Thieno[3, 2-b]thiophene-Based Discotic Liquid Crystal Mesogens: Rational Synthesis, Physical Properties and Self-Assembly

Synthesis, Thermal, and Optical Properties of Tris(5-aryl-1,3,4-oxadiazol-2-yl)-1,3,5-triazines, New Star-Shaped Fluorescent Discotic Liquid Crystals

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.

Board-like Fused-Thiophene Liquid Crystals and their Benzene Analogs: Facile Synthesis, Self-Assembly, p-Type Semiconductivity, and Photoluminescence

Fused-thiophene discotic liquid crystals were designed and easily synthesized by Suzuki coupling and FeCl₃ oxidized tandem cyclodehydrogenation reactions, including homo- and cross-coupling reactions. The resulting hexagonal and rectangular columnar mesomorphic supramolecular structures formed were characterized by polarizing optical microscopy, differential scanning calorimetry, and small-angle X-ray scattering. The charge carrier transport properties in the mesophases of two of the synthesized fused-thiophene discogens were measured by transient photocurrent time-of-flight (TOF) technique, revealing fast hole transport values in the range of 10^-3 to 10^-2  cm²  V^-1  s^-1 , thus demonstrating potential applications in electronic devices. The luminescent sanidic mesogens, with different extended π-conjugated systems, also emit blue, green, or red light, with absolute photoluminescent quantum yields as high as 18 %.