Emergent chiroptical properties in supramolecular and plasmonic assemblies

Liquid-Liquid Phase Separation Mediated Formation of Chiral 2D Crystalline Nanosheets of a Co-Assembled System

The role of macromolecule-macromolecule and macromolecule-H2O interactions and the resulting perturbation of the H-bonded network of H2O in the liquid-liquid phase separation (LLPS) process of biopolymers are well-known. However, the potential of the hydrated state of supramolecular structures (non-covalent analogs of macromolecules) of synthetic molecules is not widely recognized for playing a similar role in the LLPS process. Herein, LLPS occurred during the co-assembly of hydrated supramolecular vesicles (bolaamphiphile, BA1) with a net positive charge (zeta potential, ζ = +60 ± 2 mV) and a dianionic chiral molecule (disodium l-[+]-tartrate) is reported. As inferred from cryo-transmission electron microscopy (TEM), the LLPS-formed droplets serve as the nucleation precursors, dictating the structure and properties of the co-assembly. The co-assembled structure formed by LLPS effectively integrates the counter anion's asymmetry, resulting in the formation of ultrathin free-standing, chiral 2D crystalline sheets. The significance of the hydrated state of supramolecular structures in influencing LLPS is unraveled through studies extended to a less hydrated supramolecular structure of a comparable system (BA2). The role of LLPS in modulating the hydrophobic interaction in water paves the way for the creation of advanced functional materials in an aqueous environment.

Hierarchical assembly of Ag40 nanowheel ranging from building blocks to diverse superstructure regulation

Achieving precise and controllable hierarchical self-assembly of functional nanoclusters within crystal lattices to create distinct architectures is of immense significance, yet it creates considerable challenges. Here we successfully synthesized a silver nanowheel Ag40, along with its optically pure enantiomers S-/R-Ag40. Each species possesses an internal nanospace and exhibits host-guest interactions. These structures are constructed from primary building blocks (Ag9). By manipulating the surface anions and guest molecules, the nanowheels function as secondary building blocks, spontaneously organizing into complex double- and triple-helical crystalline superstructures or one-dimensional chains {Ag41}n through conformational matching and diverse noncovalent interactions. Moreover, we demonstrate that the water-mediated complex specifically assembled with uridine monophosphate nucleotides, resulting in chiral assemblies of Ag40 that exhibit chiroptical activity for specific recognition. Our findings provide insights into the efficient construction of assemblies with hollow frameworks and propose strategies for superstructure engineering by manipulating surface motifs.

Nanorod-associated plasmonic circular dichroism monitors the handedness and composition of α-synuclein fibrils from Parkinson's disease models and post-mortem brain

Human full-length (fl) αSyn fibrils, key neuropathological hallmarks of Parkinson's disease (PD), generate intense optical activity corresponding to the surface plasmon resonance of interacting gold nanorods. Herein, we analysed fibril-enriched protein extracts from mouse and human brain samples as well as from SK-N-SH cell lines with or without human fl and C-terminally truncated (Ctt) αSyn overexpression and exposed them to αSyn monomers, recombinant fl αSyn fibrils or Ctt αSyn fibrils. In vitro-generated human recombinant fl and Ctt αSyn fibrils and fibrils purified from SK-N-SH cells with fl or Ctt αSyn overexpression were also analysed using transmission electron microscopy (TEM) to gain insights into the nanorod-fibril complexes. We found that under the same experimental conditions, bisignate circular dichroism (CD) spectra of Ctt αSyn fibrils exhibited a blue-wavelength shift compared to that of fl αSyn fibrils. TEM results supported that this could be attributed to the different properties of nanorods. In our experimental conditions, fibril-enriched PD brain extract broadened the longitudinal surface plasmonic band with a bisignate CD couplet centred corresponding to the absorption band maximum. Plasmonic CD (PCD) couplets of in vivo- and in vitro-generated fibrils displayed sign reversal, suggesting their opposite handedness. Moreover, the incubation of in vitro-generated human recombinant fl αSyn fibrils in mouse brain extracts from αSyn null mice resulted in PCD couplet inversion, indicating that the biological environment may shape the handedness of αSyn fibrils. These findings support that nanorod-based PCD can provide useful information on the composition and features of αSyn fibrils from biological materials.

Highly enhanced chiroptical effect from self-inclusion helical nanocrystals of tetraphenylethylene bimacrocycles

The helical structure is often the key factor for forming and enhancing chiroptical properties, such as circular dichroism (CD) and circular polarized luminescence (CPL) effects. However, no matter whether helical molecules or helical aggregates, they usually display modest chiroptical signals, which limits their practical applications. Herein, chiral tetraphenylethylene (TPE) bimacrocycles prepared in almost quantitative yield show strong and repeatable CD signals up to more than 7000 mdeg, which is very rare for general organic compounds, besides emitting very strong CPL light with an absolute g lum value up to 6.2 × 10-2. It is found that the superhelices formed by self-inclusion between the cavity and outward cyclohexyl ring of TPE bimacrocycles in crystal state are the key factor for highly enhanced chiroptical effect, and the self-inclusion superhelices in assemblies are confirmed by High Resolution Transmission Electron Microscopy (HR-TEM), Powder X-ray Diffraction (XRD) and Fourier Transform Infrared Spectrometry (FT-IR) data. Furthermore, the chiral TPE bimacrocycle shows great potential in chiral recognition and chiral analysis not only for chiral acids but also for chiral amines, chiral amino acids, and neutral chiral alcohol. Using self-inclusion helical nanocrystals of chiral macrocycles, this work provides a new strategy for chiroptical materials with excellent chiroptical properties.

