Liquid Organic Frameworks: The Single-Network “Plumber’s Nightmare” Bicontinuous Cubic Liquid Crystal

Thermotropic "Plumber's Nightmare"-A Tight Liquid Organic Double Framework

Gyroid, double diamond and the body-centred "Plumber's nightmare" are the three most common bicontinuous cubic phases in lyotropic liquid crystals and block copolymers. While the first two are also present in solvent-free thermotropics, the latter had never been found. Containing six-fold junctions, it was unlikely to form in the more common phases with rod-like cores normal to the network columns, where a maximum of four branches can join at a junction. The solution has therefore been sought in side-branched mesogens that lie in axial bundles joined at their ends by flexible "hinges". But for the tightly packed double framework, geometric models predicted that the side-chains should be very short. The true Plumber's nightmare reported here, using fluorescent dithienofluorenone rod-like mesogen, has been achieved with, indeed, no side chains at all, but with 6 flexible end-chains. Such molecules normally form columnar phases, but the key to converting a complex helical column-forming mesogen into a framework-forming one was the addition of just one methyl group to each pendant chain. A geometry-based explanation is given.

Fe3O4-doped mesoporous carbon cathode with a plumber's nightmare structure for high-performance Li-S batteries

Shuttling of lithium polysulfides and slow redox kinetics seriously limit the rate and cycling performance of lithium-sulfur batteries. In this study, Fe3O4-dopped carbon cubosomes with a plumber's nightmare structure (SP-Fe3O4-C) are prepared as sulfur hosts to construct cathodes with high rate capability and long cycling life for Li-S batteries. Their three-dimensional continuous mesochannels and carbon frameworks, along with the uniformly distributed Fe3O4 particles, enable smooth mass/electron transport, strong polysulfides capture capability, and fast catalytic conversion of the sulfur species. Impressively, the SP-Fe3O4-C cathode exhibits top-level comprehensive performance, with high specific capacity (1303.4 mAh g-1 at 0.2 C), high rate capability (691.8 mAh gFe3O41 at 5 C), and long cycling life (over 1200 cycles). This study demonstrates a unique structure for high-performance Li-S batteries and opens a distinctive avenue for developing multifunctional electrode materials for next-generation energy storage devices.

Coarse-Grained Molecular Simulation of Bolapolyphiles with a Multident Lateral Chain: Formation and Structural Analysis of Cubic Network Phases

Bolapolyphiles constitute a versatile class of materials with a demonstrated potential to form a wide variety of complex ordered mesophases. In particular, cubic network phases (like the gyroid, primitive, and diamond phases) have been a target of many studies for their ability to create percolating 3D nanosized channels. In this study, molecular simulations are used to explore the phase behavior of bolapolyphiles containing a rigid rodlike core, associating hydrophilic core ends and a hydrophobic side chain with a multident architecture, i.e., where the branching pattern can vary from bident (two branches) to hexadent (six branches). Upon network phase formation, its skeleton is made up of "nodes" populated by the core ends and "struts" populated by the cores. It is shown that, by varying the side chain length, branching pattern, and attachment point to the core, one can alter the crowding around the cores and hence tune the nodal size and nodal valence (i.e., number of connecting struts) which lead to different types of network morphologies. For example, for a fixed total side chain length, having more branches generates a stronger crowding around the molecular core, driving them to form bundlelike domains with curvier interfaces that result in thinner struts. Also, attaching the lateral chain closer to one core end breaks the symmetry between the environments around the two core ends, leading to networks with bimodal nodal sizes. Importantly, since the characterization of (ordered or partially ordered) network phases is challenging given the potential incompatibilities between the simulation box size with the structure's space group periodic symmetry and the effect of morphological defects, a detailed framework is presented to analyze and fully characterize the unit cell parameters and structure factor of such systems.

