Search

Suzuki cross‐couplings either between chlorinated N‐methyliminodiacetic acid (MIDA)‐protected aryl boronates and 1,3,5‐tribromobenzene or between chlorinated aryl bromides and phenyltrisboronic species to star‐shaped 1,3,5‐triphenylbenzenes with different substitution patterns and chloro substituents at the outer phenyl rings were studied. The chlorinated precursors required for the respective reaction were synthesized and characterized. Depending on the used coupling reaction target triphenylbenzenes were isolated in yields between 42 % and 88 %. Their mesomorphic properties were influenced by the substitution pattern and number of peripheral chlorine atoms. Triphenylbenzene with 3,5‐alkoxy substitution and H in para‐position self‐assembled into either columnar hexagonal (Colh) mesophases or a soft crystal. While threefold chloro substitution in meta‐position of the outer phenyl rings led to stable room temperature Colho phases, triphenylbenzenes with threefold para‐chloro or 3,5‐dichloro substitution were non‐mesomorphic. Based on X‐ray diffraction data a helical packing model for the observed phases similar to that of related alkoxy‐substituted triphenylbenzenes was proposed. [ABSTRACT FROM AUTHOR]

Star-shaped nonaalkoxy-1,3,5-triphenyltriazines were prepared and their mesomorphism was investigated by differential scanning calorimetry (DSC), polarised optical microscopy (POM) and X-ray diffraction (WAXS and SAXS). Compounds with chain lengths C9 – C12 displayed enantiotropic hexagonal columnar mesophases over a wide range of temperature. Their similarity in molecular size and mesomorphism prompted us to study their binary mixtures with previously reported planar 1,3,5-triphenylboroxines and propeller-shaped 1,3,5-triphenylbenzenes. All three compounds are fully miscible in their hexagonal columnar mesophases, but mixtures of planar with propeller-shaped compounds generated columnar stacks that contain only one type of molecule to avoid their shape incompatibility. However, the two types of columnar stacks were fully miscible which circumvented macroscopic phase separation. [ABSTRACT FROM AUTHOR]

A small series of dendrimers consisting of a star-shaped triphenylbenzene core unit and bulky lateral groups was synthesised and their mesomorphic properties were investigated via differential scanning calorimetry, polarising optical microscopy and small- and wide-angle X-ray scattering (WAXS). The dendrimers showed two enantiotropic hexagonal columnar mesophases. The combination of temperature-dependent and fibre-extruded WAXS revealed a helical arrangement in the low-temperature and a zig-zag orientation in the high-temperature mesophase. Furthermore, at the mesophase-to-mesophase transition, the intracolumnar reorganisation and the intercolumnar lattice extension occurred at different time scales, with the latter process being the slower one. [ABSTRACT FROM AUTHOR]

A series of MIDA ( N-methylimino diacetic acid) boronates carrying 4-alkoxy, 3,4-bisalkoxy, or 3,4,5-trisalkoxyphenyl substituents were synthesized and their mesomorphic properties characterized by differential scanning calorimetry (DSC), polarizing optical microscopy (POM), and X-ray diffraction (XRD) techniques such as small- and wide-angle X-ray scattering (SAXS and WAXS, respectively). Most derivatives were liquid crystalline. In the case of mono- and bisalkoxy-substituted derivatives, C6 chains already induced smectic A (SmA) mesophases despite the bulky MIDA head group. With increasing chain length, columnar hexagonal (Colh) phases replaced SmA phases in the disubstituted series. Quantum chemical calculations on a series of MIDA boronates show that the B−N bond is a dative bond with a positive charge on the boron atom and negative charges on the nitrogen and oxygen atoms. In addition, no π-interaction between the aryl moiety and B−N bond was found, thus the mesogenic unit is electronically decoupled from the MIDA head group. These theoretical findings were supported by IR and Raman spectra as well as by asingle crystal structure analysis of 4-ethoxyphenyl MIDA boronate. Calculations of the electrostatic potential of the MIDA boronate reveal a special polarity pattern that can support the formation of a two-dimensional network and is likely to explain the liquid crystalline self-assembly. The absence of any electronic cross-talk between the MIDA head group and B-aryl or B-alkyl substituents allows the efficient tailoring of the mesophase type through variation of the substituents. [ABSTRACT FROM AUTHOR]

Sterically congested o-terphenyl crown ethers with alkoxy substituents at the 2,3,4-position or 3,4,5-position were synthesized from the corresponding tetrabromodibenzo[15]crown-5 and the corresponding boronic acids or borolanes via Suzuki cross-coupling and subsequently cyclized to the corresponding triphenylenes utilizing the Scholl reaction. Both series of compounds were investigated by differential scanning calorimetry, polarizing optical microscopy, and X-ray diffraction (SAXS, WAXS) regarding their mesomorphic properties. While all but one of the 3,4,5-substituted derivatives displayed liquid crystalline behavior (Colh and Colr), only the 2,3,4-substititued triphenylene with the shortest alkoxy chains was liquid crystalline (Colr). [ABSTRACT FROM AUTHOR]

A new synthetic approach to highly substituted triphenylboroxines 11 is described. Their mesomorphic properties were investigated by differential scanning calorimetry (DSC), polarizing optical microscopy (POM) and X-ray diffraction (SAXS, WAXS). The tris(3,4,5-trialkyloxy)phenyl functionalized derivatives 11b-e showed broad mesophases for a minimum alkyl chain length of C9. The phase widths ranged from 110 K to 77 K near room temperature, thus decreasing with enhanced alkyl chain lengths. Textures observed under POM indicated a columnar hexagonal (Colh) mesophase symmetry that was confirmed by X-ray diffraction experiments. [ABSTRACT FROM AUTHOR]

