Liquid Crystalline Behavior Research Articles

Controlling the Self-Assembly Behavior of Aqueous Chitin Nanocrystal Suspensions

As with many other biosourced colloids, chitin nanocrystals (ChNCs) can form liquid crystalline phases with chiral nematic ordering. In this work, we demonstrate that it is possible to finelytune the liquid crystalline behavior of aqueous ChNC suspensions finely. Such control was made possible by carefully studying how the hydrolysis conditions and suspension treatments affect the colloidal and self-assembly properties of ChNCs. Specifically, we systematically investigated the effects of duration and acidity of chitin hydrolysis required to extract ChNCs, as well as the effects of the tip sonication energy input, degree of acetylation, pH and ionic strength. Finally, we show that by controlled water evaporation, it is possible to retain and control the helicoidal ordering in dry films, leading to a hierarchical architecture analogous to that found in nature, e.g. in crab shells. We believe that this work serves as a comprehensive insight into ChNC preparation and handling which is required to unlock the full potential of this material in both a scientific and industrial context.

Luminescence Tuning of Fluorinated Bistolanes via Electronic or Aggregated-Structure Control

Organic luminescent materials have a wide range of practical applications, but the understanding of the relationship between molecular structure and luminescent behavior is lacking. Herein, we synthesized fluorinated bistolanes with an electron-donating alkoxy substituent at one terminal and an electron-withdrawing substituent at the other to realize systematic control of the electron-density distribution. Evaluation of the phase transition behavior revealed that most of the fluorinated bistolanes showed liquid-crystalline (LC) behavior, with the phase transition temperature depending on the terminal substituents. Additionally, the fluorinated luminophores displayed intense photoluminescence (PL) in solution and in their crystal phases. Remarkably, the PL color shifted dramatically depending on the dipole moment (μ||) along the long molecular axis; thus, PL tuning can be achieved through electronic modulation by precise control of the μ|| of the luminophore. Interestingly, in the LC phases under thermal conditions, the maximum PL band shifted by 0.210 eV upon phase transition from the crystal to smectic A LC phases, indicating that PL tuning can also be achieved by controlling the aggregated structure. These results offer a new molecular design for easily tunable PL materials using the molecular properties or external stimuli for promising applications, including light-emitting displays and PL sensing materials.

Synthesis of novel (-)-menthol-based azobenzene chiral liquid crystals and effect of terminal alkyl chains on mesomorphic behaviour

ABSTRACTA series of novel azobenzene chiral liquid crystals (Mt4AZOnB) containing (-)-menthyl were successfully synthesised. Terminal alkyl chains of the molecules varied from methyl to hexyl. The chemical structures were characterised by Fourier transform infrared and 1H-NMR spectra. Liquid crystalline behaviour of the chiral liquid crystals was characterised by differential scanning calorimetry and polarising optical microscopy. The effect of terminal alkyl chains on mesomorphic and photoisomerisation behaviour of azobenzene-based liquid crystals is discussed. The lower members (n = 1, 2, 3, 4) are monotropic and only the higher members (n = 5, 6) show enantiotropic behaviour. These compounds show a distinct odd-even effect for the phase transition temperature when the parity of the terminal chain is varied.

A Photoaddressable Liquid Crystalline Phase Transition in Graphene Oxide Nanocomposites

AbstractThe multifunctionality of graphene has the potential to unlock important developments in nanocomposite science. However, the manipulation of graphene without interfering with its unique properties and while controlling its spatial organization remains challenging. Here, the formation of a photoaddressable liquid crystalline (LC) solution through the stabilization of graphene oxide (GO) with photocleavable brushes is described. The LC behavior leads to the thermodynamic entrapment of GO into low aspect ratio domains that fail to display the properties typically predicted for graphene nanocomposites. The morphology and structural and electronic performance of these nanocomposites are regenerated through the brush cleavage, which controls the phase transition of the LC phase. These results show that kinetic control of graphene assembly can be an attractive tool toward the dynamic regulation of processable sol states and structured percolated networks for rational composite manufacturing.

Soft biomimetic nanoconfinement promotes amorphous water over ice.

