Polymerizable hexacatenar liquid crystals containing a luminescent oligo(p-phenylenevinylene) core

Polymerizable hexacatenar mesogens containing a photo-active oligo(p-phenylenevinylene) core were successfully synthesized by replacing the traditional n-alkoxy tails on the molecules with polymerizable hydrocarbon tails containing terminal isoprenyl or 1,3-dienyl units. It was found that for this particular liquid crystal (LC) platform, the incorporation of conventional radical polymerizable groups such as acrylates in the tails was not conducive to the formation of thermotropic LC phases, presumably due to their polar nature. The resulting photoluminescent isoprenyl and 1,3-dienyl hexacatenar monomers were found to form columnar hexagonal phases at elevated temperatures (c. 45-75°C), as determined by powder X-ray diffraction. Unfortunately, photoinitiated radical polymerization studies revealed that the mesogens are susceptible to photodegradation in the LC state at elevated temperatures, resulting in the loss of both LC order and emission properties during photopolymerization. Thermally initiated radical polymerization in the absence of light, however, afforded effective crosslinking with retention of both LC order and the desired emission properties. The resulting crosslinked columnar hexagonal phases were found to exhibit emission maxima at nearly identical wavelengths, with comparable intensities relative to the unpolymerized starting materials. The effect of the different polymerizable groups on the mesogenic behaviour, polymerization characteristics, and emission properties of the hexacatenar compounds is presented.     

Synthesis and properties of new materials with banana-shaped achiral cores and chiral end groups

New chiral bent-core mesogens, derivatives of 1,3-phenylene bis[4-(alkanyloxyphenyliminomethyl)benzoate], were synthesized with variation of a substituent (X=F, Cl); their antiferroelectric properties are described. The mesomorphic and switching properties were characterized by differential scanning calorimetry, polarizing optical microscopy, triangular wave method, and X-ray diffractometry in the small and wide angle regions. The presence of chiral tails at the terminals of side wings in the bent-core molecules induced a decrease in transition temperature and formation of the switchable SmC* phase in the melt. In addition, the introduction of a lateral halogen substituent in the Schiff's base moiety prevented the regular stacking of the molecules, resulting in the formation of very complex optical textures. The smectic phase with F-substituted PBFDOB and Cl-substituted PBCDOB showed layer spacings of 39 and 38.5?Å, respectively, corresponding to the end-to-end distance of molecules with a bent conformation. Significantly, the smectic phases of PBFDOB and PBCDOB exhibited a period of 179.5 and 131?Å, respectively, compatible with a helical structure with periodicity about 4.6 and 3.4 times the layer spacings.     

Synthesis,liquid crystalline properties and fluorescence of polycatenar 1,3,4‐oxadiazole derivatives

A series of hexacatenar liquid crystals containing the 1,3,4‐oxadiazole group as rigid core, i.e. 1,4‐bis[(3,4,5‐trialkoxyphenyl)‐1,3,4‐oxadiazolyl]‐ benzene (P‐P‐oxd‐n), were designed and synthesised. Based on a detailed study of their thermotropic phase behaviour and mesophase structures, it was revealed that columnar phases are generated in these materials. Furthermore, combination of experimental and calculated results enabled a proposal for the molecular packing in the mesophase. The photoluminescent properties of these materials were examined using P‐P‐oxd‐8 as an example. A strong blue light emission (λ_max = 456 nm) was observed in P‐P‐oxd‐8 and a higher quantum yield was obtained in dilute chloroform solution.     

Synthesis and characterization of liquid crystalline elastomers bearing fluorinated mesogenic units and crosslinking mesogens

