Chiral Superstructures Research Articles

Responsive Chirality: Tailoring Supramolecular Assemblies with External Stimuli as Future Platforms for Electronic/Spintronic Materials.

Supramolecular chirality is the major branch of supramolecular chemistry, which not only plays important roles in biological processes but also in synthetically designed aggregated systems. To understand the complex processing of biological systems, the only way is to design supramolecular chiral ensembles that mimic natural biomolecules such as Deoxyribonucleic acid (DNA), Ribonucleic acid (RNA), amino acids, etc. In addition, chiral systems and self-assemblies as molecular motifs with breaking spatial inversion symmetry have been regarded as key substances in electronics and spintronics as well as in fundamental chemistry and physics. Here, in this review, our major concern is understanding modulation in spatial arrangements and packing modes under the impact of any external stimuli, which results in tailoring the handedness of resulted supramolecular chiral superstructures. We, in this review, highlighted the role of external stimuli such as solvent, chemical additives, photo exposure, etc. in altering the supramolecular chirality for their future utility as "active switches" in optoelectronic and spintronic devices and applications.

Circularly Polarized Lasing from Helical Superstructures of Chiral Organic Molecules.

Chiral supramolecular aggregates have the potential to explore circularly polarized lasing with large dissymmetry factors. However, the controllable assembly of chiral superstructures towards deterministic circularly polarized laser emission remains elusive. Here, we design a pair of chiral organic molecules capable of stacking into a pair of definite helical superstructures in microcrystals, which enables circularly polarized lasing with deterministic chirality and high dissymmetry factors. The microcrystals function as optical cavities and gain media simultaneously for laser oscillations, while the supramolecular helices endow the laser emission with strong and opposite chirality. As a result, the microcrystals of two enantiomers allow for circularly polarized laser emission with opposite chirality and high dissymmetry factors up to ~1.0. This work demonstrates the chiral supramolecular assemblies as an excellent platform for high-performance circularly polarized lasers.

Circularly Polarized Lasing from Helical Superstructures of Chiral Organic Molecules

Chiral supramolecular aggregates have the potential to explore circularly polarized lasing with large dissymmetry factors. However, the controllable assembly of chiral superstructures towards deterministic circularly polarized laser emission remains elusive. Here, we design a pair of chiral organic molecules capable of stacking into a pair of definite helical superstructures in microcrystals, which enables circularly polarized lasing with deterministic chirality and high dissymmetry factors. The microcrystals function as optical cavities and gain media simultaneously for laser oscillations, while the supramolecular helices endow the laser emission with strong and opposite chirality. As a result, the microcrystals of two enantiomers allow for circularly polarized laser emission with opposite chirality and high dissymmetry factors up to ~1.0. This work demonstrates the chiral supramolecular assemblies as an excellent platform for high‐performance circularly polarized lasers.

Optically Ambidextrous Reflection Circularly Polarized Luminescence Film with High Dissymmetry Factor and On‐Demand Handedness

AbstractThe self‐assembled cellulose nanocrystal (CNC) film has a left‐handed layered structure, which makes the reflection of right‐handed circularly polarized (CP) light a challenge. Herein, a nematic phase layer is designed and inserted into the chiral organization, to work as a half‐wave retarder and make the ambidextrous CP light reflection. The maximum reflectivity exceeds 80%, which breaks the 50% limitations of single‐direction light reflection and is the current maximum in all the reported CNC‐based films. This “sandwich‐like” structure displays different optical properties on both sides, displayed as the chromatism and the inversion of the circular dichroism signals. The dual CP light reflection and direction‐dependent optical phenomena are reserved in the synthesized circularly polarized luminescence (CPL) film, with the dissymmetry factor (glum) of −0.4245. However, this luminescent intensity and single‐direction emission are not enough in advanced optical systems. This work designs a triple CPL amplification path and develops the handedness inversion strategy, with the glum of −1.0551 and 0.4082. Then, the dual‐directional CPL emission films are designed, where the chiral optics can be switched on‐demand. Finally, the photonic crystal films are applied in the anti‐counterfeit and chiral superstructure induction.

