Polycatenar amphiphilic liquid crystals

In order to study the effect on mesophase organisation of incorporating groups (hydrocarbon and fluorocarbon) that normally phase separate into the same liquid-crystalline molecules, a series of tri- and tetra-catenar mesogens has been prepared containing various combinations of hydrocarbon (CnH2n+1–: n = 12 or 14) and semiperfluorocarbon (CmF2m+1(CH2)4–; m = 8 or 10) chains. In addition, many of the intermediate compounds prepared en route were studied for their liquid crystal properties. The semiperfluorocarbon chains were added using Williamson ether chemistry with CmF2m+1(CH2)4Br, itself prepared via a radical addition of CmF2m+1I to 3-buten-1-ol to give a secondary iodide which was deiodinated in a radical process. Conversion of the alcohol to the bromide used HBr under phase-transfer conditions. The properties of the new compounds were elucidated using optical microscopy, differential scanning calorimetry and low-angle X-ray diffraction. The all-hydrocarbon compounds had been prepared previously and their mesomorphism was qualitatively identical to that of the all-semiperfluorocarbon analogues. However, when both hydrocarbon and semiperfluorocarbon chains were mixed in the same molecule, there was a significant change in behaviour as the mesogens organised themselves in order to maximise hydrocarbon-hydrocarbon and fluorocarbon-fluorocarbon interactions while minimising hydrocarbon-fluorocarbon interactions. For example, with tricatenar mesogens with a fluorocarbon chain at one end, this manifested itself as a doubling of the lamellar periodicity, while in unsymmetric tetracatenar mesogens, a reduction in phase symmetry from hexagonal (p6mm) to rectangular (p2gg) was seen along with a massive increase in lattice parameter

pH and Solvent Influence on p-Aminobenzoic Acid

Through X-ray absorption and emission spectroscopies, the chemical, electronic and structural properties of organic species in solution can be observed. Near-edge X-ray absorption fine structure (NEXAFS) and resonant inelastic X-ray scattering (RIXS) measurements at the nitrogen K-edge of para- aminobenzoic acid reveal both pH- and solvent-dependent variations in the ionisation potential (IP), 1s→π* resonances and HOMO–LUMO gap. These changes unequivocally identify the chemical species (neutral, cationic or anionic) present in solution. It is shown how this incisive chemical state sensitivity is further enhanced by the possibility of quantitative bond length determination, based on the analysis of chemical shifts in IPs and σ* shape resonances in the NEXAFS spectra. This provides experimental access to detecting even minor variations in the molecular structure of solutes in solution, thereby providing an avenue to examining computational predictions of solute properties and solute–solvent interactions

Incompatibility-Driven Self-Organization in Polycatenar Liquid Crystals Bearing Both Hydrocarbon and Fluorocarbon Chains

The synthesis and liquid crystal properties are reported for tri-and tetra-catenar mesogens in which both hydrocarbon and semiperfluorocarbon chains have been incorporated. In the tricatenar mesogens, the lamellar spacing in the smectic C phase of the all-hydrocarbon mesogen almost doubles when the isolated hydrocarbon chain is replaced by a semiperfluorinated chain on account of the localized segregation in different sublayers between the two chain types. In the tetracatenar materials, the replacement of at least one hydrocarbon chain by semiperfluorocarbon chains is sufficient to promote columnar phase formation, but when the molecule has two hydrocarbon chains at one end and two semiperfluorocarbon chains at the other, the requirement for localized phase segregation leads to the formation of a rectangular phase with very large lattice parameters. The juxtaposition of terminal chains of different nature within the same molecular structure thus leads to a reduction in mesophase symmetry and the emergence of more complex supramolecular organization

Intermolecular Bonding of Hemin in Solution and in Solid State Probed by N K-edge X-ray Spectroscopies

X-ray absorption/emission spectroscopy (XAS/XES) at the N K-edge of iron protoporphyrin IX chloride (FePPIX-Cl, or hemin) has been carried out for dissolved monomers in DMSO, dimers in water and for the solid state. This sequence of samples permits identification of characteristic spectral features associated with the hemin intermolecular bonding. These characteristic features are further analyzed and understood at the molecular orbital (MO) level based on the DFT calculations

NEXAFS Sensitivity to Bond Lengths in Complex Molecular Materials: A Study of Crystalline Saccharides

Detailed analysis of the C K near-edge X-ray absorption fine structure (NEXAFS) spectra of a series of saccharides (fructose, xylose, glucose, galactose, maltose monohydrate, α-lactose monohydrate, anhydrous β-lactose, cellulose) indicates that the precise determination of IPs and σ* shape resonance energies is sensitive enough to distinguish different crystalline saccharides through the variations in their average C–OH bond lengths. Experimental data as well as FEFF8 calculations confirm that bond length variations in the organic solid state of 10–2 Å can be experimentally detected, opening up the possibility to use NEXAFS for obtaining incisive structural information for molecular materials, including noncrystalline systems without long-range order such as dissolved species in solutions, colloids, melts, and similar amorphous phases. The observed bond length sensitivity is as good as that originally reported for gas-phase and adsorbed molecular species. NEXAFS-derived molecular structure data for the condensed phase may therefore be used to guide molecular modeling as well as to validate computationally derived structure models for such systems. Some results indicate further analytical value in that the σ* shape resonance analysis may distinguish hemiketals from hemiacetals (i.e., derived from ketoses and aldoses) as well as α from β forms of otherwise identical saccharides

X-ray powder diffraction patterns for each saccharide compared to calculated crystal structure patterns; results of FEFF8 calculations for each C atom in glucose with equilibrium, elongated and shortened C–O bond lengths (PDF); Raw NEXAFS data files (ZIP) Athena project file with fitted NEXAFS spectra (ZIP)

Detailed analysis of the C K near-edge X-ray absorption fine structure (NEXAFS) spectra of a series of saccharides (fructose, xylose, glucose, galactose, maltose monohydrate, α-lactose monohydrate, anhydrous β-lactose, cellulose) indicates that the precise determination of IPs and σ* shape resonance energies is sensitive enough to distinguish different crystalline saccharides through the variations in their average C–OH bond lengths. Experimental data as well as FEFF8 calculations confirm that bond length variations in the organic solid state of 10–2 Å can be experimentally detected, opening up the possibility to use NEXAFS for obtaining incisive structural information for molecular materials, including noncrystalline systems without long-range order such as dissolved species in solutions, colloids, melts, and similar amorphous phases. The observed bond length sensitivity is as good as that originally reported for gas-phase and adsorbed molecular species. NEXAFS-derived molecular structure data for the condensed phase may therefore be used to guide molecular modeling as well as to validate computationally derived structure models for such systems. Some results indicate further analytical value in that the σ* shape resonance analysis may distinguish hemiketals from hemiacetals (i.e., derived from ketoses and aldoses) as well as α from β forms of otherwise identical saccharides