Several new side‐chain liquid crystalline (LC) polysiloxanes and elastomers ( IP ‐ VIP ) bearing fluorinated mesogenic units and crosslinking mesogens were synthesized by a one‐step hydrosilylation reaction with poly(methylhydrogeno)siloxane, a fluorine‐containing LC monomer 4′‐undec‐10‐enoyloxy‐biphenyl‐4‐yl 4‐fluoro‐benzoate and a crosslinking LC monomer 4′‐(4‐allyloxy‐benzoxy)‐biphenyl‐4‐yl 4‐allyloxy‐benzoate. The chemical structures and LC properties of the monomers and polymers were characterized by use of various experimental techniques such as FTIR, ¹H‐NMR, EA, TGA, DSC, POM and XRD. The effect of crosslinking mesogens on mesomorphic properties of the fluorinated LC polymers was studied as well. The obtained polymers and elastomers were soluble in many solvents such as toluene, tetrahydrofuran, chloroform, and so forth. The temperatures at which 5% weight loss occurred (T_d) were greater than 250°C for all the polymers, and the weight of residue near 600°C increased slightly with increase of the crosslinking mesogens in the fluorinated polymer systems. The samples IP , IIP , IIIP and IVP showed both smectic A and nematic phases when they were heated and cooled, but VP and VIP exhibited only a nematic mesophase. The glass transition temperature (T_g) of polymers increased slightly with increase of crosslinking mesogens in the polymer systems, but the mesophase–isotropic phase transition temperature (T_i) and smectic A–nematic mesophase transition temperature (T_S‐N) decreased slightly. It suggests that the temperature range of the mesophase became narrow with the increase of crosslinking mesogens for all the fluorinated polymers and elastomers. In XRD curves, the intensity of sharp reflections at low angle decreased with increase of crosslinking mesogens in the fluorinated polymers systems, indicating that the smectic order derived from fluorinated mesogenic units should be destroyed by introduction of more crosslinking mesogens. Copyright © 2008 John Wiley & Sons, Ltd.     

Polycatenar Mesogens with Various Degree of Flexibility of Molecular Structure

A series of newly synthesised rod‐like polycatenar mesogens forms columnar phases, with the number of molecules in the column cross section depending on the core rigidity. For non‐symmetric molecules, an additional density modulation, namely helical arrangement of molecules with a periodicity of approximately 10 molecular distances develops along the columns. For one of the compounds, a new type of columnar liquid crystal phase with 3D positional order is observed. Introducing a stilbene unit in the mesogenic core enhances the fluorescent properties of the compounds. In the hexagonal columnar phase, polarised light emission is observed.     

Facile Synthesis of Liquid Crystal Dimers Bridged with a Phosphonic Group

Liquid crystal (LC) dimers with well-defined composition and structure arouse broad attentions for their exhibiting LC properties beyond conventional low molar mass mesogens and serving as fascinating model compounds for LC polymers. Here in this work, a series of LC dimers bridged with a phosphonic group have been synthesized through a facile free radical mediated addition reaction between hypophosphorous acid and vinyl terminated cyanobiphenyl mesogens with variant length alkyl spacers. In addition, two esterified derivatives and a group of mono-addition homologues with a terminal phosphonic acid group have also been prepared for comparison study. All the newly synthesized compounds exhibit monotropic nematic (N) phase with typical schlieren textures except for the LC dimer with the longest eleven-methylene spacer, which surprisingly shows twist-bend nematic (N_TB) phase directly from the isotropic state upon cooling. Moreover, the thermal transition properties such as the nematic-isotropic transition temperatures and associated entropy changes of the series LC dimers display a modest odd-even effect. Furthermore, both the LC dimers and the mono-addition homologues in N phase are quite easy to achieve homeotropic alignment upon annealing thanks to the supramolecular interactions between the introduced phosphonic acid group and the hydroxylated glass surface. This work thus provides a novel synthesis strategy for a class of LC materials bridged with a phosphonic acid group prone to further functionalization, which may serve as promising vertical alignment agents and pave the way for developing a new kind of functionalized LC materials of N_TB phase.     

Syntheses and Properties of meso‐Substituted Porphyrin Mesogens with Triazole Linkages and Peripheral Alkyl Chains

Discotic mesogens P/n‐M (n=12, 16, 18, M=2 H, Zn and Cu) bearing a porphyrin core, triazole linkages and peripheral 3,4,5‐trialkoxybenzyl units have been synthesized by a click‐chemistry approach. The thermal behavior, photophysical properties and morphologies of these compounds were investigated by polarized optical microscopy (POM), differential scanning calorimetry (DSC), XRD, UV and PL, SEM and TEM. These compounds can self‐assemble into hexagonal columnar phases in their pure states and form organogels in 1,4‐dioxane with unusually flower‐like sphere morphology. The supramolecular complexes of P/18‐Zn with C₇₀ or 4,7‐di‐4‐pydriyl‐2,1,3‐benzothadiazole can display hexagonal columnar phases too. Additionally, zinc porphyrin compounds P/n‐Zn show binding selectivity to Cu²⁺ among a series of cations in THF/H₂O.     