Intense Circularly Polarized Luminescence Induced by Chiral Supramolecular Assembly: The Importance of Intermolecular Electronic Coupling

Herein we report on circularly polarized luminescence (CPL) emission originating from supramolecular chirality of organic microcrystals with a |glum| value up to 0.11. The microcrystals were prepared from highly emissive difluoroboron β‐diketonate (BF2dbk) dyes R‐1 or S‐1 with chiral binaphthol (BINOL) skeletons. R‐1 and S‐1 exhibit undetectable CPL signals in solution but manifest intense CPL emission in their chiral microcrystals. The chiral superstructures induced by BINOL skeletons were confirmed by XRD analysis. Spectral analysis and theoretical calculations indicate that intermolecular electronic coupling, mediated by the asymmetric stacking in the chiral superstructures, effectively alters excited‐state electronic structures and facilitates electron transitions perpendicular to BF2bdk planes. The coupling increases cosθµ,m from 0.05 (monomer) to 0.86 (tetramer) and triggers intense optical activity of BF2bdk. The results demonstrate that optical activity of chromophores within assemblies can be regulated by both orientation and extent of intermolecular electronic couplings.

Intense Circularly Polarized Luminescence Induced by Chiral Supramolecular Assembly: The Importance of Intermolecular Electronic Coupling.

Herein we report on circularly polarized luminescence (CPL) emission originating from supramolecular chirality of organic microcrystals with a |glum| value up to 0.11. The microcrystals were prepared from highly emissive difluoroboron β-diketonate (BF2dbk) dyes R-1 or S-1 with chiral binaphthol (BINOL) skeletons. R-1 and S-1 exhibit undetectable CPL signals in solution but manifest intense CPL emission in their chiral microcrystals. The chiral superstructures induced by BINOL skeletons were confirmed by single-crystal XRD analysis. Spectral analysis and theoretical calculations indicate that intermolecular electronic coupling, mediated by the asymmetric stacking in the chiral superstructures, effectively alters excited-state electronic structures and facilitates electron transitions perpendicular to BF2bdk planes. The coupling increases cosθμ,m from 0.05 (monomer) to 0.86 (tetramer) and triggers intense optical activity of BF2bdk. The results demonstrate that optical activity of chromophores within assemblies can be regulated by both orientation and extent of intermolecular electronic couplings.

Fast selective edge-enhanced imaging with topological chiral lamellar superstructures.

Edge detection is a fundamental operation for feature extraction in image processing. The all-optical method has aroused growing interest owing to its ultra-fast speed, low energy consumption and parallel computation. However, current optical edge detection methods are generally limited to static devices and fixed functionality. Herein, we propose a fast-switchable scheme based on a ferroelectric liquid crystal topological structure. The self-assembled chiral lamellar superstructure, directed by the azimuthally variant photo-alignment agent, can be dynamically controlled by the polarity of the external electric field and respectively generates the vector beams with nearly orthogonal polarization distribution. Even after thousands of cycles, the horizontal and vertical edges of the object are selectively enhanced with an ultra-fast switching time of ∼57 μs. Broadband edge-enhanced imaging is efficiently demonstrated. This work extends the ingenious building of topological heliconical superstructures and offers an important glimpse into their potential in the emerging frontiers of optical computing for artificial intelligence.

When quantum dots meet blue phase liquid crystal elastomers: visualized full-color and mechanically-switchable circularly polarized luminescence

Polymer-based circularly polarized luminescence (CPL) materials with the advantage of diversified structure, easy fabrication, high thermal stability, and tunable properties have garnered considerable attention. However, adequate and precise tuning over CPL in polymer-based materials remains challenging due to the difficulty in regulating chiral structures. Herein, visualized full-color CPL is achieved by doping red, green, and blue quantum dots (QDs) into reconfigurable blue phase liquid crystal elastomers (BPLCEs). In contrast to the CPL signal observed in cholesteric liquid crystal elastomers (CLCEs), the chiral 3D cubic superstructure of BPLCEs induces an opposite CPL signal. Notably, this effect is entirely independent of photonic bandgaps (PBGs) and results in a high glum value, even without matching between PBGs and the emission bands of QDs. Meanwhile, the lattice structure of the BPLCEs can be reversibly switched via mechanical stretching force, inducing on-off switching of the CPL signals, and these variations can be further fixed using dynamic disulfide bonds in the BPLCEs. Moreover, the smart polymer-based CPL systems using the BPLCEs for anti-counterfeiting and information encryption have been demonstrated, suggesting the great potential of the BPLCEs-based CPL active materials.

Induced Huge Optical Activity in Nanoplatelet Superlattice.

