Circularly Polarized Laser Emission from Homochiral Superstructures based on Achiral Molecules with Conformal Flexibility

Nanoaggregation-Enhanced and Inverted Circularly Polarized Luminescence in Isomeric Schiff Base Bis(boron difluoride) Complexes

To elucidate the emergence and amplification of circularly polarized luminescence (CPL) in chiral molecules and their assemblies, we designed positionally isomeric chiral V-shaped Schiff base ligands and their corresponding bis(boron difluoride) complexes. The ligands were synthesized by condensing chiral cyclohexanediamine with either 1-hydroxy-2-naphthaldehyde or 2-hydroxy-1-naphthaldehyde, followed by complexation with boron difluoride (BF2) to yield CNB1 and CNB2, respectively. While the parent Schiff bases exhibited no CPL, BF2 coordination induced strong CPL signals in solution. Remarkably, upon aggregation in a mixed solvent system, CNB2 displayed enhanced and inverted CPL, whereas its isomer CNB1 showed attenuated emission. Through comprehensive characterization and singlecrystal analysis, we attribute this divergent behavior to distinct molecular packing modes: CNB2 forms tightly stacked aggregates with efficient π─π interactions, while CNB1 adopts a less ordered arrangement. This study establishes a clear correlation between subtle structural modifications, supramolecular packing, and CPL performance, offering a rational strategy for tailoring chiroptical properties through precise molecular design and controlled self-assembly.

Acid/Base-Responsive Circularly Polarized Luminescence Emitters with Configurationally Stable Nitrogen Stereogenic Centers

A way to prevent the fast configurational interconversion of tertiary amines is to invoke Tröger's base analogs, which display methano- or ethano-bridged diazocine cores fused to aromatic rings. These derivatives are configurationally stable, even in acidic media when their structures bear ethylene bridges. Here, a two- to three-step synthesis is presented of methano- and ethano-bridged Tröger's base analogs with two peripheral fluorophores, i.e., anthracene, pyrene, and 9,9-dimethylfluorene units. These compounds, possessing two nitrogen stereogenic centers, exhibit good circularly polarized luminescence (CPL) dissymmetry factors (|glum| up to 1.2 × 10-3) and brightnesses (BCPL up to 26.3 M-1 cm-1), as well as excellent fluorescence quantum yields, demonstrating the Tröger´s base core to be a convenient scaffold to prepare CPL emitters upon functionalization with simple achiral fluorophores. Furthermore, the configurationally stable ethano-bridged Tröger's base analogs are employed to modulate their CPL response, generating a CPL switch through their protonation/deprotonation by consecutive additions of acid and base. The reversibility of the switching process is demonstrated for two cycles without altering the CPL performance of the molecule. It is believed that this straightforward and efficient approach to building CPL emitters employing the Tröger's base core could lead to its incorporation in CPL-based sensors and materials.

Phase-transfer-catalyst enabled enantioselective C-N coupling to access chiral boron-stereogenic BODIPYs

Tetracoordinate boron-based fluorescent materials have shown extensively applications in chemistry, biology and materials science owing to their unique optoelectronic properties. However, constructing chiral boron-stereogenic fluorophores through practical and universal strategies remains rare and challenging. Herein, as a proof of concept, we report an enantioselective postfunctionalization of boron dipyrromethene dyes (BODIPYs), to acess boron-stereogenic BODIPYs in moderate to good yields with commendable enantioselectivity. Chiral BODIPYs have attracted increasing attention owing to not only their distinctively photophysical properties and applications in circularly polarized luminescence (CPL) materials, but also diversely structural modification. In this·work, we present a phase-transfer-catalyst enabled enantioselective C-N coupling reaction of BODIPYs with diverse nucleophiles. This method serves as a practical SNAr (nucleophilic aromatic substitution reaction) route to achieve a series of boron-stereogenic amido/amino BODIPYs as well as demonstrates their promising CD and·CPL·activities, excellent biocompatibility, and high specificities, showing potential applications as chiral fluorescent imaging agents.