Synthesis,characterisation and mesomorphic behaviours of non-symmetrically substituted 1,2,4- and 1,3,4-oxadiazole derivatives

Two series of non-symmetrically substituted bent-core mesogens derived from the central 3,5 and 2,5 cores of the 1,2,4- and 1,3,4-oxadiazole derivatives, respectively, containing ether and ester linkage have been synthesised by several straightforward synthetic procedures, and their mesomorphic behaviour was studied by optical polarising microscopy (OPM) and differential scanning calorimetry (DSC). The last five homologues of the 1,2,4-oxadiazole series exhibit a monotropic nematic phase on cooling, while the 1,3,4-oxadiazole derivatives do not show any liquid crystalline properties but rather a crystal to isotropic transition is observed by OPM. We show that the bent angles of the 1,2,4- and 1,3,4-oxadiazole rings are crucial in observing the liquid crystal (LC) phases formed, and also that the length of the alkyl substituent is observed to have a significant effect on the nature of the LC phases.     

Pyrrolidinium Ionic Liquid Crystals

N‐Alkyl‐N‐methylpyrrolidinium cations have been used for the design of ionic liquid crystals, including a new type of uranium‐containing metallomesogen. Pyrrolidinium salts with bromide, bis(trifluoromethylsulfonyl)imide, tetrafluoroborate, hexafluorophosphate, thiocyanate, tetrakis(2‐ thenoyltrifluoroacetonato)europate(III) and tetrabromouranyl counteranions were prepared. For the bromide salts and tetrabromouranyl compounds, the chain length of the alkyl group C_nH_2n+1 was varied from eight to twenty carbon atoms (n=8, 10–20). The compounds show rich mesomorphic behaviour: highly ordered smectic phases (the crystal smectic E phase and the uncommon crystal smectic T phase), smectic A phases, and hexagonal columnar phases were observed, depending on chain length and anion. This work gives better insight into the nature and formation of the crystal smectic T phase, and the molecular requirements for the appearance of this highly ordered phase. This uncommon tetragonal mesophase is thoroughly discussed on the basis of detailed powder X‐ray diffraction experiments and in relation to the existing literature. Structural models are proposed for self‐assembly of the molecules within the smectic layers. In addition, the photophysical properties of the compounds containing a metal complex anion were investigated. For the uranium‐containing mesogens, luminescence can be induced by dissolving them in an ionic liquid matrix. The europium‐containing compound shows intense red photoluminescence with high colour purity.     

Imidazolium‐based polymerized ionic liquid crystals containing fluorinated cholesteryl mesogens

A series of polymerized ionic liquid crystals (PILCs) bearing fluorinated cholesteryl mesogens were synthesized in this work, which include polymerized imidazolium bromides (PIBs) and polymerized imidazolium hexafluorophosphates (PIHs). The PIBs were synthesized using alkyl bromine‐containing polysiloxanes and 1‐butyl‐1H‐imidazole, and the PIHs were synthesized by anion metathesis reaction using the corresponding PIBs and KPF₆. The chemical structures, liquid crystalline (LC) properties, and electrorheological (ER) effect of these PILCs were characterized by use of various experimental techniques. All the PILCs showed smectic A mesophase on heating and cooling cycles. The smectic layer structure of these PILCs are originated from the rigid fluorinated cholesteryl mesogens and the flexible moieties in the LC phase, but the ion pairs (imidazolium cations–PF₆^?, Im⁺–PF₆^?; or imidazolium cations–Br^?, Im⁺–Br^?) can disperse in the polysiloxane matrix and expand the d‐spacing in the smectic layers. The PIHs show lower T_g and T_i than the corresponding precursor PIBs, which is due to the larger ion volume of Im⁺–PF₆^? for PIHs than that of Im⁺–Br^? for PIBs. A series of 40 V% ER fluids were prepared by mixing the PILCs with polydimethylsiloxane (PDMS), and the ER behaviors were studied. All the PILC/PDMS fluids showed ER effect, and the PIH/PDMS fluids show a little greater ER effect than the PIB/PDMS fluids. The PILC droplets in the ER fluids become deformed owing to both the orientation of fluorinated cholesteryl mesogens and the suppression of ionic migration when a DC electric field was applied, resulting in the occurrence of ER effect. Copyright © 2015 John Wiley & Sons, Ltd.     