Chiral superstructures with unique chiroptical properties that are not inherent in the individual units are essential in applications such as 3D displays, spintronic devices, biomedical sensors, and beyond. Generally, chiral superstructures are obtained by tedious procedures exploring various physical and chemical forces to break spatial symmetry during the self-assembly of discrete nanoparticles. In contrast, we herein present a simple and efficient approach to chiral superstructures by intercalating small chiral molecules into preformed achiral superstructures. As a model system, the chiral CdSe nanoplatelet (NPL) superlattice exhibits a giant and tunable optical activity with the highest g-factor reaching 3.09 × 10-2 to the excitonic transition of the NPL superlattice, nearly 2 orders of magnitude higher than that of the corresponding separated chiral NPLs. The theoretical analysis reveals that the chiral deformation in the NPL superlattice induced by the chiral perturbation of the small chiral molecules is critical to the observed huge optical activity. We anticipate that this research lays a foundation for understanding and applying chiral inorganic nanosystems.

Assembly of large-area helical nanowire and nanosphere superstructures by PS-b-P2VP/S-mandelic acid via interfacial nanoarchitectonics

Chiral supramolecules have attracted great research interest due to their unique properties and functions. How to assemble them into the ordered superstructures, however, remains a challenge. In this paper, two methods have been developed to fabricate such superstructures. In method I, polystyrene-b-poly (2-vinylpyridine) (PS-b-P2VP) and S-mandelic acid (S-MA) diffused from the oil and aqueous phases respectively to the oil/water interface, combined and self-assembled into helical nanowires and nanospheres with monochirality, and formed parallel-aligned nanowire arrays and close-packed arrays at the liquid/liquid interface. In method II, PS-b-P2VP in DMF droplets was introduced into the aqueous solution of S-MA through a liquid/liquid interfacial phase transfer process. Then the polymer molecules self-assembled into helical nanowires and nanospheres with monochirality in the aqueous phase, which adsorbed at the air/liquid interface and organized into superstructures. The formation of chiral aggregates should be attributed to the induction of S-MA, while the superstructures at the interfaces were considered to result from the modulation by the interfacial pressures. This study has developed one-step techniques to assemble the chiral aggregates and superstructures, which is expected to become universal for fabrication of functional superstructures.

Magnetic Assembly of Magnetite/Perovskite Hybrid Nanorods for Circularly Polarized Luminescence

AbstractMagnetic fields are uniquely valuable for creating colloidal nanostructured materials, not only providing a means for controlled synthesis but also guiding their self‐assembly into distinct superstructures. In this study, a magnetothermal process for synthesizing hybrid nanostructures comprising ferrimagnetic magnetite nanorods coated with fluorescent perovskite nanocrystals is reported and their magnetic assembly into superstructures capable of emitting linear and circularly polarized light are demonstrated. Under UV excitation, the superstructures assembled in a liner magnetic field produce linear polarized luminescence, and those assembled in a chiral magnetic field exhibit strong circularly polarized luminescence (CPL) with a glum value up to 0.44 (±0.004). The CPL is believed to originate from the dipolar interaction between neighboring perovskite nanocrystals attached to the chiral assemblies and the chiral‐selective absorption of the perovskite emission by the magnetite phase. The magnetic synthesis and assembly approaches and the resulting distinctive chiral superstructures are anticipated to open up new avenues for designing diverse functional chiroptical devices.

Chiral Transfer and Evolution in Cysteine Induced Cobalt Superstructures.

Chiral organic additives have unveiled the extraordinary capacity to form chiral inorganic superstructures, however, complex hierarchical structures have hindered the understanding of chiral transfer and growth mechanisms. This study introduces a simple hydrothermal synthesis method for constructing chiral cobalt superstructures with cysteine, demonstrating specific recognition of chiral molecules and outstanding electrocatalytic activity. The mild preparation conditions allow in situ tracking of chirality evolution in the chiral cobalt superstructure, offering unprecedented insights into the chiral transfer and amplification mechanism. The resulting superstructures exhibit a universal formation process applicable to other metal oxides, extending the understanding of chiral superstructure evolution. This work contributes not only to the fundamental understanding of chirality in self-assembled structures but also provides a versatile method for designing chiral inorganic nanomaterials with remarkable molecular recognition and electrocatalytic capabilities.

