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.

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.

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.

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.

Thermotropic properties and molecular packing of discotic tristriazolotriazines with rigid substituents.

Tristriazolotriazines with a threefold dialkoxyaryl substitution have been prepared by Huisgen reaction of cyanuric chloride and the corresponding tetrazoles. Although these dyes show a negative or inverted solvatochromism of the UV/Vis absorption, their fluorescence is strongly positive solvatochromic. These discotic fluorophores are also emissive in their solid state and in their broad liquid-crystalline mesophase. The structural study indicates that the thermotropic properties and organization of these systems can be well tuned by the steric demand of the aryl groups. Depending on the substituents, the compounds showed either a pure crystalline phase or a highly complex helical superstructure with a characteristic liquid-crystalline phase at elevated temperatures. Changing the steric demand of the attached aryls allowed controlling the discs arrangement within the columnar helix, which is of great importance for the molecular orbital overlap.

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) Šfor 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) Šbetween the triazole and benzene rings is the closest contact between individual mol-ecules in the crystal.

3,7,11-Tris{4-[(1R,3S,4S)-neomenth-yl-oxy]phen-yl}tri[1,2,4]triazolo[4,3-a:4',3'-c:4'',3''-e][1,3,5]triazine-chloro-form-ethanol (1/1/1).

The title compound, C54H69N9O3·CHCl3·C2H5OH, was prepared by a threefold nucleophilic substitution of p-neomenthyloxyphenyl-tetra-zole on cyanuric chloride followed by threefold cyclo-elimination of nitro-gen and ring closure. The central tris-triazolotriazine is roughly planar with a maximum deviation of 0.089 (7) Šbut the adjacent benzene rings are twisted out of this plane. N-C-C-C torsion angles of -80.2 (9), 159.3 (7) and 50.6 (10)° destroy the formal C3 symmetry. Cavities are found between the phen-oxy residues: one is occupied by a chloro-form mol-ecule, another by ethanol forming a hydrogen bond to a triazole ring while two isopropyl groups point into the third void. One methyl group and the chloro-frm mol-ecule are disorderd and were refined using a split model.

(E)-N,N-Diethyl-2,6-diisopropyl-4-[2-(4-nitro-phen-yl)ethen-yl]aniline.

The title compound, C24H32N2O2, was prepared by Horner olefination of 4-di-ethyl-amino-3,5-diiso-propyl-benzaldehyde and diethyl p-nitro-benzyl-phospho-nate. There are two independent mol-ecules (A and B) in the asymmetric unit. Their main axes, defined by the line connecting the N atoms of the nitro and amino groups, open an angle of 79.42 (3)°. Steric hindrance around the amino group is reflected in a long aryl C-N bond [1.434 (3) Šfor mol-ecule A and 1.440 (3) Šfor mol-ecule B], a pyramidal geometry [angle sum = 350.0 (2)° for mol-ecule A and 349.6 (2)° for mol-ecule B], and dihedral angles between the phenyl-ene group and the plane defined by the CH2-N-CH2 unit of 86.9 (3)° for mol-ecule A and 88.3 (3)° for mol-ecule B. This gives structural support for the electronic decoupling of the amino group from the nearly planar nitro-stilbene moiety (r.m.s. deviation for C, N and O atoms = 0.097 for mol-ecule A and 0.107 Šfor mol-ecule B).

5,11-Dimethyl-6,12-dimeth-oxy-indolo[3,2-b]carbazole.

The title compound, C(22)H(20)N(2)O(2), was prepared in a twofold Cadogan cyclization followed by double N-methyl-ation. The crystal structure is characterized by a zigzag arrangement of centrosymmetric mol-ecules. The indolocarbazole framework is essentially planar [maximum deviation = 0.028 (2) Å] and the meth-oxy groups are orthogonal to this plane [C-C-O-C torsion angle = -88.2 (2)°]. The lengths of the C-N bonds are nearly identical and all C-C bonds of the pyrrole subunit are significantly longer than the C-C bonds in the benzene rings.

6,12-Bis(hex-yloxy)-5H,11H-indolo[3,2-b]carbazole.

The title compound, C30H36N2O2, was prepared in a twofold Cadogan cyclization. The mol-ecule is located about a center of inversion. The indolocarbazole skeleton is essentially planar [maximum deviation = 0.028 (2) Å], the C-N bond lengths are nearly identical and the C-C bond lengths of the pyrrole unit are significantly longer than those of the benzene subunits.

(Z)-4,5-Di-bromo-3,3,6,6-tetra-methyl-2,3,6,7-tetra-hydro-thiepine-1,1-dione.

The crystal of the title compound, C10H16Br2O2S, is formed from layers built from centrosymmetric pairs of mol-ecules. The mol-ecule adopts a twist conformation with the carbon atoms next to sulfur above or below the mean plane.

2,5-Bis[5-(3,5-dido-decyl-oxyphen-yl)-1,3,4-oxa-diazol-2-yl]-3,6-di-methyl-pyrazine.

The nearly planar mol-ecule of the title compound, C70H112N6O6, is centrosymmetric with two all-s-trans chains, the other two chains have an s-cis unit starting with the oxygen atoms. The chains are inter-digitated in the packing.

5-[(4-Methyl-phen-yl)sulfon-yl]-1-phenyl-thio-pyrano[4,3-b]indole-3(5H)-thione di-chloro-methane monosolvate.

Rhodium-catalyzed [2+2+2] cyclo-addition of carbon di-sulfide to o,N-dialkynyl-tosyl-anilines gives two isomeric indolo-thio-pyran-thio-nes, a violet and a red isomer. This is the first crystal structure of a red isomer, which crystallizes with one solvent mol-ecule of di-chloro-methane in the asymmetric unit, C24H17NO2S3·CH2Cl2. In the extended structure, centrosymmetric pairs of the planar annulated system are arranged in strands and solvent mol-ecules fill the space between the strands.

