Heiner Detert

In the title compound, C ₈ H ₁₀ N ₂ OSe, an almost planar 1,2,3-selenadiazole ring is annulated to a cyclooctenone ring with a twist-boat conformation. The heterocycle and C—C(=O)—C carbonyl moieties subtend a dihedral angle of 54.25 (11)°. In the extended structure, weak C—H...O and C—H...N interactions link the molecules into double layers lying parallel to the bc plane.

The title compound, C ₄₀ H ₅₆ N ₂ O ₂ , was prepared via a Horner olefination reaction. Contrary to the previous structure, in which the complete molecule was generated by inversion symmetry and displayed unreasonable geometrical features [Zhang et al. (2005). Chin. J. Struct. Chem. 24 , 669–672], the molecule has C ₁ symmetry and the dihedral angles between the central and peripheral aromatic rings are 39.29 (9) and 18.95 (9)°. A weak C—H...π interaction occurs in the extended structure.

The complete molecule of the title compound, C ₈ H ₈ N ₄ Se ₂ , is generated by a crystallographic twofold axis: the almost planar 1,2,3-selenadiazole ring and its symmetry-generated partner are annulated to a cyclodeca-1,3-diene ring. Their dihedral angle amounts to 88.4 (2)° and the conformation of the hexamethylene chain is mostly staggered ( gauche ) except for a near- anti arrangement in the middle.

Cruciforms with a distyryldiphenylpyrazine structure are prepared via aldol condensation of dimethylpyrazines and benzaldehydes. The structure is confirmed via X-ray diffraction and NMR spectroscopy, including ¹⁵N-NMR. The impact of basic and non-basic donor groups on the terminal positions, as well as the extension of the conjugated system by styryl groups on the optical properties, is studied. These quadrupolar dyes are solvatochromic in their absorption and more pronounced in their emission. TFA interacts with the basic sites, resulting in multiple changes in the optical spectra.

The complete molecule of the title compound, C ₅₆ H ₆₀ N ₂ O ₂ , which was prepared via a Horner olefination, is generated by a crystallographic centre of symmetry. Whereas the terminal cyanostilbene units are almost planar, the central dioctoxybenzene unit is substantially tilted [dihedral angle = 51.68 (8)°], which limits conjugation. van der Waals forces between the alkyl chains connect the molecules, arranged in layers lying parallel to the ac plane.

The title β-carboline, C ₂₆ H ₂₀ N ₂ O ₄ S, which was synthesized via 2 + 2+2-cycloaddition to an alkynylynamide, is presented. There is one molecule in the asymmetric unit. The tricyclic carbolin framework is essentially planar and subtends an angle of 68.43 (19)° with the attached phenyl ring. In the crystal, the molecules are arranged in a zigzag pattern in the ac plane. Neighbouring molecules are connected via a twofold screw axis or a C ₂ axis parallel to the b axis or via a center of inversion.

This study investigates the fluorescent and mesomorphic properties of tetrakis(oxadiazolyl)benzenes (TOBEs) and -pyrazines (TOPYs), novel cruciform liquid crystals. The impact of a set of four side chains on optical and mesomorphic properties is reported. TOBE absorbs in the UV range (~360 nm), while substituting the central benzene ring by pyrazine (TOPY) shifts the absorption maximum to 396 nm but lowers the fluorescence quantum yield (TOBE: 72%; TOPY: 21%; in toluene). Fluorescence in the green-to-orange range is influenced by solvent polarity. Mesophase analysis shows quite narrow phases (~20 K) for TOBE. As the pyrazine core lowers the melting point and elevates the clearing temperature, huge mesophase ranges (~80–90 K) are detected for TOPY. Side chain variations further influence material properties: TOBE with linear alkyl chains exhibits multiple crystal–crystal transitions, while branching enhances mesophase stability and alters fluorescence characteristics. The Huisgen reaction provides a cost-effective synthetic route for these fluorescent mesogens, offering high yields and efficiency.

The tricyclic molecule of the title compound, C ₁₂ H ₁₄ O ₂ , is composed of four nearly planar subunits. Hydrogen bonds connect the ketol units to chains along the a -axis direction. The structure is further consolidated by two C—H...O hydrogen bonds, one to the carbonyl and one to the hydroxy group.

In the title salt, C ₂₁ H ₁₇ ⁺ ·ClO ₄ ⁻ , two hydrogen bonds from the tropylium moiety and the vinyl group connect the cation with oxygen atoms of the perchlorate anion. The perchlorate anion is surrounded by three tropylium cations. The tropylium rings of the cations, which are related via a C ₂ axis, are mostly parallel with a short distance between the centroids.

The molecules of the title compound, C ₁₉ H ₁₂ O ₂ , adopt a saddle shape, the o -xylylene fragments are almost planar. The carbonyl group and the ether oxygen atom are located on the same side of the carbon skeleton. The molecules are arranged in strands with alternating directions.