Water is a ubiquitous liquid with unique physicochemical properties, whose nature has shaped our planet and life as we know it. Water in restricted geometries has different properties than in bulk. Confinement can prevent low-temperature crystallization of the molecules into a hexagonal structure and thus create a state of amorphous water. To understand the survival of life at subzero temperatures, it is essential to elucidate this behaviour in the presence of nanoconfining lipidic membranes. Here we introduce a family of synthetic lipids with designed cyclopropyl modifications in the hydrophobic chains that exhibit unique liquid-crystalline behaviour at low temperature, which enables the maintenance of amorphous water down to ~10 K due to nanoconfinement. The combination of experiments and molecular dynamics simulations unveils a complex lipid-water phase diagram in which bicontinuous cubic and lamellar liquid crystalline phases that contain subzero liquid, glassy or ice water emerge as a competition between the two components, each pushing towards its thermodynamically favoured state.

Amphotropic liquid-crystalline behaviour of glycolipids in amino acid ionic liquids

ABSTRACTWe examined lyotropic liquid-crystalline behaviour of glycolipids (GLs) with a normal alkyl chain or a diacetylene-functionalised alkyl chain in several amino acid ionic liquids (AAILs). It was found that the mixtures of GL and AAIL form various nanosegregated liquid-crystalline phases, such as smectic, bicontinuous cubic and hexagonal columnar phases, depending on the two-component ratio and AAIL species. The observed liquid-crystalline behaviours were summarised as phase diagrams. It is noteworthy that the employment of amino acid anions with superior hydrogen-bonding ability, such as aspartic and glutamic acid anions, gives a phase diagram with a wide liquid-crystalline region. Comparing with a phase diagram obtained for the GL/water mixtures, we gained insights on the similarity/dissimilarity between water and AAILs as self-organisation media of amphiphiles. For the diacetylene-functionalised molecule, UV irradiation was carried out to progress polymerisation. It is of interest that the polymerisation reaction progressed when the glycolipid formed a smectic phase in an AAIL while a reaction progress was not found when it formed a bicontinuous cubic phase in another AAIL. We believe that AAILs have a great potential to be a liquid media not only for amphiphiles but for various functional materials, such as polymers and colloids, to form novel assemblies.

“Synthesis, Mesomorphic and DFT Studies of Chalcone Derived Room Temperature Liquid Crystal with Presence of Lateral Nitro and N, N-Dimethyl Amino Terminal Group”

In this present article, we wish to report on the liquid-crystalline properties of chalcone-ester based homologous series of compounds having aliphatic chain length in n-alkoxy group (n = 1 to 10, 12, 14, 16, 18). The present series consisted thirteen compounds, in which comp.C1 and C2 shows nonliquid crystalline properties, while comp.C3 to C7 display SmC phase and comp.C8 to C18 exhibits only nematic phase. Textural pattern of presently synthesized compounds are schlieren and threaded type. All this compounds were well characterized by elemental analysis, FT-IR and 1H NMR. Phase transition temperatures of present synthesised compounds were determined by optical polarising microscopy (POM), differential scanning calorimetric (DSC). Detailed XRD investigation endorses the presence of the nematic phase in higher homologues and SmC phase in lower homologues. It is shown that chalcone with ester as linking unit favors a calamitic liquid crystalline behaviour in molecules. To get more insights, the DFT based HOMO, LUMO studies are carried out which supports intramolecular charge transfer interactions in this class of mesogens. Chalconyl ester based compounds C3 to C12 shows antibacterial as well as antifungal activity compared with corresponding standard drugs.

Surface functionalization effect of graphene oxide on its liquid crystalline and assembly behaviors

Surface functionalization effect of graphene oxide (GO) on its liquid crystalline and assembly behavior was investigated to examine the potential of surface modification strategy to produce a strong assembled structure. As a model study, a carboxylated GO (GO-COOH) was synthesized and its liquid crystalline and assembly behavior were systematically compared with pristine GO. Based on this study, we found that the transition concentration of GO from isotropic to biphasic phase decreased with carboxylation and the resulting lamella-assembled structures of GO-COOH exhibited much higher mechanical properties compared to GO after Ca2+ ion cross-linking.

Exploiting molecular symmetry reduction to enrich liquid crystal phase diversity

ABSTRACTThe strategic tuning of liquid crystalline phase behaviour by adjusting molecular symmetry was investigated. A family of sixteen symmetrical and unsymmetrical 2,6-di(4ʹ-n-alkoxybenzoyloxy) naphthalene derivatives were prepared and their liquid crystal properties examined by differential scanning calorimetry, polarised optical microscopy, and x-ray diffraction. All mesogens formed nematic phases, with longer-chain analogues also exhibiting smectic C phases at lower temperatures. Melting temperatures of the compounds strongly depend on molecular symmetry, whereas clearing transitions are relatively insensitive to this effect. A detailed analysis indicates that the clearing point can be predicted based on the nature of the terminal alkyl chains, with only a secondary effect from molecular symmetry. Moreover, low symmetry molecules showed a greater tendency to form smectic C phases, which was ascribed to the selective depression of the melting point versus the SmC-N transition. This demonstrates that molecular symmetry-breaking is a valuable tool both for tuning liquid crystalline phase range and for increasing a material’s polymorphism.

