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In lyotropic chromonic liquid crystals (LCLCs), twist distortion of the nematic director costs much less energy than splay or bend distortion. This feature leads to novel mirror-symmetry breaking director configurations when the LCLCs are confined by interfaces or contain suspended particles. Spherical colloids in an aligned LCLC nematic phase, for example, induce chiral director perturbations (“twisted tails”). The asymmetry of rod-like particles in an aligned LCLC offer a richer set of possibilities due to their aspect ratio (α) and mean orientation angle (〈θ〉) between their long axis and the uniform far-field director. Here we report on the director configuration, equilibrium orientation, and angular diffusion of rod-like particles with planar anchoring suspended in an aligned LCLC. Video microscopy reveals, counterintuitively, that two-thirds of the rods have an angled equilibrium orientation (〈θ〉 ≠ 0) that decreases with increasing α, while only one-third of the rods are aligned (〈θ〉 = 0). Polarized optical video-microscopy and Landau–de Gennes numerical modeling demonstrate that the angled and aligned rods are accompanied by distinct chiral director configurations. Angled rods have a longitudinal mirror plane (LMP) parallel to their long axis and approximately parallel to the substrate walls. Aligned rods have a transverse and longitudinal mirror plane (TLMP), where the transverse mirror plane is perpendicular to the rod's long axis. Effectively, the small twist elastic constant of LCLCs promotes chiral director configurations that modify the natural tendency of rods to orient along the far-field director. Additional diffusion experiments confirm that rods are angularly confined with strength that depends on α.

Understanding how soft matter deforms in response to mechanical interactions is central to the design of functional synthetic materials as well as elucidation of the behaviors of biological assemblies. Here we explore how cycles of thermally induced transitions between nematic (N) and isotropic (I) phases can be used to exert cyclical elastic stresses on dispersions of giant unilamellar vesicles (GUVs) and thereby evolve GUV shape and properties. The measurements were enabled by the finding that I–N–I phase transitions of the lyotropic chromonic liquid crystal disodium cromoglycate, when conducted via an intermediate columnar (M) phase, minimized transport of GUVs on phase fronts to confining surfaces. Whereas I to N phase transitions strained spherical GUVs into spindle-like shapes, with an efflux of GUV internal volume, subsequent N to I transitions generated a range of complex GUV shapes, including stomatocyte, pear- and dumbbell-like shapes that depended on the extent of strain in the N phase. The highest strained GUVs were observed to form buds (daughter vesicles) that we show, via a cycle of I–N–I–N phase transitions, are connected via a neck to the parent vesicle. Additional experiments established that changes in elasticity of the phase surrounding the GUVs and not thermal expansion of membranes were responsible for the shape transitions, and that I–N–I transformations that generate stomatocytes can be understood from the Bilayer-Coupling model of GUV shapes. Overall, these observations advance our understanding of how LC elastic stresses can be regulated to evolve the shapes of soft biological assemblies as well as provide new approaches for engineering synthetic soft matter.

Ionic self-assembly is a simple yet powerful method to obtain robust nanostructures. Herewith, we use mixtures of oppositely-charged porphyrins that can act as mesogens to form chromonic liquid crystals in water, i.e., molecular stacks with orientational (nematic) or positional (hexagonal) order. Electrostatic locking coupled with π–π interactions between aromatic groups within the stacks, together with inter-stack hydrogen bonding induce formation of all-organic crystalline nanofibers with high aspect ratio (a few tenths of nanometers in width but several tenths of micrometers in length) and that display branching. The nanofibers prepared from metal-free porphyrin units feature interesting optical properties, including an absorption spectrum that is different from the simple sum of the individual spectra of the components, which is attributed to a striking aggregation-induced chromism. When in contact with some polar organic solvents the materials become fluorescent, as a result of disaggregation. In a proof-of-concept, the obtained self-assembled one-dimensional (1D) materials were carbonized (yield ca. 60%) to produce nitrogen-doped carbon nanofibers that can be used as active electrode materials for energy storage applications., C. R. acknowledges the financial support from Generalitat de Catalunya (2017SGR1778 grant), and from the Spanish Ministry of Science, Innovation and Universities (CTQ2017-84998-P project). C. R. is also grateful to the Agencia Estatal de Investigación and to the European Regional Development Fund (Fondo Europeo de Desarrollo Regional, FEDER). We thank ALBA staff for their help and support in the Synchrotron SAXS experiments performed at BL11-NCD beamline at ALBA (Spain). This work is partially supported by supported by JSPS KAKENHI Grant Number JP 16H06518 (Coordination Asymmetry), CREST JST Grant Number JPMJCR1665, and Grants-in-Aid for Scientific Research (C) Grant Number 20K05590.