Self-Assembly of Unusually Stable Thermotropic Network Phases by Cellobiose-Based Guerbet Glycolipids

Bicontinuous thermotropic liquid crystal (LC) materials, e.g., double gyroid (DG) phases, have garnered significant attention due to the potential utility of their 3D network structures in wide-ranging applications. However, the utility of these materials is significantly constrained by the lack of robust molecular design rules for shape-filling amphiphiles that spontaneously adopt the saddle curvatures required to access these useful supramolecular assemblies. Toward this aim, we synthesized anomerically pure Guerbet-type glycolipids bearing cellobiose head groups and branched alkyl tails and studied their thermotropic LC self-assembly. Using a combination of differential scanning calorimetry, polarized optical microscopy, and small-angle X-ray scattering, our studies demonstrate that Guerbet cellobiosides exhibit a strong propensity to self-assemble into DG morphologies over wide thermotropic phase windows. The stabilities of these assemblies sensitively depend on the branched alkyl tail structure and the anomeric configuration of the glycolipid in a previously unrecognized manner. Complementary molecular simulations furnish detailed insights into the observed self-assembly characteristics, thus unveiling molecular motifs that foster network phase self-assembly that will enable future designs and applications of network LC materials.

Aquatic Functional Liquid Crystals: Design, Functionalization, and Molecular Simulation

Aquatic functional liquid crystals, which are ordered molecular assemblies that work in water environment, are described in this review. Aquatic functional liquid crystals are liquid-crystalline (LC) materials interacting water molecules or aquatic environment. They include aquatic lyotropic liquid crystals and LC based materials that have aquatic interfaces, for example, nanoporous water treatment membranes that are solids preserving LC order. They can remove ions and viruses with nano- and subnano-porous structures. Columnar, smectic, bicontinuous LC structures are used for fabrication of these 1D, 2D, 3D materials. Design and functionalization of aquatic LC sensors based on aqueous/LC interfaces are also described. The ordering transitions of liquid crystals induced by molecular recognition at the aqueous interfaces provide distinct optical responses. Molecular orientation and dynamic behavior of these aquatic functional LC materials are studied by molecular dynamics simulations. The molecular interactions of LC materials and water are key of these investigations. New insights into aquatic functional LC materials contribute to the fields of environment, healthcare, and biotechnology.

Highly branched bolapolyphilic liquid crystals with a cubic A15 network at the triangle-square transition

Rod-like bolapolyphiles with highly branched carbosilane-based side-chains self-assemble into several honeycomb structures if the oligo(p-phenylene ethynylene) core is polyfluorinated, whereas for the non-fluorinated series an A15 type cubic network of rod-bundles was observed instead, suggesting a brand new pathway for the transition between triangular and square honeycomb phases.

Stereochemistry-dependent thermotropic liquid crystalline phases of monosaccharide-based amphiphiles

Conformational rigidity controls the bulk self-assembly and liquid crystallinity from amphiphilic block molecules to copolymers. The effects of block stereochemistry on the self-assembly have, however, been less explored. Here, we have investigated amphiphilic block molecules involving eight open-chain monosaccharide-based polyol units possessing different stereochemistries, derived from D-glucose, D-galactose, L-arabinose, D-mannose and L-rhamnose (allylated monosaccharides t-Glc*, e-Glc*, t-Gal*, e-Gal*, t-Ara*, e-Ara*, t-Man*, and t-Rha*), end-functionalized with repulsive tetradecyl alkyl chain blocks to form well-defined amphiphiles with block molecule structures. All compounds studied showed low temperature crystalline phases due to polyol crystallization, and smectic (lamellar) and isotropic phases upon heating in bulk. Hexagonal cylindrical phase was additionally observed for the composition involving t-Man*. Cubic phases were observed for e-Glc*, e-Gal*, e-Ara*, and t-Rha* derived compounds. Therein, the rich array of WAXS-reflections suggested that the crystalline polyol domains are not ultra-confined in spheres as in classic cubic phases but instead show network-like phase continuity, which is rare in bulk liquid crystals. Importantly, the transition temperatures of the self-assemblies were observed to depend strongly on the polyol stereochemistry. The findings underpin that the stereochemistry in carbohydrate-based assemblies involves complexity, which is an important parameter to be considered in material design when developing self-assemblies for different functions.