Some observations on the liquid crystalline and gel behaviors of aqueous dispersions of a prodrug

BMS-830216 is a diprotic acid prodrug of two pKa values (<2 and 6.8) with high apparent solubility at pH ≥ 7. At ∼ pH 4 solutions of BMS-830216 appear to be surface active, in which their surface tension can be reduced from 72 to 65 dynes when its concentrations is above the critical aggregation concentration (CAC∼0.2 mM). Additionally, at this pH, BMS-830216 tends to form liquid crystalline phases (at ≥ 2 mg/mL) in acetate buffer when using tris salt. Furthermore, after raising the concentration beyond 20 mg/g, formation of gel-like dispersions was noted. These gel-like dispersions exhibited a strong elastic strength, significantly impacting the dissolution behavior of the tris salt. Mechanistically, it is likely that BMS-830216 tris salt in solution first forms a lamellar phase followed by formation of a gel phase at higher concentrations (≥20 mg/mL). As indicated by SAXS, the lamellar phase formed seems to have two d-spacing values (∼5 nm and ∼10 nm (weak), which seems to correspond to two molecules connected tail by tail (5 nm). Further investigation is needed for phase identification, as their properties can affect the physical behavior of BMS-830216 in the development of pharmaceutical dosage forms.

Preparation of Series Schiff Bases and Studying of their Liquid Crystalline Behavior

Preparation of Series Schiff Bases and Studying of their Liquid Crystalline Behavior

Preparation of Series Schiff Bases and Studying of their Liquid Crystalline Behavior

Our study deals with preparation of two types of imine compounds differ in the type of terminal group, where one of them has a terminal carboxyl group COOH while the other contains methoxyOCH3 as a terminal group. In the first part of this research it was Identification by spectroscopy methods using infrared IR and nuclear magnetic resonance H NMR spectrum, besides elemental analysis shows the exact chemical structure of the expected synthesized compounds. In the second part was the study of liquid-crystalline behavior by polarized optical microscopy POM and differential scanning calorimetry DSC that showed a liquid crystal phase in the compounds that has odd number of carbon atoms in the terminal chain compounds in the first series, while the second series compounds showed liquid crystal phase in the compounds that containing even number of atoms of carbon in the terminal chain. DOI: https://doi.org/10.5281/zenodo.3376373

Room-Temperature Columnar Liquid Crystals as Efficient Pure Deep-Blue Emitters in Organic Light-Emitting Diodes with an External Quantum Efficiency of 4.0%

A novel design of aggregation-induced emission (AIE) active columnar (Col) luminomesogens is reported, and they are demonstrated to act as highly efficient deep-blue emitters in organic light-emitting diodes (OLEDs). All derivatives exhibit Col liquid crystalline (LC) behavior at room temperature over a wide temperature range and desirable alignment properties, which is very important in using them as materials for organic electronic devices. These new AIE active luminomesogens were found to act as highly efficient emitters in OLEDs and unveiled a maximum external quantum efficiency of 4.0% for the first time in Col LCs with Commission International de l'E'clairage coordinates of (0.17, 0.07), which closely matches the National Television System Committee (NTSC) standard, corresponding to pure deep blue color. The detailed supramolecular assembly of the compounds has been characterized by modeling in the mesophase derived from small- and wide-angle X-ray scattering results.

Mesomorphism behaviour and photoluminescent properties of new asymmetrical 1,2-di(4-alkoxybenzylidene)hydrazines

{1-[4-( n-Alkoxy)]-2-(4’-decyloxy)benzylidene}hydrazines ( n-alkoxy = O(CH2) nH, n = 1–9, 12, 16 or 18), an asymmetrical series of 1,2-disubstituted hydrazines, were prepared in a simple two-step procedure as a part of our continuing work in evaluating hydrophobic azine compounds as photoluminescent liquid crystalline materials. The compounds were characterized spectroscopically and their liquid crystalline behaviour and luminescent properties were evaluated using polarized light optical microscopy, differential scanning calorimetry and X-ray powder diffraction techniques. The studies revealed that all of these compounds are liquid crystalline materials exhibiting photoluminescent properties in the crystalline and liquid crystal states.