Chiroptical properties of cyanine aggregates: hierarchical modelling from monomers to bundles

Some achiral cyanine dyes form well-ordered chiral assemblies exhibiting pronounced Circular Dichroism (CD) and Circularly Polarized Luminescence (CPL). Notably, achiral C8O3 cyanines self-assemble into tubular J-aggregates, which further organize into bundles displaying bisignate CD spectrum - hallmark of an exciton coupled system - and an unusual bisignated CPL. In contrast, the tubular aggregates display a monosignate CD spectrum. The mechanism underlying these intriguing features remains elusive. In the present work, a quantum-mechanical exciton model is proposed to elucidate the (chir)optical behaviour of C8O3 aggregates. A herringbone arrangement of C8O3 dyes within the tubular aggregates well reproduces the observed spectral signatures. The anomalous observation of a singular CD peak in tubular aggregates is ascribed to the intrinsic chirality of the monomeric units inside the aggregate, whereas the CD doublet characterizing the bundles is attributed to the exciton coupling between the constituent tubes. The bisignated CPL signal observed in bundles reveals significant anti-Kasha emission at room temperature and is quantitatively addressed accounting for a very tiny exciton splitting leading to a sizable thermal population of both exciton states. This study provides crucial insights on the complexity of C8O3 aggregation and on the origin of chiroptical response at various aggregation stages.

Unravelling denaturation, temperature and cosolvent-driven chiroptical switching in peptide self-assembly with switchable piezoelectric responses

Herein, we explore the intricate pathway complexity, focusing on the dynamic interplay between kinetic and thermodynamic states, during the supramolecular self-assembly of peptides. We uncover a multiresponsive chiroptical switching phenomenon influenced by temperature, denaturation and content of cosolvent in peptide self-assembly through pathway complexity (kinetic vs. thermodynamic state). Particularly noteworthy is the observation of chiroptical switching during the denaturation process, marking an unprecedented phenomenon in the literature. Furthermore, the variation in cosolvent contents produces notable chiroptical switching effects, emphasizing their infrequent incidence. Such chiroptical switching yields switchable piezoresponsive peptide-based nanomaterials, demonstrating the potential for dynamic control over material properties. In essence, our work pioneers the ability to control piezoresponsive behavior by transforming nanostructures from kinetic to thermodynamic states through pathway complexity. This approach provides new insights and opportunities for tailoring material properties in self-assembled systems.

Self-Assembled Pure Covalent Tubes Exhibiting Circularly Polarized Luminescence

Here, we successfully synthesized four structurally analogous, self-assembled chiral molecular tubes with relatively high yields. This achievement involved the condensation of six equivalents of enantiomerically pure trans-cyclohexane-1,2-diamine (trans-CHDA) and three equivalents of the corresponding tetraformyl precursor. Each precursor was equipped with a luminescent linker terminated by two m-phthalaldehyde units. Even though these tetraformyl precursors are barely soluble in almost all organic solvents, the molecular tubes are highly soluble in nonpolar solvents such as chloroform, allowing us to fully characterize them in solution. The stereo-chirality of the chiral bisamino building blocks endows the frameworks of molecular tubes with planar chirality. As a consequence, all of these molecular tubes exhibit circularly polarized luminescence (CPL) with relatively large dissymmetry values |glum| up to 7×10-3, providing an efficient method for synthesizing CPL-active materials.

Giant chiral amplification of chiral 2D perovskites via dynamic crystal reconstruction

Chiral hybrid perovskites show promise for advanced spin-resolved optoelectronics due to their excellent polarization-sensitive properties. However, chiral perovskites developed to date rely solely on the interaction between chiral organic ligand cations exhibiting point chirality and an inorganic framework, leading to a poorly ordered short-range chiral system. Here, we report a powerful method to overcome this limitation using dynamic long-range organization of chiral perovskites guided by the incorporation of chiral dopants, which induces strong interactions between chiral dopants and chiral cations. The additional interplay of chiral cations with chiral dopants reorganizes the morphological and crystallographic properties of chiral perovskites, notably enhancing the asymmetric behavior of chiral 2D perovskites by more than 10-fold, along with the highest dissymmetry factor of photocurrent (gPh) of ~1.16 reported to date. Our findings present a pioneering approach to efficiently amplify the chiroptical response in chiral perovskites, opening avenues for exploring their potential in cutting-edge optoelectronic applications.

Cooperative Binding and Chirogenesis in an Expanded Perylene Bisimide Cyclophane

The encapsulation of more than one guest molecule into a synthetic cavity is a highly desirable yet a highly challenging task to achieve for neutral supramolecular hosts in organic media. Herein, we report a neutral perylene bisimide cyclophane, which has a tailored chiral cavity with an interchromophoric distance of 11.2 Å, capable of binding two aromatic guests in a π-stacked fashion. Detailed host-guest binding studies with a series of aromatic guests revealed that the encapsulation of the second guest in this cyclophane is notably more favored than the first one. Accordingly, for the encapsulation of the coronene dimer, a cooperativity factor (α) as high as 485 was observed, which is remarkably high for neutral host-guest systems. Furthermore, a successful chirality transfer, from the chiral host to encapsulated coronenes, resulted in a chiral charge-transfer (CT) complex and the rare observation of circularly polarized emission originating from the CT state for a noncovalent donor-acceptor assembly in solution. The involvement of the CT state also afforded an enhancement in the luminescence dissymmetry factor (glum) value due to its relatively large magnetic transition dipole moment. The 1:2 binding pattern and chirality-transfer were unambiguously verified by single-crystal X-ray diffraction analysis of the host-guest superstructures.

