-to-mesophase transition. At the same time, the three long, bent protrusions from the threefold-symmetric core led to a very extended supra-ambient temperature range of the rigid glass. This extreme robustness of the anisotropic glass state may be due to the interdigitation of the extended yet poor space-filling shape of the arene moiety. The columnar-glass-forming triphenyltriazine displayed blue photoluminescence under UV excitation in solution, as well as in the glassy columnar solid state. Thus, molecular interdigitation of star-shaped large-bandgap mesogens enables a conveniently attainable clearing temperature in combination with a high glass transition temperature, as desired for robust anisotropic emitter or transport layers in organic optoelectronic devices.