Symmetry Breaking: Case Studies with Organic Cage-Racemates

ConspectusSymmetry is a pervasive phenomenon spanning diverse fields, from art and architecture to mathematics and science. In the scientific realms, symmetry reveals fundamental laws, while symmetry breaking─the collapse of certain symmetry─is the underlying cause of phenomena. Research on symmetry and symmetry breaking consistently provides valuable insights across disciplines, from parity violation in physics to the origin of homochirality in biology. Chemistry is particularly rich in symmetry breaking studies, encompassing areas such as asymmetric synthesis, chiral resolution, chiral structure assembly, and so on. Across different disciplines, a well-defined methodology is fundamental and necessary to analyze the symmetry or symmetry breaking nature behind the phenomenon, enabling researchers to uncover the underlying principles and mechanisms. Basically, three key points underpin symmetry-related research: the scale-dependency of symmetry/symmetry breaking, the driving force behind symmetry breaking phenomena, and the properties arising from symmetry breaking.This Account will focus on the three aforementioned key points elucidated with organic cages as proof-of-concept models, as organic cages exhibit shape-persistent 3D molecular frameworks, well-defined molecular motion, and a high propensity for crystallization.First, we examine racemization processes of organic cages with dynamic molecular motions to illustrate that symmetry and symmetry breaking are time-scale-dependent. Specifically, the racemization, driven by molecular motion, is influenced by hydrogen bonding and the rigidity of the cage framework, which may or may not be observable within the experimental temporal scale. This determines whether the enantiomeric excess system, namely, the symmetry broken system, can be detected experimentally. We also investigate the hierarchical structures self-assembled by racemic organic cages, demonstrating that symmetry and asymmetry manifest differently across spatial scales, from molecular to supramolecular and macroscopic levels. Second, we discuss the driving force behind spontaneous chiral resolution─a classic symmetry-breaking event during crystallization─from a thermodynamic perspective. We suggest that racemic compounds, compared to conglomerates, are more entropy-favored, explaining their greater prevalence in nature. Spontaneous chiral resolution can take place only when a favorable enthalpy compensates for unfavorable entropy. In conglomerates composed of organic cages, strong intermolecular interactions along the screw axes provide the necessary compensation. Finally, we explore the unique properties that emerge from symmetry-broken molecular packing within crystals of cage racemates, such as second-harmonic generation and piezoelectricity. It turns out that the symmetry operation in molecular packing plays a critical role in determining material properties. By comprehensively analyzing symmetry and symmetry-breaking in organic cage racemates, this Account provides insights into symmetry-related phenomena across scientific disciplines. It also paves the way for designing novel materials with tailored properties for applications in optics, electronics, and beyond.

Emerging devices based on chiral nanomaterials

As advanced materials, chiral nanomaterials have recently gained vast attention due to their special geometry-based physical and chemical properties. The fast development of the related science and technology means that various devices involving polarization-based information encryption, photoelectronic and spintronic devices, 3D displays, biomedical sensors and measurement, photonic engineering, electronic engineering, solar devices, etc., been explored extensively. These fields are at their beginning, and much effort needs to be made, including improving the optical, electronic, and magnetic properties of advanced chiral nanomaterials, precisely designing materials, and developing more efficient construction methods. This review tries to offer a whole picture of these state-of-the-art conditions in these fields and offers perspectives on future development.

Tröger's base-embedded macrocycles with chirality

The birth and development of supramolecular chemistry have heralded a new era, where macrocycles have become an irreplaceable research tool. Therefore, the construction of novel macrocycles has become a hot spot. Tröger's base (TB), as a fragment with both rigidity and chirality, promises tremendous potential in the realm of supramolecular chemistry, and its unique properties continue to motivate researchers to explore its inclusion in macrocycles. However, the construction of a TB-embedded macrocycle is always difficult due to the frequent occurrence of excessive tension. For successful synthesis, part of the function of TB in macrocycle is often overlooked or sacrificed to facilitate the macrocyclization process, leading to serious deficiencies in the utilization of the functions of TB. Thus, the research on TB-embedded macrocycles is still in its preliminary stage. Hence, in this review, TB-embedded macrocycles are highlighted, focusing not only on the linkers of these macrocycles but also on the correlation between the properties of TB and TB-embedded macrocycles. We hope that this review will further guide the synthesis of more excellent macrocycles.

A Carbazole-Centered Expanded Helicene Stabilized with Hexabenzocoronene (HBC) Units

The synthesis and stabilization of heteroatom-doped nanocarbon molecules, such as carbazole-containing (super)helicenes, present significant challenges due to the complexities involved in maintaining structural integrity and electronic functionality. In this study, we successfully synthesized a carbazole-centered expanded tris-hexabenzo[7]helicene (1) via a facile FeCl3-mediated Scholl coupling reaction. 1 exhibits both chemical and chiral stability and demonstrates fluorescence at 628 nm with a quantum yield of 0.40. Additionally, the enantiomers of 1 display pronounced chiroptical properties, including a distinct circular dichroism (CD) signal spanning from 300 to 600 nm. The absorption dissymmetry factor (|gabs|) is determined to be 2.98×10-3, while the circularly polarized luminescence brightness (BCPL) is measured as 32.50 M-1 cm-1.

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.

