Twist Sense Research Articles

Spatial Control of 2D Nanomaterial Electronic Properties Using Chiral Light Beams.

Single-layer two-dimensional (2D) nanomaterials exhibit physical and chemical properties which can be dynamically modulated through out-of-plane deformations. Existing methods rely on intricate micromechanical manipulations (e.g., poking, bending, rumpling), hindering their widespread technological implementation. We address this challenge by proposing an all-optical approach that decouples strain engineering from micromechanical complexities. This method leverages the forces generated by chiral light beams carrying orbital angular momentum (OAM). The inherent sense of twist of these beams enables the exertion of controlled torques on 2D monolayer materials, inducing tailored strain. This approach offers a contactless and dynamically tunable alternative to existing methods. As a proof-of-concept, we demonstrate control over the conductivity of graphene transistors using chiral light beams, showcasing the potential of this approach for manipulating properties in future electronic devices. This optical control mechanism holds promise in enabling the reconfiguration of devices through optically patterned strain. It also allows broader utilization of strain engineering in 2D nanomaterials for advanced functionalities in next-generation optoelectronic devices and sensors.

Twisted domains in ferroelectric nematic liquid crystals

Ferroelectric nematics present properties promising for applications, which strongly depend on the confinement conditions and the presence of defects. In this work, we have observed and analysed textures in the cells with homogeneous geometry for a ferroelectric nematogen. The studied compound designated NF6 reveals the ferroelectric nematic phase, NF, directly on cooling from the isotropic phase. The NF phase is stable and persists down to the room temperatures. Textures in the homogeneous cell with antiparallel alignment prefer to be arranged in twisted domains with borderlines oriented preferentially in the perpendicular direction with respect to the surface alignment (rubbing direction). We have described these domains and developed a model of 2π disclinations, which are separating the areas with an opposite twist sense. We discuss the character of disclination charge and explained why these disclination lines prefer to be oriented perpendicularly to the rubbing direction.

Probing the Sense of Spin Twisting in Magnetic Skyrmion Lattice by Resonant X-ray Scattering

Probing the Sense of Spin Twisting in Magnetic Skyrmion Lattice by Resonant X-ray Scattering

Controlling nano- and microfilament morphology by strategically placing chiral centers in the side chains of bent-core molecules.

Self-assembled lamellar nano- and microfilaments formed by select types of bent-core molecules are prime examples of the interplay between molecular conformation and morphological chirality. Here, we demonstrate how the strategic placement of chiral centers at C-1 and/or C-3 in the terminal alkyloxy side chains, largely based on a priori calculations of molecular conformation, leads to the predictable formation of increasingly complex nano- and microfilament morphologies. Adding to the previously described diversity of twisted and writhed filament types, we here demonstrate and explain the formation and coexistence of flat nanoribbons, nanocylinders, or nano- as well as microfilaments where the morphology spontaneously changes along the filament long axis. For some these more exotic types of filament morphology, helical multilayer filaments suddenly unwind to form flat nanoribbons that also twist again under preservation (not perversion) of the helical twist sense. Moreover, the morphologies formed by this series of molecules now allows us to demonstrate the complete transformation from flat multilayer ribbons over microfilaments and helical-wrapped nanocylinders to helical nanofilaments depending on the number and position of chiral centers in the aliphatic side chains.

Tracing chirality from molecular organization to triply-periodic network assemblies: Threading biaxial twist through block copolymer gyroids

Chirality transfer from the level of molecular structure up to mesoscopic lengthscales of supramolecular morphologies is a broad and persistent theme in self-assembled soft materials, from biological to synthetic matter. Here, we analyze the mechanism of chirality transfer in a prototypical self-assembly system, block copolymers (BCPs), in particular, its impact on one of the most complex and functionally vital phases: the cubic, triply-periodic, gyroid network. Motivated by recent experimental studies, we consider a self-consistent field model of ABC* triblock copolymers possessing an end-block of chiral chain chemistry and examine the interplay between chirality at the scale of networks in alternating double network phases and the patterns of segmental order within tubular network domains. We show that while segments in gyroids exhibit twist in both polar and nematic segmental order parameters, the magnitude of net nematic twist is generically much larger than polar twist, and more surprising, reverses handedness relative to the sense of polar order as well as the sense of dihedral twist of the network. Careful analysis of the intra-domain nematic order reveals that this unique chirality transfer mechanism relies on the strongly biaxial nature of segmental order in BCP networks and relates the biaxial twist to complex patterns of frame rotation of the principal directors in the intra-domain texture. Finally, we show that this mechanism of twist reversal leads to chirality selection of alternating gyroid networks in ABC* triblocks, in the limit of very weak chirality.

Collimating the growth of twisted crystals of achiral compounds.

