Non-symmetric liquid crystal dimer containing a carbohydrate-based moiety

Abstract

The synthesis and characterisation of a novel non-symmetric liquid crystal dimer, 1-[3-O-(D-glucopyranos-3-yl)]-8-[(4-methoxyazobenzene-4'-oxy)]octane is reported. This exhibits glassy behaviour and a highly interdigitated smectic A phase in which the aromatic and alkyl structural fragments overlap. Variable temperature infrared spectroscopy reveals that the strength and extent of hydrogen bonding within the system does not show a marked change at either the glass transition or at the smectic A-isotropic transition. This observation indicates that the smectic A-isotropic transition is driven by changes in the van der Waals interactions between the molecules while hydrogen bonded aggregates persist into the isotropic phase.

New insights into the transitional behaviour of methyl-6-O-(n-dodecanoyl)-α-D-glucopyranoside using variable temperature FTIR spectroscopy and X-ray diffraction

“…[29,30] The regions of linear behaviour are also indicated in Figure 8, and we found a WTC Cr value of 0.79 cm −1 K −1 in the crystal phase. This is rather higher than those typically measured in a sugar-based glass or melt [28] and presumably reflects an equilibrium shifting towards free OH groups with temperature.…”

The role of hydrogen bonding in the phase behaviour of supramolecular liquid crystal dimers

“…We attribute this to the tendency of these mixtures to spontaneously align as evidenced by the observation of homeotropic textures when viewed through the polarised microscope. We saw similar, but more extreme behaviour, for hydrogen bonded liquid crystal sugars [34,35]. By contrast, the C-type band does not appear to change significantly on cooling, and this may reflect the different nature of the vibrations associated with this resonance band [48].…”

“…5. The decrease associated with crystallisation may be attributed to orientation effects discussed in detail elsewhere [34,35,46,47]. The observation of the B-type Fermi bands on cooling from the isotropic phase through the nematic and smectic C phases indicates extensive hydrogen bonding even at high temperatures.…”

Hydrogen bonding and liquid crystallinity of low molar mass and polymeric mesogens containing benzoic acids: a variable temperature Fourier transform infrared spectroscopic study

“…Similar behaviour has been reported for other liquid crystalline systems. [22,23,51] We also observe changes in bands in the 1480-1400 cm À1 region, associated with inplane bending, d, of the aliphatic CH groups, see Figure 5 inset. At the low-frequency end of this region (1450-1400 cm À1 ), the bands assigned earlier to C-H bonds in close proximity to the ether bond increase in intensity on increasing temperature, showing step changes at the phase transitions.…”

“…[16][17][18] Hydrogen bonding also plays a key role in driving liquid crystalline behaviour in a diverse range of other materials including commercially important high-performance fibres, [19] protonic conductors [20,21] and liquid crystal sugars. [22][23][24][25] Supramolecular SCLCPs have attracted particular attention and these have been assembled not only using hydrogen bonding (see, for example, [7,26,27]), but also by utilising other types of non-covalent interactions such as ionic bonding [28] and quadrupolar interactions. [29] In approaching the design of a supramolecular SCLCP, it is useful first to consider the molecular architecture of a conventional SCLCP, which comprises three structural elements: a polymer backbone, a flexible spacer and a mesogenic group.…”