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2D X-ray diffraction images of a film of poly-F·T with a macroscopically oriented structure. A square-shaped film (3 × 3 mm, ~20 μm thick) was used. (a) Through view image (X-ray||N, X-ray⊥B). (b) Edge view image (X-ray⊥N, X-ray||B). (c) End view image (X-ray⊥N, X-ray⊥B). (i), (ii) and (iii) highlight signals due to aliphatic chain packing, π-stacking and 3D lattice, respectively. B, Magnetic field applied during the LC film-preparation process. N, Normal vector of the film surface.
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Helical nanostructures have attracted continuous attention, not only as media for chiral recognition and synthesis, but also as motifs for studying intriguing physical phenomena that never occur in centrosymmetric systems. To improve the quality of signals from these phenomena, which is a key issue for their further exploration, the most straightfo...
Citations
... Subsequent crosslinking of the LC monomers to fixate the nanostructures is necessary to provide sufficient mechanical strength to obtain robust free-standing LC polymer membranes. So far, LC polymer membranes have mainly been investigated for water separations [13][14][15][16][17][18][19][20][21][22][23][24], but hardly for gas separations [25][26][27]. Studies show the importance of molecular order and orientation in LC polymer membranes, see, for example, our previous work [26]. ...
The effect of layer spacing and halogenation on the gas separation performances of free-standing smectic LC polymer membranes is being investigated by molecular engineering. LC membranes with various layer spacings and halogenated LCs were fabricated while having a planar aligned smectic morphology. Single permeation and sorption data show a correlation between gas diffusion and layer spacing, which results in increasing gas permeabilities with increasing layer spacing while the ideal gas selectivity of He over CO2 or He over N2 decreases. The calculated diffusion coefficients show a 6-fold increase when going from membranes with a layer spacing of 31.9 Å to membranes with a layer spacing of 45.2 Å, demonstrating that the layer spacing in smectic LC membranes mainly affects the diffusion of gasses rather than their solubility. A comparison of gas sorption and permeation performances of smectic LC membranes with and without halogenated LCs shows only a limited effect of LC halogenation by a slight increase in both solubility and diffusion coefficients for the membranes with halogenated LCs, resulting in a slightly higher gas permeation and increased ideal gas selectivities towards CO2. These results show that layer spacing plays an important role in the gas separation performances of smectic LC polymer membranes.
... Helicenes are helically shaped chiral polycyclic aromatic compounds. [48][49][50][51][52][53][54][55] Their inherent twist originates from their intramolecular steric demands and leads to special optical and electronic properties, [56][57][58][59][60][61][62][63][64][65][66][67][68][69][70][71][72][73] in comparison to their non-twisted counterparts. Deviations from planarity are generally associated with geometric distortions and with increased strain in these polycyclic structures. ...
We describe reductive dehydrogenative cyclizations that form hepta-, nona- and decacyclic anionic graphene subunits from mono- and bis-helicenes with an embedded five-membered ring. The reaction of bis-helicenes can either proceed to the full double annulation or be interrupted by addition of molecular oxygen at an intermediate stage. The regioselectivity of the interrupted cyclization cascade for bis-helicenes confirms that relief of antiaromaticity is a dominant force for these facile ring closures. Computational analysis reveals the unique role of the preexisting negatively charged cyclopentadienyl moiety in directing the 2nd negative charge at a specific remote location and, thus, creating a localized antiaromatic region. This region is the hot-spot that promotes the initial cyclization. Computational studies, including MO analysis, molecular electrostatic potential maps, and NICS(1.7)ZZ calculations evaluate the interplay of the various effects including charge delocalization, helicene strain release, and antiaromaticity. The role of antiaromaticity relief is further supported by efficient reductive closure of the less strained mono-helicenes where the relief of antiaromaticity promotes the cyclization even when the strain is substantially reduced. The latter finding significantly expands the scope of this reductive alternative to the Scholl ring closure.
... This approach has been utilized to fabricate size-selective adsorbents for ions 68 and small organic molecules, 69−72 guest−host recognition, 73−77 and optically active materials. 77 1.1.3. Smart Materials with Stimuli-responsive, Selfhealing, and Recyclable Properties. ...