A great proportion of molecular crystals can be made to grow as twisted fibrils. Typically, this requires high crystallization driving forces that lead to spherulitic textures. Here, it is shown how micron size channels fabricated from poly(dimethylsiloxane) (PDMS) serve to collimate the circular polycrystalline growth fronts of optically banded spherulites of twisted crystals of three compounds, coumarin, 2,5-bis(3-dodecyl-2-thienyl)-thiazolo[5,4-d]thiazole, and tetrathiafulvalene. The relationships between helicoidal pitch, growth front coherence, and channel width are measured. As channels spill into open spaces, collimated crystals "diffract" via small angle branching. On the other hand, crystals grown together from separate channels whose bands are out of phase ultimately become a single in-phase bundle of fibrils by a cooperative mechanism yet unknown. The isolation of a single twist sense in individual channels is described. We forecast that such chiral molecular crystalline channels may function as chiral optical wave guides.

Conformational Control of ortho-Phenylenes by Terminal Amides.

Control over the folding of oligomers, be it broad induction of a preferred helical handedness or subtle changes in the orientations of individual functional groups, is important for applications ranging from molecular recognition to long-range conformational communication. Here, we report a series of ortho-phenylene hexamers functionalized with achiral and chiral amides at their termini. NMR spectroscopy, taking advantage of 19F labeling, allows multiple conformers to be detected for each compound. In combination with CD spectroscopy and DFT calculations, specific geometries corresponding to each conformer have been identified and quantified. General conclusions about the effect of sterics and the amide linker on conformational behavior have been drawn, revealing some similarities to and key differences from previously reported imines. A model for twist sense control has been developed that is supported by computational models.

Engineering Chiral Induction in Centrally Functionalized o-Phenylenes.

Work on foldamers, nonbiological oligomers that mimic the hierarchical structure of biomacromolecules, continues to yield new architectures of ever increasing complexity. o-Phenylenes, a class of helical aromatic foldamers, are well-suited to this area because of their structural simplicity and the straightforward characterization of their folding in solution. However, control of structure requires, by definition, control over folding handedness. Control over o-phenylene twist sense is currently lacking. While chiral induction from groups at o-phenylene termini has been demonstrated, it would be useful to instead direct twisting from internal positions to leave the ends free. Here, we explore chiral induction in a series of o-phenylenes with chiral imides at their centers. Conformational behavior has been studied by nuclear magnetic resonance and circular dichroism spectroscopies and density functional theory calculations. Chiral induction in otherwise unfunctionalized o-phenylenes is generally poor. However, strategic functionalization of the helix surface with trifluoromethyl or methyl groups allows it to better interact with the imide groups, greatly increasing diastereomeric excesses. The sense of chiral induction is consistent with computational models that suggest that it primarily arises from a steric effect.

The Search for Magnetotail Twisting at Mercury: Comparing MESSENGER Observations With the Terrestrial Case

AbstractPrevious studies reported that the terrestrial and Martian magnetotails can become twisted due to the solar wind‐planetary interaction; however, the associated physical processes proper of intrinsic and induced magnetospheres are still under debate. In particular, there is evidence that the Interplanetary Magnetic Field (IMF) dawn‐dusk component (By) plays a major role in both environments, affecting the sense of twist. Here, we analyze all MErcury, Surface, Space ENvironment, GEochemistry and Ranging Magnetometer observations to investigate the IMF By influence on Mercury's magnetotail. We find that Mercury's tail twist is very small (≲3°), for a median downtail distance of ∼2 Mercury radii. We also identify a correlation between the IMF By and the local By component around the magnetotail current sheet. These results suggest the small (or lack of) twist may be explained by the dipolar field strength in the near‐magnetotail. We examine this hypothesis by putting these observations into context with studies on the terrestrial magnetotail.

The comparison of self-assembling behaviour of phenyl biphenylcarboxylate and biphenyl benzoate compounds with the different length and shape of chiral terminal chain

Our recent advances on polymer-stabilised orthoconic antiferroelectric liquid crystals (PSOAFLCs) eliminated the asymmetry of switching times in electro-optical effect based on surface stabilized OAFLCs and paved the way for their effective use in many photonic and optoelectronic devices requiring very fast switching. To fabricate new modifications of PSOAFLCs, besides bi- and tetrafunctional monomers, multicomponent AFLCs mixtures with a very low meting point, high stability of the antiferroelectric phase at lower temperatures and higher helical pitch length are desirable. Herein, a very convenient synthetic method of new AFLC compounds with a phenyl biphenylcarboxylate structure of the rigid core with different length and shape of terminal chains is reported. The resulting mesomorphic properties and helical parameters are compared with those of analogues with a biphenyl benzoate structure of the rigid core. The designed AFLC compounds clearly possess definite advantages. Specifically, they exhibit lower meting points, higher clearing points, broader temperature range of the antiferroelectric phase (SmCA*) and much longer helical pitch length, especially for analogues with the shortest achiral terminal chain, but unexpectedly lower tendency to give the direct transition between the antiferroelectric and isotropic phase. The introduction of the cycloalkyl ring at the end of the chiral terminal chain increases the melting points, flattens the temperature dependence of the helical pitch and changes the sense of the helical twist, but also enhances the ability of the direct SmCA*-Iso phase transition, regardless the type of the rigid core. The obtained results highlight a possibility of utilizing compounds with the phenyl biphenylcarboxylate structure of the rigid core, designed under this work, together with previously prepared compounds with the biphenyl benzoate rigid core to formulate multicomponent OALFC mixtures with a very low melting point and a very high helical pitch length.

