Room Temperature Phosphorescence in Solution from Thiophene-Bridged Triply Donor-Substituted Tristriazolotriazines

Most organic room-temperature phosphorescence (RTP) emitters do not show their RTP in solution. Here, we incorporated sulfur-containing thiophene bridges between the donor and acceptor moieties in D₃ A-type tristriazolotriazines (TTTs). The thiophene inclusion increased the spin-orbit coupling associated with the radiative T₁ →S₀ pathway, allowing RTP to be observed in solution for all compounds, likely assisted by protection of the emissive TTT-thiophene core from the environment by the bulky peripheral donors.

Impact of Substitution Pattern and Chain Length on the Thermotropic Properties of Alkoxy-Substituted Triphenyl-Tristriazolotriazines

Tristriazolotriazines (TTTs) with a threefold alkoxyphenyl substitution were prepared and studied by DSC, polarized optical microscopy (POM) and X-ray scattering. Six pentyloxy chains are sufficient to induce liquid-crystalline behavior in these star-shaped compounds. Thermotropic properties of TTTs with varying substitution patterns and a periphery of linear chains of different lengths, branching in the chain and swallow-tails, are compared. Generally, these disks display broad and stable thermotropic mesophases, with the tangential TTT being superior to the radial isomer. The structure-property relationships of the number of alkyl chains, their position, length and structure were studied.

Fused tetracyclic tris[1,2,4]triazolo[1,3,5]triazine as a novel rigid electron acceptor for efficient thermally activated delayed fluorescence emitters

Tris[1,2,4]triazolo[1,3,5]triazine, a new acceptor based on a fused triazole and triazine moiety, is utilized to construct D₃–A star-shaped tristriazolotriazine derivatives, named 3,7,11-tris(4-(10H-phenoxazin-10 yl)phenyl)tris([1,2,4]triazolo)[1,3,5]triazine (TTT-PXZ) and 3,7,11-tris(4-(9,9-dimethylacridin-10(9H)yl)phenyl)tris([1,2,4])triazolo[1,3,5]triazine (TTT-DMAC). Both TTT-PXZ and TTT-DMAC emitters feature TADF activities and AIEE properties. Consequently, solution processed OLEDs based on TTT-PXZ green emitters exhibited good performances, with an external quantum efficiency (EQE) of up to 6.2%.

Tris[1,2,4]triazolo[1,3,5]triazine, a new acceptor based on a fused triazole and triazine moiety, has been utilized to construct two new star-shaped TADF emitters.

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.

A first porphyrin liquid crystal with strong fluorescence in both solution and aggregated states based on the AIE-FRET effect

Porphyrins are good near-infrared fluorescent materials, but the strong self-assembly stacking resulted in the aggregation-caused quenching (ACQ) effect, limiting their emissive performance in aggregated states. In this work, a novel diphenylacrylonitrile-porphyrin derivative with multiple polyglycol chains on the periphery was designed and synthesized as an excellent near-infrared-emissive liquid crystalline material in both solution and aggregated states, which was first observed for porphyrin liquid crystals. It exhibited a high self-assembly ability with the ordered hexagonal columnar mesophase between 70 and 120 °C approximately. The strong AIE-FRET effect was produced based on the overlap of the emission wavelength of diphenylacrylonitrile and the absorption wavelength of the porphyrin, resulting in the excellent near-infrared emission in both solution and aggregated states. The pseudo Stokes shift was as large as 210 nm and the fluorescence quantum yield reached 0.12 in the solid state. Moreover, this porphyrin liquid crystal displayed low biotoxicity and excellent fluorescence bio-imaging ability in living cells, opening a new application prospect for porphyrin liquid crystalline materials.