Decachloro-hexa-1,5-diene.

The title compound, C(6)Cl(10), cystallizes in a nearly C2-symmetrical gauche conformation. Both trichloro-vinyl groups are nearly planar [Cl-C-C-Cl torsion angles = -178.47 (12) and -179.93 (11)°] and the lengths of their C-Cl bonds increase from the terminal trans and cis C-Cl bonds to the inter-nal bonds. The Cl-C-Cl bond angles of the terminal dichloro-methyl-ene units are compressed to 111.75 (11) and 111.40 (11)°.

1,4-Dihex-yloxy-2,5-bis-(2-nitro-phen-yl)benzene.

The title compound, C(30)H(36)N(2)O(6), was prepared via twofold Suzuki coupling of a diboronic acid with bromo-nitro-benzene. The mol-ecule is located on a crystallographic inversion centre. The lateral benzene ring and the central ring make a dihedral angle of 48.75 (14)° and the nitro group is twisted by 41.47 (13)° out of the plane of the benzene ring. The nitro and hex-yloxy groups are in close proximity and the hex-yloxy chain adopts an all-anti conformation.

4-[2-(Benzyl-amino)-phen-yl]-2,6-dimethyl-quinoline N-oxide.

The title compound, C(24)H(22)N(2)O, was obtained in a two-step procedure from the corresponding 4-(2-iodo-phen-yl)quinoline. The quinoline system is approximately planar [maximum deviation from the least-squares plane = 0.021 (2) Å]. The planes of the quinoline system and the phenyl ring subtend a dihedral angle of 78.08 (8)°. In the crystal, pairs of mol-ecules are connected via a center of symmetry and linked by a pair of angular N-H⋯O hydrogen bond. These dimers form columns oriented along the c axis.

2,7-Bis(2-nitro-phen-yl)-9-octyl-9H-carbazole.

The title compound, C(32)H(31)N(3)O(4), was obtained in a Suzuki coupling of carbazole diboronic acid and bromo-nitro-benzene. In the crystal, the mol-ecule adopts a non-symmetric conformation. The carbazole ring system is approximately planar [maximum deviation from the least-squares plane = 0.039 (2) Å]. The planes of the carbazole unit and the benzene rings subtend dihedral angles of 48.42 (7) and 41.81 (6)°. The dihedral angles between the planes of the nitro-phenyl rings and the nitro groups are 44.34 (19) and 61.64 (15)°. The crystal is built from two strands of parallel mol-ecules with inter-digitated octyl chains. These strands are symmetry related by a twofold screw axis.

13,13'-Bi(dibenzo[a,i]fluorenyl-idene).

The asymmetric unit of the title compound, C42H24, contains two almost identical mol-ecules. The mol-ecules have approximate D 2 symmetry. They show a largely twisted double bond, the mol-ecular halves enclosing dihedral angles of 62.86 (4) and 61.22 (3)°. The crystal studied was twinned by non-merohedry.

N,N-Dihexyl-4-[2-(4-nitro-phen-yl)vin-yl]aniline.

The title compound, C(26)H(36)N(2)O(2), was prepared by Horner olefination of p-dihexyl-amino-benzaldehyde and diethyl p-nitro-benzyl-phospho-nate. It crystallizes with two independent mol-ecules in the asymmetric unit. Both have similar geometries of the π-systems but the conformations of all hexyl chains are different. Whereas one hexyl chain of the first mol-ecule shows the typical all-anti conformation, the second is arranged in a gauche-anti-gauche-anti conformation with N-C-C-C, C-C-C-C, C-C-C-C and C-C-C-C torsion angles of -65.1 (4), 167.3 (3), 63.3 (4), and 179.4 (3)°. One of the hexyl chains in the other mol-ecule has an anti-anti-gauche-anti conformation [N-C-C-C, C-C-C-C, C-C-C-C and C-C-C-C torsion angles = 179.6 (3), -179.8 (3), -68.7 (5) and -178.8 (4)°], the other starts with an anti-gauche-gauche sequence. Molecules A and B are composed of five planar subunits. The angle sums around the N atoms are in the range 356 (2)-360.0 (2)°. Torsion angles between these segments do not exceed 4.9 (4)°, except for one of the alkyl chains each [molecule A = 26.2 (4)°; molecule B = -6.0 (4)°]. The high planarity of the molecules and the short aniline C-N bonds [1.385 (3) Šin molecule A and 1.378 (3) Šin molecule B] indicate a strong electronic coupling through the stilbene unit. One methylene group is disordered over two positions with an occupancy ratio of 0.72:0.28.

Methyl 1-(7-acetamido-5,8-dimeth-oxy-quinolin-2-yl)-4-methyl-ß-carboline-3-carboxyl-ate.

The title compound, C(27)H(24)N(4)O(5), is an inter-mediate in the synthesis of lavendamycin via a ruthenium-catalysed [2 + 2 + 2] cyclo-addition. An intra-molecular hydrogen-bond bridge from the carboline to the quinoline stabilizes a highly planar geometry [maximum deviation = 0.065 (6) Å] for the two rigid units. This hydrogen-bond-stabilized coplanarity has a very close analogy in the structure of the anti-tumor anti-biotic streptonigrin in the solid state and in solution. Inter-molecular hydrogen-bond bridges of amides groups along the a axis and π-π stacking inter-actions [centroid-centroid distance = 3.665 (9) Å] connect mol-ecules arranged in a parallel manner.