Binaphthalene-Assisted Axial Chirality in Porphyrins: Toward Solid-State Circularly Polarized Luminescence from Self-Assembled Nanostructures

Circularly polarized luminescence (CPL) is emerging as an effective tool to study the excited-state optical activity in molecules and their self-assembled nanostructures. Chiral porphyrins are a class of optically active molecules wherein the ground-state chirality has been extensively studied in recent times using circular dichroism (CD) spectroscopy. However, obtaining CPL from porphyrin nanostructures, which would have vast implications in biological applications, has remained an uphill task. In this work, we design and synthesize a pair of chiral porphyrin enantiomers functionalized by axially chiral binaphthalene units at the four meso-positions. The molecule undergoes self-assembly following an isodesmic polymerization model, leading to the formation of a spherical nanostructure possessing opposite chirality. Favorable thermodynamic parameters achieved through the controlled experimental conditions helped drive the self-assembly in the forward direction. The limitations imposed by a large nonradiative decay constant arising due to the aggregation-induced quenching could be overcome by fabricating self-standing polymeric films of the nanostructures. The films exhibited relatively high radiative decay and, more interestingly, good CPL activity with clear mirror image spectra for the nanostructures with opposite chirality. The work on CPL-active solid-state materials opens avenue for the design and synthesis of a variety of porphyrin-based chromophoric systems and their nanoaggregates that can find potential application in the field of chiral biosensing and bioimaging, security tags, and display devices.

Nature-Inspired Helicoidal Nanocellulose-Based Multi-Compartment Assemblies with Tunable Chiroptical Properties

Cellulose-based nanocomposites are highly appealing for the development of next-generation sustainable functional materials. Although many advances have been made in this direction, the true potential of fibrillar nanocomposites has yet to be realized because available fabrication approaches are inadequate for achieving precise structural control at the sub-micrometer scale. Here a spray-assisted alignment methodology of cellulose nanofibrils is combined with the layer-by-layer assembly into an additive manufacturing process in which the alignment direction of each cellulose layer is rationally selected to achieve thin films with a helicoidal arrangement of the nanofibrils. The helicoidal structure of the films is verified by measuring the circular dichroism (CD) of the samples. The sign and position of the structural CD peak show that the handedness and the pitch of the chiral structures can be easily tuned by deliberately selecting simple parameters, such as the number of consecutive cellulose layers sprayed in the same direction, and the angle of rotation between successive stacks of layers. To the authors' knowledge, this approach is unique as it offers the possibility to prepare complex nanocomposite architectures with various nanoscale-controlled sub-structures from different anisometric objects, which is enabling novel designs of composite films with damage-resistant and/or optical filtering functionalities.

Biomimetic Chiral Nanomaterials with Selective Catalysis Activity

Chiral nanomaterials with unique chiral configurations and biocompatible ligands have been booming over the past decade for their interesting chiroptical effect, unique catalytical activity, and related bioapplications. The catalytic activity and selectivity of chiral nanomaterials have emerged as important topics, that can be potentially controlled and optimized by the rational biochemical design of nanomaterials. In this review, chiral nanomaterials synthesis, composition, and catalytic performances of different biohybrid chiral nanomaterials are discussed. The construction of chiral nanomaterials with multiscale chiral geometries along with the underlying principles for enhancing chiroptical responses are highlighted. Various biochemical approaches to regulate the selectivity and catalytic activity of chiral nanomaterials for biocatalysis are also summarized. Furthermore, attention is paid to specific chiral ligands, materials compositions, structure characteristics, and so on for introducing selective catalytic activities of representative chiral nanomaterials, with emphasis on substrates including small molecules, biological macromolecule, and in-site catalysis in living systems. Promising progress has also been emphasized in chiral nanomaterials featuring structural versatility and improved chiral responses that gave rise to unprecedented chances to utilize light for biocatalytic applications. In summary, the challenges, future trends, and prospects associated with chiral nanomaterials for catalysis are comprehensively proposed.

Electronically and geometrically complementary perylenediimides for kinetically controlled supramolecular copolymers

The synthesis of 3,4,9,10-benzo[d,e]isoquinolino[1,8-g,h]quinoline-tetracarboxylic diimide (BQQDI) 1 endowed with peripheral trialkoxybenzamide fragments is reported and its self-assembling features investigated. The peripheral benzamide moieties generate metastable monomeric species that afford a kinetically controlled supramolecular polymerization. The electron-withdrawing character of 1 in comparison with previously reported PDIs 2, together with the similar geometry, makes this dye an optimal candidate to perform seeded supramolecular copolymerization yielding four different supramolecular block copolymers. Whilst heteropolymers poly-1-co-2a, poly-2a-co-1 and poly-1-co-2b present an H-type arrangement of the monomeric units, heteropolymer poly-2b-co-1, prepared by seeding the chiral, metastable monomers of 2b with achiral seeds of 1, produces chiral, J-type aggregates. Interestingly, the monosignated CD signal of pristine poly-2b changes to a bisignated CD signal most probably due to the formation of columnar domains around the seeds of 1 which implies the blocky nature of the supramolecular copolymers formed.