Logical rotation of non-separable states via uniformly self-assembled chiral superstructures

The next generation of high-capacity, multi-task optical informatics requires sophisticated manipulation of multiple degrees of freedom (DoFs) of light, especially when they are coupled in a non-separable way. Vector beam, as a typical non-separable state between the spin and orbital angular momentum DoFs, mathematically akin to entangled qubits, has inspired multifarious theories and applications in both quantum and classical regimes. Although qubit rotation is a vital and ubiquitous operation in quantum informatics, its classical analogue is rarely studied. Here, we demonstrate the logical rotation of vectorial non-separable states via the uniform self-assembled chiral superstructures, with favorable controllability, high compactness and exemption from formidable alignment. Photonic band engineering of such 1D chiral photonic crystal renders the incident-angle-dependent evolution of the spatially-variant polarizations. The logical rotation angle of a non-separable state can be tuned in a wide range over 4π by this single homogeneous device, flexibly providing a set of distinguished logic gates. Potential applications, including angular motion tracking and proof-of-principle logic network, are demonstrated by specific configuration. This work brings important insight into soft matter photonics and present an elegant strategy to harness high-dimensional photonic states.

Magnetic Assembly of Eu-Doped NaYF4 Nanorods for Field-Responsive Linearly and Circularly Polarized Luminescence.

Colloidal assembly has emerged as an effective avenue for achieving polarized light emission. Here, we showcase the efficacy and versatility of the magnetic colloidal assembly in enabling both linearly and circularly polarized luminescence. Colloidal europium-doped NaYF4 nanorods with surface-bound Fe3O4 nanoparticles are magnetically assembled into linear or chiral superstructures using corresponding fields created in permanent magnets. In a uniform magnetic field generated by opposing poles, the assemblies exhibit photoluminescence with intensity tunable in response to the magnetic field direction, which is higher when the nanorods are perpendicular to light propagation than when they are parallel. The obtained superstructures display strong linearly polarized luminescence when the nanorods are aligned vertically, exhibiting a high degree of polarization up to 0.61. In a quadrupole chiral field generated by permanent magnets, the assemblies emit left-handed or right-handed polarized light depending on the position of the sample placement, attaining a g-factor of 0.04. Furthermore, the superstructures immobilized in a hydrogel film are found to retain their chirality, exhibiting opposite chiroptical responses depending on the sample orientation. The magnetic colloidal assembly approach facilitates the convenient and efficient generation of polarized light emissions from nonmagnetic luminescent materials, thus creating opportunities for tailoring light behavior in developing innovative optoelectronic devices.

Self-similar chiral organic molecular cages

The endeavor to enhance utility of organic molecular cages involves the evolution of them into higher-level chiral superstructures with self-similar, presenting a meaningful yet challenging. In this work, 2D tri-bladed propeller-shaped triphenylbenzene serves as building blocks to synthesize a racemic 3D tri-bladed propeller-shaped helical molecular cage. This cage, in turn, acts as a building block for a pair of higher-level 3D tri-bladed chiral helical molecular cages, featuring multilayer sandwich structures and displaying elegant characteristics with self-similarity in discrete superstructures at different levels. The evolutionary procession of higher-level cages reveals intramolecular self-shielding effects and exclusive chiral narcissistic self-sorting behaviors. Enantiomers higher-level cages can be interconverted by introducing an excess of corresponding chiral cyclohexanediamine. In the solid state, higher-level cages self-assemble into supramolecular architectures of L-helical or D-helical nanofibers, achieving the scale transformation of chiral characteristics from chiral atoms to microscopic and then to mesoscopic levels.

Spontaneous Symmetry Breaking of Achiral Molecules Leading to the Formation of Homochiral Superstructures that Exhibit Mechanoluminescence

AbstractChirality, with its intrinsic symmetry‐breaking feature, is frequently utilized in the creation of acentric crystalline functional materials that exhibit intriguing optoelectronic properties. On the other hand, the development of chiral crystals from achiral molecules offers a solution that bypasses the need for enantiopure motifs, presenting a promising alternative and thereby expanding the possibilities of the self‐assembly toolkit. Nevertheless, the rational design of achiral molecules that prefer spontaneous symmetry breaking during crystallization has so far been obscure. In this study, we present a series of six achiral molecules, demonstrating that when these conformationally flexible molecules adopt a cis‐conformation and engage in multiple non‐covalent interactions along a helical path, they collectively self‐assemble into chiral superstructures consisting of single‐handed supramolecular columns. When these homochiral supramolecular columns align in parallel, they form polar crystals that exhibit intense luminescence upon grinding or scraping. We therefore demonstrate our molecular design strategy could significantly increase the likelihood of symmetry breaking in achiral molecular synthons during self‐assembly, offering a facile access to novel chiral crystalline materials with unique optoelectronic properties.