We investigated the pitches of cholesteric liquid crystals prepared by mixing disodium cromoglycate (DSCG) in water with 5 different water-soluble chiral additives. The measurements are based on the Grandjean-Cano wedge cell method. Overall, the twisting effect is weak, and the shortest pitch of 2.9 ± 0.2 μm is obtained using trans-4-hydroxy-l-proline, by which the cholesteric sample is iridescent at certain viewing angles. Freeze-fracture transmission electron microscopy (FFTEM) was also performed for the first time on both the nematic and cholesteric phases, revealing that stacked chromonic aggregates are very long, up to a few hundred nm, which explains why cholesteric chromonic liquid crystals hardly have pitches in the visible wavelength region.

The spontaneous aggregation of binary mixtures of lyotropic chromonic liquid crystals (LCLCs) was investigated using atomistic molecular dynamics simulations. Equimolecular binary mixtures were simulated in a highly dilute regime using three LCLC mesogens, namely, Sunset Yellow FCF (SSY), disodium cromoglycate (DSCG) and Bordeaux dye (BD). The influence of their molecular shape, conformational flexibility and hydrogen bonding capability in the formation of aggregates was studied in detail. Stacking distance comparison, hydrogen bond distribution analysis and solvent accessible surface area calculations were performed along with molecular visualization. The mixtures exhibited three different molecular segregation modes where the number of mixed π–π stacks was minimized. Aggregation of chromonic binary mixtures depends strongly on mesogen cross-sectional area differences. However, the distribution of LCLC solubilizing groups and their H-bonding density formed around mixed stacks contributed significantly to achieving different mixture segregation patterns. Average stacking distances between π–π interactions were consistently seen to be around 0.34 nm. Mesogens with similar long axis molecular length and high hydrogen bonding capacity represent a likely choice for the preparation of chromonic binary mixtures. These findings contribute to the understanding of general aggregation rules for chromonic mesophases which are required for the design of novel chromonic supramolecular applications.

Lyotropic chromonic liquid crystals (LCLCs) have attracted attention for their potential applications as thin-film polarizers. Although it is well reported that template-assisted method can efficiently align LCLCs for thin-film polarizers, the polarizer performance using the technique has not been well demonstrated. In this study, we report for the first time that the high-resolution (∼10 nm) pattern was found to be able to overcome the issue of dead space in the channel, and the LCLC columns were well aligned along the nanoscale array. The nanoscale array templates were fabricated by secondary sputtering lithography, and the chromonic nematic phase of the LCLC materials were prepared by dissolving the hydrogen chloride salt of bis-(N,N-diethylaminoethyl)-perylene-3,4,9,10-tetracarboxylic diimide in deionized water. A polarizing performance was observed (79.1% DOP and 29.5% TT at 475 nm) using a nanoscale array template with a high resolution (∼10 nm) and a high aspect ratio (>30). To further enhance polarizer performance, the combination of a nanoscale array template and mechanical shearing was exploited. With this combined route, an LCLC polarizer exhibiting a total transmission of 40.6% and a degree of polarization of 99.5% was obtained. Compared to mechanical shearing, nanoscale array templates were found to dominantly align highly mobile LCLCs.

Correction for ‘Shear-induced polydomain structures of nematic lyotropic chromonic liquid crystal disodium cromoglycate’ by Hend Baza et al., Soft Matter, 2020, 16, 8565–8576.

In this review we have collated various supramolecular designs, all surrounding H-bonding among well-known functional groups (peptides, nucleic acids, amides, ureas, carboxylic acids, pyridine-hydroxyls, urethanes, imides and others), to dictate self-assembly of naphthalenediimide (NDI) π-systems (both small molecules and polymeric building blocks) that exhibit several exciting features including strong propensity for π-π interactions, π-acidity, excellent n-type semiconductivity, CT-complexation, ion-π interactions, ring-substitution dependent redox properties and photophysical properties. This article reveals that H-bonding can indeed serve as a very powerful and versatile tool to programmed self-assembly of a single or multiple dye system producing a wide range of tailored soft materials, including fibrillar gels, chromonic mesophases, foldamers, nanotubes, vesicles, reverse micelles and polymersomes, both in water and organic medium with distinct photophysical properties, charge transport properties, conductivity properties and functional group displays that are highly relevant in the fields of biology and organic electronics.