Engineering copper plasmonic chirality via ligand-induced dissolution for enantioselective recognition of amino acids

The formation of chiral nanosystems and their subsequent enantioselective interaction with chiral amino acids are vital steps in many biological processes. Due to their potential to mimic biological systems, the synthesis of chiral nanomaterials has garnered significant attention over the years. Despite the emergence of diverse nanomaterials showcasing strong chiral responses, the in-depth understanding of the mechanism of plasmonic chirality in copper nanoparticles and their subsequent application in various fields are least explored. Herein, we demonstrate a facile approach for the synthesis of chiral copper nanoparticles using cysteine as a chiral precursor and capping ligand. Ligand-mediated chiral induction, established through experimental findings and a theoretical model, is ascribed as the major contributor to the origin of plasmonic chirality. The enantioselective recognition of chiral copper nanoparticles towards histidine, an amino acid with vast biological functions, was meticulously investigated by leveraging the strong copper-histidine binding ability. Ligand-induced dissolution, a unique phenomenon in nanoparticle reactions, was identified as the underlying mechanism for the nanoparticle-to-complex conversion. Understanding the mechanism of chiral induction in copper nanoparticles coupled with their enantioselective recognition of biomolecules not only holds promise in biomedical research but also sheds light on their potential as catalysts for asymmetric synthesis.

Chiral Covalent Organic Framework Films with Enhanced Photoelectrical Performances

The desirable superimposed stacking of two-dimensional covalent organic frameworks (2D COFs) benefits out-of-plane charge transfer, whereas the actual stacking deviation cannot leverage the potential of 2D COFs for optoelectrical applications. Herein, we report a chirality-induced strategy to control the parallel AA-stacking sequence for the β-ketoenamine-linked COF film supported on a FTO substrate. The resulting chiral modules are periodically distributed at the framework node, ensuring identical mirrored configurations of layers for parallel stacking. Such unique architectonics exhibit the prolonged charge carrier lifetime, fast charge-transfer dynamics, and ultrahigh electron collection efficiency, thereby allowing for the excellent photocurrent response of 38 μA/cm2 at 0.25 V (vs RHE). The origin of superior performances lies in the intensified exciton gradient distribution and electron density for photoinduced electron-hole dissociation and charge transfer, in stark contrast to achiral analogues. This study highlights the stacking sequence regulated by chiral nanoarchitectonics and promises great potential of chiral COFs in photoelectrical catalysis.

Red Circularly Polarized Luminescence from Dimeric H-Aggregates of Acridine Orange by Chiral Induction

Understanding the mechanism of chirality transfer from a chiral surface to an achiral molecule is essential for designing molecular systems with tunable chiroptical properties. These aspects are explored herein using l- and d-isomers of alkyl valine amphiphiles, which self-assemble in water as nanofibers possessing a negative surface charge. An achiral chromophore, acridine orange, upon electrostatic binding on these surfaces displays mirror-imaged bisignated circular dichroism and red-emitting circularly polarized luminescence signals with a high dissymmetry factor. Experimental and computational investigations establish that the chiroptical properties emerge from surface-bound asymmetric H-type dimers of acridine orange, further supported by fluorescence lifetime imaging studies. Specifically, atomistic molecular dynamics simulations show that the experimentally observed chiral signatures have their origin in van der Waals interactions between acridine orange dimers and the amphiphile head groups as well as in the extent of solvent exposure of the chromophore.

Supramolecular Polymerization of a Pyrene-Substituted Diamide and Its Ensemble of Kinetically Trapped Configurations

The prevalence of kinetically accessible states in supramolecular polymerization pathways has been exploited to control the growth of the polymer and thereby to obtain niche morphologies. Yet, these pathways themselves are not easily amenable for experimental delineation but could potentially be understood through molecular dynamics (MD) simulations. Herein, we report an extensive investigation of the self-assembly of pyrene-substituted diamide (PDA) monomers in solution, conducted using atomistic MD simulations and advanced sampling methods. We characterize such kinetic and thermodynamic states as well as the transition pathways and free energy barriers between them. PDA forms a dimeric segment with the N- to C-termini vectors of the diamide moieties arranged either in parallel or anti-parallel fashion. This characteristic, combined with the molecule's torsional flexibility and pyrene-solvent interactions, presents an ensemble of molecular configurations contributing to the kinetic state in the polymerization pathway. While this ensemble primarily comprises short oligomers containing a mix of anti-parallel and parallel dimeric segments, the thermodynamic state of the assembly is a right-handed polymer featuring parallel ones only. Our work thus offers an approach by which the landscape of any specific supramolecular polymerization can be deconstructed.

Chiroptical switching in the azobenzene-based self-locked [1]rotaxane by solvent and photoirradiation

Because of its dynamic reversible nature and simple regulation properties, rotaxane systems provided a good route for the construction of responsive supramolecular chiral materials. Here, we covalently encapsulate the photo-responsive guest molecule azobenzene (Azo) in a chiral macrocycle β-cyclodextrin (β-CD) to prepare self-locked chiral [1]rotaxane [Azo-CD]. On this basis, the self-adaptive conformation of [Azo-CD] was manipulated by solvent and photoirradiation; meanwhile, dual orthogonal regulation of the [1]rotaxane chiroptical switching could also be realized.

