Vance E. Williams

Self-assembly of hydrogen-bonded molecules: discotic and elliptical mesogens

The effect of hydrogen bonding on the phase behaviour of discotic mesogens was investigated with a series of dibenzophenazine carboxylic acids and their methyl ester analogues. The esters exhibit only columnar hexagonal phases, while the acids form columnar hexagonal, columnar rectangular and nematic mesophases. The acids have much higher transition temperatures and supercool to room temperature while maintaining the liquid crystalline ordering. These differences could be explained by the ability of the acids to form hydrogen-bonded dimers, which may also be regarded as supramolecular elliptically-shaped mesogens.

Synthesis of unsymmetrical dibenzoquinoxaline discotic mesogensElectronic supplementary information (ESI) available: full synthetic and analytical details, POM images. See http://www.rsc.org/suppdata/cc/b4/b400998c/

Unsymmetrical dibenzophenazine discotic mesogens were prepared via the corresponding tetraalkoxybenzil derivatives. These dibenzophenazines exhibit Colho phases over extremely broad temperature ranges.

An investigation of the mesogenic properties of dibenzoquinoxaline derivatives

Abstract The syntheses of two new discotic molecules based on the dibenzoquinoxaline core are reported; comparison of their phase behaviors to a known dinitrile compound demonstrates the importance of specific functional groups in stabilizing columnar mesophases.

Synthesis of a hexaalkoxybenzo[b]triphenylene mesogenElectronic supplementary information (ESI) available: full synthetic and analytical details. See http://www.rsc.org/suppdata/cc/b3/b305462d/

The synthesis of the first mesogenic hexaalkoxybenzo[b]triphenylene derivative is reported; this compound exhibits a broad columnar liquid crystal phase at temperatures only slightly above room temperature.

Modular assembly of elliptical mesogens

Discotic mesogens featuring a pyridine ring were synthesized, and were found either to form ordered hexagonal columnar liquid crystalline phases or melt directly from a crystal to an isotropic liquid, depending on the position of the pyridyl nitrogen atom. Binary mixtures of the mesogenic pyridine derivatives with a similar discotic mesogen having a carboxylic acid group resulted in the formation of modular elliptical complexes through hydrogen bonding. The binary mixtures were found to exhibit ordered hexagonal columnar or ordered rectangular columnar and nematic mesophases, depending on the length of the alkyl chains, and displayed dramatically different properties from their constituent components. Binary mixtures of the non‐mesogenic pyridine derivatives with carboxylic acid‐functionalized discotic mesogens did not result in the formation of hydrogen‐bonded complexes.

Structural Design Parameters for Highly Birefringent Coordination Polymers.

A series of coordination polymer materials incorporating the highly anisotropic 2-(2-pyridyl)-1,10-phenanthroline (phenpy) building block have been synthesized and structurally characterized. M(phenpy)[Au(CN)2]2 (M = Cd, Mn) are isostructural and form a 1-D chain through bridging [Au(CN)2](-) units and extend into a 2-D sheet through aurophilic interactions. M(phenpy)(H2O)[Au(CN)2]2·2H2O (M = Cd, Mn, and Zn) are also isostructural but differ from the first set via the inclusion of a water molecule into the coordination sphere, resulting in a 1-D topology through aurophilic interactions. In(phenpy)(Cl)2[Au(CN)2]·0.5H2O forms a dimer through bridging chlorides and contains a free [Au(CN)2](-) unit. In the plane of the primary crystal growth direction, the birefringence values (Δn) of 0.37(2) (Cd(phenpy)[Au(CN)2]2), 0.50(3) (In(phenpy)(Cl)2[Au(CN)2]·0.5H2O), 0.56(3) and 0.59(6) (M(phenpy)(H2O)[Au(CN)2]2·2H2O M = Cd and Zn, respectively) were determined. β, a structural parameter defined by phenpy units rotated in the A-C plane relative to the light propagation (C) direction, was found to correlate to Δn magnitudes. The addition of a carbon-carbon double bond to terpy has increased the molecular polarizability anisotropy of the building block, and all structures have reduced deviation from planarity in comparison to terpy and terpy derivative structures, leading to these higher Δn values, which are among the highest reported for crystalline solids.

Dibenz[a,c]anthracene derivatives exhibiting columnar mesophases over broad temperature ranges

We report the synthesis and characterization of a series of novel hexaalkoxydibenz[a,c]anthracenes. While the parent compound is not mesomorphic, the introduction of substituents in the 10- and 13-positions yields compounds with columnar liquid crystalline phases over very broad temperature ranges.

A simple and inexpensive capillary furnace for variable-temperature X-ray diffraction

An inexpensive capillary furnace has been developed for variable-temperature X-ray diffraction in transmission geometry of air-stable liquid crystals and other materials. It offers temperature control with fluctuations of less than ±1 K in the range of interest for these samples, from room temperature to near 573 K. Phases can be accessed through heating or cooling with no significant overshooting of the target temperature. The furnace is designed to fit on a classical goniometer, and can be controlled by any standard temperature controller. The simple design of this furnace means that it is both inexpensive to build and easy to operate.

Investigation into the role of the hydrogen bonding network in cyclodextrin-based self-assembling mesophases

A series of novel amphiphilic β-CD derivatives capable of forming hydrogen bonding networks of different strengths have been synthesized to probe the role of the hydrogen bonding network in the formation of self-assembled mesophases. Using differential scanning calorimetry (DSC), cross-polarized optical microscopy (POM) and X-ray diffractometry, two compounds were found to exhibit smectic mesophases. These correlated well with their abilities to form a hydrogen bonding network with sufficient strength to self-assemble. It was also observed that modifying the secondary face to interfere with the hydrogen bonding network significantly affects the Tc of a CD amphiphiles while the Tm temperature was not greatly affected.

Birefringent, emissive coordination polymers incorporating bis(benzimidazole)pyridine as an anisotropic building block

Coordination polymers Ln(BBP)2[Au(CN)2]3·2(CH3CN) (Ln = Eu, Gd) and Ln(BBP)(NO3)2[Au(CN)2]·(CH3CN) (Ln = Eu, Gd, Tb) have been synthesized. They incorporate bis(benzimidazole)pyridine (BBP), a highly anisotropic building block which, in conjunction with Ln centres and [Au(CN)2]− units generates the first highly birefringent, emissive coordination polymer materials.