Strong coupling of plasmons and molecules generates intriguingly hybridized resonance. The IR-806 molecule is a near-infrared cyanine liquid crystal dye with multiple molecular bands and its tunable absorption spectrum varies dramatically with concentration. In this article, we investigate multiple hybridized resonances of the Au nanorods (AuNRs) strongly coupled to IR-806 molecules. Five hybridized resonance peaks are observed in the extinction spectra of the AuNR@IR-806 hybrids. Two resonance peaks at approximately 840 and 912 nm in the hybrids are reported for the first time. The dependence of the multiple hybridized peaks on the bare plasmon resonance wavelength of AuNRs and the molecular concentration is also demonstrated. The observations presented herein provide a plasmon-molecule coupling route for tuning optical responses of liquid crystal molecules.

The behavior of mono-disperse colloidal particles in a chromonic liquid crystal was investigated. Poly(methyl methacrylate) spherical particles with three different functionalizations, with and without surface charges, were utilized in the nematic and columnar phases of disodium cromoglycate solutions. The nematic phase was completely aligned parallel to the glass substrates by a simple rubbing technique, and the columnar phase showed regions of similar alignment. The behavior of the colloidal particles in the chromonic liquid crystal depended critically on the functionality, with bromine functionalized particles not dispersing at all, and cationic trimethylammonium and epoxy functionalized particles dispersing well in the isotropic phase of the liquid crystal. At the transition to the nematic and especially the columnar phase, the colloidal particles were expelled into the remaining isotropic phase. Since the columnar phase grew in parallel ribbons, the colloidal particles ended up in chain-like assemblies. Such behavior opens the possibility of producing patterned assemblies of colloidal particles by taking advantage of the self-organized structure of chromonic liquid crystals.

We report the formation and characterization of hierarchical ordering in systems comprised of micrometer-sized droplets of thermotropic nematic liquid crystals (LCs) dispersed in continuous nematic phases of a lyotropic chromonic LC (disodium cromoglycate (DSCG)). Significantly, we find the orientations of the two LC phases to be coupled, with nematic droplets of 4'-pentyl-4-cyanobiphenyl (5CB) exhibiting a bipolar configuration with an axis of symmetry aligned orthogonal to the far-field director of the DSCG phase. We determine that this coupling of orientations does not result from either anisometric LC droplet shape or interfacial ionic phenomena but rather is consistent with the influence of van der Waals interactions that arise from the anisotropic polarizabilities of nematic 5CB (Δn = +0.18) and DSCG (Δn = -0.02) phases. We also find that it is possible to rotate and uniformly align the nematic droplets by using a weak magnetic field (B ∼ 0.3 T). An analysis of the dynamics of relaxation of the orientations of the 5CB droplets following removal of the magnetic field reveals the DSCG and 5CB droplets to be coupled by energies of ∼10(4) kT, consistent with a simple theoretical estimate of the influence of anisotropic van der Waals interactions. We also observed the nematic 5CB droplets to form dimers and larger assemblies mediated by the elasticity of the nematic DSCG. Overall, these results reveal that LC-in-LC emulsions define a new class of hierarchically ordered soft matter in which both thermotropic and lyotropic LCs are coupled in their ordering.

The surface-mediated alignment control of a lyotropic liquid crystal (LLC) of aqueous solutions of a water-soluble dye, C. I. Direct blue 67, by using thin films of poly(4-phenylazophenyl methacrylate) as a command surface is described. Concentrated aqueous solutions of the dye in the presence of a non-ionic surfactant displayed mesophases as a chromonic LLC as a result of stacking of the aromatic ring systems leading to a columnar structure. A uniaxially oriented texture of LLC was obtained when the LLC, in the presence of a non-ionic surfactant was filled in a cell, which had been exposed in advance to linearly polarised light and was surface-modified with thin films of the polymer. The orientational direction of the dye molecules was in parallel with the electric vector of the actinic light, implying that the alignment of LLC is determined by perpendicularly photooriented azobenzene chromophores in such a way that columnar supramolecular aggregates of the dye align in parallel with the azobenzene molecular axis. Factors affecting the photoalignment control of the LLC were discussed on the basis of the results of the effects of exposure doses, excitation wavelength and photo-rewritability.

