Stereochemical Control of Nonamphiphilic Lyotropic Liquid Crystals: Chiral Nematic Phase of Assemblies Separated by Six Nanometers of Aqueous Solvents

Abstract

Unlike conventional thermotropic and lyotropic liquid crystals, nonamphiphilic lyotropic liquid crystals consist of hydrated assemblies of nonamphiphilic molecules that are aligned with a separation of about 6 nm between assemblies in an aqueous environment. This separation raises the question of how chirality, either from chiral mesogens or chiral dopants, would impact the phase as the assemblies that need to interact with each other are about 6 nm apart. Here, we report the synthesis of three stereoisomers of disodium chromonyl carboxylate, 5′DSCG-diviol, and the correlation between the molecular structure, bulk assembly, and liquid crystal formation. We observed that the chiral isomers (enantiomers 5′DSCG-(R,R)-diviol and 5′DSCG-(S,S)-diviol) formed liquid crystals while the achiral isomer 5′DSCG-meso-diviol did not. Circular dichroism indicated a chiral conformation with bisignate cotton effect. The nuclear Overhauser effect in proton NMR spectroscopy revealed conformations that are responsible for liquid crystal formation. Cryogenic transmission electron microscopy showed that chiral 5′DSCG-diviols form assemblies with crossings. Interestingly, only planar alignment of the chiral nematic phase was observed in liquid crystal cells with thin spacers. The homeotropic alignment that permitted a fingerprint texture was obtained only when the thickness of the liquid crystal cell was increase to above ∼500 μm. These studies suggest that hydrated assemblies of chiral 5′DSCG-diviol can interact with each other across a 6 nm separation in an aqueous environment by having a twist angle of about 0.22°throughout the sample between the neighboring assemblies.

Planar anchoring strength and pitch measurements in achiral and chiral chromonic liquid crystals using 90-degree twist cells

“…Some substituted oxiranes and thiiranes in the nematic liquid crystal p-methoxybenzylidene p-n butylaniline yield HTPs in the range of (0.5 to 40) × 10 −2 μm −1 wt% −1 [27]. A chiral isomer of a molecule very similar to DSCG has been synthesized, 5'DSCG-(R,R)-divol, and an 18 wt% mixture in water has a pitch of about 10 μm [12].…”

“…Fingerprint textures have been observed for chromonic liquid crystals, but they are not nearly as robust as for thermotropic liquid crystals [3,11,12]. The best one can do seems to be a texture with some areas showing the half-pitch repeat distance because the helical pitch axis is parallel to the glass surfaces, but with many areas in between showing no repeating pattern.…”

“…Examples of such studies include measurements of the order parameter, birefringence, elastic constants, and polar anchoring strength [6][7][8][9][10]. Almost all of these measurements have been in achiral systems, with only a few reports of studies done on chiral nematic chromonic liquid crystals [3,11,12].…”

“…It is known that addition of a water soluble chiral compound causes the chromonic liquid crystal orientation to twist in what is known as the chiral nematic phase [3,11,12]. Understanding how these chiral nematics orient in a 90-degree twist cell allows the intrinsic pitch of the chiral nematic phase to be measured from optical measurements because the anchoring strength is known.…”

Fully Stable and Homogeneous Lyotropic Liquid Crystal Alignment on Anisotropic Surfaces

“…Earlier works to obtain large‐scale alignment follow substrate‐based approaches developed for thermotropic LCs, including alignment on polyimide (PI) substrates, rubbed glass, nanopatterned polymer films, self‐assembling monolayers, photosensitive surfaces and, very recently with photonic metamasks . In general, such substrates align thermotropics much better than LCLC solutions.…”