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

Abstract

The synthesis of tris(aryloxadiazolyl)triazines (TOTs), C 3‐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.

2-{3,5-Bis-[5-(3,4-didodecyloxyphenyl)thien-2-yl]phenyl}-5-(3,4-didodecyloxyphenyl)thiophene

“…A peculiarity should be mentioned: While melting enthalpies are generally higher than the associated clearing transition enthalpies, the values found for 4 are ∆H = 15.7 kJ/mol for melting and ∆H = 24.0 kJ/mol for clearing. A similar behavior has been observed for structural congeners with a tris-1,3,4-oxadiazolyltriazine center [33].…”

“…Both transitions appear at temperatures abo counterparts in the cooling scan. A peculiarity s thalpies are generally higher than the associated found for 4 are ΔH = 15.7 kJ/mol for melting and behavior has been observed for structural conge center [33].…”

Perylene Bisimide-Based Luminescent Liquid Crystals with Tunable Solid-State Light Emission

“…Taking into consideration the dimension of the hydrogen-bonded supramolecular complex Z , Z , Z -TCS–MPBI (Scheme S3) and the X-ray-determined lattice parameter, a possible molecular packing structure is depicted in Figure d, while other cases cannot be precluded due to the lack of a well-aligned sample to give additional X-ray scattering information. In contrast to the helically stacked columns by star-like mesogens, , the strong π-stacking ability between discotic PBI moieties around the TCS core may dominate the assembly process to adopt such a weakly interdigitated structure with minimized interfacial energy and maximized nanosegregation of each component including the TCS core, PBI skeleton, and aliphatic segments. , In addition, the density (ρ) was calculated on the basis of the parameter measured by X-ray analysis by using the relationship ρ = ( M · Z )/( N A · V ), where M is the molar mass of the supramolecular complex, Z is the number of molecules in the unit cell, N A is Avogadro’s number, and V is the unit cell volume. The density was calculated to be 0.94 g cm –3 for this hexagonal columnar structure, which was reasonable for common organic compounds, and thus supported the formation of a hydrogen-bonded supramolecular complex and validated such a molecular packing manner.…”

Mesogens with aggregation‐induced emission properties: Materials with a bright future

“…Detert and coworkers reported a series tetrakis(oxadiazolyl-phenyl)pyrazine-based emissive mesogens, which showed temperature ranges of columnar mesophases of up to 250 • C depending on the substitution [31,32] pattern (Figure 18). [45,46] Interestingly, the emissive behavior of the tetraphenylpyrazine derivatives (OXA-3) remained nearly unaffected by the substitution pattern as proven UVvis and fluorescence spectroscopy in solution using different solvents (λ em 440-455 nm). This observation also applied for OXA-3 derivatives (R 1 = H, R 2 = R 3 = C 14 H 29 or R 1 = C 12 H 25 , R 2 = H, R 3 = C 12 H 25 ) spin-coated thin films in the liquid crystalline phase.…”