Spontaneous Symmetry Breaking of Achiral Molecules Leading to the Formation of Homochiral Superstructures that Exhibit Mechanoluminescence.

Chirality, with its intrinsic symmetry-breaking feature, is frequently utilized in the creation of acentric crystalline functional materials that exhibit intriguing optoelectronic properties. On the other hand, the development of chiral crystals from achiral molecules offers a solution that bypasses the need for enantiopure motifs, presenting a promising alternative and thereby expanding the possibilities of the self-assembly toolkit. Nevertheless, the rational design of achiral molecules that prefer spontaneous symmetry breaking during crystallization has so far been obscure. In this study, we present a series of six achiral molecules, demonstrating that when these conformationally flexible molecules adopt a cis-conformation and engage in multiple non-covalent interactions along a helical path, they collectively self-assemble into chiral superstructures consisting of single-handed supramolecular columns. When these homochiral supramolecular columns align in parallel, they form polar crystals that exhibit intense luminescence upon grinding or scraping. We therefore demonstrate our molecular design strategy could significantly increase the likelihood of symmetry breaking in achiral molecular synthons during self-assembly, offering a facile access to novel chiral crystalline materials with unique optoelectronic properties.

Simultaneous formation of helical and sheet-like assemblies from short azapeptides enables spontaneous resolution.

As determined by the homochirality of amino acid building units, protein secondary structures α-helix and β-sheet are single-handed chiral superstructures extending in one and quasi-two dimensions, respectively. Synthetic molecular assemblies that mimic the structural homochirality of proteins would provide insights into the origin of biological homochirality and inform the development of chiral separation techniques. Here we fabricated a homochiral 3D assembly consisting of 1D helical and 2D sheet-like assemblies that feature molecular packings resembling α-helix and β-sheet, respectively. This was achieved by using an alanine derivative, a β-turn structured short azapeptide from p-iodobenzoylalanine-based N-amido-N'-phenylthiourea. While N-H⋯SC/OC hydrogen bonds between the β-turn scaffolds afford a 2D pleated sheet-like structure, the head-to-tail C-I⋯π halogen bonds, together with the N-H⋯OC hydrogen bonds, support a 1D helical-like assembly, serving as linkers to connect the 2D sheet-like structures into a 3D superstructure. The two biomimetic assembly modes share the N-H⋯OC hydrogen bonds and can allow 3D homochiral elongation, driving spontaneous resolution of the short azapeptides to generate conglomerate crystals.

Magnetic assembly of plasmonic chiral superstructures with dynamic chiroptical responses.

Plasmonic nanostructures exhibiting dynamically tunable chiroptical responses hold great promise for broad applications such as sensing, catalysis, and enantioselective analysis. Despite the successful fabrication of chiral structures through diverse templates, creating dynamic chiroptical materials with fast and reversible responses to external stimuli is still challenging. This work showcases reversible magnetic assembly and active tuning of plasmonic chiral superstructures by introducing a chiral magnetic field from a cubic permanent magnet. Manipulating the strength and direction of the magnetic field controls both the chiral arrangement and plasmonic coupling of the nanoparticle assembly, enabling fast and reversible tunability in not only the handedness of the superstructures but also the spectral characteristics of their chiroptical properties. The dynamic tunability further enables the fabrication of color-changing optical devices based on the optical rotatory dispersion effect, showcasing their potential for application in anti-counterfeiting and stress sensors.

Circularly Polarized Organic Ultralong Room-Temperature Phosphorescence with A High Dissymmetry Factor in Chiral Helical Superstructures.

Long-lived room-temperature phosphorescence (RTP) of organic materials holds a significant potential for optical information. Circularly polarized organic ultralong room-temperature phosphorescence (CP-OURTP) with extremely high dissymmetry factor (glum ) values is even highly demanded and considerably challenging. Here, an effective strategy is introduced to realize CP-OURTP with an emission decay time of 735ms and a glum value up to 1.49, which exceeds two orders of magnitude larger than previous records, through a system composed of RTP polymers and chiral helical superstructures. The system exhibits excellent stability under multiple cycles of photoirradiation and thermal treatment, and is further employed for information encryption based on optical multiplexing. The results are anticipated to lay the foundation for the development of CP-OURTP materials in advanced photonic applications.