Synthesis and properties of polyacetylenes with directly attached bis(4‐alkoxyphenyl)terephthalate mesogens as pendants

Liquid‐crystalline, monosubstituted polyacetylenes containing lateral pendants of bis(4‐alkoxyphenyl)terephthalate with no flexible spacers and alkoxy tails {RO, where R is CH₃ [P(1)] or C₆H₁₃ [P(6)]} were synthesized, and the effects of the backbone structure and alkoxy tails on the properties of the polymers were investigated. The polymerizations of acetylene monomers were carried out with chloronorbornadiene rhodium(I) dimer as a 1,2‐insertion catalyst in toluene. The structures and properties of the monosubstituted polyacetylenes were characterized and evaluated with nuclear magnetic resonance, infrared spectroscopy, thermogravimetry, differential scanning calorimetry, polarized optical microscopy, ultraviolet spectroscopy, and photoluminescence analyses. The molecular weights of the polymers were measured by gel permeation chromatography. The polymer with long tails (p‐hexyloxy), that is, P(6), formed a smectic mesophase upon heating above the melting temperature, but the other one with short tails (p‐methoxy), that is, P(1), could not exhibit liquid crystallinity at elevated temperatures. The steric effect of bulky, liquid‐crystalline mesogens and a direct connection with the main chain prevented the planar conformation of the polyene backbone and, therefore, led to the lower absorption and emission wavelength of the polymers. © 2006 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 44: 2499–2509, 2006     

T-shaped ionic liquid crystals based on the imidazolium motif: exploring substitution of the C-2 imidazolium carbon atom

In this contribution the first examples of so‐called rigid‐core, T‐shaped imidazolium ionic liquid crystals, in which the C‐2 atom of the imidazolium ring is substituted with an aryl moiety decorated with one or two alkoxy chains, are described. The length of the alkoxy chain(s) was varied from six to eighteen carbon atoms (n=6, 10, 14–18). Whereas the compounds with one long alkoxy chain display only smectic A phases, the salts containing two alkoxy chains exhibit smectic A, multicontinuous cubic, as well as hexagonal columnar phases, as evidenced by polarising optical microscopy, differential scanning calorimetry, and powder X‐ray diffraction. Structural models are proposed for the self‐assembly of the molecules within the mesophases. The imidazolium head groups and the iodide counterions were found to adopt a peculiar orientation in the central part of the columns of the hexagonal columnar phases. The enantiotropic cubic phase shown by the 1,3‐dimethyl‐2‐[3,4‐bis(pentadecyloxy)phenyl]imidazolium iodide salt has a multicontinuous Pm$\bar 3In this contribution the first examples of so-called rigid-core, T-shaped imidazolium ionic liquid crystals, in which the C-2 atom of the imidazolium ring is substituted with an aryl moiety decorated with one or two alkoxy chains, are described. The length of the alkoxy chain(s) was varied from six to eighteen carbon atoms (n=6, 10, 14-18). Whereas the compounds with one long alkoxy chain display only smectic A phases, the salts containing two alkoxy chains exhibit smectic A, multicontinuous cubic, as well as hexagonal columnar phases, as evidenced by polarising optical microscopy, differential scanning calorimetry, and powder X-ray diffraction. Structural models are proposed for the self-assembly of the molecules within the mesophases. The imidazolium head groups and the iodide counterions were found to adopt a peculiar orientation in the central part of the columns of the hexagonal columnar phases. The enantiotropic cubic phase shown by the 1,3-dimethyl-2-[3,4-bis(pentadecyloxy)phenyl]imidazolium iodide salt has a multicontinuous Pm ?3m structure. To the best of our knowledge, this is the first example of a thermotropic cubic mesophase of this symmetry.     

Induction of Columnar and Smectic Phases for Spiropyran Derivatives: Effects of Acidichromism and Photochromism

Liquid‐crystalline (LC) properties have been induced in a number of spiropyran derivatives by the addition of methanesulfonic acid. Spiropyran derivatives containing one or two gallic acid moieties with one, two, or three long alkyl chains were prepared. Acid‐induced spiro–protonated‐merocyanine isomerization induced mesomorphism for these materials. Equimolar mixtures of methanesulfonic acid and the spiropyran derivatives with one or two dodecyloxy chains exhibited smectic A phases, whereas the spiropyran derivatives containing the gallic acid moiety with three dodecyloxy chains showed hexagonal columnar phases. On the contrary, photoirradiation of the spiropyran compounds in the bulk liquid state did not lead to the induction of mesomorphism, although the merocyanine form was induced. These results suggest that these merocyanine derivatives with ionic and nonionic moieties cannot simply form nanosegregated LC structures. Complex formation of the merocyanine form with methanesulfonic acid may play a key role in the formation of LC molecular assemblies.     

