Assembly of supramolecular polymers in ultrathin films

The first series of liquid crystal dimers to contain an isoflavone-based moiety has been prepared, the α-(4'-methoxy-3-phenyl-4H-1-benzopyran-4-one-7-oxy)-ω-(4-methoxyazobenzene-4'-oxy)alkanes. All eight members of this homologous series exhibit an enantiotropic nematic phase. The nematic–isotropic transition temperatures and associated entropy changes exhibit a dramatic dependence on the length and parity of the flexible spacer. This characteristic behaviour for a homologous series of liquid crystal dimers has been interpreted in terms of how the flexible alkyl spacer controls the average molecular shape. A comparison of the transitional properties of this series with those of the symmetric parent dimers, the α,ω-bis(4-methoxyazobenzene-4'-oxy)alkanes, reveals that replacing a methoxyazobenzene unit by the isoflavone-based group reduces the melting point but increases the nematic–isotropic transition temperature. Three other non-symmetric dimers are reported: 1-(4'-methoxy-3-phenyl-4H-1-benzopyran-4-one-...

Non-symmetric liquid crystal dimers containing an isoflavone moiety

The structural and acidic properties of sol–gel prepared alumina powders as catalyst supports were modified by adjusting the hydrolysis ratio, R (i.e. molar ratio of water relative to the alumina precursor, R=[H2O]/[aluminium-tri-sec-butoxide (ASB)]). Structural properties (e.g. porosity) and acidic properties were measured for alumina powders prepared with various R values, from 3 to 13. For R 10, first-order particles were closely packed with ink-bottle-type pore structures, whereas for R=9 or 10, first-order particles were loosely packed with a spatial fractal arrangement that yielded pseudo-cylindrical pore structures. In addition, the alumina powders prepared with R=9 or 10 had larger water pore volume and stronger acidity than those with other R values. These properties unique to the powders prepared with R=9 or 10 were ascribed to relatively short Al–O–Al chain lengths that resulted in loose packing of first-order particles. The results here indicate that alumina powders with favorable properties as catalyst supports (e.g. mean pore diameter) can be tailored by selecting the appropriate R in the sol–gel synthesis process.

Modification of structural and acidic properties of sol–gel-prepared alumina powders by changing the hydrolysis ratio

A new homologous series of 7‐acyloxy‐3‐(4‐acyloxyphenyl)‐4H‐1‐benzopyran‐4‐ones was synthesized and characterized by elemental analysis and spectroscopic techniques along with thermal behaviour study using differential scanning calorimetry. Texture observation was performed under the polarizing optical microscope from which the derivatives were found to exhibit different molecular organizations as exemplified by various mesophases. Whilst the compounds containing butanoyloxy and hexanoyloxy groups behave as nematogens, the other compounds with heptanoyloxy and longer side chains show a SmC phase. The octadecanoyloxy derivative was the only member showing a monotropic SmC phase. The difference in phase behaviour is discussed based on the molecular structure and the presence of a lateral dipole which can be associated with the intermolecular interaction within the mesophase.

Synthesis and mesomorphic properties of 7‐acyloxy‐3‐(4‐acyloxyphenyl)‐4H‐1‐benzopyran‐4‐one

Side chain liquid crystalline polymers at interfaces

With few mesogenic chromone derivatives in the literature the synthesis of 7-[4′-n-alkyloxybenzoyloxy) isoflavones was carried out. The resulting homologous series was characterized by elemental an...

Synthesis and characterization of 3-phenyl-4[H]-4-[one]-benzopyran (isoflavone) derivatives as potential mesogens

A series of alumina samples were prepared with aluminium secondary butoxide (ASB) as precursor. The effect of variations in preparation parameters like nature of hydrolysing solvents and pH during hydrolysis were investigated. The total surface area (SA), pore size distribution, pore volume (PV), alumina phase and morphology were determined for various samples. It was observed that alumina prepared in this method has a high surface ml/g. A major part of the surface area is present in mesoporous region with radii around the dominant pore radius of 105. Changes in the pore-structure and pore size distribution could be observed by : (i) varying the medium of hydrolysis from water to a mixture of water and iso- propyl alcohol and (ii) carrying out hydrolysis at base / alkoxide mole ratios 0.3 to 1.1. For a given ratio of water / ASB, PV and SA increased with base / alkoxide ratio.

Rajan Bosco

Papers

Synthesis and characterization of 3-phenyl-4[H]-4-[one]-benzopyran (isoflavone) derivatives as potential mesogens

Alumina through sol-gel route : Influence of preparation parameters