Spin-polarized lasing in manganese doped perovskite microcrystals

Spin-polarized lasers have demonstrated many superiorities over conventional lasers in both performance and functionalities. Hybrid organic-inorganic perovskites are emerging spintronic materials with great potential for advancing spin-polarized laser technology. However, the rapid carrier spin relaxation process in hybrid perovskites presents a major bottleneck for spin-polarized lasing. Here we report the identification and successful suppression of the spin relaxation mechanism in perovskites for the experimental realization of spin-polarized perovskite lasers. The electron-hole exchange interaction is identified as the decisive spin relaxation mechanism hindering the realization of spin-polarized lasing in perovskite microcrystals. An ion doping strategy is employed accordingly to introduce a new energy level in perovskites, which enables a long carrier spin lifetime by suppressing the electron-hole exchange interaction. As a result, spin-polarized lasing is achieved in the doped perovskite microcrystals. Moreover, the doped cation is a magnetic species allowing for the magnetic field control of the spin-polarized perovskite lasing. This work unlocks the potential of perovskites for spin-polarized lasers, providing guidance for the design of perovskites towards spintronic devices.

Spin-Valley-Locked Electroluminescence for High-Performance Circularly Polarized Organic Light-Emitting Diodes

Circularly polarized (CP) organic light-emitting diodes (OLEDs) have attracted attention in potential applications, including novel display and photonic technologies. However, conventional approaches cannot meet the requirements of device performance, such as high dissymmetry factor, high directionality, narrowband emission, simplified device structure, and low costs. Here, we demonstrate spin-valley-locked CP-OLEDs without chiral emitters but based on photonic spin-orbit coupling, where photons with opposite CP characteristics are emitted from different optical valleys. These spin-valley-locked OLEDs exhibit a narrowband emission of 16 nm, a high external quantum efficiency of 3.65%, a maximum luminance of near 98,000 cd/m2, and a gEL of up to 1.80, which are among the best performances of active single-crystal CP-OLEDs, achieved with a simple device structure. This strategy opens an avenue for practical applications toward three-dimensional displays and on-chip CP-OLEDs.

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.

Adaptive Helical Chirality in Supramolecular Microcrystals for Circularly Polarized Lasing

Chiral organic molecules offer a promising platform for exploring circularly polarized lasing, which, however, faces a great challenge that the spatial separation of molecular chiral and luminescent centers limits chiroptical activity. Here we develop a helically chiral supramolecular system with completely overlapped chiral and luminescent units for realizing high-performance circularly polarized lasing. Adaptive helical chirality is obtained by incorporating chiral agents into organic microcrystals. Benefiting from the efficient coupling of stimulated emission with the adaptive helical chirality, the supramolecular microcrystals enable high-performance circularly polarized lasing emission with dissymmetry factors up to ~0.7. This work opens up the way to rational design of chiral organic materials for circularly polarized lasing.

Exceptionally High-glum Circularly Polarized Lasers Empowered by Strong 2D-Chiroptical Response in a Host-Guest Supramolecular Microcrystal

Circularly polarized (CP) lasers hold tremendous potential for advancing spin information communication and display technologies. Organic materials are emerging candidates for high-performance CP lasers because of their abundant chiral structures and excellent gain characteristics. However, their dissymmetry factor (glum) in CP emission is typically low due to the weak chiral light matter interactions. Here, we presented an effective approach to significantly amplifying glum by leveraging the intrinsic 2D-chiroptical response of an anisotropic organic supramolecular crystal. The organic complex microcrystal was designed to exhibit large 2D-chiroptical activities through strong coupling interactions between their remarkable linear birefringence (LB) and high degree of fluorescence linear polarization. Such 2D-chiroptical response can be further enhanced by the stimulated emission resulted from an increased degree of linear polarization, yielding a nearly pure CP laser with an exceptionally high glum of up to 1.78. Moreover, exploiting the extreme susceptibility of LB to temperature, we demonstrate a prototype of temperature-controlled chiroptical switches. These findings offer valuable insights for harnessing organic crystals to facilitate the development of high-performance CP lasers and other chiroptical devices.