From smectic to columnar phase of polypedal liquid crystals based on tetrathiafulvalene/1,3-dithiol-2-thione and cholesterol

Bipedal 1,3-dithiole-2-thiones attached two cholesteryl through a ω-thioalkanoyloxy spacer of varying length were synthesized. The bipedals were easily transformed to the appropriate tetrapedal tetrathiafulvalene derivatives by self-coupling reaction in net triethyl phosphite. All the synthesized compounds exhibit mesogenic phases in a wide temperature region, no crystallization but vitrifying to form glassy mesogens during cooling from the isotropic melt. The liquid crystals with shorter spacer (n=2-6) exhibited only a smectic A phase and those with the longest spacer (n=7) exhibited only a hexagonal columnar. In these series, the molecular packing depended on the length of spacers.     

From Mesomorphic Phosphine Oxide to Clustomesogens Containing Molybdenum and Tungsten Octahedral Cluster Cores

New clustomesogens (i.e., metal atom clusters containing liquid crystalline (LC) materials) have been obtained by grafting neutral cyanobiphenyl (CB)‐ or cholesteryl‐containing tailor‐made dendritic mesomorphic triphenylphosphine oxide ligands on luminescent (M₆Clⁱ₈)⁴⁺ octahedral cluster cores (M=Mo, W). The LC properties were studied by a combination of polarizing optical microscopy (POM), differential scanning calorimetry (DSC), and X‐ray powder diffraction analyses. While the organic ligands showed various mesophase types ranging from nematic, SmA columnar (SmA_Col), SmA, and SmC phases, it turned out that the corresponding clustomesogens formed layered phases (SmA) over a wide range of temperatures that depend on the nature and density of mesogenic groups employed. Intrinsic luminescence properties of the cluster precursors are preserved over the entire range of LC phase existence.     

Controlling domain orientation of liquid crystalline block copolymer in thin films through tuning mesogenic chemical structures

Controlling the macroscopic orientation of nanoscale periodic structures of amphiphilic liquid crystalline block copolymers (LC BCPs) is important to a variety of technical applications (e.g., lithium conducting polymer electrolytes). To study LC BCP domain orientation, a series of LC BCPs containing a poly(ethylene oxide) (PEO) block as a conventional hydrophilic coil block and LC blocks containing azobenzene mesogens is designed and synthesized. LC ordering in thin films of the BCP leads to the formation of highly ordered, microphase‐separated nanostructures, with hexagonally arranged PEO cylinders. Substitution on the tail of the azobenzene mesogen is shown to control the orientation of the PEO cylinders. When the substitution on the mesogenic tails is an alkyl chain, the PEO cylinders have a perpendicular orientation to the substrate surface, provided the thin film is above a critical thickness value. In contrast, when the substitution on the mesogenic tails has an ether group the PEO cylinders assemble parallel to the substrate surface regardless of the film thickness value. © 2017 Wiley Periodicals, Inc. J. Polym. Sci., Part B: Polym. Phys. 2017 , 55, 532–541     

C?H/π‐Interaction‐Guided Self‐Assembly in π‐Conjugated Oligomers

We report CH/π hydrogen‐bond‐driven self‐assembly in π‐conjugated skeletons based on oligophenylenevinylenes (OPVs) and trace the origin of interactions at the molecular level by using single‐crystal structures. OPVs were designed with appropriate pendants in the aromatic core and varied by hydrocarbon or fluorocarbon tails along the molecular axis. The roles of aromatic π‐stack, van der Waals forces, fluorophobic effect and CH/π interactions were investigated on the theromotropic liquid crystallinity of OPV molecules. Single‐crystal structures of hydrocarbon OPVs provided direct evidence for the existence of CH/π interactions between the π‐ring (H‐bond acceptor) and alkyl C? H (H‐bond donor). The four important crystallographic parameters, d_c?x=3.79 Å, θ=21.49°, φ=150.25° and d_Hp?x=0.73 Å, matched in accordance with typical CH/π interactions. The CH/π interactions facilitate the close‐packing of mesogens in x–y planes, which were further protruded along the c axis producing a lamellar structure. In the absence of CH/π interactions, van der Waals interactions drove the assembly towards a Schlieren nematic texture. Fluorocarbon OPVs exhibited smectic liquid‐crystalline textures that further underwent Smectic A (SmA) to Smectic C (SmC) phase transitions with shrinkage up to 11 %. The orientation and translational ordering of mesogens in the liquid‐crystalline (LC) phases induced H‐ and J‐type molecular arrangements in fluorocarbon and hydrocarbon OPVs, respectively. Upon photoexcitation, the H‐ and J‐type molecular arrangements were found to emit a blue or yellowish/green colour. Time‐resolved fluorescence decay measurements confirmed longer lifetimes for H‐type smectic OPVs relative to that of loosely packed one‐dimensional nematic hydrocarbon‐tailed OPVs.     