Electron spin polarization in supramolecular polymers with complex pathways

Mastering the manipulation of the electron spin plays a crucial role in comprehending the behavior of organic materials in several applications, such as asymmetric catalysis, chiroptical switches, and electronic devices. A promising avenue for achieving such precise control lies in the Chiral Induced Spin Selectivity (CISS) effect, where electrons with a favored spin exhibit preferential transport through chiral assemblies of specific handedness. Chiral supramolecular polymers emerge as excellent candidates for exploring the CISS effect due to their ability to modulate their helical structure through noncovalent interactions. In this context, systems capable of responding to external stimuli are particularly intriguing, sometimes even displaying chirality inversion. This study unveils spin selectivity in chiral supramolecular polymers, derived from single enantiomers, through scanning tunneling microscopy conducted in scanning tunneling spectroscopy mode. Following two distinct sample preparation protocols for each enantiomer, we generate supramolecular polymers with opposite handedness and specific spin transport characteristics. Our primary focus centers on chiral π-conjugated building blocks, with the aim of advancing novel systems that can inspire the organic spintronics community from a supramolecular chemistry level.

Stereoselective Plasmonic Interaction in Peptide-tethered Photopolymerizable Diacetylenes Doped with Chiral Gold Nanoparticles

Designing polymeric systems with ultra-high optical activity is instrumental in the pursuit of smart artificial chiroptical materials, including the fundamental understanding of structure/property relations. Herein, we report a diacetylene (DA) moiety flanked by chiral D- and L-FF dipeptide methyl esters that exhibits efficient topochemical photopolymerization in the solid phase to furnish polydiacetylene (PDA) with desired control over the chiroptical properties. The doping of the achiral gold nanoparticles provides plasmonic interaction with the PDAs to render asymmetric shape to the circular dichroism bands. With the judicious design of the chiral amino acid ligand appended to the AuNPs, we demonstrate the first example of selective chiral amplification mediated by stereo-structural matching of the polymer-plasmonic AuNP hybrid pairs. Such ordered self-assembly aided by topochemical polymerization in peptide-tethered PDA provides a smart strategy to produce soft responsive materials for applications in chiral photonics.

Chiral MOF Derived Wearable Logic Sensor for Intuitive Discrimination of Physiologically Active Enantiomer

Chiral sensors have attracted growing interest due to their application in health monitoring. However, rational design of wearable logic chiral sensors remains a great challenge. In this work, a dual responsive chiral sensor RT@CDMOF is prepared through in situ self-assembly of chiral γ-cyclodextrin metal-organic framework (CDMOF), rhodamine 6G hydrazide (RGH), and tetracyanovinylindane (TCN). The embedded RGH and TCN inherit the chirality of host CDMOF, producing dual changes both in fluorescence and reflectance. RT@CDMOF is explored as a dual channel sensor for chiral discrimination of lactate enantiomers. Comprehensive mechanistic studies reveal the chiral binding process, and carboxylate dissociation is confirmed by impedance and solid-state 1 H nuclear magnetic resonance (NMR). A flexible membrane sensor is successfully fabricated based on RT@CDMOF for wearable health monitoring. Practical evaluation confirms the potential of fabricated membrane sensor in point-of-care health monitoring by indexing the exercise intensity. Based on above, a chiral IMPLICATION logic unit can be successfully achieved, demonstrating the promising potential of RT@CDMOF in design and assembly of novel smart devices. This work may open a new avenue to the rational design of logic chiral sensors for wearable health monitoring applications.

Enantiopure J-Aggregate of Quaterrylene Bisimides for Strong Chiroptical NIR-Response

Chiral polycyclic aromatic hydrocarbons can be tailored for next-generation photonic materials by carefully designing their molecular as well as supramolecular architectures. Hence, excitonic coupling can boost the chiroptical response in extended aggregates but is still challenging to achieve by pure self-assembly. Whereas most reports on these potential materials cover the UV and visible spectral range, systems in the near infrared (NIR) are underdeveloped. We report a new quaterrylene bisimide derivative with a conformationally stable twisted π-backbone enabled by the sterical congestion of a fourfold bay-arylation. Rendering the π-subplanes accessible by small imide substituents allows for a slip-stacked chiral arrangement by kinetic self-assembly in low polarity solvents. The well dispersed solid-state aggregate reveals a sharp optical signature of strong J-type excitonic coupling in both absorption (897 nm) and emission (912 nm) far in the NIR region and reaches absorption dissymmetry factors up to 1.1 × 10^-2. The structural elucidation was achieved by atomic force microscopy and single-crystal X-ray analysis which we combined to derive a structural model of a fourfold stranded enantiopure superhelix. We could deduce that the role of phenyl substituents is not only granting stable axial chirality but also guiding the chromophore into a chiral supramolecular arrangement needed for strong excitonic chirality.

Nanoparticle Self-Assembly: From Design Principles to Complex Matter to Functional Materials

The creation of matter with varying degrees of complexities and desired functions is one of the ultimate targets of self-assembly. The ability to regulate the complex interactions between the individual components is essential in achieving this target. In this direction, the initial success of controlling the pathways and final thermodynamic states of a self-assembly process is promising. Despite the progress made in the field, there has been a growing interest in pushing the limits of self-assembly processes. The main inception of this interest is that the intended self-assembled state, with varying complexities, may not be "at equilibrium (or at global minimum)", rendering free energy minimization unsuitable to form the desired product. Thus, we believe that a thorough understanding of the design principles as well as the ability to predict the outcome of a self-assembly process is essential to form a collection of the next generation of complex matter. The present review highlights the potent role of finely tuned interparticle interactions in nanomaterials to achieve the preferred self-assembled structures with the desired properties. We believe that bringing the design and prediction to nanoparticle self-assembly processes will have a similar effect as retrosynthesis had on the logic of chemical synthesis. Along with the guiding principles, the review gives a summary of the different types of products created from nanoparticle assemblies and the functional properties emerging from them. Finally, we highlight the reasonable expectations from the field and the challenges lying ahead in the creation of complex and evolvable matter.