Tetrakis(oxadiazolylphenyl)pyrazines: New St. Andrew's Cross-Shaped Liquid Crystals

π-Conjugated molecules with the shape of St. Andrew's cross have been synthesized via fourfold Huisgen reaction. Four 2,5-diaryl-1,3,4-oxadiazol arms are attached to a central pyrazine nucleus. These fluorescent stars, when decorated with a rim of eight alkoxy side chains are discotic liquid crystals. Depending on the substitution pattern, the width of the liquid phase varies within a broad range of 25 °C to 250 °C. In their liquid crystalline phase, the molecules assemble in a typical hexagonal columnar supramolecular arrangement.

2,6,10-Trichlorotris[1,2,4]triazolo[1,5-a:1′,5′-c:1′′,5′′-e][1,3,5]triazine

Three very similar and nearly planar molecules are present in the asymmetric unit of the title compound, C6Cl3N9. Whereas the threefold 1,5-annulation of the chlorotriazole moieties is obvious, all of the C and N atoms in the central triazine ring are equally disordered on the same site, approachingD3hsymmetry for each of the molecules.

Isomerisation of Liquid-Crystalline Tristriazolotriazines

Star-shaped discotic liquid crystals with columnar superstructures constitute a highly interesting class of organic materials. Phenyl-substituted tris[1,2,4]triazolo-[1,3,5]triazine, prepared by a Huisgen reaction of phenyltetrazole and cyanuric chloride, represents an excellent core for discotic liquid crystals (DLCs). The thermal stability is not perfect, at temperatures above the clearing point, a successive threefold isomerization leads to a highly planar, C₃ -symmetrical isomer, which mainly differs in the orientation of the aryl substituents to the centre of the molecule. A new class of discotic liquid crystals has been obtained: Equipped with peripheral alkoxy chains both isomers can form broad thermotropic mesophases. The optical, thermal, and physical properties were investigated by polarized optical microscopy, differential scanning calorimetry, wide-angle X-ray scattering, UV/Vis absorption and fluorescence spectroscopic measurements. The thermotropic properties are decisively affected by the molecular structure of the isomers, isomerisation leads to higher melting points but also the loss or even gain of mesomorphism is observed.

Columnar self-assembly of luminescent bent-shaped hexacatenars with a central pyridine core connected with substituted 1,3,4-oxadiazole and thiadiazoles

Multifunctional pyridine based bent shaped polycatenars stabilizing liquid crystalline and organogel self-assembly.

Contrasting effects of heterocycle substitution and branched tails in the arms of star-shaped molecules

Herein, heterocycle based star-shaped liquid crystalline tris(N-salicylideneaniline)s (TSANs) are reported.

Triphenylene-Based Room-Temperature Discotic Liquid Crystals: A New Class of Blue-Light-Emitting Materials with Long-Range Columnar Self-Assembly

A straightforward synthesis of multialkynylbenzene-bridged triphenylene-based dyad systems (via flexible alkyl spacers) that self-organize into room-temperature columnar structures over a long range is reported. The compounds with spacer lengths (n) of 8 and 10 exhibit a columnar rectangular mesophase whereas a compound with n = 6 shows a columnar rectangular plastic phase. Interestingly, the later compound (n = 6) shows the formation of well-nucleated spherulites of about several hundred micrometers that suggest the existence of a long-range uniform self-assembly of columns. All of these compounds show blue luminescence in solution and in the thin-film state under long-wavelength (365 nm) UV light. These compounds fulfill the described demands such as long-range columnar self-assembly at room temperature, a good yield with high purity, and blue-light emitters under the neat condition for possible potential applications in semiconductor devices. They also match the criteria of facile processing from the isotropic state because of their low isotropization temperature. This new class of materials is promising, considering the emissive nature and stabilization of the columnar mesophase at ambient temperature.

