Modulating the Conductivity of Light-Responsive Ionic Liquid Crystals.

In this work, we describe the phase behaviour and the dielectric and conductivity response of new light-responsive ionic liquid crystals, ILCs, which can be applied as controllable electrolytes. The materials include two different dicationic viologens, the asymmetric 6BP18 and the symmetric EV2ON(Tf)2, containing bistriflimide as the counterions, mixed with 5% and 50% molar, respectively, of one new photoresponsive mesogen called CNAzO14. These mixtures exhibit liquid crystal behaviour, light responsiveness through the E-Z photoisomerisation of the azobenzene groups in CNAzO14, and strong dielectric responses. The 5%-CNAzO14/Ev2ON(Tf)2 mixture displays direct current conductivities in the 10-7 S·cm-1 range, which can be increased by a two-fold factor upon the irradiation of UV light at 365 nm. Our findings set the grounds for designing new smart ionic soft materials with nanostructures that can be tuned and used for energy conversion and storage applications.

Investigation of the Crystal Structure and Ionic Pathways of the Hexagonal Perovskite Derivative Ba3-xVMoO8.5-x.

The hexagonal perovskite derivatives Ba3NbMoO8.5, Ba3NbWO8.5, and Ba3VWO8.5 have recently been reported to exhibit significant oxide ion conductivity. Here, we report the synthesis and crystal structure of the hexagonal perovskite derivative Ba3-xVMoO8.5-x. Rietveld refinement from neutron and X-ray diffraction data show that the cation vacancies are ordered on the M2 site, leading to a structure consisting of palmierite-like layers of M1Ox polyhedra separated by vacant octahedral layers. In contrast to other members of the Ba3M'M″O8.5 family, Ba3-xVMoO8.5-x is not stoichiometric and both barium and oxygen vacancies are present. Although synthesized in air at elevated temperatures, Ba3-xVMoO8.5-x is unstable at lower temperatures, as illustrated by the formation of BaCO3 and BaMoO4 by heat treatment in air at 400 °C. This precludes measurement of the electrical properties. However, bond-valence site energy (BVSE) calculations strongly suggest that oxide ion conductivity is present in Ba3-xVMoO8.5-x.

Liquid Crystalline Copolymers Containing Sulfonic and Light-Responsive Groups: From Molecular Design to Conductivity.

In the search for novel smart multifunctional liquid crystalline materials, we report the synthesis, thermal and structural characterisation, and the conductivity, of a set of new block and statistical copolymers, containing light-responsive mesogenic groups (MeOAzB), polar sulfonic acids (AMPS), and methyl(methacrylate) groups (MMA). By using a cascade of reversible addition-fragmentation chain polymerisations, RAFT, we have tailored different side-chain polymeric structures by controlling monomer composition (MeOAzB/AMPS/MMA) and configuration. We have yielded simultaneous liquid crystalline behaviour and appreciable conductivity in polymers with low concentrations of polar acid groups, by the formation of smectic phases in narrow aggregates. The light-responsiveness of the polymers, via reversible trans-to-cis photoisomerization of azobenzene groups, and the local activation of conductivity at relatively low temperatures, opens the possibility to prepare polymer electrolytes for energy conversion and storage, whose conductivity could be controlled and optimised by external stimuli, including light irradiation.

Molecular Recognition via Hydrogen Bonding in Supramolecular Complexes: A Fourier Transform Infrared Spectroscopy Study.

We assess the assembly of supramolecular complexes by hydrogen bonding between azocompounds and a diacylaminopyridine monomer by temperature-dependent Fourier transform infrared spectroscopy (FT-IR) and density functional theory (DFT) calculations. The electronic delocalisation in the supramolecular rings formed by multiple hydrogen bonds stabilises the complexes, which coexist with dimeric species in temperature-dependent equilibria. We show how the application of readily available molecular modelling and spectroscopic techniques can predict the stability of new supramolecular entities coexisting in equilibria, ultimately assessing the success of molecular recognition.

A twist-bend nematic phase driven by hydrogen bonding.

The liquid crystalline phase behavior of 4-[6-(4'-cyanobiphenyl-4-yl)hexyloxy]benzoic acid (CB6OBA) and 4-[5-(4'-cyanobiphenyl-4-yloxy)pentyloxy]benzoic acid (CBO5OBA) is described. Both acids show an enantiotropic nematic phase attributed to the formation of supramolecular complexes by hydrogen bonding between the benzoic acid units. In addition, CB6OBA provides the first example of hydrogen bonding driving the formation of the twist-bend nematic phase. The observation of the twist-bend nematic phase for CB6OBA, but not CBO5OBA, is attributed to the more bent molecular shape of the complexes formed by the former, reinforcing the view that shape is a key factor in stabilizing this new phase. Temperature-dependent FTIR spectroscopy reveals differences in hydrogen bonding between the two nematic phases shown by CB6OBA which suggest that the open hydrogen-bonded complexes may play an important role in stabilizing the helical arrangement found in the twist-bend nematic phase.

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

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.