Structurally Induced Chirality of an Achiral Chromophore on Self-Assembled Nanofibers: A Twist Makes It Chiral

The surface domains of self-assembled amphiphiles are well-organized and can perform many physical, chemical, and biological functions. Here, we present the significance of chiral surface domains of these self-assemblies in transferring chirality to achiral chromophores. These aspects are probed using l- and d-isomers of alkyl alanine amphiphiles which self-assemble in water as nanofibers, possessing a negative surface charge. When bound on these nanofibers, positively charged cyanine dyes (CY524 and CY600), each having two quinoline rings bridged by conjugated double bonds, show contrasting chiroptical features. Interestingly, CY600 displays a bisignated circular dichroic (CD) signal with mirror-image symmetry, while CY524 is CD silent. Molecular dynamics simulations reveal that the model cylindrical micelles (CM) derived from the two isomers exhibit surface chirality and the chromophores are buried as monomers in mirror-imaged pockets on their surfaces. The monomeric nature of template-bound chromophores and their binding reversibility are established by concentration- and temperature-dependent spectroscopies and calorimetry. On the CM, CY524 displays two equally populated conformers with opposite sense, whereas CY600 is present as two pairs of twisted conformers in each of which one is in excess, due to differences in weak dye-amphiphile hydrogen bonding interactions. Infrared and NMR spectroscopies support these findings. Reduction of electronic conjugation caused by the twist establishes the two quinoline rings as independent entities. On-resonance coupling between the transition dipoles of these units generates bisignated CD signals with mirror-image symmetry. The results presented herein provide insight on the little-known structurally induced chirality of achiral chromophores through transfer of chiral surface information.

How are N-methylcarbamates encapsulated by β-cyclodextrin: insight into the binding mechanism

Guest molecules containing chromophore groups encapsulated by β-cyclodextrin (β-CD) generate circular dichroism (CD) signals, which enables a preliminary prediction of their binding modes. However, the accurate determination of the representative binding conformation (RC) remains a challenging task due to the complex conformational space of these host-guest systems. Here, we combine a molecular dynamics/quantum mechanics/continuum solvent model (MD/QM/CSM) with induced circular dichroism (ICD) data (N. L. Pacioni, A. B. Pierini and A. V. Veglia, Spectrochim. Acta A Mol. Biomol. Spectrosc., 2013, 103, 319-324.) to explore the binding mechanism of β-CD with four N-methylcarbamate molecules: promecarb (PC), bendiocarb (BC), carbaryl (CY) and carbofuran (CF). In aqueous solution, their stability decreases as: PC > BC > CY > CF. Comparing the ECD spectra computed from TD-DFT with the ICD data can help eliminate many common binding configurations and identify the RC. The host-guest binding affinities (BAs) estimated using a ONIOM2(B971:PM6)/SMD model reproduce the measured binding trend, reveal the competition between the non-covalent interaction and solvent effect and explain the large difference in their binding modes. We also examine the fluctuations in the computed BA using similar structures.

Large Optical Asymmetry in Silver Nanoparticle Assemblies Enabled by CH-π Interaction-Mediated Chirality Transfer

Transfer of asymmetry from the molecular system to the other distinct system requires appropriate chemical interactions. Here, we show how the CH-π interaction, one of the weakest hydrogen bonds, can be applied to transfer the asymmetry from π-conjugated chiral molecules to the assemblies of plasmonic Ag nanoparticles, where the aliphatic chains of chiral molecules and the polystyrene chains grafted on Ag nanoparticles are served as the hydrogen donor and acceptor, respectively. The optical asymmetry g-factor of the chiral assemblies of plasmonic nanoparticles is strongly dependent on the molecular weight of the polystyrene ligand, the core structure of the molecule, and the aliphatic chain length of the chiral molecule. Importantly, we explore a molecular mixing strategy to enhance the asymmetry g-factor of chiral molecular assemblies, which consequently promotes the g-factor of chiral plasmonics efficiently, reaching a high value of ∼0.05 under optimal conditions. Overall, we rationalize the chirality transfer from chiral molecules to inorganic nanoparticles, providing the guidance for structural design of chiral nanocomposites with a high g-factor.

Overall structure of Au12Ag60(S-c-C6H11)31Br9(Dppp)6: achieving a stronger assembly of icosahedral M13 units

Precise atomically assembled nanoclusters provide a great platform to elucidate the evolution of the assembly of building blocks. Herein, a large icosahedral (M₁₃)-based silver-gold alloy nanocluster [Au₁₂Ag₆₀(S-c-C₆H₁₁)₃₁Br₉(Dppp)₆]Br₂ (dppp = 1,3-bis(diphenylphosphino)propane) is reported. Structurally, Au₁₂Ag₆₀ consists of an Au₁₂Ag₄₀ kernel, which is viewed as the interpenetration of ten twisted complete icosahedrons (M₁₃) and two missing icosahedrons (M₁₂), and this is surrounded by a complex metal-organic shell. Benefiting from the extra doping of eight to twelve Au atoms, the octameric assembly was increased to a twelve-mer assembly. The time-dependent density functional theory (TDDFT) method with a Tamm-Dancoff approximation (TDA) was performed to investigate the difference in the optical properties of Au₁₂Ag₆₀ and Au₈Ag₅₇. The results indicate that the difference in the amount of Au atoms results in different optical properties. Furthermore, transient absorption spectroscopy (TA) was also performed, revealing that a twelve-mer assembly greatly enhances the excited-state lifetime. The [Au₁₂Ag₆₀(S-c-C₆H₁₁)₃₁Br₉(Dppp)₆]Br₂ alloy nanocluster has provided a breakthrough in the number of icosahedral M₁₃ assemblies, i.e., achieving a twelve-mer assembly, helping to elucidate the fusion growth of M₁₃-based assembled nanoclusters as well as their geometric/electronic structure correlations, which will promote further research on the assembly of M₁₃ nano-building blocks, especially on their optical properties.