Perylo[1,12-b,c,d] Thiophene Tetraesters: A New Class of Luminescent Columnar Liquid Crystals

Perylo[1,12-b,c,d] thiophene tetraesters exhibiting wide-range hexagonal columnar phase have been synthesized. These compounds also exhibit good homeotropic alignment in the liquid-crystalline phase which is very important for the device fabrication. These compounds showed sky-blue luminescence in solution under the long-wavelength UV light. With high solubility and high quantum yield these compounds can serve as standards to measure quantum yields of unknown samples. This new class of materials is promising, considering the emissive nature and stabilization of hexagonal columnar mesophase over a wide thermal range and ease of synthesis.

A DFT approach to the charge transport related properties in columnar stacked π-conjugated N-heterocycle cores including electron donor and acceptor units

Theoretical design of new, ambipolar DLC donor–acceptor systems based on tris[1,2,4]triazolo[1,3,5]triazine cores.

3-(4-Hexyl-oxyphen-yl)-1,2,4-triazolo[3,4-b]benzo-thia-zole

The title compound, C20H21N3OS, was prepared by Huisgen reaction of 5-(4-hexyl-oxyphen-yl)tetra-zole and chloro-benzo-thia-zole. The essentially planar benzo-thia-zolotriazole framework [maximum deviation from the mean plane of 0.077 (1) Å for the bridgehead N atom] and the phenyl ring form a dihedral angle of 53.34 (5)°. The hex-yloxy chain adopts a gauche-all-anti conformation. The intra-centroid separation of 3.7258 (8) Å between the triazole and benzene rings is the closest contact between individual mol-ecules in the crystal.

Specific Cu(ii) detection using a novel tricarbazolyl-tristriazolotriazine based on photoinduced charge transfer

A novel tricarbazolyl-tristriazolotriazine for specific Cu(ii) detection.

Tristriazolotriazines with π-Conjugated Segments: Star-Shaped Fluorophors and Discotic Liquid Crystals

C3-symmetrical tristriazolotriazines substituted with phenylene rings carrying lateral flexible alkoxy side chains were prepared via condensation/ring transformation of cyanuric chloride and tetrazoles. These star-shaped, planar compounds can form broad thermotropic mesophases. Due to the extensive π-conjugation, these compounds are highly emissive and the octupolar donor-acceptor electronic structure results in non-linear optical properties like solvatochromism. Brønstedt acids provoke halochromism of the absorption and of the fluorescence.

Luminescent columnar liquid crystals based on tristriazolotriazine

Five discotic molecules comprising a tris[1,2,4]triazolo[1,3,5] triazine core were designed and synthesized to obtain luminescent and charge-transporting columnar liquid crystalline materials. With the exception of one compound containing terminal hydroxyl groups all compounds presented a wide thermal range and stable columnar liquid crystalline phase, characterized by differential scanning calorimetry, polarized optical microscopy, and X-ray diffraction (XRD) techniques. The phase formation appeared to be associated to some extent with interdigitation of the alkoxy and benzylalkoxy portion, as suggested by the XRD results. All compounds have a strong blue luminescence in solution and solid phase. At the temperature at which the compounds enter in the mesophase the luminescence decreases significantly. This result suggests that entrance into the Col(h) phase is accompanied by a better π-stacking of the peripheral phenyl rings compared to the solid phase, consistent with the intramolecular distances (3.5 Å) observed in the XRD analysis. These compounds based on tristriazolotriazine are quite robust with good optical and thermal properties for application as solid state emitters, and we anticipate that they may provide an interesting alternative to other discotic molecules based on N-heterocycles, which generally present a high-temperature Col(h) phase.

Star-Shaped Conjugated Systems

The present review deals with the preparation and the properties of star-shaped conjugated compounds. Three, four or six conjugated arms are attached to cross-conjugated cores, which consist of single atoms (B, C⁺, N), benzene or azine rings or polycyclic ring systems, as for example triphenylene or tristriazolotriazine. Many of these shape-persistent [n]star compounds tend to π-stacking and self-organization, and exhibit interesting properties in materials science: Linear and non-linear optics, electrical conductivity, electroluminescence, formation of liquid crystalline phases, etc.