Hydrogen-bonded liquid crystalline polymers have emerged as promising “smart” supramolecular functional materials with stimuli-responsive, self-healing, and recyclable properties. The hydrogen bonds can either be used as chemically responsive (i.e., pH-responsive) or as dynamic structural (i.e., temperature-responsive) moieties. Responsiveness can be manifested as changes in shape, color, or porosity and as selective binding. The liquid crystalline self-organization gives the materials their unique responsive nanostructures. Typically, the materials used for actuators or optical materials are constructed using linear calamitic (rod-shaped) hydrogen-bonded complexes, while nanoporous materials are constructed from either calamitic or discotic (disk-shaped) complexes. The dynamic structural character of the hydrogen bond moieties can be used to construct self-healing and recyclable supramolecular materials. In this review, recent findings are summarized, and potential future applications are discussed.
... Li et al. explored the template strategy even further by complexation of a chiral template molecule with a gallate acid monomer (Fig. 8) [69]. The chiral template was used to translate its chirality to a polymer host and by aligning the LCs in a magnetic field planar helical columns with an estimated diameter of 3.1 nm were obtained. ...
... By subsequent removal of the template pores were obtained. Adsorption experiments showed that various basic and cationic guest molecules can occupy up to 90% of the pores and order the guest molecules in a helical arrangement [69]. Although future work needs to be done regarding membrane studies and large-scale alignment in a homeotropic fashion, these examples show the potential of LCs as nanoporous membranes for the separation of ions and molecules or even chiral separations. ...
... Another powerful method to obtain well organized nanopores is by alignment in magnetic fields [49][50][51]69]. Feng et al. obtained highly aligned LC films by rotating the film in a 3-6 T magnetic field, prior to a photo-polymerization to fixate the morphology. ...
The transition from the current “linear” economy to a “circular” economy with a strong focus on the recovery and reuse of materials and resources undoubtedly necessitates efficient and effective separation technologies. Membrane technology will play an important role in this transition to a circular economy. In that perspective, separation at the molecular level to separate and fractionate e.g. individual ions and small molecules for reuse is especially essential. Unfortunately, conventional membrane materials and their fabrication methods mostly lack design and control over pore size and selectivity at a true molecular level. In view of this challenge, nanostructured polymer membranes based on self-assembled materials are gaining more and more interest. Using the self-assembly properties of polymerizable liquid crystal molecules ensures control at a molecular level and gives rise to narrow pore size distributions, high pore densities and control of pore size and functionality.
In this review, the potential of liquid crystal materials and their self-assembly properties to fabricate nanoporous membranes for water purification, desalination and selective recovery is presented. The basic principles of liquid crystals, the self-assembling characteristics and methods to control pore size and functionality are discussed in the perspective of membrane properties and applications. Efforts reported in the literature highlighting advances and pointing out important limitations for different pore morphologies are discussed. The versatility of liquid crystal based membranes is highlighted by exploring approaches for post-modification of the nanopores to further tune the pore size and control the pore functionality after polymerization of the liquid crystals.
The work provides readers with a thorough understanding of the design and fabrication of nanoporous liquid crystal membranes combined with a perspective on the potential of liquid crystal membranes. Next to recent advances, future challenges are presented as well, with the most crucial two: 1) The formation of thin, defect-free nanoporous liquid crystal layers supported on a microporous support; 2) Large-scale production combined with alignment control over longer length scales.
... As a scaffold for guest chromophores to be arranged with such particular geometries, Ishida and co-workers reported a polymer framework composed of helical pores with unidirectional orientation over a large area (∼10 cm 2 ). 160 The synthesis of the polymer framework was essentially identical to that described in the earlier sections (i.e., by in situ cross-linking of the chiral ILC exhibiting a Col phase, which was composed of the salt of polymerizable trialkylated gallic acid 1 and chiral amino alcohol (1R,2S)-14), 42,43,56 except for magnetically aligning the LC columns before the cross-linking. The resultant polymer framework with macroscopically oriented helical nanopores served as a useful scaffold for incorporating and organizing various functional molecules with a basic or cationic moiety in a helical arrangement. ...