Strong Coupling of Chiral Frenkel Exciton for Intense, Bisignate Circularly Polarized Luminescence

We show that chiral Frenkel excitons yield intense circularly polarized luminescence with an intrinsic dissymmetry factor in emission g_lum as high as 0.08. This outstanding value is measured through thin films of cyanine J-aggregates that form twisted bundles. Our measurements, obtained by a Mueller polarization analysis, are artifact-free and reveal a quasi-perfect correlation between the dissymmetry factors in absorption, g_abs , and in emission g_lum . We interpret the bisignate dissymmetry factors as the signature of a strong coupling between chiral Frenkel excitons longitudinally excited along the bundles. We further resolve by polarimetry analysis the split in energy between the excited states with a Davydov splitting as small as 28 meV. We finally show the anti-Kasha nature of the chiral emission bands with opposite optical chirality. These mirror-imaged emissive chiroptical features emerge from the structural rigidity of the bundles that preserves the ground- and excited-state chirality.

Liquid crystal-templated chiral nanomaterials: from chiral plasmonics to circularly polarized luminescence

Chiral nanomaterials with intrinsic chirality or spatial asymmetry at the nanoscale are currently in the limelight of both fundamental research and diverse important technological applications due to their unprecedented physicochemical characteristics such as intense light-matter interactions, enhanced circular dichroism, and strong circularly polarized luminescence. Herein, we provide a comprehensive overview of the state-of-the-art advances in liquid crystal-templated chiral nanomaterials. The chiroptical properties of chiral nanomaterials are touched, and their fundamental design principles and bottom-up synthesis strategies are discussed. Different chiral functional nanomaterials based on liquid-crystalline soft templates, including chiral plasmonic nanomaterials and chiral luminescent nanomaterials, are systematically introduced, and their underlying mechanisms, properties, and potential applications are emphasized. This review concludes with a perspective on the emerging applications, challenges, and future opportunities of such fascinating chiral nanomaterials. This review can not only deepen our understanding of the fundamentals of soft-matter chirality, but also shine light on the development of advanced chiral functional nanomaterials toward their versatile applications in optics, biology, catalysis, electronics, and beyond.

Chiroptical detection of self-aggregating fluorescent rhodamine conjugates: mistakes and prospects

Fluorescent conjugation can be considered as the chromophoric derivatization of the target and as such it may provide additional, structure-related information quickly available by using circular dichroism (CD) spectroscopy. In this essay, peculiar CD spectroscopic data reported earlier for thyroid hormone-rhodamine conjugates have been re-evaluated. Contrary to the original proposal of the intramolecular folding of the labeled hormone, the bisignate motif in the CD spectrum is a clear evidence of dye-dye, intermolecular chiral exciton coupling indicating supramolecular self-association of the conjugates. This anomalous solution behaviour undermines the credibility of experimental results reported with such conjugates still being used in the laboratory practice. The extension of routine far-UV CD spectroscopic scans of chiral fluorophore conjugates into the near-UV and visible spectral region is strongly recommended.

Cyclodextrin-pillar[n]arene hybridized macrocyclic systems

Cyclodextrin (CD) and pillar[n]arene are significant macrocyclic host molecules in supramolecular chemistry, and have either similar or contrasting physicochemical properties, for example, both can provide capable cavities available for recognizing various favorite guest molecules, while they usually possess different solubility in aqueous solutions, and exhibit diverse chiral characteristics. To balance their similarity and differences inherited from each chemical structure and incorporate both advantages, the CD-pillar[n]arene hybrid macrocyclic system was recently developed. In this review, we will focus on the preparation and application of CD-pillar[n]arene hybrid macrocyclic systems. Both noncovalent interactions and covalent bonds were employed in the synthesis strategies of building the hybrid macrocyclic system, which was in the form of host-guest inclusion, self-assembly, conjugated molecules, and polymeric structures. Furthermore, the CD-pillar[n]arene hybrid macrocyclic system has been primarily applied for the removal of organic pollutants from water, induced chirality, as well as photocatalysis due to the integration of both cavities from CD and pillar[n]arene as hybrid hosts and chiral characteristics inherited from their chemical structures.