Intrinsically chiral ferronematic liquid crystals: An inversion of the helical twist sense at the chiral nematic – Chiral ferronematic phase transition

The ferroelectric nematic phase is a unique example of a polar phase without positional order of the constituent molecules. The properties of the ferronematic phase formed by intrinsically chiral molecules are discussed. Chirality makes the phase structure helical with the similar pitch length in the N* and N F * phases, but with opposite sense. The materials show strong non-linear optical properties. • Intrinsically chiral mesogens forming ferroelectric fluidic nematic, N F *, phase were obtained and studied. • In both, paraelectric and ferroelectric nematic phases, molecular chirality leads to helical structure. • Inversion of helix twist sense was observed at the N*-N F *phase transition. • Giant dielectric permittivity, above 10 4 , was determined in ferroelectric nematic phase. • Strong nonlinear optical properties were confirmed for ferronematic phase. Strongly dipolar mesogenic compounds with a chiral center located in a lateral alkyl chain were synthesized, and shown to form the ferroelectric nematic phase. The presence of molecular chirality induced a helical structure in both the N* and N F * phases, but with opposite helix sense in the two phases. The relaxation frequency of the polar fluctuations is only weakly affected by helical structure, it was found to be slightly lower for the chiral N F * phase than for its achiral, non-branched counterpart with the same lateral chain length.

Guest-Driven Control of Folding in a Crown-Ether-Functionalized ortho-Phenylene.

A crown-ether-functionalized o-phenylene tetramer has been synthesized and coassembled with monotopic and ditopic, achiral and chiral secondary ammonium ion guests. NMR spectroscopy shows that the o-phenylene forms both 1:1 and 1:2 complexes with monotopic guests while remaining well-folded. Binding of an elongated ditopic guest, however, forces the o-phenylene to misfold by pulling the terminal rings apart. A chiral ditopic guest biases the o-phenylene twist sense.

Polymeric Indolenine–Squaraine Foldamers with a Preferred Helix Twist Sense and Their Chiroptical Absorption and Emission Properties

Polymeric Indolenine–Squaraine Foldamers with a Preferred Helix Twist Sense and Their Chiroptical Absorption and Emission Properties

Thin smectic liquid crystalline fibrils of chiral rodlike particles.

Inspired by recent experimental work on virus-polymer mixtures, we study the properties of thin smectic fibrils composed of chiral rodlike particles using Monte Carlo simulations. Due to the interplay between surface energy, elastic deformation energy, and entropic effects, the fibril's layers relax into a twisted state. We focus our study on the layers' twist direction and map our results to the antiferromagnetic Ising model. In this view, the chiral interaction mimics an external field that drives the layers to have the same sense of twist. Besides, we determine the free energy difference and barrier height between an alternating and a nonalternating sequence of twisted layers composed of achiral rods and find that an alternating sequence is slightly preferred. We also see that the fibrils contract on increasing the chiral interaction strength and think that further studies on self-assembled functional materials can use our results.

On a class of orientable and nonorientable strip surfaces

In this paper a class of regular surfaces, generated by rotation and twist of a rigid line segment, is considered. Firstly a complete description of those surfaces by means of local charts is obtained and then its orientability is characterized in terms of the number of half-twists, taking into account their direction (clockwise or counterclockwise) since changes in the sense of twist are allowed. Indeed a procedure to construct nonorientable surfaces is provided. Illustrative examples and computer-generated plots using the free software Maxima are included.