Peripheral chain length-dependent complex phase behaviour in C3-symmetric hexa-alkylated liquid crystals

We report the thermal and self-assembly properties of C₃-symmetric liquid crystalline (LC) molecules consisting of a conformationally tunable triazole-based mesogen and six-fold alkyl chains. Unlike the LC compound (1) based on non-crystallisable octyl chains, 2 and 3, which have crystallisable dodecyl and tetradecyl chains, respectively, exhibit a cold crystallisation which only takes place under slow heating conditions (2°C/min). In contrast with the vertically interdigitated lamellar crystalline phase of 1, a laterally interdigitated bilayered lamellar structure driven by the crystallisation of the dodecyl or tetradecyl chains is observed in the cold crystallisation temperature range. In addition to their crystalline morphology, 2 and 3 show LC morphological behaviour distinct from that of 1, 2 and 3 exhibit a hexagonal columnar LC phase consisting of T-shaped conformers rather than the lamellar LC phase of 1. The morphological transformation from the lamellar (1) to the columnar phase (2 and 3) can be rationalised by the alleviation of the conformational energy of the longer alkyl chains. Consequently, the simple variation of alkyl chain length in the C₃-symmetric LC system results in contrasting thermal and assembly properties in the crystalline and LC phases.     

Self‐Assembly of Imidazolium‐Based Rodlike Ionic Liquid Crystals: Transition from Lamellar to Micellar Organization

By using aryl‐amination chemistry, a series of rodlike 1‐phenyl‐1H‐imidazole‐based liquid crystals (LCs) and related imidazolium‐based ionic liquid crystals (ILCs) has been prepared. The number and length of the C‐terminal chains (at the noncharged end of the rodlike core) and the length of the N‐terminal chain (on the imidazolium unit in the ILCs) were modified and the influence of these structural parameters on the mode of self‐assembly in LC phases was investigated by polarizing microscopy, differential scanning calorimetry, and X‐ray diffraction. For the single‐chain imidazole derivatives nematic phases (N) and bilayer SmA₂ phases were found, but upon increasing the number of alkyl chains the LC phases were lost. For the related imidazolium salts LC phases were preserved upon increasing the number and length of the C‐terminal chains and in this series it leads to the phase sequence SmA–columnar (Col)–micellar cubic (Cub_I/Pm3n). Elongation of the N‐terminal chain gives the reversed sequence. Short N‐terminal chains prefer an end‐to‐end packing of the mesogens in which these chains are separated from the C‐terminal chains. Elongation of the N‐terminal chain leads to a mixing of N‐ and C‐terminal chains, which is accompanied by complete intercalation of the aromatic cores. In the smectic phases this gives rise to a transition from bilayer (SmA₂) to monolayer smectic (SmA) phases. For the columnar and cubic phases the segregated end‐to‐end packing leads to core–shell aggregates. In this case, elongation of the N‐terminal chains distorts core–shell formation and removes Cub_I and Col phases in favor of single‐layer SmA phases. Hence, by tailoring the length of the N‐terminal chain, a crossover from taper‐shaped to polycatenar LC tectons was achieved, which provides a powerful tool for control of self‐assembly in ILCs.     

New Type of Columnar Liquid Crystal Superlattice in Double-Taper Ionic Minidendrons

Wedge-shaped molecules, such as dendrons, are among the most important building blocks for directed supramolecular self-assembly. Here we present a new approach aimed at widening the range and complexity of potential mesophases by introducing double-tapered mesogens. Two series of compounds are presented, both alkali metal salts (Li, Na, Cs) of 3,4,5-tris-alkoxybenzoic acid with a second tapered tris-alkoxyaryl group attached at the end of an alkoxy chain. The double-tapered compounds all display an unusual hexagonal columnar phase consisting of one ionic and three non-ionic columns per unit cell. The cation size has an unexpectedly drastic effect on unit cell size. Unlike most columnar phases, the current phases show unusually high dimensional stability on heating, and high stiffness in spite of being 80–85 % aliphatic, attributed to their molecular topology. The described approach may lead to co-assemblies of multifunctional materials, for example, parallel p- and n-semiconducting nanowires or parallel ionic and electronic conductors.