Molecular dynamics simulation of α-unsubstituted oligo-thiophenes: dependence of their high-temperature liquid-crystalline phase behaviour on molecular length

Phase diagram of α-nT oligomers with n = 5–8 from the MD simulations.

Improving the mesomorphic behaviour of supramolecular liquid crystals by resonance-assisted hydrogen bonding

A significant impact of resonance-assisted hydrogen-bonding (RAHB) on the liquid crystalline behavior of hydrogen-bonded mesogens is reported and systematically investigated.

Photoresponsive halogen bonded polycatenar liquid crystals

Photosensitive liquid crystalline materials whose properties could be modified with UV–visible light irradiation are of special interest for photosensitive and photoswitching materials. Herein we represent the first examples of light-responsive halogen bonded supramolecular polycatenars. Photoswitchable liquid-crystalline aggregates were designed and prepared via halogen bond formation between a non-mesogenic taper shaped tetrafluoroiodobenzene based halogen bond-donor and non-mesogenic or mesogenic azopyridine derivatives as halogen bond-acceptors. The liquid crystalline behaviour of the prepared materials was characterized by differential scanning calorimetry (DSC), polarized optical microscope (POM) and X-ray diffraction (XRD). Upon irradiation with UV light, the complexes undergo fast and reversible photoinduced phase transition. Interestingly, some of these halogen-bonded polycatenars exhibit enantiotropic liquid crystalline phases over wide temperature ranges which are the widest among all previously reported photoresponsive perfluoroaryliodide based supramolecular halogen bonded liquid crystals.

Circularly polarized luminescence based on columnar self-assembly of tetraphenylethylene with multiple cholesterol units

The influence of different states of AIE derivative with columnar liquid crystalline phase on circularly polarized luminescence (CPL) was investigated in this work. Two novel tetraphenylethylene derivatives with multiple cholesterol units (TPE-C and TPE-SC) were prepared. They exhibited enantiotropic liquid crystalline behaviours with the ordered hexagonal columnar mesophase. They possessed excellent AIE properties in H2O-THF system. The fluorescence quantum yields of TPE-C and TPE-SC at solid state were as high as 28.8% and 22.6%, respectively. The chiral transfer from cholesterol units to TPE cores was confirmed by CD spectra. The studies on CPL spectra suggested that their CPL behaviors were tuned by the different states. They showed weak CPL properties at solid and isotropic state but strong CPL luminescence at liquid crystalline phase based on the orderly columnar self-assembly. The glum of TPE-SC at liquid crystalline phase reached 8.83 × 10−2.

Identifying Structural Determinants of Mesomorphism from Focused Libraries of Tripedal Mesogens Prepared via the Passerini Three‐Component Reaction

Heterolithic tripedal mesogens are branched, multifunctional molecules that exhibit liquid crystalline properties. The liquid crystalline phase behavior of heterolithic tripedal mesogens can be challenging to predict from the structures of the different branches. To elucidate the structural basis for smectic mesomorphism in the first examples of heterolithic ABC tripedal mesogens, we synthesized and characterized six homolithic, three heterolithic AB2, and seven heterolithic ABC tripedes. The synthesis strategy took advantage of the Passerini three‐component reaction to elaborate focused compound libraries in a combinatorial and high throughput manner. The phase behavior of the tripedes was characterized by a combination of polarized optical microscopy (POM), differential scanning calorimetry (DSC), and powder X‐ray diffraction techniques. We show that one end‐group of the heterolithic mesogens is responsible for the emergence of smectic mesomorphism in the presence of other groups that prefer nematic mesomorphism. Understanding how these structurally complex, non‐conventional mesogens self‐organize in liquid crystalline mesophases is significant for designing functional materials with predictable hierarchical order.

Phase-dependent photoluminescence of non-symmetric 2,1,3-benzothiadiazole liquid crystals

In order to understand the effect of disubstitution on calamitic liquid crystals, a series of non-symmetric 2,1,3-benzothiadiazole compounds were synthesized and characterized. These specific molecular architectures without the C2 axis were prepared to investigate their mesomorphism and physical properties and to compare them with symmetric molecules. Their liquid crystalline behavior was studied by differential scanning calorimetry, polarized optical microscopy and X-ray diffraction. The thermal properties evidenced the influence of non-symmetric design on the formation of liquid crystalline phases. Photophysical studies were performed in solution and with films, where these materials displayed intense photoluminescence between 500–650 nm, high quantum yields (ΦF = 0.62 – 0.96) and strong solvatochromism. Photoluminescence was measured as a function of temperature, displaying a strong dependence on the phase.