The synthesis of tris(aryloxadiazolyl)triazines (TOTs), C3 -symmetrical star-shaped mesogenes with a 1,3,5-triazine center, 5-phenyl-1,3,4-oxadiazole arms, and various peripheral alkoxy side chains is reported. Threefold Huisgen reaction on a central triazine tricarboxylic acid and suitable aryltetrazoles yields the title compounds. Selected analogues with a benzene center are included in this study and allow for an evaluation of the impact of the central unit on the physical properties. Thermal (differential scanning calorimetry, DSC; polarization optical microscopy, POM), optical (UV/Vis, fluorescence), electric (time of flight, TOF), and structural (single crystal; wide-angle X-ray scattering, WAXS) properties of these compounds were investigated. The modification of alkoxy chain length and substitution pattern allows for a tuning of the physical properties. TOTs emit blue to yellow light, depending on conjugation length, donor-acceptor substitution, and solvent polarity, whereas concentration quenches and aggregation enhances the emission. The width of the mesophases is typically around ΔT=100-150 K but can even exceed 220 K. Polarization optical microscopy and X-ray diffraction on oriented filaments reveal that TOTs are highly ordered liquid crystals (LCs) with long-range hexagonal columnar structure.
Keywords: X-ray scattering; fluorescence; heterocycles; liquid crystals; solvatochromism.
© 2019 The Authors. Published by Wiley-VCH Verlag GmbH & Co. KGaA.