Ionic liquid crystals have emerged as a new class of functional soft materials in the last two decades, which exhibit synergistic characteristics of ionic liquids and liquid crystals, such as (1) macroscopic orientability, (2) miscibility with various species, (3) phase stability, (4) tunability of nanostructures, and (5) formation of polar nanochannels. Owing to these characteristics, the structures, properties, and functions of ionic liquid crystals have been a hot topic in materials chemistry, finding various applications including (i) host frameworks for guest binding, (ii) separation membranes, (iii) ion/proton-conducting membranes, (iv) reaction media, and (v) optoelectronic materials. Although several excellent review articles of ionic liquid crystals have been published recently, they mainly focused on fundamental aspects, structures, and specific properties of ionic liquid crystals, while these various applications of ionic liquid crystals have not yet been discussed at once. The aim of this feature article is to overview the applications of ionic liquid crystals in a comprehensive manner.
... NATURE COMMUNICATIONS | https://doi.org/10.1038/s41467-020-16127-6 ARTICLE crystalline state, where the precise positions of the molecular components were obtained based on the determination of space group (P6 1 22) by X-ray diffraction (XRD) studies 38 . In this work, 1•2 S was found to exhibit a thermotropic liquid crystalline phase, whose XRD pattern (Supplementary Methods) was quite resembling to that in our previous report 38 ; all reflections were elucidated on the supposition of the same space group (P6 1 22; for details, see Supplementary Fig. 8). ...
... ARTICLE crystalline state, where the precise positions of the molecular components were obtained based on the determination of space group (P6 1 22) by X-ray diffraction (XRD) studies 38 . In this work, 1•2 S was found to exhibit a thermotropic liquid crystalline phase, whose XRD pattern (Supplementary Methods) was quite resembling to that in our previous report 38 ; all reflections were elucidated on the supposition of the same space group (P6 1 22; for details, see Supplementary Fig. 8). Therefore, a double helix structure similar to that we reported previously 38 was considered to be a possible structural model of the supramolecular polymer of 1•2 S . ...
Since various helical supramolecular polymers became available, their application to molecular chirality recognition have been anticipated but not extensively studied. So far, only a few examples of chiral reactions have been reported, but none for chiral separation. Here, we report the application of a helical supramolecular polymer to the enantio-separation of chiral guest molecules. The monomer of this supramolecular polymer is the salt-pair of a dendritic carboxylic acid with an enantiopure amino alcohol. In an apolar solvent, this salt-pair stacks via hydrogen bonds to form a helical polymer. In conjunction with this carboxylic acid, various amino alcohols afford supramolecular polymers, whose helical handedness is determined by the stereochemistry of the amino alcohols. When two salts with the same chirality are mixed, they undergo copolymerization, while those with opposite chirality do not. Owing to this stereoselective copolymerizability, the helical supramolecular polymer could bias the enantiomeric composition of chiral amino alcohols. Since various helical supramolecular polymers became available, their application in molecular chirality recognition have been anticipated but not extensively studied. Here, the authors report the application of a helical supramolecular polymer for the enantio separation of chiral guest molecules.
... Magnetic fields provide another way to direct the self-assembly of Col mesophases [32][33][34][35] . Anisotropic field interactions are driven primarily by the anisotropic magnetic susceptibility associated with the aromatic cores of discotic mesogens or 'discogens' . ...
Creating well-defined single-crystal textures in materials requires the biaxial alignment of all grains into desired orientations, which is challenging to achieve in soft materials. Here we report the formation of single crystals with rigorously controlled texture over macroscopic areas (>1 cm²) in a soft mesophase of a columnar discotic liquid crystal. We use two modes of directed self-assembly, physical confinement and magnetic fields, to achieve control of the orientations of the columnar axes and the hexagonal lattice along orthogonal directions. Field control of the lattice orientation emerges in a low-temperature phase of tilted discogens that breaks the field degeneracy around the columnar axis present in non-tilted states. Conversely, column orientation is controlled by physical confinement and the resulting imposition of homeotropic anchoring at bounding surfaces. These results extend our understanding of molecular organization in tilted systems and may enable the development of a range of new materials for distinct applications.