Leveraging Macromolecular Isomerism for Phase Complexity in Janus Nanograins

It remains intriguing whether macromolecular isomerism, along with competing molecular interactions, could be leveraged to create unconventional phase structures and generate considerable phase complexity in soft matter. Herein, we report the synthesis, assembly, and phase behaviors of a series of precisely defined regioisomeric Janus nanograins with distinct core symmetry. They are named B₂DB₂ where B stands for iso-butyl-functionalized polyhedral oligomeric silsesquioxanes (POSS) and D stands for dihydroxyl-functionalized POSS. While BPOSS prefers crystallization with a flat interface, DPOSS prefers to phase-separate from BPOSS. In solution, they form 2D crystals owing to strong BPOSS crystallization. In bulk, the subtle competition between crystallization and phase separation is strongly influenced by the core symmetry, leading to distinct phase structures and transition behaviors. The phase complexity was understood based on their symmetry, molecular packing, and free energy profiles. The results demonstrate that regioisomerism could indeed generate profound phase complexity.

Network Phases with Multiple-Junction Geometries at the Gyroid-Diamond Transition

A novel phase sequence for the transition from the double diamond to the double gyroid cubic phases via two non-cubic intermediate phases, an orthorhombic Fmmm (O⁶⁹) phase and a hexagonal P6₃/m (H¹⁷⁶) phase, is reported for specifically designed bolapolyphiles composed of a linear rod-like bistolane core with sticky glycerol ends and two branched central and two linear peripheral side chains. These liquid crystalline (LC) phases represent members of a new class of unicontinuous network phases, formed by longitudinal rod bundles with polar spheres acting as junctions and the alkyl chains forming the continuum around them. In contrast to previously known bicontinuous cubic networks, they combine different junctions with different angles in a common structure, and one of them even represents a triple network instead of the usually found double networks. This provides new perspectives for the design of soft network phases with enhanced structural complexity, inspiring the search for new supramolecular networks, nano-particle arrays, and photonic band-gap materials.

Tetrahedral Liquid-Crystalline Networks: An A15-Like Frank-Kasper Phase Based on Rod-Packing

The Pm 3 ‾ n cubic and other low-symmetry Frank-Kasper phases are known to be formed by soft spheres, ranging from metals to block copolymer micelles and colloidal nanoparticles. Here, we report a series of X-shaped polyphiles composed of sticky rods and two non-symmetric branched side-chains, which self-assemble into the first example of a cubic liquid-crystalline phase representing a tetrahedral network of rods with a Pm 3 ‾ n lattice. It is the topological dual to the Weaire-Phelan foam, being the Voronoi tessellation of the A15 sphere packing, from which this network is obtained by Delaunay triangulation.

Advanced Functional Liquid Crystals

Liquid crystals have been intensively studied as functional materials. Recently, integration of various disciplines has led to new directions in the design of functional liquid-crystalline materials in the fields of energy, water, photonics, actuation, sensing, and biotechnology. Here, recent advances in functional liquid crystals based on polymers, supramolecular complexes, gels, colloids, and inorganic-based hybrids are reviewed, from design strategies to functionalization of these materials and interfaces. New insights into liquid crystals provided by significant progress in advanced measurements and computational simulations, which enhance new design and functionalization of liquid-crystalline materials, are also discussed.