Macrocycle-Based Charge Transfer Cocrystals with Dynamically Reversible Chiral Self-Sorting Display Chain Length-Selective Vapochromism to Alkyl Ketones

Chirality-driven self-sorting plays an essential role in controlling the biofunction of biosystems, such as the chiral double-helix structure of DNA from self-recognition by hydrogen bonding. However, achieving precise control over the chiral self-sorted structures and their functional properties for the bioinspired supramolecular systems still remains a challenge, not to mention realizing dynamically reversible regulation. Herein, we report an unprecedented saucer[4]arene-based charge transfer (CT) cocrystal system with dynamically reversible chiral self-sorting synergistically induced by chiral triangular macrocycle and organic vapors. It displays efficient chain length-selective vapochromism toward alkyl ketones due to precise modulation of optical properties by vapor-induced diverse structural transformations. Experimental and theoretical studies reveal that the unique vapochromic behavior is mainly attributed to the formation of homo- or heterochiral self-sorted assemblies with different alkyl ketone guests, which differ dramatically in solid-state superstructures and CT interactions, thus influencing their optical properties. This work highlights the essential role of chiral self-sorting in controlling the functional properties of synthetic supramolecular systems, and the rarely seen controllable chiral self-sorting at the solid-vapor interface deepens the understanding of efficient vapochromic sensors.

True and False Chirality in Chiral Magnetic Nanoparticles

Determining the true or false chirality of a system is essential for the design of advanced chiral materials and for improving their applications. Typically, a magnetic field would cause false optical activity in the chiral material system, thus confusing the true chirality's influence. Here, we provide a simple way to uncover the true and false chirality in chiral ferrimagnetic nanoparticles (FNPs) by using the gel as a rigid frame. The remnant local magnetic field of the FNP gel can be easily adjusted by an external magnetic field or by controlling the concentration of the FNPs. Moreover, the potential application of the FNP gel is detected by induced magnetic circularly polarized luminescence. This work provides deep insight into the true and false chirality in magnetic nanosystems and offers a strategy to construct new optic elements with an adjustable local magnetic field.

Boosting Circularly Polarized Luminescence from Alkyl-Locked Axial Chirality Scaffold by Restriction of Molecular Motions

Boosting the circularly polarized luminescence of small organic molecules has been a stubborn challenge because of weak structure rigidity and dynamic molecular motions. To investigate and eliminate these factors, here, we carried out the structure-property relationship studies on a newly-developed axial chiral scaffold of bidibenzo[b,d]furan. The molecular rigidity was finely tuned by gradually reducing the alkyl-chain length. The environmental factors were considered in solution, crystal, and polymer matrix at different temperatures. As a result, a significant amplification of the dissymmetry factor glum from 10-4 to 10-1 was achieved, corresponding to the situation from (R)-4C in solution to (R)-1C in polymer film at room temperature. A synergistic strategy of increasing the intramolecular rigidity and enhancing the intermolecular interaction to restrict the molecular motions was thus proposed to improve circularly polarized luminescence. The though-out demonstrated relationship will be of great importance for the development of high-performance small organic chiroptical systems in the future.

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.

Chiral metal-organic cages decorated with binaphthalene moieties

The construction of chiral nanoobjects with atomically precise nanostructures has attracted much more attention in the past decades. However, this field is still in its early stages. We designed and synthesized a series of chiral ligands containing the binaphthalene moiety and isophthalate module. Then, four chiral metal-organic cages (MOCs) were obtained through the coordination between isophthalate modules and copper ions. These chiral MOCs exhibit discrete, uniform and stable structures, good solubility and photoluminescence behaviors.

Supra-Cyanines: Ultrabright Cyanine-Based Fluorescent Supramolecular Materials in Solution and in the Solid State

Fluorescent materials with high brightness play a crucial role in the advancement of various technologies such as bioimaging, photonics, and OLEDs. While significant efforts are dedicated to designing new organic dyes with improved performance, enhancing the brightness of existing dyes holds equal importance. In this study, we present a simple supramolecular strategy to develop ultrabright cyanine-based fluorescent materials by addressing long-standing challenges associated with cyanine dyes, including undesired cis-trans photoisomerization and aggregation-caused quenching. Supra-cyanines are obtained by incorporating cyanine moieties in a cyclic peptide-based supramolecular scaffold, and exhibit high fluorescence quantum yields (up to 50 %) in both solution and in the solid state. These findings offer a versatile approach for constructing highly emissive cyanine-based supramolecular materials.

Angular Control of Circularly Polarized Emission from Achiral Molecules via Magnetic Dipoles Sustained in a Chiral Metamirror

Circularly polarized emission (CPE) plays an important role in the designs of advanced displays and photonic integrated circuits. Unfortunately, the control of CPE handedness is limited by the chiral metasurfaces employed to emit chiral light. Particularly, the switching of the handedness with chiral metasurfaces relies on flipping the metasurfaces, which adds some constraints to practical applications. Herein, we propose an angle-sensitive chiral metamirror with Mie resonators to realize handedness switching. The Mie resonator supports a magnetic dipole having large field enhancement. This chiral metamirror is applied to excite CPEs with opposite handedness at emission angles within 10°. In contrast to the conventional methods, this work proposes a more efficient approach to manipulate the handedness of CPE.