A new synthetic approach to highly substituted triphenylboroxines 11 is described. Their mesomorphic properties were investigated by differential scanning calorimetry (DSC), polarizing optical microscopy (POM) and X-ray diffraction (SAXS, WAXS). The tris(3,4,5-trialkyloxy)phenyl functionalized derivatives 11b-e showed broad mesophases for a minimum alkyl chain length of C9. The phase widths ranged from 110 K to 77 K near room temperature, thus decreasing with enhanced alkyl chain lengths. Textures observed under POM indicated a columnar hexagonal (Colh) mesophase symmetry that was confirmed by X-ray diffraction experiments. [ABSTRACT FROM AUTHOR]

Cover Feature: Columnar Propeller-Like 1,3,5-Triphenylbenzenes: Probing the Effect of Chlorine on the Suzuki Cross-Coupling and Liquid Crystalline Properties (Eur. J. Org. Liquid crystalline properties, visualized by POM textures and SAXS diffraction patterns, were strongly dependent on the symmetry of the chloro vs. alkoxy substitution pattern. Liquid crystalline properties, visualized by POM textures and SAXS diffraction patterns, were strongly dependent on the symmetry of the chloro vs. alkoxy substitution pattern. [Extracted from the article]

Discotic liquid crystals are promising materials for electronic device applications. Combining extended π-systems with crown ethers may further open access to functional supramolecular hybrid materials. In the present publication, we briefly summarise recent literature developments and focus in a second part on our work in the field of discotic crown ethers. The crown ether derivatives are conveniently accessible by convergent syntheses which allow a high degree of variation with respect to side chains, mesogenic unit, size and symmetry of the crown core, metal complexation and counterion. This set of compounds provides a basis for systematic structure–property relationship investigations. Numerous experimental studies identified factors being crucial for mesophase stabilisation and geometry and furthermore led to novel room-temperature crown ether mesogens. The latter were obtained by congestion of the mesogenic units and even introduction of peripheral δ-methyl branched side chains. The formation of molybdenum clustomesogens and their application as luminescent hybrid materials is also described. [ABSTRACT FROM AUTHOR]

A series of ionic liquid crystals with an alkoxy biphenyl unit tethered via an alkyl spacer to a guanidinium head group were synthesised and the mesomorphic properties were studied by differential scanning calorimetry, polarising optical microscopy and X-ray diffraction (XRD; WAXS and SAXS). Whereas all symmetrical guanidinium chlorides with the same chain lengths in alkyl tail and spacer displayed enantiotropic SmA2phases, monotropic SmC2phases with 1–2 K temperature range were only formed for chain lengths ≥ C10. Shifting the calamitic core more closely to the ionic head group by decreasing the tether length and simultaneously increasing the terminal alkyl chain improved the stability of both SmA and SmC phases considerably and led to enantiotropic SmC phases for the guanidinium chloride with C14alkyl tail and C6spacer. An even more pronounced effect was detected during anion exchange. Bromide, iodide, hexafluorophosphate, thiocyanate and triflate suppressed any SmC phase, whereas tetrafluoroborate behaved similar to chloride maintaining the SmC phase. However, acetate stabilised the SmC phase at the expense of the SmA phase. Based on temperature-dependant XRD measurements, a bilayer structure was proposed. [ABSTRACT FROM PUBLISHER]

A series of cyanobiphenyl dimers attached via alkoxy spacers to a central malonate were prepared, and the mesomorphic behaviour was studied by differential scanning calorimetry (DSC), polarised optical microscopy and X-ray diffraction (Wide-angle X-ray scattering and Small-angle X-ray scattering). Depending on spacer lengths and substitution of the malonate, nematic and smectic A mesophases with pronounced odd-even effect were observed. C-2-unsubstituted malonates formed nematic phases for chain lengths C6-C14, while C12 and C14 homologues displayed additional smectic A phases. In contrast, malonates with fluorinated tails at C-2 displayed exclusively smectic A phases. Remarkably, the X-ray diffraction profile of the smectic A phase of the C-2-unsubstituted C12 malonate showed a fundamental (001) and the corresponding third-order (003) diffraction peak, but no (002) reflection. Using Fourier analysis, the diffraction pattern was converted to an electron density profile, which was in good agreement with the proposed packing model of the SmA mesophase based on a horseshow- or hairpin-like conformation of the malonate. [ABSTRACT FROM AUTHOR]

Synthetic strategies were developed to prepare l-tyrosine-based ionic liquid crystals with structural variations at the carboxylic and phenolic OH groups as well as the amino functionality. Salt metathesis additionally led to counterion variation. The liquid-crystalline properties were investigated by differential scanning calorimetry (DSC), polarizing optical microscopy (POM) and X-ray diffraction (WAXS, SAXS). The symmetrical ILC chlorides bearing the same alkyl chain at both the ester and ether but either an acyclic or cyclic guanidinium group displayed enantiotropic SmA2 mesophases with phase widths of 31-88 K irrespective of the head group. It was particularly the replacement of chloride in the acyclic guanidinium ILC by hexafluorophosphate that induced a phase change from SmA2 to Colr. This phase change was attributed to a higher curvature of the interface due to the larger anion, which increased the effective head group cross-sectional area of the amphiphilic ILC. The unsymmetrical acyclic guanidinium chlorides, bearing a constant C14 ester and variable alkyl chains on the phenolic position, formed enantiotropic SmA2 phases. The derivative with the largest difference in chain lengths, however, displayed a Colr phase, resulting from discoid aggregates of the cone-shaped guanidinium chloride. The results are discussed in terms of the packing parameters, which indicate that the phase behaviour of the thermotropic tyrosine-based ILCs shows analogies to those of lyotropic liquid crystals. [ABSTRACT FROM AUTHOR]