Handedness Inversion in Chiral Nematic (Ethyl)cellulose Solutions: Effects of Substituents and Temperature

Various acylates and phenylcarbamates of (ethyl)cellulose (EC) were synthesized by acylation and carbanilation, respectively, of the residual hydroxyls of an EC (ethyl DS = 2.50). The acyl substituents adopted were propionyl, butyryl, cyclohexanoyl, and adamantoyl groups, and the phenylcarbamoyl substituents included 3-chlorophenylcarbamoyl, 4-chlorophenylcarbamoyl, 3-methylphenylcarbamoyl, and bare phenylcarbamoyl groups. Chiral nematic mesophases of the EC derivatives, formed in chloroform, acetic acid (AA), and dichloroacetic acid (DCA), were examined by various optical techniques for evaluation of the helical pitch (P) in a set of absolute value and twist sense. The lyotropic samples prepared with DCA (20 °C) always assumed a right-handed chiral nematic structure, regardless of the degree of acyl (or phenylcarbamoyl) substitution (DSAcyl (or DSPC), ≤0.50). The chiral nematic series with AA (20 °C) and chloroform (5 °C) showed an inversion of the twist sense from being left-handed to right-handed, when DSAcyl (or DSPC) of each derivative was increased. The critical DS value for the inversion varied depending on the chain length, bulkiness, and polar nature of the employed substituent. For all of the lyotropic series explored, it was generalized that a temperature elevation strengthens a left-handed twisting power in each chiral nematic mesophase. Reversal of the twist handedness was also observed in a cycle of heating and cooling of some chiral nematics in AA. This was interpreted as being due to compensation in the strength of the two chiral interactions, i.e., steric repulsion and dispersion interaction between mesogenic molecules, contributing in mutually opposite signs to the twisting power (2πP–1) of the mesophase.

Computational investigation of the thermo-fluidic effects of inserting twisted tape with alternating twists with notches

A study on the effect of using a clockwise and anti-clockwise twisted tape with semi-circular notches has been carried out with the help of computational fluid dynamics software ANSYS FLUENT in 3-dimensional flow domain. The study involves a counter flow tube heat exchanger carrying water in inner and annulus pipe. The inlet temperature used was 328 K for hot inlet and 288.5 K for cold inlet. Alternating sense of twist with twist ratio of 2.5 over lengths of 500 mm, 1000 mm, 1500 mm, and 2000 mm has been inserted in inner hot fluid carrying tube. The inlet Reynolds number (Re) was varied simultaneously in both tubes in the range of 10,000 to 30000. After validation of the simulation, effect on rate of heat transfer, drop in pressure and thermal efficacy index was reported. The maximum increment in the Nusselt number (Nu) was up to 1.8 times that obtained in bare tube whereas corresponding friction factor (f) was found to be increased by 5 times. The Thermal Efficacy Index (η) for the tape with length ratio 1 was highest among rest i.e., 0.25, 0.5, and 0.75.

Chiroptical Differentiation of Twisted Chiral and Achiral Polymer Crystals

Charles Mauguin, in his groundbreaking 1911 paper on mechanically twisted, nematic liquid crystal cells, speculated on the possibility of measuring the effects on polarized transmitted light along a sufficiently plastic crystalline material with a preserved twist. This experiment is realized in crystalline, spherulitic polymers wherein twisted, fibrous lamellae emanating from the cores are directed along the wave vector of the incident light. Twisted lamellae of synthetic polymers are found in optically banded spherulites of both chiral and achiral polymers. The material’s chirality (the mesoscopic twist sense) is established at the cores where crystals nucleate. However, determining the twist sense directly by microstructural analyses (e.g., scanning probe or electron microscopy) is possible only in favorable cases. An optical assay, of the kind suggested by Mauguin, would be universal. The differential transmission of circularly polarized light in the cores of polymer spherulites was imaged by complete ...

The Chiral Twist-Bend Nematic Phase (N*TB ).

The twist-bend nematic, NTB , phase has been observed for chiral materials in which chirality is introduced through a branched 2-methylbutyl terminal tail. The chiral twist-bend nematic phase, N*TB , is completely miscible with the NTB phase of the standard achiral material, CB6OCB. The N*TB phase exhibits optical textures with lower birefringence than those observed for the achiral NTB phase, suggesting an additional mechanism of averaging molecular orientations. The N*-N*TB transition temperatures for the chiral materials are higher than the NTB -N transition temperatures seen for the corresponding racemic materials. This suggests the double degeneracy of helical twist sense in the phase is removed by the intrinsic molecular chirality. A square lattice pattern is observed in the N* phase over a temperature range of several degrees above the N*TB -N phase transition, which may be attributed to a non-monotonic dependence of the bend elastic constant.

Lemon twist catalysis

Organic Chemistry The limonene in citrus peels is a readily available and environmentally friendly chiral compound. Nonetheless, it lacks the functionality for direct use in most types of asymmetric catalysis. Nagata et al. report that when used as a solvent, limonene can bias the twist sense of an otherwise achiral polymer through subtle collective interactions. This polymer can then act as an asymmetric ligand, binding palladium at pendant phosphines to catalyze formation of binaphthyl compounds via Suzuki coupling in 98% enantiomeric excess. Asymmetric hydrosilylation was also demonstrated. ACS Cent. Sci. 10.1021/acscentsci.9b00330 (2019).