Supramolecular meso-Trick: Ambidextrous Mirror Symmetry Breaking in a Liquid Crystalline Network with Tetragonal Symmetry

Bicontinuous and multicontinuous network phases are among nature's most complex structures in soft matter systems. Here, a chiral bicontinuous tetragonal phase is reported as a new stable liquid crystalline intermediate phase at the transition between two cubic phases, the achiral double gyroid and the chiral triple network cubic phase with an I23 space group, both formed by dynamic networks of helices. The mirror symmetry of the double gyroid, representing a meso-structure of two enantiomorphic networks, is broken at the transition to this tetragonal phase by retaining uniform helicity only along one network while losing it along the other one. This leads to a conglomerate of enantiomorphic tetragonal space groups, P4₁2₁2 and P4₃2₁2. Phase structures and chirality were analyzed by small-angle X-ray scattering (SAXS), grazing-incidence small-angle X-ray scattering (GISAXS), resonant soft X-ray scattering (RSoXS) at the carbon K-edge, and model-dependent SAXS/RSoXS simulation. Our findings not only lead to a new bicontinuous network-type three-dimensional mesophase but also reveal a mechanism of mirror symmetry breaking in soft matter by partial meso-structure racemization at the transition from enantiophilic to enantiophobic interhelical self-assembly.

Transition from lamellar to nanostructure mesophases in azobenzene-based hockey-stick polycatenars

Tuning from 1D to 3D mesophases by alkyl chain engineering. Multichain π-conjugated hockey-stick molecules form lamellar SmA and meso-structure Ia3̄d with continuous networks. The effect of the position of the central bent-core unit on helical self-assembly is discussed.

Gyroid-Nanostructured All-Solid Polymer Films Combining High H+ Conductivity with Low H2 Permeability

Gyroid-nanostructured all-solid polymer films with exceedingly high proton conductivity and low H₂ gas permeability have been created via crosslinking polymerization of mixtures of a zwitterionic amphiphilic monomer and a polymerizable imide-type acid that co-organize into bicontinuous cubic liquid-crystalline phases. The gyroid nanostructures are visualized by reconstructing a 3D electron map from the synchrotron X-ray diffraction patterns. These films exhibit high proton conductivity of the order of 10^-1 S cm^-1 and extremely low H₂ gas permeability of the order of 10^-15 mol m m^-2 s^-1 Pa^-1 . These properties can be ascribed to the presence of the ionic liquid-like layer along the gyroid minimal surface. Since these two characteristics are required for improving the performance of proton-exchange membrane fuel cells, the present membrane design represents a promising strategy for the development of advanced devices, pertinent to establishing sustainable energy sources.

A phase-dependent photoluminescent discotic liquid crystal bearing a graphdiyne substructure

In recent years, graphdiyne and its derivatives with fascinating electro-optic properties have attracted tremendous scientific attention. Here we design and synthesize a graphdiyne-derived discotic liquid crystal material by decorating six wedge-shaped 3,4,5-tris(dodecyloxy)benzoate groups on the fundamental structural unit of graphdiyne, the dehydrotribenzo[18]annulene core. This graphdiyne-derived liquid crystal material exhibits a cubic phase and a hexagonal columnar phase at varied temperatures. Most interestingly, this molecule displays a tunable phase-dependent photoluminescence behavior. Under the irradiation of 365 nm wavelength ultraviolet light, the luminescent material emits pale blue, green and azure light in the cubic, hexagonal columnar and isotropic phases respectively. This graphdiyne-derived discotic liquid crystal with excellent optical characteristics might have application potentials in organic optoelectronic functional materials and devices.

Frustrated Layered Self-Assembly Induced Superlattice from Two-Dimensional Nanosheets

Here we reported a hierarchical self-assembly approach toward well-defined superlattices in supramolecular liquid crystals by fullerene-based sphere-cone block molecules. The fullerenes crystallize to form monolayer nanosheets intercalated by the attached soft hydrocarbon cones. The frustration caused by cross-sectional area mismatch between the spheres and the somewhat oversize cones leads to a unique lamellar superlattice whereby each stack of six pairs of alternating sphere-cone sublayers is followed by a cone double layer. While such areal mismatch problems in soft matter are usually solved by interface curvature, the lamellar superlattice solution is best suited to systems with rigid layers. Meanwhile, formation of the superlattice significantly improves the material's transient electron conductivity, with the maximum value being among the highest for π-conjugated organic materials. The design principle of solving steric frustration by forming a superlattice opens a new avenue toward self-assembled optoelectronic materials.