We have developed an approach to generate micropatterns of anisotropic organic materials which exploits the self-organization, driven by π-stacking and hydrophobic interactions, of an ionic perylenebis(dicarboximide) 1 in aqueous solutions.

A new class of dinuclear cyclometalated platinum(II) complexes with [PtII(C^N^N)CNR]+ (HC^N^N = 6-phenyl-2,2′-bipyridyl, CNR = 2,6-dimethylphenyl isocyanide) motifs covalently connected by oligo(oxyethylene) chains form luminescent lyotropic chromonic liquid crystals or hydrogels in aqueous dispersions with intra- and intermolecular Pt⋯Pt and π–π interactions as the driving force. Their solution behaviour is modulated by the length of the oligo(oxyethylene) chain connecting the two cyclometalated platinum(II) motifs. One of the dinuclear Pt(II) complexes with a long oligo(oxyethylene) bridge and which does not display intramolecular Pt⋯Pt and π–π interactions can act as an effective ‘gelling stimulus’ for mononuclear [PtII(C^N^N)CNR]+ complexes in aqueous solutions, resulting in the formation of a nematic hydrogel that is persistent and displays red photoluminescence.

We report results on the high-field magneto-optical response of four aqueous, lyotropic, chromonic liquid crystal formulations in the isotropic phase. Measurements of the field-induced birefringence at temperatures above the isotropic-nematic coexistence region at high magnetic fields reveal qualitative differences in different materials; these differences can be attributed to the nature of aggregation and are discussed within the context of competing aggregation models. Extending these measurements to very high fields and large optical phase differences reveals the presence of an unexpected optical phenomenon: magnetic field-induced circular birefringence, measured in the Voigt geometry, in a system containing no molecularly chiral species. Possible origins of this effect are discussed.

A macroscopically oriented anisotropic nanofiber mat embedding self-assembled Sunset-Yellow FCF nanocolumns was fabricated by the electrospinning technique. From the 2D WAXD and polarized FTIR results, it was realized that the nanocolumns were aligned parallel to the long axis of the nanofiber.

We report on our latest studies on alignment of chromonic liquid crystals, a special class of molecules which recently attracted the attention of researchers. In particular, we show a detailed study of planar anchoring of disodium cromoglycate (DSCG) and, for the first time in the literature, a stable homeotropic alignment, achieved using a surface property of the alignment layer, i.e. the hydrophobicity. Excellent candidates from this point of view are pure polybutadiene (PB) and polydimethylsiloxane (PDMS). In fact, for the former the homeotropic anchoring stabilizes after one day, while for the latter stabilization occurs soon after cooling from the isotropic phase. After a long time both types of alignments (planar and homeotropic) evolve into thermodynamically stable configurations, i.e. ribbon structures. An explanation of the behaviour is given.

We report a novel thin film polarizer fabricated from a photocurable lyotropic chromonic liquid crystal (LCLC) solution. An organic-based photocurable solution having a lyotropic liquid crystalline phase was prepared by dissolving 25–35 wt% of basic chromonic dye in an acidic monomer (acrylic acid) solution. The shear-coated film after UV irradiation exhibited the maximum polarization efficiency, P = 95.2%. Compared to the conventional aqueous-based technique, the new method provided many advantages such as outstanding coating processibility, high thermal stability, good solvent resistance, moderate surface hardness, and excellent adhesion to various substrates, especially on a plastic substrate.