... For practical application, it is very important to realize and keep large macroscopic NLO properties for a long time. From this standpoint, it is the most crucial factor that inducing and keeping chromophore moieties to form ordered non- centrosymmetric arrangement by convenient processes [2,[7][8][9][10][11]. Although the poling procedure is usually applied to enhance the orderly arrangement of chromophores (Chart S1, Supporting Information online), the strong dipole-dipole interactions among the chromophore moieties will greatly hinder this poling process, which has become one of the major problems in this field [12][13][14]. ...
Large nonlinear optical (NLO) coefficient and good stability, two essential factors to evaluate second-order NLO materials, are difficult to be achieved in one molecule simultaneously. Herein, by utilizing the concept of “isolation chromophore”, “isolation group” and dendritic structure, a dendritic molecule D-NS and a dendronized hyperbranched polymer DHP-NS are prepared to investigate their structure-property relationship. For the small dendritic molecule D-NS, it exhibits a high d33 value of 140 pm/V. But this value can be easily dropped when the temperature is higher than 50 °C, which extremely limits its real application. After introducing D-NS into a dendronized hyperbranched polymer chains, the obtained DHP-NS also shows a high d33 value of 101 pm/V, but much better stability than D-NS. Even when its thin film was heated to 120 °C, no obvious decay can be observed in the d33 value of DHP-NS. This work demonstrates an effective strategy to realize both large NLO effect and good stability simultaneously.
... Later on, however, the paradigm changed, and in more recent work pores are usually introduced in the membranes after fixation of the LC morphology. Nanopores can be introduced in the LC network in many ways, which can be classified into two distinct approaches: (1) disrupting non-covalent bonds such as hydrogen bonds inherent in the network, creating voids because of for example Coulomb repulsion of the resulting charged head groups [36,37]; and (2) removal of a covalently, or non-covalently, linked template from the network, creating uniform pores [24,26,27,[38][39][40][41][42]. ...
... The second approach utilises a template molecule which is hydrogen bonded to three gallic acid monomers to form an AB3 complex, Figure 3b, yielding a nanoporous material after fixation of the morphology by polymerisation followed by selective removal of the template molecule (porogen). Smaller molecules (2-amino alcohols) have also been used as templates in a 1:1 stoichiometry [42,[51][52][53]. The order in the material after template removal was improved by using diene instead of acrylate reactive groups [53]. ...
... The reactive gallic acid derivatives were cross-linked with an acyclic diene metathesis reaction, and after removal of the benzimidazole porogen, a nanoporous material was obtained. The small anionic Smaller molecules (2-amino alcohols) have also been used as templates in a 1:1 stoichiometry [42,[51][52][53]. The order in the material after template removal was improved by using diene instead of acrylate reactive groups [53]. ...
In the present review, we discuss recent advances in the field of nanoporous networks based on polymerisable liquid crystals. The field has matured in the last decade, yielding polymers having 1D, 2D, and 3D channels with pore sizes on the nanometer scale. Next to the current progress, some of the future challenges are presented, with the integration of nanoporous membranes in functional devices considered as the biggest challenge.
Liquid crystal polymers (LCPs) have gained tremendous attention in recent years due to their great potentials from fabrication of responsive actuators and sensors to construction of intelligent soft robotic and light modulators. However, conventional LCPs with permanent cross‐links present tedious and unmodifiable stimuli‐responsiveness. Recently, dynamic bonds capable to reversibly break and reform have been integrated into LCP, imparting intrinsic dynamic characteristics. The dynamic LCP possesses unprecedented diverse functionalities including reprogrammability, recyclability, and self‐healing ability, becoming much more adaptive to surrounding environmental changes compared with the conventional counterpart. In this review, recent progress of dynamic bond‐based LCPs is summarized. The mechanism, preparation, and functionalities of dynamic LCPs based on dynamic noncovalent bond (DNCB) and dynamic covalent bond (DCB) are poised to be discussed, followed by introducing emergent LCPs combining both of DNCB and DCB. Consequently, the unique functionalities of dynamic bond‐based LCPs will be given. Finally, outlooks of development of the dynamic bond‐based LCPs are presented.