A Chirality-Based Quantum Leap

There is increasing interest in the study of chiral degrees of freedom occurring in matter and in electromagnetic fields. Opportunities in quantum sciences will likely exploit two main areas that are the focus of this Review: (1) recent observations of the chiral-induced spin selectivity (CISS) effect in chiral molecules and engineered nanomaterials and (2) rapidly evolving nanophotonic strategies designed to amplify chiral light-matter interactions. On the one hand, the CISS effect underpins the observation that charge transport through nanoscopic chiral structures favors a particular electronic spin orientation, resulting in large room-temperature spin polarizations. Observations of the CISS effect suggest opportunities for spin control and for the design and fabrication of room-temperature quantum devices from the bottom up, with atomic-scale precision and molecular modularity. On the other hand, chiral-optical effects that depend on both spin- and orbital-angular momentum of photons could offer key advantages in all-optical and quantum information technologies. In particular, amplification of these chiral light-matter interactions using rationally designed plasmonic and dielectric nanomaterials provide approaches to manipulate light intensity, polarization, and phase in confined nanoscale geometries. Any technology that relies on optimal charge transport, or optical control and readout, including quantum devices for logic, sensing, and storage, may benefit from chiral quantum properties. These properties can be theoretically and experimentally investigated from a quantum information perspective, which has not yet been fully developed. There are uncharted implications for the quantum sciences once chiral couplings can be engineered to control the storage, transduction, and manipulation of quantum information. This forward-looking Review provides a survey of the experimental and theoretical fundamentals of chiral-influenced quantum effects and presents a vision for their possible future roles in enabling room-temperature quantum technologies.

Ligand-Induced Ground- and Excited-State Chirality in Silicon Nanoparticles: Surface Interactions Matter

Silicon-based light-emitting materials have emerged as a favorable substitute to various organic and inorganic systems due to silicon's high natural abundance, low toxicity, and excellent biocompatibility. However, efforts on the design of free-standing silicon nanoparticles with chiral non-racemic absorption and emission attributes are rather scare. Herein, we unravel the structural requirements for ligand-induced chirality in silicon-based nanomaterials by functionalizing with D- and L-isomers of a bifunctional ligand, namely, tryptophan. The structural aspects of these systems are established using high-resolution high-angle annular dark-field imaging in the scanning transmission electron microscopy mode, solid-state nuclear magnetic resonance, Fourier transform infrared, and X-ray photoelectron spectroscopy. Silicon nanoparticles capped with L- and D-isomers of tryptophan displayed positive and negative monosignated circular dichroic signals and circularly polarized luminescence indicating their ground- and excited-state chirality. Various studies supported by density functional theory calculations signify that the functionalization of indole ring nitrogen on the silicon surface plays a decisive role in modifying the chiroptical characteristics by generating emissive charge-transfer states. The chiroptical responses originate from the multipoint interactions of tryptophan with the nanoparticle surface through the indole nitrogen and -CO₂^- groups that can transmit an enantiomeric structural imprint on the silicon surface. However, chiroptical properties are not observed in phenylalanine- and alanine-capped silicon nanoparticles, which are devoid of Si-N bonds and chiral footprints. Thus, the ground- and excited-state chiroptics in tryptophan-capped silicon nanoparticles originates from the collective effect of ligand-bound emissive charge-transfer states and chiral footprints. Being the first report on the circularly polarized luminescence in silicon nanoparticles, this work will open newer possibilities in the field of chirality.

Exciton interactions in helical crystals of a hydrogen-bonded eumelanin monomer

Eumelanin, a naturally occurring group of heterogeneous polymers/aggregates providing photoprotection to living organisms, consist of 5,6-dihydroxyindole (DHI) and 5,6-dihydroxyindole-2-carboxylic acid (DHICA) building blocks. Despite their prevalence in the animal world, the structure and therefore the mechanism behind the photoprotective broadband absorption and non-radiative decay of eumelanin remain largely unknown. As a small step towards solving the incessant mystery, DHI is crystallized in a non-protic solvent environment to obtain DHI crystals having a helical packing motif. The present approach reflects the solitary directional effect of hydrogen bonds between the DHI chromophores for generating the crystalline assembly and filters out any involvement of the surrounding solvent environment. The DHI single crystals having an atypical chiral packing motif (P212121 Sohncke space group) incorporate enantiomeric zig-zag helical stacks arranged in a herringbone fashion with respect to each other. Each of the zig-zag helical stacks originates from a bifurcated hydrogen bonding interaction between the hydroxyl substituents in adjacent DHI chromophores which act as the backbone structure for the helical assembly. Fragment-based excited state analysis performed on the DHI crystalline assembly demonstrates exciton delocalization along the DHI units that connect each enantiomeric helical stack while, within each stack, the excitons remain localized. Fascinatingly, over the time evolution for generation of single-crystals of the DHI-monomer, mesoscopic double-helical crystals are formed, possibly attributed to the presence of covalently connected DHI trimers in chloroform solution. The oligomeric DHI (in line with the chemical disorder model) along with the characteristic crystalline packing observed for DHI provides insights into the broadband absorption feature exhibited by the chromophore.

Two-Dimensional Chiral Polyrotaxane Monolayer with Emergent and Steerable Circularly Polarized Luminescence

Here, we propose a mechanically interlocked strategy to achieve a 2D chiral polyrotaxane (2D CPR) monolayer with emergent and steerable CPL activity by utilizing β-cyclodextrin as the chiral wheel and a luminescent dynamic covalent organic framework as 2D polymeric axle. Such methodology, integrating host-guest and dynamic covalent chemistry, enabled the direct construction of a delaminated 2D CPR monolayer with extraordinarily large size (up to tens of micrometers) and simultaneously endowed chirality to the extended 2D CPR network to generate CPL activity. Importantly, not only the structure but also the CPL performance of the 2D CPR network can be further regulated by the feeding amount of β-cyclodextrin. This work demonstrated a monolayered 2D CPR with CPL activity for the first time. The insightful structure-property relationship of the induced CPL will be of benefit for a deeper understanding of the excited-state chirality of 2D chiral nanomaterials.