Many soft-matter and biophysical systems are composed of monomers that reversibly assemble into rod-like aggregates. The aggregates can then order into liquid-crystal phases if the density is high enough, and liquid-crystal ordering promotes increased growth of aggregates. Systems that display coupled aggregation and liquid-crystal ordering include wormlike micelles, chromonic liquid crystals, DNA and RNA, and protein polymers and fibrils. Coarse-grained molecular models that capture key features of coupled aggregation and liquid-crystal ordering common to many different systems are lacking; in particular, the roles of monomer aspect ratio and aggregate flexibility in controlling the phase behavior are not well understood. Here we study a minimal system of sticky cylinders using Monte Carlo simulations and analytic theory. Cylindrical monomers interact primarily by hard-core interactions but can stack and bind end to end. We present results for several different cylinder aspect ratios and a range of end-to-end binding energies. The phase diagrams are qualitatively similar to those of chromonic liquid crystals, with an isotropic-nematic-columnar triple point. The location of the triple point is sensitive to the monomer aspect ratio. We find that the aggregate persistence length varies with temperature in a way that is controlled by the interaction potential; this suggests that the form of the interaction potential affects the phase behavior of the system. Our analytic theory shows improvement compared to previous theory in quantitatively predicting the I–N transition for relatively stiff aggregates, but requires a better treatment of aggregate flexibility.

Dense multicomponent systems with macromolecules and small solutes attract a broad research interest as they mimic the molecularly crowded cellular interiors. The additives can condense and align the macromolecules, but they do not change the degree of covalent polymerization. We chose a lyotropic chromonic liquid crystal with reversibly and non-covalently assembled aggregates as a much softer system, reminiscent of “living polymers”, to demonstrate that small neutral and charged additives cause condensation of aggregates with ensuing orientational and positional ordering and nontrivial morphologies of phase separation, such as tactoids and toroids of the nematic and hexagonal columnar phase coexisting with the isotropic melt. Scanning transmission X-ray microscopy (STXM) with near edge X-ray absorption fine structure (NEXAFS) analysis as well as fluorescent microscopy demonstrates segregation of the components. The observations suggest that self-assembly of chromonic aggregates in the presence of additives is controlled by both entropy effects and by specific molecular interactions and provide a new route to the regulated reversible assembly of soft materials formed by low-molecular weight components.

We recently found that the chromonic mesophase structure of an azo dye can be immobilized by a silica network to form a chromonic–silica nanohybrid. This work reports the first demonstration of the macroscopic photoalignment and photopatterning of this nanohybrid via surface-mediated orientational transfer from a photocrosslinkable liquid crystalline polymer (PPLC). Irradiation with linearly polarized light (LPL) 300 nm above the PPLC film followed by an appropriate annealing process led to strong in-plane molecular orientation in the film. The precursor sol solution containing a chromonic forming azo dye and tetraethoxysilane in the presence of an anionic surfactant and 2-(2-aminoethoxy)ethanol was placed onto this aligned film by the static deposition or dipping method. After drying, the chromonic columns hybridized with silica were macroscopically oriented orthogonal to the LPL direction, namely the orientation of the dye molecule being parallel to it. In the dip coating process, a combination of photoalignment and flow induced orientation allowed clear micropatterning of the column orientations, which could be readily discerned when observed with a polarizing film.

Chromonic liquid crystals (or chromonics) are formed by the self-organization of aromatic compounds with ionic or hydrophilic groups in aqueous solutions. This review summarizes the research on chromonic liquid crystals in the last two decades. The research embraced the studies of commercially available chromonic dyes and drugs, the syntheses and investigations of molecularly designed mesogens, the invention of novel processes for aligning chromonic liquid crystals, and the development of new applications as functional materials and biosensors.

A new series of polyamides (ph-azo-PAMs) was synthesized by the polycondensation of isophthalic acids having a photoisomerizable phenyl azo unit with 4,4′-diamino-3,5,3′,5′-tetraethyldiphenylmethane or by the esterification of poly(imino-5-oxyisophthaloylimino-1,4-(3,5-diethyl)phenylenemethylene-1,4-(3,5-diethyl)phenylene) with 4-(phenylazo)- or 4-(4′-substituted phenylazo)phenoxyalkanoic acid chlorides in the presence of triphenyl phosphate and pyridine in N-methylpyrrolidone. It has been confirmed that the spin-coated films of ph-azo-PAMs thus produced show reversible trans–cis photoisomerization of the azobenzene moieties. To examine the ability of the polymer films to act as command surfaces for a chromonic lyotropic liquid crystal (LLC), they were exposed to linearly polarized light and coated with aqueous LLC solutions of a chromonic dye compound. After drying the LLC solution, polarizing microscopic measurements were carried out to see whether the phototreated polymer films could bring about the in-plane anisotropic alignment of the dye molecule. The result was that 5h having an azo moiety with a dimethylamino substituent as a side group was among the most promising candidates.