Controlling Mirror Symmetry Breaking and Network Formation in Liquid Crystalline Cubic, Isotropic Liquid and Crystalline Phases of Benzil-Based Polycatenars

Spontaneous development of chirality in systems composed of achiral molecules is important for new routes to asymmetric synthesis, chiral superstructures and materials, as well as for the understanding of the mechanisms of emergence of prebiotic chirality. Herein, it is shown that the 4,4'-diphenylbenzil unit is a universal transiently chiral bent building block for the design of multi-chained (polycatenar) rod-like molecules capable of forming a wide variety of helically twisted network structures in the liquid, the liquid crystalline (LC) and the crystalline state. Single polar substituents at the apex of tricatenar molecules support the formation of the achiral (racemic) cubic double network phase with Ia 3 ‾ d symmetry and relatively small twist along the networks. The combination of an alkyl chain with fluorine substitution leads to the homogeneously chiral triple network phase with I23 space group, and in addition, provides a mirror symmetry broken liquid. Replacing F by Cl or Br further increases the twist, leading to a short pitch double gyroid Ia 3 ‾ d phase, which is achiral again. The effects of the structural variations on the network structures, either leading to achiral phases or chiral conglomerates are analyzed.

Liquid Organic Frameworks: A Liquid Crystalline 8-Connected Network with Body-Centered Cubic Symmetry

Liquid state self-assembly is important for the understanding of the complex structures developed in abiogenesis and biogenesis as well as for numerous potential technological applications. Herein we report the first body-centered cubic liquid crystalline phase with 8-connected network topology and open octahedral network structure. It is formed by dynamic soft self-assembly of X-shaped polyphiles with oligo(para-phenylene-ethynylene) cores. The π-conjugated rods with perfluorinated inner benzene rings form networks conjoined by eight-way junctions, which are formed by nano-segregated spheres involving hydrogen-bonded polar end groups, while the branched aliphatic chains at opposite sides of the cores fill the continuum. This novel cubic phase is based on the I-WP minimal surface separating the frameworks of polyaromatic cores from the most disordered chain segments. It can also be considered as a dense sphere packing. Such liquid organic frameworks, representing hybrids of sphere packings and networks could be of interest for organic photonics and other technologies.

Mirror Symmetry Breaking in Liquids and Their Impact on the Development of Homochirality in Abiogenesis: Emerging Proto-RNA as Source of Biochirality?

Recent progress in mirror symmetry breaking and chirality amplification in isotropic liquids and liquid crystalline cubic phases of achiral molecule is reviewed and discussed with respect to its implications for the hypothesis of emergence of biological chirality. It is shown that mirror symmetry breaking takes place in fluid systems where homochiral interactions are preferred over heterochiral and a dynamic network structure leads to chirality synchronization if the enantiomerization barrier is sufficiently low, i.e., that racemization drives the development of uniform chirality. Local mirror symmetry breaking leads to conglomerate formation. Total mirror symmetry breaking requires either a proper phase transitions kinetics or minor chiral fields, leading to stochastic and deterministic homochirality, respectively, associated with an extreme chirality amplification power close to the bifurcation point. These mirror symmetry broken liquids are thermodynamically stable states and considered as possible systems in which uniform biochirality could have emerged. A model is hypothesized, which assumes the emergence of uniform chirality by chirality synchronization in dynamic “helical network fluids” followed by polymerization, fixing the chirality and leading to proto-RNA formation in a single process.